ACUS01 KWNS 202001
SWODY1
SPC AC 201959
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0259 PM CDT TUE JUL 20 2010
VALID 202000Z - 211200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE CNTRL HI PLNS EAST TO
THE MID ATLANTIC CST...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE NRN PLNS...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE UPR MS VLY...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF ERN WY...
...NRN PLNS...
A FEW TSTMS HAVE FORMED IN THE PAST 90 MINUTES IMMEDIATELY E OF SRN
SK UPR VORT....AND IN WAA AREA FARTHER E OF VORT IN SW MB/NRN ND.
AS LOW LVL LAPSE RATES CONTINUE TO STEEPEN DUE TO AFTN
HEATING...STORMS SHOULD CONTINUE TO STRENGTHEN IN BOTH AREAS. MID
LVL THERMODYNAMIC PROFILES AND MODERATE DEEP UNIDIRECTIONAL WLY FLOW
WILL BE FAVORABLE FOR HAIL PRODUCTION IN ANY SUSTAINED UPDRAFTS.
WHILE WEAK LOW LVL CONVERGENCE SHOULD LIMIT COVERAGE OF SUCH
ACTIVITY...GIVEN CONTINUED LARGE SCALE FORCING FOR ASCENT... THREAT
FOR HAIL APPEARS SUFFICIENT ENOUGH TO JUSTIFY UPGRADE TO SLIGHT RISK
THROUGH EARLY THIS EVE.
...CNTRL HI PLNS...
WEAK COLD FRONTAL SURGE HAS MOVED S TO AROUND THE RATON RIDGE IN NE
NM. ASSOCIATED POST-FRONTAL UPSLOPE FLOW AND TERRAIN-INDUCED
CIRCULATIONS SUGGEST POSSIBILITY FOR STRONG TO POSSIBLY SVR STORMS
WITH WIND/HAIL IN NRN NM/S CNTRL AND SE CO THROUGH EARLY THIS EVE.
THIS ACTIVITY MAY EVOLVE INTO A SMALL CLUSTER BEFORE WEAKENING LATER
TONIGHT.
...UPR MS VLY...
RELATIVELY MINOR AREAL ADJUSTMENTS MADE TO EXISTING SLIGHT RISK IN
UPR MI/WI AND SRN MN...BASED ON LATEST SFC DATA SHOWING WEAK
SE-MOVING COLD FRONT IN MN/WI...AND WATER VAPOR IMAGERY SHOWING AXIS
OF IMPLIED ASCENT/MOISTURE EXTENDING SW INTO SRN MN.
...LWR MO/MID MS VLYS...
LOW LVL CONVERGENCE INTO STALLED OUTFLOW BOUNDARY/FRONT INTERSECTION
IN NE KS/NW MO EXPECTED TO SUPPORT STRONG STORM DEVELOPMENT IN THIS
AREA BY LATE AFTN...WHERE CIN ALSO APPEARS TO BE COMPARATIVELY WEAK.
COMBINATION OF GREAT INSTABILITY/HIGH PW WITH MODEST WLY MID LVL
FLOW SUGGESTS THAT STORMS COULD EVOLVE INTO AN MCS...WITH ASSOCIATED
BOWING SEGMENTS POTENTIALLY EXTENDING A THREAT FOR DMGG WIND E/SE
INTO SE MO/SRN IL. WIND PROBABILITIES AND AREAL EXTEND OF SLIGHT
RISK ADJUSTED TO REFLECT THESE POSSIBILITIES.
OTHERWISE...REMAINDER OF 1630Z OTLK UNCHANGED...
..CORFIDI.. 07/20/2010
.PREV DISCUSSION... /ISSUED 1059 AM CDT TUE JUL 20 2010/
ZONAL FLOW PATTERN PERSISTS ACROSS THE NORTHERN STATES TODAY...
WHILE A FLAT RIDGE CONTROLS THE WEATHER FROM THE SOUTHWEST INTO THE
SOUTHEAST US. THE PRIMARY SURFACE BAROCLINIC ZONE EXTENDS FROM
EASTERN CO...THROUGH THE MID MS VALLEY...INTO THE MID ATLANTIC
STATES. THIS ZONE WILL BE THE FOCUS FOR STRONG TO SEVERE
THUNDERSTORMS THROUGH THIS FORECAST PERIOD.
...MID MS AND LOWER OH VALLEYS...
