Sig Severe on SPC SWODY3 Prob?

[Andy Wehrle]

I have noticed SPC putting a hatched significant severe area on their Day 3 outlooks a couple of times this year. This must be a new addition, given that their product description still states that:

Because of the large and increasing amount of uncertainty forecasting severe weather 3 days ahead of time no attempt is made to forecast areas of significant severe weather hazards.

The first time they did this was on January 10, 2005:



and again today:



What are everybody's thoughts on this? I personally think that since this is a newly introduced feature on the Day 3 outlook, it should be reserved for those outlooks when there is relatively high confidence of a major severe weather outbreak for the Day 3 period (which does not seem to be the case for this coming Sunday).

Some examples of what I think would be a more appropriate situation for the use of a sig severe line on the SWODY3 would be May 27, 2004:

View attachment 44e76ff6b51208db6b3b7345c078649c.gif

...SEVERE THUNDERSTORM OUTBREAK POSSIBLE SATURDAY ACROSS PARTS OF OK/KS/NEB...

or May 2, 2003:

...LWR/MID MS VLYS INTO TN/OH VLYS...
POTENTIAL WILL EXIST FOR A SEVERE WEATHER OUTBREAK ON SUNDAY AS 70+ KT MID LEVEL SPEED MAX ASSOCIATED WITH EXITING UPPER LOW OVERSPREADS REGION OF STRONG LOW LEVEL MOISTURE ADVECTION OVER THE LWR TO MID MS VLY.

 

[Michael Auker]

Tulsa NWS has really been hyping Sunday's event, apparently they feel it has high potential. I'm wondering if Monday won't be the worst of the two days, Jackson NWS states it's a "classic severe weather set-up"?

 

[Ben Prusia]

I am also confused by that, since the SPC explicitally says on their Convective Outlooks Product Page:

Note: The 10% and greater probability thunder line is not included on the Day 3 Outlook.

They might be bending the rules here, but I am not sure.

 

[Jeff Snyder]

I am also confused by that, since the SPC explicitally says on their Convective Outlooks Product Page:

Note: The 10% and greater probability thunder line is not included on the Day 3 Outlook.

They might be bending the rules here, but I am not sure.

Ben,

The SPC doesn't show the "General Tstorm" line on Day 3 graphics... The "10% and greater prob of thunder" is the brown line on SPC SWODYs...

I think it really depends upon the situation (referring to the original topic now)... If there is good consensus among the numerical models, then I think one can, with reasonable confidence, outline an area of 'significant severe'. I would have hatched the SWODY3 as well, given the dynamics, kinematics, thermodynamics, etc... Nobody said that hatched area is only for big tornadoes... They probably hatched it for very large hail potential and maybe very damaging winds.

 

[Jared Guyer]

Andy et al.,

A couple of weeks ago we adjusted our probability criteria on Day 3, namely to mesh with our experimental Day 4-8 product (NWS internal at this time). Aside from the allowance of sig 25%, we have even modified our criteria such that a MDT risk (35% prob) can now be issued on Day 3 -- naturally this will be used very sparingly. Along those lines, high risks are now possible in Day 2.

We'll have to get this change updated on the product description page.

Jared

 

[Jeff Snyder]

Andy et al.,

A couple of weeks ago we adjusted our probability criteria on Day 3, namely to mesh with our experimental Day 4-8 product (NWS internal at this time). Aside from the allowance of sig 25%, we have even modified our criteria such that a MDT risk (35% prob) can now be issued on Day 3 -- naturally this will be used very sparingly. Along those lines, high risks are now possible in Day 2.

We'll have to get this change updated on the product description page.

Jared

Jared, nice to see another SPC voice on here... I was wondering when ya'll would start doing High risks on Day 2 outlooks. It made sense to limit it to MDT back when the models were lower resolution and generally performed more poorly than they do now. With modeling advances, however, I think that, in situations with excellent forecast confidence (good run-to-run and model-to-model consistency and agreement, good upper-air sampling, etc), one can have enough confidence to issue that most rare of outlooks that is HIGH.