FXUS62 KRAH 091728
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1230 PM EST WED DEC 9 2009
.SYNOPSIS...
A COLD FRONT WILL MOVE EAST THROUGH THE REGION EARLY THIS EVENING...
USHERING IN A MUCH COLDER AIR MASS FOR THURSDAY THROUGH FRIDAY.
ANOTHER STORM SYSTEM WILL AFFECT THE SOUTHEAST STATES OVER THE
WEEKEND.
&&
.NEAR TERM /THROUGH TODAY/...
AS OF 1050 AM WEDNESDAY...
WIDESPREAD RAINFALL AMOUNTS OF THREE-QUARTERS OF AN INCH TO ONE AND
ONE QUARTER OF AN INCH HELPED IN LOCKING IN THE STABLE WEDGE AIRMASS
REGIME OVER THE FORECAST AREA...AND THWARTING ANY SEVERE THREAT AS
THE CONVECTIVE LINE RACED EASTWARD ACROSS THE CWA OVER THE PAST
COUPLE OF HOURS. STRONGEST WIND GUST REPORTED WAS 37KTS AT WADESBORO
(KAFP) IN ANSON COUNTY. OTHERWISE...WIND GUSTS WERE GENERALLY 25 TO
30KTS.
WITH THE CONVECTION CURRENTLY MOVING OFFSHORE...THE REST OF TODAY
WILL BE DRY...WITH ABRUPT CLEARING (ALREADY NOTED ON VISIBLE
IMAGERY)...OVERSPREADING THE AREA IN THE REGION OF STRONG SUBSIDENCE
AND DRY MID-LEVEL SURGE BEHIND THE EXITING S/W ENERGY.
THE WEDGE REGIME WILL INDEED ERODE TODAY...BUT NOT BY THE PSEUDO
WARM/WEDGE FRONT AS PREVIOUSLY THOUGHT...BUT RATHER BY STRONG
VERTICAL MIXING AND WAA...COMPLIMENTS OF A 50 TO 60KT LOW-LEVEL JET.
HOWEVER...THE EROSION OF THE DAMMING REGION ACROSS THE WESTERN
PIEDMONT COULD BE WELL DELAYED UNTIL LATE IN THE DAY ~21Z AND/OR
HOLD UNTIL THE COLD FRONTAL PASSAGE...AS DEPICTED BY THE NAM BUFR
SOUNDINGS. THIS WILL HAVE NEGATIVE IMPACTS ON BOTH TEMPERATURES
(COOLER) AND THE EXPECTED GUSTY/STRONG WINDS TODAY(WEAKER). OTHER
THAN BEING DELAYED BY A FEW HOURS...THE IMPACTS ACROSS THE EASTERN
HALF OF THE FORECAST AREA WILL NOT BE AS SIGNIFICANT... WITH THE
WEDGE REGIME MIXING OUT BY NOON...ALLOWING PERIODIC GUSTS OF
30-40MPH. WILL CONTINUE THE WIND ADVISORY FOR THE ENTIRE CWA UNTIL
6PM...BUT BELIEVE THE WESTERN PIEDMONT WILL LIKELY SEE
WIND GUSTS MUCH WEAKER...IN THE 20 TO 30 MPH AND DELAYED UNTIL LATE
IN THE AFTERNOON.
WITH THE SLOWER WEDGE EROSION ACROSS THE WEST...HAVE LOWERED
HIGHS TODAY A FEW DEGREES...INTO THE MID TO UPPER 50S.
ELSEWHERE...WELL IN THE WARM AIR REGIME...HIGHS IN THE MID 60S
CENTRAL LOCATIONS TO LOWER 70S SE.
&&
.SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/...
AS OF 230 AM WEDNESDAY...
FOR TONIGHT: THE COLD FRONT IS EXPECTED TO HAVE MOVED EASTWARD INTO
THE COASTAL PLAIN BY EARLY EVENING. ONCE IT SHIFTS OFF THE COAST
TOWARD MIDNIGHT... WINDS IN THE LOWEST HALF KM BEGIN TO DECREASE
ACCORDING TO THE LATEST MODEL GUIDANCE... AND WE SHOULD BE ABLE TO
LET THE WIND ADVISORY EXPIRE AT THAT TIME. BUT THIS SURFACE BASED
LAYER WILL REMAIN WELL MIXED THROUGH THE NIGHT AS IT COOLS
UNIFORMLY... THUS EXPECT GUSTS TO STILL BE UP IN THE 30-35 MPH RANGE
IN THE EVENING... TAPERING DOWN THROUGH THE NIGHT. THE LOW AND MID
LEVELS DRY OUT NICELY BUT THE VERY FAST FLOW FROM 500 MB ON UP AND
MODEL ACCORD REGARDING A STREAM OF MOISTURE ON THE 320K SURFACE
PASSING OVER NC INDICATE CONSIDERABLE HIGH CLOUDINESS THROUGH THE
NIGHT... THUS EXPECT SKIES TO BE PARTLY TO MOSTLY CLOUDY. TIMING OF
THE RUSH OF COLDER AIR EAST OF THE MOUNTAINS IS DIFFICULT TO GAUGE
BUT CONSIDERING THE LATEST MODEL OUTPUT AND THE VERTICAL MIXING
OVERNIGHT... EXPECT LOWS TO RANGE FROM 34 TO 45.
