SWODY1
SPC AC 211957
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0157 PM CST THU JAN 21 2010
VALID 212000Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF NRN FL...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE MID
SOUTH REGION...
...THERE IS A SLGT RISK OF SVR TSTMS OVER COASTAL PORTIONS OF
CENTRAL/SRN CA...
...NRN AND CENTRAL FL...
LARGE/STRONG SUPERCELL -- WHICH PRODUCED ONE OR MORE APPARENT
TORNADOES IN THE PAST 1-2 HOURS -- IS NOW MOVING OFF OF COASTAL ST.
JOHNS CO FL. A TRAILING LINE OF STORMS EXTENDS WWD ACROSS THE NRN
FL PENINSULA...AND WHILE SURFACE FLOW HAS VEERED IN THE WAKE OF THE
PRIOR STORM...SOME SEVERE THREAT REMAINS NEAR AND S OF THE ONGOING
W-E LINE. WHILE THE MAIN THREAT APPEARS TO BE HEAVY RAINFALL...WILL
MAINTAIN A SLIGHT RISK ACROSS THIS REGION.
...MID SOUTH...
CONVECTION HAS BEEN SLOW TO ORGANIZE ACROSS THE MID SOUTH REGION
THIS AFTERNOON...WHERE MODEST INSTABILITY HAS DEVELOPED INVOF THE
UPPER LOW NOW CROSSING WRN TN/WRN KY. WHILE LOW-LEVEL FLOW HAS
VEERED TO SWLY ACROSS MUCH OF THE AREA...AMPLE SHEAR PERSISTS TO
SUPPORT SOME SEVERE POTENTIAL. WHILE PRIMARY THREAT APPEARS TO BE
TRENDING TOWARD HAIL/WIND...AN ISOLATED TORNADO OR TWO REMAIN
POSSIBLE BEFORE STORMS DIMINISH THIS EVENING.
...COASTAL PORTIONS OF THE SRN HALF OF CA...
WEAK INSTABILITY IS INDICATED BY MODEL/OBJECTIVE ANALYSIS OUTPUT
ACROSS THE SRN HALF OF CA ATTM...AND FURTHER IMPLIED BY A LACK OF
LIGHTNING WITH THE ONGOING SHALLOW CONVECTION.
HOWEVER...STRONG FLOW ALOFT WILL LIKELY SUPPORT STRONG
CONVECTIVELY-ENHANCED WIND GUSTS AT THE SURFACE...WITH ANY
LOOSELY-ORGANIZED LINE OF LOW-TOPPED CONVECTION. THUS...WILL
MAINTAIN SLIGHT RISK ACROSS THIS REGION.
...PARTS OF SRN AZ...
WILL MAINTAIN LOW SEVERE PROBABILITY ACROSS THIS REGION...AS A
NARROW/FORCED LINE OF CONVECTION REMAINS A POSSIBILITY OVERNIGHT
AHEAD OF A SMALL-SCALE UPPER FEATURE MOVING OUT OF THE ERN
PAC/ACROSS SRN CA. STRONG FLOW ALOFT SUGGESTS THE POTENTIAL FOR AN
ISOLATED DAMAGING WIND EVENT OR TWO...BUT GIVEN THE FORECAST FOR
MEAGER INSTABILITY...WILL NOT UPGRADE TO SLIGHT RISK THIS FORECAST.
..GOSS.. 01/21/2010
.PREV DISCUSSION... /ISSUED 1017 AM CST THU JAN 21 2010/
...NRN FL/SRN GA/FAR SRN SC...
MCS CONSISTING OF EMBEDDED SUPERCELLS AND SMALL LINES WILL LIKELY
CONTINUE EWD ACROSS NRN FL TODAY...BEING FED BY MODEST INSTABILITY
OFF THE NERN GOM AND WITH SLY LOW LEVEL FLOW ACROSS CENTRAL FL.
APPEARS E-W ORIENTED WARM FRONT WILL BECOME ESTABLISHED THIS
AFTERNOON...POSSIBLY AS FAR NORTH AS THE NERN FL/SERN GA BORDER...
ALLOWING MID 60F SURFACE DEW POINTS TO PUSH NWD BEHIND THIS
BOUNDARY. LOW LEVEL SHEAR WILL LIKELY BE ENHANCED ALONG THE
FRONT...WITHIN VERY STRONG MID/UPPER LEVEL WLY FLOW...SUPPORTING
BOTH A RISK OF DAMAGING WINDS AND ISOLATED TORNADOES WITH POTENTIAL
FOR A BOW ECHO TO EVOLVE AND PROGRESS RAPIDLY EWD ALONG THE
BOUNDARY. NORTH OF THE FRONT...SEVERE THREAT WILL BE MORE
PROBLEMATIC WITH EXTENSIVE RAIN REINFORCING COOLER...MORE STABLE
BOUNDARY LAYER AIR. HOWEVER...IF PRESSURE FALLS AND INCREASING
SSWLY LOW LEVEL FLOW ALLOW SURFACE WARM FRONT TO LIFT INTO SERN
GA/FAR SRN SC THEN ATTENDANT SEVERE THREAT WILL ALSO SHIFT INTO THIS
REGION LATER TODAY.
