Severe weather outbreak possible on the Plains Sunday, May 19

The Storm Prediction Center in Norman, Oklahoma, is using the “O” word (for “outbreak”) in its outlook for tomorrow, Sunday, May 19th.  They’re quite careful about that word, and when they do use it, it’s time for a heads up, especially if you live in the area that’s hatched on tomorrow’s outlook map:

 

SPC/NOAA/NWS

SPC/NOAA/NWS

DAY 2 CONVECTIVE OUTLOOK CORR 1
NWS STORM PREDICTION CENTER NORMAN OK
0111 AM CDT SAT MAY 18 2013

VALID 191200Z – 201200Z

…THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF ECNTRL OK…ERN
KS AND WRN MO…

…THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE GREAT
PLAINS AND LOWER TO MID MO VALLEY…

CORRECTED TO MAKE MINOR WORDING CHANGES

…REGIONAL SEVERE WEATHER OUTBREAK POSSIBLE ACROSS PARTS OF THE SRN
PLAINS…CNTRL PLAINS AND LOWER MO VALLEY…

…SRN AND CNTRL PLAINS/LOWER MO VALLEY…
A NEGATIVELY-TILTED UPPER-LEVEL TROUGH WILL TRANSLATE EWD INTO THE
SRN AND CNTRL PLAINS ON SUNDAY AS A MID-LEVEL JET MOVES EWD THROUGH
THE CENTER OF THE TROUGH. AT THE SFC…A LOW IS FORECAST TO DEEPEN
AND MOVE NEWD FROM CNTRL KS INTO ERN NEB AS A COLD FRONT ADVANCES
SEWD ACROSS ECNTRL KS AND CNTRL OK. SFC DEWPOINTS TO THE EAST OF THE
FRONT SHOULD BE IN THE MID TO UPPER 60S F WITH MODERATE TO STRONG
DESTABILIZATION LIKELY ACROSS THE MODERATE RISK AREA BY MID TO LATE
AFTERNOON. FORECAST SOUNDINGS AROUND MIDDAY SHOW A CAPPING INVERSION
IN PLACE ACROSS MUCH OF THE WARM SECTOR. THE MODELS WEAKEN THE CAP
BY 21Z ALLOWING FOR CONVECTIVE INITIATION ALONG AND AHEAD OF THE
FRONT. STORMS SHOULD FIRST INITIATE IN NRN AND CNTRL KS…QUICKLY
EXPANDING SWD INTO NRN AND CNTRL OK. AS STORM COVERAGE INCREASES
DURING THE EARLY EVENING…A SEVERE PRODUCING MCS MAY ORGANIZE
ACROSS ERN KS AND ECNTRL OK…MOVING ESEWD ACROSS THE MODERATE RISK
AREA.

FORECAST SOUNDINGS BY 21Z SUNDAY AT TULSA…OKLAHOMA CITY AND KANSAS
CITY SHOW STRONG INSTABILITY WITH MLCAPE VALUES OF 2500 TO 3500
J/KG. DEEP LAYER SHEAR IS FORECAST TO INCREASE DURING THE LATE
AFTERNOON ACROSS THE MODERATE RISK AREA AS A MID-LEVEL JET MOVES
INTO THE REGION FROM THE WEST. THIS COMBINED WITH 850 TO 500 MB
LAPSE RATES EXCEEDING 8.0 C/KM SHOULD BE VERY FAVORABLE FOR
SUPERCELLS WITH LARGE HAIL. HAILSTONES OF GREATER THAN 2 INCHES IN
DIAMETER WILL BE POSSIBLE WITH THE MORE INTENSE SUPERCELLS. IN
ADDITION…A LOW-LEVEL JET IS FORECAST TO BECOME FOCUSED BY EARLY
SUNDAY EVENING FROM SW MO SWWD INTO ECNTRL OK. SUPERCELLS ON THE WRN
EDGE OF THE LOW-LEVEL JET WILL HAVE A CHANCE TO BECOME TORNADIC WITH
A CLUSTER OF TORNADOES POSSIBLE ACROSS THE MODERATE RISK AREA. THE
GREATEST CHANCE FOR STRONG TORNADOES SHOULD EXIST ACROSS ECNTRL OK
AND SE KS WHERE 0-3 KM STORM RELATIVE HELICITIES ARE FORECAST TO
REACH 400 M2/S2 IN THE 00Z TO 03Z TIMEFRAME. DUE TO THE STRONG DEEP
LAYER SHEAR…CELLS SHOULD REMAIN DISCRETE DURING MUCH OF THE EVENT.
SUPERCELLS COULD ALSO PRODUCE SWATHS OF WIND DAMAGE. THE WIND DAMAGE
THREAT COULD BECOME ENHANCED DURING THE EVENING IF A LINEAR MCS CAN
ORGANIZE.

