Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 161131
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
730 AM EDT TUE SEP 16 2014

.SYNOPSIS...A COLD FRONT APPROACHING THE REGION FROM THE WEST
WILL TRACK SLOWLY SOUTHWARD THROUGH THE CAROLINAS LATER TODAY
AND TONIGHT. THE FRONT WILL GRADUALLY MOVE OFFSHORE THE
SOUTHEAST COAST ON WEDNESDAY AND THURSDAY AS HIGH PRESSURE
STRENGTHENS OVER THE GREAT LAKES AND EXTENDS SOUTHWARD THROUGH THE
MID ATLANTIC.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 330 AM TUESDAY...

TODAY...WEAK MID-UPPER LEVEL DISTURBANCE EXITING THE REGION EARLY
THIS MORNING. PATCHES OF LIGHT RAIN OR SHOWERS SHOULD CONTINUE TO
DECREASE IN COVERAGE/INTENSITY THROUGH DAYBREAK. ABUNDANT LOW LEVEL
MOISTURE SHOULD RESULT IN THE FORMATION OF A LOW CLOUD DECK BY
DAYBREAK.  WEAK SUBSIDENCE IN THE WAKE OF THIS EXITING FEATURE
COMBINED WITH A DOWNSLOPE COMPONENT TO THE 925-850MB WIND AFTER 12Z
SHOULD AID TO DIMINISH/DISSIPATE THE WIDESPREAD LOW CLOUDS BY LATE
MORNING-MID DAY.

HEATING OF THE ATMOSPHERE IN COMBINATION WITH RESIDUAL MOISTURE AND
THE APPROACH OF ANOTHER MID-UPPER LEVEL DISTURBANCE SHOULD TRIGGER
SCATTERED SHOWERS-ISOLATED THUNDERSTORMS. LATEST ROUND OF WRF MODEL
RADAR PRESENTATIONS ALONG WITH THE HRRR FAVOR INITIAL DEVELOPMENT IN
THE WESTERN PIEDMONT AROUND MID AFTERNOON. THE 00Z GFS  (AND MORE SO
THE 00Z NAM) INDICATE SLIGHT INSTABILITY OVER THE WESTERN PIEDMONT
ALONG WITH SOME BULK SHEAR OF SUFFICIENT MAGNITUDE (25-30KTS) TO
ALLOW FOR SOME LOOSELY ORGANIZED CONVECTION. SOME WRF MODELS SUGGEST
BROKEN BAND OF CONVECTION MAKING IT INTO THE TRIANGLE REGION BEFORE
WEAKENING/DISSIPATING. CONSIDERING THE LACK OF RADAR ECHOES UPSTREAM
ASSOCIATED WITH THE NEXT DISTURBANCE...NOT READY TO INCREASE ANY
MORE THAN CURRENT 20-40 PERCENT. HOWEVER...HAVE SHIFTED POP EMPHASIS
MORE TO THE WESTERN PIEDMONT RATHER THAN THE SOUTHERN COASTAL PLAIN
DUE TO BETTER PROXIMITY OF UPPER LEVEL SUPPORT.

MOS GUIDANCE CONTINUES TO ADVERTISE MAX TEMPS SOLIDLY IN THE MID
80S. THESE TEMPS ACHIEVABLE IF LOW CLOUDS DEPART/DISSIPATE PRIOR TO
15Z AND SCATTERED CONVECTION HOLDS OFF UNTIL MID AFTERNOON. FAVOR
MAX TEMPS SLIGHTLY COOLER THAN MOS (LOWER 80S NW TO MID 80S
ELSEWHERE).

TONIGHT...SCATTERED CONVECTION WILL GRADUALLY WEAKEN WITH LOSS OF
HEATING AND EXITING OF MID LEVEL DISTURBANCE. STILL...COULD SEE A
FEW SHOWERS PERSIST PAST MIDNIGHT TOT EH EAST-SOUTH OF RDU.
CLOUDINESS AND LACK OF APPRECIABLE LOW LEVEL CAA SUGGEST MIN TEMPS A
FEW DEGREES WARMER THAN EARLIER THINKING. MIN TEMPS LOW-MID 60S.


