WINTER STORM FCST 12/14/07 - 12/17/07: SOUTHERN US - NORTHEAST US

[Brandon Smith]

I'm unsure how to label the states as I'm not sure where the freezing line is going to fall this weekend. *Mods, feel free to edit the title.*

It appears that a slight trough is going to get dug out in the west, starting the flow of colder than normal air out of Canada in the middle and eastern parts of the country. A low looks like it's going to develop across southern TX, moving it's way along the Gulf coast before turning more northeasterly. As this is happening, the cold air is really going to get drawn in towards the system, as the system begins to deepen late Saturday.

According to the GFS, it appears to be a classic nor'easter type setup. The low rapidly strengthens off the Delmarva Peninsula and rapidly moves along the New England coast. The freezing line, which in the DC area, usually plays havoc with where snow will fall, appears to be further to the south than usual.

As of now, it could be fairly nasty this weekend across the Mid-Atlanic and Northeast. I think the only issue we might be having besides track (which always plays a factor in these systems) is when the cold air will arrive. Sooner will be better than later as the air looks cold enough that when it comes, it will be sticking around for awhile. If it's too soon, it'll most likely mean all rain for the DC - Philly area and south from there.

As a word of warning, this is my first time starting one of these, so pardon me if my wording and weather knowledge is a bit off. I've been a long time lurker of the forum and don't have nearly as much meteorolgy knowledge as many do on here.

[Heidi Farrar]

I've been paying special attention to this one since I have family stretching from Maine to northern VA to western MD ... Just this afternoon I sent out an "unsolicited weather bulletin" alerting them to this situation. I have noticed the GFS being heavier-handed as far as precip intensity on 0Z Sunday all the way through 0Z Monday, at least on the last three runs. Surface temps so far are looking like this is going to be an all-snow event, and so if those precip models verify there could be much of the east coast, from DC to the Canadian border, dealing with over a foot of snow. It will definitely be interesting to watch how the WRF & GFS continue to handle this over the next few days ...

Not to forget, though, is that areas of PA & western MD could be dealing with this ice storm beginning tomorrow night and lasting for a day or so, depending on how the temperature situation works out. I think that there is defnintely a chance for a worst-case scenario playing out for some perhaps isolated areas, where there could be somewhat significant icing and then have 12+ inches of snow on top of that. Sounds like a mess, if nothing else!

[Mikey Gribble]

Wichita should get a little snow on Friday night. I am glad we are finally getting snow instead of sleet, ice, or rain. Anything but snow is a waste of a winter storm IMO. It's nothing major for us. Just a weak wave in zonal flow, but I'll take what I can get. I'm waiting for the NAM to pick up on this with the 00Z run before I do much forecasting, but right now I am thinking the southern most 3 or 4 counties in Kansas from Liberal all the way past Wichita should get a swath of 1 to 3 inches of snow. It should be a night time event and temperatures should be well below freezing, so there won't be any issues with melting. Anyways, I'm pumped. I'll do some forecasting tonight after the 00Z runs come out.

[Dan Robinson]

Been watching this one since it started showing up a few GFS runs ago. This has the potential to have it all - severe weather in the south, ice/sleet storm and/or flooding in the central Appalachians, and a major snow event/blizzard for the northeast. Too early to nail down specifics but one to keep an eye on.

[Mikey Gribble]

The track for the short wave coming through the southern plains has shifted South a bit with the 12Z run and I am not happy about it. We were the bullseye for snow accumulation in the last two runs, now central and northern Oklahoma into northern Arkansas have the heaviest swath of snow. I'm surprised nobody is talking about this, especially the Oklahoma boys. It should be a pretty good snow storm for this part of the country. I am not sold on the new track that is farther South yet. I'll wait to check the other models and see if there is any continuity with tonight's runs on the track change. Everything is looking good for a decent snow event though. I wouldn't be surprised to see a swath of > 6 inches in northern half of Oklahoma into southern Kansas.

[BrianBaker]

Probably because most of us Oklahoma boys and girls don't have power. I am at work posting this. Will be interesting to see what happens.

[Jeff Miller]

http://rap.ucar.edu/weather/model/gfs096hr_sfc_prcp.gif
http://rap.ucar.edu/weather/model/gfs096hr_sfc_mslp.gif

Watch out, New England, that's all I can say right now on this one.

[Wesley Luginbyhl]

The last thing central OK needs right now is snow, especially "significant" amounts according to Norman NWS. I got power back yesterday after a 24 hour downtown, I was expecting at least 3 days of no power. Last night I thought I would go to Wal-mart to get something to drink, considering everything in my fridge smells really bad right now. From what I saw most of Norman doesnt have power, most restautrants were packed and the tree damage here is going to take weeks (at least) to clean up. You add a significant snow storm and this place will be a mess. I was going leave before friday to go to Texas, but I may wait around for this one. If Norman gets a decent snow storm out of this, the bubble is definitely broke or atleast has a crack finally.

