FXUS62 KRAH 051955
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
255 PM EST SAT DEC 5 2009

.SYNOPSIS...

LOW PRESSURE CENTERED NEAR THE NC OUTER BANKS THIS AFTERNOON WILL 
INTENSIFY AND TRACK NORTHEASTWARD OFFSHORE THE MID ATLANTIC AND NEW 
ENGLAND COASTS THROUGH TONIGHT. MEANWHILE... COLD HIGH PRESSURE WILL 
BUILD IN FROM THE WEST AND LINGER THROUGH SUNDAY NIGHT.

&&

.NEAR TERM /THROUGH SUNDAY NIGHT/... 
AS OF 255 PM SATURDAY...

WHILE SHALLOW SATURATION SHOULD MAINTAIN PERIODS OF LIGHT RAIN AND 
DRIZZLE THROUGH THIS EVENING... IT APPEARS THAT THE ARRIVAL OF THE 
MID LEVEL DRY AIR AND DEPARTING STRONGEST AND DEEPEST FORCING FOR 
ASCENT MAY REDUCE THE THREAT OF A MIX OR CHANGEOVER TO SNOW. THE 
THREAT IS NOT NON-EXISTENT... HOWEVER... MAINLY ALONG THE NC 
COUNTIES ADJACENT TO THE VA BORDER. THAT WILL BE WHERE THE SATURATED 
LAYER SHOULD BE DEEPEST/COLDEST ON THE SOUTHERN PERIPHERY OF THE 
PROGRESSIVE DEFORMATION BAND OVER THE NORTHERN NC MOUNTAINS AND 
FOOTHILLS... WHICH IS EXPECTED TO SLIDE EASTWARD ALONG THE VA 
BORDER. LITTLE (ON GRASSY AND ELEVATED SURFACES SUCH AS CAR TOPS) TO 
NO ACCUMULATION EXPECTED... IF ANY FLAKES FLY AT ALL... GIVEN THE 
RELATIVELY UNFAVORABLE CLOUD MICROPHYSICS. 

WITH COLDER TEMPERATURES SET TO ARRIVE OVERNIGHT... BLACK ICE WILL 
BECOME A CONCERN. WILL COVER THIS THREAT IN THE HAZARDOUS WEATHER 
OUTLOOK... AND DEFER TO THE EVENING SHIFT TO ASSESS THE POTENTIAL 
FOR AN ADVISORY ONCE IT IS BETTER DETERMINED HOW MUCH LINGERING 
MOISTURE REMAINS ON AREA ROADWAYS. 

TONIGHT: CLEARING AND COLDER IN THE WAKE OF THE DEPARTING COASTAL 
LOW... WITH CAA-DRIVEN OVERNIGHT LOWS BETWEEN 26 DEGREES TO AROUND 
FREEZING... WARMEST SOUTHEAST. 

SUNDAY AND SUNDAY NIGHT: CHILLY HIGH PRESSURE WILL SETTLE INTO THE 
MID ATLANTIC STATES AND DOMINATE THIS PERIOD. HIGH TEMPERATURES 
MAINLY IN THE MIDDLE TO UPPER 40S EXPECTED... OR ABOUT A DEGREE 
COOLER THAN WHAT PROJECTED LOW LEVEL THICKNESSES IN THE 1300 TO 1310 
METER RANGE WOULD SUGGEST GIVEN LOW MIXING HEIGHTS AND A WARM 
SUBSIDENCE INVERSION ABOVE. (IE. THE THICKNESSES ARE INFLATED BY 
UNATTAINABLE WARMTH WITHIN THE SUBSIDENCE INVERSION/ABOVE THE 
BOUNDARY LAYER). AFTER A SUNNY START... CIRRUS OVER THE SOUTHERN AND 
CENTRAL PLAINS STATES THIS AFTERNOON WILL STEADILY SPREAD EASTWARD 
AND PROVIDE FOR PARTLY CLOUDY CONDITIONS BY SUNDAY NIGHT. WEAK 
ISENTROPIC LIFT -- ATOP THE AFOREMENTIONED MID ATLANTIC SURFACE 
RIDGE -- MAY YIELD MVFR STRATUS AND RESULTANT MOSTLY CLOUDY SKIES 
OVER THE SOUTHERN COASTAL PLAIN AND SANDHILLS BY MONDAY MORNING. 
TEMPERATURES SHOULD FALL QUICKLY AFTER SUNSET GIVEN INITIALLY GOOD 
RADIATIONAL COOLING CONDITIONS (ASIDE FROM THE INCREASED CIRRUS)... 
WITH OVERNIGHT LOWS IN GENERALLY IN THE UPPER 20S TO LOWER 30S. 
TEMPERATURES MAY RISE A BIT TOWARD MORNING OWING TO DOWNWARD L/W IR 
ASSOCIATED WITH THE POSSIBLE STRATUS. 

