Dryline Storms in Late May

[Jason Caster]

Greetings!

This being my first post I'd like to give an enthusiastic hello to all the members of this forum. Before I pose my question I'll tell a bit about myself.

I live in the Pacific NW in a small city named Medford. Always fascinated by weather I've had a life long dream of seeing severe storms. Unfortunately we do not see that type of weather in Oregon (may not be a bad thing). So last year in May (2007), I decided to begin researching meteorology, storm spotting, and the art of chasing. My very first trip will be this May (24th through June 1). I've researched many internet resources including Mr. Drummond's SkyWarn module (which is wonderful by the way).

So my question, since I will be traveling in May, does the dryline tend to be NWD during late May? I was looking through the threads for the nowcasts during last year's time frame, and noticed many of the storms were further north. Is it a completely separate factor?
Thanks in advance!

[Chris Nuttall]

It tends to vary. I've chased tornadoes east of Lubbock, TX, in the middle of June. I've seen tornadic storms in eastern Oklahoma/NW Arkansas at the end of May. I've also seen the storms up in Nebraska during the same time frame.

Your chase vacation is the exact same time mine is, so I'm hoping the storms stay a bit south and west. That's be great for me. :)

[Jason Caster]

Thanks for the info Chris. I'll be flying into DFW May 24th, so south would be ideal for me as well. Less gas and travel time would be nice. Where is your starting point?

[Mikey Gribble]

The highest tornado probability area shifts North through the spring. For instance a lot of good chases are in Oklahoma and Texas in April, Kansas is good in May, and Nebraska and South Dakota in June. This is an extremely loose trend. We get outbreaks in every one of these states in each of those months, but like I mentioned the setups tend to migrate North with the jet stream. It's not that the dryline moves North. The jet stream migrates northward and in effect so do the surface lows.
Just going off of historical averages I would station myself a little farther North than Dallas for chasing in late May. OKC or Wichita would be good choices IMO.

[Jason Caster]

Good to know Mikey, thanks!
Unfortunately we already bought tickets out of DFW (it was much less expensive than OKC). Our original fly in location was planned for OKC until we saw the big price difference. Although when calculating the cost of gas it may have cancelled itself out.

I was monitoring your blog on Wednesday and noticed you were spot on for the prediction of that supercell that ended up producing the Breckenridge Tornado. While I'm on the road in May I will probably utilize your blog for extra information, I appreciate the extra Nowcasting you provide.

[Dustin Wilcox]

Based on my experience if chasing late May and Early June one will frequent the Grand Island NE area, though as mentioned above it certainly varies, you may be chasing in TX one day and ND the next.

[Laura Duchesne]

Yep I can vouch for that... during the last two years, we went the last week of May and first week of June, and going down again this year during that time frame as well. In 2006, we were all over the place, from chasing a dryline storm in OK, to chasing a haboob in Colorado, then catching tubes in South Dakota. Last year, we went from South Dakota to Texas once again. So it really depends... one day south, the next day north.

[Chris Bowman]

May 24th - June 1st. I would say from ICT to GID would be roughly the climate peak. I think the peak for the Lincoln, NE is around June 12th. One thing you have going for you is the Memorial Day weekend seems to always be an active weekend IMO.

http://www.nssl.noaa.gov/hazard/hazardmap.html You can pretty much follow the climate peak northward using this app.

[Mikey Gribble]

Memorial Day weekend does always seem to produce some severe weather.
As far as where you are flying into Jason, I think Dallas is just fine. I thought maybe you were wondering about what area you should stay in while waiting on storms.
Thanks for the compliment on the forecast I posted on my blog. I got extremely lucky on Wednesday's foreast. If you do check my forecasts this spring you'll quickly learn I can bust forecasts with the best of them. I try though. I am always glad to help out any way I can. BTW I usually mention in my forecast whether or not I'm chasing and if I'm not chasing on any particular day while you're here I can help out with nowcasting/relaying data to you while you're on the road if you need it.