[Robert Dewey]

There's a pretty big spread in regards to this system... The threat area looks pretty large and probably won't be refined until things come into agreement. Right now, everything from the southern Plains through the Great Lakes and into the Northeast have a pretty equal shot at seeing some decent snows.

GFS supports a more eastern solution, while the latest GGEM would support a Great Lakes to Northeast transition of some fairly substantial snows.

The latest NAM supports the latter with it's slower and further southwest solution.

[Chad Cowan]

This system has the potential to be a huge snow producer in the Northeast. The one saving grace could be the quick progression without a major high to hold the storm in place once it bombs out. Even with that, there is still the possiblitiy this storm could dump more than a foot over a wide area.

[Brandon Smith]

One thing I did notice while at work today were the number of seagulls that were situated inland. From living through a couple of other nor'easters and coastal storms, I have always seen shore birds (like seagulls) move their way inland in advance of a major system. Even though a system may not play out as large inland, any type of coastal storm storm will seem to bring them in at least a week prior. It almost seems like they can sense the pattern changing and begin to prepare.

The LWX and CCX forecast offices seem to have temperatures hovering right around the freezing mark during the day on Saturday and Sunday, with temperature in the mid 20's during the night. From the models, it appears that there is going to be a punch of colder air right before the sytem begins to bomb out along the coast. The timing of this cold air might play havoc with whether the mid-atlantic will see snow, ice, or rain. Right now, temperatures are in the 50's, with a slight cool down tomorrow, followed by a rebound. Should be interesting to see when the cold air will begin to settle in on Saturday.

[John Olexa]

Thats what were looking at here in MD this weekend. A real Smorgishboard of weather LOL

[B Ozanne]

Meanwhile we need to get through the current winter storm warning before we get to this weekend's storm.

We're looking at 4-8" in southern CT on Thursday with heavy snow warnings about 15 miles inland. Its still fairly warm here but dewpoints have fallen into the 20's.

[Bob Johnson]

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/nam/00/images/nam_pcp_084l.gif

Yikes. 00z NAM is very progressive thus takes this storm well SE of the Northeast.

[Brandon Smith]

From my experience, you usually get a secondary low developing to the west or southwest of the main low, which really gets the precipitation forming. Do the models typically pick up this formation or do they lump both of the lows together?

[Patrick Martin]

It's usually the development of the coastal low which turns the winds SE/E/NE (depending on where you are in new england) and pumps in copious amounts of moisture off the Atlantic.

Current GFS develops the surface low off the Delaware coast, and tracks it over outter Cape Cod at which point pressures shown down to 989mb. I am anxciously waiting for it to come into better range of the WRF and hoping the low end up tracking just a tick further east which would bring heavier snow to my location, which will be northern CT. I fly into BDL Friday afternoon. Hoping to be in position to capture some good images.

[Dan Robinson]

Interesting to note that the 0z NAM (WRF) scraps the storm. Outlier, yes - but interesting nonetheless.

[Rob Lightbown]

One problem that I have in forecast snowstorms here in northern Maine (Where there is 2 feet of snow on the ground) is snow to water ratios. Is there any tried and true method on accurately determining this aspect of snowfall forecasting. Take this weekend's storm. The 00 UTC GFS model is painting around 0.90 inch of water equivelent and the BUFKIT snow tool is indicating 20-30:1 ratios, while the Kuchera algorithm is showing around a 20:1 ratio. One thing I have read in the past is that coastal storms usually have a 12-15:1 ratio, so I guess I'm not sure what to believe and let me tell you the discrepencies in snow ratios gives some large snow total possibilities. Any thoughts would be welcome.

[Bob Johnson]

06z GFS seems like it has trended furthur NW. H in Midwest looks like it's killing moisture availability on the Lakes and OV concentrating most of the heavy precipatation along frontal boundary as vort steers this into the Upper ridge.

[Mikey Gribble]

Tricky forecast for the snow storm that will affect Kansas and Oklahoma tomorrow night. The GFS had been steady as a rock over the last several days (along with several other models) with the track and intensity of the storm. The NAM was completely out to lunch (I mean waaayyyy off) until the 12Z run this morning and now it has fallen in line with the GFS. The 12Z of the GFS moved the track northward though so now I'm not sure what to believe. I am leaning towards the track of the 12Z NAM with a blend of precipitation intensities of both the NAM and GFS. The current track of the NAM is more in line and consistent with what the other models have been showing in the past several days and the NAM has done a pretty good job on past storm tracks once you get within 48 hours. Right now my thinking is that an area from Ashland to Ark City to Wichita cone (facing NE) will be the western edge of the heavier swath of snow, with that cone of heavier snow extending East to east central Kansas. I am thinking 5-8 inches should be common in this area. If I had to stick a number on snow fall amount for Wichita right now I would go with 6 inches. That is a good snow storm for us. For some reason we always dodge the bullseye on good snow storms, but we are actually in pretty good position for this one. I still need to do my forecasting this morning and check the 12Z run of all the models, so right now I'm only fairly confident on the track of the heaviest snow.

