FXUS62 KRAH 290759
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
259 AM EST SUN NOV 29 2009
.SYNOPSIS...
HIGH PRESSURE WILL MOVE OFFSHORE THIS AFTERNOON IN ADVANCE OF AN
APPROACHING COLD FRONT. THE COLD FRONT WILL SWEEP THROUGH CENTRAL
NORTH CAROLINA DURING THE DAY MONDAY. HIGH PRESSURE WILL BUILD BACK
INTO THE AREA FROM THE WEST MONDAY NIGHT AND TUESDAY. A POTENT LOW
PRESSURE SYSTEM IS EXPECTED TO DEVELOP ALONG THE GULF COAST TUESDAY
NIGHT...BRINGING WIDESPREAD HEAVY RAIN TO CENTRAL NORTH CAROLINA
WEDNESDAY AND WEDNESDAY NIGHT.
&&
.NEAR TERM /THROUGH MONDAY/...
AS OF 255 AM SUNDAY...
SFC ANALYSIS THIS MORNING SHOWED 1021 MB HIGH PRESSURE CENTERED OVER
SOUTHERN GA. A SFC TROUGH AXIS WAS NOTED OVER VA/CAROLINAS. A
FRONTAL ZONE WAS LOCATED OVER THE CENTRAL CONUS. ALOFT...00Z RAOB
ANALYSIS AND THE LATEST WV IMAGERY SHOWED A SOUTHERN STREAM
SHORTWAVE OVER THE DEEP SOUTH. A POTENT SOUTHERN STREAM UPPER LOW
WAS LOCATED OVER SOUTHERN CA. A NORTHERN STREAM SHORTWAVE WAS
LOCATED OVER THE UPPER MIDWEST.
TODAY:
THE SOUTHERN STREAM SHORTWAVE OVER THE DEEP SOUTH IS EXPECTED TO
PASS BY JUST TO THE SOUTH OF NORTH CAROLINA AND MOVE OFFSHORE THE
SOUTHEAST COAST THIS AFTERNOON. BROKEN UPPER LEVEL CLOUD COVER
ASSOC/W THIS FEATURE WILL AFFECT THE AREA THROUGH THE MORNING INTO
THE AFTERNOON HORUS. BY LATE AFT/EVE...ADDITIONAL UPPER LEVEL CLOUD
COVER SHOULD BEGIN MOVING EAST TOWARD/INTO THE CAROLINAS DOWNSTREAM
OF A STRENGTHENING FRONTAL ZONE AND WESTERLY UPPER LEVEL JET ACROSS
THE MID-MISSISSIPPI RIVER VALLEY. HIGH TEMPS TODAY WILL BE
COMPLICATED PRIMARILY BY THE AMOUNT AND OPACITY OF UPPER LEVEL CLOUD
COVER OVER THE AREA. THICKNESSES ARE PROGGED AT 1360-1365M THIS
AFTERNOON...AND WITH FULL SUN...LOCAL RESEARCH WOULD SUGGEST HIGHS
IN THE UPPER 60S TO NEAR 70F. A MAV/MET MOS GUIDANCE BLEND YIELDS
VERY SIMILAR VALUES. WILL FCST HIGHS RANGING FROM 67-69F...WARMEST
IN THE SOUTH. IF UPPER LEVEL CLOUD COVER IS PERVASIVE/OPAQUE...HIGH
TEMPS WILL BE A BIT COOLER.
