SWODY1
SPC AC 312127
DAY 1 CONVECTIVE OUTLOOK AMEND 1
NWS STORM PREDICTION CENTER NORMAN OK
0427 PM CDT SAT JUL 31 2010
VALID 312000Z - 011200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF THE NRN
INTERMOUNTAIN WEST...NRN ROCKIES AND NRN PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE LOWER OH/TN VLYS TO
THE SERN ATLANTIC SEABOARD...
AMENDED FOR SEVERE THUNDERSTORM WATCH WRN SD/ERN WY
...NRN HIGH PLAINS...
UPDATED TO ACCOUNT FOR SEVERE THUNDERSTORM WATCH IN WRN SD AND ERN
WY.
/JPR
.PREV DISCUSSION... /ISSUED 244 PM CDT SAT JUL 31 2010/
...NRN INTERMOUNTAIN REGION INTO NRN PLAINS...
ONLY CHANGE TO THIS GROUP WAS TO TRIM THE SEVERE RISKS OUT OF
CABINET AND NRN ROCKY MOUNTAIN FRONT REGIONS OF MT. A COLD SURGE
HAS SPREAD SWD...ESPECIALLY E OF THE NRN ROCKY MOUNTAIN FRONT WITH
SFC TEMPERATURES HAVING FALLEN INTO THE 60S. THIS SHOULD SET THE
WRN END OF THE SEVERE RISKS TODAY. PRIMARY SEVERE THREAT SHOULD
EVOLVE FARTHER E AND S ACROSS SW-CNTRL MT. STRONG STORMS HAVE
ALREADY DEVELOPED OVER THE SW MT MOUNTAINS AHEAD OF A MID-LEVEL
WAVE. DOWNSTREAM INVERTED-V SOUNDING STRUCTURES AND HOT BOUNDARY
LAYER SHOULD AUGMENT WIND GUSTS WITH SEVERE/DAMAGING WINDS POSSIBLE
WWUS20 SEVERE THUNDERSTORM WATCH FOR FURTHER DETAILS.
REMAINDER OF FORECAST DISCUSSION REMAINS VALID FOR LOCATIONS FARTHER
E IN THE NRN PLAINS.
...CNTRL HIGH PLAINS...
HAVE EXTENDED LOW PROBABILITIES FOR SEVERE HAIL/WIND INTO ERN CO
WHERE A CLUSTER OF SLOW MOVING MULTICELL STORMS CONTINUE IN THE
VICINITY OF A WEAK BOUNDARY. ALTHOUGH THERMODYNAMIC/KINEMATIC
SET-UPS WERE VERY MARGINAL FOR SUSTAINED SEVERE STORMS...AN ISOLATED
DAMAGING WET MICROBURST CANNOT BE RULED OUT.
...SERN ATLANTIC COAST...
THUNDERSTORM WATCH FOR DETAILS. NO CHANGES TO THIS GROUP NEEDED.
FORECAST ON TRACK WITH SMALL CONVECTIVELY-INDUCED SHORTWAVE
MIGRATING INTO THE CAROLINAS. LARGELY MULTICELL STORMS CONTINUE TO
THRIVE ALONG/SW OF A STALLED NW-SE ORIENTED FRONT FROM N GA INTO
COASTAL SC/GA. STORM MERGERS AND VERY HOT BOUNDARY LAYER/LARGE
DCAPE VALUES WILL RESULT IN PRECIPITATION LOADING AND SUBSEQUENT WET
MICROBURSTS WITH A FEW STORMS. SEVERE THREATS WILL DIMINISH WITH
SUNSET.
...LOWER OH/TN VALLEYS...
THUNDERSTORM WATCH FOR DETAILS. NO CHANGES TO THIS GROUP NEEDED.
LARGE-SCALE UPPER TROUGH ROTATING THROUGH THE MIDWEST WILL GRAZE THE
WARM/UNSTABLE WARM SECTOR ACROSS THE REGION THROUGH THIS EVENING.
THUNDERSTORMS CONTINUE TO DEEPEN ACROSS THE KY BLUEGRASS AND MIDDLE
TN AT MID-AFTERNOON. A FEW STORMS MAY PRODUCE DAMAGING WINDS AND
PERHAPS HAIL.
/JPR
..SELECT A FORECASTER.. 07/31/2010
.PREV DISCUSSION... /ISSUED 1109 AM CDT SAT JUL 31 2010/
...SYNOPSIS...
WHILE RIDGE DOMINATES SRN U.S. WITH UPR HIGH CENTER SRN PLAINS...THE
TROUGH THAT HAS BEEN OFFSHORE PAC NW HAS MOVED TO THE COAST WHILE
TROUGH PERSISTS NERN STATES.
..NRN INTERMOUNTAIN REGION INTO NRN PLAINS...
AHEAD OF THE PRIMARY UPPER TROUGH AN IMPULSE/SPEED MAX MOVING NEWD
ACROSS WA/OR WILL MOVE TO NRN INTERMOUNTAIN REGION BY THIS EVENING.
MEANWHILE...A WEAKER DOWNSTREAM IMPULSE /NOW OVER CNTRL PORTIONS OF
MT INTO NRN WY/ WILL TRANSLATE EWD TODAY INTO ND AND NRN SD. IN THE
LOW LEVELS...WEAK LOW PRESSURE WILL CONSOLIDATE OVER ERN MT BY THIS
AFTERNOON WITH A NNW-SSE ORIENTED TROUGH/BAROCLINIC ZONE PERSISTING
FROM FAR ERN MT INTO THE CNTRL HIGH PLAINS. FARTHER W...A WEAK
PACIFIC FRONT WILL PROGRESS THROUGH THE PACIFIC NW INTO NRN
INTERMOUNTAIN REGION TODAY.