…MID-MO VALLEY/NRN PLAINS/UPPER MS VALLEY…
SOUTH TO SOUTHWEST FLOW WILL BE IN PLACE ACROSS THE NCNTRL U.S.
SUNDAY AS AN UPPER-LEVEL TROUGH MOVES INTO THE SRN AND CNTRL PLAINS.
AT THE SFC…A LOW IS FORECAST TO DEEPEN AND MOVE NEWD INTO THE
MID-MO VALLEY DURING THE DAY. A MODERATELY UNSTABLE AIRMASS SHOULD
BE IN PLACE BY MID AFTERNOON TO THE EAST AND NORTHEAST OF THE LOW
ACROSS ERN NEB…SERN SD…IA AND SRN MN WHERE SFC DEWPOINTS MAY
REACH THE LOWER TO MID 60S F. THE AIRMASS SHOULD BE UNCAPPED ACROSS
MUCH OF THE REGION ALLOWING FOR CONVECTIVE INITIATION TO TAKE PLACE
EARLY IN THE DAY. THUNDERSTORMS COULD BE ONGOING DURING THE MORNING
ACROSS IA AND MN ALONG WRN EDGE OF THE LOW-LEVEL JET WITH ADDITIONAL
THUNDERSTORM DEVELOPMENT TAKING PLACE BENEATH THE UPPER-LEVEL LOW
EARLY SUNDAY AFTERNOON. SEVERAL CLUSTERS OF ORGANIZED THUNDERSTORMS
APPEAR LIKELY TO PERSIST THROUGH THE AFTERNOON WITH MCS DEVELOPMENT
POSSIBLE ACROSS PARTS OF THE REGION BY EVENING.

FORECAST SOUNDINGS AT OMAHA AND DES MOINES AT 21Z SHOW MODERATE
INSTABILITY WITH MLCAPE VALUES IN THE 2000 TO 3000 J/KG RANGE. THIS
COMBINED WITH 30 TO 40 KT OF 0-6 KM SHEAR SHOULD SUPPORT SUPERCELL
DEVELOPMENT WITH A THREAT FOR LARGE HAIL. HAILSTONES OF GREATER THAN
2 INCHES IN DIAMETER WILL BE POSSIBLE WITH THE MORE DOMINANT
SUPERCELLS MAINLY IN SE NEB AND SRN IA WHERE INSTABILITY IS FORECAST
TO BE THE GREATER THAN IN AREAS TO THE NORTH. A FEW TORNADOES MAY
ALSO OCCUR WITH THE MORE INTENSE SUPERCELLS AS THE LOW-LEVEL JET
STRENGTHENS EARLY SUNDAY EVENING. WIND DAMAGE WILL BE POSSIBLE WITH
SUPERCELLS AND BOWING LINE-SEGMENTS ESPECIALLY IF AN MCS CAN
ORGANIZE DURING THE EARLY EVENING.

…TN VALLEY/CNTRL AND ERN GULF COAST STATES…
AN UPPER-LEVEL TROUGH IS FORECAST TO MOVE SEWD ACROSS THE ERN GULF
COAST STATES SUNDAY AFTERNOON. THUNDERSTORMS SHOULD DEVELOP ALONG
AND AHEAD OF THE TROUGH AXIS AS SFC TEMPS WARM. FORECAST SOUNDINGS
FROM MIDDLE TN SEWD ACROSS NCNTRL AL INTO WRN GA AT 21Z SUNDAY SHOW
MLCAPE VALUES IN THE 1500 TO 2500 J/KG RANGE WITH STEEP LOW-LEVEL
LAPSE RATES. THIS COULD BE ENOUGH FOR A MARGINAL WIND DAMAGE THREAT
WITH MULTICELL STORMS THAT DEVELOP DURING THE AFTERNOON.

..BROYLES.. 05/18/2013

Stay safe, people.



Categories: Weather

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