SWODY1
SPC AC 142000
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT WED JUL 14 2010
VALID 142000Z - 151200Z
...THERE IS A MDT RISK OF SVR TSTMS ACROSS PORTIONS OF NORTHEAST
IA/SOUTHEAST MN AND MUCH OF CENTRAL/SOUTHERN WI...
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE GREAT LAKES REGION TO
THE CENTRAL HIGH PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE CO FRONT RANGE...
...UPPER MIDWEST/GREAT LAKES TO CENTRAL PLAINS...
A MULTI-MODAL/MULTI-FACETED CONSIDERABLE SEVERE WEATHER EPISODE WILL
CONTINUE TO UNFOLD THROUGH THE LATE AFTERNOON/EVENING HOURS. THE
GREATEST TORNADO THREAT SEEMS LIKELY TO FOCUSED ACROSS SOUTHEAST
MN/FAR NORTHEAST IA INTO MUCH OF WESTERN/CENTRAL WI...CHIEFLY WITH
TSTMS NOW INITIATING ALONG A PRE-COLD FRONTAL SURFACE TROUGH...WITH
SUBSEQUENT INTERACTION WITH A SURFACE WARM FRONT/MODIFYING OUTFLOW
FROM SOUTHEAST MN INTO WESTERN WI. PLEASE SEE MESOSCALE DISCUSSION
1302.
ADDITIONAL TSTM DEVELOPMENT WILL CONTINUE TO OCCUR/GROW UPSCALE
ALONG THE SYNOPTIC COLD FRONT A BIT FARTHER WEST ACROSS
MN...SOUTHWESTWARD ACROSS IA INTO EASTERN/SOUTHERN NEB AND NORTHERN
KS. SPECIAL 18Z RAOBS FROM MINNEAPOLIS/OMAHA SAMPLE THE ROBUST
BUOYANCY ACROSS THE REGION...WITH MLCAPES OF 4000-6000 J/KG NOW
ESTIMATED TO BE IN PLACE FROM SOUTHEAST MN/FAR WESTERN WI INTO MUCH
OF IA/EASTERN NEB. THE 18Z MINNEAPOLIS OBSERVED RAOB ALSO SAMPLED
STRENGTHENING MID TROPOSPHERIC FLOW WITH 50 KT ABOVE 3 KM. THIS IS
SIMILAR TO A MULTI-HOUR TREND OF MARKEDLY INCREASING FLOW ALOFT
UPSTREAM PER THE SIOUX FALLS WSR-88D VWP AND WOOD LAKE MN
PROFILER...AHEAD OF A POTENT/COMPACT BASAL SHORTWAVE TROUGH NOTED TO
BE CROSSING THE DAKOTAS AT MID AFTERNOON PER WATER VAPOR IMAGERY.
PLEASE CONSULT THE LATEST WATCHES/MESOSCALE DETAILS FOR THE MOST
CONTEMPORARY SHORT TERM INFORMATION.
..GUYER.. 07/14/2010
.PREV DISCUSSION... /ISSUED 1116 AM CDT WED JUL 14 2010/
...UPPER GREAT LAKES/UPPER MIDWEST...
STRONG/SEVERE MCS IS IN PROGRESS THIS MORNING OVER NWRN WI WITH MORE
DISCRETE STORM DEVELOPMENT OBSERVED OVER SRN MN/NERN IA. SURFACE
AND UPPER-AIR ANALYSES SUGGEST THAT THIS ACTIVITY IS OCCURRING
WITHIN A ZONE OF STRONG WAA ALONG THE NOSE OF A 40-45 KT LLJ...AND
GENERALLY STRADDLING A WARM FRONT EXTENDING FROM LOW PRESSURE OVER
E-CNTRL SD ENEWD INTO CNTRL WI. 12Z OBSERVED SOUNDINGS SHOW THE
PRESENCE OF STEEP MIDLEVEL LAPSE RATES /ASSOCIATED WITH AN EML/
ATOP A MOIST BOUNDARY LAYER /I.E. 100 MB MEAN MIXING RATIO IN EXCESS
OF 18 G PER KG AT MPX/. WHEN COUPLED WITH DAYTIME HEATING...AIR
MASS WILL BECOME MODERATE TO STRONGLY UNSTABLE BY AFTERNOON WITH
MLCAPE RANGING FROM 1000-2000 J/KG AHEAD OF ONGOING MCS OVER
NRN/CNTRL WI...TO AS HIGH AS 3500-4500 J/KG FARTHER S ACROSS IA.
