SWODY2
SPC AC 211721
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1221 PM CDT SAT APR 21 2007
VALID 221200Z - 231200Z
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CNTRL
PLAINS AND UPPER MIDWEST...
..CNTRL PLAINS/UPPER MIDWEST...
LATEST WATER VAPOR IMAGERY SHOWS AN AMPLIFIED PATTERN WITH A
WELL-DEFINED UPPER-LEVEL TROUGH OVER THE INTERMOUNTAIN WEST. THIS
TROUGH WILL MOVE QUICKLY NEWD INTO THE CNTRL PLAINS AND INTO THE
UPPER MIDWEST SUNDAY. AT THE SFC...A LOW WILL ORGANIZE AND MOVE NEWD
ACROSS THE CNTRL PLAINS SUNDAY. A CONVECTIVE COMPLEX SHOULD BE
ONGOING ALONG THE AXIS OF THE UPPER-TROUGH SUNDAY MORNING AND THIS
MCS SHOULD MOVE NEWD INTO MN...IA AND NRN MO DURING THE DAY. THE
UPPER-TROUGH IS FORECAST TO WEAKEN SOME ESPECIALLY DURING THE LATTER
HALF OF THE PERIOD AND THIS MAY CAUSE A DECREASE IN THUNDERSTORM
COVERAGE SUNDAY NIGHT ACROSS THE REGION.
NAM FORECAST SOUNDINGS JUST AHEAD OF THE UPPER-LEVEL SYSTEM SUNDAY
AFTERNOON SHOW 0-6 KM SHEAR VALUES OF 30 TO 40 KT WITH GFS FORECAST
SOUNDINGS SHOWING SLIGHTLY STRONGER SHEAR PROFILES. CONSIDERING
INSTABILITY IS NOT FORECAST TO BE THAT STRONG...THE DIFFERENCE IN
MODEL FORECASTS SUGGESTS THE SUPERCELL THREAT REMAINS CONDITIONAL.
MULTICELLS SHOULD BE THE MOST COMMON STORM TYPE...HOWEVER THE CHANCE
FOR SUPERCELLS MAY STILL OCCUR MAINLY IN A NARROW WINDOW DURING THE
LATE AFTERNOON ALONG THE AXIS OF GREATEST INSTABILITY. FORECAST
SOUNDINGS SHOW STRONG SWLY LOW-LEVEL FLOW AND SOMEWHAT
UNIDIRECTIONAL WINDS BELOW 850 MB WHICH SHOULD BE FAVORABLE FOR
DAMAGING WINDS. IN ADDITION...NAM FORECASTS SHOW A BOWING STRUCTURE
IN THE QPF FIELD FOR TOMORROW EVENING SUGGESTING A LINEAR MCS WITH
WIND DAMAGE POTENTIAL WILL BE POSSIBLE SUNDAY EVENING IN THE OMAHA
NEB...DES MOINES IA AND LACROSS WI AREAS. ALTHOUGH MID-LEVEL LAPSE
RATES ARE NOT FORECAST TO BE THAT STEEP...500 MB TEMPS WILL BE COLD
ASSOCIATED WITH THE CORE OF THE UPPER-TROUGH AND THIS SHOULD ALSO BE
FAVORABLE FOR LARGE HAIL ESPECIALLY NEAR PEAK HEATING. THE SEVERE
THREAT SHOULD DIMINISH QUICKLY AT SOME POINT DURING THE EVENING DUE
TO WEAKENING OF THE UPPER-LEVEL SYSTEM AND DECREASING INSTABILITY.
..WRN OZARKS/ERN OK/NE TX...
AT THE SFC...A LOW WILL ORGANIZE ACROSS THE CNTRL PLAINS SUNDAY WITH
A STRONG LOW-LEVEL JET IN PLACE FROM ERN OK/WRN AR EXTENDING NWD
INTO ERN KS/WRN MO. THIS WILL HELP SUSTAIN A LOW-LEVEL MOIST AXIS
FROM ECNTRL TX EXTENDING NNEWD INTO ERN OK. ALTHOUGH MODEL FORECASTS
LIFT THE UPPER-LEVEL TROUGH AWAY FROM THE REGION DURING THE
DAY...LOW-LEVEL CONVERGENCE AND INSTABILITY STILL MAY BE SUFFICIENT
FOR THE DEVELOPMENT OF ISOLATED THUNDERSTORMS ALONG THE INSTABILITY
AXIS SUNDAY AFTERNOON.
MODEL FORECASTS ACROSS THE REGION SUNDAY AFTERNOON SHOW 0-6 KM SHEAR
VALUES AROUND 40 KT WHICH SHOULD BE SUFFICIENT FOR SUPERCELL
DEVELOPMENT IF CONVECTION INITIATES. HOWEVER...A LACK OF LARGE-SCALE
ASCENT AND RELATIVELY WEAK LAPSE RATES WILL NOT PROVIDE MUCH
ADDITIONAL SUPPORT TO THE SEVERE THREAT. IF A SUPERCELL OR TWO
DEVELOPS...HAIL AND MARGINALLY SEVERE WIND DAMAGE COULD OCCUR SUNDAY
AFTERNOON.
.BROYLES.. 04/21/2007
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