FXUS62 KRAH 010815
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
315 AM EST TUE DEC 01 2009

.SYNOPSIS...
DRY HIGH PRESSURE WILL BUILD ACROSS THE AREA TODAY...AND THEN MOVE
OFFSHORE TONIGHT. A STRONG LOW PRESSURE SYSTEM OVER THE GULF COAST 
REGION WILL MOVE NORTHEAST LATE WEDNESDAY AND WEDNESDAY 
NIGHT...BRINGING WIDESPREAD RAIN AND GUSTY WINDS.

&&

.NEAR TERM /TUESDAY AND TUESDAY NIGHT/...
AS OF 300 AM TUESDAY...
TODAY...
FLAT RIDING ALOFT AND FURTHER MODIFICATION OF A NORTH PACIFIC HIGH 
PRESSURE CELL WILL RESULT IN DRY CONDITIONS AND SEASONABLE TEMPS  
TODAY. HIGHS IN THE UPPER 50S NORTH TO LOWER 60S SE. 

TONIGHT...
SURFACE HIGH SHIFTS OFFSHORE LATER THIS EVENING. MEANWHILE...THE 
VIGOROUS CLOSED CYCLONE OVER TEXAS WILL INDUCE SFC CYCLOGENESIS OVER 
THE NW GULF OF MEXICO. AS THE SURFACE WAVE LIFTS NORTH INTO 
AL/MS...MOISTURE AND OVERRUNNING PRECIP WILL SPREAD NORTH FROM THE 
GULF COAST STATES...ACROSS THE SAVANNAH RIVER VALLEY...AND ON UP 
INTO THE CAROLINAS THROUGH DAYBREAK WEDNESDAY. SOUTHERN PORTIONS OF 
CENTRAL NC WILL REMAIN ON THE FAR NORTHERN PERIPHERY OF THIS 
EXPANSIVE RAIN SHIELD WITH RESIDUAL LOW-LEVEL CONTINENTAL DRY 
AIRMASS REQUIRING ADDITIONAL TIME TO SATURATE AND SUPPORT MEASURABLE 
RAINFALL.   WILL KEEP SLIGHT CHANCE POPS PRIOR TO 12Z WEDNESDAY 
CONFINED TO SOUTHERN PIEDMONT AND SANDHILLS. OTHERWISE...A FEW 
SPRINKLES POSSIBLE WITH CONSIDERABLE MID AND HIGH CLOUD THICKENING 
OVERNIGHT WITH OVERRUNNING STRATOCUMULUS DEVELOPING TOWARDS 
DAYBREAK. LOWS IN THE MID 30S TO AROUND 40...COOLEST IN THE NE WHERE 
LATER ARRIVAL OF THICKER CLOUD SHIELD WILL ALLOW FOR BETTER 
RADIATIONAL COOLING THIS EVENING. 

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
AS OF 300 AM TUESDAY...

A SIGNIFICANT STORM SYSTEM WILL AFFECT THE REGION WEDNESDAY THROUGH 
WEDNESDAY NIGHT... BRINGING WIDESPREAD MODERATE TO HEAVY RAIN 
RAINSHOWERS... BLUSTERY CONDITIONS... AND A SEVERE WEATHER THREAT. 

FOR WEDNESDAY/WEDNESDAY NIGHT: 

OVERVIEW...
THE LATEST MODEL GUIDANCE CONTINUES TO INDICATE A MILLER "A" TYPE 
CYCLOGENESIS EVENT WITH THE SURFACE LOW TRACKING NE IN CONJUNCTION 
WITH THE DAMPENING BUT NEGATIVE TILED KICKER SHORTWAVE TROUGH  
THROUGH THE LOWER MS VALLEY AND EASTERN TN ON WEDNESDAY. THE STORM 
SYSTEM BEGINS TO ACCELERATE WEDNESDAY EVENING AND OVERNIGHT...RACING 
NE INTO WESTERN NY BY DAYBREAK THURSDAY AS IT GETS PICKED BY THE 
DIGGING NORTHERN STREAM ENERGY OVER THE NORTHERN AND CENTRAL PLAINS. 

