FXUS62 KRAH 301921
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
220 PM EST MON NOV 30 2009

.SYNOPSIS...
A COLD FRONT WILL CROSS THE REGION LATE THIS AFTERNOON. HIGH 
PRESSURE WILL BUILD INTO THE AREA LATE TONIGHT AND SETTLE OVERHEAD 
ON TUESDAY. A STRONG LOW PRESSURE SYSTEM OVER GULF COAST REGION WILL 
THEN MOVE NORTHEAST LATE WEDNESDAY AND WEDNESDAY NIGHT...BRINGING 
WIDESPREAD RAIN AND BLUSTERY WINDS.

&&

.NEAR TERM /THROUGH TUESDAY/...
AS OF 210 PM...

TONIGHT...SURFACE COLD FRONT WILL BE CROSSING THE FORECAST AREA 
BETWEEN 21Z-02Z. OVERALL PRECIP INTENSITY HAS DECREASED AHEAD AND 
ALONG THIS FEATURE...INDICATIVE OF MARGINAL LIFT AND MOISTURE. HAVE 
NOTED BAND OF HEAVIER PRECIP OCCURRING ALONG AND IMMEDIATELY WEST OF 
THE MOUNTAINS. THIS BAND OF PRECIP APPEARS TO BE OCCURRING ALONG THE 
850MB TROUGH. THIS FEATURE PROGGED TO SWEEP THROUGH THE AREA BETWEEN 
00Z-03Z. WHILE PRECIP AMOUNTS ARE EXPECTED TO BE LIGHT...STILL 
EXPECT TO SEE MEASURABLE RAIN AT MOST SITE LATE THIS AFTERNOON AND 
EARLY EVENING. THUS WILL MAINTAIN LOW END CATEGORICAL POPS IN THE NW 
PIEDMONT AND LIKELY POPS ELSEWHERE AS THE SURFACE AND 850MB TROUGH 
CROSS THE REGION. 

CLEARING IN THE WESTERN TN VALLEY AT 18Z ALIGNS WELL WITH THE 700MB 
TROUGH AXIS. THIS MID LEVEL TROUGH WILL ENTER THE REGION AFTER 
00Z AND SHOULD EXIT THE COASTAL PLAIN SHORTLY AFTER 06Z. 

COLD AIR ADVECTION WILL RESULT IN A PERIOD OF BLUSTERY CONDITIONS 
WITH THE PASSAGE OF THE FRONT. MAY SEE INFREQUENT WIND GUSTS OUT OF 
THE N-NW BETWEEN 20-25KTS WITHIN 3-4 HOURS OF FRONTAL PASSAGE.

TUESDAY...S/W RIDGE AND ASSOCIATED SURFACE HIGH PRESSURE WILL 
PROVIDE OUR REGION WITH PLENTY OF SUNSHINE. LOW LEVEL THICKNESSES 
SUPPORT MAX TEMPS IN THE MID/UPPER 50S IN THE PIEDMONT/NORTHERN 
COASTAL PLAIN TO AROUND 60 IN THE SE.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
AS OF 245 AM MONDAY...

...SIGNIFICANT STORM SYSTEM EXPECTED TO AFFECT CENTRAL NORTH 
CAROLINA ON WEDNESDAY AND WEDNESDAY NIGHT...

OVERVIEW:
A POTENT SOUTHERN STREAM UPPER LOW CURRENTLY CENTERED OVER THE 
NORTHERN GULF OF CALIFORNIA WILL MOVE EASTWARD INTO CENTRAL TX BY 
12Z WED MORNING...INITIATING CYCLOGENESIS ALONG THE TX/LA GULF 
COAST. AT THE SAME TIME...A POTENT NORTHERN STREAM TROUGH IS 
EXPECTED TO BEGIN DIGGING/AMPLIFYING SOUTHWARD THROUGH THE UPPER 
MIDWEST. LATER WED AND WED NIGHT...THE SOUTHERN STREAM UPPER LOW IS 
EXPECTED TO WEAKEN INTO AN OPEN WAVE AND LIFT NORTHEASTWARD THROUGH 
THE TN/OH VALLEYS ALONG THE EASTERN PERIPHERY OF THE AMPLIFYING 
NORTHERN STREAM TROUGH. THE SURFACE LOW INITIALLY ALONG THE TX/LA 
GULF COAST IS EXPECTED TO INTENSIFY OVER THE DEEP SOUTH DURING THE 
DAY WED...FURTHER INTENSIFYING WED NIGHT OVER THE EASTERN TN/OH 
VALLEYS. VIRTUALLY ALL MODEL GUIDANCE NOW SUGGESTS A MILLER TYPE-A 
SCENARIO...WITH ONE PARENT SFC LOW MOVING NORTHEAST ALONG OR JUST 
WEST OF THE SOUTHERN APPALACHIANS...AND LITTLE OR NO COASTAL 
DEVELOPMENT OVER THE CAROLINAS/MID-ATLANTIC. A WEAK (~1020-1022 MB) 
SFC HIGH WILL BE IN PLACE OVER THE CAROLINAS ON TUE...MOVING QUICKLY 
OFFSHORE TUE NIGHT. AS A RESULT OF THE DRY AIR DEPOSITED BY THE SFC 
HIGH...WE WILL SEE AN IN-SITU CAD WEDGE DEVELOP AT THE ONSET OF 
PRECIPITATION ON WED. HOWEVER...GIVEN THAT THE PARENT HIGH WILL BE 
WELL OFFSHORE AND THAT THE PARENT SURFACE CYCLONE IS EXPECTED TO 
TRACK WEST OF THE MOUNTAINS...STRONG LOW LEVEL SOUTHERLY/SE FLOW AND 
WARM ADVECTION OFF THE ATLANTIC SHOULD EFFECTIVELY ERODE THE IN-SITU 
WEDGE...WITH MOST OR ALL OF CENTRAL NC GETTING WARM-SECTORED LATE 
WED EVENING/NIGHT.