[Bobby Prentice]

So my question, since I will be traveling in May, does the dryline tend to be NWD during late May? I was looking through the threads for the nowcasts during last year's time frame, and noticed many of the storms were further north. Is it a completely separate factor?
Thanks in advance!

dryline—A low-level mesoscale (http://amsglossary.allenpress.com/glossary/search?id=mesoscale1) boundary or transition zone hundreds of kilometers in length and up to tens of kilometers in width separating dry air (http://amsglossary.allenpress.com/glossary/search?id=dry-air1) from moist air (http://amsglossary.allenpress.com/glossary/search?id=moist-air1).

The length of the dryline is related to large-scale terrain or large-scale weather system features, whereas its width is related to mesoscale processes. In its quiescent state, the dryline may be considered the intersection of the top of a low-level moist layer with large-scale features of sloping terrain. In this state the shallow layer of moisture near the higher terrain is eroded by turbulent mixing (http://amsglossary.allenpress.com/glossary/search?id=mixing1) with daytime heating. Moisture gradients are additionally strengthened by horizontal convergence (http://amsglossary.allenpress.com/glossary/search?id=convergence1) resulting from downward transport (http://amsglossary.allenpress.com/glossary/search?id=transport1) of horizontal momentum (http://amsglossary.allenpress.com/glossary/search?id=momentum1) in the dry air (http://amsglossary.allenpress.com/glossary/search?id=dry-air1). In a more dynamically active state the dryline often advances away from the higher terrain as an integral component of an extratropical cyclone (http://amsglossary.allenpress.com/glossary/search?id=extratropical-cyclone1) or frontal wave (http://amsglossary.allenpress.com/glossary/search?id=frontal-wave1). In such cases it extends equatorward from the cyclone or wave. In this state moisture gradients and boundary motion are largely influenced by downward transport of horizontal momentum resulting from larger-scale sinking in the dry air. The dryline is found all over the world. In the United States the dryline, which marks the boundary between moist air from the Gulf of Mexico and dry continental air (http://amsglossary.allenpress.com/glossary/search?id=continental-air1) from the west, is found in the Plains region. It is most often present during the spring, where it is often the site of thunderstorm (http://amsglossary.allenpress.com/glossary/search?id=thunderstorm1) development. Typically the dryline in the United States advances eastward during the day and retreats westward at night.

In the U.S., the dryline forms in the high plains (east of the Rockies), generally south of the polar front (http://amsglossary.allenpress.com/glossary/search?id=polar-front1). It's most commonly found from southeast Colorado/southwest Kansas southward across eastern New Mexico/west Texas. Its length can extend further north (particularly during late spring) and it can move further east into the low plains due to strong weather systems.

Dryline: a moisture boundary (WW2010 - UIUC) (http://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/af/frnts/dfdef.rxml)

If you're trying to plan your chase vacation, I've written an article on the subject titled: When and Where to Chase by Robert Prentice (http://members.cox.net/rprentice/storm_chasing.htm)

http://members.cox.net/rprentice/images/other/toralley.gif http://members.cox.net/rprentice/images/other/Chasealley.gif
http://members.cox.net/rprentice/images/other/toralley.gif%5Bimg%5D%5Bimg%5Dhttp://members.cox.net/rprentice/images/other/Chasealley.gif

In my article, I say that if you are trying to determine when to chase, Harold Brooks (National Severe Storms Lab) has created an excellent Severe Thunderstorms Climatology web page (http://www.nssl.noaa.gov/hazard/index.html) that details the risks from tornado, wind, and hail for the United States. I believe his most informative animations for storm chasers are these:

Probability of Any Tornado 1980-1999 (Java animation) (http://www.nssl.noaa.gov/hazard/tanim/torw8099.html)

The above Java animation is important to chasers for obvious reasons. I think it is better than simply looking at Significant Tornado (F2 or greater) (http://www.nssl.noaa.gov/hazard/tanim8094/sigtanim2195.html) or Violent Tornado (F4 or greater) (http://www.nssl.noaa.gov/hazard/tanim8094/viotanim2195.html) java animations because the latter two are more heavily biased by population density and don't show the true tornado threat on the sparsely populated high plains.