[jladue]

One problem that I have in forecast snowstorms here in northern Maine (Where there is 2 feet of snow on the ground) is snow to water ratios. Is there any tried and true method on accurately determining this aspect of snowfall forecasting. Take this weekend's storm. The 00 UTC GFS model is painting around 0.90 inch of water equivelent and the BUFKIT snow tool is indicating 20-30:1 ratios, while the Kuchera algorithm is showing around a 20:1 ratio. One thing I have read in the past is that coastal storms usually have a 12-15:1 ratio, so I guess I'm not sure what to believe and let me tell you the discrepencies in snow ratios gives some large snow total possibilities. Any thoughts would be welcome.

Rob, you sure hit on a sore topic in the realm of what we should know vs what we do know. You know there's no decent network that measures ratios over hourly to 24 hr time spans. You come close with SNOTEL sites but they're in the mountains. The METAR sites are terrible because there's no adequate shielding around the bucket and so the catch efficiency goes below 50% with a wind above 10 mph. Snow spotters typically don't measure ratios. COCORAHS members do measure ratios but only once per day. In the course of a snowstorm, the crystal density habits change drastically from one hour to the next, especially when you get convective bands passing by.

So with all the lack of quality obs, there's been a terrible lack of good research. Nevertheless a few folks made some decent attempts. You can take two of our lessons (lesson 5) on snow ratio basics from our winter weather course at
http://www.wdtb.noaa.gov/courses/winterawoc/IC6/index.html

There's two techniques besides just going with 10:1 or some other guess in the lesson.

1. The Caribou snow technique which forecasts high ratios when the level of maximum vertical motion phases with the dendrite production zone (-12 to -18 C). The thinking is if most of the vertical motion is where dendrites form, then fluffy snow forms.

2. The Roebber et al. 2003 technique which forecasts snow ratios based on a neural network. The best inputs come from month, compaction due to wind speed, and warmest temp in the layer. Here's a link to their online forecasting site: http://sanders.math.uwm.edu/cgi-bin-snowratio/sr_intro.pl

Note that the Caribou technique doesn't take into account settling and compaction and so it may be better related to short duration snow ratio measurements. I find that the Caribou technique often overestimates snow ratios. If most of the vertical motion is confined to the dendrite production zone and there's no warm layers, it might work better. But broad vertical motion where riming and graupel can form around dendrites, the ratios would go down. But I'm guessing because there's a huge dearth of ground truth (i.e. no snow ratio, snow flake type reports).

regards,

Jim

[Chris Hayes]

I'm hoping the forecast discussion is right for our area. NWS mentioned 8-12 inches of snow possible from Saturday to Sunday over NE Ohio. Just need the storm to go south and east just enough to keep it all snow, and hopefully no dryslot move in.

[Bob Johnson]

Ya def looks good for Ohio. Bullseye for them. Congrats.

We chicagoans can wait. Plenty of winter left.

[Andrew Francis]

Difficult forecast. Everything was off on the heaviest ice accum for the ice storm by about 60 mi SE of where the original heavy precip core was forecasted. So maybe the snowstorm here in KS and OK will also be shifted SE. I just want to see a good amount of snow lol :'[

[mark plate]

Difficult forecast. Everything was off on the heaviest ice accum for the ice storm by about 60 mi SE of where the original heavy precip core was forecasted. So maybe the snowstorm here in KS and OK will also be shifted SE. I just want to see a good amount of snow lol :'[


New 00Z WRF/NAM has trended back that way...closer to its outlier 12Z run from 12/11. Will see if other models follow suit.

[Andrew Francis]

This morning I was dissapointed when i checked and the Winter Storm Watch had been dropped for central OK. And the forecast changed to 1-2 inches.

Now nearly all of central and NW OK just got upgraded to a Heavy Snow Warning with 5-7 inches likely?!!

How does that change that drastically in a matter of hours??? Maybe the dropping of the winter storm watch was an error?


Anyways, snow breaking out now in SW KS and TX panhandle

Time for a NOW thread

[mark plate]

Looks like the deformation zone sets up Saturday morning along roughly the I-44 corridor. 5-7 inches seems excessive and will be very localized if it occurs. 2 to maybe 3 inches will be more widespread within the deformation zone during the day Saturday.