MODEL DIFFERENCES...
IT IS WITH THIS PHASING THAT MODEL DIFFERENCES BEGIN TO ARISE...WITH 
THE GFS A FAST OUTLIER...DRY SLOTTING THE REGION AS EARLY AS 00Z 
THU...WITH THE SLOWER ENVELOPE OF MODELS OF THE NAM AND EC SOME 6 TO 
9 HOURS SLOWER. DESPITE THE GFS BEING AS OUTLIER...THE FASTER 
SOLUTION IS CERTAINLY PLAUSIBLE GIVEN THE STRENGTH/AMPLITUDE
OF THE UPSTREAM STREAM. BUT FOR NOW WILL CONTINUE WITH THE
SLOWER TIMING...BUT THIS TIMING DISCREPANCY WILL NEED TO BE 
EVALUATED AND SCRUTINIZED FURTHER WITH THE UPCOMING 12Z/01 MODEL RUN 
AS THE POTENTIAL FOR A HIGH IMPACT/SEVERE WEATHER EVENT IS POSSIBLE 
DURING THIS IMPORTANT TIME PERIOD. 

IMPACTS...
A 60 TO 70KT WARM AIR CONVEYOR BELT WILL DELUGE THE REGION WITH 
TROPICAL MARITIME AIR ON WEDNESDAY. RESIDUAL LOW-LEVEL DRY AIR
FORMERLY DEPOSITED BY THE OFFSHORE SURFACE HIGH WILL UNDERGO 
COOLING AS IT PRECIPITATES INTO THE AIRMASS...ESTABLISHING A 
VERY SHALLOW IN-SITU CAD AIRMASS ACROSS CENTRAL NC. DUE TO THE 
STRONG WAA OF TROPICAL AIRMASS AND THE SHALLOW RESIDUAL COOL 
POOL...TEMPERATURES SHOULD STILL BE ABLE TO RISE DURING THE
DAYTIME HOURS...BUT MUCH SLOWER IN THE NW PIEDMONT. 
AFTERNOON TEMPS IN THE LOWER TO MID 50S NW TO MID 60S SE. 

STRONGER/DEEPER LAYER ASCENT SPREADS ACROSS THE AREA LATE
WEDNESDAY AFTERNOON AND INTO THE EVENING AS DAMPENING
S/W TROUGH LIFTS ACROSS THE AREA...WITH MODELS OFFERING
SOME SIGNALS OF DUAL UPPER JET JUXTAPOSITION ATTEMPTING
TO CONGLOMERATE ACROSS SE NC. COMBINED WITH A CONVECTIVE
MODE OF PRECIP AS LOW-LEVEL FORCING ARRIVES WITH SURFACE
COLD FRONT PASSAGE...MUCH OF CENTRAL NC COULD SEE RAINFALL AMOUNTS
OF 1 TO 2 INCHES. 

AS WEDGE BOUNDARY LIFTS NORTH INTO VA...TEMPS AND DEWPOINTS RISE 
WELL INTO THE 60S WITH ALL OF CENTRAL NC WELL IN THE WARM SECTOR. IT 
IS AT THIS TIME PERIOD THAT THE AFOREMENTIONED MODEL DIFFERENCES ARE 
CRITICAL...AS THE SLOWER NAM SOLUTION ALLOWS A LONGER PERIOD TO 
ADVECT A TRUE MARITIME TROPICAL AIRMASS WITH SFC BASED INSTABILITY 
OF 500 TO 700 J/KG INTO CENTRAL AND EASTERN NC....WHILE THE GFS AND 
EC KEEP THE SFC BASED INSTABILITY OFFSHORE. IF THE SFC BASE 
INSTABILITY CAN DEVELOP...THE STRONG KINEMATICS WITH GOOD LOW-LEVEL
VEERING WILL RESULT IN A THREAT OF STRONG DAMAGING WINDS(WITHIN  
A CONVECTIVE LINE SEGMENT) AND ISOLATED TORNADOES (WITH DISCRETE 
SUPERCELLS). TIMING REMAINS DIFFICULT GIVEN THE MODEL DIFFERENCES.
THE FASTER GFS WOULD SUGGEST A SEVERE THREAT FROM NOON TO 
TO 8PM...WITH THE SLOWER NAM FAVORING 6PM TO 2AM. 

