SPC Outlooks

[Jason McKittrick]

I wonder if anyone else has noticed that it seems like in the last two years SPC has been issuing MOD and HGH risks with a little more frequency than in years prior and with fewer verifications. I am curious as to whether this is an intentional shift in forecast philosophy or just a stretch of bad luck.
That said, I thought it would be nice to give the SPC forecasters a little love. Their day 1 forecast for Wednesday was one of the better forecasts I have seen them make in quite some time. Their MOD risk verified almost perfectly. Congratulations guys and thanks for all of your hard work. I sure you don't here that enough.

http://i55.photobucket.com/albums/g157/Jason_McKittrick/day1otlk_20070523_1300_prt.gif



http://i55.photobucket.com/albums/g157/Jason_McKittrick/070523_rpts.png

[Scott Overpeck]

SPC has had a good year so far. I'm sure Rich Thompson and others might correct me on this, but I believe the last couple of years they have changed the severe probabilities and criteria. I think a couple of years ago what is now a "high end" slight risk would have been a "low end" moderate risk, etc. I could be wrong on that, but I thought I remember them shifting the probabilities with regard to their categorical outlooks. Still, a better evaluation would be to compare the verification stats against their probabilistic forecasts. I'm not sure if that has anything to do with them forecasting better, or forecast philosophy, but maybe them getting used to forecasting the probabilities than categories. Just my guess. Regardless, then have done quite well indeed!

[Jason Boggs]

Yes, they have and continue to do a very good job. Rich, you and the others that work your tail off day after day......we thank you very much!!!

[Robert Dewey]

I too notice the increasing frequency of MDT's, HIGH's, and PDS watches. It seems like the 90's and early 00's featured fewer, but more accurate, MDT's and HIGH's. I haven't looked at any data, so this may not even be correct... However, it "feels" like something has changed. I know something is wrong when Michigan has more than two MDT's a year :)

[Shane Adams]

Important to note that risks are verified by sheer number and concentration of reports, all levels have their own set criteria for "verified" or not. Many times what may be a disappointing day from a chaser perspective will actually verify throughout the night (the OTHER half of the period) and therefore in fact be a "verified" risk. SPC outlooks are for public risks, not chaser forecasts.

[John MacKay]

You're right, Shane. There have been a few MODs and Highs that have verified in relation to severe weather reports, not tornado reports.

April 24th was the one many of us remember. A MDT risk was verified in certain areas that day, but the late day HIGH upgrade in Northern Texas did not in the sense of what a HIGH stands for. The April 23rd convection cloudied the skies along with an advancing dry line around noon on the 24th allowed things to pop too soon.

On the other hand, the forecasts for May 22nd and May 23rd were very accurate (look at the tornado probabilities on the 22nd and then the reports on the 22nd). I give the SPC props on those forecasts.

[Scott Olson]

As noted, SPC changed how their probalistic categories releate to the risk categories. It's important to note that it has been a fairly active year, so that is part of the reason for the more MDT and HIGH. Certainly much more active than the last two years. I'm not sure I'd agree with the statement that fewer verifications are taking place with the moderate and high risks that have been issued this year as with previous years. I'm sure Jared or Richard could shed a bit more light on your question.

[Joey Ketcham]

I think a lot of people have began to associate MDT and High Risks with tornado outbreaks, and thus if a MDT risk is issued and it's not a tornado outbreak day storm chasers will say the SPC busted. This is not true.

As someone else already mentioned, these outlooks are generated for the public. According to the SPC's website, a MDT risk means that they expect 30 reports of hail 1" or larger, 6-19 tornadoes, and at least 30 reports of damagig winds (58+ MPH).

So the Storm Report graphic that Jason used as an example, you can see that's not a bust for SPC. There were 15 tornado reports, 62 wind reports, and 150 hail reports with 12 of those being large hail. This far exceeds their MDT risk criteria.

[rdale]

Not quite right -- skimming over a few words changes things dramatically! You left out "Within a moderate risk area..." and there were not 62 wind reports or 150 hail reports in the moderate risk area.

Not at all saying they busted, but it wasn't as extreme as you mentioned. It still verified, but based on maybe a dozen tornadoes and a few dozen hail reports.

[Joey Ketcham]

Not quite right -- skimming over a few words changes things dramatically! You left out "Within a moderate risk area..." and there were not 62 wind reports or 150 hail reports in the moderate risk area.
.

You got me on that one.. the reports were scattered around. But still, many times I see people talk about how SPC busted, but per their criteria they really didn't. I just think people don't realize that their definition of a MDT risk and ours won't be the same.