CAPPING ASSOCIATED WITH EML WILL GRADUALLY BE ERODED THROUGH THE DAY
OWING TO LARGE-SCALE FORCING ASSOCIATED WITH UPSTREAM
TROUGH...STRONG STORM AND MESOSCALE COLD POOLS AND FRONTAL
CONVERGENCE. THESE PROCESSES SHOULD ALLOW INITIAL STORMS TO BECOME
FULLY SURFACE-BASED WHILE AT THE SAME TIME PERMITTING SUBSEQUENT
STORM DEVELOPMENT FARTHER S ACROSS SRN MN...CNTRL/SRN WI AND IA.
EXPECT A COMBINATION OF FORWARD-PROPAGATING QLCS AND SUPERCELL MODES
TO CO-EXIST WITH THE THREAT FOR CORRIDORS OF DAMAGING WIND
GUSTS...LARGE HAIL AND TORNADOES /SOME POSSIBLY STRONG/.
CURRENTLY...IT APPEARS THE GREATEST THREAT FOR SIGNIFICANT TORNADOES
WILL EXIST ACROSS SRN MN INTO W-CNTRL OR SWRN WI LATER TODAY.
HERE...LATEST MODEL GUIDANCE INDICATES THAT THE HIGHEST LIKELIHOOD
FOR MORE DISCRETE STORM MODES WILL COINCIDE WITH STRONG INSTABILITY
AND MORE THAN SUFFICIENT LOW AND DEEP-LAYER SHEAR.
EXPECT THE THREAT FOR MAINLY LARGE HAIL AND DAMAGING WIND GUSTS TO
CONTINUE OVERNIGHT ACROSS PARTS OF IA...SRN WI INTO IL IN
CONJUNCTION WITH ONE OR MULTIPLE MCS/S.
...MID MO VALLEY INTO CNTRL HIGH PLAINS...
ISOLATED TO SCATTERED TSTMS ARE ONGOING THIS MORNING FROM CNTRL NEB
INTO ERN SD IN ASSOCIATION WITH A WELL-DEFINED SHORT WAVE TROUGH
PROGRESSING EWD THROUGH THE DAKOTAS AND WRN NEB. 12Z OBSERVED
SOUNDINGS SUGGEST THAT THIS ACTIVITY IS LIKELY SITUATED ABOVE THE
STRONG CAP CENTERED IN THE 800-850 MB LAYER. GIVEN THE PRESENCE OF
THE STEEP LAPSE RATES AND MODEST CLOUD-BEARING SHEAR...SOME HAIL
WILL BE POSSIBLE WITH THE STRONGER STORMS.
SURFACE-BASED TSTM DEVELOPMENT WILL BECOME INCREASINGLY LIKELY ALONG
THE COLD FRONT BY MID/LATE AFTERNOON FROM ERN NEB/WRN IA SWWD INTO
WRN KS AS THE COMBINATION OF STRONG HEATING AND FORCING ASSOCIATED
WITH SRN EXTENSION OF ABOVE-MENTIONED SHORT WAVE TROUGH
PROGRESSIVELY OVERSPREAD THE REGION. AMBIENT...PRE-FRONTAL AIR MASS
WILL BE HOT AND QUITE MOIST WITH DEWPOINTS IN THE MID/UPPER 70S F.
WHEN COUPLED WITH THE STEEP MIDLEVEL LAPSE RATES...ENVIRONMENT IS
EXPECTED TO BECOME STRONGLY TO EXTREMELY UNSTABLE WITH MLCAPE
RANGING FROM 4000-5500 J/KG OVER THE MID MO VALLEY...TO 2000-3000
J/KG ACROSS WRN KS. WHILE LOW AND DEEP-LAYER SHEAR WILL NOT BE AS
STRONG AS THAT OVER THE UPPER MIDWEST...IT WILL BE SUFFICIENT TO
SUPPORT SUPERCELLS CAPABLE OF LARGE HAIL...DAMAGING WINDS AND
PERHAPS A FEW TORNADOES...GIVEN THE DEGREE OF INSTABILITY.
...CHEYENNE RIDGE INTO CO FRONT RANGE...
THE COMBINATION OF STEEP LAPSE RATES AND RESIDUAL BOUNDARY LAYER
DEWPOINTS IN THE 40S TO LOWER 50S F WITHIN POST-FRONTAL UPSLOPE
REGIME WILL YIELD POCKETS OF MODEST INSTABILITY BY AFTERNOON WITH
MLCAPE OF 500-1500 J/KG. ISOLATED STORM DEVELOPMENT WILL BE
POSSIBLE THROUGH THE LATTER HALF OF THE DIURNAL HEATING CYCLE WITH
FORECAST WIND PROFILES SUPPORTIVE OF SUPERCELLS CAPABLE OF LARGE
HAIL AND LOCALLY STRONG WIND GUSTS.
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