SWODY1
SPC AC 101959
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0259 PM CDT FRI JUL 10 2009
VALID 102000Z - 111200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE LOWER/MIDDLE MO
VALLEY AND UPPER MIDWEST...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE CENTRAL HIGH
PLAINS...
...MIDWEST AND MIDDLE/LOWER MO VALLEY...
EARLY DAY TSTMS/EXTENSIVE OUTFLOW HAS SERVED TO STABILIZE THE
AIRMASS ACROSS A LARGE PART OF IA/NORTHERN MO/NORTHERN IL AS OF MID
AFTERNOON...WITH A COMPLEX/LIMITED CONFIDENCE SCENARIO IN ITS WAKE.
OBSERVATIONAL DIAGNOSTIC DATA SUGGEST A WEAK MCV MAY EXIST/CONTINUE
TO SPREAD SOUTHEASTWARD COINCIDENT WITH EXISTING LOOSELY ORGANIZED
TSTM CLUSTERS ACROSS THE LOWER OH VALLEY. THE IMMEDIATE DOWNSTREAM
AIRMASS IS NOT PARTICULARLY FAVORABLE FOR AN ORGANIZED SEVERE RISK
LARGELY OWING TO WEAK VERTICAL SHEAR...BUT A FEW STORMS WILL BE
CAPABLE OF DAMAGING WINDS/PERHAPS HAIL ON AN ISOLATED BASIS THROUGH
EARLY EVENING.
FARTHER WEST/NORTHWEST...OTHER STRONG/POTENTIALLY SEVERE TSTMS MAY
DEVELOP WITHIN A RELATIVELY CONFINED/RESIDUAL WARM/MOIST PRE-COLD
FRONTAL SECTOR ACROSS CENTRAL/SOUTHERN WI INTO THE U.P. OF MI AND
PERHAPS FAR SOUTHERN MN/FAR NORTHERN IA. HOWEVER...LIMITED FORCING
ON THE LARGE SCALE AND MODEST LOW LEVEL CONVERGENCE HINDERS
CONFIDENCE/THE LIKELIHOOD OF AN APPRECIABLE SEVERE RISK...ALTHOUGH A
MODEST MID LEVEL IMPULSE CURRENTLY CROSSING ND MAY CONTRIBUTE TO
SEMI-ORGANIZED DEVELOPMENT LATER THIS AFTERNOON/EARLY EVENING.
OTHER SEVERE STORMS COULD DEVELOP LATE THIS AFTERNOON/TONIGHT ACROSS
THE LOWER MO VALLEY VICINITY...INCLUDING PORTIONS OF EASTERN
KS/SOUTHEAST NEB AND MO. ELEVATED CONVECTION HAS BEEN COMMON ACROSS
THESE AREAS SINCE THIS MORNING...AND SOME OF THIS ACTIVITY COULD
BECOME BETTER ORGANIZED/NEAR SURFACE BASED LATE THIS
AFTERNOON/EVENING...SUBSEQUENTLY SPREADING EAST-SOUTHEASTWARD WITH
TIME ALONG THE NORTHWEST-SOUTHEAST ORIENTED EFFECTIVE FRONTAL ZONE.
HOWEVER...THE MOST LIKELY TIME FOR APPRECIABLE DEVELOPMENT MAY NOT
ARRIVE UNTIL LATER TONIGHT AS A SOUTHWESTERLY LOW LEVEL JET/WARM
ADVECTION REGIME INCREASES ACROSS THE CENTRAL PLAINS/LOWER MO
VALLEY. REGARDLESS...DAMAGING WINDS AND HAIL WOULD BE THE PRIMARY
HAZARDS.
...CO/WY FRONT RANGE AND CENTRAL HIGH PLAINS...
FEW CHANGES TO PREVIOUSLY DISCUSSED SCENARIO...WITH INCIPIENT
STRONG/SEVERE TSTM DEVELOPMENT STILL EXPECTED LATER THIS AFTERNOON
ALONG THE HIGHER TERRAIN OF CO/WY. A RATHER MOIST/UNSTABLE AND
WELL-SHEARED ENVIRONMENT WILL SUPPORT SUPERCELLS CAPABLE OF LARGE
HAIL/DAMAGING WINDS AND PERHAPS A TORNADO OR TWO ACROSS THE CENTRAL
HIGH PLAINS.
..GUYER.. 07/10/2009
.PREV DISCUSSION... /ISSUED 1130 AM CDT FRI JUL 10 2009/
...MS VALLEY REGION TODAY INTO TONIGHT...
