FXUS62 KRAH 041808 CCA
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
108 PM EST FRI DEC 04 2009
.SYNOPSIS...
WEAK SURFACE RIDGING WILL EXTEND OVER THE AREA THIS AFTERNOON.
BENEATH A VERY ENERGETIC SOUTHWEST FLOW ALOFT... LOW PRESSURE WILL
CONSOLIDATE FROM THE NORTHERN GULF OF MEXICO TO OFFSHORE THE COAST
OF THE CAROLINAS TONIGHT. THE STORM SYSTEM WILL INTENSIFY AND TRACK
QUICKLY NORTHEASTWARD OFFSHORE THE MID ATLANTIC COAST SATURDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS OF 1025 AM FRIDAY...
LITTLE CHANGE TO FORECAST THROUGH THE REST OF TODAY... THOUGH RECENT
SATELLITE AND SIMULATED HIGH/MID LEVEL MOISTURE TRENDS SUGGEST WE
MAY SEE A LITTLE MORE SUNSHINE (ESPECIALLY SOUTHEAST OF THE
TRIANGLE). CURRENT RADAR RETURNS OVER EASTERN GA ARE ASSOCIATED WITH
A MID CLOUD DECK... AND ACCORDINGLY HAVE LITTLE PROBABILITY OF
PRODUCING ANY LIGHT RAIN FOR US THIS AFTERNOON. EXPECT HIGH
TEMPERATURES TO RANGE FROM THE LOWER 50S WITH THICKER AND ALREADY
PRESENT MID/HIGH CLOUDS... TO NEAR 60 DEGREES OVER THE EASTERN
SANDHILLS AND COASTAL PLAIN.
WHILE THE 12Z NAM CONTINUES TO SUPPORT OUR FORECAST RATIONALE AND
THE PREVIOUS FORECAST TIMING OF PRECIPITATION AND RESULTANT ONLY
BRIEF CHANGEOVER/MIX WITH SNOW SATURDAY AFTERNOON/EVENING... THE
DYNAMICS OF THE PATTERN ALOFT ARE OF SOME CAUSE FOR CONCERN.
IT IS SNOWING OVER A GOOD PORTION CENTRAL AND PARTS OF SOUTHERN
TX... AFTER ALL. IN FACT... IT IS THAT AREA OF RAPIDLY EVOLVING
PRECIPITATION (DRIVEN PRIMARILY BY MID LEVEL DEFORMATION/
FRONTOGENESIS) THAT WILL BE THE CULPRIT FOR ANY FLAKES HERE IN
CENTRAL NC. MORE ON THE TONIGHT-SATURDAY NIGHT WETNESS (AND POSSIBLE
BRIEF SNOW) WITH THE AFTERNOON PACKAGE. -MWS
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 310 AM FRIDAY...
MEDIUM RANGE MODELS ARE IN FAIRLY GOOD AGREEMENT WITH THE OVERALL
PATTERN DURING THE EXTENDED PORTION OF THE FORECAST... WITH ANOTHER
GOOD CHANCE FOR RAIN/SHOWERS LATE IN THE PERIOD.
MONDAY AND MONDAY NIGHT:
A NORTHERN STREAM S/W TROUGH IS EXPECT TO QUICKLY TRACK
NORTHEASTWARD OUT OF THE MIDWEST AND INTO THE GREAT LAKES REGION AND
INTO NEW ENGLAND... WHILE DAMPENING OUT... AS IT DOES A WEAK AND
GENERALLY DRY COLD FRONT WILL CROSS CENTRAL NORTH CAROLINA ON MONDAY
AFTERNOON/EVENING. WILL MAINTAIN A DRY FORECAST WITH THE FRONTAL
PASSAGE... AS LOW LEVEL MOISTURE TRANSPORT DOES NOT LOOK IMPRESSIVE
AND MID LEVEL FLOW GENERALLY REMAINS WSW'ERLY. LOW LEVEL THICKNESS
VALUES INCREASE ON MONDAY INTO THE 1330S AND 1340S. HOWEVER... WITH
AN INCREASE IN CLOUD COVER... EXPECT TEMPS TO GENERALLY RANGE FROM
AROUND 50 IN THE NORTHWEST TO THE LOWER TO MID 50S IN THE SOUTHEAST.
WITH SKIES REMAINING PARTLY CLOUDY ON MONDAY NIGHT... OVERNIGHT LOWS
ON LOOK TO RANGE FROM THE LOWER TO MID 30S IN THE NORTHWEST TO UPPER
30S IN THE SOUTHEAST.
