FXUS62 KRAH 301149
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
645 AM EST MON NOV 30 2009
.SYNOPSIS...
A COLD FRONT WILL SWEEP EAST THROUGH THE REGION THIS AFTERNOON.
HIGH PRESSURE WILL BUILD BRIEFLY OVER THE AREA FROM THE TONIGHT
THROUGH TUESDAY. A STRONG LOW PRESSURE SYSTEM OVER GULF COAST REGION
WILL THEN MOVE NORTHEAST ACROSS THE AREA...BRINGING WIDESPREAD
RAIN AND BLUSTERY WINDS WEDNESDAY AND WEDNESDAY NIGHT.
&&
.NEAR TERM /THROUGH TUESDAY NIGHT/...
AS OF 230 AM MONDAY...
TODAY AND TONIGHT...
THE NORTHERN STREAM S/W TROUGH EXTENDING FROM ONTARIO SOUTH THROUGH
THE CENTRAL PLAINS WILL CONTINUE TO PUSH EAST THROUGH THE NORTH EAST
AND MID-ATLANTIC STATE TODAY. THE ATTENDANT SFC COLD FRONT WILL
FOLLOW SUITE...PUSHING THROUGH THE CWA BETWEEN 18Z TO 00Z TUESDAY.
DESPITE MODEST H5 HEIGHT FALLS ON THE ORDER OF 60 TO 100 METERS AND
DECENT JET EXIT REGION DIVERGENCE OF A STRAIGHT 140 KT WEST TO EAST
JET NOSING ACROSS THE AREA...WEAK LOW-LEVEL CONVERGENCE (MOSTLY
SPEED CONVERGENCE) AND NO INSTABILITY TO SPEAK OF WILL RESULT IN A
LIGHT QPF EVENT WITH RAINFALL TOTALS LESS THAN A QUARTER OF AN INCH.
WILL LEAVE POPS PRETTY MUCH UNCHANGED WITH HIGH LIKELY POPS
BEGINNING IN THE WEST BY MIDDAY AND SPREADING EAST THROUGH THE
AFTERNOON. MODELS ARE CONSISTENT WITH SHOWING STRONG SUBSIDENCE AND
GOOD CAA RESULTING IN ABRUPT WEST TO EAST CLEARING BEHIND THE FROPA
THIS EVENING...MOVING THROUGH THE FORECAST AREA BY 06Z. HIGH IN THE
UPPER 50S NW TO MID 60S SE. LOWS IN THE MID TO UPPER 30S.
TUESDAY AND TUESDAY NIGHT...
FLAT RIDING ALOFT AND FURTHER MODIFICATION OF A NORTH PACIFIC
HIGH PRESSURE CELL WILL RESULT IN DRY CONDITIONS AND SEASONABLE
TEMPS ON TUESDAY. HIGHS IN THE UPPER 50S NORTH TO LOWER 60S SE.
SURFACE HIGH SHIFTS OFFSHORE TUESDAY EVENING AS GULF OF MEXICO
LOW PRESSURE SYSTEM BEGINS TO DEEPEN WITH THE APPROACH OF THE
CLOSED UPPER CYCLONE OVER WESTERN TEXAS. WARM CONVEYOR
BELT MOISTURE AND LIFT BEGINS TO SPREAD NORTH AND EAST INTO THE
REGION AHEAD OF THE LOW TUESDAY NIGHT. THE GFS IS STILL THE FASTEST
AND POSSIBLY PREMATURE WITH THE MOISTENING AND PRECIP ACROSS THE FAR
SOUTH LATE TUESDAY NIGHT/PREDAWN HOURS WEDNESDAY MORNING. WILL
CONTINUE WITH SLIGHT CHANCE POPS ACROSS THE SW PIEDMONT AT THIS
TIME...BUT BULK OF PRECIP WILL HOLD OFF UNTIL AFTER DAYBREAK.
OVERNIGHT LOWS WILL DEFINITELY BE HINDERED BY INCREASING MID AND
HIGH LEVEL MOISTURE OVERSPREADING THE AREA. WILL BUMP UP MIN TEMPS
SLIGHTLY...35 TO 40...WITH COLDEST TEMPS ACROSS THE FAR NORTHEAST
WHERE MID AND HIGH CLOUD DECK WILL BE LESS OPAQUE.
&&
.SHORT TERM /WEDNESDAY 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 /12Z MONDAY THROUGH FRIDAY/...
AS OF 645 AM MONDAY...
EXPECT SOME SURFACE GUSTINESS LATER THIS MORNING AND INTO THE
AFTERNOON AS PRESSURE GRADIENT TIGHTENS WITH APPROACH OF RAPIDLY
MOVING COLD FRONT. THE COLD FRONT WILL PUSH THROUGH CENTRAL NORTH
CAROLINA FROM 18Z IN THE FAR WEST TO AROUND 00Z TOWARD INTERSTATE
95. AS MOISTURE AND LIFT INCREASE DURING THE LATE MORNING
HOURS...EXPECT AT LEAST NUMEROUS SHOWERS AND MVFR CONDITIONS WITH
THE FRONT. THERE COULD BE A BRIEF PERIOD OF IFR CONDITIONS IN THE
HEAVIER/STRONGER SHOWERS BEFORE DRY AIR ADVECTION AND SUBSIDENCE
BEHIND THE FRONT RESULT IN ABRUPT CLEARING FROM WEST TO EAST DURING
THE EVENING.
AFTER VFR CONDITIONS TUESDAY AND TUESDAY NIGHT...A STRONG LOW
PRESSURE SYSTEM OVER THE GULF COAST STATES WILL MOVE NE ACROSS THE
CAROLINAS WEDNESDAY AND WEDNESDAY NIGHT. WIDESPREAD SHOWERS...IFR TO
LIFR CEILING/VIS RESTRICTIONS...AND STRONG TURBULENCE WILL ACCOMPANY
THE PASSAGE OF THE LOW. VFR CONDITIONS RETURN BY THURSDAY AFTERNOON.
MODESTLY GUSTY SURFACE WINDS WILL PERSIST INTO THURSDAY AFTERNOON...
WITH LIGHTER WINDS AND CONTINUED VFR CONDITIONS FRIDAY.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...CBL
NEAR TERM...CBL
SHORT TERM...VINCENT
LONG TERM...VINCENT/WSS
AVIATION...CBL/DJF
