Thursday, May 22, 2008

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 221228
SWODY1
SPC AC 221225

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0725 AM CDT THU MAY 22 2008

VALID 221300Z - 231200Z

...THERE IS A MDT RISK OF SVR TSTMS OVER PORTIONS SWRN NEB...WRN
KS...EXTREME NWRN OK...

...THERE IS A SLGT RISK OF SVR TSTMS ELSEWHERE FROM WRN NEB AND
EXTREME SERN WY TO PORTIONS NW TX/SW OK...

...CENTRAL/SRN HIGH PLAINS...
DEEP UPPER LOW WILL REMAIN NEARLY STATIONARY DURING THE PERIOD...OR
EVEN RETROGRADE SOME...AS STRONG UPPER JET DIGS ALONG THE WEST
COAST. AHEAD OF THIS SYSTEM...SURFACE LOW WILL LIKELY REMAIN IN
PLACE OVER ERN CO WITH DRY LINE BECOMING BETTER DEFINED SWD FROM
THIS LOW ACROSS FAR WRN KS INTO THE ERN TX PANHANDLE THIS AFTERNOON.
WARM FRONT IS BECOMING ESTABLISHED THIS MORNING ACROSS THE CENTRAL
PLAINS FROM NERN CO INTO CENTRAL MO...WITH WEAKENING SURFACE FRONT
FROM NERN OK INTO THE CENTRAL GULF COAST STATES. S-SW OF THIS
DIMINISHING FRONT...VERY RICH GULF MOISTURE HAS SURGED NWD EARLY
THIS MORNING WITH NEAR 70F DEW POINTS NOW INTO SRN OK AND MID 60S
INTO FAR S-CENTRAL/SWRN KS. STRONG 70-80 KT SLY MID LEVEL JET WILL
OVERSPREAD THE CENTRAL HIGH PLAINS ATOP NWRN EDGE OF THIS MOISTURE
RETURN WITH 50-60 KT SWLY H5 WINDS DEVELOPING ACROSS DRY LINE OVER
THE SRN HIGH PLAINS. GIVEN VERY STEEP LAPSE RATES AND RICH LOW
LEVEL MOISTURE...SETUP WILL THEREFORE BECOME QUITE VOLATILE OVER
MUCH OF THE REGION WITH POTENTIAL FOR VERY LARGE HAIL AND A FEW
SIGNIFICANT TORNADOES INTO THE MID EVENING.

DEVELOPMENT IS EXPECTED TO PERSIST WITHIN STRONG ELY UPSLOPE FLOW
INTO NERN CO/NWRN NEB/SERN WY NORTH OF THE SURFACE LOW...WITH THREAT
OF ISOLATED LARGE HAIL AS MODEST SURFACE HEATING SUPPORTS MARGINAL
INSTABILITY. OTHERWISE...EXPECT SFC-BASED TSTMS TO DEVELOP INVOF
ELONGATED SFC LOW AND NEARBY DRYLINE AND WARM FRONTAL SEGMENTS FROM
SRN NEB INTO WRN KS WHICH SHOULD MOVE ACROSS WARM FRONTAL ZONE.
RELATIVELY BACKED FLOW INVOF WARM FRONT WILL ENHANCE EFFECTIVE BULK
SHEAR...LOW LEVEL SRH AND BOUNDARY LAYER VORTICITY. THUS ANY MATURE
STORMS INTERACTING WITH THE FRONTAL ZONE MAY PRODUCE TORNADOES BUT
THEN MOVE QUICKLY INTO UNFAVORABLE SFC AIR MASS.

