SWODY1
SPC AC 220550
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1250 AM CDT SUN MAR 22 2009
VALID 221200Z - 231200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
PROGRESSIVE SYNOPTIC PATTERN FCST TO CONTINUE ACROSS CONUS THROUGH
PERIOD...AS CENTRAL STATES RIDGING AND STG ERN PACIFIC TROUGH EACH
MOVE EWD FROM CURRENT POSITIONS. RELATED HEIGHT FALLS WILL SPREAD
OVER MOST OF WRN CONUS...ROCKIES AND HIGH PLAINS BY END OF PERIOD.
THIS WILL CONTRIBUTE TO CONTINUATION OF BROAD LOW LEVEL WAA REGIME
ACROSS PLAINS STATES. STG SHORTWAVE TROUGH WILL MOVE ASHORE CA
DURING 22/12-15Z TIME FRAME THEN EWD ACROSS GREAT BASIN...EVOLVING
CLOSED 500 MB LOW INVOF UT/WY BORDER BY 23/06Z. PRECEDING SHORTWAVE
TROUGH -- NOW EVIDENT FROM NV SWWD ACROSS PACIFIC...OFFSHORE NRN
BAJA -- WILL MOVE EWD ACROSS CENTRAL/SRN ROCKIES AND ADJACENT
PLAINS. BY 23/00Z...STG CONSENSUS OF SREF...AS WELL AS OPERATIONAL
NAM/SPECTRAL...SHOW 500 MB VORTICITY AXIS WITH THIS FEATURE
EXTENDING FROM S-CENTRAL NEB ACROSS W-CENTRAL KS...NWRN OK...THEN
SWWD OVER TX SOUTH-PLAINS AND TRANS-PECOS REGIONS.
AT SFC...INITIAL AREA OF LEE-SIDE LOW PRESSURE OVER MT IS EXPECTED
TO REDEVELOP SWD OVER NERN CO/SRN NEB PANHANDLE BORDER AREA BY END
OF PERIOD...CONNECTED TO LOW-LEVEL COLD FRONTOGENESIS REGIME THAT
SHOULD REACH FAR WRN KS AND CENTRAL NM AT 23/12Z. FARTHER
E...WITHIN EXPANSIVE LOW-LEVEL RETURN FLOW/WAA ZONE...EXPECT ONLY
SLOW/FRAGMENTED INCREASE IN LOW LEVEL MOISTURE...GIVEN INCOMPLETE
NATURE OF PRIOR AIR MASS MODIFICATION OVER GULF. NEVERTHELESS...BY
23/00Z...DRYLINE IS FCST TO BECOME MORE SHARPLY DEFINED FROM SW TX
NWD ACROSS TX PANHANDLE...WRN KS...SW/W-CENTRAL NEB...W-CENTRAL/NWRN
SD...TO FRONTAL INTERSECTION OVER SWRN ND/NWRN SD AREA.
...PLAINS STATES...
E OF DRYLINE...SFC DEW POINTS 40S F SHOULD BE COMMON OVER
NRN/CENTRAL PLAINS...WITH POCKETS OF 50S OVER PORTIONS KS...OK AND
TX. GIVEN FAVORABLE UPPER AIR PATTERN...THIS MOISTURE FIELD IS FAR
FROM IDEAL FOR SPRINGTIME SEVERE SETUP UNDER PROGGED -13 TO -16 DEG
C 500 MB TEMPS AND ROBUST ELEVATED MIXED LAYER OVER MOST OF PLAINS.
SVR RISK APPEARS VERY CONDITIONAL AND/OR ISOLATED ACROSS BROAD SWATH
OF CENTRAL/NRN PLAINS AND SWD INVOF KS-TX DRYLINE...AND THERE ARE
TOO MANY UNCERTAINTIES AND OFFSETS OF MOST FAVORABLE PARAMETERS TO
WARRANT ANYTHING MORE THAN MRGL UNCONDITIONAL PROBABILITIES ATTM.
THREE PRIMARY AREAS OF CONCERN EXIST IN THIS SWATH...WHICH OVERLAP
TO SOME EXTENT IN SPACE AND TIME...
