SWODY1
SPC AC 311952
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0252 PM CDT SAT MAR 31 2012
VALID 312000Z - 011200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE LOWER TO
MID MS VALLEY AND TN VALLEY...
SEVERAL CHANGES HAVE BEEN MADE TO THE OUTLOOK AT 20Z. THE FIRST
CHANGE IS TO EXTEND THE SLIGHT RISK FURTHER EAST ACROSS SE TN AND
INTO NW GA WHERE SEVERE THUNDERSTORM WW 121 IS CURRENTLY LOCATED.
THE SECOND CHANGE IS TO REMOVE PARTS OF NRN LA AND SCNTRL AR FROM
THE SLIGHT RISK AND EXTEND THE SLIGHT RISK FURTHER NORTHWEST INTO SE
MO WHERE SHORT-TERM MODEL FORECASTS INITIATE CONVECTION LATER ON
THIS AFTERNOON. THE THIRD CHANGE IS TO ADD SRN FLORIDA INTO THE 5
PERCENT WIND DAMAGE PROBABILITY WHERE STRONG THUNDERSTORMS ARE
ONGOING. OTHERWISE...THE OUTLOOK LOOKS TO BE ON TRACK.
..BROYLES.. 03/31/2012
.PREV DISCUSSION... /ISSUED 1123 AM CDT SAT MAR 31 2012/
...SYNOPSIS...
INTENSE...ERN PACIFIC TROUGH WILL MOVE ONSHORE TODAY...REACHING THE
NRN INTER-MOUNTAIN REGION AND GREAT BASIN TONIGHT. THIS WILL RESULT
IN THE BUILDING OF DOWNSTREAM RIDGE AXIS ACROSS THE CNTRL CONUS AND
CANADIAN PRAIRIE PROVINCES...AND THE EWD PROGRESSION OF MIDLEVEL
TROUGH ACROSS THE ERN THIRD OF THE NATION. IN THE LOW LEVELS...
SURFACE CYCLONE OFF THE ORE COAST IS FORECAST TO REDEVELOP OVER THE
NRN ROCKIES BY THIS EVENING...ALONG A PACIFIC FRONT MOVING ACROSS
THE PACIFIC NW. ELSEWHERE...A WEAK SURFACE LOW OVER CNTRL VA WILL
DEVELOP SEWD TO OFF THE NC COAST WHILE A TRAILING COLD FRONT SETTLES
SWD THROUGH THE TN VALLEY. THE NWWD EXTENSION OF THIS FRONT IS
EXPECTED TO SLOWLY PROGRESS EWD/NEWD THROUGH THE MID/LOWER MO AND
MID MS VALLEYS AS A WARM FRONT.
...MID SOUTH/LOWER MS AND TN VALLEYS THIS AFTERNOON INTO TONIGHT...
12Z REGIONAL SOUNDINGS INDICATE THAT AN EML /CHARACTERIZED BY
MIDLEVEL LAPSE RATES OF 7.5-9.0 C PER KM/ HAS OVERSPREAD THE REGION
WITHIN PREVAILING NWLY MIDLEVEL FLOW REGIME. THESE LAPSE RATES
COINCIDE WITH A RELATIVELY MOIST BOUNDARY LAYER WITH DEWPOINTS IN
THE 60S AND LOWEST 100-MB MEAN-MIXING RATIOS OF 12-13 G/KG.
MOREOVER... VISIBLE SATELLITE SUGGESTS THAT STRONG DIABATIC HEATING
WILL OCCUR TODAY ACROSS PRE-FRONTAL WARM SECTOR...BOOSTING MLCAPE
VALUES TO 2000-4000 J/KG.
SIMILAR TO SATURDAY OVER THE SRN PLAINS...LARGE-SCALE FORCING FOR
ASCENT WILL REMAIN NEGLIGIBLE...WITH ONLY MODEST LOW-LEVEL
CONVERGENCE FORECAST ALONG THE COLD FRONT. AS SUCH...EVENTUAL TSTM
COVERAGE REMAINS UNCERTAIN...AND VERTICAL SHEAR WILL REMAIN ON THE
MARGINS OF THAT SUPPORTIVE OF ORGANIZED STORM MODES /I.E. AROUND 30
KT/. HOWEVER...THE STEEP LAPSE RATES AND MODERATE TO STRONG
INSTABILITY SHOULD COMPENSATE...PROMOTING MULTICELLS AND POSSIBLE
LINE SEGMENTS CAPABLE OF SEVERE HAIL AND DAMAGING WIND GUSTS.