FOR THURSDAY THROUGH FRIDAY NIGHT: QUIET BUT COLD. THE UPPER LEVEL
MOISTURE CLEARS OUT EARLY THURSDAY... AND WITH DEEP LAYER SUBSIDENCE
AND DRY AIR THROUGH THE COLUMN... WE SHOULD SEE MOSTLY SUNNY SKIES
THROUGH MUCH OF THE DAY. ANOTHER ROUND OF BETTER MOISTURE IN THE
315-330K LAYER ARRIVES WITHIN THIS FAST FLOW FRIDAY INTO FRIDAY
NIGHT... SO EXPECT MORE HIGH CLOUDS... LIKELY OROGRAPHICALLY
ENHANCED FRIDAY MORNING GIVEN THE VERTICAL THERMAL STRUCTURE.
OTHERWISE... AT THE SURFACE... CHILLY HIGH PRESSURE WILL BUILD INTO
AND OVER NC THROUGH FRIDAY NIGHT. THIS HIGH IS CURRENTLY PRODUCING
SUBZERO TEMPS OVER EASTERN CO AND WESTERN NE/KS... AND WILL ONLY
HAVE TIME TO MODIFY SOMEWHAT BEFORE ITS CORE REACHES NC. LOW LEVEL
THICKNESSES CONTINUE TO FALL THROUGH THURSDAY AND REALLY BOTTOM OUT
FRIDAY... BELOW 1270 M IN THE MORNING... OVER 40 M BELOW NORMAL. THE
LOCAL TEMP FORECASTING TOOL FACTORING IN A DRY ADIABATIC PROFILE
BELOW 900 MB YIELDS HIGHS IN THE MID 40S TO LOWER 50S THURSDAY AND
IN THE 40S ON FRIDAY... AND HAVE ADJUSTED HIGHS DOWN SLIGHTLY BOTH
DAYS. LOWS MAINLY IN THE 20S THURSDAY NIGHT AND FRIDAY NIGHT. VERY
DRY AIR PERSISTS BELOW 12 THOUSAND FEET ACCORDING TO NAM/GFS
FORECAST SOUNDINGS... THUS DO NOT EXPECT ANY PRECIP IN THE CWA
BEFORE DAYBREAK SATURDAY. -GIH
&&
.LONG TERM /SATURDAY THROUGH TUESDAY/...
AS OF 450 AM WEDNESDAY...
FOR SATURDAY THROUGH SUNDAY: THE LATEST MODELS ARE SHOWING
SIGNIFICANT CHANGES FROM THEIR EARLIER RUNS... LEADING TO A
LOW-CONFIDENCE MEDIUM RANGE FORECAST. A VERY FAST MID LEVEL FLOW
PERSISTS FROM THE SOUTHWEST STATES AND NORTHWEST MEXICO ACROSS THE
CAROLINAS THROUGH THE WEEKEND... WHILE THE SURFACE HIGH SETTLES OVER
NC THROUGH SATURDAY BEFORE DRIFTING NORTHEAST OFF THE MIDATLANTIC
COAST BY SUNDAY. THE LATEST GFS/ECMWF/CANADIAN HAVE THROWN QUITE A
WRENCH INTO THE FORECAST... WITH ALL OF THEM TRENDING MUCH SLOWER
BOTH WITH THE NORTHWARD MOVEMENT OF THE FRONT TO OUR SOUTH AND WITH
THE ASSOCIATED ONSET OF ISENTROPIC UPGLIDE ATOP THE SURFACE RIDGE.
THE GFS FOR EXAMPLE IS 12-18 HOURS SLOWER THAN JUST TWO RUNS AGO...
AND A SIMILAR DELAY IS NOTED ON THE ECMWF AND GEFS MEAN AS WELL.