VERTICAL SHEAR INCREASINGLY WILL FAVOR SUPERCELLS/TORNADOES FARTHER
S IN WRN PORTION OF MOIST SECTOR WITH TIME...AS CAPPING WEAKENS
ALONG DRYLINE. THIS ESPECIALLY IS A CONCERN LATE AFTERNOON INTO
EARLY EVENING WHEN LIFTED PARCELS STILL ARE SFC-BASED AND
STRENGTHENING LLJ GREATLY ENLARGES HODOGRAPHS IN ENVIRONMENT OF ANY
EXISTING SUPERCELLS. POTENTIAL WILL BUILD SWD ALONG KS SEGMENT OF
DRYLINE THROUGH AFTERNOON. STRONG MERIDIONAL COMPONENT OF MEAN FLOW
AND POTENTIAL FOR SCATTERED-NUMEROUS TSTM COVERAGE PROVIDES SOME
STORM-SCALE UNCERTAINTIES PRECLUDING GREATER SIGNIFICANT
HAIL/TORNADO PROBABILITIES ATTM. HOWEVER...THERE SHOULD BE
SUFFICIENT SBCAPE-- E.G. 2000-2500 J/KG OVER MUCH OF WRN KS AND
PERHAPS A SMALL PART OF SWRN NEB -- TO SUPPORT POTENTIAL FOR SEVERAL
DISCRETE/CYCLIC/TORNADIC SUPERCELLS DURING AFTERNOON AND EARLY
EVENING HOURS. SUPERCELLS/TORNADO POTENTIAL MAY PERSIST WELL INTO
NIGHTTIME HOURS...ESPECIALLY WITH SWD EXTENT...ALTHOUGH EVOLUTION
INTO MORE LINEAR SEGMENTS IS EXPECTED AFTER DARK.
INCREASING/ELEVATED TSTM COVERAGE WELL N OF WARM FRONT -- ACROSS
N-CENTRAL PLAINS...WILL RESULT IN POTENTIAL FOR SVR HAIL AS FAR N AS
PORTIONS SD.

...SRN HIGH PLAINS...
STRONGER BUOYANCY -- E.G. 3000-4000 J/KG MLCAPE -- AND GREATER
MLCINH EACH ARE FCST SWD OVER ERN PANHANDLES AND WRN OK...COMPARED
TO FARTHER N. STRONG CAPPING AND MID LEVEL HEIGHT RISES ARE
EXPECTED TO LIMIT POTENTIAL COVERAGE...AND THREAT THEREFORE BECOMES
MORE ISOLATED AND CONDITIONAL WITH SWD EXTENT ACROSS SRN HIGH
PLAINS. HOWEVER...ENVIRONMENT SHOULD BE MORE CONDUCIVE TO
LONGER-LIVED SUPERCELLS SHOULD CAP BREAK GIVEN GREATER STEERING FLOW
ACROSS THE DRY LINE. ANY SUPERCELL WHICH DEVELOPS COULD PRODUCE A
STRONG TORNADO ALONG WITH VERY LARGE HAIL INTO THE EARLY TO MID
EVENING.

...ERN TX INTO ARKLATEX AND ERN OK...
SCATTERED TSTMS ARE EXPECTED TO DEVELOP THIS AFTERNOON IN ZONE OF
WEAK LARGE SCALE ASCENT/DESTABILIZATION ALOFT...JUXTAPOSED WITH STG
DIURNAL HEATING...RICH BOUNDARY LAYER MOISTURE...AND RELATIVELY WEAK
SBCINH. MAIN LIMITING FACTOR WILL BE LACK OF SUBSTANTIAL LOW LEVEL
FOCI...ESPECIALLY PRIOR TO DEVELOPMENT OF ANY OUTFLOW BOUNDARIES.
HOWEVER...12Z LCH/FTW SOUNDINGS INDICATE VERY STEEP MID LEVEL LAPSE
RATES AND FCST SOUNDINGS DEPICT ENLARGED LOW LEVEL HODOGRAPHS...
ESPECIALLY IN NARROW ZONE OF SELY SFC WINDS IMMEDIATELY AHEAD OF
UPPER LOW AND S OF WARM FRONTAL ZONE. ALTHOUGH MID-UPPER LEVEL FLOW
SHOULD BE RELATIVELY WEAK...BRIEF SUPERCELL ORGANIZATION IS POSSIBLE
AMONG MORE PREDOMINANT MULTICELLULAR MODES. THEREFORE WILL INCLUDE
MRGL PROBABILITIES FOR HAIL AND DAMAGING CONVECTIVE GUSTS.

..EVANS/EDWARDS/SMITH.. 05/22/2008

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