FXUS62 KRAH 281127
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
627 AM EST SAT NOV 28 2009
.SYNOPSIS...
HIGH PRESSURE WILL BUILD TOWARD THE CAROLINAS FROM THE SOUTHWEST
TODAY AND MOVE OFFSHORE TO THE SOUTH ON SUNDAY. A COLD FRONT WILL
APPROACH THE CAROLINAS FROM THE WEST SUNDAY NIGHT...MOVING THROUGH
THE AREA MONDAY AFTERNOON AND EVENING.
&&
.NEAR TERM /THROUGH SUNDAY/...
AS OF 235 AM SATURDAY...
SFC ANALYSIS THIS MORNING SHOWED AN IMPRESSIVELY DEEP 970 MB LOW
CENTERED OVER THE GULF OF MAINE. A TROUGH AXIS EXTENDED
SOUTHWESTWARD INTO THE MID-ATLANTIC AND CAROLINAS. 1021 MB HIGH
PRESSURE WAS CENTERED OVER THE DEEP SOUTH GULF COAST. ALOFT...00Z
RAOB ANALYSIS SHOWED A DEEP UPPER LOW OVER THE GULF OF MAINE...WITH
A TROUGH AXIS EXTENDING SOUTHWARD BETWEEN CAPE HATTERAS AND BERMUDA.
AN UPPER RIDGE WAS CENTERED OVER THE MID-SECTION OF THE COUNTRY. A
SOUTHERN STREAM WAVE WAS LOCATED OVER NORTH-CENTRAL TX.
TODAY:
THE CAROLINAS/MID-ATLANTIC ARE CURRENTLY LOCATED IN A ZONE OF STRONG
SYNOPTIC SUBSIDENCE UPSTREAM OF THE OFFSHORE TROUGH AND DOWNSTREAM
OF THE MIDWEST RIDGE. FCST SOUNDINGS FOR TODAY INDICATE AS
MUCH...SHOWING A PRONOUNCED MID-LEVEL SUBSIDENCE INVERSION IN
PLACE...WITH PWAT VALUES AROUND 0.30". AS A RESULT...CLEAR SKIES ARE
EXPECTED...AND THE PRIMARY FORECAST PROBLEM WILL BE MAX
TEMPERATURES. 1000-850 MB THICKNESSES ARE PROGGED TO BE ~1315-1320M
AT 12Z...INCREASING TO 1340-1350M BY 21-00Z THIS EVENING. BOTH MOS
GUIDANCE AND THICKNESSES ARGUE FOR HIGHS IN THE MID/UPPER 50S TO
~60F...COOLEST NE AND WARMEST SW.
TONIGHT:
THE SOUTHERN STREAM WAVE CURRENTLY OVER TX IS PROGGED TO MOVE EAST
THROUGH THE DEEP SOUTH INTO THE SOUTHEAST STATES BY 12Z SUN.
ALTHOUGH LIMITED MOISTURE AND MARGINAL FORCING ASSOC/W THIS WAVE
WILL PRECLUDE THE POSSIBILITY OF ANY PRECIPITATION...AN INCREASE IN
UPPER LEVEL CLOUD COVER IS LIKELY...PRIMARILY AFTER MIDNIGHT. IT
IS DIFFICULT TO ASCERTAIN JUST HOW MUCH UPPER LEVEL CLOUD COVER
THERE WILL BE...NOT TO MENTION THE OPACITY. AT THIS TIME PREFER TO
SHOW PARTLY CLOUDY SKIES IN THE SOUTH/WEST PORTIONS OF THE AREA BY
SUNRISE SUN...WITH MOSTLY CLEAR TO PARTLY CLOUDY SKIES ELSEWHERE.
MIN TEMPS TONIGHT WILL BE COMPLICATED PRIMARILY BY HOW MUCH UPPER
LEVEL CLOUD COVER IS AROUND. MOS GUIDANCE IS IN PRETTY GOOD
AGREEMENT WITH LOWS IN THE MID/UPPER 30S...AND GIVEN THAT TEMPS
SHOULD DROP PRECIPITOUSLY AFTER SUNSET WITH CLEAR SKIES AND CALM
WINDS...PREFER TO REMAIN ON THE LOW SIDE OR JUST BELOW MOS GUIDANCE
WITH LOWS IN THE MID 30S IN MOST LOCATIONS...ALTHOUGH LOWER 30S WILL
BE POSSIBLE IN THE TYPICAL COLD AREAS...ESPECIALLY IF UPPER LEVEL
CLOUD COVER IS MINIMAL OR ABSENT.
