Another multi-day outbreak (April 17-18)

[TropicalAnalystwx13]

Setup looks a bit more favorable this time around.



DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0331 AM CDT SUN APR 14 2013

VALID 171200Z - 221200Z

...DISCUSSION...
BOTH THE ECMWF AND GFS ARE IN GENERAL AGREEMENT THROUGH THE DAY4
PERIOD REGARDING THE EVOLUTION OF UPPER TROUGH AS IT PROGRESSES INTO
THE MIDDLE OF THE CONUS. HOWEVER...MAJOR DIFFERENCES ARE EXPOSED BY
WEDNESDAY IN THAT THE GFS ERODES THE CP AIR MASS ACROSS THE CNTRL
PLAINS ALLOWING A SIGNIFICANT SFC CYCLONE TO TRACK NEWD ACROSS KS
INTO SRN IA BY MIDNIGHT. ECMWF IS MUCH MORE AGGRESSIVE WITH POLAR
SURGE AND THE LACK OF A MEANINGFUL SFC LOW. GIVEN THE MAGNITUDE OF
CP AIR ACROSS THE HIGH PLAINS THIS MAY BETTER REPRESENT THE TRUE
SURGE THAT COULD OCCUR BY DAY4. FOLLOWING THE ECMWF...AMPLE
MOISTURE/INSTABILITY WILL BE IN PLACE FROM TX NEWD INTO THE MID MS
VALLEY AND A SQUALL LINE SHOULD EVOLVE ALONG THE COLD FRONT EARLY IN
THE PERIOD ACROSS OK THEN PROGRESS AND EXPAND IN AREAL COVERAGE AS
COLD FRONT MOVES TOWARD THE ARKLATEX. IN ADDITION TO A SQUALL
LINE...MORE DISCRETE STORMS COULD DEVELOP ACROSS THE WARM SECTOR
OVER CNTRL/NERN TX. WHILE THE ECMWF MAY BETTER DEPICT THE SCENARIO
IF THE GFS IS CORRECT A MORE SIGNIFICANT SEVERE EVENT WOULD
POTENTIALLY UNFOLD ACROSS THE PLAINS INTO THE MID MS VALLEY.

..DARROW.. 04/14/2013

More on this later.

[Ntxw]

I would generally agree this system looks better on paper than the last. ECMWF does initiate convection on the dryline this go around. More energy is bundled at the base of the trough than meridional flow we saw last week (too positive tilt). The cap will still be there but we should see a better warm front.

Still a few questions to be answered, will there be good southeasterly flow to tap into the gulf? How warm is the air mass coming in from the gulf and is all of that enough to break the cap that will present itself again most likely especially in the southern plains before another stout cold front races south.

[WeatherGuesser]

I was just looking at this one, getting ready to post.

HPC also has some heavy rains in the forecast, on the order of 3" or more for some areas.

[TropicalAnalystwx13]

Some of the hodographs from Thursday across Arkansas and Missouri (eastern) are downright scary. Some questions remain...but with the type of setup...assuming nothing changes...I would not be surprised at all to see a few significant to violent tornadoes.

Especially considering stronger tornadoes seem to be occurring more often even in a more marginal environment (MS EF3 tornado on Thursday).

[EF-5bigj]

Again? well I hope everyone stays safe in that area yeah that EF-3 was something....

[TwisterFanatic]

Looks like possibly a significant outbreak across Oklahoma, Missouri and Kansas on Wednesday. SPC issued a Day 3 Moderdate.

[WeatherGuesser]

Fairly rare, no?

[cycloneye]

Looks like possibly a significant outbreak across Oklahoma, Missouri and Kansas on Wednesday. SPC issued a Day 3 Moderdate.

http://www.spc.noaa.gov/products/outloo ... k_0730.gif

Here is the discussion for day 3.

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0224 AM CDT MON APR 15 2013

VALID 171200Z - 181200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS OK/SERN KS/SWRN MO...

...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK FROM
NWRN TX INTO CNTRL IL...

...SIGNIFICANT SEVERE WEATHER EVENT IS POSSIBLE ACROSS PARTS OF THE
SOUTHERN PLAINS INTO THE MID MS VALLEY WEDNESDAY...

...SRN PLAINS TO MID MS VALLEY...

