FXUS62 KRAH 022002
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
305 PM EST WED DEC 02 2009
.SYNOPSIS...
A STRONG LOW PRESSURE SYSTEM OVER THE LOWER MISSISSIPPI VALLEY WILL
LIFT RAPIDLY NORTHEAST TONIGHT. THE LOW PRESSURE SYSTEM WILL LIFT
THROUGH SOUTHERN ONTARIO AND SOUTHERN QUEBEC THURSDAY. HIGH PRESSURE
WILL BUILD INTO THE REGION ON FRIDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS OF 255 PM WEDNESDAY...
STRONG LOW PRESSURE COMPLEX OVER THE LOWER MS VALLEY BEGINNING TO
LIFT NE. A MESO-LOW(POSSIBLY AS RESULT OF OVERNIGHT/EARLY CONVECTION
ALONG THE GULF COAST) LOCATED OVER CENTRAL GA AT 19Z. THIS FEATURE
WILL LIKELY TRACK E-NE ALONG NWD MOVING SURFACE WARM FRONT AND
SHOULD REMAIN JUST SOUTH OF OUR FORECAST AREA.
IN OUR REGION...WEDGE FRONT APPEARS TO HAVE ADVANCE WEST PAST GSO
WHERE SE WINDS NOW REPORTED. STILL QUESTIONABLE HOW FAR WEST THIS
FEATURE WILL MOVE. AS UPPER LEVEL LOW LIFTS INTO THE TN VALLEY THIS
EVENING...LOW LEVEL JET WILL STRENGTHEN TO AROUND 60KTS. IN
ADDITION...STRONG UPPER DIVERGENCE WILL PERSIST OVER THE REGION.
NEAR SURFACE FLOW WILL REMAIN E-SE IN THE VICINITY OF THE WEDGE
FRONT. SINCE LOW LEVEL CONFLUENCE COUPLED WITH UPPER DIVERGENCE WILL
PERSIST OVER THE WESTERN PIEDMONT AND RADAR TRENDS DEPICT PRECIP
INTENSITY INCREASING TO OUR SW...WILL LEAVE FLASH FLOOD WATCH IN
EFFECT. MODEL GUIDANCE SUGGEST BACK EDGE OF PRECIP CROSSING THE
WESTERN PIEDMONT BETWEEN 00-03Z. THUS WATCH MAY BE CANCELED BEFORE
IT EXPIRES. WHILE RAINFALL AMOUNTS THUS FAR HAVE BEEN FAIRLY
LIGHT...MAY SEE HOURLY RAINFALL RATES ON THE ORDER OF A HALF INCH
BETWEEN 22-02Z OVER THE PIEDMONT.
STILL A CONCERN FOR SEVERE WEATHER THIS EVENING...ESPECIALLY AREAS
ALONG AND EAST OF I-95. WHILE THIS AREA STILL RELATIVELY STABLE AT
THE SURFACE...SLIGHT TO MODERATE INSTABILITY NOTED JUST S-SE OF THIS
REGION. AS LOW LEVEL SLY FLOW INCREASED TONIGHT...EXPECT NEAR
SURFACE INSTABILITY TO INCREASE. LATEST NAM DEPICTS AXIS OF MUCAPE
1200-1400J/KG OVER THE FAR SE COUNTIES AT 00Z SURGING NWD AFTERWARDS
WITH MUCH OF THE COASTAL PLAIN AROUND 1000 J/KG THIS EVENING. MLCAPE
PROJECTED TO BE AROUND 700 J/KG. CONSIDERING THE KINEMATICS (SR
HELICITY 400-650 M2/S2)...THERE MAY BE ENOUGH SURFACE BASED
INSTABILITY TO CAUSE DAMAGING WINDS TO REACH THE SURFACE WITH ANY
HEAVY SHOWERS OR THUNDERSTORMS THAT OCCUR. NAM BUFR SOUNDINGS DO
DEPICT A THIN STABLE LAYER JUST ABOVE THE SURFACE OVER THE COASTAL
PLAIN THROUGH 02Z. AFTER 06Z...MID LEVEL TROUGH CROSSES THE REGION
DRYING OUT THE MID/UPPER LAYERS. THUS PRECIP CHANCES SHOULD
DECREASE IN THE COASTAL PLAIN AFTER 06Z.
