SPC AC 240550
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1250 AM CDT WED JUN 24 2009
VALID 241200Z - 251200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CENTRAL AND
NRN PLAINS AND INTO THE MID MO VALLEY REGION...
...SYNOPSIS...
UPPER TROUGHS/LOWS ARE FORECAST TO REMAIN JUST OFF BOTH THE E AND W
COASTS...WHILE A RIDGE REMAINS OVER THE CENTRAL U.S. THROUGH THE
PERIOD. ON THE SMALLER SCALE...THE SRN FRINGE OF A MID-LEVEL
SHORT-WAVE TROUGH CROSSING CENTRAL CANADA WILL MOVE ANTICYCLONICALLY
EWD AROUND THE NRN FRINGE OF THE CENTRAL U.S. RIDGE...AFFECTING THE
N CENTRAL CONUS THROUGH THE PERIOD.
AT THE SURFACE...THE PATTERN IS FORECAST TO REMAIN FAIRLY
WEAK/NONDESCRIPT....THOUGH A WEAK LOW IS FORECAST IN LEE OF THE
ROCKIES/OVER THE CENTRAL HIGH PLAINS REGION WITH AN
ASSOCIATED/OUTFLOW-REINFORCED FRONT EXTENDING EWD ACROSS NEB. THIS
LOW/FRONT SHOULD SERVE AS A FOCUS FOR NEW CONVECTIVE DEVELOPMENT
THIS AFTERNOON.
...PARTS OF SD/NEB EWD TO IA AND VICINITY...
COMPLEX FORECAST WITH RESPECT TO TIMING AND LOCATION OF CONVECTION
THIS PERIOD...AS A DECAYING MCS CURRENTLY MOVING SSWWD ACROSS W
CENTRAL MO AND A SECOND/EVOLVING ONE MOVING EWD ACROSS WRN AND
CENTRAL NEB CONTINUE TO ALTER THE BACKGROUND ENVIRONMENT. THE
CONVECTION ACROSS NEB SHOULD CONTINUE -- AIDED BY A SLY LOW-LEVEL
JET OVER THE PLAINS. ATTM...IT APPEARS THAT THE COMBINATION
FRONT/OUTFLOW -- PROGGED BY THE NAM TO EXTEND FROM NWRN NEB ESEWD TO
E CENTRAL NEB AT THE START OF THE PERIOD -- WILL LIKELY END UP A BIT
FARTHER S...WITH CLOUDINESS/CONVECTIVE DEBRIS LIKELY ACROSS A GOOD
BIT OF THE SLIGHT RISK AREA.
IN ANY CASE...A COMPLEX SHORT-WAVE TROUGH CROSSING THE REGION
THROUGH THE DAY WILL MAINTAIN A LOW OVER THE WRN NEB/NERN CO
VICINITY...WITH SLY FLOW E OF THE LOW LIKELY TO ALLOW SOME RETREAT
OF THE FRONT INTO NEB THROUGH THE AFTERNOON. THIS LOW/FRONT SHOULD
SERVE AS A FOCUS FOR NEW STORM DEVELOPMENT -- WITH SOME
RE-INTENSIFICATION OF REMNANT CONVECTION ALSO EXPECTED INVOF THE MID
MO VALLEY DURING THE AFTERNOON. WHILE QUESTIONS WITH RESPECT TO THE
QUALITY OF THE AIRMASS LINGER DUE TO THE AFOREMENTIONED/ONGOING
STORMS...INSTABILITY WILL LIKELY BE SUFFICIENT -- AT LEAST LOCALLY
-- TO SUPPORT VIGOROUS STORMS. WITH 30 TO 40 KT WLYS AT MID-LEVELS
PROGGED ACROSS NEB...AMPLE SHEAR FOR ORGANIZED STORMS WILL ACT TO
ENHANCE CONVECTIVE INTENSITY -- AND ASSOCIATED SEVERE POTENTIAL.
ALONG WITH THREATS FOR HAIL AND DAMAGING WINDS...ISOLATED TORNADOES
WILL BE POSSIBLE -- MAINLY TO THE COOL SIDE OF THE FRONT/OUTFLOW
WHERE ELY COMPONENT OF THE LOW-LEVEL FLOW FIELD WILL EXIST.
ATTM...WILL MAINTAIN RELATIVELY LOW SEVERE PROBABILITY -- AS
DEPICTING AREAS OF HIGHER RELATIVE THREAT REMAINS DIFFICULT ATTM.
OVERNIGHT...THE DEVELOPMENT OF A SSWLY/SWLY LOW-LEVEL JET SHOULD
SUSTAIN STORMS -- AND A MARGINAL SEVERE THREAT...AS CONVECTION
LIKELY TURNS INCREASINGLY-SEWD ACROSS THE MO VALLEY REGION LATE IN
THE PERIOD.
FARTHER N...STORMS MAY DEVELOP DURING THE AFTERNOON ACROSS WRN ND
AHEAD OF A WEAK SURFACE LOW/TROUGH...AND SWD INTO WRN SD --
PARTICULARLY INVOF THE BLACK HILLS WHERE ELY UPSLOPE FLOW SHOULD BE
PRESENT. WITH AMPLE INSTABILITY FORECAST TO DEVELOP -- PARTICULARLY
INTO SD -- AND MODERATE WLYS AT MID LEVELS CONTRIBUTING TO FAVORABLE
SHEAR...SOME SEVERE POTENTIAL IS EXPECTED. THREAT SHOULD DIMINISH
INTO THE EVENING IN CONJUNCTION WITH DIURNAL STABILIZATION.
...CENTRAL GULF COAST REGION INTO W CENTRAL AND SRN FL...
SCATTERED SHOWERS AND THUNDERSTORMS ARE FORECAST TO DEVELOP FROM THE
CENTRAL GULF COAST REGION ESEWD ACROSS THE GULF INTO W CENTRAL AND
SRN FL...AS AIRMASS DESTABILIZES BENEATH A BELT OF NLY/NNELY FLOW
ALOFT. WHILE DEGREE OF SHEAR SHOULD REMAIN INSUFFICIENT FOR
WELL-ORGANIZED STORMS...CLUSTERS OF MULTICELL CONVECTION SPREADING
SWD/SSWWD MAY PRODUCE LOCAL HAIL/GUSTY WINDS THROUGH MID EVENING.
..GOSS.. 06/24/2009
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