FXUS62 KRAH 300213
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
912 PM EST SUN NOV 29 2009
.SYNOPSIS...
A COLD FRONT WILL SWEEP EAST THROUGH THE REGION ON MONDAY... THEN
HIGH PRESSURE WILL BUILD BACK INTO THE AREA FROM THE WEST MONDAY
NIGHT THROUGH TUESDAY. A STRONG LOW PRESSURE SYSTEM IS EXPECTED TO
DEVELOP ALONG THE GULF COAST LATE TUESDAY NIGHT... AND BRING
WIDESPREAD RAIN AND BLUSTERY WINDS TO THE AREA WEDNESDAY AND
WEDNESDAY NIGHT.
&&
.NEAR TERM /THROUGH MONDAY NIGHT/...
AS OF 910 PM SUNDAY...
WHILE SURFACE HIGH PRESSURE CONTINUED OVER CENTRAL NORTH CAROLINA...
THE 18Z GFS AND NAM SHOWED WEAK 700MB LIFT OVER CENTRAL NORTH
CAROLINA THIS EVENING WHICH...WITH DECENT MOISTURE ON THE 00Z KGSO
UPPER-AIR SOUNDING BETWEEN 700MB AND 500MB...RESULTED IN A FEW
SPRINKLES MAINLY NORTH OF U.S. 64 THIS EVENING. IN A RELATIVE
SENSE...COOLEST CLOUD TEMPERATURES WERE LOCATED ALONG AND NORTH OF
U.S. 64 ON IR IMAGES...AND WITH A FEW EVEN COOLER CLOUD TOPS TOWARD
THE MOUNTAINS AND THE GFS BUFR SOUNDINGS SUGGESTING LINGERING
MOISTURE IN THAT LAYER THROUGH MUCH OF THE REST OF THE NIGHT...WILL
MAINTAIN A SLIGHT CHANCE OF SPRINKLES NORTH. TOWARD THE SOUTHWEST...
LATEST REGIONAL RADAR IMAGES SHOW SCATTERED SHOWERS OVER FAR
SOUTHWEST NORTH CAROLINA TOWARD CHATTANOOGA...ON THE NOSE OF GOOD
850MB THETA-E ADVECTION BUT NOT HANDLED BY THE 18Z GFS...NAM...OR
THE LATEST RUC. WHILE LOW-LEVEL DRY AIR STILL NEEDS TO BE OVERCOME
IN CENTRAL NORTH CAROLINA...BOTH THE NAM AND THE GFS SHOW THE NOSE
OF THE 850MB THETA-E RIDGE MOVING INTO THE SOUTHWEST PIEDMONT LATE.
INTRODUCED A SLIGHT CHANCE OF A SHOWER LATE THERE AS A RESULT.
OTHERWISE...AS THE SURFACE GRADIENT TIGHTENS OVERNIGHT...ENOUGH OF A
WIND SHOULD CONTINUE ALONG WITH A GENERAL...GRADUAL INCREASE IN
CLOUDS TO RESULT IN LOWS FROM THE MID 40S TO LOWER 50S...LIKELY THE
IMMEDIATE TRIAD BEING ONE OF THE WARMER LOCATIONS.
FOR MONDAY/MONDAY NIGHT: THE COLD FRONT IS EXPECTED TO MOVE INTO THE
NORTHWEST CWA BY 16Z... PROPELLED BY THE SWIFT MID LEVEL TROUGH AXIS
AS IT MOVES TO A NEW ENGLAND / SOUTHERN APPALACHIANS POSITION BY
MONDAY EVENING...AND BY THE SURFACE HIGH PUSHING EASTWARD FROM THE
CENTRAL PLAINS. MID LEVEL HEIGHT FALLS 60-120M TO THE NORTHWEST AND
WILL BE DECENT OVER NC (40-70 M IN 12 HRS) BUT THE BETTER UPPER
FORCING IS SHUNTED TO OUR NORTHEAST WHERE HEIGHT FALLS AND MID-LEVEL
DPVA ARE GREATER. ISENTROPIC UPGLIDE IS VERY WEAK/SHALLOW/ELEVATED
TO NONEXISTENT OVER CENTRAL NC...AND FRONTAL CONVERGENCE IS MINIMAL.