THUS APPEARS THAT SEVERE WEATHER THREAT WILL INCREASE IN AREAS ALONG
AND EAST OF HIGHWAY 1 AFTER 01Z-02Z...DECREASING AFTER 06Z. WILL
DEPICT A POP TREND DECREASING FROM WEST-TO-EAST BETWEEN 01Z-08Z.
INCREASING SLY FLOW THIS EVENING WILL CAUSE TEMPS TO WARM WITH
MID/UPPER 60S POSSIBLE IN THE SE...AND APPROACHING UPPER 50S/AROUND
60 IN THE NW. TEMPS WILL GRADUAL COOL IN THE WEST AFTER
MIDNIGHT...AND TOWARD DAYBREAK IN THE COASTAL PLAIN.
FINALLY...EXPECTING SURFACE WIND GUSTS AROUND 30 MPH THIS EVENING.
IF STABLE AIR ERODES MORE QUICKLY...MAY SEE GUSTS UP TO 40 MPH. WAS
CONSIDERING A WIND ADVISORY BUT WITH CONVECTION EXPECTED...MAY BE
ABLE TO HANDLE WITH SPS OR NEAR TERM WARNINGS.
&&
.SHORT TERM /THURSDAY THROUGH FRIDAY/...
AS OF 155 PM WEDNESDAY...
THE COLD FRONT PUSHES THROUGH AROUND MID DAY ON THURSDAY...WITH
INITIAL SOUTHWEST FLOW IN THE MORNING VEERING TO WESTERLY IN THE
AFTERNOON. SKIES WILL BE MOSTLY SUNNY...AND WITH A FAIRLY WARM HEAD
START IN THE MORNING (UPPER 40S TO MID 50S FOR MORNING LOWS) EXPECT
HIGHS TO REACH UPPER 50S TO MID 60S BEFORE COLD AIR ADVECTION GETS
UNDERWAY LATE IN THE DAY. SKIES WILL REMAIN MOSTLY CLEAR OVERNIGHT
AND MINS THURSDAY NIGHT WILL TUMBLE INTO THE 30S AS A COLDER AIRMASS
EDGES ACROSS THE MOUNTAINS IN NORTHWEST FLOW.
BENIGN WEATHER CONTINUES INTO FRIDAY WITH WEAK HIGH PRESSURE DRAPED
ACROSS SOUTHERN NEW ENGLAND. LIGHT NORTHERLY FLOW AT THE SURFACE
WILL HINDER THE WARMUP DESPITE PARTLY SUNNY SKIES...HIGHS ARE
EXPECTED TO STALL IN THE LOW AND MID 50S.
&&
.LONG TERM/FRIDAY NIGHT THROUGH WEDNESDAY/...
AS OF 300 PM WEDNESDAY...
THE INITIAL COLD FRONT WHICH MOVED OFFSHORE THURSDAY WILL BE
LINGERING OFF THE EAST COAST...WITH MODEL CONSENSUS ON GRADUAL
CYCLOGENESIS FROM FRIDAY INTO SATURDAY. MOISTURE RETURN OFF THE
ATLANTIC WILL BE UNDERWAY FRIDAY NIGHT IN EAST TO SOUTHEAST LOW
LEVEL FLOW. RAIN WILL BE DEVELOPING IN THIS ENSUING ISENTROPIC
FLOW...WITH CHANCE POPS FOR LIGHT RAIN BY SUNRISE IN THE EAST.
PROXIMITY OF THE FRONT TO THE COAST AS WELL AS THE STRENGTH OF THE
DEVELOPING LOW WILL BE A DETERMINING FACTOR IN THE WESTWARD EXTENT
OF HIGH RAINFALL AMOUNTS...AND WILL RAISE POPS ACROSS THE BOARD TO
CHANCE WEST AND LIKELY IN THE EAST WITH EASTERN RAINFALL AMOUNTS OF
ONE HALF INCH. RAIN WILL BE TAPERING OFF EARLY SATURDAY NIGHT AS THE
SURFACE LOW LIFTS NORTHEAST UP THE FRONT WHILE CONCURRENTLY...A
SHORT WAVE DIGGING SOUTHEAST ACROSS THE OHIO VALLEY NUDGES THE WHOLE
SYSTEM EAST.