Heaviest snow tonight will target the Wichita vicinity.

[Mikey Gribble]

I'm not sure what to think anymore. I've been pouring over model data for the last two days trying to work out the small scale details and I'm no better off than I was 48 hours ago. My current thinking is in line with the NWS, that the heaviest swath will run SW-NE from DDC to Emporia, just North of the Wichita area. Four days ago I was afraid the heaviest snow would go South of us, but with each run of the GFS it kept creeping the heaviest snow North. Now it is going to go to far North for us to get the heaviest stuff. It will be close though. You never really know the small scale amounts on snow. The bottom line is that the DDC-Emporia swath (either side of that line) is going to get a good 4-8 snow. Localized higher amounts are definitely possible, but that just depends on where the bands set up. I always bite my nails thinking we are going to miss out on the snow until we get a big band coming at us.

[Bill Schintler]

Yet another winter storm will affect portions of the Midwest on Saturday, however the heaviest snowfalls will remain well south of the eastern Iowa area.

Cedar Rapids:
Light snowfall will start at 10 AM CST Saturday and continue until 8 PM. Expect 0.5 inch of snowfall at the Eastern Iowa Airport with lesser amounts further north. Marion and County Home road will see a dusting of accumulation.

Iowa City:
Light snowfall will start at 8:30 AM and continue until 9 PM. Expect 1.0 inch of accumulation.

Marengo:
Light snowfall will start at 8 AM and continue until 8 PM. Expect 0.8 inche of accumulation.

Synopsis:
At the SFC, a CF pushed through the area last night, bringing a reinforcing shot of cold air with NW winds gusting to 20 mph. WV satellite imagery indicated digging cutoff low over AZ/NM while the developing moisture conveyer belt aloft was evident in the form of wispy CI and a baroclinic leaf structure from TX through IA. In WRN KS, radar indicated developing returns with moisture reaching the ground in KDDC after 18Z in a zone of isentropic lift on the 285-295K SFCS.

Discussion:
MDLS in decent agreement with regard to the evolution of a coupled H3 jet structure and regions of ULVL divergence and attendant UVM, with the strongest lift remaining well S of the area. A 70kt H5 streak over NV will dive S and phase with the SRN stream wave now over NM/TX. The GFS is slightly faster more open with the EWD progression of the trough while the NAM maintains a more closed solution. This trend continues though Sunday as additional energy dives S from CAN to phase with the SRN stream energy while a major nor’easter develops in the NERN CONUS.

Tricky part of FCST is predicting the NRN extent of the precipitation given SWRD intrusion of dry air at the SFC through the mid-levels. Model soundings indicate dry air from H8 to H6 at the onset, so will adjust MDL QPF downward accordingly. The strongest forcing will occur between 14Z and 19Z as the right-entrance region of a 130kt H3 streak along with a healthy shot of isentropic lift overspreads the area. A suit of snowfall FCST methods were considered. Investigating QPF, the GFS is most bullish and brings over 0.2 inches of QPF along I-80. Given the aforementioned dry air, this will be adjusted down to 0.1 inch along I-80 and 0.05 along US-30, which also brings it into better agreement with the other MDLS. Cold temperatures will be in place aloft, with H8 in the -10C range and H7 about -13C. A 14/1 snow/water ratio will be used, which gives 1.5 inches along I-80 with lesser amounts to the N. Looking at the Garcia method, considering 1-2 g/kG mean mixing ratio lifted along the 290K SFC for a duration of 6 hrs suggests about 1 inches of snowfall at best.

Looking ahead, the recent active pattern will slow down for the next six days as the pattern transitions to a split-flow regime and a parade of weak disturbances transitions E within the NRN branch. Finally, late in the week a potentially strong system will then affect the upper-Midwest.

- bill
1:30 PM CDT, 12/14/07

[Robert Dewey]

Westward trend continues... Looks like quite a snowstorm will setup from MI eastward. I think HPC's latest snowfall graphic is a bit too far east, but that's just a first guess and not really an accurate portrayal of amounts.

I'll probably spend more time looking over things tomorrow morning, or perhaps the 00Z run if things get even more interesting.

Needless to say, I suspect some areas in eastern MI will see totals in the 12-16 inch range (perhaps lake enhancement areas, or if the westward trend continues as I suspect it will; and yes Rob, I am "predicting the models" ;)).

The BUFKIT forecast shows a mean snow ratio of 18:1, for a storm total of 16-18 inches over Detroit, with a solid 30-40knt wind gust potential. That certainly has my attention.