FOR THURSDAY: ANY LINGERING SHOWERS SHOULD QUICKLY EXIT BY 
DAYBREAK. BRIEF GRADIENT W-NW GUSTINESS POSSIBLE FIRST HALF OF THE 
DAY AS HIGH BUILDS INTO THE AREA FROM THE WEST. HIGHS NEAR 60 NW TO
MID 60S SE.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... 
AS OF 245 AM TUESDAY...

THURSDAY NIGHT THROUGH FRIDAY NIGHT: AS A MID LEVEL POLAR LOW DIGS 
ACROSS THE UPPER MIDWEST THROUGH FRIDAY...A LARGE TROUGH WILL BE 
LOCATED ACROSS MUCH OF THE EASTERN 2/3RDS OF THE COUNTRY. AS SURFACE 
HIGH PRESSURE BUILDS IN FROM THE WEST...THE SURFACE FRONT WILL 
CONTINUE TO MOVE OFFSHORE THURSDAY NIGHT. WITH INCREASING 
SUBSIDENCE/DOWN SLOPE LOW LEVEL FLOW IN PLACE...CLOUDS SHOULD 
GRADUALLY CLEAR OUT AND ALLOW OVERNIGHT LOWS TO FALL INTO THE MID 
30S TO UPPER 40S. CONTINUED COLD AIR ADVECTION ON FRIDAY WILL RESULT 
IN THICKNESS VALUES RANGING FROM 1315-1325M. ALSO...AMPLE HIGH 
CLOUDS WILL BE IN PLACE ACROSS THE REGION AS A STRONG JET REMAINS 
OVER THE REGION. AS A RESULT...TEMPS WILL BE ON THE COOL SIDE ON  
FRIDAY...GENERALLY IN THE 50S AREAWIDE.   

SATURDAY THROUGH SATURDAY NIGHT: AS A SHORT WAVE ROUNDS THE BASE OF 
THE BROAD TROUGH THAT IS IN PLACE ACROSS THE EASTERN UNITED 
STATES...BOTH THE ECMWF AND GFS ARE SHOWING A SURFACE LOW DEVELOPING 
OFF THE NORTH CAROLINA COAST. GFS SHOWS A DEEPER LOW DEVELOPING AND 
THEREFORE RESULTS IN SIGNIFICANTLY MORE ATLANTIC MOISTURE MOVING 
INTO CENTRAL NORTH CAROLINA...ESPECIALLY THE NORTHERN PORTIONS OF 
THE CWA. AM A LITTLE SKEPTICAL ABOUT THE AMOUNT OF QPF THE GFS 
GENERATES ACROSS THE REGION...GIVEN THE LOCATION OF THE LOW BEING AS 
FAR OFFSHORE AS THE MODEL PROGS IT TO BE. NEVERTHELESS...GIVEN THE 
SURFACE LOW AND STRONG UPPER SUPPORT (STRONG UPPER JET CORE REMAINS 
OVER THE REGION THROUGH AT LEAST SATURDAY AFTERNOON)...MEASURABLE 
PRECIP WILL BE POSSIBLE ESPECIALLY OVER THE NORTHERN PIEDMONT AND 
COASTAL PLAIN. ON ANOTHER NOTE...PRELIMINARY SOUNDINGS/THICKNESS 
VALUES WOULD INDICATE A CHANCE FOR WET SNOW ACROSS THE FAR NORTHWEST 
PORTION OF THE CWA. HOWEVER...GIVEN THE GFS HAS ONLY RECENTLY BEGUN 
TO HINT AT THIS SCENARIO AND THE ECMWF HAS BEEN FAIRLY CONSISTENT 
WITH NOT DEEPENING THE LOW AS MUCH AND ALSO THAT THIS IS THE DAY 5 
TIME FRAME...WILL MAINTAIN A SLIGHT CHANCE OF RAIN OVER THE 
EAST/NORTHWEST CWA SATURDAY. THIS WILL HAVE TO BE MONITORED CLOSELY 
BY FUTURE SHIFTS. LOWS WILL GENERALLY BE IN THE UPPER 20S TO LOWER 
30S... AND HIGHS IN THE MID 40S TO LOWER 50S.  