...MID SOUTH ACROSS THE TN VALLEY INTO SRN/CENTRAL APPALACHIANS...
POTENT LOW AND MID LEVEL LOW PRESSURE OVER CENTRAL/NERN AR THIS
MORNING WILL PROGRESS EWD ACROSS THE TN VALLEY THROUGH THE DAY.
ATTENDANT 70-90 KT WLY MID LEVEL JET WILL LIKEWISE SHIFT ACROSS NRN
MS/AL WITH ENHANCED ASCENT AND PRONOUNCED SHEAR OVERSPREADING THIS
REGION. LOW LEVEL DESTABILIZATION WILL LIKELY REMAIN TEMPERED BY
LOWER TO MID 50S F SURFACE DEW POINTS IN PLACE...ESPECIALLY GIVEN
CONVECTIVELY MODIFIED BOUNDARY LAYER ACROSS MUCH OF AL/GA IN WAKE OF
OVERNIGHT STORMS. HOWEVER...AXIS OF NEAR 60F DEW POINTS SHOULD
BEGIN TO NOSE ACROSS NRN MS AND INTO THE LOWER TN RIVER VALLEY
REGION AS SURFACE WINDS VEER TO A MORE SWLY DIRECTION OVER THE LOWER
MS RIVER VALLEY. COMBINED WITH STEEPENING LOW LEVEL LAPSE RATES
FROM DIURNAL HEATING...EXPECT AXIS OF MODEST INSTABILITY AND
STEEPENING LOW LEVEL LAPSE RATES WILL DEVELOP AHEAD OF THE LOW
CENTER. SURFACE-BASED STORMS IN THE FORM OF LOW-TOPPED
SUPERCELLS/SMALL BOW ECHOES SHOULD EVOLVE DURING THE EARLY AFTERNOON
ACROSS THE MID SOUTH AND SPREAD GENERALLY EWD THROUGH THE DAY. SRN
EXTENT OF THE GREATER RISK AREA SHOULD BE MODULATED BY DEEPER
SUBSIDENCE AND VEERING LOW LEVEL WINDS ACROSS CENTRAL MS/AL...WITH
NRN EXTENT POSSIBLY SHIFTING INTO FAR SRN KY AS DESTABILIZATION
OCCURS OVER TN. THREAT SHOULD GRADUALLY DIMINISH WITH LOSS OF SFC
HEATING TOWARDS THE SRN/CENTRAL APPALACHIANS THIS EVENING.
...SRN CA...
ANOTHER ACTIVE DAY OVER THE REGION WITH NEXT STRONG IMPULSE AND
ASSOCIATED LOW-TOPPED CONVECTION SPREADING ACROSS THE SRN CA COAST
THROUGH THE DAY. FORECAST SOUNDINGS MAINTAIN WEAK SURFACE-BASED
INSTABILITY AND POTENTIAL FOR LOW-TOPPED SMALL
LINES/SUPERCELLS...ESPECIALLY WITH MODEST DIURNAL WARMING ALONG THE
COAST. ALONG WITH HAIL AND ISOLATED DAMAGING WINDS AND POSSIBLY
WATERSPOUTS/BRIEF TORNADOES SHOULD ACCOMPANY THE STRONGER STORMS.
...SRN/CENTRAL AZ...
WITH APPROACHING STRONG MID/UPPER LEVEL SYSTEM NOW OFF THE SRN CA
COAST PROGRESSING EWD ACROSS THE LOWER CO RIVER VALLEY
OVERNIGHT...ENHANCED DEEP ASCENT WILL COLLOCATE ALONG A SURFACE COOL
FRONT SHIFTING QUICKLY EWD ACROSS AZ. WIND FIELDS REMAIN QUITE
STRONG WITH ENHANCED LOW AND DEEP LAYER SHEAR. ATTM...FORECAST
SOUNDINGS SUGGEST INSTABILITY WILL BE QUITE WEAK WITH NEAR
MOIST-ADIABATIC LAPSE RATES AHEAD OF THE FRONT. HOWEVER...IT IS NOT
OUT OF THE QUESTION FOR A NARROW LINE OF FORCED CONVECTION TO EVOLVE
AND INCREASE THE RISK OF ISOLATED STRONG/DAMAGING WINDS LATE TONIGHT
INTO PARTS OF CENTRAL/SRN AZ. ATTM...WILL OPT TO MAINTAIN LOW
SEVERE PROBABILITIES BUT AREA MAY NEED SLGT RISK IN LATER OUTLOOKS.
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