SPC AC 290600
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0100 AM CDT WED APR 29 2009
VALID 291200Z - 301200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS MUCH OF THE CENTRAL AND
SRN PLAINS...
...SYNOPSIS...
CLOSED LOW OVER THE NWRN U.S. IS EXPECTED TO WEAKEN TODAY AS A
LEADING SHORT WAVE TROUGH...CURRENTLY CENTERED OVER ID PER WATER
VAPOR IMAGERY...BREAKS AWAY FROM THIS UPPER LOW AND TRACKS THROUGH
THE NRN PLAINS. A STRONG BAND OF CYCLONIC MID/UPPER LEVEL FLOW WILL
ACCOMPANY THESE UPPER FEATURES...EXTENDING FROM NRN CA/ORE INTO THE
NRN PLAINS. FARTHER S...A BROAD CORRIDOR OF WSWLY MID/UPPER LEVEL
FLOW WILL EXTEND FROM THE SWRN TO SOUTH CENTRAL STATES AND TO THE
ERN SEA BOARD. AN EMBEDDED SHORT WAVE TROUGH WITHIN THIS FLOW
REGIME IS EXPECTED TO TRACK ACROSS THE SRN HIGH PLAINS THIS MORNING
AND REACH THE ERN PORTION OF THE CENTRAL/SRN PLAINS BY 30/00Z.
IN THE LOW LEVELS...PRIMARY SURFACE LOW ATTENDANT TO NRN STREAM
EJECTING SHORT WAVE TROUGH IS EXPECTED TO DEVELOP OVER THE NRN HIGH
PLAINS EARLY TODAY AND THEN DEEPEN TONIGHT AS IT TRACKS NEWD ACROSS
ND. A TRAILING COLD FRONT WILL MOVE ACROSS THE DAKOTAS AND SHOULD
EXTEND FROM THE CENTRAL DAKOTAS TO NERN CO BY LATE AFTERNOON...WHILE
A WARM FRONT EXTENDS SEWD FROM THE LOW IN WRN ND TO ERN SD TO IA.
MEANWHILE...A SURFACE BOUNDARY STRETCHED FROM VA TO OK AT THE START
OF THE PERIOD WILL MOVE SLOWLY SWD THROUGH NC TODAY...WITH THE
PORTION OVER THE TN VALLEY BECOMING QUASI-STATIONARY. THE WRN
EXTENT OF THIS BOUNDARY SHOULD MOVE NWD AS A WARM FRONT REACHING THE
LOWER MO VALLEY TO NRN KS BY LATE AFTERNOON. A DRY LINE IS EXPECTED
TO MIX EWD TODAY AND SHOULD EXTEND FROM W TX NWD THROUGH WRN KS
WHERE IT SHOULD INTERSECT THE SEWD MOVING COLD FRONT OVER NWRN
KS/SWRN NEB.
...SRN AND CENTRAL PLAINS...
MODELS SUGGEST ONE OR TWO CLUSTERS OF TSTMS...SOME SEVERE...WILL BE
ONGOING AT 12Z TODAY ACROSS THE ERN TX/OK PANHANDLES INTO SRN KS/
WRN HALF OF OK AND MUCH OF NRN TX. THIS ACTIVITY WILL PROGRESS EWD
ACROSS THE REST OF THE SRN PLAINS AND WILL BE AIDED BY FORCING FOR
ASCENT AHEAD OF SHORT WAVE TROUGH MOVING ACROSS THIS REGION INTO THE
AFTERNOON. IN ADDITION...WAA ALONG 35-50 KT SLY LLJ WILL HELP TO
MAINTAIN ACTIVITY AS WELL THROUGH THE DAY...WITH THE LLJ AXIS
TRANSLATING EWD AHEAD OF THE SRN STREAM TROUGH.
SURFACE HEATING IS EXPECTED ACROSS THE SRN/CENTRAL HIGH PLAINS IN
THE WAKE OF THE MORNING TSTM COMPLEX AS THIS SYSTEM MOVES EWD AWAY
FROM THIS REGION. THIS COMBINED WITH STEEP MID LEVEL LAPSE RATES
ATOP WRN EXTENT OF LOW LEVEL MOISTURE RETURN WILL RESULT IN A NARROW
CORRIDOR OF MLCAPE RANGING FROM 1000-2000 J/KG OVER THE WRN PORTION
OF THE SRN/CENTRAL PLAINS BY PEAK HEATING. MODELS SUGGEST TSTM
DEVELOPMENT SHOULD BE GENERALLY ISOLATED TO SCATTERED DUE TO MID
LEVEL SUBSIDENCE/WARMING OVER THIS REGION IN THE WAKE OF THE MORNING
PASSAGE OF THE SRN STREAM SHORT WAVE TROUGH. HOWEVER... GIVEN THE
FAVORABLE THERMODYNAMIC ENVIRONMENT AND EFFECTIVE BULK SHEAR UP TO
40 KT...SUPERCELLS WILL BE LIKELY WITH ANY TSTM DEVELOPMENT THIS
AFTERNOON FROM W TX/WRN OK TO WRN KS. WEAK LOW LEVEL WINDS DURING
THE AFTERNOON MAY LIMIT TORNADO DEVELOPMENT... BUT AN INCREASING SLY
LLJ DURING THE EARLY EVENING WILL INCREASE LOW LEVEL SHEAR
SUPPORTING A THREAT FOR ISOLATED TORNADOES. HAIL AND DAMAGING WINDS
WILL ALSO BE POSSIBLE WITH THESE STORMS.
FARTHER N...TSTMS WILL BE POSSIBLE ALONG THE NRN WARM FRONT WHERE IT
EXTENDS SEWD THROUGH SERN SD/NERN NEB/FAR NWRN IA. A 40-50 KT SSWLY
LLJ WILL ADVECT MOISTURE NWD BENEATH STEEP LAPSE RATES RESULTING IN
MLCAPE AROUND 500 J/KG. INCREASING EFFECTIVE BULK SHEAR ALONG SRN
EXTENT OF STRONG SWLY MID LEVEL JET SHOULD PROMOTE THE POTENTIAL FOR
A FEW SEVERE TSTMS.
FARTHER E...SURFACE HEATING ALONG LEADING EDGE OF SRN PLAINS
CONVECTIVE CLOUD SHIELD AND THE RETREATING WARM FRONT MAY ACT TO
PROMOTE A FAVORABLE THERMODYNAMIC ENVIRONMENT GIVEN A NWD SURGE OF
SURFACE DEWPOINTS IN THE LOWER-MID 60S ALONG THE LLJ. HOWEVER...
WEAK MID LEVEL LAPSE RATES FROM AR/MO TO ERN KS/OK WILL LIMIT THE
DEVELOPMENT OF STRONG INSTABILITY. DESPITE...STRONGER DEEP LAYER
SHEAR EXPECTED OVER AR AND NERN KS...THE OVERALL SEVERE WEATHER
THREAT SHOULD BE LOW.
..PETERS/GARNER.. 04/29/2009
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
|