&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
AS OF 330 AM TUESDAY...

WEDNESDAY...ABUNDANT LOW LEVEL MOISTURE TRAPPED BENEATH A LOW LEVEL
INVERSION SHOULD RESULT IN EXTENSIVE CLOUDINESS OVER MOST OF THE
REGION WEDNESDAY MORNING...AND POTENTIALLY LINGERING INTO THE
AFTERNOON ACROSS THE PIEDMONT. (THIS MAY BE CLASSIFIED AS A HYBRID
OR INSITU DAMMING EVENT THOUGH PARENT HIGH RELATIVELY WEAK AND QUITE
TRANSITORY). IF EXTENSIVE CLOUDS DO LINGER PAST MID DAY ACROSS THE
PIEDMONT...THIS MAY CREATE A DIFFERENTIAL HEATING BOUNDARY BETWEEN
THE PIEDMONT AND THE SANDHILLS/SOUTHERN COASTAL PLAIN. THE APPROACH
OF YET ANOTHER DISTURBANCE IN THE WEST-NW FLOW ALOFT INTERACTING
WITH THIS FEATURE MAY TRIGGER MORE SCATTERED CONVECTION...MAINLY
OVER THE SE THIRD OF OUR FORECAST AREA. THE LOW LEVEL STABLE AIR
MASS SUGGEST MAINLY PATCHY STRATIFORM RAIN OVER THE NORTHERN
PIEDMONT (OR ELEVATED SHOWERS. SINCE LEANING TOWARD MORE CLOUDINESS
ACROSS THE PIEDMONT...HAVE LOWERED MAX TEMPS A COUPLE OF DEGREES BUT
RAISED MAX TEMPS TO NEAR/ABOVE 80 OVER THE SE COUNTIES.

CONTINUED CYCLONIC FLOW ALOFT WILL MAINTAIN CLOUDINESS WEDNESDAY
NIGHT ALONG WITH A SMALL THREAT FOR SHOWERS...MAINLY EAST OF HIGHWAY
1. MIN TEMPS SEVERAL DEGREES COMPARED TO THE PREVIOUS NIGHT. MIN
TEMPS UPPER 50S NW TO LOWER 60S SE.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
AS OF 330 AM TUESDAY...

THE MEDIUM RANGE WILL FEATURE A LONGWAVE TROUGH THAT WILL MOVE
OFFSHORE THE EAST COAST THU AND CONSEQUENTLY YIELD TO RISING HEIGHTS
ALOFT AS A FLAT MID LEVEL RIDGE RIDGE BRIEFLY BUILDS EAST FROM THE
SOUTHERN PLAINS AND LOWER MS VALLEY FRI-SAT. THE RE-ESTABLISHMENT OF
A WESTERN NOAM RIDGE WILL THEN RESULT IN DOWNSTREAM TROUGH
AMPLIFICATION FROM SOUTH-CENTRAL CANADA TO THE EAST-CENTRAL US SUN-
MON...THE LEAD SHORTWAVE TROUGH OF WHICH WILL INCLUDE THE REMNANTS
OF TROPICAL STORM ODILE.

MEANWHILE AT THE SFC...A CANADIAN-SOURCE SFC HIGH (AROUND 1030 MB)
WILL BUILD FROM CENTRAL CANADA TO THE CANADIAN MARITIMES AND RIDGE
SOUTH/SOUTHWESTWARD IN DAMMING ORIENTATION EAST OF THE APPALACHIANS
THU THROUGH THE WEEKEND...FOLLOWED BY A COLD FRONTAL PASSAGE -
DRIVEN BY THE AFOREMENTIONED RE-AMPLIFICATION OF THE LONGWAVE TROUGH
INTO THE EAST-CENTRAL US - ON MON.