PRECIPITABLE WATER VALUES DO INCREASE FROM 0.75 INCH TO 1.25 INCHES
BY 18Z. JET DYNAMICS APPEAR ROBUST... AS AN UPPER JETLET CORE
INCREASES TO OVER 140 KTS OVER NORTHERN GA RESULTING IN LOCALLY
ENHANCED UPPER DIVERGENCE OVER NC. AS SUCH... HIGH RAIN CHANCES
STILL LOOK GOOD. WILL RETAIN HIGH-END LIKELY POPS OVER THE NORTHWEST
CWA BY MID-MORNING MONDAY... EXPANDING ACROSS THE AREA IN THE
AFTERNOON. STRONG NVA...SUBSIDENCE...AND DRYING TAKE PLACE FROM WEST
TO EAST LATE MONDAY AFTERNOON THROUGH 06Z TUESDAY WITH FRONTAL
PASSAGE IN THE EAST PRIOR TO MIDNIGHT. BOTH THE 18Z GFS AND NAM
FORECAST PRECIPITABLE WATER VALUES FALLING QUICKLY TO LESS THAN 0.5
INCH BY 06Z. WITH BRISK WARM AIR ADVECTION MONDAY KEEPING LOW LEVEL
THICKNESSES OVER 1360 M... EXPECT HIGHS TO BE A BIT MILDER THAN
EARLIER EXPECTED... 59-67. MODELS AGREE ON 925 MB WINDS INCREASING
LATE TONIGHT INTO MONDAY TO 25-30 KTS... AND WITH THE ONSET OF
VERTICAL MIXING... THESE SHOULD START TO MIX DOWN TO THE SURFACE AND
HAVE INCLUDED GUSTS UP TO 25 MPH FROM MID MORNING THROUGH THE
AFTERNOON. LOWS 33-40 MONDAY NIGHT WITH CLEARING SKIES AND
DIMINISHING WINDS EARLY.
&&
.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
AS OF 230 PM SUNDAY...
TUESDAY AND TUESDAY NIGHT...S/W RIDING AND ASSOCIATED SURFACE HIGH
WILL BUILD INTO CENTRAL NC FROM THE WEST TUESDAY AND SETTLES
OVERHEAD TUESDAY NIGHT. EXPECT DRY AND SEASONABLE CONDITIONS WITH
THIS WEATHER SYSTEM WITH PLENTIFUL SUNSHINE. USING A BLEND OF THE
NAM/GFS THICKNESSES YIELD MAX TEMPS IN THE MID/UPPER 50S NW TO
AROUND 60 SE. TUESDAY NIGHT MIN TEMPS DEPENDENT UPON
ARRIVAL/OPAQUENESS OF CIRRUS SHIELD AHEAD OF STRONG UPPER LEVEL LOW
OVER TX. GFS RH PROFILE SUGGEST RATHER THICK CIRRUS SHIELD OVERHEAD
BY SUNSET TUESDAY WHILE NAM SUGGEST THICKENING CIRRUS HOLDING OFF
UNTIL CLOSER TO DAYBREAK WED. SINCE GFS HAS A TENDENCY TO
OVER-EMPHASIZE UPPER LEVEL MOISTURE AND THE GFS CURRENTLY A FAST
OUTLIER WITH THIS SYSTEM..PREFER TO LEAN TOWARD LESS CLOUDS TUESDAY
NIGHT. WITH A RELATIVELY DRY AIR MASS OVER THE REGION...NEAR SURFACE
TEMPS SHOULD COOL SIGNIFICANTLY AFTER SUNSET TUESDAY. WILL LEAN
TOWARD OR GO SLIGHTLY BELOW THE COOL SIDE OF MOS GUIDANCE TUESDAY
NIGHT.
WEDNESDAY...UNUSUALLY STRONG UPPER LEVEL LOW OVER TX 12Z WED
CONTINUES TO DEEPEN AND LIFTS NEWD DUE TO AMPLIFYING TROUGH IN THE
NORTHERN STREAM (VICINITY OF THE DAKOTAS). CONTINUED DEEPENING OF
UPPER LOW WILL INDUCE SURFACE CYCLONE OVER THE LWR MS VALLEY TO
STRENGTHEN AND LIFT NE INTO THE MID-SOUTH REGION BY 00Z. THIS WILL
INITIATE/STRENGTHEN ISENTROPIC LIFT OVER CENTRAL NC ON WEDNESDAY.
INITIAL PRECIP WILL GO TOWARD MOISTENING THE SUB CLOUD LAYER WHICH
IS PROGGED TO BE QUITE DRY AT PRECIP ONSET. AGAIN...GFS APPEARS TOO
FAST SO LEANED TOWARD A PRECIP ARRIVAL CLOSER TO THE NAM/CANADIAN.
THUS EXPECT RAIN TO DEVELOP PRIOR TO NOON IN THE WESTERN AND
SOUTHERN PIEDMONT...THEN ENVELOP THE REMAINDER OF THE REGION DURING
THE AFTERNOON. SURFACE PRESSURE PATTERN SUGGEST FOR AN
INSITU-DAMMING EVENT FOR THE PIEDMONT COUNTIES...MORE SO IN THE NW.
ONCE RAIN BECOMES ESTABLISHED...EXPECT TEMPS TO COOL 3-5 DEGREES.
THUS...MAX TEMPS WED SHOULD OCCUR PRIOR TO NOON IN THE WEST...AND BY
EARLY AFTERNOON IN THE EAST.