THE REMNANT MCS OVER MO/IL IS CONSIDERABLY WEAKER THAN A SIMILAR
SYSTEM IN THIS REGION YESTERDAY...BUT DOES HAVE SOME MESOSCALE
ORGANIZATION. POCKETS OF HEATING AND A VERY MOIST AIR MASS AHEAD OF
THIS SYSTEM WILL POSE THE RISK OF REDEVELOPMENT THIS AFTERNOON OVER
PARTS OF IND/OH/KY WITH DAMAGING WINDS THE MAIN THREAT.
...CENTRAL APPALACHIANS INTO MID ATLANTIC...
A WARM/MOIST AIR MASS IS PRESENT TODAY FROM EASTERN KY/WV TO THE MID
ATLANTIC COAST. EARLY AFTERNOON VISIBLE IMAGERY ALREADY SHOWS SOME
CU DEVELOPMENT OVER THE MOUNTAINS...SUGGESTING AT LEAST SCATTERED
THUNDERSTORMS WILL FORM AND SPREAD SLOWLY EASTWARD. HIGH
TEMPERATURES WELL INTO THE 90S WILL CONTRIBUTE TO STEEP LOW LEVEL
LAPSE RATES...WHILE PWAT VALUES APPROACHING 2 INCHES AID IN PRECIP
LOADING. STRONGER STORMS IN THIS REGION WILL POSE A RISK OF LOCALLY
DAMAGING DOWNBURST WINDS THIS AFTERNOON AND EVENING.
...EASTERN KS/MO THIS AFTERNOON AND EVENING...
THE CURRENT MCS OVER MO/IL WILL TRACK EASTWARD THIS
AFTERNOON...ALLOWING RAPID HEATING AND DESTABILIZATION OF MUCH OF
MO. LIFT ALONG AND NORTH OF OUTFLOW BOUNDARY MAY RESULT IN
RE-DEVELOPMENT OF THUNDERSTORMS. MLCAPE VALUES OVER 2500 J/KG AND
SUFFICIENT EFFECTIVE SHEAR PROFILES INDICATE A RISK OF ORGANIZED
MULTICELL AND SUPERCELL STORMS CAPABLE OF DAMAGING WINDS...HAIL...OR
EVEN A TORNADO.
...SOUTHEAST CO INTO CENTRAL KS...
WEAK SURFACE BOUNDARY CURRENTLY EXTENDS FROM NEAR LHX TO SLN. THIS
AXIS IS EXPECTED TO BE THE FOCUS FOR SCATTERED THUNDERSTORMS LATE
THIS AFTERNOON INTO EVENING. STRONGER CAPPING AND WEAK FORCING IN
THIS REGION MAY LIMIT THE NUMBER OF STORMS. HOWEVER...STEEP MID
LEVEL LAPSE RATES AND TURNING/INCREASING WINDS WITH HEIGHT POSE A
CONDITIONAL RISK OF SUPERCELLS CAPABLE OF LARGE HAIL AND DAMAGING
WINDS.
...WY/MT/SD...
WEAK UPSLOPE FLOW REGIME REMAINS TODAY OVER NORTHEAST WY AND
ADJACENT PORTIONS OF MT/SD. FORCING MECHANISMS ARE HARDER TO
IDENTIFY IN WATER VAPOR IMAGERY TODAY VS YESTERDAY. HOWEVER...IT
APPEARS LIKELY THAT AT LEAST A FEW STORMS WILL FORM IN THIS REGION
AND DEVELOP SOUTHEASTWARD. COLD TEMPERATURES ALOFT... STEEP LAPSE
RATES...AND STRONG EFFECTIVE SHEAR SUPPORT A RISK OF SUPERCELLS WITH
LARGE HAIL AND DAMAGING WINDS.
...WI/UPPER MI...
A MID LEVEL SHORTWAVE TROUGH IS PASSING EASTWARD ACROSS MN. LARGE
SCALE FORCING FOR ASCENT WILL OVERSPREAD WI BY EARLY
AFTERNOON...WHERE BREAKS IN THE CLOUDS ARE ALLOWING SOME
DESTABILIZATION. FORECAST SOUNDINGS SHOW FAVORABLE CAPE/SHEAR
COMBINATIONS FOR A RISK OF ISOLATED SEVERE STORMS CAPABLE OF LARGE
HAIL.
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