AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
627 AM CDT WED MAY 22 2013
.UPDATE...
FOR 12Z TAFS
&&
.SYNOPSIS...
/ISSUED 254 AM CDT WED MAY 22 2013/
WEAKENING 'OUTFLOW-DRIVEN' SQUALL LINE AFFECTING NW ALABAMA WILL
CONTINUE TO MOVE SLOWLY EAST ACROSS THE AREA THIS MORNING. SHEAR
VECTORS ARE PARALLEL TO THE STORM/LINE MOVEMENT...MINIMIZING "BOWING"
AND POTENTIAL FOR DAMAGING WINDS. KMSL REPORTED WIND GUST TO 28 KTS
/32 MPH/ AS LINE MOVED THROUGH. SHORT RANGE/HI-RES MODELS DID NOT
HANDLE THIS SITUATION WELL AT ALL...BUT HRRR/RAP ARE CATCHING UP TO
CURRENT TRENDS AND APPEAR TO BE IN BETTER LINE NOW. LOOKING AHEAD TO
LATER TODAY THROUGH THURSDAY...AM A LITTLE CONCERNED THAT 00Z MODEL
OUTPUT COULD BE SLIGHTLY UNRELIABLE GIVEN POOR INITIALIZATION.
PRIMARY UPR LVL VORTEX IS BEGINNING TO MOVE EAST FROM THE NRN PLAINS
TO THE UPR MIDWEST. SRN STREAM VORT MAX RESPONSIBLE FOR THE ONGOING
CONVECTION ACROSS THE REGION CURRENTLY OVER THE OZARK REGION (SW
MO/NW AR). FOLLOWING PASSAGE OF AFOREMENTIONED CONVECTIVE LINE...
AIRMASS SHOULD STABILIZE FOR A FEW HOURS THIS MORNING BEFORE
ADDITIONAL CONVECTION REDEVELOPS DURING THE DAY. A FEW SHRA ARE
DEVELOPING AHEAD OF THE MAIN CONVECTIVE BAND...ALONG THE COLD
POOL/GUST FRONT. EXPECT THIS TO CONTINUE OVER THE NEXT SEVERAL HOURS.
DJN.83
&&
.DISCUSSION...
/ISSUED 254 AM CDT WED MAY 22 2013/
DRIVING FORCE FOR SHRA/TSRA TODAY WILL BE SRN STREAM S/W ENERGY
THAT WILL CROSS THE AREA THIS AFTN. STILL SOME UNCERTAINTY AS TO
WHERE/WHEN CONVECTION WILL REDEVELOP. LOW LVL MOISTURE CONVG IS
RATHER WEAK BUT 20-30KT LOW LVL SHEAR SHOULD BE ENOUGH TO SUPPORT
ADDITIONAL SHRA/TSRA THIS AFTN WITH UPR LVL ENERGY. TEMPERATURES
TODAY WILL BE SLIGHTLY CHALLENGING DUE TO CURRENT CONVECTION AND
CLOUD COVER. UNDERCUT GUIDANCE A COUPLE DEGREES...ESPECIALLY ACROSS
NW AL WHERE RAIN-COOLED AIR WILL EXIST. LOW/MID LVL FLOW TURNS TO THE
WEST-NORTHWEST TONIGHT AS MORE STABLE CONDITIONS DEVELOP. ASIDE FROM
A COUPLE OF WEAK MID LVL WAVES PASSING THROUGH WHICH COULD RESULT IN
A FEW -SHRA...THERE IS NOT A WHOLE LOT TO FOCUS ON REGARDING
ORGANIZED CONVECTION OVERNIGHT.
THURSDAY...AS MAIN UPR VORTEX CONTINUES TO SLIDE EAST ACROSS THE
GREAT LAKES/OHIO VALLEY REGION...A PUSH OF COOLER/MUCH DRIER AIR
WILL SURGE SOUTH TOWARD THE AREA. ONE FINAL PIECE OF S/W ENERGY WILL
CROSS THE AREA. STEEP LOW TO MID LVL LAPSE RATES COUPLED WITH H85
WINDS OF 20-30KTS COULD GENERATE A FEW SHOWERS/STORMS ALONG THE LOW
LVL BOUNDARY/FRONT. DEPENDING ON HOW MUCH DESTABILIZATION OCCURS IN
"WARM SECTOR"...THERE WILL BE THE POTENTIAL FOR HAIL WITH STORMS.
