FXUS62 KRAH 040739
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
240 AM EST THU DEC 03 2009
.SYNOPSIS...
WEAK SURFACE RIDGING WILL EXTEND OVER THE AREA TODAY. A SURFACE LOW
WILL DEVELOP OFF THE CAROLINA COAST TONIGHT...AND WILL QUICKLY TRACK
NORTHEAST UP THE COAST ON SATURDAY AS A STRONG UPPER LEVEL
DISTURBANCE MOVES THROUGH THE REGION SATURDAY EVENING.
&&
.NEAR TERM /THROUGH TODAY/...
AS OF 230 AM FRIDAY...
TODAY...
A BROAD LONGWAVE TROUGH CENTERED OVER THE NATIONS MID-SECTION WILL
ENCOMPASS MUCH OF THE CONUS THROUGH THE WEEKEND. WEAK SHORTWAVE
IMPULSES EMBEDDED IN THE ENERGIZED +140KT SUBTROPICAL JET EXTENDING
OVER THE GULF COAST NE THROUGH THE MID-ATLANTIC REGION WILL BRING
ABUNDANT MID AND HIGH LEVEL MOISTURE OVER THE CAROLINAS TODAY.
THIS MILKY/FILTERED SUNSHINE COMBINED WITH LIGHT
NORTHERLY/NORTHEASTERLY WINDS WILL RESULT IN SEASONABLE HIGH TEMPS
THIS AFTERNOON. HIGHS IN THE LOWER TO MID 50S.
TONIGHT...
A MORE ROBUST VORTMAX(CURRENTLY OVER THE SOUTHERN ROCKIES)ROUNDING
THE BASE OF THE LONG WAVE TROUGH...WILL EJECT EASTWARD ACROSS THE
LOWER MS VALLEY TONIGHT. THE RESULTANT STRONG...80 METER HEIGHT
FALLS WILL STRENGTHEN THE LOW-LEVEL FLOW ACROSS THE SOUTHEAST
..REJUVENATING THE THERMAL GRADIENT ALONG THE OFFSHORE BAROCLINIC
ZONE AND INDUCING CYCLOGENESIS NEAR THE CAROLINA COAST. ISENTROPIC
ASCENT ATOP THE OFFSHORE FRONTAL ZONE WILL OVERSPREAD RAIN INTO
CENTRAL FROM EAST TO WEST LATE FRIDAY NIGHT. MODELS IN GOOD
AGREEMENT OF CATEGORICAL POPS OVER THE COASTAL SECTIONS BY
DAYBREAK...TO GOOD CHANCE OVER THE WESTERN PIEDMONT. LOWS IN THE IN
THE UPPER 30 NW TO MID 40S SOUTHEAST.
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
AS OF 230 AM FRIDAY...
SATURDAY AND SUNDAY NIGHT...
MODELS HAVE REALLY ACCELERATED THE TIMING OF BOTH THE COASTAL
LOW AND THE UPPER WAVE PASSAGE THE PAST COUPLE OF MODEL
RUNS...WITH THE NAM THE ONLY MODEL KEEPING PRECIP ACROSS THE AREA
AFTER 00Z SUNDAY. IN FACT THE GFS...GEM AND THE EC NOW HAVE THE
SURFACE LOW APPROXIMATELY 500 MILES EAST OF THE DELAWARE/MARYLAND
SHORE...WITH THE UPPER WAVE CLOSE BY. IN SHORT...THE FASTER TIMING
RESULTS IN LESS TIME FOR TEMPERATURES TO REACH VALUES THAT FAVOR
DENDRITIC GROWTH. THUS DON'T EXPECT MORE THAN A FEW FLAKES ACROSS
THE NORTHERN TIER BEFORE PRECIP COMPLETELY SHUTS DOWN...MAKING THIS
A NONE EVENT.
HAVE ADJUSTED GRIDS/FORECAST TO REFLECT THIS FASTER TIMING...
