FXUS62 KRAH 100239
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
939 PM EST WED DEC 9 2009
.SYNOPSIS...
A COLD FRONT WILL MOVE EAST OF THE AREA AND OFFSHORE TONIGHT...
USHERING IN A MUCH COLDER AIR MASS FOR THURSDAY THROUGH FRIDAY.
ANOTHER STORM SYSTEM WILL AFFECT THE SOUTHEAST STATES OVER THE
WEEKEND.
&&
.NEAR TERM /THROUGH THURSDAY NIGHT/...
AS OF 935 PM WEDNESDAY...
WINDS HAVE STARTED TO DECREASE THIS EVENING A BIT... AS THE MIXED
LAYER DECREASES KEEPING THE HIGHER MOMENTUM AIR FROM TRANSPORTING
TO THE SURFACE. STILL EXPECT WE WILL SEE WINDS REMAIN IN THE 5 TO
15 MPH RANGE OVERNIGHT... WITH GUSTS OF UP TO 30 MPH POSSIBLE
UNTIL MIDNIGHT ACROSS EASTERN LOCATIONS OF CENTRAL NORTH
CAROLINA. THE COLD FRONT THIS EVENING HAS MADE ITS WAY INTO THE
CENTRAL AND SOUTHERN COASTAL PLAIN AND EASTERN SANDHILLS... WITH
DEWPOINTS SOUTH AND EAST OF THE FRONT STILL IN THE 60S... WITH
DEWPOINTS ACROSS THE TRIANGLE AREA BEHIND THE FRONT IN THE 30S.
TEMPS HAVE BEEN SLOW TO FALL BEHIND THE FRONT THIS EVENING...
THANKS IN PART TO THE WINDS THIS EVENING AND THE FACT THAT THE
GOOD CAA DOESN'T MAKE IT HEAR UNTIL AROUND DAYBREAK... WHEN THE
850 MB TROUGH BEGINS TO SWING THROUGH THE AREA. IN ADDITION...
HIGH CLOUDS ASSOCIATED WITH THE STRONG UPPER LEVEL JET ARE MOVING
INTO THE AREA... WHICH ARE REFLECTED WELL IN MODEL SOUNDINGS. THIS
SHOULD ALSO HELP TEMPS FROM FALLING TO MUCH TONIGHT. THUS... HAVE
SLOWED THE FALL OF TEMPS TONIGHT AND RAISED OVERNIGHT LOWS BY
SEVERAL DEGREES OVERNIGHT. EXPECT OVERNIGHT LOW TEMPS TO RANGE
FROM AROUND 4O IN THE NORTHWEST... TO NEAR 50 IN THE SOUTHEAST.
-BSD
AS OF 230 PM WEDNESDAY...
THURSDAY AND THURSDAY NIGHT...
COLD...DRY POLAR HIGH WILL BUILD SLOWLY INTO THE REGION THROUGH
FRIDAY WITH STRONG 850 CAA THROUGH THE DAY ON THURSDAY...WITH
1000-850MB THICKNESSES BOTTOM OUT TO AROUND 1265M FRIDAY MORNING.
NAM 10 M BACKWARD TRAJECTORIES INDICATE AIR SOURCE REGION BUILDING
IN FROM THE IOWA/MISSOURI...WHERE TEMPERATURES ARE CURRENTLY IN THE
SINGLE DIGITS TO LOWER TEENS. SO DEFINITELY A TRUE ARCTIC AIRMASS
BUILDING INTO THE AREA. HIGHS THURSDAY IN THE MID 40S NW TO MID 50S
SE. LOWS THURSDAY NIGHT IN THE 24 TO 29...WITH THE TYPICAL COLDER
SITES DIPPING DOWN INTO THE LOWER 20S. -CBL
&&
.SHORT TERM /FRIDAY THROUGH SATURDAY/...
AS OF 300 PM WEDNESDAY...
FRIDAY:
ARCTIC HIGH PRESSURE IS PROGGED TO BE CENTERED DIRECTLY OVER THE
CAROLINAS AND MID-ATLANTIC ON FRIDAY. A BLEND OF GFS/ECMWF
THICKNESSES ARE QUITE COLD...STARTING OUT AT 1265-1285M AND RISING
ONLY TO 1290-1300M BY 21-00Z. DECIDED TO BASE HIGH TEMPS PRIMARILY
ON THICKNESSES GIVEN EXPECTED FULL SUN AND LITTLE/NO ADVECTION...
