PWO for MDT risk days?

[Andy Wehrle]

I have noticed a few instances in the past where the SPC has issued a Public Severe Weather Outlook, yet never upgraded the categorical convective outlook risk beyond Moderate. A couple of examples are June 08, 1995 (Pampa, Allison, Kellerville, TX), and October 04, 1998 (Oklahoma October Outbreak). In the SPC's ZIP files of archived products, the 6-5-95 convective outlooks include the wording "a public severe weather outlook will be issued shortly" but none of them go to high risk. Likewise for 10-04-98. Eric Nguyen's page even has both archived PWOs from that day. http://www.mesoscale.ws/98~documents/#981004

Does the SPC still do this? I wonder what the criteria are seeing as there are many MDT risk days on which PWOs are never issued.

 

[Morgan Palmer]

I, for one, would hope SPC wouldn't refrain from putting out a PWO when they think they should.

Kind of a qualitative vs. quantitative kind of think.

I am curious as to what policy is in place.

mp

 

[Andy Wehrle]

I'm not so much saying SPC should refrain from issuing a PWO if they feel it is necessary, but rather wondering why if they feel a PWO is necessary why they then don't also upgrade to high risk? Don't the two kind of go hand in hand as ways to emphasize a dangerous outbreak situation?

 

[Morgan Palmer]

I want to know too. I wasn't disagreeing. Maybe someone can help us!

mp

 

[Robert Dewey]

I asked John Hart at the SPC, we'll see what he says...

 

[Andy Wehrle]

Thanks Robert. For some reason I always run into technical problems when I try to contact the SPC.

 

[rdale]

Here's what SPC says:

The Public Severe Weather Outlooks (PWO) are issued when a potentially significant or widespread tornado outbreak is expected. This plain-language forecast is typically issued 12-24 hours prior to the event and is used to alert NWS field offices and other weather customers concerned with public safety of a rare, dangerous situation. The PWO is reserved for only the most serious weather situations where a HIGH risk is forecast for a potential tornado outbreak. The SPC issues around 5 PWO's each year.

 

[Robert Dewey]

Here's what SPC says:

The Public Severe Weather Outlooks (PWO) are issued when a potentially significant or widespread tornado outbreak is expected. This plain-language forecast is typically issued 12-24 hours prior to the event and is used to alert NWS field offices and other weather customers concerned with public safety of a rare, dangerous situation. The PWO is reserved for only the most serious weather situations where a HIGH risk is forecast for a potential tornado outbreak. The SPC issues around 5 PWO's each year.

Well, my guess is they will issue a PWO on a MDT risk day that has the potential for being very widespread... I think we are getting mixed up with "probability" and "coverage"... A very small HIGH risk area (a very small portion of a state) may not warrant a PWO, whereas a MDT risk spanning several states just might fit the bill...

 

[rdale]

I think what you are saying _should_ be the case, but it's clear (capital letters and all) that a HIGH risk needs to be in place or SPC won't issue one.

Here's the exact wording from their directives:

5.3.3 Content. SPC will issue a Public Severe Weather Outlook when it forecasts any of the following conditions:

a. High risk of severe thunderstorms in the Categorical Day One Outlook;

b. 25% or greater probability of tornadoes, and a forecast of a 10% or greater probability of tornadoes which could cause F2 or greater damage within this area; or

c. 45% or greater probabilities of convective damaging wind gusts in conjunction with a 10% chance or 65 knot or greater wind gusts.

If a High Risk is initiated on the 0600 UTC Day 1 Outlook, a PWO will be issued at approximately 1000 and 1700 UTC. If the High Risk is initialized at 1300 a PWO will be issued at 1300 and 1700 UTC. A PWO may also be written around 2000 UTC for a high risk that is expected to occur during the overnight hours.

 

[Robert Dewey]

John Hart:

Our guidelines for PWOs have changed over the past few years. There
was a period (1993-1997) when we issued PWOs for high-end MDT risk
days. However, for the last several years, we have not done that.
Our current guidelines specify only issuing a PWO when a HIGH risk has
been issued. PWOs are issued so rarely that we often wonder about the
distribution and/or receipt of the product.

 

[Andy Wehrle]

Well the SPC has issued a public severe weather outlook, so either they are planning to upgrade to high risk at the 1630Z outlook or they have changed their guidelines again.

http://www.spc.noaa.gov/products/outlook/pwo.html

It's a pretty screwed-up PSWO too...several sections are missing, and there's no forecaster signature at the bottom. WTF? :?

 

[Jeff Snyder]

LOL Yep... probably the latter, though the current PSWO is incorrectly-formatted, which still makes me suspicious that they were debating about making it /sending it out, but sent it prematurely and/or accidentally.

I would think that the a PSWO would be issue if they were forecasting :

+ WIDESPREAD severe with damaging winds or very large hail
+ Scattered/isolated SIGNIFICANT strong/violent tornadoes

So, it's a case of numerous middle-end events, or at least scattered high-end events (strong/violent tornadoes, very damaging winds, etc). I think some of this may be SLIGHTLY political with metro areas possibly at risk (Tulsa, Springfield, Kansas City it appears in this case), but I don't want to make it sound like I think SPC folks let that stand in their way of outlooking objectively. This was brought up last year regarding whether population density (which, given a set area, would determine the number of people at risk) should be considered when issuing a high risk.

Anyways, I think they are anticipating widespread moderate-level severe, thus the issuance of a PSWO (despite that I'm still questioning the legitimacy of the PSWO given the atypical formattting)...

 

[Andy Wehrle]

Interesting to see the discussion about this in Target Area...some are predicting an upgrade to high risk while others think the moderate risk/15% tornado prob will be removed.

My opinion regarding the PSWO is that it should be reserved for high risk days with an outbreak of strong/violent tornadoes anticipated (25% or 35% tornado probability with hatching) or an extreme derecho (45% hatched damaging wind).

 

[Mikel Shively]

LOL Yep... probably the latter, though the current PSWO is incorrectly-formatted, which still makes me suspicious that they were debating about making it /sending it out, but sent it prematurely and/or accidentally.

I would think that the a PSWO would be issue if they were forecasting :

+ WIDESPREAD severe with damaging winds or very large hail
+ Scattered/isolated SIGNIFICANT strong/violent tornadoes

So, it's a case of numerous middle-end events, or at least scattered high-end events (strong/violent tornadoes, very damaging winds, etc). I think some of this may be SLIGHTLY political with metro areas possibly at risk (Tulsa, Springfield, Kansas City it appears in this case), but I don't want to make it sound like I think SPC folks let that stand in their way of outlooking objectively. This was brought up last year regarding whether population density (which, given a set area, would determine the number of people at risk) should be considered when issuing a high risk.

Anyways, I think they are anticipating widespread moderate-level severe, thus the issuance of a PSWO (despite that I'm still questioning the legitimacy of the PSWO given the atypical formattting)...

Intesting thing happend....refreshed the SPC page. the PWO was gone. nowhere to be found.... This leads me to the conlusion it must have been some kind of error.

 

[Karen Politte]

Andy -

It likely means that any severe weather encountered will be high-end severe, but the chances of actually encountering that severe weather are only MODERATE.

KR

EDIT: Although, after reading more of the posts on this thread, I would agree that I was fairly surprised to see the PSWO issued this morning.....I wasn't really expecting it and I DON'T know if it is really warranted.......maybe the button was pushed prematurely......we'll see.