Probability of Hail 2-inches in diameter or greater 1980-1994 (Java animation) (http://www.nssl.noaa.gov/hazard/tanim8094/bhaianim8094.html)

Since most/virtually all giant hail (1.75 inches or greater) is produced by supercells, this java animation is a great proxy for supercell which is the storm type most-coveted by storm chasers.

My current conclusions for the best time periods to chase storms in Chase Alley:

Best 67-day period: April 25 - June 30
Best 36-day period: May 11 - June 15
Best 14-day period: May 21 - June 3

Storm chase season peaks over Chase Alley (http://members.cox.net/rprentice/images/other/Chasealley.gif) around May 31st.

My recommendations are skewed a bit more toward late chase season than the sheer numbers would suggest because storm motions tend to slow down later in the season which makes them easier (and more enjoyable) to chase. Plus, chase season runs a week or so later later if you are willing to chase further north to the Canadian Border and southern Minnesota/Iowa.

[John Wetter]

As you transition to June, you can get the great triple-point setups and also warm front tornadoes. Living in Minnesota, I would modify Bobby's chaser alley to include Minnesota south of I-94 and west of I-35, along with Iowa west of I-35 and north of I-80. Both of those areas are mostly flat, and have a nice section road grid, but the non-asphalt roads up here are actual gravel, not red clay so you can actually use them!

-John

[Darrin Rasberry]

I think Dallas might be a little too hot for that time, unless tornadoes aren't your only target. That being said, when Texas cools off from the usual 90's temps in late May, I've seen some hellacious storms come out of it. In particular, around the Lubbock area at that time there is usually one or two potential setups - which ends either in a beautiful outbreak or a blue sky with deep-fried temperatures and an atmosphere as dry as a biscuit.

If you want to gamble on seeing long-track tornadoes, Southeastern Nebraska has the highest incidence for those in the entire United States except for Northeast Mississippi (source (http://ams.confex.com/ams/11aram22sls/techprogram/paper_81872.htm)), and the end of May, as per Mr. Prentice's model, shows that the area receives its highest threat around that time.

If I were you, I'd play the middle in Wichita, Kansas. The area is so wide open at that time that you might want to plan on driving if you can get off of work, unless you can find a chase buddy to split the bills with.

[Bobby Prentice]

<snip>
If you want to gamble on seeing long-track tornadoes, Southeastern Nebraska has the highest incidence for those in the entire United States except for Northeast Mississippi (source (http://ams.confex.com/ams/11aram22sls/techprogram/paper_81872.htm))
<sip>

Be very leery about using these long-track tornado path lengths in any studies because the data base is heavily biased and outright flawed. Many times tornado paths were set by the Weather Bureau / National Weather service storm data focal point who basically connected the tornado damage dots on a map and (either by ignorance or laziness) assumed a continuous path between the dots. Tom Grazulis highlights this fact in table 5.2 "The Longest Tornado Paths" in his book Significant Tornadoes 1680-1991. He lists 23 of the 26 longest paths as "tornado families."

The concept of mesocyclone occlusion wasn't invented until the advent of Doppler radar in the 1970's and NWS meteorologists weren't heavily trained in the concept until the WSR-88D Doppler radar network was implemented in the 1990's (I know since I was one of the trainers!).

http://www.crh.noaa.gov/lmk/soo/docu/super8.gif

You can really see the bad offices if you study the data base. South Dakota, Nebraska, Mississippi, and central Florida pre-1990's are especially bad. Part of the problem in SD and NE is that damage indicators are few and far between on the open Great Plains.
</sip></snip>

[Jason Caster]

As we approach late may, I've noticed a large number of the recent storms have been more southern in location. OK, TX, MO, MS, AR, and AL have seen a high number of storms within the last few weeks.

For those with experience, how would you say this pattern relates prior years and the location of storms for early to mid May?

A second and perhaps more important question regards the frequency of MCS. We've seen a large frequency of storms in the past few weeks. What do you think that indicates, if anything, for the likelihood of tornadic supercells during the last week of May?