LATEST MODEL GUIDANCE CONTINUES TO SUGGEST A CORRIDOR OF STRONG SWLY
FLOW ALOFT WILL SPREAD ACROSS THE PLAINS WEDNESDAY AFTERNOON. THIS
LARGE SCALE INCREASE IN HIGH LEVEL FLOW IS CONSISTENT AMONG THE
NAM/GFS/ECMWF. OF PARTICULAR CONCERN ARE THE DIFFERENCES REGARDING
THE SYNOPTIC POSITIONS OF THE COLD FRONT WITH THE ECMWF BEING THE
MOST AGGRESSIVE...ALBEIT SLOWER THAN EARLIER RUNS...AND THE GFS
CONSIDERABLY SLOWER WITH THE PRIMARY FRONTAL ZONE AT 18/00Z FROM
SERN NEB ACROSS NWRN KS INTO SERN CO. LATEST THINKING IS THE NAM
MAY BE MORE ACCURATE DEPICTING AN EARLY FRONTAL SURGE THAT WILL
STALL ACROSS THE SRN PLAINS DURING THE DAY1-2 TIME FRAME BEFORE
SLOWLY RETREATING INTO SERN KS/NWRN OK BY LATE AFTERNOON. GIVEN
THIS SCENARIO THE GREATEST BUOYANCY WILL EXIST ACROSS THE BODY OF OK
WHERE STEEPEST LAPSE RATES WILL RESIDE...WHILE SIGNIFICANT
INSTABILITY SHOULD EXTEND DOWNSTREAM INTO PORTIONS OF THE MID MS
VALLEY REGION.

EARLY IN THE PERIOD 50KT+ LLJ WILL BE FOCUSED ACROSS OK/KS.
SCATTERED ELEVATED STRONG STORMS MAY BE ONGOING ACROSS KS INTO
PORTIONS OF EXTREME NWRN MO. THIS SHOULD SERVE TO MAINTAIN
AFOREMENTIONED BOUNDARY ACROSS SERN KS/NWRN OK WHICH WILL BECOME THE
PRIMARY FOCUS FOR RENEWED SEVERE THUNDERSTORM DEVELOPMENT LATER IN
THE DAY. ADDITIONALLY...STRONG HEATING WILL SHARPEN A DRYLINE NEAR
THE TX PANHANDLE/OK BORDER...SSWWD INTO WEST TX. LARGE SCALE
PATTERN APPEARS FAVORABLE FOR SCT-NUMEROUS THUNDERSTORMS FROM LATE
AFTERNOON INTO THE NIGHTTIME HOURS FROM OK NEWD INTO MO. ANY STORMS
THAT DEVELOP SOUTH OF THE SRN MOST STALLED BOUNDARY WILL POSE THE
GREATEST RISK OF MAINTAINING SUPERCELL CHARACTERISTICS THAT WILL
FAVOR VERY LARGE HAIL/DAMAGING WINDS AND TORNADOES. DURING THE
OVERNIGHT HOURS A SECONDARY STRONG COLD FRONTAL PUSH WILL ENCOURAGE
A FORCED LINE OF THUNDERSTORMS ALONG THE WIND SHIFT THAT WILL
PROPAGATE SEWD. BY EARLY THURSDAY AN EXTENSIVE CORRIDOR OF
CONVECTION MAY BE NOTED FROM NRN IL...SWWD ACROSS MO INTO NWRN TX.

..DARROW.. 04/15/2013

[TropicalAnalystwx13]

Fairly rare, no?

Only the 12th time in history.

[CrazyC83]

Not sure if I would have gone that extreme this far out, but this does look to have significant potential. I probably would have held back at 30% for Wednesday personally though.

[WeatherGuesser]

Don't get me wrong, I like Sun, but I get concerned about it compounding things in these situations.

I think I'd rather it stay cloudy for a few days right now.

[TwisterFanatic]

Dr. Forbes has given a TorCon of 6 for Wednesday already.

[TwisterFanatic]

Fairly rare, no?

Only the 12th time in history.

Do you know where to find a list of the other 11 times? I'm very curious.

[WeatherGuesser]

^ I didn't have time to pull this up earlier:

Day 3 moderate risks are quite rare; it has been used only twelve times since the product became operational (most recently for April 17, 2013).

http://en.wikipedia.org/wiki/Storm_Prediction_Center

It doesn't specifically list them though. There is a footnote that linked to an article from CRH, but is now invalid.

[WeatherGuesser]

Just found this page that lists them, but I can't vouch for the site's credibility:

http://www.pmarshwx.com/2012/04/spc-day ... ey-become/

Note: That shows 11 since Jan 2000, which I don't consider 'history' unless they just started issuing them then.

[EF-5bigj]

So are violent tornadoes possible with this one?

[Ntxw]

So are violent tornadoes possible with this one?

It's very likely someone somewhere will get effected by some. Whether it is a localized event or more regional event is yet to be seen. This storm is definitely much more potent than the last one with a much warmer air mass already in place.

[EF-5bigj]

More instability in the place not a good thing how much wind energy is it supposed to have?

[Cyclenall]

I'm surprised to see they went with a Day 3 moderate, just two days ago I was reading how this system will be a carbon copy of last week. Maybe things are changing quick, believe me I like to see something not copied. I also didn't get a sense from the text why they went that high.