SO AFTER CATEGORICAL RAIN THROUGH EARLY SATURDAY AFTERNOON...POPS
WILL QUICKLY TAPER OFF FROM SW TO NE ACROSS THE AREA...ENDING ACROSS
THE ENTIRE AREA AOA 06Z SUNDAY...IF NOT SOONER. RAINFALL AMOUNTS
WILL AVERAGE FROM A QUARTER ACROSS THE WEST TO AS MUCH AS
THREE-QUARTERS ACROSS THE NE.
WITH WIDESPREAD RAIN SET IN AT THE START OF THE DAY ON
SATURDAY...DIURNAL TEMP TREND WILL BE ONLY A FEW DEGREES FROM
MORNING LOWS. AFTERNOON HIGHS NEAR 40 NW TO MID/UPPER 40S SE. STRONG
LOW-LEVEL COLD AIR ADVECTION AND CLEARING SKIES WILL OVERSPREAD THE
AREA AFTER MIDNIGHT. LOWS IN THE MID 20S NW TO AROUND 30 SE. -CBL
SUNDAY AND SUNDAY NIGHT:
A COOL DRY SURFACE HIGH IS EXPECTED TO SETTLE ACROSS CENTRAL NORTH
CAROLINA ON SUNDAY... WITH A WEST-SOUTHWESTERLY FLOW ALOFT. THIS
WILL ALLOW FOR MOSTLY SUNNY SKIES AND LIGHT WINDS. AFTERNOON LOW
LEVEL THICKNESS VALUES ARE EXPECTED TO GENERALLY RANGE FROM 1310 TO
1320 METERS... ROUGHLY 10 TO 15 METERS BELOW NORMAL. THUS... EXPECT
HIGH TEMPS... EVEN WITH MOSTLY SUNNY SKIES... TO BE IN THE UPPER 40S
TO LOWER 50S.
THE SURFACE HIGH IS EXPECT TO SHIFT OFFSHORE ON SUNDAY NIGHT/MONDAY
MORNING... AS A WEAK COLD FRONT ASSOCIATED WITH A NORTHERN STREAM
TROUGH APPROACHES THE AREA. THIS SHOULD HELP TO INCREASE MOISTURE
ACROSS THE REGION A BIT ALLOWING SKIES TO BECOME PARTLY CLOUDY...
WHICH SHOULD HELP KEEP LOW TEMPS FROM FALLING OFF A CLIFF. THUS...
WITH SKIES BECOMING PARTLY CLOUDY... AND LOW LEVEL THICKNESS VALUES
INCREASING SOME 10 TO 15 METERS OVERNIGHT... EXPECT LOW TO ONLY DROP
INTO THE UPPER 20S ACROSS THE NORTH TO THE LOWER TO MID 30S ACROSS
THE SOUTH. -BSD
&&
.LONG TERM /MONDAY THROUGH THURSDAY/...
AS OF 250 PM THURSDAY...
LATEST GFS HAS COME AROUND TO A SOLUTION SIMILAR TO THE 00Z ECMWF
THROUGH MOST OF THIS PERIOD.
MONDAY...MODIFIED CANADIAN HIGH DRIFTS EAST IN ZONAL FLOW ALOFT. S/W
IN THE NORTHERN STREAM IN THE VICINITY OF THE GREAT LAKES WILL
ADVANCE INTO NEW ENGLAND...LIKELY DRAGGING A SURFACE COLD FRONT
ACROSS REGION LATE MONDAY/MONDAY NIGHT. CONSIDERING WLY FLOW AHEAD
OF THIS FEATURE AND NARROW WINDOW AVAILABLE FOR LOW LEVEL MOISTURE
TRANSPORT...NOT EXPECTING MUCH/IF ANY PRECIP WITH THIS FEATURE.
MONDAY NIGHT/TUESDAY...COOLER DRIER AIR WILL ADVECT INTO REGION IN
WAKE OF THE FRONT. CONSIDERING THAT THERE IS THE POTENTIAL FOR
MODIFIED ARCTIC AIR IN THIS AIR MASS...DEWPOINTS TUESDAY MAY BE MUCH
DRIER THAN CURRENTLY FORECAST. THIS MAY HAVE SOME IMPACTS INTO THE
TEMP FORECAST FOR TUESDAY NIGHT INTO WED.