&&

.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
AS OF 220 PM...

MONDAY A MIDWEST LOW PRESSURE SYSTEM WILL APPROACH AND MOVE THROUGH 
MICHIGAN WHILE SURFACE HIGH PRESSURE LINGERS OFF THE NORTH CAROLINA 
COAST. THE GFS IS STRONGEST WITH THE PRESSURE GRADIENT ACROSS NORTH 
CAROLINA MONDAY AND DEVELOPS A SIGNIFICANT 925 MILLIBAR TROUGH OVER 
THE WESTERN PIEDMONT AT MIDDAY... MOVING IT TO THE COASTAL PLAIN AT 
SUNSET WHILE RETAINING A LEE SIDE TROUGH IN THE FOOTHILLS. 
ISENTROPIC LIFT IS QUITE IMPRESSIVE ON THE GFS. HOWEVER THERE IS 
MINIMAL SUPPORT FROM THE ECMWF AND CANADIAN FOR THIS FEATURE. I HAVE 
FOUND THE GFS TO BE FREQUENTLY OVERDONE IN LOW LEVEL WINDS... BUT 
STILL SUPERIOR IN RELATION TO THE NAM MODEL. THUS WILL ADD A SLIGHT 
CHANCE FOR MEASURABLE RAIN TO MONDAY. SHOULD DRIZZLE OR LIGHT RAIN 
DEVELOP TEMPERATURES WILL BE DAMPENED A BIT AND HAVE DROPPED 
AFTERNOON HIGHS A FEW DEGREES... TO 49 TO 53.

NORTH FLOW MONDAY NIGHT AROUND SURFACE HIGH PRESSURE WILL BEGIN TO 
SHUNT LOW LEVEL MOISTURE TO THE SOUTH. NORTH PARTS WILL HAVE BEST 
RADIATIONAL COOLING CONDITIONS AND AS MUCH AS A TEN DEGREE GRADIENT  
IN TEMPERATURES NORTH TO SOUTH POSSIBLE... WITH MOST LOW 
TEMPERATURES IN THE 30S. 

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
AS OF 220 PM...

A STRONG UPPER LEVEL SHORT WAVE WILL EXIT THE ROCKIES TUESDAY... 
REACHING THE EASTERN PARTS OF THE OKLAHOMA PANHANDLE BY SUNSET. A 
STRONG SURFACE LOW IN CLOSE PROXIMITY TO THE UPPER TROUGH WILL BRING 
STRONG SOUTH RETURN FLOW AHEAD OF THE LOW INTO THE TENNESSEE VALLEY 
AND THE SOUTHEAST. RIDGING OVER THE EAST COAST HOLDS STRONG AND 
WINDS RELATIVELY LIGHT OVER NORTH CAROLINA TUESDAY. THUS MOISTURE 
ADVECTION AND DYNAMICS SHOULD BE RELATIVELY WEAK AND WILL CONTINUE 
TO LIMIT SLIGHT RAIN CHANCES TO THE WESTERN PIEDMONT TUESDAY. 
AFTERNOON HIGHS 50 TO 55. 

THE UPPER TROUGH IS FORECAST TO REACH MISSOURI MIDNIGHT TUESDAY 
NIGHT AND OVERRUNNING SOUTH FLOW OVER THE WEAKENING AND RETREATING 
SURFACE HIGH SHOULD GENERATE RAIN IN CENTRAL NORTH CAROLINA 
OVERNIGHT. WARMING ALOFT MAY BE ABLE TO WORK TO THE SURFACE CAUSING 
LOW TEMPERATURES TO OCCUR WELL BEFORE SUNRISE. LOW TEMPERATURES 38 TO
45. RAINFALL OF ONE QUARTER TO ONE HALF INCH POSSIBLE OVERNIGHT. 
STRONG WARMING ALOFT DURING THIS EVENT AND AT THIS TIME 
PRECIPITATION EXPECTED TO BE ALL RAIN. THE ONLY POSSIBLE RISK WOULD 
BE FOR INITIAL RAINS TO COOL TEMPERATURES TO FREEZING FOR A BRIEF 
PERIOD OF FREEZING RAIN OF LITTLE TO NO CONSEQUENCE. THIS IS NOT 
EXPECTED... BUT NOT ENTIRELY IMPOSSIBLE.

