SWODY2
SPC AC 281719
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1219 PM CDT WED MAY 28 2008
VALID 291200Z - 301200Z
...THERE IS A SLGT RISK OF SVR TSTMS THU/THU NIGHT ACROSS PARTS OF
THE CNTRL PLAINS INTO THE UPPER MISSISSIPPI VALLEY....
...SYNOPSIS...
MODEL GUIDANCE IS SUGGESTIVE THAT THE AMPLIFIED UPPER PATTERN WILL
BECOME A BIT MORE ZONAL ACROSS THE U.S. DURING THIS FORECAST PERIOD.
THE DEEP NORTHERN STREAM TROUGH IS PROGGED TO SHIFT EAST OF THE
CANADIAN MARITIMES/NORTH ATLANTIC COAST REGION. AND...THE
SUBTROPICAL RIDGE AXIS OVER THE NORTH CENTRAL STATES IS PROGGED TO
FLATTEN...WHILE RIDGING REMAINS STRONG ACROSS THE NORTHERN MEXICAN
PLATEAU INTO THE GULF STATES. THIS IS FORECAST TO OCCUR AS A STRONG
MID/UPPER JET STREAK CONTINUES TO EMERGE FROM THE BASE OF THE BROAD
SOUTHERN BRANCH TROUGH OVER THE EASTERN PACIFIC/WESTERN U.S....AND
NOSE THROUGH THE CREST OF THE DOWNSTREAM RIDGE.
WITHIN THIS REGIME...ONE SIGNIFICANT SHORT WAVE IMPULSE APPEARS
LIKELY TO ALREADY BE PROGRESSING THROUGH BROADER SCALE ANTICYCLONIC
FLOW ACROSS THE NORTHERN PLAINS/UPPER MISSISSIPPI VALLEY BY 12Z
THURSDAY. THIS FEATURE IS EXPECTED TO BE TRAILED BY A MORE
PROMINENT IMPULSE...LIFTING THROUGH THE GREAT BASIN... BEFORE
CONTINUING THROUGH THE NORTH CENTRAL ROCKIES AND NORTHERN PLAINS
LATER THURSDAY/THURSDAY NIGHT.
...CENTRAL PLAINS INTO THE UPPER MISSISSIPPI VALLEY...
DESTABILIZATION ASSOCIATED WITH ELEVATED MOISTURE RETURN AND
LOWER/MID TROPOSPHERIC WARM ADVECTION IS EXPECTED TO BE ONGOING
NEAR/NORTHEAST OF THE MIDDLE MISSOURI VALLEY AT 12Z THURSDAY...IN
ASSOCIATION WITH THE LEAD IMPULSE. INSTABILITY MAY BE SUFFICIENT
FOR SOME MARGINALLY SEVERE HAIL IN STRONGER CELLS. THIS ACTIVITY
LIKELY WILL WEAKEN AS IT SPREADS EASTWARD THROUGH THE UPPER
MISSISSIPPI VALLEY...BUT MODELS ARE SUGGESTIVE THAT LIFT AND
STRONGER CONVECTION ASSOCIATED WITH WARM ADVECTION WILL REMAIN
FOCUSED NEAR THE MID MISSOURI VALLEY THROUGH MUCH OF THE DAY. CLOUD
COVER/PRECIPITATION WILL LIKELY MAINTAIN COOL/STABLE BOUNDARY LAYER
CONDITIONS ACROSS MUCH OF MINNESOTA AND IOWA...AS STRONG HEATING AND
BOUNDARY LAYER MOISTURE RETURN CONTRIBUTE TO STRONG DESTABILIZATION
FROM PARTS OF SOUTHERN SOUTH DAKOTA/NEBRASKA SOUTHWARD THROUGH THE
SOUTH CENTRAL HIGH PLAINS.
INHIBITION ACROSS THE WARM SECTOR OF A DEVELOPING SURFACE LOW TO THE
LEE OF THE NORTH CENTRAL ROCKIES IS EXPECTED TO SUPPRESS CONVECTIVE
DEVELOPMENT UNTIL LATE THURSDAY AFTERNOON...WHEN CONVECTIVE
TEMPERATURES SHOULD BE APPROACHED AND FORCING INCREASES AHEAD OF THE
NEXT IMPULSE. STORMS MAY INITIATE NEAR THE LEE SURFACE TROUGH
ACROSS THE CENTRAL HIGH PLAINS FIRST...BEFORE THIS ACTIVITY SPREADS
EASTWARD...WITH ADDITIONAL DEVELOPMENT ALONG A WARM FRONT EAST OF
THE SURFACE LOW. THIS SEEMS MOST PROBABLE ACROSS NORTHERN/EASTERN
NEBRASKA...BEFORE ACTIVITY CONSOLIDATES WITH INCREASINGLY FOCUSED
LARGE-SCALE ASCENT ACROSS THE MID MISSOURI VALLEY DURING THE
EVENING.
WITH MOISTURE NOT YET RETURNING TO THE REGION...UNCERTAINTIES
CONCERNING THE MAGNITUDE OF INSTABILITY EXIST. BUT...WITH THE
EVOLUTION OF STEEP LAPSE RATES LIKELY...A RETURN OF MID/UPPER 60S
SURFACE DEW POINTS PROBABLY WILL CONTRIBUTE TO AFTERNOON MIXED LAYER
CAPE OF 2000-3000+ J/KG. IN THE PRESENCE OF STRONG DEEP LAYER
SHEAR...AND SIZABLE CLOCKWISE CURVED LOW-LEVEL HODOGRAPHS... A FEW
SUPERCELLS WITH THE RISK FOR TORNADOES WILL CERTAINLY BE POSSIBLE
EARLY...BEFORE UPSCALE GROWTH INTO AN INCREASINGLY ORGANIZED
MESOSCALE CONVECTIVE SYSTEM OCCURS THURSDAY EVENING. MODELS SUGGEST
THAT THIS WILL OCCUR NEARLY COINCIDENT WITH THE INTENSIFICATION OF
AN 850 MB JET IN A BROAD WEST SOUTHWEST BELT ACROSS THE CENTRAL
PLAINS INTO THE UPPER MISSISSIPPI VALLEY. AND ...AT LEAST SOME
POTENTIAL APPEARS TO EXISTS FOR A DERECHO TYPE DAMAGING WIND EVENT
ACROSS THE MID MISSOURI VALLEY TOWARD THE UPPER GREAT LAKES REGION
THURSDAY NIGHT. BUT...UNCERTAINTY IS STILL LARGE DUE TO UNCERTAIN
STABILIZING INFLUENCE OF EARLY PERIOD CONVECTION.
..KERR.. 05/28/2008
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