TUESDAY NIGHT THROUGH WEDNESDAY NIGHT...WELL DEFINED S/W IN THE
NORTHERN STREAM MOVES INTO THE CENTRAL U.S. TUESDAY NIGHT AND
ADVANCES EAST INTO THE OH VALLEY WEDNESDAY. SURFACE LOW ASSOCIATED
WITH THIS SYSTEM TRACKS FROM THE SOUTHERN PLAINS TUESDAY NIGHT INTO
THE LOWER OH VALLEY WEDNESDAY MORNING. DEVELOPING LOW LEVEL JET MAY
PULL WARM MOST AIR OVER THE COOL STABLE LAYER DEPOSITED BY DEPARTING
HIGH PRESSURE SYSTEM. THIS MAY SET-UP A HYBRID DAMMING EVENT FOR
TUESDAY NIGHT INTO WEDNESDAY. ON WEDNESDAY...BOTH ECMWF AND GFS
SUGGESTING POTENTIAL FOR A MILLER "B" EVENT WITH A SECONDARY LOW
DEVELOPING ALONG THE WEDGE FRONT ASSOCIATED WITH THE CAD OVER THE
CAROLINAS. THIS LOW MOVES NE...DEEPENING AS IT DOES. MODEL WINDS
SURFACE THROUGH 850MB SUGGEST DECENT LOW LEVEL TURNING WITH A LOW
LEVEL JET 45-50KTS (GFS MUCH STRONGER AT 65-70KT). THIS SET-UP MAY
SUPPORT ISOLATED STRONG CONVECTION. PLENTY OF TIME TO ASSESS
SCENARIO. OTHERWISE WILL MAINTAIN CHANCE POPS FOR NOW DUE TO TIMING
ISSUES. IF LATER MODEL RUNS CONSISTENT...AN INCREASE IN POPS
WARRANTED. WILL HAVE COOLER THAN NORMAL TEMPS WED DUE TO POTENTIAL
CAD EVENT.
HIGH PRESSURE SHOULD BUILD INTO REGION BEHIND EXITING SYSTEM THU
WITH DRY AND COOLER THAN NORMAL CONDITIONS ANTICIPATED.
&&
.AVIATION /06Z FRIDAY THROUGH MONDAY/...
AS OF 1230 AM FRIDAY...
WEAK SFC RIDGING WILL EXTEND INTO THE AREA FROM THE WEST TODAY.
VFR CONDITIONS ARE EXPECTED THROUGH THE AFTERNOON AS DRIER AIR
ASSOCIATED WITH SFC RIDGE CONTINUES TO FILTER INTO THE AREA. SURFACE
WINDS WILL REMAIN LIGHT VEERING TO NORTHERLY THIS MORNING...AND THEN
NORTHEASTERLY DURING THE DAY.
A SFC LOW IS THEN EXPECTED TO DEVELOP OFF THE CAROLINA COAST
TONIGHT...OVERSPREADING RAIN AND IFR TO MVFR CEILINGS FROM EAST TO
WEST ACROSS CENTRAL NC AFTER MIDNIGHT.
RAIN WILL CONTINUE THROUGH THE DAY ON SATURDAY WITH WIDESPREAD
LIFR TO IFR CEILINGS ACROSS THE AREA. THE RAIN COULD BRIEFLY
CHANGEOVER TO SNOW BEFORE ENDING LATE SATURDAY AFTERNOON/EARLY
SATURDAY EVENING. VFR CONDITIONS UNDER CLEAR SKIES ARE EXPECTED
BY PREDAWN HOURS SUNDAY AS HIGH PRESSURE BUILDS INTO THE AREA
FROM THE WEST.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...CBL
NEAR TERM...CBL
SHORT TERM...CBL/BSD
LONG TERM...WSS
AVIATION...CBL
