FXUS62 KRAH 252358
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
700 PM EST WED NOV 25 2009
.SYNOPSIS...
THE SHALLOW COOL WEDGE DOME AND ASSOCIATED LOW LEVEL CLOUDS WILL
CONTINUE TO ERODE AS DRY SOUTHWESTERLY FLOW CONTINUES ACROSS THE
REGION. A POTENT UPPER LEVEL DISTURBANCE AND ASSOCIATED COLD FRONT
WILL CROSS THE REGION LATE THURSDAY AND THURSDAY NIGHT... FOLLOWED
BY HIGH PRESSURE FRIDAY THROUGH THE WEEKEND.
&&
.NEAR TERM /THROUGH THURSDAY NIGHT/...
AS OF 215 PM WEDNESDAY...
AN INVERTED TROUGH OF LOW PRESSURE OFF THE CAROLINA COAST WILL
CONTINUE TO MOVE NORTHEAST AND PROVIDE A FOCUS FOR RAIN SHOWERS
ACROSS THE COASTAL AREAS THIS AFTERNOON AND INTO THE EARLY EVENING
HOURS. AN AREA OF DRIZZLE/SPRINKLES WILL CONTINUE GENERALLY FROM THE
TRIANGLE AND EAST FOR THE NEXT COUPLE OF HOURS. HOWEVER...WITH THE
INCREASING SOUTHWESTERLY FLOW IN PLACE ACROSS CENTRAL NORTH
CAROLINA...THIS AREA OF PRECIP WILL CONTINUE TO PUSH EAST. SOME
DRIER AIR HAS ALREADY MOVED INTO THE EXTREME WESTERN PORTIONS OF THE
CWA...WHICH IS EVIDENT FROM THE EROSION OF THE LOW LEVEL CLOUDS
ACROSS THE TRIAD. THIS CLEARING TREND WILL CONTINUE TOWARDS THE EAST
AS THE MOISTURE AXIS IS PUSHED FURTHER TOWARDS THE COAST. AMPLE MID
AND HIGH LEVEL CLOUDS WILL STILL BE IN PLACE ACROSS THE REGION DUE
TO AN ELONGATED JET MOVING ACROSS THE AREA. THE DRIER AIR
MASS/MOSTLY CLEAR SKIES WILL LEAD TO OVERNIGHT LOWS IN THE UPPER 30S
TO LOWER 40S.
MAX TEMPS ON THURSDAY SHOULD WARM NICELY AHEAD OF AN APPROACHING
COLD FRONT. THICKNESS VALUES ARE PROGGED TO RANGE BETWEEN 1340 AND
1350M...WHICH IS EXPECTED TO RESULT IN AFTERNOON HIGHS IN THE 60S
AREAWIDE. THE COLD FRONT IS EXPECTED TO MOVE THROUGH THE REGION ON
THURSDAY NIGHT. DESPITE FAIRLY DECENT UPPER LEVEL FORCING (STRONG
UPPER LOW...INCREASING UPPER LEVEL DIVERGENCE ASSOCIATED WITH THE
LEFT EXIT REGION OF THE SUBTROPICAL JET)...LACK OF SIGNIFICANT
MOISTURE WILL RESULT IN A MOSTLY DRY FRONTAL PASSAGE. THE ONLY
EXCEPTION MAY BE THE NORTHERN CWA...WHERE SLIGHT CHANCE POPS WERE
MAINTAINED DUE TO THE PROXIMITY OF THE UPPER LOW. BEHIND THE
FRONT...AN INCREASING PRESSURE GRADIENT WILL LEAD TO BREEZY
CONDITIONS LATE THURSDAY NIGHT. TEMPS ON THURSDAY NIGHT ARE EXPECTED
TO BE IN THE UPPER 30S TO LOW 40S AS THE BOUNDARY LAYER REMAINS WELL
MIXED DUE TO THE BREEZY CONDITIONS.
&&
.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
AS OF 215 PM WEDNESDAY...
FRIDAY AND FRIDAY NIGHT...
