FXUS62 KTAE 230122
AFDTAE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
815 PM EST TUE DEC 22 2009
...SHOWERS AND STORMS EXPECTED CHRISTMAS EVE INTO CHRISTMAS DAY...
.SYNOPSIS...
AT 8 PM EST...TEMPS RANGED FROM MID 40S N TO UPPER 40S COAST. 24 HR
TEMP/DEW POINT COMPARISON CONTINUES TO INDICATE AN AIRMASS
MODIFICATION WITH WITH TEMPS/DEW POINTS GENERALLY RUNNING 2 (EAST)
TO 6 (WEST) DEGREES WARMER AND WETTER THAN SAME TIME YESTERDAY. THIS
REFLECTED IN TUES AFTN MAX TEMPS...GENERALLY IN MID 60S OR NEAR 10
DEGREES ABOVE MONDAY. WINDS WERE CALM.
AT UPPER LEVELS...
THE LARGE SCALE PATTERN HIGHLIGHTED BY TROUGHS ON BOTH THE ATLANTIC
AND PACIFIC COASTS THAT BOOKEND A RIDGE IN THE NORTHERN PLAINS. A
SERIES OF UPPER LOWS EXTEND FROM THE GREAT LAKES EASTWARD INTO THE
ATLANTIC. LOOKING SOUTH...THERE IS A TROUGH IN THE SOUTHEAST GULF OF
MEXICO THAT DIGS DEEP INTO CENTRAL AMERICA. HIGH CLOUDS AHEAD OF
THIS TROUGH WILL BEGIN TO STREAM NEWD AND OVER LOCAL AREA NEXT 12
HRS.
AT LOWER LEVELS...
MAIN CONUS FEATURE IS A COMPLEX SET OF SURFACE LOWS IN THE GREAT
BASIN ASSOCIATED WITH ABOVE INTENSE SHORT WAVE DIGGING DOWN THROUGH
THE WRN CONUS. PRIMARY LOW OF INTEREST WILL DEVELOP NNE THROUGH ERN
KS INTO THE ARK/LA/TX REGION ON WED IN ADVANCE OF INTENSIFYING
COLD FRONT WHICH WILL BEGIN TO SURGE FROM ERN AZ THIS EVE RAPIDLY
SEWD INTO TX ON WED AND EVENTUALLY REACH LOCAL REGION EARLY FRI.
DOWNSTREAM OF THESE LOWS...AREA IS DOMINATED BY A NORTH-SOUTH RIDGE
OF HIGH PRESSURE SITUATED FROM SOUTH CENTRAL CANADA SOUTHWARD INTO
1023MB OVER SOUTH GEORGIA. THIS REFLECTED IN 00Z REGIONAL OBS I.E.
TAE WITH ONLY 0.30 INCH PWAT. A STATIONARY FRONT WAS SEEN EXTENDING
FROM THE TENNESSEE VALLEY WESTWARD ACROSS OKLAHOMA...AND BACK TO THE
NORTHWEST ALONG THE FRONT RANGE OF THE ROCKIES INTO SOUTHWEST
CANADA. AHEAD OF THIS FRONT...THE SURFACE RIDGE WILL CONT TO SHIFT
EWD WITH VEERING LOW LEVEL FLOW INTO THE EAST ON WEDNESDAY THEN
SOUTHEAST ON THURSDAY WITH GULF RETURN FLOW SHIFTING PROGRESSIVELY
EWD. LOCAL WINDS WILL INCREASE TOMORROW AS THE PRESSURE GRADIENT
BETWEEN THE SE HIGH AND THE NEXT COLD FRONT BEGINS TO IMPACT THE
LOCAL REGION..
NEXT STORM SYSTEM...
THE NEXT WEATHER LOCAL WX MAKER IS FULL LATITUDE PAC UPPER TROUGH
WITH ASSOCD LOW THAT WILL DIG SOUTHWARD...AMPLIFY AND INTENSIFY AS
IT SHIFTS EWD WITH LOW THROUGH GREAT BASIN INTO WED THEN WSW INTO
THE DESERT SW WED EVENING BEFORE LIFTING INTO THE CENTRAL PLAINS
THROUGH THURSDAY NIGHT. MODELS CONTINUE TO ADVERTISES A VORT LOBE
SWINGING EAST...THEN NORTHEAST AROUND THE MAIN UPPER LOW OVER THE
NORTHERN PLAINS. THIS WILL SERVE TO NOTICEABLY AMPLIFY TROUGHS/
RIDGES YIELDING A DIGGING TROUGH OFF THE EAST COAST...MASSIVE RIDGE
ALONG THE EAST COAST...AND THE AFOREMENTIONED TROUGH OVER CONUS
COVERING MUCH OF THE MIDDLE OF THE COUNTRY WITH ERN STEERING FLOW
BECOMING INCREASING SW OVER TIME. THE UPPER LOW APPEARS TO HIT A
WALL ON THURSDAY MORNING AND BEGINS TO MOVE NORTHWARD...BEING
AFFECTED BY THE DOWNSTREAM RIDGE AND A SECOND SHORT WAVE DROPPING
OUT OF CANADA...WHICH THEN BECOMES THE DOMINANT LOW. THIS LOW WILL
TRACK NORTHEAST ACROSS MS VALLEY REGION WITH ASSOCD COLD FRONT
EXPECTED TO TRACK EAST OVER WRN GULF COAST REGION DURING DAY THURS
AND TO NE GULF BY EARLY FRI...WITH SQUALL LINE DEVELOPING ALONG
FRONT. INTERESTINGLY...MODELS ALSO SUGGESTING A WEAK LOW DEVELOPS
ALONG FRONT OVER LA/MS GULF COAST THU EVNG TRACKING TO N GA BY FRI
MRNG BENEATH DIFFLUENT UPR FLOW.