WEDNESDAY NIGHT...MAJORITY OF MODEL GUIDANCE SUGGESTING A MILLER "A"
SCENARIO WITH THE SURFACE LOW TRACKING NEAR OR WEST OF THE MOUNTAINS
(A BIT UNUSUAL WITH THIS TYPE OF PATTERN). THE LATEST 12Z ECMWF IS
TRENDING SLOWER WITH ITS MILLER "B" SCENARIO...DELAYING THE
FORMATION OF THE SECONDARY/COASTAL LOW UNTIL CLOSER TO 12Z THU IN
VICINITY OF NORTHERN NC OR VA. VERY STRONG KINEMATICS WORRISOME AS
NOSE OF LOW LEVEL JET (50-60KTS) MOVING INTO CENTRAL NC AROUND 06Z
THU WITH MID LEVEL WINDS STRENGTHENING TO 65-70KTS. LOW LEVEL STORM
RELATIVE HELICITY THROUGH THE ROOF. MAIN WILD CARD IS THE
AVAILABILITY OF LOW LEVEL INSTABILITY. LATEST INSTABILITY PARAMETERS
NOT VERY IMPRESSIVE WITH ONLY THE CANADIAN ABLE TO MUSTER UP
ANYTHING NOTEWORTHY (500 J/KG MLCAPE OVER THE FAR SE). IF THE NEAR
SURFACE AIR MASS IS ABLE TO OBTAIN SURFACE-BASED CAPE BETWEEN
500-1000J/KG (FEASIBLE WITH THE LOW LEVEL FLOW OFF THE NORTHERN GULF
AND ATLANTIC GULFSTREAM)...THEN CENTRAL NC COULD BE LOOKING AT A
SIGNIFICANT DAMAGING WIND/ISOLATED TORNADO EVENT LATE WED NIGHT.
&&
.LONG TERM /THURSDAY THROUGH SUNDAY/...
AS OF 255 PM SUNDAY...
THURSDAY...DEEPENING SURFACE LOW IN VICINITY OF SOUTHERN NEW ENGLAND
WILL GRADUALLY SWEEP A SURFACE COLD FRONT ACROSS CENTRAL NC LATE
THU OR THU NIGHT. MID LEVEL DRY PUNCH ASSOCIATED WITH MATURE UPPER
LEVEL CYCLONE WILL CROSS THE REGION THU MORNING. THUS EXPECT SHOWERS
TO EXIT/DIMINISH FROM THE SW THU MORNING. IF SKIES CLEAR EARLY
ENOUGH...MAY EXPERIENCE BREEZY CONDITIONS THU WITH THE POTENTIAL FOR
WIND GUSTS AROUND 30 MPH. WHILE 850MB TEMPS PLUMMET DURING THE
DAY...LOW LEVEL SW-WLY FLOW SHOULD OFFSET COOLDOWN SOMEWHAT. THUS
HAVE RAISED MAX TEMPS 2-3 DEGREES ROM PREVIOUS FORECAST (UPPER 50S
NE TO MID 60S SE).
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.
&&
.AVIATION /00Z MONDAY THROUGH FRIDAY/...
AS OF 650 PM SUNDAY...
VFR CONDITIONS WILL PERSIST OVERNIGHT WITH THE PRIMARY AVIATION
CONCERN BEING LOW-LEVEL WIND SHEAR. GFS MODEL IS HIGHER WITH THE
WINDS JUST OFF OF THE SURFACE...WHEREAS THE NAM IS GENERALLY LIGHTER
AND BELOW LLWS THRESHOLD. WITH THE GRADIENT INCREASING OVERNIGHT ON
BOTH MODELS...WILL CONTINUE WITH LLWS IN THE 00Z VALID TAF FROM LATE
TONIGHT INTO EARLY MONDAY MORNING. GFS ACTUALLY FORECASTS WINDS
ABOUT 1500FT INCREASING TO 24040KT BY 12Z.
EXPECT SOME SURFACE GUSTS IN THE 20S KTS MONDAY IN THE TIGHT
GRADIENT EVEN WITH JUST MODEST MIXING. THE COLD FRONT WILL PUSH
THROUGH CENTRAL NORTH CAROLINA FROM ABOUT 16Z IN THE FAR NORTHWEST
TO AROUND 00Z TOWARD INTERSTATE 95. AS MOISTURE AND LIFT INCREASE
DURING THE MORNING...EXPECT AT LEAST NUMEROUS SHOWERS AND MVFR
CONDITIONS WITH THE FRONT. THERE COULD BE A BRIEF PERIOD OF IFR
CONDITIONS BEFORE DRIER AIR AND SUBSIDENCE IMPROVE CONDITIONS
QUICKLY FROM WEST TO EAST LATE MONDAY AFTERNOON...AND JUST BEYOND
THE 00Z VALID TAF PERIOD EAST.
AFTER IMPROVING CONDITIONS QUICKLY THROUGHOUT THE AREA MONDAY
EVENING...AVIATION CONCERNS WILL BE NUMEROUS TO WIDESPREAD SHOWERS...
STRONG WINDS ALOFT...AND IFR CONDITIONS WEDNESDAY INTO WEDNESDAY
NIGHT. AS A STRONG STORM SYSTEM MOVES TOWARD NEW ENGLAND...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...HARTFIELD/DJF
NEAR TERM...HARTFIELD/DJF
SHORT TERM...WSS
LONG TERM...WSS
AVIATION...DJF
