Awesome new products

SPC added to their mesoscale page the following:

Effective Shear
Supercell Composite (left-moving)
Signifigant Tornado (with CIN and MLCIN)
Signifigant Hail

These should come in handy!
 
Re: New Products-Watch Probability Table

Originally posted by Andy Wehrle
I also noticed that they have FINALLY made the watch probability tables publically available! It lends more meaning to the severe thunderstorm or tornado watch by giving the probability of different severe events in the watch area.

http://www.spc.noaa.gov/products/watch/ww0042_prob.html

Hmmm... I don't really like how they use "0%" for their tornado risk. Whenever there are severe thunderstorms, the unexpected can always happen - And I can see a few people putting blame on the SPC for saying that there was a "0% chance for tornadoes". I would stick it at <1%, and that would end that :wink:
 
I see where you're coming from; and I do agree that forecasters should be very judicious about their use of extreme values in the probabilities. Remember, though, those zeros do not represent a "0% chance for tornadoes." Look more closely. They actually are for "2 or more tornadoes" and "1 or more strong (F2-F5) tornadoes." The singular, weak, rogue tornado touchdown is acceptable in any severe thunderstorm watch -- even in one carrying zero probabilities for those two tornado categories.

Zero or 100 should not appear very commonly; but there would be some solidly justifiable occasions. For example, I would risk using a zero probability for the hail categories (10 or more, or a two inch stone) for a tornado watch covering a tropical cyclone landfall, where neither such condition has ever been documented nor is supported by the wretchedly unfavorable thermodynamic situation. A 100 could be justified in a necessary replacement or "tack on" watch, covering a major, violent tornado outbreak, when multiple cyclic and tornadic supercells are ongoing and moving through the area of concern shortly before the time of prior watch expiration.

Ultimately, any forecast should be judged by the results; for the atmosphere always provides the answer key to test of forecasting. In this event, Jon Racy put a zero for the probability of F2 tornadoes and for two or more tornadoes, and guess what: there were none, and for sound reasoning which I won't expend bandwidth upon but which can be found in the watch and MCDs for that event. The overwhelming majority of severe events were firmly within Jon's watch too. This one worked out as well as could be expected, especially considering the strange ambient situation characterized by the presence of 35-45 degree preconvective surface dew points in the Carolinas. :thumbup:

Thanks for the great words on the mesoscale page. I was glad they could be made ready before the bulk of the convective season.
 
Gotcha, that makes perfect sense...

What made me think about the 0% was the April 20, 2004 event last year (see: http://www.spc.noaa.gov/climo/reports/040420_rpts.html ). The SLGT risk was about 75 miles southwest of the outbreak region, which looked like a very good forecast, at the time. CAPE during that event was around 800J/KG at ILX, and even less further north, where the actual outbreak occured. That area was socked in by clouds and rain ahead of a strong warm front, with sub 55F temps all the way up until 20Z - The first tornado touched down around 19Z. The temp then shot up to a whopping 65F at ILX as the warm front surged northward (which is when ILX reported a massive CAPE of 800J/KG).

Anyway, that's when a couple people felt that SPC/NWS was at fault (the media is good for that one, namely newspapers) - But that can be rebutted by saying: What benefit would SPC have to miss a forecast? - And the same goes for any other meteorologist that makes a mistake.

But again, I still feel that extreme caution should be used when using extreme probabilistic values (0 and 100)... And today was a good example, where it does appear that caution was excercised, since as you said, there were 0 tornado reports.
 
Originally posted by Joel Wright+--><div class='quotetop'>QUOTE(Joel Wright)</div>
<!--QuoteBegin-rdewey
(which is when ILX reported a massive CAPE of 800J/KG).


That is absolutely tremendous CAPE for mid April anywhere, let alone IL.[/b]

800 J/KG CAPE is tremendous?! 8000 is tremendous, 800 is rather measely actually... Perhaps I'm not picking up your sarcasm, however. :lol:
 
Originally posted by Jeff Snyder+--><div class='quotetop'>QUOTE(Jeff Snyder)</div>
Originally posted by Joel Wright@
<!--QuoteBegin-rdewey

(which is when ILX reported a massive CAPE of 800J/KG).



That is absolutely tremendous CAPE for mid April anywhere, let alone IL.

800 J/KG CAPE is tremendous?! 8000 is tremendous, 800 is rather measely actually... Perhaps I'm not picking up your sarcasm, however. :lol:[/b]


Nope, that wasn't sarcasm. I'm blind as a bat apparently LOL. Woops. :oops:

I'll go sit in the corner now...
 
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