THE RESULT WILL BE A RELATIVELY PROLONGED PERIOD OF EAST TO
NORTHEAST LOW LEVEL FLOW AND ASSOCIATED BELOW NORMAL TEMPERATURES...
TEMPERED FURTHER BY PERIODS OF BKN MULTI-LAYERED CLOUD
COVER...THROUGH EARLY THIS WEEKEND. THE RELATIVE GREATEST CLOUD
COVERAGE WILL LINGER THU (FROM WED NIGHT)...WHEN A LINGERING CHANCE
OF SHOWERS WILL ALSO REMAIN...MAINLY OVER THE COASTAL WHERE A
DEPARTING H85 WAVE/TROUGH WILL AUGMENT WEAK FORCING ALOFT ATTENDING
A PAIR OF SHORTWAVE TROUGHS FORECAST TO CROSS THE CAROLINAS AND
MIDDLE ATLANTIC THROUGH MID-LATE THU AFTERNOON. UNDER ASSOCIATED
VARIABLY CLOUDY SKY COVER...WITH RELATIVE GREATEST COVERAGE
EAST...TEMPERATURES SHOULD FALL ABOUT A CATEGORY OR SO SHY OF WHAT
FULL SUN THICKNESSES OF AROUND 1385 METERS WOULD OTHERWISE SUPPORT.
COOL AGAIN OVERNIGHT WITH DEEP LAYER DRYING/FALLING PRECIPITABLE
WATER VALUES TO AROUND AN INCH...AS THE AFOREMENTIONED MID LEVEL
RIDGE EXPANDS EASTWARD AND CAUSES - LOWS MIDDLE 50S TO AROUND 60.

OTHERWISE...THE INCREASING INFLUENCE OF THE RIDGING AT THE SFC AND
ALOFT SHOULD PROMOTE DRY CONDITIONS FRI-SUN...THOUGH WITH
TEMPERATURES MODERATING ONLY SLOWLY THROUGH THE 70S...TO AROUND 80
DEGREES BY SUN. THE PASSAGE OF THE SFC COLD FRONT EARLY NEXT WEEK
SHOULD THEN SUPPORT A CHANCE OF SHOWERS IN CENTRAL NC ON MON. ONCE
THE INHERENT D7 TIMING DIFFERENCES ARE IRONED OUT...A SLIGHT CHANCE
OF THUNDER MAY BE INTRODUCED WITH LATER FORECASTS IF IT APPEARS
FAVORABLE DIURNAL TIMING OF THE FRONTAL PASSAGE WILL OCCUR.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
AS OF 730 AM TUESDAY...

WIDESPREAD MVFR/IFR CEILINGS WITH AREAS OF MVFR FOG WILL SLOWLY
IMPROVE AFTER 14Z WITH MAINLY VFR CONDITIONS EXPECTED BY 16Z.
SURFACE WINDS WILL BE LIGHT AND VARIABLE...BECOMING NORTH NORTHWEST
AT 7KTS OR LESS AFTER 14Z. THE APPROACH OF A SURFACE COLD FRONT LATE
TODAY AND THIS EVENING WILL LIKELY TRIGGER SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS AROUND MID AFTERNOON IN THE WESTERN PIEDMONT
INCLUDING THE TRIAD TERMINALS. IF THESE SHOWERS HOLD TOGETHER...THEY
WOULD THREATEN THE KRDU VICINITY CLOSE TO UNSET...AND KRWI AND KFAY
DURING THE EVENING HOURS.

VFR CONDITIONS ANTICIPATED TONIGHT THROUGH WEDNESDAY WITH  A BRIEF
PERIOD OF MVFR CEILING/VISIBILITY POSSIBLE EARLY WEDNESDAY MORNING.
SCATTERED CONVECTION MAY DEVELOP WEDNESDAY AFTERNOON-WEDNESDAY NIGHT
AS ANOTHER DISTURBANCE MOVES ACROSS THE REGION.

THE PERIOD THURSDAY THROUGH SATURDAY APPEARS TRANQUIL WITH MAINLY
VFR CONDITIONS. A BRIEF PERIOD OF MVFR CEILING OR VISIBILITY MAY
OCCUR EACH MORNING...MAINLY IN THE VICINITY OF KRWI AND KFAY.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SYNOPSIS...WSS/VINCENT
NEAR TERM...WSS
SHORT TERM...WSS
LONG TERM...MWS
AVIATION...WSS



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