SUNDAY THROUGH MONDAY: A CHILLY SURFACE HIGH WILL DOMINATE THROUGH 
THIS PART OF THE FORECAST...WITH DRY AND PARTLY CLOUDY CONDITIONS 
EXPECTED...AS WELL AS BELOW NORMAL TEMPERATURES.

&&

AVIATION /06Z TUESDAY THROUGH SATURDAY/...
AS OF 1230 AM TUESDAY...

VFR CONDITIONS WILL PREVAIL DURING THE NEXT 24 HOURS... AS HIGH 
PRESSURE BUILDS INTO THE REGION FROM THE WEST. HIGH PRESSURE WILL 
SETTLE OVERHEAD BY TUESDAY AFTERNOON ALLOWING WINDS TO BECOME LIGHT 
AND VARIABLE...WITH MOSTLY SUNNY SKIES.

A STRONG LOW PRESSURE SYSTEM OVER THE GULF COAST STATES WILL MOVE NE 
TOWARD THE CAROLINAS WEDNESDAY AND AFFECT THE REGION LATE WEDNESDAY 
THROUGH WEDNESDAY NIGHT. WIDESPREAD SHOWERS...IFR TO LIFR 
CEILING/VISIBILITY RESTRICTIONS...AND STRONG TURBULENCE WILL 
ACCOMPANY THIS WEATHER FEATURE. POTENTIAL FOR LOW LEVEL WIND SHEAR 
BY EARLY WEDNESDAY MORNING AS WINDS JUST ABOVE THE SURFACE INCREASE 
SUBSTANTIALLY OUT OF THE SE WHILE NEAR SURFACE WINDS WILL BE LIGHT 
AND VARIABLE. THESE CONDITIONS MAY PERSIST WELL INTO WEDNESDAY 
AFTERNOON. 

THE MOST ADVERSE WEATHER CONDITIONS ASSOCIATED WITH THE AREA OF LOW 
PRESSURE SHOULD OCCUR FROM MID DAY WEDNESDAY THROUGH LATE WEDNESDAY 
NIGHT. EXPECT WIDESPREAD IFR/MVFR CEILINGS AND VISIBILITIES WITH 
RAIN WEDNESDAY MORNING INTO WEDNESDAY AFTERNOON TRANSITIONING TO 
SHOWERS AND ISOLATED THUNDERSTORMS WEDNESDAY NIGHT. 

THE AREA OF LOW PRESSURE WILL EXIT CENTRAL NORTH CAROLINA EARLY 
THURSDAY...ALLOWING HIGH PRESSURE TO BUILD IN FROM THE WEST. A 
FAIRLY TIGHT PRESSURE GRADIENT WILL RESULT IN BLUSTERY CONDITIONS 
THURSDAY...SUBSIDING BY LATE AFTERNOON.

VFR CONDITIONS EXPECTED FRIDAY THROUGH SATURDAY.

&&

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

&&

$$

SYNOPSIS...CBL
NEAR TERM...CBL
SHORT TERM...CBL
LONG TERM...KRR
AVIATION...KRR/WSS