THE PRIMARY FOCUS FOR STRONG TO SEVERE TSTM DEVELOPMENT APPEARS TO
BE ALONG THE FAVORED TERRAIN AND EWD-ADVANCING PACIFIC FRONT BY
MID/LATE AFTERNOON FROM ERN WA/NERN ORE ACROSS THE ID PNHDL INTO WRN
MT. HERE...INCREASED HEIGHT FALLS/DYNAMIC FORCING FOR ASCENT
ATTENDANT TO ABOVE-MENTIONED SYSTEM WILL INTERACT WITH A STEEP LAPSE
RATE THERMODYNAMIC ENVIRONMENT WHERE MLCAPE WILL APPROACH 1000 J/KG.
THE EWD PROGRESSION OF 80-90 KT UPPER-LEVEL JET STREAK AND 50+ KT
MIDLEVEL WIND MAXIMUM WILL RESULT IN 45-60 KT OF DEEP SWLY
SHEAR...SUFFICIENT FOR ORGANIZED STORM MODES...INCLUDING SUPERCELLS
AND BOWING STRUCTURES. LARGE HAIL AND DAMAGING WIND GUSTS WILL BE
THE PRIMARY HAZARDS GIVEN THE COOLING THERMODYNAMIC PROFILES AND
STEEP LAPSE RATE/HIGH LCL ENVIRONMENT.
HAVE EXTENDED THE RISK EWD ACROSS SRN ID GIVEN THE GREATER
AVAILABILITY OF THE MONSOON MOISTURE FROM THE S TO AID THE
INSTABILITY ALONG WITH UP TO 40 KT OF SHEAR.
STORM INITIATION AND EVOLUTION IS A BIT MORE UNCERTAIN FARTHER E
ACROSS ERN MT INTO THE DAKOTAS TODAY OWING TO EWD PROGRESSION OF
LEAD IMPULSE AWAY FROM N-S ORIENTED SURFACE BOUNDARY.
NONETHELESS...IT APPEARS THAT AT LEAST ISOLATED...DIURNAL
STORMS WILL BE POSSIBLE IN ADVANCE OF THE LEAD IMPULSE OVER ND...AS
WELL AS ALONG THE PRIMARY BOUNDARY WHICH SHOULD BE SITUATED OVER FAR
ERN PARTS OF MT/WY. ALSO...SOME MODEL GUIDANCE SUGGESTS THE
POSSIBILITY OF STORMS PROGRESSING SEWD FROM SERN SASKATCHEWAN/SRN
MANITOBA INTO CNTRL/ERN ND. IN ANY EVENT...THE COMBINATION OF 40-50
KT OF DEEP-LAYER SHEAR AND AFTERNOON MLCAPE VALUES APPROACHING
1000-1500 J/KG SUGGESTS THE POTENTIAL FOR SUSTAINED/ROTATING
UPDRAFTS CAPABLE OF LARGE HAIL AND DAMAGING WIND GUSTS.
TSTMS WILL LIKELY PERSIST OVERNIGHT MAINLY ACROSS ND IN ASSOCIATION
WITH STRENGTHENING WAA REGIME ATTENDANT TO 40+ KT LLJ. A FEW OF THE
MORE INTENSE STORMS WILL REMAIN CAPABLE OF HAIL AND STRONG WIND
GUSTS INTO SUNDAY MORNING.
..SERN ATLANTIC COAST...
REF MCD 1510
MIDLEVEL IMPULSE RESPONSIBLE FOR ONGOING TSTMS NOW MOVING ACROSS ERN
TN WILL CONTINUE SEWD TODAY...SUPPORTING AN INCREASE IN TSTM
COVERAGE AND INTENSITY WITHIN A VERY MOIST AND MODERATELY UNSTABLE
AIR MASS WITH MLCAPE OF 1500-3000 J/KG. THE MODERATE
INSTABILITY COUPLED WITH VEERING WIND PROFILES AND AROUND 30 KT OF
DEEP NWLY SHEAR WILL FAVOR UPSCALE GROWTH OF STORMS INTO MULTICELL
CLUSTERS WITH THE THREAT FOR DAMAGING WIND GUSTS.
...LOWER OH/TN VALLEYS...
A FAIRLY STRONG MIDLEVEL IMPULSE AND ASSOCIATED 40-45 KT WIND
MAXIMUM TRANSLATING SEWD THROUGH THE UPPER MIDWEST. THIS IMPULSE
WILL CONTINUE SEWD TODAY IN CONJUNCTION WITH A SURFACE LOW AND
ATTENDANT FRONTAL SYSTEM. STRONG DIABATIC HEATING UNDERWAY LWR OH
AND WRN TN VLYS THIS AM AND WILL SUPPORT THE DEVELOPMENT OF A
MODERATELY UNSTABLE AIR MASS BY AFTERNOON AHEAD OF SWD-MOVING FRONT
WITH MLCAPE OF 1000-2500 J/KG.
EXPECT TSTMS TO GRADUALLY INCREASE IN COVERAGE AND INTENSITY THROUGH
THE AFTERNOON IN ADVANCE OF UPPER SYSTEM WITHIN A KINEMATIC
ENVIRONMENT FEATURING VERTICALLY-VEERING WIND PROFILES AND 30-40 KT
OF DEEP NWLY SHEAR. AS SUCH...THE SETUP WILL FAVOR THE DEVELOPMENT
OF ORGANIZED STORM CLUSTERS...PERHAPS EVOLVING INTO AN MCS WITH
DAMAGING WINDS BEING THE PRIMARY HAZARD.
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