PREFERRED GFS/EURO IS STRONGER AND FASTER THAN THE NAM AND BRINGS
FRONTAL PASSAGE ACROSS EARLY FRIDAY MORNING AS OPPOSED TO NAM FRIDAY
AFTERNOON. AS FAR AS SEVERE WX POTENTIAL...IT LOOKS LIKE OUR TYPICAL
CONVECTIVE SCENARIO...WEAK INSTABILITY AND DECENT SHEAR WITH A NICE
COUPLED JET STRUCTURE WITH DIFFLUENCE ALOFT AND NEGATIVE TILT.
MODELS SUGGEST ENOUGH MARINE MODIFICATION AHEAD OF SYSTEM TO ALLOW
AT LEAST MID 60S DEWPTS TO ADVECT INTO N FL PNHDL. SO A MARGINAL
SEVERE WEATHER THREAT COULD EXIST...MOSTLY FOR OUR WRN COUNTIES...
DURING THE NIGHT SHOULD STRONGER CONVECTION MOVE INLAND FROM NE GULF
OF MEX. SPS CONTS TO KEEP SLGT RISK TO OUR WEST.
&&
.SHORT TERM (REST OF TONIGHT INTO WEDNESDAY)...
AS LOCAL SURFACE HIGH MOVES TOWARDS ATLC COAST...PREDAWN MIN TEMPS
WILL MODERATE FROM W-E COMPARED TO EARLY THIS MORNING. EXPECT INLAND
LOWS FROM 35-40 WEST OF APALACHICOLA RIVER TO AROUND 35 EAST OF THIS
RIVER. PATCHY FROST REMAINS POSSIBLE MAINLY ERN MOST INLAND COUNTIES
OF BIG BEND AND GA.
&&
.AVIATION...VFR CONDITIONS WILL CONTINUE ACROSS THE TRI-STATE AREA
THROUGH THE FORECAST PERIOD AND BEYOND. THE EXCEPTIONS WILL BE
AREAS OF MVFR VISIBILITY...PRIMARILY OVER PORTIONS OF SOUTH CENTRAL
GEORGIA AND THE FLORIDA BIG BEND FOR A FEW HOURS BEFORE SUNRISE. LOW
LEVEL MOISTURE WILL SLOWLY INCREASE AS HIGH PRESSURE MOVES EAST OF
THE AREA AND WINDS VEER TO THE SOUTHEAST. MVFR CONDITIONS WILL
BECOME MORE WIDESPREAD EACH NIGHT. LOOKING AHEAD...RAIN AND ISOLATED
THUNDERSTORMS WILL SPREAD MVFR AND IFR CONDITIONS EASTWARD ACROSS
THE AREA ON THURSDAY...AHEAD OF AN APPROACHING COLD FRONT.
&&
.MARINE...HIGH PRESSURE CENTERED NORTH OF THE COASTAL WATERS...WHICH
WILL BEGIN TO MOVE NORTHEAST OVER THE NEXT 18 HOURS. CURRENT
OBSERVATIONS AT THE BUOYS SHOW EAST WINDS IN THE 10 TO 14-KNOT RANGE
WITH TWO FOOT SEAS. WINDS AND SEAS WILL BEGIN TO STEADILY INCREASE
STARTING OVERNIGHT AS HIGH PRESSURE SHIFTS NORTHEAST AND THE
GRADIENT TIGHTENS WITH LOW PRESSURE DEEPENING OVER THE PLAINS. SMALL
CRAFT ADVISORY CONDITIONS ARE EXPECTED TO REACH THE WATERS WEDNESDAY
NIGHT AHEAD OF THE APPROACHING STORM SYSTEM WITH SEAS APPROACHING 10
FEET OFFSHORE THURSDAY. NORTHWEST FLOW WILL KICK IN BEHIND THE FRONT
ON FRIDAY WITH A GRADUAL DECREASE IN WINDS AND SEAS AS HIGH PRESSURE
BUILDS IN.
&&
.FIRE WEATHER...AS WINDS VEER TO THE SOUTHEAST...LOW LEVEL MOISTURE
WILL BEGIN TO INCREASE. ANOTHER WIDESPREAD RAIN EVENT WILL DEVELOP
ON THURSDAY...AHEAD OF A COLD FRONT THAT WILL SWEEP EASTWARD ACROSS
THE AREA ON CHRISTMAS DAY WITH NO RED FLAG CONCERNS. BEHIND THE
FRONT...ANOTHER SURGE OF COLDER DRIER AIR WILL SPREAD ACROSS THE
AREA...AND CONDITIONS WILL NEED TO BE MONITORED FOR POSSIBLE LONG
DURATIONS OF LOW RELATIVE HUMIDITY THE FIRST OF NEXT WEEK.
&&
.TAE WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
GA...NONE.
FL...NONE.
GM...NONE.
&&
$$
BLOCK