THERE IS A CHANCE THAT STRONG COLD AIR ADVECTION BEHIND THIS SYSTEM
MIGHT BE UNDERWAY QUICKLY ENOUGH TO END THE LIGHT RAIN AS A
RAIN/SNOW MIX EARLY SATURDAY NIGHT. CONFIDENCE IN THIS HAPPENING IS
NOT HIGH AND IT WOULD BE OF LITTLE CONSEQUENCE REGARDLESS. WILL
CONTINUE A LIQUID FORECAST AS THE RAIN PULLS OUT OF THE NORTHEAST
CORNER OF THE CWFA BY MIDNIGHT SATURDAY NIGHT AND ALLOW THE SCENARIO
TO CLARIFY ITSELF IN LATER MODEL RUNS. HIGHS SATURDAY WILL BE ONLY
IN THE LOWER 40S NORTHWEST TO MID 40S EAST. GRADIENT WINDS WILL
PROVIDE MIXING AND PREVENT A TEMPERATURE CRASH SATURDAY NIGHT...BUT
MINS WILL SLIP INTO THE UPPER 20S ACROSS MUCH OF THE AREA.
HIGH PRESSURE BUILDING OVERHEAD WILL PROVIDE CLEAR SKIES AND
UNSEASONABLY COOL TEMPERATURES SUNDAY AND MONDAY. HIGHS WILL BE
MOSTLY IN THE 45 TO 50 RANGE...AS COMPARED TO NORMALS IN THE MID
50S. MONDAY MORNINGS LOW WILL BE IN THE UPPER 20S. MOISTURE WILL BE
ON THE INCREASE TUESDAY AS THE HIGH MOVES OFFSHORE...WITH SHOWERS
LOOMING ON THE HORIZON TUESDAY NIGHT AND WEDNESDAY AHEAD OF OUR NEXT
COLD FRONT.
&&
AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
AS OF 1235 PM WEDNESDAY...
WARM MOIST AIR BEING LIFTED OVER A COOL/STABLE SURFACE LAYER
RESULTING IN WIDESPREAD RAIN...AT TIMES MODERATE...OVER A MAJORITY
OF CENTRAL NC AT MID DAY. LOW LEVEL WIND SHEAR STILL OF A CONCERN
OVER THE REGION THROUGH THIS AFTERNOON AS SURFACE WINDS SLOWLY VEER
FROM E-NE TO A SLY DIRECTION WHILE WINDS 1000-2000FT SE AROUND 40
KTS.
PRECIP TYPE WILL GRADUALLY EVOLVE INTO SHOWERS LATER THIS AFTERNOON
AS AIR MASS DESTABILIZES ALOFT WITH APPROACH OF NEGATIVELY TILT MID
LEVEL TROUGH. ISOLATED THUNDERSTORMS WILL BE POSSIBLE IN VICINITY OF
GSB AND FAY. AFTER 00Z...EXPECT A BAND OF SHOWERS AND ISOLATED
THUNDERSTORMS TO DEVELOP AHEAD OF THE LEVEL TROUGH SW OF CENTRAL NC
OVER EASTERN GA/SC. THIS BAND WILL LIFT RAPIDLY NE ACROSS THE REGION
BETWEEN 7 PM AND 2 AM. EXPECT WIDESPREAD IFR/LIFR CEILINGS AHEAD OF
THIS FEATURE IN ASSOCIATION WITH THE SHOWERS.
WITH THE PASSAGE OF THE TROUGH...SURFACE WINDS WILL VEER TO A SE
DIRECTION WITH SPEEDS AROUND 15KTS AND OCCASIONAL GUSTS 25KTS. GUSTS
WILL BECOME MORE LIKELY AFTER SUNRISE. AS THE AIR MASS DRIES OUT
FROM THE SW LATE TONIGHT/EARLY THU...CEILINGS WILL LIFT INTO THE
MVFR RANGE WITH CLOUDS DISSIPATING AROUND SUNRISE.
VFR CONDITIONS WILL RETURN THURSDAY AND PERSIST UNTIL FRIDAY
EVENING. A COLD UPPER LEVEL LOW PRESSURE SYSTEM MAY BRING ANOTHER
ROUND OF MVFR/IFR CEILING BY LATE FRIDAY NIGHT OR SATURDAY WITH A
CHANCE OF PRECIPITATION. VFR CONDITIONS EXPECTED SUNDAY THROUGH
MONDAY.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH FROM WEDNESDAY AFTERNOON THROUGH WEDNESDAY EVENING
FOR NCZ021>023-038-039-073-074-083-084.
&&
$$
SYNOPSIS...WSS
NEAR TERM...WSS
SHORT TERM...MLM
LONG TERM...MLM
AVIATION...WSS