FORECAST SOUNDINGS FROM BOTH THE GFS AND 06Z NAM HOLD ONTO A RATHER
DRY SUBCLOUD LAYER WELL INTO SATURDAY... AND IT SHOULD TAKE SOME
TIME TO SATURATE THIS LAYER. WITH SUCH A CLEAR MODEL TREND... HAVE
SLOWED DOWN BRINGING PRECIP INTO THE AREA... KEEPING CENTRAL NC DRY
THROUGH SATURDAY (ALBEIT WITH MOSTLY CLOUDY SKIES) THEN BRINGING
RAIN CHANCES ACROSS SOUTHERN SECTIONS SATURDAY NIGHT BEFORE
EXPANDING THEM CWA-WIDE ON SUNDAY. HAVE LOWERED POPS TO CHANCES
BASED IN LARGE PART ON THE LATEST GEFS MEAN... WHICH HOLDS THE
BETTER PROBABILITIES OF MEASURABLE RAIN MAINLY TO OUR SOUTH AND
EAST. ALSO... WITH SUCH A FAST FLOW ALOFT... THE MODELS SHOULD
CONTINUE TO HAVE A TOUGH TIME WITH THEIR MAGNITUDE AND TIMING OF
FORCING FEATURES... LEADING US TO FAVOR A CONSERVATIVE SOLUTION WITH
THE LOWER POPS. TEMPERATURES STAY RATHER COOL THROUGH THE WEEKEND...
PARTICULARLY IF WE GET PRECIP FALLING INTO THE COOL SURFACE WEDGE
INTO SUNDAY. BASED ON GFS FORECAST SOUNDINGS WE STILL HAVE A CHANCE
OF SUBFREEZING SURFACE AIR OVER THE PIEDMONT AT THE TIME OF PRECIP
ONSET... HOWEVER GIVEN THAT CONFIDENCE IN THIS ONSET TIMING IS
PRETTY LOW... AND WITH INDICATIONS ON THE GFS OF DRYING ABOVE -9C
JUST AS THE LOW LEVELS SATURATE... WILL KEEP TEMPS AT OR ABOVE
FREEZING SATURDAY NIGHT/SUNDAY AND HOLD ALL PRECIP AS LIQUID FOR
NOW.
FOR SUNDAY NIGHT THROUGH TUESDAY: HAVE KEPT THE FORECAST MAINLY AS
IS. THE GFS/ECMWF SHOW A SHORTWAVE TROUGH APPROACHING MONDAY NIGHT/
TUESDAY AS WEAK HIGH PRESSURE GIVES WAY TO A MILD SOUTHWEST FLOW
AHEAD OF A COLD FRONT. WILL RETAIN THE CHANCE OF RAIN AHEAD OF THE
FRONT ON TUESDAY. EXPECT TEMPS NEAR NORMAL. -GIH
&&
.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
AS OF 1230 PM WEDNESDAY...
A COLD FRONT WILL MOVE EAST ACROSS THE STATE THIS AFTERNOON.
STRONG WINDS AHEAD OF THE FRONT AND ASSOCIATED WITH A STRONG
LOW PRESSURE SYSTEM OVER THE GREAT LAKES REGION WILL RESULT IN GUSTY
SWLY WINDS OF 20 TO 25 MPH WITH GUSTS TO 35 MPH THIS AFTERNOON.
ANY SUB VFR CEILINGS ARE EXPECTED TO QUICKLY LIFT AND DISSIPATE AS
SUBSIDENT DRYING OVERSPREADS THE AREA. WINDS WILL DIMINISH AFTER
SUNSET...VEERING TO NWLY OVERNIGHT AT 5 TO 10KTS.
A COLD AND DRY ARCTIC HIGH PRESSURE WILL BEGIN TO BUILD INTO THE AREA
ON THURSDAY...BRINGING VFR CONDITIONS THROUGH SATURDAY. THE NEXT
CHANCE FOR SUB VFR CONDITIONS WILL ARRIVE SATURDAY EVENING/NIGHT AS
AN AREA OF LOW PRESSURE DEVELOPS ALONG THE GULF COAST AND TRACKS
NORTHEAST UP THE SOUTHEAST COAST ON SUNDAY.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY FROM 6 AM TO 6 PM EST WEDNESDAY FOR NCZ007>011-
021>028-038>043-073>078-083>086-088-089.
&&
$$
SYNOPSIS...CBL
NEAR TERM...CBL
SHORT TERM...HARTFIELD
LONG TERM...HARTFIELD
AVIATION...CBL