[rdale]

I just think people don't realize that their definition of a MDT risk and ours won't be the same.

No denying that is true, especially with newer chasers who use it as gospel...

[Bob Schafer]

According to the SPC's website, a MDT risk means that they expect 30 reports of hail 1" or larger, 6-19 tornadoes, and at least 30 reports of damagig winds (58+ MPH).

There are a LOT of reasons for two (theoretical) days with the same weather events to have WIDELY different reports counts. Just thought I'd point that out.

Surely the SPC wouldn't go with MDT just because an affected area is densely populated, and therefore a lot of reports would be expected to come in. ...or if it was in, say, W Oklahoma on a Saturday in May, when 42,000 chasers would be there. Would they?

[rdale]

If that were the case, I assume we'd also think NWS offices don't issue Tornado Warnings on storms that will only affect rural areas in a non-chaser zone?

[Jason McKittrick]

My intention with this thread was to try and sharpen my definition of what to expect given a MOD or HGH risk. For some reason I have been left with the impression that over the last couple of years there have been a lot of elevated risks that have not verified. However, after looking back over the archived Outlooks and storm reports it appears that with few exceptions SPC has done a superb job this year. I am pretty sure that they did not fair as well last year but I cannot be certain without actually looking at the data. As far as this spring is concerned I could only find two forecasts that I would consider to be busts. The first was on March 30th.

http://i55.photobucket.com/albums/g157/Jason_McKittrick/day1otlk_20070330_1630_prt.gif
http://i55.photobucket.com/albums/g157/Jason_McKittrick/070330_rpts.png

This event IMO failed to verify the MOD risk. I would be interested to know if this technically verified by SPC standards.

The second event was on April 3rd this event IMO exceeded the MOD risk forecast.


http://i55.photobucket.com/albums/g157/Jason_McKittrick/day1otlk_20070403_1630_prt.gif

http://i55.photobucket.com/albums/g157/Jason_McKittrick/070403_rpts.png

Given the above examples, am I in the ball park as far as what would qualify as a MOD and HGH risk? I am not trying to knock the job SPC is doing and in fact after actually looking back it would appear that they have done a remarkable job this year. I know that everyone that makes there own chase forecasts knows how difficult it can be to pinpoint where and what to expect. I have to applaud SPC for a job well done this year.

[beaudodson]

SPC has had a good year so far. I'm sure Rich Thompson and others might correct me on this, but I believe the last couple of years they have changed the severe probabilities and criteria. I think a couple of years ago what is now a "high end" slight risk would have been a "low end" moderate risk, etc. I could be wrong on that, but I thought I remember them shifting the probabilities with regard to their categorical outlooks. Still, a better evaluation would be to compare the verification stats against their probabilistic forecasts. I'm not sure if that has anything to do with them forecasting better, or forecast philosophy, but maybe them getting used to forecasting the probabilities than categories. Just my guess. Regardless, then have done quite well indeed!
Killer tornadoes this year

http://kamala.cod.edu/SPC/latest.nwus23.KWNS.html

All but one was in a watch!

[Scott Overpeck]

Jason, I'd say you have the right idea on the first case. The second is a bit more unclear. I agree there is a high concentration of hail and wind reports with some tornado reports. As I understand...high risks generally are reserved for extreme events with violent tors and >80mph damaging winds. Not sure if that case fits the extreme wind/hail reports they look for. Certainly have the concentration for a high risk...but doesn't seem to be enough extreme severe reports. The tornado reports do not fit in the high risk. So on that...in hindsight...perhaps they could have gone with a high risk but maybe the mdt was better since there were not may violent tors. If anything, they needed to extend the mdt risk farther east, but splitting hairs. Just my 2 cents worth.

For those interested, here's a link to SPC's Outlook criteria:
SPC Outlook Criteria (http://www.spc.noaa.gov/misc/SPC_Prob_Conv_Otlk_Change_20060214.html)

[Nick Smith]

Here's those two outlooks above overlayed onto the corresponding severe weather reports maps.

http://img.photobucket.com/albums/v118/hookecho80/20070330.jpg

http://img.photobucket.com/albums/v118/hookecho80/20070403.jpg

[Paul Knightley]

How can you exactly verify these forecasts though?! Surely the number of reports depends on many non-meteorological factors, mainly the number of people who are there to actually report. The number of expected reports is surely just a guideline to try to convey how extensive the SPC expect the severe threat to be.

The verification of any weather forecast is highly problematic - things like temperature are fairly easy to verify, but only if you do a spot forecast. Once you start forecasting for a region, which temperature would you take to be the one you verify?