THE GFS IS STRONGEST AT DEPICTING A WEAK MILLER B SECONDARY SURFACE 
LOW DEVELOPMENT OVER NORTH CAROLINA OR OFF THE COAST OF VIRGINIA 
LATE TUESDAY NIGHT OR WEDNESDAY MORNING... WITH THE INLAND LOW 
REMAINING DOMINATE. GIVEN THE LOCATION OF THE UPPER TROUGH THIS IS 
ACCEPTED. MODELS IN AGREEMENT IN PUSHING A STRONG DRY SLOT INTO 
NORTH CAROLINA BY NOON WEDNESDAY...SHUTTING DOWN PRECIPITATION IN 
SPITE OF THE SURFACE TROUGH STILL BEING OVER CENTRAL NORTH CAROLINA. 
WEDNESDAY HIGH TEMPERATURES NEAR 50 NORTHWEST TO MID 60S SOUTHEAST. 

SURFACE HIGH PRESSURE OVER THE MIDWEST WEDNESDAY NIGHT WILL ADVANCE 
EAST ON STRONG UPPER LEVEL WEST FLOW... REACHING THE EAST COAST 
FRIDAY. THE 12Z ECMWF AND THE LATEST GFS ARE IN AGREEMENT IN
BRINGING AN UPPER LEVEL SHORT WAVE INTO THE OHIO VALLEY
SATURDAY... BUT SURFACE FEATURES ARE SIGNIFICANTLY DIFFERENT...
THOUGH BOTH MANAGE TO GENERATE RAINFALL FRIDAY NIGHT AND SATURDAY.
ACCEPTING THIS SOLUTION FOR NOW... BUT WITH TIMING OF THE EVENT
SUSPECT THIS FAR OUT IN TIME IN A FAST FLOW PATTERN.

AFTERNOON HIGHS THURSDAY THROUGH FRIDAY IN THE UPPER 40S TO MID 50S. 
LOW TEMPERATURES 35 TO 45 WEDNESDAY NIGHT. SURFACE HIGH PRESSURE AND 
A DRY AIR MASS WITH THICKNESSES BELOW 1300 METERS WILL DROP LOW 
TEMPERATURES INTO THE UPPER 20S TO LOW 30S THURSDAY NIGHT. CLOUDS
AND SOUTH RETURN FLOW WILL WARM LOW TEMPERATURES FRIDAY NIGHT TO
THE MID 30S TO LOWER 40S.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
AS OF 100 PM SATURDAY...

THE PASSAGE OF AN UPPER LEVEL DISTURBANCE COMBINED WITH MOIST 
SOUTHEASTERLY FLOW FROM THE ATLANTIC WILL RESULT IN IFR/LIFR 
CONDITIONS AT ALL CENTRAL NORTH CAROLINA TERMINAL SITES THROUGH
THE EARLY TO MID AFTERNOON. AS COLD AIR RUSHES INTO THE REGION
THROUGH THE DEPTH OF THE ATMOSPHERE... THE RAIN MAY MIX WITH OR
CHANGE OVER TO SNOW (WITH ASSOCIATED REDUCED VISIBILITIES) FOR A
FEW HOURS (MAINLY AT TRIAD TERMINALS AND PERHAPS AS FAR EAST AS
RDU AND RWI). PRECIPITATION SHOULD END WITH A RETURN TO VFR FROM
SOUTHWEST TO NORTHEAST IN THE 22Z TO 04Z/5TH TIME FRAME... AS COLD
BUT DRY HIGH PRESSURE BUILDS INTO THE REGION FROM THE WEST TONIGHT
AND LINGERS THROUGH SUNDAY.

LOOKING BEYOND 18Z SUNDAY: THERE WILL BE ANOTHER CHANCE OF MVFR 
CONDITIONS AND A LITTLE LIGHT RAIN OR DRIZZLE... MAINLY AT EASTERN 
TERMINALS... AHEAD OF A WEAKER STORM SYSTEM ON MONDAY. AFTER A 
RETURN TO VFR FOR MONDAY NIGHT AND TUESDAY... EXPECT LIFR/IFR 
CONDITIONS AND A COLD RAIN ASSOCIATED WITH A STRONGER STORM SYSTEM 
TUESDAY NIGHT AND WEDNESDAY.

&&

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

&&

$$

SYNOPSIS...MWS
NEAR TERM...MWS
SHORT TERM...
LONG TERM...
AVIATION...MWS