SPC modification for PWO's for nighttime events

[CrazyC83]

http://www.spc.noaa.gov/misc/cool_seaso ... e_PWO.html

Public Severe Weather Outlooks for nighttime tornado potential will be issued December 1 through March 31.

Cool-season nighttime tornadoes pose a particular challenge to forecasters, and are also a substantial threat to the public (see: Ashley, Weather and Forecasting Volume 22, Issue 6 (December 2007) pp. 1214–1228). In the wake of the Super Tuesday Tornado Outbreak of February 2008, it was found that many people did not expect tornadoes, especially in February, and especially at night. Late night tornado events also pose a significant challenge to public safety officials when alerting the public to the impending threat can be extremely difficult after people have gone to bed. While it is recognized that the bulk of these events will remain difficult to forecast and highly uncertain, the SPC is in the best position to offer guidance and meteorological support ahead of these "high impact, low probability" events. To that end, this is a initial attempt to improve our commitment to saving lives and protecting property.

Below is an outline of what SPC and a few Southern Region WFOs have collectively decided to do in an attempt to increase public awareness of the potential for significant cool-season nighttime tornadoes. This practice will commence on December 1st, 2009 and end on March 31, 2010. This is only a minor modification of the current Public Severe Weather Outlook (PWO) issuance criteria that requires a PWO for slightly greater forecast probabilities of tornado/wind events. The climatology of nighttime 10 percent significant tornado forecasts over the past several years suggests that this type of PWO may be issued about 3 to 5 times during the cool season (December-March).
The Storm Prediction Center Station Duty Manual was updated on November 30, 2009 to include the following instructions to SPC forecasters:

A Public Severe Weather Outlook (PWO) will be composed and transmitted by the Outlook forecaster following the issuance of a 2000 UTC and/or 0100 UTC Day 1 Outlook (SWODY1) when a 10 percent probability of significant tornadoes (hatched area) is forecast after dark anywhere in the CONUS. These PWOs will be specifically worded to address the threat of nighttime tornadoes and issued even if an earlier PWO was issued for significant severe weather during daylight hours. A preformat has been added to SPC product generation software for the purpose of overnight PWOs. The forecaster will need to add the states included in the threat area to this preformat. These types of PWOs will be issued for the December 1st through March 31st period. We will assess the impacts of this change and determine if this is a practice that should be continued for every cool-season at the close of the cool season in early 2010.

Here is an example of this type of PWO:

PUBLIC SEVERE WEATHER OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0600 PM CST WED JAN 06 2010

...SEVERE THUNDERSTORMS EXPECTED OVER PARTS OF XXXX OVERNIGHT...

THE NWS STORM PREDICTION CENTER IN NORMAN OK IS FORECASTING THE
POSSIBLE DEVELOPMENT OF TORNADOES OVER PARTS OF XXXX OVERNIGHT.

CONDITIONS ARE EXPECTED TO SUPPORT THE POTENTIAL FOR A FEW STRONG AND
POSSIBLY LONG-LIVED TORNADOES.

WHILE OVERALL SEVERE THUNDERSTORM COVERAGE IS NOT EXPECTED TO BE
WIDESPREAD...THE POTENTIAL FOR A SIGNIFICANT TORNADO AFTER DARK WARRANTS
HEIGHTENED SAFETY PRECAUTIONS.

TORNADOES DURING THE OVERNIGHT HOURS AT THIS TIME OF YEAR CAN BE
PARTICULARLY DANGEROUS BECAUSE THEY ARE USUALLY FAST-MOVING
AND OBSCURED BY RAIN AND DARKNESS.

THE AREAS MOST LIKELY TO EXPERIENCE THIS ACTIVITY INCLUDE

XXXX AND XXXX

STATE AND LOCAL EMERGENCY MANAGERS ARE MONITORING THIS DEVELOPING
SITUATION. THOSE IN THE THREATENED AREA ARE URGED TO REVIEW SEVERE
WEATHER SAFETY RULES AND TO LISTEN TO RADIO...TELEVISION...AND NOAA
WEATHER RADIO FOR POSSIBLE WATCHES...WARNINGS...AND STATEMENTS
TONIGHT.

(I am also writing an e-mail based on the suggestion for use of different enhanced wording for such events, after the questionable PDS use last night)

[CrazyC83]

Here was my submission (minus the header and salutation which I left out here):

I think it is an excellent idea to issue a PWO for nighttime events, and it should run for any event with at least a 5% tornado threat.

