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FXUS62 KRAH 290642
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
140 AM EST TUE JAN 29 2008

.SYNOPSIS...

HIGH PRESSURE WILL SETTLE SOUTHEAST OF THE AREA TONIGHT. A COLD FRONT
WILL APPROACH FROM THE WEST WITH INCREASING SOUTHWESTERLY WINDS
AND MILD AIR TUESDAY. THE COLD FRONT WILL CROSS THE AREA LATE TUESDAY
NIGHT. HIGH PRESSURE WILL BUILD INTO THE AREA FROM THE MIDWEST WED.

&&

.NEAR TERM /THROUGH TUESDAY/...
AS OF 853 PM MONDAY...A 1022 MB SURFACE HIGH CENTERED JUST SOUTH OF 
SAVANNAH WILL MOVE OFF THE SOUTHEAST COAST OVERNIGHT. ALTHOUGH...THE 
DRY SFC DEWPOINTS HAVE BEEN HANGING TOUGH SO FAR...MODELS DEPICT 
RIDGE AXIS SHOULD SHIFT EAST OF THE AREA BY 06Z...WITH 925MB WINDS 
STRENGTHENING TO 25 TO 30 KTS FROM THE SW BY 12Z. EXPECT TO SEE 
REALLY GOOD DEWPOINT RECOVERY BY DAYBREAK...WITH DEWPOINTS IN THE 
LOWER 30S ACROSS MUCH OF CENTRAL NC. 

THICKENING MID AND HIGH LEVEL MOISTURE ASSOCIATED WITH THE DIFFLUENT 
AREA OF THE UPPER JET ON THE BACKSIDE OF THE RIDGE WILL PROVIDE 
OVERCAST SKY CONDITIONS FOR THE REMAINDER OF THE NIGHT...AND 
RESULTING IN A MUCH MILDER TEMPERATURES OVERNIGHT...COMPARED TO 24 
HOURS AGO. FORECAST MINS IN THE MID 30S SEEMS TOO FAR OF A STRETCH 
DUE TO THE FASTER ARRIVAL OF THE HIGH CLOUDS. 01Z METAR PLOT SHOWS 
THAT TEMPERATURES ARE STILL IN THE MID 40S ACROSS MUCH OF THE 
WESTERN PIEDMONT. EXPECT TEMPERATURES COULD DROP ANOTHER 4 TO 6 
DEGREES OVERNIGHT...BUT NOT MUCH MORE AS SOUTHERLY WINDS PICKING UP 
AS WELL. WILL RAISE MIN TEMPERATURES ACROSS THE WESTERN PIEDMONT TO 
AROUND 40...WITH UPPER 30S ACROSS CENTRAL SECTIONS...INCLUDING THE 
TRIANGLE. THE LOWER 30S IN THE NORTHEAST COASTAL PLAIN STILL LOOK 
ATTAINABLE AS TEMPERATURES HAVE DROPPED MORE SHARPLY THUS FAR. 

SOUTHERLY FLOW INCREASES IN EARNEST TOMORROW IN ADVANCE OF THE NEXT 
COLD FRONT AND MID LEVEL TROUGH. WINDS AS LOW AS 925 MB INCREASE TO 
30-40 KT BY TOMORROW AFTERNOON. WARM AIR ADVECTION WARMS THICKNESSES 
TO NEAR 1350M WHICH SHOULD RESULT IN ABOVE NORMAL TEMPS ACROSS THE 
ENTIRE AREA. HIGHS 60 N TO 64 S. ALL POPS HAVE BEEN REMOVED FROM THE 
NORTHWEST PIEDMONT TOMORROW AFTERNOON DUE TO GUIDANCE CONTINUING TO 
SLOW DOWN THE TIMING OF THE FRONT. ANY APPRECIABLE LIFT AND MOISTURE 
FOR PRECIP GENERATION LOOKS TO HOLD OFF UNTIL TUESDAY NIGHT.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
AS OF 135 PM MONDAY...
A MODERATE AMPLITUDE WAVE IN THE WESTERLIES ACROSS THE CONUS DAMPENS 
AS IT MOVES FROM THE MID MISSISSIPPI VALLEY TO NEW ENGLAND TUE NIGHT 
AND WED.  THIS TAKES THE STRONGEST DYNAMICS FOR LIFT NORTH OF THE 
AREA AND LEAVES MOST OF THE PREFRONTAL THERMODYNAMIC ENERGY SOUTH 
AND EAST OF THE AREA.  THOUGH FLOW AT 850 MB IS VIGOROUS WITH SPEEDS 
OF 50-70 KNOTS...IT IS DIRECTED MORE AWAY FROM THE FRONT AS IT 
CROSSES THE MOUNTAINS.  THIS LIMITS MOISTURE CONVERGENCE AND SUPPORT 
FOR DEEPER CONVECTION THAN JUST SHALLOW LIGHT SHOWERS.  MODELS 
CONSENSUS FAVORS COLD FRONTAL PASSAGE BETWEEN MIDNIGHT AND DAYBREAK 
WED. QPF FROM THE LIKELY SHOWERS WILL BE IN THE ONE TO TWO TENTHS 
RANGE. COLD AIR ADVECTION BEHIND THE FRONT MAY BRING TEMPERATURES 
DOWN TO LOWER 40S EXTREME WEST...BUT TEMPERATURE SHOULD HOLD TO 50 
OR ABOVE MOST OF THE NIGHT AND THROUGH DAYBREAK DOWN EAST.