AND THAT ARGUES FOR HIGHS RANGING FROM 40-47F...COOLEST NORTH AND
WARMEST SOUTH. THIS IS A FEW DEGREES BELOW MOS GUIDANCE IN MOST
INSTANCES.
FRIDAY NIGHT:
FAST MOVING SOUTHERN STREAM IMPULSES ARE EXPECTED TO TRAVERSE THE
SOUTHERN CONUS FRIDAY NIGHT...ENHANCING PRECIPITATION IN VICINITY OF
A BAROCLINIC ZONE ALONG THE GULF COAST AND INITIATING WEAK
CYCLOGENESIS OFFSHORE OF TX/LA BY 12Z SAT. THE LATEST 12Z MODEL
GUIDANCE IS INDICATING THAT PRECIPITATION ASSOC/W SOUTHERN STREAM
SHORTWAVE ENERGY AND INCREASING ISENTROPIC LIFT/WARM ADVECTION OVER
THE DEEP SOUTH AND SOUTHEAST STATES SHOULD REMAIN WELL SOUTH ALONG
THE GULF COAST AREA. AS A RESULT...WILL CONTINUE TO KEEP THE
FORECAST DRY FRIDAY NIGHT. EXPECT SOME INCREASE IN UPPER LEVEL CLOUD
COVER AFTER MIDNIGHT...HOWEVER...WITH THE LATEST MODEL GUIDANCE
CONTINUING TO DELAY THE DEVELOPING SOUTHERN STREAM SYSTEM...CLOUD
COVER SHOULD HAVE LESS OF AN EFFECT ON LOW TEMPS THAN ANTICIPATED
YESTERDAY. AS A RESULT...HAVE LOWERED MIN TEMPS SEVERAL DEGREES...
INTO THE MID/UPPER 20S (24-28F) ACROSS THE ENTIRE AREA.
SATURDAY:
COMPARED TO YESTERDAY'S 12Z MODEL GUIDANCE...THE LATEST 12Z
GFS/NAM/CANADIAN/ECMWF GUIDANCE HAVE ALL SLOWED DOWN THE UPCOMING
LOW-AMPLITUDE SOUTHERN STREAM SYSTEM...BY AS MUCH AS 12-24 HOURS. AS
A RESULT...OTHER THAN INCREASING MID/UPPER LEVEL CLOUD COVER...AT
THIS TIME DO NOT SEE ANY CHANCE FOR PRECIPITATION DURING THE DAY
SATURDAY. WITH ARCTIC HIGH PRESSURE IN PLACE...THICKNESSES ARE
PROGGED TO REMAIN ON THE COLD SIDE. WITH MORNING LOWS IN THE
MID/UPPER 20S AND WITH THICKNESSES NO HIGHER THAN 1300-1315M AT 00Z
SUN...EXPECT RATHER CHILLY HIGHS RANGING FROM 40-45F NW-SE. -VINCENT
&&
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
AS OF 300 PM WEDNESDAY...
SATURDAY NIGHT THROUGH SUNDAY NIGHT:
LATEST MODEL GUIDANCE HAS SLOWED THE UPCOMING SOUTHERN STREAM SYSTEM
BY A GOOD 12-24 HOURS...DELAYING OUR NEXT CHANCE FOR PRECIPITATION
UNTIL LATE SAT NIGHT INTO SUN. THE SYNOPTIC PATTERN FOR THIS
UPCOMING EVENT WILL BE VERY LOW AMPLITUDE...WITH UPPER LEVEL SUPPORT
IN THE FORM OF FAST MOVING SOUTHERN STREAM SHORTWAVE IMPULSES
TRAVERSING THE SOUTHERN CONUS. AS MENTIONED YESTERDAY...IT IS
DIFFICULT TO BELIEVE THAT SUCH SUBTLE SOUTHERN STREAM ENERGY IS
BEING HANDLED CORRECTLY BY THE MODELS AT THIS RANGE...ESPECIALLY
CONSIDERING THAT THE AFOREMENTIONED SOUTHERN STREAM ENERGY DOES NOT
APPEAR TO MOVE ONSHORE THE CA/MEXICO COAST (BEGIN TO GET SAMPLED BY
THE RAOB NETWORK) UNTIL LATE THU OR EARLY FRI. THIS UNCERTAINTY HAS
BEEN EVIDENCED BY THE SIGNIFICANT SLOWING IN THE TIMING OF THE
SYSTEM IN THE PAST FEW MODEL RUNS. SO...IT GOES WITHOUT SAYING...A