TEMPERATURES:
VERY TRICKY/ATYPICAL TEMPERATURE FORECAST ON WED/WED NIGHT. EXPECT 
TEMPERATURES IN THE 50S DURING THE DAY...FALLING AT LEAST SEVERAL 
DEGREES AT THE ONSET OF PRECIPITATION WED AFTERNOON. LATER WED 
EVENING/NIGHT...EXPECT TEMPERATURES TO RISE INTO THE MID/UPPER 60S 
FROM S/SE TO N/NW AS STRONG SOUTHERLY/SOUTHEASTERLY FLOW ADVECTS A 
MARITIME TROPICAL AIRMASS FROM THE ATLANTIC INTO THE CAROLINAS... 
OVERCOMING/ERODING THE IN-SITU WEDGE INITIALLY IN PLACE WED AFT/EVE. 
THERE IS SOME UNCERTAINTY STILL WITH TEMPS WED EVE/NIGHT. THE 
UNCERTAINTY PRIMARILY REVOLVES AROUND THE TIMING OF THE COLD FRONT 
MOVING INTO THE AREA FROM THE WEST. ALTHOUGH THE NAM/ECMWF/CANADIAN 
SOLUTIONS ARGUE FOR A COLD FRONTAL PASSAGE CLOSER TO SUNRISE THU... 
THE GFS ARGUES FOR A COLD FRONTAL PASSAGE AROUND MIDNIGHT...WHICH 
WOULD RESULT IN FALLING TEMPS AFTER MIDNIGHT.

PRECIPITATION:
THE OVERALL LIFT/DYNAMICS ASSOC/W THIS SYSTEM WILL BE QUITE 
STRONG...AND VIRTUALLY ALL MODEL GUIDANCE SUGGESTS AT LEAST A 
WIDESPREAD 1" OF RAIN...WITH UP TO 2" OR LOCALLY HIGHER AMOUNTS 
POSSIBLE (ESPECIALLY IF THE ECMWF SOLUTION IS CLOSER TO REALITY). 
EXPECT THE BULK OF PRECIPITATION TO FALL BETWEEN 21Z WED AND 06-12Z 
THU. IT IS WORTH NOTING THAT THE WESTWARD TREND IN THE SFC LOW TRACK 
MAY RESULT IN LOWER QPF AMOUNTS THAN PREVIOUSLY ANTICIPATED.

SEVERE THREAT:
GIVEN THAT A MILLER TYPE-A SCENARIO NOW APPEARS LIKELY BASED ON THE 
LATEST 00Z ECMWF/GFS/NAM/CANADIAN SOLUTIONS...THE CAROLINAS ARE MORE 
APT TO GET WARM-SECTORED FOR A TIME LATE WED EVENING/NIGHT. SO...IT 
IS LOOKING MORE LIKELY THAT AT *LEAST* A PORTION OF CENTRAL NC COULD 
SEE A MARITIME TROPICAL AIRMASS FROM THE ATLANTIC. GIVEN THE 
EXPECTED STRONG SYNOPTIC FORCING (SOUTHERN STREAM WAVE GOING 
NEGATIVE TILT AS IT LIFTS NORTHEAST JUST WEST OF THE MOUNTAINS...NOT 
TO MENTION A DUAL-JET CONFIGURATION OVER THE SOUTHEAST STATES/ 
CAROLINAS) AND THE STRENGTH OF LOW-LEVEL WIND FIELDS (60-65 KT 
SOUTHERLY H85 JET) AND SHEAR/HELICITY PARAMETERS... THERE WILL 
ACCORDINGLY BE A THREAT FOR SEVERE THUNDERSTORMS AND ISOLATED 
TORNADOES. THE ONLY LIMITING FACTOR PRECLUDING THE POSSIBILITY OF A 
SIGNIFICANT SEVERE WEATHER EVENT LATE WED EVENING/ NIGHT APPEARS TO 
BE TIED TO WHETHER OR NOT A TRUE MARITIME TROPICAL AIRMASS WITH SFC 
BASED INSTABILITY CAN ADVECT INTO PLACE ACROSS ALL OR PORTIONS OF 
THE AREA. THE LATEST NAM FCST SOUNDINGS ARE FAIRLY OMINOUS...SHOWING 
TEMPS RISING INTO THE MID/UPPER 60S WITH DEWPOINTS APPROACHING 65F 
LATE WED NIGHT. IT IS WORTH NOTING THAT THE OVERALL SYNOPTIC PATTERN 
IS FAIRLY SIMILAR (ALBEIT NOT AS ROBUST) TO THE PATTERN THAT 
RESULTED IN THE NOVEMBER 22, 1992 SEVERE WEATHER OUTBREAK ACROSS 
CENTRAL NC. -VINCENT

