Apr 19-21 Plains/MW Severe Weather, SPC Risk Level: Day 1-2 Slight Risk - Forecasts & OBS Options

[jdrenken]

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1230 PM CDT WED APR 18 2012

VALID 191200Z - 201200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM S-CNTRL IA TO SWRN OK...

...SYNOPSIS...
A PROGRESSIVE/ZONAL UPPER-LEVEL PATTERN OVER THE NRN TIER WILL
AMPLIFY ON THU AS A BROAD TROUGH FORMS ACROSS THE GREAT PLAINS WITH
A SERIES OF EMBEDDED IMPULSES/SPEED MAXIMA. AS MID-LEVEL HEIGHTS
LOWER ACROSS THE CNTRL/SRN PLAINS...WEAK CYCLOGENESIS WILL OCCUR
ALONG A S/SEWD MOVING COLD FRONT. AT 20/00Z...A SURFACE LOW SHOULD
BE CENTERED INVOF THE IA/MO BORDER WITH THE COLD FRONT EXTENDING
SWWD AND INTERSECTING ANOTHER LOW AND DRYLINE INVOF NWRN TX.

...MID-MO VALLEY TO THE SRN PLAINS...
ALTHOUGH LOW-LEVEL TRAJECTORIES WILL NOT BE PARTICULARLY FAVORABLE
FOR A BROAD INFLUX OF RICH WRN GULF MOISTURE IN THE WAKE OF A
DEPARTING SHORT WAVE TROUGH IN THE SOUTHEAST...A CORRIDOR OF MIDDLE
50S TO LOWER 60S SURFACE DEW POINTS WILL LIKELY SPREAD NWD AHEAD OF
THE ADVANCING COLD FRONT. WITH STEEP MID-LEVEL LAPSE
RATES...MODERATE INSTABILITY WILL DEVELOP WITH MLCAPE GENERALLY
RANGING FROM 1000-2000 J/KG AT PEAK HEATING.

MODEL GUIDANCE IS HIGHLY CONSISTENT THAT AFTERNOON THUNDERSTORMS
APPEAR MOST LIKELY TO INITIATE INVOF THE MO/IA SURFACE CYCLONE AND
THEN DEVELOP SWWD INTO EARLY EVENING AS INHIBITION WEAKENS. STRONG
MID-LEVEL W/SWLYS WILL PROMOTE UPDRAFT ROTATION AND IN CONJUNCTION
WITH THE STEEP MID-LEVEL LAPSE RATES...RESULT IN A RISK FOR LARGE
HAIL. WITH STRONG FORCING WITHIN THE FRONTAL ZONE...AND LOW-LEVEL
FLOW WEAKENING/VEERING IN MUCH OF THE WARM SECTOR...THE POTENTIAL
FOR NUMEROUS STORM-SCALE INTERACTIONS MAY LIMIT THE LONGEVITY OF
SUPERCELL STRUCTURES AND INTENSITY OF HAIL GROWTH. A BRIEF TORNADO
OR TWO COULD DEVELOP AROUND SUNSET JUST NE OF THE COLD FRONT/DRYLINE
INTERSECTION IN SWRN OK WHERE LOW-LEVEL FLOW SHOULD REMAIN BACKED
PRIOR TO A NOCTURNAL INCREASE IN MLCIN. WITH THE NOCTURNAL LLJ
FORECAST TO STRENGTHEN ACROSS NWRN/N-CNTRL TX...AN MCS COULD BECOME
SUSTAINED IN OK TO THE OZARK PLATEAU THU NIGHT. BUT GIVEN THE
RELATIVELY NARROW CORRIDOR OF MODERATE INSTABILITY...SEVERE
POTENTIAL SHOULD WANE WITH TIME AND ERN EXTENT OVERNIGHT.

..GRAMS.. 04/18/2012

[heatburst]

Just wrote a blog on this potential. The SPC brings up a great point about tornadic potential around sunset. This is because dew points are not going to be impressive and combined with the daytime heating will produce a significant dew point depression at the sfc. This would result in high based activity. But it appears EML gives way to some discrete supercells in OK around 6-8PM resulting in the potential for tornadoes. I illustrate with a map in my blog:

Severe Weather Thursday Map


Overall I think this will be the most exciting part of the day, but a few bowing segments are also possible across KS/MO.

[wxman1952]

nothing severe is called for here in lower Michigan, but I'm hoping we see some heavy rain that could come.

[jdrenken]

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1259 AM CDT THU APR 19 2012

VALID 191200Z - 201200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM NWRN TX...OK..ERN KS INTO
THE MID MS VALLEY REGION...

...SYNOPSIS...

PROGRESSIVE QUASI-ZONAL UPPER PATTERN WILL BEGIN A TRANSITION ON
THURSDAY AS A SYNOPTIC TROUGH AMPLIFIES OVER THE PLAINS AND MS
VALLEY. SEVERAL IMPULSES EMBEDDED WITHIN THIS FEATURE WILL AFFECT
PORTIONS OF THE PLAINS DURING THE DAY. A SHORTWAVE TROUGH NOW OVER
THE NRN ROCKIES WILL MOVE THROUGH THE NRN PLAINS...UPPER MS VALLEY
AND GREAT LAKES...WHILE FARTHER SOUTH ANOTHER IMPULSE WILL AFFECT
THE SRN AND CNTRL PLAINS. SFC LOW WILL TRACK ENEWD THROUGH UPPER MS
VALLEY INTO THE GREAT LAKES ALONG STALLED BOUNDARY IN ASSOCIATION
WITH THE NRN STREAM FEATURE. A COLD FRONT EXTENDING SWWD FROM THIS
LOW WILL ADVANCE THROUGH THE CNTRL AND SRN PLAINS. BY LATE AFTERNOON
THIS FRONT WILL LIKELY EXTEND FROM ERN KS SWWD TO A WEAK SFC LOW IN
NWRN TX. A DRYLINE WILL EXIST SWD FROM THE LOW THROUGH WRN TX. THE
COLD FRONT WILL CONTINUE SEWD OVERNIGHT.