SUNDAY:
THE SOUTHERN STREAM WAVE IS EXPECTED TO PASS BY JUST SOUTH OF THE
AREA SUNDAY MORNING...MOVING OFFSHORE SUN AFTERNOON. SOME UPPER
LEVEL CLOUD COVER WILL LIKELY BE ASSOC/W THIS FEATURE. BY MID/LATE
AFTERNOON...MORE UPPER LEVEL CLOUD COVER SHOULD BEGIN MOVING INTO
THE CAROLINAS DOWNSTREAM OF A STRENGTHENING FRONTAL ZONE AND
WESTERLY UPPER LEVEL JET ACROSS THE MID-MISSISSIPPI RIVER VALLEY.
EXPECT PARTLY CLOUDY SKIES BY SUNSET...WITH CEILINGS AOA 15 KFT.
HIGH TEMPS WILL BE COMPLICATED BY THE AMOUNT AND OPACITY OF UPPER
LEVEL CLOUD COVER OVER THE AREA. THICKNESSES ARE PROGGED AT ~1360M
12-21Z SUN...AND WITH FULL SUN...LOCAL RESEARCH WOULD SUGGEST HIGHS
IN THE UPPER 60S. A MAV/MET MOS GUIDANCE BLEND YIELDS SIMILAR
VALUES...IN THE MID/UPPER 60S. WILL FCST HIGHS RANGING FROM
66-69F...WARMEST IN THE SOUTH. -VINCENT
&&
.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
AS OF 315 AM SATURDAY...
SUNDAY NIGHT THROUGH MONDAY NIGHT: HARD TO IGNORE THE NOTICEABLY
FASTER TIMING OF THE COLD FRONT DEPICTED IN THE NWP MODELS THIS
PERIOD. WARM CONVEYOR BELT CLOUD COVER AHEAD OF A NORTHERN STREAM
TROUGH -- COMPRISED OF A DOMINANT S/W TROUGH CENTERED JUST NORTH OF
MONTANA THIS MORNING -- WILL EDGE INTO WEST CENTRAL NC LATE SUNDAY
NIGHT AND ESPECIALLY MONDAY. WHILE THE INITIALLY POSITIVELY-TILTED
NORTHERN STREAM TROUGH ALOFT DOES BEGIN TO ASSUME A NEUTRAL TILT AS
IT APPROACHES THE EAST COAST -- ONCE IT SEPARATES FROM AN EVOLVING
CLOSED LOW OVER CENTRAL CA THIS MORNING -- THE WINDOW OF OPPORTUNITY
FOR TRANSPORT OF ALREADY LIMITED MARITIME AIR FROM THE GOM SHOULD
LIMIT ASSOCIATED RAINFALL AMOUNTS TO AROUND A TENTH OR TWO OF AN
INCH. IT NOW APPEARS THE BEST CHANCE OF SHOWERS ATTENDANT THE
SURFACE FRONTAL PASSAGE WILL OCCUR OVER THE WESTERN AND CENTRAL
PIEDMONTS DURING THE MIDDAY TO LATE AFTERNOON HOURS... THEN INTO THE
COASTAL PLAIN DURING THE LATE EVENING HOURS UNTIL MIDNIGHT OR SO.
GIVEN PROJECTED WEAK WEAK LAPSE RATES ALOFT AND THE BRIEF AND WEAK
GOM MOISTURE ADVECTION AHEAD OF THE FAST-MOVING TROUGH ALOFT... NO
INSTABILITY/THUNDER IS ANTICIPATED. LOWS IN THE MIDDLE TO UPPER 40S
WITH INCREASING CLOUD COVER AND SOUTHWEST FLOW AHEAD OF THE FRONT
SUNDAY NIGHT. HIGHS AROUND 60 NW (WHERE CLOUDS AND SHOWERS ARRIVE
FIRST) TO UPPER 60S IN THE COASTAL PLAIN (WHERE IT IS APT TO REMAIN
PARTLY SUNNY AND DRY MOST OF THE DAY). THEN CAA-DRIVEN OVERNIGHT
LOWS IN THE MIDDLE 30S TO AROUND 40 DEGREES POST-FRONT MONDAY
NIGHT.
&&
.LONG TERM/TUESDAY THROUGH FRIDAY/...