MOISTURE IS SOMEWHAT LIMITED SO WILL JUST MAINTAIN A 20 POP ATTM.
MUCH DRIER/COOLER AIR WILL SETTLE IN ACROSS THE REGION THURSDAY
NIGHT AND FRIDAY. MIN TEMPS EXPECTED TO REACH THE MID 50S BY
DAYBREAK FRIDAY WITH DAYTIME TEMPS STRUGGLING TO REACH THE MID 70S
WITHIN PRONOUNCED CAA PATTERN /ABOUT 5-10F DEG BELOW NORMAL/. GUSTY
N/NW WINDS 10-20 MPH CAN BE EXPECTED WITH HIGHER GUSTS OVER
RIDGETOPS.
LONG TERM /SATURDAY THROUGH TUESDAY/...
MEDIUM RANGE MODELS CONTINUE TO DISAGREE OVER WEATHER PATTERN LATE
THIS WEEKEND /SUNDAY/ THROUGH EARLY NEXT WEEK /TUESDAY/. SANDWICHED
BETWEEN AN UPR VORTEX OVER NOVA SCOTIA AND AN UPR LVL RIDGE OVER THE
CENTRAL CONUS...A FAIRLY PRONOUNCED NW FLOW ALOFT WILL EXIST ACROSS
THE TN VALLEY SAT- MON. A WARM FRONT WILL LIFT BACK NORTH SUNDAY INTO
MONDAY. THE DIFFERENCES OCCUR IN WHERE THIS FRONT SETS UP -- THE
ECMWF SHOWS IT DRAPED CLOSE TO/OVERTOP THE AREA WHILE THE GFS SETS IT
UP FARTHER NORTH. THE PRECIP CHANCES WILL EXIST FROM SEVERAL UPR LVL
WAVES EMBEDDED IN THE NW FLOW...RIDING ALONG THIS FRONTAL BOUNDARY.
IF THE ECMWF IS CORRECT...WE COULD SEE AN INCREASED CHANCE OF -SHRA
/ESPECIALLY SRN MIDDLE TN/ SUNDAY AND MONDAY. FOR THE SECOND DAY IN A
ROW...THE EC IS SHOWING THIS SOLN...SO AM GOING TO INTRODUCE JUST A
'SLIGHT CHANCE' POPS /-SHRA/ FOR SUNDAY NIGHT THROUGH MONDAY NIGHT
ACROSS THE AREA.
TEMPERATURES WILL GRADUALLY WARM BACK UP INTO THE MID 80S BY EARLY
NEXT WEEK. MORNING LOWS WILL START COOL EARLY THIS PERIOD...BUT WARM
BACK TO SEASONAL LEVELS BY MON/TUES.
DJN.83
&&
.AVIATION...
FOR 12Z TAFS...
UNSETTLED WEATHER IS EXPECTED ACROSS THE TERMINALS INTO THE EARLY
EVENING. CONVECTION IS FORECAST TO REFORM DURING THE LATE MORNING/
EARLY AFTERNOON AND MOVE WEST-EAST. SHORT TERM CIG/VIS REDUCTIONS
TO MVFR ARE POSSIBLE DURING THE HEAVIER SHOWERS...ALONG WITH GUSTY
WINDS. SHOWER ACTIVITY SHOULD WIND DOWN IN THE EVENING...AS THE
STRONGEST UPPER SUPPORT MOVES EAST OF THE REGION. DEPENDING UPON
HOW MUCH RAINFALL OCCURS...VIS/CIG REDUCTIONS CANNOT BE RULED OUT
IF FOG/MIST FORMS LATE IN THE TAF PERIOD.
RSB
&&
.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&
$$
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