Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 151115
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
715 AM EDT MON SEP 15 2014

.SYNOPSIS...WEAK HIGH PRESSURE WILL EXTEND SOUTHWARD INTO CENTRAL NC
TODAY THEN DRIFT EAST TONIGHT. A COLD FRONT WILL DRIFT SOUTHEAST
ACROSS CENTRAL NC ON TUESDAY. COOL HIGH PRESSURE WILL BUILD INTO THE
REGION ON WEDNESDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 325 AM MONDAY...

CHALLENGING FORECAST IN THE NEAR TERM. MOIST STABLE LOW LEVEL AIR
MASS CURRENTLY IN PLACE WITH WEAK SURFACE HIGH RIDGING SOUTHWARD
INTO THE CAROLINAS FROM A WEAK PARENT HIGH (1024MB) CENTERED OVER
SOUTHERN NEW ENGLAND. THIS FEATURE PROJECTED TO DRIFT EAST TODAY.
UPSTAIRS...WLY FLOW ALOFT WILL ADVANCE A VORT MAX CURRENTLY CROSSING
THE SOUTHERN PLAINS EARLY THIS MORNING ACROSS THE TN VALLEY THIS
AFTERNOON AND INTO OUR REGION TONIGHT. THIS FEATURE PROJECTED TO
SLOWLY WEAKEN AS IT GETS CLOSER TO OUR AREA. WHEN IT ARRIVES...IT
WILL HAVE ENOUGH MOISTURE TO WORK WITH AS PRECIPITABLE WATER VALUES
SHOULD RANGE 1.3/1.4 INCHES ACROSS THE NORTH TO 1.75 INCHES ACROSS
THE SOUTH. ASIDE FROM THE MID/UPPER LEVEL DISTURBANCE...FORCING IS
WEAK IN THE LOWER HALF OF THE ATMOSPHERE. THUS...CANNOT SEE POP ANY
HIGHER THAN ABOUT 1-IN-3 CHANCE...AND MAINLY ACROSS THE WEST AND
SOUTH SECTIONS DURING THE EVENING HOURS.

SO...EXPECT WIDESPREAD CLOUDINESS THIS MORNING WITH AN ISOLATED
SHOWER POSSIBLE SOUTH HALF. BY MID AFTERNOON...EXPECT SOME PARTIAL
SUNSHINE. THIS HEATING MAY FUEL A FEW MORE SHOWERS AND POSSIBLY A
THUNDERSTORM...AGAIN MAINLY ACROSS THE SOUTH. THE APPROACH OF THE
UPPER LEVEL DISTURBANCE FROM TEH WEST SHOULD MAINTAIN A THREAT FOR A
FEW SHOWERS AND POSSIBLY A THUNDERSTORM...MAINLY ACROSS THE WEST AND
SOUTH...WITH THE THREAT DECREASING FROM THE NW WELL AFTER MIDNIGHT.

TEMPS TODAY DEPENDENT UPON WHEN/IF CLOUDS DIMINISH TO ALLOW SOME
SUN. USED A BLEND OF MOS GUIDANCE WITH A SLIGHT ADJUSTMENT TOWARD
THE COOLER END. MAX TEMPS UPPER 70S NORTH TO LOWER 80S SOUTH. MIN
TEMPS TONIGHT MID-UPPER 60S.

&&

.SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
AS OF 325 AM MONDAY...

WHILE MID LEVEL DISTURBANCE CROSSES OUR REGION LATE
TONIGHT...ANOTHER (THOUGH STRONGER) S/W WILL BE CROSSING THE GREAT
LAKES INTO SOUTHERN NEW ENGLAND. THIS FEATURE WILL PROPEL A SURFACE
COLD FRONT ACROSS CENTRAL NC TUESDAY. DUE TO WEAK SUBSIDENCE IN THE
WAKE OF THE DEPARTING INITIAL DISTURBANCE...FORCING ALONG THE
SURFACE COLD FRONT IS RELATIVELY WEAK. THUS...EXPECT ANY CONVECTION
ASSOCIATED WITH THE COLD FRONT TO BE NO WORSE THAN
SCATTERED...MAINLY OCCURRING ACROSS THE SOUTH HALF OF THE FORECAST
AREA. PASSAGE OF A MID LEVEL TROUGH TUESDAY NIGHT WILL MAINTAIN A
SLIGHT CHANCE POP TUESDAY NIGHT ACROSS THE FAR SOUTH.