A little sideways, but has there ever been a severe weather outbreak with tornadoes with no squall line at some point? I'm thinking the answer is no on this one.

[cycloneye]

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1215 AM CDT TUE APR 16 2013

VALID 171200Z - 181200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS OK INTO EXTREME SERN
KS...

...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK FROM
WCNTRL TX TO IL...

...SRN PLAINS TO MID MS VALLEY...

SIGNIFICANT LARGE SCALE DIFFLUENCE IS EXPECTED TO OVERSPREAD THE SRN
PLAINS WEDNESDAY AS UPPER TROUGH SHIFTS INTO THE ROCKIES. MODELS
CONTINUE TO SUGGEST A CORRIDOR OF 500MB FLOW IN EXCESS OF 50KT WILL
SPREAD ACROSS A MOISTENING WARM SECTOR THAT SHOULD BECOME QUITE
UNSTABLE BY MID DAY. INCREASING LARGE SCALE ASCENT AND FAVORABLE
BUOYANCY SUGGEST A CONSIDERABLE AMOUNT OF CONVECTION WILL ULTIMATELY
EVOLVE ACROSS THE BODY OF OK...NEWD INTO THE MID MS VALLEY...MUCH OF
IT POTENTIALLY SEVERE.

AS UPPER TROUGH APPROACHES THE SRN PLAINS THERE IS REASON TO BELIEVE
EARLY FRONTAL SURGE WILL STALL NEAR THE RED RIVER THEN ADVANCE NWD
AS A WARM FRONT DURING THE DAY2 PERIOD. THERE IS SOME UNCERTAINTY
HOW FAR NORTH THIS BOUNDARY WILL RETREAT WITH THE GFS THE MOST
AGGRESSIVE ALLOWING WARM FRONT TO ULTIMATELY REACH THE I-70 CORRIDOR
ACROSS KS. WHILE THIS MODEL HAS CONSISTENTLY FORECAST THIS SCENARIO
CURRENT AIRMASS ACROSS THE CNTRL PLAINS IS DISTURBINGLY COLD AND ANY
WARM ADVECTION PRECIPITATION ACROSS KS DURING THE DAY1 PERIOD MAY
PREVENT THE WARM SECTOR FROM ADVANCING NORTH OF THE OK BORDER. BOTH
THE NAM AND ECMWF MAINTAIN A MORE SLY POSITION AND FOR THIS REASON
HAVE OPTED TO PERPETUATE ENHANCED SEVERE RISK PRIMARILY ACROSS OK
WITH PERHAPS A NEED TO EXTEND HIGHER PROBS INTO PORTIONS OF NWRN TX.


LATEST THINKING IS LOW LEVEL WARM ADVECTION WILL LIKELY AID EARLY
MORNING ELEVATED TSTMS...POSSIBLY SEVERE...ACROSS KS INTO NRN MO.
DIURNAL HEATING ACROSS THE WARM SECTOR WILL CONTRIBUTE TO
DESTABILIZATION AS FAIRLY MOIST LOW LEVELS...DEW POINTS WELL INTO
THE 60S...CONTRIBUTE TO SBCAPE IN EXCESS OF 2000 J/KG. STRONGEST
HEATING IS EXPECTED ALONG DRYLINE WHICH SHOULD ESTABLISH ITSELF OVER
WRN OK/NWRN TX AND INSTABILITY JUST EAST OF THIS BOUNDARY SHOULD
APPROACH 3000 J/KG. GFS FORECAST SOUNDINGS ARE QUITE IMPRESSIVE
NEAR THE DRYLINE WITH STRONG VEERING WIND PROFILES WITH HEIGHT AND
LOW LCLS. IF WARM FRONT INDEED RETREATS TOWARD THE KS BORDER
DISCRETE SUPERCELLS SHOULD EVOLVE ALONG THE DRYLINE WHICH SHOULD
TRACK ENEWD INTO THE BODY OF OK. REGARDLESS...INCREASING DIFFLUENCE
ALOFT WILL CONTRIBUTE TO NUMEROUS TSTMS INTO THE OVERNIGHT HOURS
AIDED BY 50-60KT SLY LLJ.

AN EXTENSIVE CORRIDOR OF FRONTAL CONVECTION IS EXPECTED TO EXTEND
NEWD ACROSS SERN KS/MO INTO PORTIONS OF WCNTRL IL. THIS ACTIVITY
SHOULD BE WELL ORGANIZED ALONG THE WIND SHIFT BY LATE EVENING BEFORE
ADVANCING DOWNSTREAM WITH PROGRESSIVE BOUNDARY.

LARGE HAIL...DAMAGING WINDS...AND ISOLATED TORNADOES ARE POSSIBLE
ACROSS THE SEVERE RISK REGION...ESPECIALLY OK INTO PORTIONS OF NWRN
TX.

..DARROW.. 04/16/2013