WED...POST COLD FRONTAL CONDITIONS APPEAR COOL BUT NOT COLD FOR LATE 
JANUARY WITH SLACKENING NW FLOW AS HIGH PRESSURE EXPANDS INTO THE 
AREA FROM THE TENNESSEE VALLEY.  A SOMEWHAT SLOWER ARRIVAL OF COLDER 
AIR ACROSS THE MOUNTAINS AS DEPICTED BY THE GFS IS FAVORED WITH 
MODEL THICKNESS AND STATISTICAL OUTPUT SUGGESTING MAX TEMPERATURES 
IN THE 48 TO 56 DEGREE RANGE NW-SE.

WED NIGHT...A MID 1030S HIGH BUILDS OVER PA WHICH MAY BEGIN TO 
ADVECT A PIECE OF THE ARCTIC AIRMASS HOLDING UP IN THE OHIO VALLEY.  
THIS SHOULD SEND TEMPERATURES INTO THE MID TO UPPER 20S...POSSIBLY 
LOWER IN THE PIEDMONT...WITH LIGHT NE SURFACE FLOW BENEATH MOSTLY 
CLEAR SKIES. 

THU...HIGH CLOUDINESS INCREASES AND THICKENS WELL AHEAD OF ANOTHER 
PROGRESSIVE STRONG WAVE IN THE SOUTHERN STREAM CROSSING THE SOUTHERN 
PLAINS.  THIS AND RESIDUAL COLD AIR ADVECTION THU MORNING FROM A 
BREAKOFF HIGH OVER DELMARVA SHOULD KEEP TEMPERATURES DOWN IN THE 40S 
N AND W TO LOWER 50S SE.  -RFG


&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
AS OF 1130 AM MONDAY... 
THE PERIOD BEGINS WITH MODELS SHOWING A WARM FRONTAL APPROACH AND 
RAPID EROSION OF A COLD AIR DAMMING AIRMASS AS THE ORIGINATING 1032 
HIGH QUICKLY EXITS NEW ENGLAND. A PART OF THIS CAD AIRMASS MAY HAVE 
ORIGINS IN THE SUB ZERO ARCTIC COLD NOW MOVING DOWN THE EAST SIDE OF 
THE NRN ROCKIES HIGHLIGHTED BY A MINUS 36 AT 850 MB OVER ALBERTA. 
AND IF SO...A SLOWER EROSION PROCESS IS FAVORED. A 45-55 KNOT CROSS 
CONTOUR FLOW AT THE 295K THETA SURFACE IS DEPICTED BY BOTH GFS AND 
ECMWF...THOUGH SATURATION IS DEEPER AND SLOWER TO MOVE WITH THE 
ECMWF.  THIS SUGGESTS AT LEAST A 50 PCT CHANCE OF RAIN WITH LOW QPF 
THU NIGHT INTO FRI MORNING BEFORE THE DEEPER MOISTURE LIFTS NORTH OF 
THE AREA.  

LATER FRI...MODELS SHOW A VIGOROUS COLD FRONT MOVING THROUGH 
BUT WITH A LIMITED TAP TO GULF MOISTURE...LIMITED LOW LEVEL 
CONVERGENCE EAST OF THE MOUNTAINS AND LIMITED MID LEVEL INSTABILITY 
IN THE 5.5 DEG/KM RANGE TO AID DEEP CONVECTION. POPS OF 50 PCT ARE 
ADEQUATE FOR SCATTERED SHOWERS LATE FRI INTO FRI NIGHT BUT AGAIN 
WITH LOW BASIN AVERAGE QPF.  A NONDIURNAL TEMPERATURE PATTERN IS 
LIKELY WITH STEADY TO SLIGHTLY WARMING TEMPERATURES THU NIGHT.  THE 
GFS SUGGESTS AN EARLIER CFP FRI AFTN... ABOUT 6-12 HRS EARLIER THAN 
THE ECMWF AND CANADIAN.  A SLOWER FRONTAL PROGRESSION PER HPC IS 
FAVORED.  