TUESDAY THROUGH WEDNESDAY NIGHT:
SURFACE HIGH PRESSURE IS EXPECT TO EXTEND INTO THE AREA FROM THE
NORTH ON TUESDAY AND INTO TUESDAY NIGHT. MEANWHILE A POTENT UPPER
LEVEL SHORTWAVE AND ATTENDANT SURFACE LOW ARE EXPECT TO LIFT
NORTHEASTWARD OUT OF THE FOUR CORNERS REGION AND INTO THE PLAINS
STATES AND UPPER MIDWEST/GREAT LAKES REGION BY 12Z WEDNESDAY. THIS
WILL ALLOW MID AND HIGH LEVEL MOISTURE TO INCREASE ACROSS OUR AREA
ON TUESDAY. LOW LEVEL SOUTHERLY FLOW JUST OFF THE SURFACE INCREASES
ACROSS OUR AREA ON TUESDAY NIGHT/WEDNESDAY MORNING... IN RESPONSE TO
THE SYSTEM. AS THIS HAPPENS WARM MOIST AIR IS FORECAST TO OVERRIDE
THE COOL STABLE DOME OF AIR (PROVIDED BY THE SURFACE HIGH) WHICH
WILL ALLOW CHANCES FOR PRECIP TO INCREASE. GIVEN WE ARE STILL 5 TO 6
DAYS OUT... WILL ONLY INCREASE POPS TO HIGH END CHANCE. AS PRECIP
STARTS FALLING INTO THE DRY AIR... THE HIGH BEGINS TO MOVE
EASTWARD... ALLOWING FOR POSSIBLY A HYBRID DAMMING EVENT TO OCCUR ON
TUESDAY NIGHT INTO WEDNESDAY... BEFORE STRONG SOUTHERLY FLOW SCOURS
OUT THE SHALLOW STABLE LAYER WEDNESDAY AFTERNOON AS THE WARM FRONT
MOVES INTO THE AREA. THE STRONG COLD FRONT IS EXPECT TO MOVE THROUGH
THE AREA ON WEDNESDAY AFTERNOON INTO THE EVENING... WITH THE EC A
BIT FASTER (6 HOURS OR SO) THAN THE GFS. AS THE FRONT MOVES THROUGH
EXPECT WE WILL HAVE THE POTENTIAL FOR WIDESPREAD SHOWERS AND AT
LEAST A FEW THUNDERSTORMS GIVEN THE STRONG LOW LEVEL FORCING AND
EXPECTED WARM MOIST AIR SURGING INTO THE CWA. HOWEVER... GIVEN WE A
STILL 5 TO 6 OUT STILL.... WILL NOT MENTION THUNDER AT THIS POINT.
CHANCE FOR SHOWERS SHOULD COME TO AN END WITH THE PASSAGE OF THE
FRONT... WITH CLEARING SKIES ON WEDNESDAY NIGHT.
HIGH TEMPS ON TUESDAY LOOK TO BE IN THE LOWER TO MID 50S WITH
INCREASING CLOUD COVER AND SURFACE HIGH PRESSURE EXTENDING INTO THE
AREA FROM THE NORTH. LOWS ON TUESDAY NIGHT/WEDNESDAY MORNING... WILL
GREATLY DEPEND ON QPF... FOR NOW WILL KEEP LOWS IN THE UPPER 30S IN
THE NORTHWEST TO LOWER 40S IN THE SOUTHEAST. HIGH ON WEDNESDAY WILL
BE TRICKY AS WELL AND DEPEND ON HOW QUICKLY THE COOL STABLE SURFACE
LAYER WILL BE ERODED... AND THE TIMING OF THE FRONT. FOR NOW WILL GO
WITH THE HIGHS RANGING FROM THE LOWER TO MID 50S IN THE NORTHWEST...
TO LOWER TO MID 60S IN THE SOUTHEAST. WITH CLEARING CONDITIONS ON
WEDNESDAY NIGHT/THURSDAY MORNING... EXPECT LOWS TO RANGE FROM THE
MID 30S IN THE NORTHWEST TO LOWER TO MID 40S IN THE SOUTHEAST.
THURSDAY:
COLD SURFACE HIGH PRESSURE IS EXPECTED TO BUILD INTO THE AREA ON
THURSDAY... WITH MOSTLY SUNNY SKIES EXPECT. LOW LEVEL THICKNESS
VALUES ARE EXPECTED TO BE NEARLY 15 TO 20 METERS BELOW NORMAL.
THUS... WILL GO WITH HIGHS IN THE UPPER 40S IN THE NORTHWEST TO
LOWER TO MID 50S IN THE SOUTHEAST.
&&
.AVIATION /18Z FRIDAY THROUGH TUESDAY/...
AS OF 105 PM FRIDAY...
A VERY ENERGETIC SOUTHWEST FLOW ALOFT WILL INDUCE SURFACE LOW
PRESSURE DEVELOPMENT FROM THE NORTHERN GULF OF MEXICO TO THE MIDDLE
ATLANTIC COAST THROUGH SATURDAY. ATLANTIC MOISTURE WILL BE WRAPPED
INLAND ON THE NORTHWEST SIDE OF THE DEVELOPING LOW... AND CAUSE
PRESENT VFR CONDITIONS TO BECOME MVFR THEN (L)IFR WITH RAIN AT
CENTRAL NC TERMINALS AROUND 03Z AT FAY... BY 10Z FARTHER NORTHWEST
AT TRIAD TERMINALS... AND SOME TIME IN BETWEEN AT RDU AND RWI.
CONDITIONS SHOULD REMAIN (L)IFR WITH OCCASIONAL RAIN -- MODERATE AT
TIMES -- THROUGH THE 18Z TAF PERIOD.
LOOKING BEYOND 18Z SATURDAY: AS COLD AIR RUSHES INTO THE REGION
THROUGH THE DEPTH OF THE ATMOSPHERE... THE RAIN MAY BRIEFLY MIX WITH
OR CHANGE OVER TO SNOW (WITH ASSOCIATED REDUCED VISIBILITIES) FOR A
FEW HOURS -- MAINLY AT TRIAD TERMINALS -- BEFORE ENDING AND BECOMING
VFR IN THE 22Z TO 03Z/5TH TIME FRAME. THERE WILL BE ANOTHER CHANCE
OF MVFR CONDITIONS AND A LITTLE LIGHT RAIN... ESPECIALLY AT EASTERN
TERMINALS... AHEAD OF A WEAKER STORM SYSTEM ON MONDAY.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...MWS
NEAR TERM...MWS/CBL
SHORT TERM...CBL/BSD
LONG TERM...BSD
AVIATION...MWS