FAIR AMOUNT OF UNCERTAINTY CONTINUES TO PLAGUE THIS PORTION OF THE
FORECAST. THE SLOWER TIMING OF THE SYSTEM WOULD INDICATE LESS OF A
CHANCE FOR ANY P-TYPE ISSUES AT THE ONSET...AND A HIGHER LIKELIHOOD
OF ALL-LIQUID PRECIP. WHILE THE 12Z GFS/ECMWF CONTINUE TO SHOW A
WEAK LOW PRESSURE SYSTEM TRACKING NORTHEAST JUST OFF THE SOUTHEAST
COAST ON SUNDAY...THE 12Z CANADIAN KEEPS THE SFC LOW WELL TO THE
SOUTH...EAST OF FLORIDA...WITH NO PRECIP OVER CENTRAL NC. WITH ALL
THIS IN MIND...HAVE DELAYED THE ONSET OF POPS UNTIL SUNDAY
MORNING...AND WILL SHOW NO HIGHER THAN 50% POPS DURING THE DAY
SUNDAY. LOWS TEMPS SAT NIGHT WILL DEPEND ON CLOUD COVER AND THE
ONSET OF PRECIPITATION. AT THIS TIME WILL CONTINUE WITH A MOS
GUIDANCE BLEND...WITH LOWS RANGING FROM THE LOWER TO MID 30S. HIGH
TEMPS ON SUNDAY WILL LIKELY BE COOLER THAN PREVIOUSLY ANTICIPATED
DUE TO THE LATER ARRIVAL OF PRECIP AND ASSOCIATED EVAPORATIVE
COOLING. WILL TREND HIGHS DOWNWARD INTO THE LOWER/MID 40S MOST
LOCATIONS...EXCEPT UPPER 40S TO NEAR 50F IN THE SE COASTAL PLAIN.
DUE TO CONTINUED MODEL DIFFICULTY IN HANDLING THE UPCOMING SOUTHERN
STREAM SYSTEM...WILL KEEP A SLIGHT CHANCE OF RAIN IN THE FORECAST
THROUGH SUNDAY NIGHT...WITH MOSTLY CLOUDY SKIES AND LOWS ABOVE
FREEZING IN THE 30S.
MONDAY THROUGH WEDNESDAY:
CONSIDERABLE UNCERTAINTY WITH THE FORECAST EARLY/MID NEXT WEEK. THE
POTENT STORM SYSTEM PREVIOUSLY ADVERTISED BY THE GFS/ECMWF FOR
TUE/WED HAS BEEN WEAKENED (GFS) OR SUPPRESSED SOUTH OF THE AREA
ALTOGETHER (ECMWF) BY TODAY'S 12Z MODEL RUNS. THE UNCERTAINTY
APPEARS TO BE PRIMARILY TIED TO HOW THE MODELS HANDLE THE
INTERACTION OF THE SOUTHERN/NORTHERN STREAM JET EARLY NEXT WEEK. AT
THIS TIME WILL SHOW NEAR-NORMAL HIGH/LOW TEMPS...WITH CHANCE POPS
(30%) CONTINUING ON TUE. -VINCENT
&&
.AVIATION /02Z THURSDAY THROUGH MONDAY/...
AS OF 645 PM WEDNESDAY...
SURFACE WINDS WILL CONTINUE TO USHER DRIER MORE STABLE AIR INTO THE
REGION TONIGHT AND THURSDAY. THIS MORE STABLE AIR WILL AID TO
SUBSIDE THE WINDS. WIND GUSTS UP TO 30KTS WILL BE POSSIBLE AT
KRDU...KRWI AND KFAY THROUGH 02Z. OTHERWISE THE WINDS WILL GRADUALLY
SUBSIDE OVERNIGHT AND VEER TO A WLY DIRECTION AS A COLD AND DRY HIGH
PRESSURE SYSTEM BUILDS INTO THE REGION. THIS WEATHER FEATURE WILL
BRING AN EXTENDED PERIOD OF VFR CONDITIONS FROM THURSDAY THROUGH
SATURDAY.
A DEVELOPING LOW PRESSURE SYSTEM TO OUR SW SATURDAY NIGHT MAY BRING
ADVERSE AVIATION CONDITIONS LATE SATURDAY NIGHT THROUGH SUNDAY. VFR
CONDITIONS SHOULD RETURN MONDAY.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...BSD
NEAR TERM...BSD/CBL
SHORT TERM...VINCENT
LONG TERM...VINCENT
AVIATION...WSS