CLOSED UPPER CYCLONE OVER THE NORTHEAST US AND MID-ATLANTIC
STATES WILL STRENGTHEN...BECOMING A POTENT VERTICALLY STACKED STORM
SYSTEM AS IT LIFTS NE OVER NEW ENGLAND AND NEWFOUNDLAND. BUT
BEFORE THE ATTENDANT DEEP UPPER TROUGH LIFTS OUT OF THE
REGION...H5 HEIGHT ANOMALIES ON THE ORDER OF 2 TO 3 STANDARD
DEVIATIONS BELOW NORMAL WILL SPREAD OVER THE CAROLINAS ON FRIDAY.
THE RESULTANT STRONG CAA AND DAYTIME/AFTERNOON HEATING WILL RESULT
IN DEEP VERTICAL MIXING FOR THIS TIME OF YEAR (~800MB)...SUPPORTING
BREEZY COOL CONDITIONS ON FRIDAY. AFTERNOON HIGHS IN THE LOWER TO
MID 50S UNDER FULL COMPLIMENTS OF SUN AND A STEADY NWLY WIND OF 15
TO 20 MPH WITH GUSTS UP TO 30 MPH. WHILE FRIDAY NIGHT/SATURDAY
MORNING STILL LOOKS TO BE THE COLDEST NIGHT THROUGH THE PERIOD...IT
IS STILL A FAR CRY FROM IDEAL RADIATIONAL COOLING AS MODELS CONTINUE
TO SHOW 25 TO 30 KTS JUST OFF THE SURFACE (925MB). SO WOULD NOT
SURPRISED IF THE RDU INT'L AIRPORT STILL FALLS JUST SHY OF REACHING
THE FREEZING MARK FOR THE FIRST TIME THIS SEASON. MINS TEMPERATURES
IN THE LOWER TO MIDDLE 30S.
SATURDAY THROUGH SUNDAY NIGHT...
WITH THE ANOMALOUS DEEP UPPER TROUGH LIFTING OUT OF THE REGION...
THE UPPER AIR FLOW PATTERN OVER THE SOUTHEAST US WILL TEMPORARY
BECOME LOW-AMPLITUDE/NEARLY ZONAL SATURDAY AND INTO SUNDAY.
THE RISING HEIGHTS ALOFT COMBINED WITH THE RETURN SOUTHERLY
FLOW AS A MODIFIED SURFACE ANTICYCLONE BUILDS INTO THE CAROLINAS
FROM THE GULF COAST REGION WILL BRING MODERATING TEMPS THROUGH
THE WEEKEND. NEAR NORMAL HIGHS ON SATURDAY...56 TO 61...WITH LOWS
SATURDAY NIGHT IN THE LOWER TO UPPER 30S. HIGHS SUNDAY IN THE LOWER
IN THE LOWER MID 60S...WITH OVERNIGHT LOWS IN THE UPPER 30S TO
MIDDLE 40S.
&&
.LONG TERM/MONDAY THROUGH WEDNESDAY/...
AS OF 300 PM WEDNESDAY...
THERE REMAINS GOOD MODEL AGREEMENT THAT A POSITIVE-TILT TROUGH WILL
SPLIT BY THE START OF THE WORK WEEK...WITH THE NORTHERN STREAM
TROUGH PASSAGE AND ATTENDANT FRONTAL PASSAGE BRINGING CONVECTIVE
RAINSHOWERS TO THE REGION. DESPITE THIS GOOD AGREEMENT IN THE
GENERAL UPPER AIR PATTERN...THE DETERMINISTIC MODELS DIFFER WITH THE
TIMING OF THE EASTWARD PROGRESSION OF THE FRONT AND ASSOCIATED
BETTER RAIN CHANCES...WITH THE GFS WHIPPING THE FRONT THROUGH AS
QUICK AS MONDAY EVENING...WHILE THE EC DELAYS FROPA UNTIL TUESDAY
AFTERNOON. THIS TIMING UNCERTAINTY WILL RESULT IN AN EXAGGERATED
OR PROLONGED 36-48 HOUR PERIOD OF CHANCE POPS STARTING MONDAY
THROUGH TUESDAY NIGHT...WHEN IN ACTUALITY WILL BE A 18 TO 24 HOUR
WET PERIOD. IF SLOWER TIMING OF THE EC IS REALIZED...HIGHS MONDAY
SHOULD ONCE AGAIN WARM WELL INTO THE LOWER TO MID 60S...UNDER
A THICKENING HIGH AND MID LEVEL CLOUD DECK.