...NWRN TX THROUGH OK...ERN KS AND THE MID MS VALLEY AREA...

WITH DEWPOINTS OVER THE WRN GULF ONLY IN THE MID 50S...BOUNDARY
LAYER MOISTURE WILL NOT INCREASE MUCH ABOVE WHAT IS ALREADY IN PLACE
OVER THE CNTRL AND SRN PLAINS. HOWEVER...INCREASINGLY WLY FLOW
ACCOMPANYING THE UPPER TROUGH WILL TRANSPORT PLUME OF STEEPER LAPSE
RATES EWD ABOVE AXIS OF LOW-MID 50S DEWPOINTS. THIS PROCESS IN
CONJUNCTION WITH BOUNDARY LAYER WARMING AND COOLING TEMPERATURES
ALOFT ACCOMPANYING THE UPPER TROUGH SHOULD YIELD 1000-1500 J/KG
MLCAPE FROM NWRN-NCNTRL TX INTO OK AND ERN KS WITH HIGHER CAPE
LIKELY RESIDING OVER THE SRN PLAINS. THE EWD TRANSPORT OF THE EML
WILL CONTRIBUTE TO A CAP. HOWEVER...FRONTAL FORCING WILL LIKELY
RESULT IN STORMS DEVELOPING FROM IA SWWD THROUGH ERN KS INTO NWRN OK
BY LATE AFTERNOON. LARGELY UNIDIRECTIONAL SHEAR OF 35-40 KT WILL
SUPPORT BOTH MULTICELL AND POSSIBLY SOME SUPERCELL STRUCTURES...BUT
TENDENCY MAY BE FOR SOME OF THIS ACTIVITY TO GROW UPSCALE INTO LINE
SEGMENTS WITH A THREAT OF DAMAGING WIND AND LARGE HAIL.

OTHER STORMS WILL LIKELY DEVELOP IN VICINITY OF THE DRYLINE/COLD
FRONT INTERSECTION AND NEAR WEAK SFC LOW OVER NWRN TX OR SWRN OK.
DEEP VERTICAL SHEAR IN THIS REGION WILL INCREASE TO 45-50 KT BY
EVENING AS MID LEVEL JET ROTATES THROUGH BASE OF AMPLIFYING UPPER
TROUGH. THESE STORMS WILL LIKELY BE DISCRETE SUPERCELLS CAPABLE OF
VERY LARGE HAIL AND ISOLATED DAMAGING WIND. A TORNADO OR TWO CANNOT
BE RULED OUT INTO EARLY EVENING...BUT LIMITING FACTORS WILL BE WEAK
INITIAL LOW LEVEL SHEAR AND RELATIVELY HIGH BOUNDARY LAYER
TEMPERATURE-DEWPOINTS SPREADS. NEVERTHELESS...A SMALL WINDOW MAY
EXIST FOR A TORNADO AS THE LLJ STRENGTHENS AND BEFORE THE BOUNDARY
LAYER DECOUPLES.

..DIAL/SMITH.. 04/19/2012

[jdrenken]

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 183
NWS STORM PREDICTION CENTER NORMAN OK
640 PM CDT THU APR 19 2012

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

SOUTH CENTRAL OKLAHOMA
WESTERN NORTH TEXAS

EFFECTIVE THIS THURSDAY NIGHT AND FRIDAY MORNING FROM 640 PM
UNTIL 100 AM CDT.

HAIL TO 2.5 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 55
STATUTE MILES EAST AND WEST OF A LINE FROM 35 MILES WEST OF
MINERAL WELLS TEXAS TO 20 MILES NORTHEAST OF OKLAHOMA CITY
OKLAHOMA. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU3).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR 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. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

DISCUSSION...THUNDERSTORMS ARE BEGINNING TO FORM ALONG SURFACE COLD
FRONT/DRYLINE OVER WESTERN NORTH TX...AND ARE EXPECTED TO FORM IN
THE NEXT 1-2 HOURS OVER PARTS OF SOUTHWEST OK. THIS ACTIVITY WILL
BE IN A REGION OF RELATIVELY WEAK LOW LEVEL SHEAR. BUT...SUFFICIENT
EFFECTIVE SHEAR VALUES AND MODERATE CAPE WILL PROMOTE SUPERCELL
STRUCTURES CAPABLE OF LARGE HAIL AND DAMAGING WINDS. ACTIVITY MAY
PERSIST NEAR THE RED RIVER FOR MUCH OF THE EVENING.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM
MOTION VECTOR 27030.


...HART

[WeatherMonger]

BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
329 PM CDT SAT APR 21 2012

THE NATIONAL WEATHER SERVICE IN THE TWIN CITIES HAS ISSUED A

* TORNADO WARNING FOR...
  NORTHEASTERN CHIPPEWA COUNTY IN WEST CENTRAL MINNESOTA...
  SOUTH CENTRAL SWIFT COUNTY IN WEST CENTRAL MINNESOTA...

* UNTIL 415 PM CDT

* AT 325 PM CDT...LAW ENFORCEMENT REPORTED A TORNADO 14 MILES
  NORTHWEST OF GLUEK...OR ABOUT 7 MILES EAST OF BIG BEND CITY. RADAR
  SHOWED THE TORNADIC STORM MOVING SOUTHEAST AT 25 MPH.

* LOCATIONS IN THE WARNING INCLUDE...
  GLUEK...

[snowlover2]

So what's with all the tornado reports in Minnesota? Did not expect to see that.