AS OF 330 AM SATURDAY...
TUESDAY AND TUESDAY NIGHT: MOSTLY CLEAR... COOL... AND STABLE (DRY)
CONDITIONS ARE EXPECTED THIS PERIOD -- THOUGH SOME MID-HIGH CLOUDS
WILL INCREASE FROM THE SOUTHWEST LATE TUESDAY NIGHT -- OWING TO
SURFACE AND S/W RIDGING ALOFT BEHIND THE AFOREMENTIONED NORTHERN
STREAM TROUGH AND THE CA CLOSED LOW. HIGHS IN THE MIDDLE TO UPPER
50S. A POTENTIAL WIDE RANGE OF LOWS FROM AROUND FREEZING TO THE
UPPER 30S... WITH THE EXPECTATION OF GOOD... CALM RADIATIONAL
COOLING CONDITIONS... ESPECIALLY CENTRAL AND NORTHERN CWA (AWAY FROM
INCREASING CLOUD COVER).
AS OF 500 AM SATURDAY...
WEDNESDAY AND WEDNESDAY NIGHT: NOT MUCH CHANGE IN FORECAST RATIONALE
FROM 24 HOURS AGO... BUT A DIFFICULT AND HIGH IMPACT FORECAST
PERIOD... NONETHELESS. THE NWP MODELS ARE IN GOOD AGREEMENT WRT TO
THE DEAMPLIFICATION OF THE CA CLOSED LOW FROM THE ARKLATEX REGION
WEDNESDAY MORNING TO THE NORTHERN MID ATLANTIC STATES BY THURSDAY
MORNING... AHEAD OF ANOTHER NORTHERN STREAM TROUGH ALOFT EXPECTED TO
AMPLIFY OVER THE NORTH CENTRAL CONUS.
EXPECT STRONG WAA/ISENTROPIC LIFT WITH MOISTURE ORIGINS FROM BOTH
THE GOM AND ATLANTIC OCEAN -- PRECEDED BY COOL/DRY SURFACE RIDGING
OVER THE MID ATLANTIC STATES -- TO ADVANCE NORTHWARD ACROSS NC
WEDNESDAY AND WEDNESDAY NIGHT. THE UNFAVORABLE SOUTHERN LOCATION AND
EASTWARD PROGRESSION OF THE SURFACE HIGH SUGGEST THE ASSOCIATED COLD
AIR DAMMING WILL BE OF THE IN-SITU VARIETY... AND AT LEAST PARTIALLY
SUBMIT TO AN OVERWHELMING SOUTHEASTERLY SURFACE FLOW AHEAD OF THE
PRIMARY SURFACE CYCLONE. THE NWP MODELS... ASIDE FROM THE GFS...
CONTINUE TO INSIST UPON TRACKING THE SURFACE CYCLONE FROM THE
WESTERN GOM TO THE WEST SIDE OF THE CENTRAL AND SOUTHERN
APPALACHIANS AND INDEED INUNDATE CENTRAL NC WITH THE SAID
SOUTHEASTERLY FLOW. THE GFS TRACKS THE UPPER WAVE TOWARD OUR REGION
MORE QUICKLY AND ACCORDINGLY INDUCES AND HOLDS ONTO STRONGER SURFACE
RIDGING/WEDGING... WHICH IN TURN FORCES THE SURFACE WAVE ALONG THE
EASTERN PERIPHERY OF THE LOCKED-IN WEDGE OVER CENTRAL NC. THE GFS
ALSO SPINS UP A PRECEDING COASTAL SURFACE CYCLONE IN RESPONSE TO A
LATENT HEATING-INDUCED LOW LEVEL PV ANOMALY. SUSPECT THE MOST LIKELY
SCENARIO IS A COMPROMISE OF THESE SOLUTIONS... IE... ONE IN WHICH
THE INITIAL SURFACE WAVE FROM THE GULF TRACKS TOWARD THE SOUTHERN
APPALACHIANS AND SPLITS... WITH WEAKER NORTHEASTWARD DEVELOPMENT
ACROSS THE TN/OH VALLEYS ASSOCIATED WITH THE PHASING OF THE
DEAMPLIFYING SOUTHERN STREAM WAVE WITH THE NORTHERN STREAM NORTH
CENTRAL CONUS TROUGH... AND ALSO CONTINUED DEVELOPMENT ALONG THE
RETREATING COASTAL BAROCLINIC ZONE FROM THE EASTERN CAROLINAS TO THE
NORTHERN MID ATLANTIC COAST. THE TWO THEN MERGE TO FORM AN INTENSE
NEW ENGLAND STORM ON THURSDAY.