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/... 
AS OF 315 AM MONDAY...

THURSDAY AND THURSDAY NIGHT:
AS THE INTENSE LOW PRESSURE SYSTEM MOVES NORTHEAST TOWARD/INTO NEW 
ENGLAND THURSDAY...A STRONG COLD FRONT WILL SWEEP ACROSS CENTRAL NC. 
LATEST MODEL GUIDANCE INDICATES THAT THE COLD FRONT SHOULD SWEEP 
THROUGH THE ENTIRE AREA BY NOON THURSDAY. AS A RESULT...HIGH TEMPS 
WILL LIKELY BE ATTAINED DURING THE MORNING HOURS...WITH TEMPS 
FALLING INTO THE 50S BY LATE MORNING TO EARLY AFTERNOON BEHIND THE 
COLD FRONT...ALTHOUGH THIS WILL ULTIMATELY DEPEND ON THE EXACT 
TIMING OF THE FRONT. EXPECT PRECIP CHANCES TO BE OVER BY OR SHORTLY 
AFTER SUNRISE THU...WITH SKIES RAPIDLY CLEARING IN THE WAKE OF THE 
FRONT. EXPECT CHILLY LOW TEMPS BEHIND THE FRONT THU NIGHT...WITH 
LOWS IN THE MID/UPPER 30S. -VINCENT

FRIDAY THROUGH SUNDAY:
UPPER RIDGE IN VICINITY OF OR OFFSHORE OF THE PACIFIC NW WILL 
MAINTAIN A SPLIT FLOW OVER THE EASTERN TWO-THIRDS OF THE U.S. WITH 
THE NORTHERN STREAM MORE DOMINATE. THIS WILL LEAD TO CONFLUENCE NEAR 
OR NORTH OF CENTRAL NC. SURFACE HIGH WILL BUILD INTO CENTRAL NC FROM 
THE WEST THU NIGHT/FRI AND SETTLE OVER THE REGION THROUGH THE 
WEEKEND. THE AIR MASS ASSOCIATED WITH THE HIGH SHOULD BE MODIFIED 
ARCTIC SO EXPECT DRY AND SEASONABLY COOL CONDITIONS. MAY SEE A 
REINFORCING SHOT OF COOL AIR LATE FRI OR EARLY SATURDAY AS A DRY 
COLD FRONT ASSOCIATED WITH A MINOR S/W IN THE NORTHERN STREAM 
CROSSES THE AREA. -WSS

&&

AVIATION /18Z MONDAY THROUGH SATURDAY/...
AS OF 1215 PM MONDAY...

A COLD FRONT WILL AFFECT CENTRAL NC LATE THIS AFTERNOON AND THIS 
EVENING WITH NUMEROUS SHOWERS EXPECTED IN VICINITY OF THE FRONT 
ALONG WITH A PERIOD OF 3-5 HOURS OF MVFR CEILINGS. THE SURFACE FRONT 
SHOULD CROSS THE PIEDMONT COUNTIES INCLUDING KINT...KGSO AND 
KRDU...BETWEEN 21Z-00Z...AND THE SANDHILLS AND COASTAL PLAIN 
INCLUDING KFAY AND KRWI BETWEEN 23Z-02Z. WINDS WILL BE GUSTY AHEAD 
AND BEHIND THE FRONT WITH FREQUENT GUSTS BETWEEN 20-25KT. STRONG 
SUBSIDENCE BEHIND THE 850MB TROUGH THE CROSSES THE AREA BETWEEN 
00Z-06Z WILL AID IN THE RAPID DISSIPATION OF CLOUD COVERAGE FROM 
WEST-TO-EAST AFTER 00Z WITH MOST OF CENTRAL NC CLEAR BY 07Z. 

HIGH PRESSURE WILL BUILD INTO THE AREA FROM THE WEST OVERNIGHT AND 
SCOOT ACROSS THE STATE ON TUESDAY. THIS WEATHER SYSTEM WILL PROVIDE 
VFR CONDITIONS THROUGH TUESDAY NIGHT. 

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...WSS
SHORT TERM...VINCENT
LONG TERM...VINCENT/WSS
AVIATION...WSS