Areas further east (parts of NY, for example) will likely see 18-24 inches, or even more. I noticed BUF has "up to 30 inches" in some of their WSW products.

[Joel Wright]

Looks like a nice 5-8" band of snow will set up from southern MO, through the St. Louis area, up through the Ft. Wayne IN area, and up towards Detroit. A few locations up near 10" aren't out of the question. Particularly in northern IN and southeast MI. Snow ratios will be 10-12:1 in the heaviest band.

Further northwest, it looks as though snow may accumulate as far north as central IA and into extreme southern WI.

Central Kansas will get a nice burst of snow much of tonight. This area should easily get 6"+. Looks like it's centered near the Hutchinson area.

This is a lot better than ice though, isn't it guys? :-)

[HAltschule]

The Capital District is expecting a wide variety of snow accumulation. Sleet is expcected to mix in to some extend and keep the snow accumulations down but we should still see 5-9" of snow before the changeover.

The bullseye for this storm should be the deformation zone that's expected to develop to the NW of Albany. In these areas where all snow occurs, 18-24" is expected with higher amounts in the 'Dacks and the 'Skills (Adriondacks and Catskills).

NWS Boston's Walt Drag has a nice discussion about a possible gravity wave screwing around with the pcp totals.

If the storm stays a little further east, then we could stay with all snow. If that happens, then it seems that we could easily exceed a foot of snow. Stay tuned.

[Mike Peregrine]

EAX says 5-7" for metro Kansas City (http://www.crh.noaa.gov/eax/?n=webbriefing) in this briefing at 3:30 pm. Looks like heaviest snowfalls cutting through the middle of the state, from Butler across toward St. Louis ... in this area they're expecting 8"+. This system turned into quite a little snow maker. It's no wonder with a nicely saturated plume of tropical moisture flowing.

I'll take this over ice any day of the week. Not sure how I feel about this ON TOP of ice, though -

[Robert Dewey]

All I can say for the 00Z NAM is W-O-W. The westward trend continued, and it's even more intense, keeping the Ohio Valley low dominant for a longer period of time.

End result? Better than 1.25 inches of QPF across a large portion of the Great Lakes - IN, OH, MI, and portions of NY. With snow ratios running at 12:1, that would yield 15 inches... But with the -10C isotherm running so close to the heaviest QPF, and given the lift, I'm thinking closer to 15:1... Which would put out widespread +18 inch amounts.

I wonder if the 00Z GFS will be as ambitious.

EDIT: Looks like the RGEM is just as ambitious as the NAM (981MB over NY/PA at 00Z/MON). I'm actually getting a little concerned that the low might end up too far west, bringing in mixed precipitation as far NW as DTW. Hmmm... However, the RGEM brings the best slug of QPF in (40-50mm) when things cool back down.

[Dan Robinson]

The warm punch from the south is the wild card. The 0z WRF even shows a good sized pool of warm air (around 45F) sticking around west of the mountains through Sunday morning, which could limit Ohio's totals. The farther you get west away from that, the better. That cooldown on Sunday afternoon looks pretty impressive as the front swings through, with temperatures dropping 20+ degrees during the afternoon. That may be our saving grace of getting anything from this here.

The ice storm potential looks interesting on the eastern slopes, may be worth checking out tomorrow. It looks like mainly a nighttime event though. Night + mountains = no photo ops.

North of I-80 is where the most fun will be with this system.

[Robert Dewey]

Not to get too far off topic, but Rob Dale (if you're reading)... I see the new NAM snow algorithm is outputting 21 inches for KJXN with a total QPF of ~1.25 inches... am I reading that right?

BUFKIT for KDET is showing 22 inches at 1.50 inches QPF...

Of course, those snow amounts would depend on the QPF actually verifying :)

EDIT: Just noticed KLAN showing 24.7 inches :eek: I've never seen values that high here in central or eastern MI.

[Robert Dewey]

Seems the 00Z GFS is more "conservative" with 1.00 to 1.25 inches of QPF. It's also a touch colder, which would support the 15:1 snow ratios (again, taking into account other factors... and the consensus between algorithms). However, I did notice the QPF area has shifted somewhat northwestward, and increased in size slightly.

So, here's how it breaks down for the southern MI area (KLAN eastward):

NAM and RGEM: 24 inches
GFS and NGM: 14-18 inches

It just looks weird to see southern MI and >10 inches in the same paragraph.

[rdale]

NAM is a little weird with it's surface positions... I'm going on-air with 4-8" for Lansing to Jackson, 2-4" towards GRR, 8-12" for SE Mich. It certainly could be more, but at 24 hours out before first accumulations I'm already holding my breath as it is!