WHAT THE ABOVE WOULD MEAN FOR CENTRAL NC IS A BOUT OF WIDESPREAD...
SOAKING RAIN AND GRADUAL DEMISE OF THE COOL WEDGE OVER ABOUT THE
SOUTHEASTERN HALF TO TWO THIRDS OF THE CWA. THE EXTENT OF THE WEDGE
DEMISE WOULD LIKELY BE INSUFFICIENT TO TAP THE TRUE MARITIME
TROPICAL AIR MASS THAT COULD SUPPORT SEVERE SURFACE-BASED CONVECTION
OVER THE MAJORITY OF NC... EXCEPT FOR PERHAPS THE COASTAL PLAIN AND
MORE LIKELY FAR EASTERN NC. TEMPERATURES SHOULD INITIALLY DECREASE
AND STEADY AS THE RAIN AND EVAPORATIVE COOLING SPREADS
NORTHEASTWARD... THEN SLOWLY RISE VERY LATE IN THE DAY AND THROUGH
THE EVENING HOURS. CALENDAR DAY HIGHS FROM NEAR 50 NW TO NEAR 60
DEGREES SE... WITH LOW TEMPERATURES BEHIND THE STORM SYSTEM IN THE
40S TO NEAR 50 BY THURSDAY MORNING. A LAGGING... BROAD NORTHERN
STREAM TROUGH SHOULD PROVE INFERIOR TO A COOL AND STABLE SURFACE
RIDGE POISED TO BUILD INTO THE REGION BEHIND THE NEW ENGLAND STORM
SYSTEM AND ASSOCIATED WELL OFFSHORE MOIST AXIS. THUS... COOL AND
TRANQUIL CONDITIONS ARE EXPECTED THROUGH THE END OF THE WEEK. HIGH
TEMPERATURES ONLY IN THE LOWER TO MIDDLE 50S... WITH LOWS GENERALLY
IN THE 30S.
&&
.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
AS OF 630 AM SATURDAY...
24-HR TAF PERIOD:
VFR CONDITIONS WITH CLEAR SKIES ARE EXPECTED THROUGH THE 24 HOUR TAF
PERIOD AS HIGH PRESSURE BUILDS TOWARD THE CAROLINAS FROM THE
SOUTHWEST. SURFACE WINDS ARE EXPECTED TO BE NORTHWESTERLY AT 5-10 KT
THIS MORNING...WEAKENING TO ~5 KT AND BACKING TO THE WEST AND
EVENTUALLY SW BY MID/LATE AFTERNOON. A FEW SPORADIC GUSTS IN THE
10-15 KT RANGE WILL BE POSSIBLE DURING THE MORNING HOURS.
SUNDAY THROUGH SUNDAY NIGHT:
ALTHOUGH MID/UPPER LEVEL CLOUD COVER WILL INCREASE IN THIS PERIOD
AHEAD OF THE NEXT FRONTAL SYSTEM...THE LOWER LEVELS WILL REMAIN VERY
DRY...AND VFR CONDITIONS WILL REMAIN IN PLACE ACROSS CENTRAL NC.
MONDAY AND MONDAY NIGHT:
A COLD FRONT WILL MOVE INTO THE CAROLINAS FROM THE WEST ON MON/MON
NIGHT...AND A 6-12 HOUR PERIOD OF MVFR/IFR CONDITIONS ASSOC/W SHOWER
ACTIVITY IS LIKELY...WITH THE BEST CHANCE OF ADVERSE AVIATION
CONDITIONS BETWEEN 18Z MON AND 06Z TUE.
TUESDAY THROUGH WEDNESDAY:
VFR CONDITIONS WILL RETURN TO THE AREA BEHIND THE FRONT ON TUE...
HOWEVER...A SIGNIFICANT STORM SYSTEM IS EXPECTED TO DEVELOP ALONG
THE DEEP SOUTH GULF COAST TUE NIGHT...MOVING INTO THE CAROLINAS AS
EARLY AS WED MORNING. WIDESPREAD ADVERSE AVIATION CONDITIONS APPEAR
LIKELY. -VINCENT
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...VINCENT
NEAR TERM...VINCENT
SHORT TERM...MWS
LONG TERM...MWS
AVIATION...VINCENT