Also I noticed that a PDS watch was issued last night (December 2) even though the numerical parameters were not exactly warranting of such. I think that an early and enhanced warning was definitely warranted, but at the same time, the use of the words PDS on a low-coverage situation may create an issue of complacency if a major outbreak is forecast and the PDS is truly warranted. While the 70/50 numbers warranted the PDS, it is likely that the nighttime threat in December significantly influenced the decision (although I cannot speak for the forecaster). It was definitely a good move to play it safe even if the chance of verifying was lower, considering the extreme danger of even isolated nighttime tornadoes especially in the cooler season though, however it should be done differently in my opinion.

I recommend the creation of a new watch category, called "Special Awareness Situation", to be issued only on tornado watches with at least a 30% threat of strong/violent tornadoes (regardless of other numbers - and lower than current PDS criteria in most cases) from November 1 to March 31 with most of the activity expected between the hours of 11 pm and 7 am local time when awareness is lowest and the population is most vulnerable. These watches should be required to go out by 10:30 pm Central or 11:30 pm Eastern time, in order to make it onto most late local newscasts, even if the timing would not otherwise warrant such immediately (but would before 7 am).

If a PDS watch is truly warranted, that would still be included, but the special awareness paragraph and timing rules should still be in place.

On the web sites, it should be highlighted in fuchsia saying "Special Awareness" followed by Tornado Watch ### in black.

For example, Tornado Watch #791 would be modified to the following (removed PDS wording, but added separate wording before the box coordinates). Watches #792 and #793 also affecting the overnight hours had a 20% significant tornado risk.

SEL1

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 791
NWS STORM PREDICTION CENTER NORMAN OK
700 PM EST WED DEC 2 2009

THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF

EASTERN AND CENTRAL NORTH CAROLINA
EASTERN SOUTH CAROLINA
COASTAL WATERS

EFFECTIVE THIS WEDNESDAY NIGHT AND THURSDAY MORNING FROM 700 PM
UNTIL 400 AM EST.

TORNADOES...HAIL TO 1 INCH IN DIAMETER...THUNDERSTORM WIND GUSTS TO
70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THIS IS A SPECIAL AWARENESS SITUATION FOR THE RISK OF ISOLATED
SIGNIFICANT TORNADOES OVERNIGHT, WHICH ARE ESPECIALLY
DANGEROUS AS THEY CAN BE OBSCURED BY RAIN AND DARKNESS WITH
MANY PEOPLE NOT IMMEDIATELY AWARE OF THE SITUATION.

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 50 STATUTE
MILES EITHER SIDE OF A LINE FROM 20 MILES SOUTH SOUTHWEST OF
FLORENCE SOUTH CAROLINA TO 55 MILES EAST SOUTHEAST OF ELIZABETH
CITY NORTH CAROLINA. FOR A COMPLETE DEPICTION OF THE WATCH SEE
THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU1).

REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS.

OTHER WATCH INFORMATION...CONTINUE...WW 789...WW 790...

DISCUSSION...BOUNDARY LAYER WARMING/MOISTENING EXPECTED TO CONTINUE
THIS EVE/EARLY THU OVER THE NC CSTL PLN...AHEAD OF BROKEN BAND OF
SHOWERS/TSTMS NOW EXTENDING FROM W OF FLO SSW TO NEAR SAV. GIVEN
DESTABILIZING LOW LVL ENVIRONMENT...THE CONVECTION MAY INCREASE OVER
FAR ERN SC AND ERN NC LATER THIS EVE/EARLY THU AS REGION IS GLANCED
BY WAVE OF ASCENT/DPVA ASSOCIATED WITH ERN TN SHORTWAVE TROUGH.
VERY STRONG AND VEERING WIND PROFILES AND ABSENCE OF STRONG LINEAR
FORCING SUGGEST POTENTIAL FOR SEMI-DISCRETE STORMS WITH LOW LVL
ROTATION...AND POSSIBLY A COUPLE STRONG TORNADOES.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 1 INCH. EXTREME TURBULENCE AND SURFACE WIND
GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 450.
MEAN STORM MOTION VECTOR 22050.


...CORFIDI

That is just my suggestion on how to minimize confusion and complacency yet get the word out of the extremely serious situation at the same time.