COMPLEX SITUATION TODAY WITH MULTIPLE ONGOING CONVECTIVE CLUSTERS
ACROSS IA/IL/MO. THIS CONVECTION APPEARS TO HAVE BEEN DRIVEN BY
LOW-LEVEL WAA THROUGH THE MORNING HOURS...BUT THE CLUSTERS SHOULD
WEAKEN SLOWLY BY EARLY AFTERNOON AS THE LLJ AND INSTABILITY FEED
FROM THE WSW DIMINISH. IN THE MEANTIME...HOWEVER...THE STRONGER
STORMS WILL CONTINUE TO BE CAPABLE OF PRODUCING ISOLATED DAMAGING
GUSTS AND MARGINALLY SEVERE HAIL...PRIMARILY FROM ERN IA INTO NRN
IL.
THE LINGERING IMPACTS OF THE MORNING STORMS WILL BE TO STABILIZE
MUCH OF CENTRAL/ERN IA...SRN WI...NRN IL...AND MO THROUGH THE
AFTERNOON...AND SOME PART OF THIS AREA MAY BE DOWNGRADED IN THE 20Z
OUTLOOK UPDATE ONCE INITIAL STORMS WEAKEN. THE CLUSTERS WILL ALSO
LEAVE MULTIPLE OUTFLOW BOUNDARIES THAT MAY SERVE TO FOCUS ADDITIONAL
THUNDERSTORM DEVELOPMENT LATER THIS AFTERNOON/EVENING ...THOUGH
SURFACE-BASED DEVELOPMENT WILL REQUIRE SUBSTANTIAL DAYTIME HEATING
TO REDUCE CONVECTIVE INHIBITION WITH THE NERN EXTENT OF A VERY WARM
EML SPREADING ENEWD FROM THE SRN HIGH PLAINS. THE STRONGEST SURFACE
HEATING WILL OCCUR IN PROXIMITY TO THE LOW-LEVEL MOIST AXIS AND AN
OUTFLOW BOUNDARY TRAILING NWWD ACROSS WRN MO/ERN KS FROM THE
WEAKENING STORM CLUSTER IN SRN MO. STILL...CLOUDS/MID LEVEL
CONVECTION COULD INTERFERE WITH SURFACE HEATING ACROSS THIS AREA AND
IT IS NOT CLEAR THAT SURFACE-BASED STORMS WILL FORM ALONG THIS
OUTFLOW BOUNDARY OR ALONG THE SYNOPTIC FRONT FARTHER TO THE NW
ACROSS N CENTRAL KS AND SE NEB. IF STORMS DO FORM...THE ENVIRONMENT
WILL BE SUFFICIENT FOR SUPERCELLS WITH MLCAPE AOA 3000 J/KG AND
EFFECTIVE BULK SHEAR AOA 30-35 KT ALONG THE SRN FRINGE OF THE 25-40
KT MID LEVEL WESTERLIES. DAMAGING WINDS AND LARGE HAIL WILL BE THE
PRIMARY SEVERE THREATS.
...FRONT RANGE/CENTRAL HIGH PLAINS THIS AFTERNOON/EVENING...
A MOIST POST-FRONTAL AIRMASS WITH BOUNDARY LAYER DEWPOINTS IN THE
UPPER 50S TO MID 60S HAS SPREAD WWD TO THE FOOTHILLS IN NE CO AND A
WEAK CYCLONE IN SE WY. 12Z SOUNDINGS SUGGEST THAT SURFACE
TEMPERATURES WILL NEED TO REACH THE MID 80S ALONG THE HIGHER
ELEVATIONS OF THE FRONT RANGE AND THE 90S OVER THE PLAINS TO
MINIMIZE CONVECTIVE INHIBITION. HOWEVER...STRATUS WILL LIKELY SLOW
SURFACE HEATING ACROSS THE PLAINS AND A BACKGROUND ENVIRONMENT OF
RISING HEIGHTS SUGGESTS THAT STORM INITIATION WILL BE CONFINED TO
THE HIGHER TERRAIN THIS AFTERNOON. ASSUMING STORMS DEVELOP BY LATE
AFTERNOON...ANY SURVIVING CONVECTION SHOULD THEN SPREAD EWD OVER THE
HIGH PLAINS ON CONVECTIVE OUTFLOWS THIS EVENING INTO EARLY TONIGHT.
DEEP LAYER VERTICAL SHEAR AND INSTABILITY WILL BE SUFFICIENT FOR
SUPERCELLS CAPABLE OF PRODUCING LARGE HAIL AND DAMAGING WINDS...AND
THESE THREATS COULD PERSIST INTO EARLY TONIGHT WITH ANY STORM
CLUSTERS THAT EMERGE FROM THE INITIAL CONVECTION.
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