1. DIURNAL BUT NOT NECESSARILY SFC-BASED INITIATION AHEAD OF DRYLINE
ACROSS CENTRAL/ERN PORTIONS NEB/SD...SHIFTING NEWD AND INCREASING IN
COVERAGE DURING EVENING INVOF 50-65 KT LLJ. THIS ACTIVITY WILL BE
ASSOCIATED PRIMARILY WITH ELEVATED LOW LEVEL WAA PLUME AND
INCREASING MOISTURE...RESULTING IN ELEVATED MUCAPES GENERALLY IN
500-800 J/KG RANGE...ON NERN PERIPHERY OF ELEVATED MIXED-LAYER AIR
PLUME CONTAINING FAVORABLE LAPSE RATES ALOFT. ALTHOUGH PROGS
INDICATE CAPPING FOR SFC-BASED PARCELS STRENGTHENING WITH SWD/SWWD
EXTENT...SUFFICIENT SFC HEATING MAY OCCUR OVER PORTIONS CENTRAL/ERN
NEB FOR BRIEF INTERVAL OF SFC-BASED INFLOW. IN THAT CASE...STG-SVR
GUSTS MAY BE POSSIBLE IN ADDITION TO BROADER BUT MRGL THREAT FOR SVR
HAIL. ANY DISCRETE/NEARLY SFC-BASED STORMS NEAR TAIL END OF THIS
REGIME MAY BECOME SUPERCELLULAR...GIVEN ENLARGED AND STRONGLY CURVED
LOW LEVEL HODOGRAPHS PROGGED BENEATH LLJ. HOWEVER...LACK OF SPEED
CHANGE WITH HEIGHT FROM LOW-MIDLEVELS LIMITS 0-6 KM AND EFFECTIVE
SHEAR TO ONLY 30-35 KT RANGE IN FCST SOUNDINGS.
2. CONDITIONAL LATE AFTERNOON SUPERCELL THREAT EXISTS ALONG DRYLINE
FROM NEB SWD TO NW TX....UNDER FAVORABLE VERTICAL SHEAR. LOW LEVEL
HODOGRAPHS ACROSS THIS REGION WILL BE CONSISTENTLY LARGE -- WITH 0-1
KM SRH VALUES POTENTIALLY IN 200-300 J/KG RANGE. WEAKNESS OF WINDS
IN 700-500 MB LAYER BECOMES MORE PRONOUNCED WITH NWD EXTENT FROM NW
OK/NERN TX PANHANDLE NWD TO WRN NEB...BUT IS NOT EVIDENT FARTHER S
AROUND CDS. MAIN LIMITING FACTOR OTHER THAN WEAKNESS OF MOISTURE
WILL BE STG CAPPING -- BENEATH VIGOROUS EML. ALSO...NEB PORTION OF
DRYLINE COULD BE BEHIND LEADING SHORTWAVE TROUGH. FCST SOUNDINGS
SUGGEST ANY DRYLINE ACTIVITY THAT DOES DEVELOP WILL BE QUITE
ISOLATED...BUT WITH SOME POTENTIAL FOR SVR HAIL/GUSTS.
3. LEADING EDGE OF STRONGEST LARGE SCALE ASCENT -- ASSOCIATED WITH
PROGRESSIVE/MID-UPPER LEVEL CYCLONE -- IS FCST TO BEGIN SPREADING
ACROSS CENTRAL HIGH PLAINS OVERNIGHT. COMBINATION OF RELATED
DESTABILIZATION ALOFT...LOW LEVEL CONVERGENCE N-NE OF SFC
CYCLONE...FRONTOGENETIC FORCING AND LOW-LEVEL MOIST ADVECTION...MAY
CONTRIBUTE TO VIGOROUS DEEP-LAYER LIFT AND DEVELOPMENT OF NIGHTTIME
TSTMS ACROSS PORTIONS NEB PANHANDLE AND/OR CENTRAL/SWRN SD.
STEEPENING OF LAPSE RATES ALOFT MAY SUPPORT ELEVATED MUCAPE
EXCEEDING 1000 J/KG IN PARTS OF THIS AREA. STRONG BACKING WITH
HEIGHT OF WINDS IN 1-4 KM AGL LAYER -- AS MID-UPPER LOW APCHS --
INDICATES LINEAR ORGANIZATION IS POSSIBLE...WITH HAIL POTENTIAL
WEAK-MRGL. WIND THREAT WOULD BE SPORADIC AND LIMITED BY STABILITY
NEAR SFC...BENEATH ELEVATED/UNSTABLE INFLOW LAYER.
..EDWARDS/GARNER.. 03/22/2009
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