SWODY1
SPC AC 121957
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0257 PM CDT SUN SEP 12 2010
VALID 122000Z - 131200Z
...NO SVR TSTM AREAS FORECAST...
...UPPER GREAT LAKES...
MINOR CHANGES MADE ALONG THE WRN EXTENT OF THE GENERAL TSTM AREA AND
5 PERCENT PROBABILITY LINES FOR STRONG WIND GUSTS AND HAIL OVER NWRN
WI. WATER VAPOR IMAGERY INDICATED THE LEADING EDGE OF A NRN STREAM
SHORTWAVE TROUGH WAS MOVING ACROSS WRN LAKE SUPERIOR EARLY THIS
AFTERNOON. AT 18Z...SURFACE COLD FRONT HAD REACHED ERN LAKE
SUPERIOR WITH THE TRAILING PORTION EXTENDING INTO NRN IA. ANALYSES
INDICATED A SECONDARY WIND SHIFT EXTENDING FROM NWRN WI TO SRN ND.
LOW LEVEL WAA ACROSS NORTH CENTRAL-NERN WI INTO UPPER MI...COLD
MIDLEVEL TEMPERATURES /-20 C AT 500 MB/ SPREADING ESEWD WITH
ATTENDANT TROUGH AND STEEPENING LOW-MID LEVEL LAPSE RATES WILL
CONTINUE TO SUPPORT A FEW ADDITIONAL STRONGER/SUSTAINED UPDRAFTS.
CLOUD TOPS SHOULD CONTINUE TO REACH LEVELS COLD ENOUGH FOR CHARGE
SEPARATION AS RECENTLY OBSERVED IN SCHOOLCRAFT AND IRON COUNTIES MI
PER LIGHTNING DATA.
DESPITE LOWER OBSERVED SURFACE DEWPOINTS ACROSS THIS REGION DUE TO
MIXING AS COMPARED TO THE 12Z NAM...STEEPENING LAPSE RATES ARE
SUPPORTING AT LEAST MARGINAL INSTABILITY /MUCAPE AROUND 500 J PER
KG/ THIS AFTERNOON. REGIONAL RADAR IMAGERY SHOWED A BROKEN AREA OF
SHOWERS/TSTMS DEVELOPING ALONG LEADING EDGE OF STRONGER ASCENT
ACROSS UPPER MI AND ADJACENT FAR NRN WI WITH INCREASING EFFECTIVE
BULK SHEAR SUPPORTIVE OF SOME STORM ORGANIZATION. STEEP LAPSE RATES
WILL SUPPORT LOCALLY STRONG/DAMAGING WIND GUSTS AND MARGINALLY
SEVERE HAIL.
...MIDWEST...
NO CHANGES REQUIRED WITH THE LOW SEVERE PROBABILITIES AND GENERAL
TSTM AREA OVER THIS REGION.
...FAR SERN GA/NRN FL AND SRN LA/SERN TX...
REGIONAL RADAR IMAGERY SHOWED TSTMS OVER FAR SERN GA INTO NRN FL.
THIS ACTIVITY ALONG WITH TSTMS OVER SRN LA TO SERN TX WERE LOCATED
ALONG A COLD FRONT CONTINUING TO ADVANCE SWD. STRONG INSTABILITY
/MLCAPE 2000-3000 J PER KG/ WILL CONTINUE SUPPORT SUSTAINED UPDRAFTS
ALONG THE COLD FRONT AND ANY BOUNDARY INTERACTIONS WITH CONVECTIVE
OUTFLOWS AND LAKE/SEA BREEZES. HOWEVER...WEAK DEEP LAYER SHEAR IS
EXPECTED TO LIMIT THE SEVERE WEATHER THREAT...ASIDE FROM A FEW
LOCALLY STRONG WIND GUSTS. COVERAGE DOES NOT WARRANT THE INCLUSION
OF SEVERE PROBABILITIES.
..PETERS.. 09/12/2010
.PREV DISCUSSION... /ISSUED 1113 AM CDT SUN SEP 12 2010/
...UPPER GREAT LAKES INTO THE MIDWEST...
A LOW-AMPLITUDE SHORT WAVE TROUGH AND ASSOCIATED 50-60 KT MIDLEVEL
JET STREAK NOW OVER THE RED RIVER VALLEY WILL RAPIDLY TRANSLATE
ESEWD THROUGH THE REGION TODAY...ENHANCING A BAND OF DYNAMIC FORCING
FOR ASCENT ALONG SYSTEM TRACK. AT THE SURFACE...LATEST MESOANALYSIS
INDICATES A WEAK COLD FRONT FROM WRN LAKE SUPERIOR SWWD INTO S-CNTRL
MN. BY MID AFTERNOON...THIS BOUNDARY IS EXPECTED TO BECOME ALIGNED
IN MORE OF AN ENE-WSW FASHION FROM THE UPPER PENINSULA OF MI INTO
NRN WI...AND WILL LIKELY SERVE AS THE FOCUS FOR A FEW STRONG TO
MARGINALLY SEVERE STORMS DURING THE LATTER HALF OF THE DIURNAL
HEATING CYCLE.
12Z OBSERVED SOUNDINGS AND SATELLITE-DERIVED PW IMAGERY SHOW THAT
PRE-FRONTAL AIR MASS IS RELATIVELY DRY WITH BOUNDARY LAYER DEW
POINTS IN THE 50S AND PW VALUES WELL BELOW AN INCH. HOWEVER...
UPSTREAM OBSERVATIONS SUGGEST THAT NOTABLE MID-TROPOSPHERIC COOLING
WILL SPREAD SEWD THROUGH THE REGION TODAY IN CONJUNCTION WITH
ABOVE-MENTIONED SHORT WAVE TROUGH. WHEN COUPLED WITH DAYTIME
HEATING AND SUBSEQUENT STEEPENING OF LOW-LEVEL LAPSE
RATES...PRE-FRONTAL AIR MASS IS EXPECTED TO BECOME MARGINALLY
UNSTABLE WITH MLCAPE APPROACHING 500 J/KG. GIVEN THE PRESENCE OF
40-50 KT OF DEEP WNWLY SHEAR...SETUP WILL FAVOR THE DEVELOPMENT OF
SOME STORM ORGANIZATION WITH A RISK FOR LOCALLY DAMAGING WIND GUSTS
AND MARGINALLY SEVERE HAIL THROUGH THIS EVENING.
A SECONDARY...WEAKER CONFLUENCE BAND DEVELOPING FROM NRN/CNTRL IA TO
ALONG THE WI/IL BORDER MAY ALSO SERVE AS THE FOCUS FOR ISOLATED
STORM FORMATION LATE THIS AFTERNOON INTO EVENING WITHIN A SIMILAR
THERMODYNAMIC AND KINEMATIC ENVIRONMENT. WHILE THIS AREA WILL BE
MORE WEAKLY FORCED THAN ALONG THE PRIMARY FRONT/WIND SHIFT...
ISOLATED OCCURRENCES OF MARGINALLY SEVERE WIND/HAIL WILL BE
POSSIBLE.
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