TONIGHT:
THE NORTHERN STREAM SHORTWAVE CURRENTLY OVER THE UPPER MIDWEST WILL
DIG SOUTHEASTWARD AND AMPLIFY THIS EVENING/TONIGHT. THE RESULTING
POSITIVELY TILTED TROUGH IS PROGGED TO STRETCH SOUTHWEST FROM THE
LOWER GREAT LAKES TO THE CENTRAL MS RIVER VALLEY BY 12Z MON. AS THE
UPPER WAVE AMPLIFIES SOUTHEASTWARD...A WAVE OF LOW PRESSURE WILL
DEVELOP/DEEPEN OVER THE GREAT LAKES THIS EVENING...MOVING NORTHEAST
INTO NEW ENGLAND BY 12Z MON. THE ATTENDANT COLD FRONT STRETCHING
SOUTHWEST THROUGH THE OH AND CENTRAL/LOWER MS RIVER VALLEYS IS
PROGGED TO SURGE EASTWARD OVERNIGHT...MAKING IT ALL THE WAY TO THE
SOUTHERN APPALACHIANS BY 12Z MON. EXPECT INCREASING MID/UPPER LEVEL
CLOUD COVER TONIGHT IN ADVANCE OF THE APPROACHING FRONT...WITH
PRECIP CHANCES CONFINED ALONG/WEST OF THE MOUNTAINS THROUGH 12Z. MOS
GUIDANCE IS IN GOOD AGREEMENT WITH FAIRLY HOMOGENEOUS LOWS IN THE
MID 40S...WARMER THAN PREVIOUS NIGHTS DUE TO LOWERING/THICKENING
CLOUD COVER AND A LIGHT SOUTHWESTERLY BREEZE.
MONDAY:
THE POSITIVELY TILTED NORTHERN STREAM TROUGH IS PROGGED TO TRANSLATE
EASTWARD THROUGH THE OH/TN VALLEYS DURING THE DAY MONDAY...MOVING
INTO THE MID-ATLANTIC AND CAROLINAS BY ~00Z TUE. MOST OF THE LATEST
00Z MODEL GUIDANCE HAS SPED UP THE COLD FRONTAL PASSAGE A BIT
MORE...WITH THE FRONT PROGRESSING INTO THE WESTERN PIEDMONT BY
~15Z...THE TRIANGLE BY 18Z...CLEARING THE I-95 CORRIDOR AND COASTAL
PLAIN BY ~00Z TUE. FORCING FOR PRECIPITATION WILL BE TIED TO LOW
LEVEL (SFC-H85) CONVERGENCE AND DPVA ASSOC/W THE APPROACHING
NORTHERN STREAM TROUGH. BOTH THE GFS/NAM SHOW 60-100 METER H5 HEIGHT
FALLS DURING THE DAY MONDAY. THE GFS/NAM/ECMWF/GEM ALL GENERATE
~0.10" OF QPF ACROSS CENTRAL NC IN ASSOC/W THE FRONTAL PASSAGE...
WITH THE GFS A NOTABLE OUTLIER...SHOWING UP TO 0.25". ALTHOUGH THE
OVERALL FORCING ISN'T TOO BAD...MOISTURE WILL BE LIMITED DUE TO
PREDOMINATELY WESTERLY FLOW THROUGHOUT THE COLUMN. WHILE WE MAY
INDEED NEED CATEGORICAL POPS FOR MONDAY (HIGH POP/LOW QPF EVENT)...
AT THIS TIME FEEL THAT LIKELY POPS WILL SUFFICE DUE TO UNCERTAINTY
W/REGARD TO THE AVAILABLE MOISTURE. HIGH TEMPS ON MONDAY ARE
SOMEWHAT COMPLICATED DUE TO THE RELATIVELY HIGH LIKELIHOOD OF
PRECIPITATION (AND ASSOCIATED EVAPORATIVE COOLING) PROGRESSING
THROUGH THE AREA DURING THE PEAK HEATING HOURS. HAVE DECIDED TO
TREND TOWARD A MOS GUIDANCE BLEND...WITH HIGHS RANGING FROM THE
UPPER 50S IN THE NW PIEDMONT TO THE LOWER/MID 60S IN PORTIONS OF THE
SANDHILLS AND SE COASTAL PLAIN. -VINCENT
&&
.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
AS OF 245 AM SUNDAY...
MONDAY NIGHT THROUGH TUESDAY NIGHT: THE NWP MODELS CONTINUE TO
HASTEN THE SURFACE FRONTAL PASSAGE MONDAY -- PROPELLED BY A FAST
NORTHERN STREAM TROUGH -- SO EXPECT AT MOST ONLY A FEW LINGERING
SHOWERS OVER THE COASTAL PLAIN AND SANDHILLS DURING THE EVENING.