SAT-MON...THE AIRMASS FOLLOWING THE COLD FRONT LOOKS TO BE DOMINATED 
BY SOUTHERN STREAM FLOW WITH PERHAPS JUST A SHOT OF MODIFIED 
NORTHERN STREAM AIR FROM A TRANSIENT HIGH OVER THE OHIO VALLEY SUN 
AND MON.  AS SUCH...TEMPERATURES SHOULD AVERAGE SLIGHTLY ABOVE 
NORMAL WITH HIGHS MAINLY IN THE 50S AND LOWS IN THE 30S UNDER MOSTLY 
CLEAR TO PARTLY CLOUDY SKIES.  -RFG

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
AS OF 100 AM...VFR CONDITIONS ARE EXPECTED THROUGH TUESDAY. MID 
LEVEL WARM ADVECTION CLOUDINESS CENTERED AROUND 700 MILLIBARS WILL 
CONTINUE TO SPREAD NORTHEASTWARD THROUGH OUR TAF AREA AND RESULT IN 
BROKEN CEILINGS BETWEEN 10 AND 12 THOUSAND FEET THROUGH DAYBREAK. 
MID AND HIGH CLOUDS IN SOUTHWESTERLY FLOW ALOFT WILL PERSIST 
TUESDAY... WITH CLOUD BASES LOWERING TO MVFR ALONG AND IMMEDIATELY 
PRECEDING A COLD FRONT CURRENTLY STRETCHING FROM SOUTHERN ONTARIO TO 
THE CENTRAL PLAINS. THESE MVFR CEILINGS AND RAIN SHOWERS WITH THE 
FRONT WILL LIKELY NOT OCCUR AT KRDU... KFAY... AND KRWI UNTIL JUST 
AFTER THE END OF THIS VALID TAF PERIOD. 

LOW LEVEL SOUTH SOUTHWESTERLY FLOW WILL INCREASE TUESDAY... AS THE 
PRESSURE GRADIENT TIGHTENS BETWEEN RIDGING SHIFTING OFF THE GEORGIA 
COAST AND THE AFOREMENTIONED APPROACHING COLD FRONT. IN FACT... 
WINDS AT THE TOP OF AN EXPECTED 2 TO 3 THOUSAND FT MIXED LAYER ARE 
FORECAST TO INCREASE TO BETWEEN 25 AND 30 KT BY 18Z TUES... WHICH 
WILL RESULT IN SURFACE WIND GUSTS TO NEAR 25 KTS BY MIDDAY. AS THE 
PRESSURE GRADIENT TIGHTENS FURTHER WITH THE APPROACH OF THE FRONT... 
MODELS SHOW A 60 KT LOW LEVEL JET EXTENDING FROM 850 TO 925 
MILLIBARS DEVELOPING ACROSS CENTRAL NORTH CAROLINA TUESDAY NIGHT. 
THIS WILL UNDOUBTEDLY PRODUCE MECHANICAL TURBULENCE AND ASSOCIATED 
BUMPY TAKEOFFS AND LANDINGS... WITH NEAR SURFACE WINDS APPROACHING 
30 KTS IN GUSTS TUESDAY NIGHT. THE COLD FRONT AND ASSOCIATED RAIN 
SHOWERS WILL PUSH THROUGH THE AREA FROM WEST TO EAST BETWEEN 
MIDNIGHT AND DAYBREAK WEDNESDAY.

HIGH PRESSURE AND ASSOCIATED VFR CONDITIONS WILL PREVAIL FOR 
WEDNESDAY AND THURSDAY. THEN ANOTHER LOW PRESSURE SYSTEM WILL 
APPROACH THE AREA THURSDAY NIGHT AND FRIDAY... AND PROVIDE A 
PROBABILITY OF RAIN AND IFR CEILINGS... AND POSSIBLY LOW LEVEL WIND 
SHEAR.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$
SYNOPSIS...RFG
NEAR TERM...CBL/JFB
SHORT TERM...RFG
LONG TERM...RFG
AVIATION...MWS