[Robert Dewey]

NAM is a little weird with it's surface positions... I'm going on-air with 4-8" for Lansing to Jackson, 2-4" towards GRR, 8-12" for SE Mich. It certainly could be more, but at 24 hours out before first accumulations I'm already holding my breath as it is!

Yeah, it's hard to go against statistics... Seeing a widespread +16 inch event would put some areas (i.e. Detroit) into the record-book category... meaning it's very rare.

Certainly there have been many other times in the past X number of years where the models have shown good consistency and agreement with high QPF / high snow ratio environment, only to see a bust (I can think of a couple right off the top of my head).

[Mike Kovalchick]

Yeah, it's hard to go against statistics... Seeing a widespread +16 inch event would put some areas (i.e. Detroit) into the record-book category... meaning it's very rare.

Certainly there have been many other times in the past X number of years where the models have shown good consistency and agreement with high QPF / high snow ratio environment, only to see a bust (I can think of a couple right off the top of my head).

I just about passed out looking at the OOZ NAM for Lansing! :) I am starting to think that moving my snowblower to my cottage was a bad idea as I have a 1/4 mile long driveway at my house near Haslett with nothing to clear the driveway with but a snow shovel?

I haven't had a chance to look more closely at the latest model runs. Are they realistic? Ensembles? Model runs have been shifting West with almost every run. Over due to jog back East? Wow. La Nina seems to favor a strong low West of the mountains...and with only 5" this season..overdue?

[Robert Dewey]

Are they realistic? Ensembles? Model runs have been shifting West with almost every run. Over due to jog back East? Wow. La Nina seems to favor a strong low West of the mountains...and with only 5" this season..overdue?

The consistency and agreement are certainly there for +12 inch amounts from LAN eastward... But statistics argues otherwise.

There are TONS of events where I've said "if that QPF verifies, we (or they) will see 12-18 inches"... only to see 6-8 inches as the rule, and 10-12 inches to be the exception.

This looks just like those other events, relatively speaking, so it's hard to say. Rob has a good point... wait until the snow starts and you can see a radar representation, and perhaps some short-term modeling (RUC).

In most cases, it seems like 8-12 inches is the highest (or at least safest) most forecasters will go without some sort of verification to bump the totals (i.e. 8 inches on the ground, still snowing at 3 inches per hour).

[rdale]

21Z SREF showed the most snow (5-10" for eastern half of MI, N IN, NW OH) that I ever recall seeing for a winter event... Usually there's enough spread that you only get a few inches. There's pretty good agreement!

In my web story I'll be putting the potential for more and explaining why - but for onair use I'm going to stay "conservative" (although when I'm going with numbers much higher than NWS, I don't think that's a valid qualifier) until otherwise needed.

The impact of a 7" snowfall is the same as an 11" one, so there's no need to get too whacked with numbers until it starts.

Speaking of - radar looks GREAT coming out of SW IL / MO :>

[Joel Wright]

Wow, you Michigan boys will be doing some shoveling with this one!! The models have really upped their QPF with the new 00z/06z runs. Northern Indiana, extreme northwest OH, and much of lower MI is gonna get clocked. This is your storm Robert!

Looks like the rain/snow line will actually back up pretty close to the southeast tip of lower MI. If not, somewhere very close to that. You want to be just northwest of where that ends up, and that looks to be near the DTX area. 10-13", with isolated 17" totals look good for you guys.

Winds are looking pretty damn strong too, especially later in the event as the surface cyclone tightens up.

Enjoy guys! :-)

[Danny Neal]

It seems as though Skilling is predicting eight to ten inches of snow for the Chicago area. http://blogs.trb.com/news/weather/weblog/wgnweather/ Seems a bit high, but with strengthening NNE winds off a 36 degree lake....keep in mind air temperatures will be in the teens....we could get into 4-6 hours of lake effect snow fall. NWS wants to keep it conservative with 3-5 and I suppose from the synoptic system that is accurate. As Joel wrote it seems like the main snow fall in the order of the 12 to 14 inch range will be confined from Indianapolis on north and east to Cleveland. As that big Canadian high and this Low merges and tightens up, the pressure gradient will be extreme and I could see 50+ mph gusts at any given time during this event spelling big problems for the North east.

[Robert Dewey]

Well, not much has really changed with the 12Z NAM. The rain/snow line does creep up towards the MI border, but I think areas north of the state line will see all snow. However, the warmer profile could tone down snow amounts slightly from what the earlier NAM was suggesting...

I expect a rather large area of 12-18 inches from LAN eastward, as most models agree that QPF will be at or above 1.00 inch. Some of the heavier models, including the research WRF runs, the NAM, and the RGEM suggest 1.25 to as much as 1.75 inches (ARW WRF). Thus, I can't really rule out isolated +18 inch amounts.