WHILE THE MOUNTAINS WILL AT LEAST TEMPORARILY BLOCK THE POST-FRONTAL
COLD AIR... THE FRONT SHOULD BE WELL INTO THE WESTERN ATLANTIC BY
TUESDAY MORNING WITH PROLONGED CAA ACCORDINGLY EXPECTED OVER CENTRAL
NC FOR JUST ABOUT THE ENTIRE NIGHT. THUS... LOWS IN THE MIDDLE TO
UPPER 30S SEEM REASONABLE BY DAYBREAK. INDEED... TEMPERATURES
ASSOCIATED WITH THE SURFACE HIGH EXPECTED TO BUILD OVERHEAD IN THE
WAKE OF THE COLD FRONT ARE CURRENTLY IN THE TEENS FROM THE FRONT
RANGE OF THE NORTHERN ROCKIES TO 30S OVER THE NORTHERN PLAINS AT
07Z.
TUESDAY AND TUESDAY NIGHT: S/W RIDGING ALOFT -- BEHIND THE
AFOREMENTIONED NORTHERN STREAM TROUGH AND A CLOSED SOUTHERN STREAM
UPPER LOW CURRENTLY OVER SOUTHERN CA -- WILL DOMINATE THIS PERIOD.
THUS... MOSTLY CLEAR (ASIDE FROM PERHAPS SOME PASSING CIRRUS)...
COOL... AND STABLE (DRY) CONDITIONS ARE EXPECTED TUESDAY. HIGHS IN
THE MIDDLE TO UPPER 50S. MAINLY HIGH CLOUDS SHOULD THEN STEADILY
INCREASE FROM THE SOUTHWEST TUESDAY NIGHT... WELL IN ADVANCE OF THE
CLOSED UPPER LOW SCHEDULED TO BE OVER EASTERN TX BY 12Z WED. EXPECT
TEMPERATURES TO FALL RAPIDLY AFTER SUNSET... WITH THE COOL/DRY RIDGE
IN PLACE AND STILL RELATIVELY CLEAR SKIES EARLY ON. THE POTENTIAL
STILL EXISTS FOR A WIDE RANGE OF LOWS FROM AROUND FREEZING TO THE
UPPER 30S (PERHAPS SOME UPPER 20S IN THE TYPICALLY COOLER SPOTS OVER
THE NORTHERN PIEDMONT AND NORTHERN COASTAL PLAIN (AWAY FROM THE
INCREASING HIGH CLOUD COVER).
&&
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 145 PM SATURDAY...
WEDNESDAY MORNING AN UPPER LEVEL CUT OFF LOW IS FORECAST TO BE OVER
EASTERN TEXAS. AN ASSOCIATED SURFACE LOW IN THE NORTH GULF OF MEXICO
WILL LIFT NORTHEAST TOWARD THE CAROLINAS DURING THE DAY WEDNESDAY.
AT THIS TIME THE ATTEMPT OF THE GFS TO DEVELOP A MILLER B SURFACE
LOW DEVELOPMENT... BUT OVER THE EASTERN PIEDMONT IS REJECTED... AND
SOMETHING CLOSER TO THE ECMWF SOLUTION WITH A LOW WEST OF THE
MOUNTAINS WILL BE FOLLOWED. WITH CENTRAL NORTH CAROLINA IN THE WARM
SECTOR... THIS COULD BE A SIGNIFICANT RAIN EVENT... WITH AMOUNTS IN
EXCESS OF ONE INCH. HOWEVER THERE IS STILL TOO MUCH UNCERTAINTY THIS
FAR OUT IN TIME TO HAVE MUCH CONFIDENCE.
