ACUS01 KWNS 162006
SWODY1
SPC AC 162003
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0303 PM CDT THU JUL 16 2009
VALID 162000Z - 171200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER A PORTION OF THE CNTRL AND
SRN PLAINS AND LOWER MS VALLEY...
...THERE IS A SLGT RISK OF SVR TSTMS OVER A PORTION OF THE NERN
STATES...
...THERE IS A SLGT RISK OF SVR TSTMS OVER A PORTION OF THE ERN
CAROLINAS...
...SRN NEB...KS AND OK...
LATE THIS AFTERNOON A COLD FRONT EXTENDS FROM THE MID MS VALLEY WWD
THROUGH SRN NEB. SEVERAL OUTFLOW BOUNDARIES HAVE ADVANCED SWD
THROUGH PRE-FRONTAL WARM SECTOR INCLUDING AN EXPANSIVE CONVECTIVE
OUTFLOW THAT EXTENDS FROM SWRN MO SWWD THROUGH NRN OK THEN NWWD INTO
SWRN KS. ATMOSPHERE HAS BECOME MODERATELY UNSTABLE SOUTH OF THIS
BOUNDARY FROM NRN OK INTO SERN KS AND SWRN MO WHERE RELATIVELY RICH
MOISTURE RESIDES BENEATH STEEP LAPSE RATES AND WHERE DIABATIC
HEATING HAS OCCURRED OUTSIDE OF CONVECTIVE DEBRIS. THESE STORMS
RESIDE ALONG THE SRN FRINGE OF THE STRONGER FLOW ALOFT WITH 30-40 KT
BULK SHEAR SUFFICIENT FOR SOME ORGANIZED STRUCTURES. STORMS WILL
LIKELY CONTINUE INCREASING WITHIN ZONE OF LIFT ALONG THE OUTFLOW
BOUNDARY. STORMS FROM CNTRL THROUGH SWRN MO WILL BE AIDED BY DEEPER
FORCING FOR ASCENT ASSOCIATED WITH SEWD MOVING MCV. ISOLATED LARGE
HAIL AND DAMAGING WIND WILL BE THE MAIN THREATS WITH THE STRONGER
STORMS THROUGH MID EVENING. ISOLATED HAIL EXPECTED TO REMAIN THE
PRIMARY THREAT WITH ACTIVITY DEVELOPING IN POST FRONTAL ZONE.
A CONDITIONAL RISK EXISTS FOR SEVERE STORMS FARTHER NW FROM SWRN NEB
THROUGH NWRN KS WHERE SOME BOUNDARY LAYER CUMULUS ARE DEVELOPING
ALONG WRN END OF FRONTAL BOUNDARY. THREAT IN THIS REGION IS SOMEWHAT
UNCERTAIN DUE TO PRESENCE OF CAP AND STABILIZING EFFECTS OF
CONVECTIVE OUTFLOW. WITH FULL SUN...BOUNDARY LAYER RECOVERY IS
PRESENTLY UNDERWAY. HOWEVER...WITH THE EXCEPTION OF SHALLOW FRONTAL
CONVERGENCE...DEEPER FORCING FOR ASCENT REMAINS MODEST.
...NERN STATES...
SEE PREVIOUS DISCUSSION
...ERN CAROLINAS...
HAVE INCLUDED A SMALL SLIGHT RISK AREA FOR THE ERN CAROLINAS WHERE
MULTICELL STORMS HAVE ORGANIZED INTO LINE SEGMENTS AND ARE
DEVELOPING WITHIN A MODERATELY UNSTABLE ENVIRONMENT. ISOLATED
DAMAGING WIND WILL REMAIN POSSIBLE WITH THIS ACTIVITY NEXT FEW
HOURS.
..DIAL.. 07/16/2009
.PREV DISCUSSION... /ISSUED 1128 AM CDT THU JUL 16 2009/
...CENTRAL PLAINS TO THE LOWER MS VALLEY THROUGH TONIGHT...