I think a bigger story will be the combination with the wind. The latest NAM rapidly deepens this system to 985MB over northern OH, with a very tight pressure gradient. Winds right off the deck approach 40-50knts, so I expect many areas will be sustained in the 25-35MPH range, with gusts around 45MPH... perhaps even a few isolated 50MPH gusts.

If this projected solution occurs, I expect blizzard warnings to be hoisted from northern IN, northwestern OH, into southcentral and southeastern MI.

[Jeff Miller]

If this projected solution occurs, I expect blizzard warnings to be hoisted from northern IN, northwestern OH, into southcentral and southeastern MI.

I agree with this, the Cleveland AFD also is mentioning the prospect of hoisting Blizzard Warnings for their forecast area based on near-blizzard or blizzard criteria.

I want to add it is rare for the Conservative Cleveland Office to mention upgrades to Blizzard Criteria. Normally Cleveland is quite the conservative office and will downplay as much as possible (I grew up in this region).

Also, based on history growing up in this region, I don't expect the mammoth 14" plus accumulations to materialize in NW Ohio. Just based on the 30 plus winter storms I grew up with in that area, for whatever reason, the heavy heavy snow will probably remain in SC lower Michigan between Detroit and Ann Arbor. I've seen storms like this time and time again in this region. I suspect Toledo will end up with 8-10", Detroit 10-12", and locally heavier amounts further west. The big story will be low visibilities and strong blowing and drifting of snow.

[rdale]

http://wlns.com/Global/story.asp?S=1686033

[Robert Dewey]

FWIW, the 12Z GFS has continued the trend with a slightly stronger and further west solution, which gives me more confidence. It's not as heavy with the QPF as the NAM, but still a respectable +1.00... The slightly colder profile might bump snow ratios up a bit and compensate, so snow totals wouldn't be completely different between the two models.

I'm still sticking with 12-18 inches right now for LAN eastward, with blizzard conditions developing around 12Z SUN through 18-21Z SUN.

EDIT: Just noticed GRR expanded the WSW and simply states "a foot or more." I guess they don't want to put an upper limit on the totals, eh? ;)

[Brandon Smith]

It's going to be interesting further east, particularly in my area east of the Blue Ridge Mountains and south of Harrisburg. From looking at several different model runs, it appears the bulk of precip we will receive will occur during the overnight hours on Saturday, through early morning on Sunday. The only downside to this is that there is a period of time during the precip when the temperatures on the ground and aloft will be warmed than 0 C, meaning rain. However, at least until 6Z, the temperatures will be below freezing on the ground, meaning we will have several hours of accumulating frozen precipitation before the slight change over to rain between 6Z and 12Z. The warm air appears that it won't stay around for long as the low deepens over Indiana and quickly kicks in the cold air on the backside of the front. Anything that falls on the backside of this system wrapping around from the low should fall as snow for us after the front passes through.

The DC, Baltimore and Philly areas will definitely have a change over to rain for an extended period of time. It appears the cold air will get quickly over-ridden at all heights.

One thing interesting is just the slightest track to the south would guarantee my area all ice, with no rain. I'll be keeping a close eye to see how far the warm air advances in front of the low and how far north the low tracks.

[Jeff Miller]

From GRI:

THE NEWEST TRACK OF THE STORM TAKES IT TO NEAR TOLEDO. THIS TRACK
SUPPORTS HEAVIER SNOW FURTHER NORTH AND WEST. THEREFORE HAVE
UPGRADED THE WATCH (http://www.crh.noaa.gov/glossary.php?word=WATCH) AREA TO WARNINGS. ADDED A NEW WATCH (http://www.crh.noaa.gov/glossary.php?word=WATCH) FURTHER
NORTH AND WEST TOWARD LDM. WILL HAVE NEAR BLIZZARD (http://www.crh.noaa.gov/glossary.php?word=BLIZZARD) CONDITIONS IN
THE FORECAST. IT APPEARS THAT IN EXCESS OF A FOOT OF SNOW COULD
FALL IN A BAND SOMEWHERE IN THE WARNING (http://www.crh.noaa.gov/glossary.php?word=WARNING) AREA.


that could make quite the difference in NW Ohio.

[Robert Dewey]

I was just checking out the wind potential in BUFKIT. The NAM is usually over-board, so that must be taken into account here.

Here's what is shown for PTK (north of DTW):

7AM SUN: 30-40knts
2PM SUN: 40-50knts
4PM SUN: 45-55knts

BUFKIT outputs around 19-22 inches of snow, depending on the ratio algorithm used.