THE REMAINDER OF THE PERIOD WILL BE DOMINATED BY A BROAD TROUGH OVER
THE EASTERN HALF OF THE UNITED STATES. SURFACE HIGH PRESSURE TO THE
WEST WILL KEEP SKIES MOSTLY CLEAR WHILE NORTHEAST FLOW AND DRY
NIGHTS WILL KEEP TEMPERATURES BELOW NORMAL. AFTERNOON HIGH
TEMPERATURES IN THE MID 50S BEFORE FALLING TO 49 TO 55 FRIDAY... AND
NEAR 50 SATURDAY. OVERNIGHT LOWS MID 40S TO NEAR 50 WEDNESDAY NIGHT
THEN MID 30S THURSDAY AND FRIDAY NIGHTS.
&&
.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
AS OF 100 AM SUNDAY...
24-HR TAF PERIOD:
VFR CONDITIONS ARE EXPECTED THROUGHOUT THE ENTIRE TAF PERIOD AS A
DRY LOW/MID LEVEL AIRMASS PERSISTS OVER THE REGION. CLOUD COVER WILL
BE LIMITED TO THE UPPER LEVELS...WITH CEILINGS AOA 15 KFT. SURFACE
WINDS WILL BE FROM THE SOUTHWEST AT ~10 KNOTS BY THIS AFTERNOON AS
THE PRESSURE GRADIENT BEGINS TO TIGHTEN IN ADVANCE OF AN APPROACHING
COLD FRONT. SURFACE WINDS SHOULD WEAKEN TO ~5 KNOTS AFTER SUNSET IN
ASSOC/W THE DEVELOPING NOCTURNAL INVERSION. FCST MODELS SHOW THE
MSLP/HEIGHT GRADIENT TIGHTENING QUICKLY TONIGHT AS THE
BEFOREMENTIONED COLD FRONT APPROACHES THE SOUTHERN APPALACHIANS FROM
THE WEST...AND FCST SOUNDINGS SHOW A 30-40 KNOT WEST-SOUTHWEST LOW
LEVEL JET DEVELOPING BY THE END OF THE TAF PERIOD (~06Z). THE
COMBINATION OF A STRONG NOCTURNAL INVERSION AND A 30-40 KT LLJ AT
1000-2000 FT ABOVE GROUND LEVEL WILL LIKELY LEAD TO LOW LEVEL WIND
SHEAR...AND LLWS HAS THEREFORE BEEN INTRODUCED NEAR THE END OF THE
VALID TAF PERIOD.
MONDAY THROUGH MONDAY NIGHT:
A COLD FRONT WILL MOVE INTO THE CAROLINAS FROM THE WEST LATE MONDAY
MORNING THROUGH MONDAY AFTERNOON...AND A 6-9 HOUR PERIOD OF MVFR/IFR
CONDITIONS ASSOC/W SHOWER ACTIVITY IS LIKELY...WITH THE BEST CHANCE
OF ADVERSE AVIATION CONDITIONS BETWEEN 15Z MON AND 00Z TUE.
TUESDAY THROUGH TUESDAY NIGHT:
VFR CONDITIONS WILL RETURN TO THE AREA BEHIND THE FRONT MONDAY NIGHT
AS HIGH PRESSURE BUILDS INTO CENTRAL NC FROM THE WEST. HIGH PRESSURE
WILL MOVE OFFSHORE TO THE EAST TUESDAY NIGHT. VFR CONDITIONS ARE
EXPECTED TO CONTINUE THROUGH 12Z WED.
WEDNESDAY THROUGH THURSDAY:
A VERY POTENT LOW PRESSURE SYSTEM IS EXPECTED TO DEVELOP ALONG THE
DEEP SOUTH GULF COAST WEDNESDAY MORNING...MOVING NORTHEAST INTO THE
CAROLINAS WED AFT/EVE INTO WED NIGHT. ADVERSE AVIATION CONDITIONS
ASSOC/W LOW CEILINGS/VISBYS AND HEAVY RAIN ARE ANTICIPATED. VFR
CONDITIONS SHOULD RETURN TO CENTRAL NC BY THU AFT/EVE IN THE WAKE OF
A STRONG COLD FRONT. -VINCENT
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...VINCENT
NEAR TERM...VINCENT
SHORT TERM...MWS
LONG TERM...99
AVIATION...VINCENT