GRADUAL AMPLIFICATION OF THE LARGE SCALE PATTERN WILL CONTINUE
THROUGH TOMORROW AS A MID LEVEL LOW OVER WRN ONTARIO DIGS SEWD TO
THE UPPER GREAT LAKES. SEVERAL SPEED MAXIMA WILL ROTATE SEWD FROM
THE NRN PLAINS TO THE MS VALLEY...AROUND THE SRN/SWRN PERIPHERY OF
THIS LOW...WHILE AN ASSOCIATED COLD FRONT MOVES SWD ACROSS THE
CENTRAL PLAINS AND SEWD ACROSS THE MID MS VALLEY. OTHER SMALLER
SCALE MCV/S ARE EMBEDDED WITHIN THIS FLOW REGIME OVER NRN KS/SE
NEB/SW IA WITH ONGOING THUNDERSTORM CLUSTERS. THIS CONVECTION WILL
LIKELY PERSIST THROUGH THE DAY AND MOVE SEWD ACROSS CENTRAL/ERN KS
AND WRN MO...AND BUILD WWD/SWWD DURING THE AFTERNOON INTO W/SW KS.
A CORRIDOR OF 65-70 F BOUNDARY LAYER DEWPOINTS...SURFACE HEATING IN
ADVANCE OF THE ONGOING STORMS...AND STEEP MID LEVEL LAPSE RATES WILL
RESULT IN MODERATE INSTABILITY /MLCAPE 2000-3000 J/KG/ WHICH WILL
SUPPORT INTENSIFICATION OF THE STORMS THIS AFTERNOON. DEEP LAYER
WLY/NWLY SHEAR WILL ALSO BE SUFFICIENT TO MAINTAIN ORGANIZED STORM
CLUSTERS CAPABLE OF PRODUCING DAMAGING WINDS AND LARGE HAIL THIS
AFTERNOON INTO TONIGHT AS THE CONVECTION PROGRESSES SEWD ACROSS
OK/AR.
...PA/NY/WRN NEW ENGLAND TODAY...
A FEW THUNDERSTORMS ARE ONGOING OVER ERN NY IN A ZONE OF LOW-MID
LEVEL WAA AND ASCENT DOWNSTREAM FROM A WEAK LEAD SHORTWAVE TROUGH
MOVING EWD FROM CENTRAL NY. FARTHER W...A DIFFUSE COLD FRONT IS
MOVING EWD INTO WRN PA/NY AND THIS BOUNDARY WILL CONTINUE EWD INTO
CENTRAL PA/NY THIS AFTERNOON. SURFACE HEATING WITHIN CLOUD BREAKS
IN THE WAKE OF THE MORNING CONVECTION AND THE ARRIVAL OF THE COLD
FRONT AND ADDITIONAL/SUBTLE MID LEVEL SPEED MAXIMA FROM THE W WILL
SUPPORT THUNDERSTORM DEVELOPMENT DURING THE AFTERNOON ACROSS
CENTRAL/ERN PA/NY. SURFACE TEMPERATURES AOA 80 F AND DEWPOINTS IN
THE MID 60S WILL SUPPORT MLCAPE OF 1000-1500 J/KG IN AN ENVIRONMENT
WITH UNIDIRECTIONAL WIND PROFILES...AND AN ATTENDANT THREAT FOR AT
LEAST ISOLATED DAMAGING WINDS AND MARGINALLY SEVERE HAIL INTO THIS
EVENING.
...LOWER MS VALLEY AREA THIS AFTERNOON/EVENING...
ONGOING STORMS ACROSS NRN MS HAVE SHOWN SIGNS OF WEAKENING LATE THIS
MORNING AS CONVECTIVE OUTFLOW BEGINS TO SURGE S OF THE ORIGINAL
STORM CLUSTERS. STRONG SURFACE HEATING AND BOUNDARY LAYER DEWPOINTS
IN THE LOW-MID 70S COULD SUPPORT ADDITIONAL STRONG/SEVERE STORM
DEVELOPMENT THIS AFTERNOON ALONG THE OUTFLOW BOUNDARIES FROM W
CENTRAL AL ACROSS CENTRAL MS INTO SE AR. THIS AREA WILL BE ALONG
THE SRN FRINGE OF THE SOMEWHAT ENHANCED MID LEVEL FLOW WITH THE MCV
OVER WRN TN...THUS LOOSELY ORGANIZED CLUSTERS OF PULSE-TYPE STORMS
SHOULD BE THE PRIMARY CONVECTIVE MODE. THE MAIN SEVERE THREAT WILL
BE A FEW WET MICROBURSTS THIS AFTERNOON/EVENING.
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