[HAltschule]

From my blog this morning:

http://weatherexpert.blogspot.com/ (http://weatherexpert.blogspot.com/)

WINTER STORM UPDATE: 12/16-12/17


The latest computer models continue to delay the secondary low pressure development along the Mid-Atlantic coast. This means that as the main low continues further inland over the Ohio Valley, a southerly wind will pump up warmer air in the low and mid levels of the atmosphere. While snow will fall heavily and accumulate significantly during the first part of the storm, I now believe that a changeover to sleet and even rain will occur into the Albany area. This will cut down on snow accumulation quite a bit. Nevertheless, snowfall will be heavy begining around 11pm-1am Sunday morning before the changeover during the day Sunday. Total snow accumulation will be 5-9" followed by sleet and rain. The storm should gradually wind down as some additional snow comes to an end by about 3am Monday morning.

Many areas in the Adirondacks southwestward to Syracuse, NY will see upwards of a foot of snow with many higher elevations close to 24" before all is said and done.

COMMENTS WELCOME!!

[rdale]

From GRI:



that could make quite the difference in NW Ohio.

Not sure that Grand Island Nebraska does much forecasting for NW Ohio :>

[Jeff Miller]

GRR. My apologies. :)

[Joel Wright]

18z models rolling on in. Looking very similar to the previous ones.

Sharpen up your shovels in Michigan. Actually, northern Indiana looks to really get slammed too.

Hell, even Chicago's looking like they may get up to 7-8" on the south side. It seems that every run slows the storm just the slightest bit, adding some QPF accordingly.

Looks like even in my area of NW IL we'll receive a good 4-5" of snow, due to the very dry nature of the snow. (15:1). So far about one inch here as of 2pm.

[Robert Dewey]

Looks like the NAM has locked in its solution with the 18Z run, and the experimental NCEP WRF runs.

ALL of the models agree on over an inch of QPF for the snow area near IN, OH, and MI. The majority agree on amounts around 1.25 inches... and a few are showing +1.25 inch amounts.

I'm always a little concerned about dry slotting when systems wrap up and the heaviest snow area is predicted to be within the closed 500MB isoheight. The WRF shows the dry slot getting pretty close, cutting into northern OH... while the operational NAM keeps this a bit further southeast.

All-in-all, I'm still sticking with 12-18 inches southeast of a line from MBS to SBN, and northwest of a line from FWA to TOL. I think several areas will see closer to 18 inches, and I wouldn't be surprised to see a 24 inch amount. If this were a general public forecast, I would tone it down and simply go with 12-18 inches until the system evolves further.

As for winds... 925MB winds pick up to 50-55knts in response to the rapid deepening and very tight pressure gradient. I suspect blizzard conditions will be more than met across much of the above area by 06-09Z SUN.

[rdale]

Interesting that HPC says there will be no snow in Chicago...

[Robert Dewey]

I usually take HPC's forecasts as a general "guideline."

[Jeff Snyder]

Interesting that HPC says there will be no snow in Chicago...

Not according to the Winter Weather snow probs --> http://www.hpc.ncep.noaa.gov/wwd/day1_psnow_gt_04.gif ... That shows anywhere from low to high probability of >4" snow falls from 00z Sun to 00z Mon. The "Selected Cities" forecast at http://www.hpc.ncep.noaa.gov/discussions/scs.html shows Snow for Saturday and flurries for Sunday in Chicago.

[Nevermind about my other comment]

[rdale]

Sorry - I was referring to their snowfall amount forecast map, which I forgot was still an internal product.

[rdale]

Based on LSR's so far, I think that Chicago hole was a mistake :>

Still expecting 6-10" Lansing, 8-12" Jackson south to the state line with horrible driving in the gusty north winds tomorrow... I'm thinking we'll avoid the blizzard conditions by not ramping them up until the snow slows.

[Joel Wright]

I wonder if that hole over chicago was caused by the models warming the lower atmosphere too much because of Lake Michigan. Assuming of course that the HPC map was based on some computer projection. I would highly doubt a human would have hand drawn that forecast bust for Chicago.

[Rob Lightbown]

With the dynamical nature of this storm and the influx of tropical moisture from Olga, a question came up in my mind. Is there any synoptic or mesoscale features I should look for in determining whether there may be thundersnow or thundersleet at a particular location? If so, what should I be looking for in the maps and models?

[Mike Umscheid]

Assuming of course that the HPC map was based on some computer projection.

The chart that Rob posted is an un-official collaboration product produced by the HPC winter weather desk (hidden behind a password protected directory for internal collaboration among HPC and local WFOs). It is typically generated by some blending schemes of various models -- more or less as a baseline "thinking"... I'm not sure how much hand-editing is done to that graphic. The OFFICIAL HPC winter weather forecast products are the probabilistic graphics that are on the main HPC winter weather desk (http://www.hpc.ncep.noaa.gov/wwd/winter_wx.shtml) page.