SPC AC 141244
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0744 AM CDT THU AUG 14 2008
VALID 141300Z - 151200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE
SRN/CENTRAL PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS OVER THE NRN FL PENINSULA...
..SYNOPSIS...
A BROAD LONGWAVE TROUGH WILL REMAIN SITUATED ACROSS THE ERN
THREE-FOURTHS OF THE CONUS...WITH A RIDGE IN THE WEST. A CLOSED LOW
OVER SRN SASKATCHEWAN WILL DROP SWD...DOWN THE BACKSIDE OF THE
LARGER SCALE TROUGH...THROUGH ERN MT AND INTO WY BY FRI MORNING.
THOUGH NO WELL DEFINED SURFACE CYCLONE IS EXPECTED TO DEVELOP...
BROAD SURFACE HIGH PRESSURE WILL BUILD FROM THE NRN/CENTRAL ROCKIES
EWD INTO THE MID/UPPER MS VALLEY...WITH EVOLVING COLD FRONT EXPECTED
TO STRETCH FROM NERN NM NEWD INTO MID MO VALLEY BY LATE AFTERNOON.
...SRN/CENTRAL PLAINS...
EARLY MORNING CONVECTION OVER NRN OK IS EXPECTED TO WEAKEN
AS IT SPREADS SEWD INTO A MORE STABLE ENVIRONMENT. THUNDERSTORMS ARE
LIKELY TO ONCE AGAIN REDEVELOP THIS AFTERNOON/EVENING ALONG THE
SURFACE FRONT...AS A SHORTWAVE TROUGH IN WY IS EJECTED AHEAD OF THE
SASKATCHEWAN CLOSED LOW INTO NEB/KS. THE STORMS SHOULD BE MOST
NUMEROUS FROM SWRN KS SWD INTO THE TX PANHANDLE/NWRN OK WHERE
STRENGTHENING LOW LEVEL JET/WARM ADVECTION SHOULD MAXIMIZE LIFT NEAR
AND NORTH OF FRONT/OUTFLOW BOUNDARY. OTHER SCATTERED STORMS ARE
ANTICIPATED ACROSS ERN CO DUE TO DEEPENING MOIST UPSLOPE FLOW. EVEN
THOUGH RICHER GULF MOISTURE WILL BE CONFINED TO FAR SRN TX...
DIURNAL HEATING COMBINED WITH STEEP MID LEVEL LAPSE RATES AND 500 MB
TEMPERATURES FROM -8C TO -10C WILL RESULT IN MODERATE INSTABILITY.
THIS INSTABILITY COMBINED WITH 30-40 KT DEEP LAYER SHEAR SHOULD BE
SUFFICIENT FOR AT LEAST WEAK SUPERCELLS. HOWEVER...GIVEN THE
RELATIVELY DRY BOUNDARY LAYER AND NWLY FLOW ALOFT...STORM OUTFLOWS
ARE LIKELY TO MERGE INTO ONE OR TWO SEWD MOVING MCS/S BY EVENING.
WHILE HAIL MAY BE THE INITIAL THREAT DURING THE FIRST COUPLE HOURS
AFTER STORM INITIATION...AS STORM DOWNDRAFTS STRENGTHEN AND
CONSOLIDATE...WIND DAMAGE IS EXPECTED TO BECOME THE PRIMARY SEVERE
THREAT.
...NRN FL...
CONVECTION ASSOCIATED WITH A LOW AMPLITUDE IMPULSE WAS MOVING EWD AT
AROUND 25 KT THROUGH THE COASTAL PORTIONS OF THE FL PANHANDLE.
RADAR LOOPS SHOWS A MID LEVEL CIRCULATION/POSSIBLE BOW STRUCTURE N
OF CTY...AND THIS FEATURE IS EXPECTED TO REACH DAB/JAX AREA AROUND
16Z AND OFFSHORE BY 18Z. EVEN THOUGH THESE STORMS WILL NOT BE MOVING
THROUGH DURING THE PERIOD OF MAX HEATING...THE ORGANIZED RADAR
STRUCTURE COMBINED WITH UNIDIRECTIONAL WLY WINDS INCREASING WITH
HEIGHT...PER TLH 12Z SOUNDING...MAY BE FAVORABLE FOR A FEW
STRONG/SEVERE WIND GUSTS THIS MORNING.
...MID/UPPER MS VALLEY...
RADAR DATA SHOWED AN MCV...WHICH EVOLVED FROM EARLIER CONVECTION
...WAS LOCATED NEAR MHK AT SUNRISE. STORMS ARE EXPECTED TO DEVELOP
AHEAD OF THIS SYSTEM AS IT MOVES EWD INTO MO. ALSO...UPPER LOW
DROPPING SWD INTO MT WILL STRENGTHEN THE DIFFLUENT FLOW ALOFT ACROSS
SRN MN/IA AND RESULT IN SUFFICIENT LIFT FOR STORMS. GIVEN A WARMING
AND DESTABILIZING AIR MASS...STRONG TO MARGINALLY SEVERE STORMS ARE
POSSIBLE ACROSS THIS REGION DURING THE AFTERNOON HOURS.
...NRN MID ATLANTIC STATES...
DAYTIME HEATING ON THE LEE OF THE NORTH CENTRAL APPALACHIANS COUPLED
WITH MOIST ENVIRONMENT FROM THE SFC-700 MB AND BROAD CYCLONIC FLOW
ALOFT SHOULD RESULT IN SCATTERED CONVECTION. 500 MB TEMPERATURES
FROM -12 TO -14C AND MID LEVEL LAPSE RATES NEAR 6.5 C/KM MAY SUPPORT
MARGINALLY SEVERE HAIL...THOUGH WEAK INSTABILITY AND SHEAR SUGGESTS
THE THREAT SHOULD BE ISOLATED.
...SRN AZ...
SWD MOVING ROCKIES UPPER LOW HAS ALREADY INCREASED THE E/NELY
COMPONENT OF THE MID LEVEL WINDS ACROSS THE REGION PER 12Z TUS
SOUNDING. THESE WINDS WOULD AID STORM PROPAGATION OFF THE HIGHER
TERRAIN INTO THE LOWER DESERTS. HOWEVER...BAND OF THUNDERSTORMS
OVERNIGHT HAS STABILIZED BOUNDARY LAYER...AND MORNING CLOUDS AND
MOIST BOUNDARY LAYER MAY LIMIT THREAT FOR WIND DAMAGE.
..IMY/CROSBIE.. 08/14/2008
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
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