...SOUTHEAST THIS AFTERNOON/EVENING...
FORCING FOR ASCENT ATTENDANT TO MIDLEVEL VORTICITY MAXIMUM OVER THE
FL PNHDL WILL CONTINUE TO FOSTER SCATTERED-NUMEROUS TSTMS TODAY
ACROSS NRN FL/SRN GA. STRONGER WIND FIELDS ASSOCIATED WITH THE ERN
U.S. TROUGH WILL SHIFT EWD INTO THE ATLANTIC...RESULTING IN
GENERALLY WEAK VERTICAL SHEAR ACROSS THE REGION. NONETHELESS...
GIVEN THE MOIST AND MODERATELY UNSTABLE AIR MASS...SOME POTENTIAL
WILL EXIST FOR LOCALLY STRONG WIND GUSTS OWING TO WATER-LOADING
EFFECTS.
...NRN ROCKIES/NRN GREAT BASIN LATE THIS AFTERNOON/EVENING...
LARGE-SCALE FORCING WILL INCREASE LATER TODAY AS THE LEADING EDGE OF
SIGNIFICANT HEIGHT FALLS ATTENDANT TO ERN PACIFIC TROUGH OVERSPREAD
THE REGION. THIS FORCING WILL ALIGN WITH LOW-LEVEL UPLIFT ALONG THE
PACIFIC FRONT AND OROGRAPHY TO GIVE RISE TO WIDELY SCATTERED...
LOW-TOPPED TSTMS. WHILE THE RELATIVELY DRY AIR MASS /I.E. PW VALUES
OF LESS THAN 0.5-0.6 INCH/ WILL LIMIT PARCEL BUOYANCY...THE PRESENCE
OF STEEP LAPSE RATES AND A STRENGTHENING WIND FIELD MAY YIELD A FEW
LOCALLY STRONG WIND GUSTS AND PERHAPS SOME SMALL HAIL.
...PACIFIC NW/NRN CA COASTS THIS AFTERNOON/EVENING...
THE EWD PROGRESSION OF WARM CONVEYOR BELT CLOUD BAND WILL ALLOW FOR
INCREASED DIABATIC WARMING WITHIN THE BOUNDARY LAYER THIS AFTERNOON.
WHEN COUPLED WITH CONSIDERABLE MIDLEVEL COOLING AND MOIST ONSHORE
FLOW IN THE LOW-LEVELS...ENVIRONMENT IS EXPECTED TO BECOME
MARGINALLY UNSTABLE WITH SBCAPE OF A COUPLE HUNDRED J/KG. VERTICAL
SHEAR WILL REMAIN QUITE STRONG AND SOME POTENTIAL WILL EXIST FOR
ROTATING...LOW-TOPPED STORMS CAPABLE OF SOME HAIL...LOCALLY GUSTY
WINDS AND PERHAPS A BRIEF TORNADO.
...MIDWEST TONIGHT...
THE DEVELOPMENT OF A NOCTURNAL LOW-LEVEL WIND MAXIMUM IS
FORECAST...PERHAPS IN RESPONSE TO THE APPROACH OF A WEAK MIDLEVEL
IMPULSE CRESTING THE RIDGE AXIS OVER THE DAKOTAS TODAY. THIS WILL
ENHANCE LOW-LEVEL ASCENT AND MOISTURE ADVECTION BENEATH EML...GIVING
RISE TO WIDELY SCATTERED...ELEVATED TSTMS WITHIN AN ENVIRONMENT
FEATURING MUCAPE OF 1000-1500 J/KG. SOME HAIL IS POSSIBLE WITH
THESE STORMS DUE TO THE STEEP LAPSE RATES AND MODERATELY STRONG
CLOUD-BEARING SHEAR.
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