FXUS62 KRAH 260639
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
139 AM EST THU NOV 26 2009
.SYNOPSIS...
A POTENT UPPER LEVEL DISTURBANCE AND ASSOCIATED COLD FRONT WILL
CROSS THE REGION TODAY AND THIS EVENING. BLUSTERY...CHILLY
CONDITIONS FOLLOW ON FRIDAY. HIGH PRESSURE BUILDS OVERHEAD SATURDAY
INTO THE WEEKEND...WITH MODERATING TEMPERATURES BY SUNDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS OF 139 AM THURSDAY...
WITH HIGH CLOUDS MOVING EAST...OBSERVATIONS BEGINNING TO SHOW AREAS
OF DENSE FOG BECOMING WIDESPREAD WEST AND GRADUALLY SPREADING EAST.
ALONG WITH GOOD COLLABORATION FROM ADJACENT OFFICES...ISSUED A DENSE
FOG ADVISORY FOR ALL OF CENTRAL NORTH CAROLINA UNTIL 9 AM. AREAS OF
DENSE FOG SHOULD DEVELOP IN THE KFAY AND KCTZ AREAS AS WELL DURING
THE EARLY MORNING AS HIGH CLOUDS THIN. ALREADY...VISIBILITIES WERE
LOWERING AT KPOB.
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
AREA WIDE. 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 /06Z THURSDAY THROUGH MONDAY/...
AS OF 1230 AM THURSDAY...
EARLY MORNING AVIATION CONCERN WILL BE AREAS OF LOW CLOUDS AND FOG.
SCATTERED AREAS OF IFR CONDITIONS SHOULD BECOME MORE NUMEROUS OR
WIDESPREAD BEHIND DEPARTING COMMA CLOUD/CIRRUS SHIELD DEPARTING TO
THE NORTHEAST AS DRIER...MID-LEVEL AIR MOVES INTO CENTRAL NORTH
CAROLINA. AREAS OF IFR CONDITIONS WILL IMPROVE TO VFR LATER IN THE
MORNING 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 00Z...WHICH WILL CAUSE WINDS TO
EVENTUALLY INCREASE AND TURN MORE TO THE WEST AND NORTHWEST. A
STRONG UPPER-LEVEL DISTURBANCE COULD EVEN PROVIDE A FEW RAIN SHOWERS
VERY LATE IN THE AFTERNOON AND THE EVENING.
LOOKING AHEAD...STRONG PRESSURE GRADIENT BEHIND THE DRY COLD FRONTAL
PASSAGE TONIGHT 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...
DENSE FOG ADVISORY FOR ALL OF CENTRAL NORTH CAROLINA UNTIL 9 AM.
&&
$$
SYNOPSIS...KRR/BADGETT/DJF
NEAR TERM...KRR/BADGETT/DJF
SHORT TERM...CBL
LONG TERM...CBL
AVIATION...SMITH/DJF
