SWODY2
SPC AC 231742
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1242 PM CDT SUN MAY 23 2010
VALID 241200Z - 251200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CENTRAL
PLAINS NWD THROUGH THE NRN PLAINS...
...SYNOPSIS...
BLOCKING PATTERN /REX BLOCK/ WILL CONTINUE TO EVOLVE OVER THE ERN
U.S. INTO THE DAY 2 PERIOD...WITH HEIGHT RISES ACROSS THE GREAT
LAKES TO NEW ENGLAND/ADJACENT ERN CANADA...AND A BROAD UPPER LOW
WILL BE MAINTAINED FROM THE WRN ATLANTIC TO SERN STATES. THE ERN
BLOCK WILL PLAY A KEY ROLE IN THE DAY 2 OUTLOOK...RESULTING IN A NWD
TRACK OF A STRONG MID AND UPPER-LEVEL LOW FROM THE FOUR CORNERS TO
THE CENTRAL CANADIAN U.S. BORDER AREA LATE MONDAY/EARLY TUESDAY.
THIS WILL SUPPORT THE SYSTEM DEEPENING AS IT BECOMES
NEGATIVELY-TILTED ACROSS THE CENTRAL ROCKIES/HIGH PLAINS MONDAY
AFTERNOON TO THE NRN PLAINS MONDAY NIGHT.
...NRN AND CENTRAL PLAINS...
THE DEEPENING MID-UPPER LEVEL SYSTEM WILL BE ACCOMPANIED BY A FAIRLY
STRONG SURFACE CYCLONE TRACKING NWD FROM SERN WY/NEB BORDER AT 12Z
MONDAY TO EXTREME SERN SASKATCHEWAN BY 12Z TUESDAY. AN E/NEWD
SURGING COLD FRONT IS EXPECTED TO OVERTAKE A WRN PLAINS DRY LINE BY
MONDAY EVENING AND SHOULD EXTEND FROM MN SWWD THROUGH MID MO VALLEY
TO SRN HIGH PLAINS BY END OF DAY 2.
TSTMS...SOME SEVERE...ARE EXPECTED TO BE ONGOING ACROSS PARTS OF THE
NRN PLAINS AT 12Z MONDAY ALONG AND N OF A WARM FRONT WHICH SHOULD
EXTEND ENEWD FROM THE WY/NEB SURFACE LOW THROUGH CENTRAL SD TO
CENTRAL MN. THIS ACTIVITY WILL BE DRIVEN BY WAA REGIME ALONG NOSE
OF A STRONG SLY LLJ...BUT SHOULD WEAKEN MONDAY MORNING AS IT SHIFTS
NWD AND A CAPPING ELEVATED MIXED LAYER SPREADS NWD THROUGH THE
REGION. THE AMOUNT OF ASSOCIATED CLOUDINESS/PRECIPITATION WITH THE
MORNING ACTIVITY WILL LIKELY RESULT IN HOW FAR N THE WARM FRONT WILL
BE ABLE TO RETURN. DESPITE THIS UNCERTAINTY MODELS ARE IN FAIRLY
GOOD AGREEMENT SHOWING THE WARM FRONT EXTENDING NEWD FROM WRN SD
THROUGH SRN ND TO NWRN MN BY 24/21Z. SURFACE HEATING WITHIN A MOIST
WARM SECTOR /SURFACE DEWPOINTS MID-UPPER 60S AND BENEATH STEEP MID
LEVEL LAPSE RATES /7-8.5 C PER KM/ WILL SUPPORT MLCAPE /1500-3000 J
PER KG/.
NEW TSTM DEVELOPMENT WILL BE POSSIBLE MONDAY AFTERNOON ALONG THE DRY
LINE FROM THE SURFACE LOW IN WRN SD TO PARTS OF WRN KS AS THE
LEADING EDGE OF THE STRONGER FORCING FOR ASCENT AND COOLER MID LEVEL
TEMPERATURES SPREAD ACROSS THIS REGION. ADDITIONAL STORMS WILL BE
POSSIBLE ALONG THE WARM FRONT. ALTHOUGH STRONG MID-UPPER LEVEL
WINDS WILL BE NEARLY UNIDIRECTIONAL /SSWLY/...RE-STRENGTHENING SLY
LLJ /40-50 KT/ FROM NRN KS TO THE DAKOTAS AND SELY SURFACE WINDS IN
THE WARM SECTOR WILL PROMOTE STRONG EFFECTIVE BULK SHEAR /40-60 KT/.
THIS COMBINED WITH THE MODERATE TO VERY STRONG INSTABILITY WILL
SUPPORT SUPERCELLS WITH THE INITIAL DRY LINE AND WARM FRONT STORMS.
PRIMARY SEVERE THREATS SHOULD BE TORNADOES AND LARGE HAIL...SOME
VERY LARGE. GIVEN THESE FACTORS...SEVERE PROBABILITIES HAVE BEEN
INCREASED TO A HIGH END SLIGHT RISK FOR MUCH OF CENTRAL SD INTO SRN
ND. GIVEN THAT THERE REMAINS SOME UNCERTAINTY IN THE PLACEMENT OF
THE WARM FRONT MONDAY AFTERNOON...THIS OUTLOOK WILL NOT BE UPGRADED
TO A MODERATE RISK. HOWEVER...SEVERE PARAMETERS ARE BECOMING MORE
CONVINCING THAT A SIGNIFICANT SEVERE WEATHER THREAT SHOULD OCCUR
OVER THE DAKOTAS DURING DAY 2.
MODELS REMAIN CONSISTENT FOR MONDAY NIGHT SHOWING AN UPSCALE GROWTH
INTO A MESOSCALE CONVECTIVE SYSTEM SPREADING NNEWD ACROSS THE
DAKOTAS/NEB WITH THE PRIMARY SEVERE THREAT TRANSITIONING TO DAMAGING
WINDS ALONG THE SURGING COLD FRONT.
..PETERS.. 05/23/2010
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