AGAIN DUE TO THE UNCERTAINTY...EXPECT THERE TO BE A 24 TO 36 HOUR
PERIOD OF DRY CONDITIONS SOMETIME TUESDAY AND INTO WEDNESDAY BEFORE
THE LEFT BEHIND SOUTHERN STREAM UPPER WAVE MAKES A RUN AT THE
REGION...OVERSPREADING WARM AIR ADVECTION RAINS ATOP ANOTHER DAMMING
HIGH. HAVE LOWERED TEMPS TUESDAY AND WEDNESDAY WITH COOLER AND DRIER
CONDITIONS BUILDING INTO THE AREA BEHIND THE FRONT AND THE PROSPECTS
OF CAD EVENT BY WEDNESDAY.
&&
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
AS OF 700 PM WEDNESDAY...
DEEP LAYER DRY AIR HAS WORKED ITS WAY ACROSS THE WESTERN HALF OF THE
STATE...WITH ONLY HIGH CLOUDS STREAMING FROM SW TO NE ACROSS CENTRAL
NC. THESE HIGH CLOUDS ARE MOST DENSE ACROSS THE COASTAL PLAIN.
CLOUD COVER WILL EVENTUALLY SHIFT EAST OFF THE COAST BY THURSDAY
MORNING...ALLOWING A PERIOD OF CLEAR SKIES ACROSS OVER AT LEAST THE
WESTERN HALF OF NC FOR THE OVERNIGHT PERIOD. ALTHOUGH SURFACE
DEWPOINTS ARE EXPECTED TO BEGIN TO FALL AFTER MIDNIGHT AS A WEAK
BOUNDARY CROSS NC...STARTING FIRST IN THE TRIAD...LIGHT WINDS AND
CLEARING SKIES WILL PROMOTE THE DEVELOPMENT OF FOG BY DAYBREAK.
MVFR VSBYS CAN BE EXPECTED AT ALL TAF SITES...BUT EXPECT THE BEST
POTENTIAL FOR A PERIOD OF IFR TO LIFR VSBYS AT KGSO AND KINT WHERE
SKIES CLEAR FIRST...ALTHOUGH KRDU MAY ALSO SEE SIMILAR RESTRICTION
IF CLOUD CLEAR FAST ENOUGH.
VFR CONDITIONS WILL RETURN QUICKLY AFTER SUNRISE...WITH ONLY A LIGHT
N-NW WIND AND A FEW HIGH CLOUDS EXPECTED DURING THE DAY. A COLD
FRONT IS EXPECTED TO BE NEARING THE WESTERN PIEDMONT BY THE END OF
THE TAF PERIOD...WHICH WILL CAUSE WINDS TO EVENTUALLY INCREASE AND
TURN TO MORE W-NWRLY.
LOOKING AHEAD...STRONG PRESSURE GRADIENT BEHIND THE DRY COLD FRONTAL
PASSAGE THURSDAY NIGHT WILL LEAD TO WINDS INCREASING OVERNIGHT INTO
FRIDAY. WINDS WILL BECOME NWRLY AT 15-20 MPH...WITH GUSTS OF UP TO
30MPH ON FRIDAY...WHICH COULD BE A POTENTIAL HAZARD FOR SMALLER
AIRCRAFT. VFR CONDITIONS SHOULD THEN PERSIST THROUGH THE WEEKEND.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...KRR
NEAR TERM...KRR
SHORT TERM...CBL
LONG TERM...CBL
AVIATION...SMITH