DOWNSLOPE FLOW IN THE WAKE OF THE DEPARTING INITIAL DISTURBANCE WILL
AID TO MIX OUT ANY LOW LEVEL CLOUDINESS AND RESULT IN SOME
SUBSIDENCE WARMING. MOS GUIDANCE APPEARS TOO WARM BY ABOUT A
CATEGORY AS CLOUDINESS MAY HOLD ON LONGER THAN PROJECTED BY THE
MODELS PLUS DOWNSLOPE FLOW RATHER WEAK. FAVOR MAX TEMPS 2-4 DEGREES
COOLER THAN GUIDANCE (LOW-MID 80S). MIN TEMPS TUESDAY NIGHT NEAR 60
FAR NORTH-NW TO THE MID 60S SOUTH.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
AS OF 330 AM MONDAY...

THE MEDIUM RANGE WILL FEATURE A LONGWAVE TROUGH THAT WILL AMPLIFY
OVER THEN MOVE OFFSHORE THE EAST COAST MID-LATE WEEK. THE TROUGH
WILL THEN LIFT OUT AND YIELD BRIEFLY TO A FLAT SUB-TROPICAL RIDGE
FORECAST TO BUILD EAST FROM THE SOUTHERN PLAINS AND LOWER MS VALLEY
EARLY THIS WEEKEND...BEFORE RENEWED TROUGHING AMPLIFIES FROM CENTRAL
CANADA TO THE EAST COAST SUN-MON.

MEANWHILE AT THE SFC...A LEAD SFC HIGH WILL BUILD FROM THE OH VALLEY
TO THE MIDDLE ATLANTIC COAST WED...THEN BE OVERWHELMED BY A STRONGER
(1028-1030 MB) ONE FORECAST TO BUILD FROM CENTRAL CANADA TO THE
CANADIAN MARITIMES...AND RIDGE SOUTH/SOUTHWESTWARD IN A DAMMING
ORIENTATION EAST OF THE APPALACHIANS...THU THROUGH THE WEEKEND. 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.

THE RELATIVE GREATEST CLOUD COVERAGE WILL OCCUR WED-THU...WHEN A
SLIGHT-LOW CHANCE OF SHOWERS WILL ALSO BE INTRODUCED...AS WEAK
DISTURBANCES RIPPLE THROUGH THE AFOREMENTIONED LONGWAVE TROUGH
AMPLIFYING OVER THE EASTERN STATES. IN FACT...WED MAY WELL BE A
RATHER DREARY DAY THROUGH AT LEAST EARLY AFTERNOON...AS ISENTROPIC
LIFT IN RETURN FLOW AROUND A 925-850 MB RIDGE ALONG THE COASTAL
CAROLINAS AUGMENTS THE WEAK FORCING ATTENDING THE PASSING MID LEVEL
DISTURBANCES. SOME PARTIAL CLEARING FROM THE WEST WILL BE POSSIBLE
BY MID LATE AFTERNOON...WHEN THE FLOW BECOMES INCREASINGLY
WESTERLY/DOWNSLOPE AS THE AFOREMENTIONED LOW LEVEL ANTICYCLONE
DRIFTS OFFSHORE. AS SUCH...HIGH TEMPERATURES SHOULD CLIMB ONLY INTO
THE 69 TO 76 DEGREE RANGE...COOLEST OVER THE NE PIEDMONT AND
NORTHERN COASTAL PLAIN.

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.

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
AS OF 715 AM MONDAY...

WIDESPREAD MVFR CEILINGS WILL PERSIST ACROSS CENTRAL NC THIS
MORNING...AND MAY LAST UNTIL MID-AFTERNOON. BETWEEN 12Z-16Z...MAY
SEE POCKETS OF IFR CEILING. BETWEEN
19Z-21Z...MVFR CEILINGS MAY GRADUALLY SCATTER OUT....BUT MVFR
CEILINGS MAY RETURN BY 00Z TUESDAY.

SURFACE WINDS WILL BE LIGHT (LESS THAN 10KTS)...AND SLOWLY VEER FROM
THE CURRENT EAST-NORTHEAST TO A SOUTH-SOUTHEAST DIRECTION BY 22Z.

LATE TONIGHT INTO EARLY TUESDAY MORNING...AREAS OF LOW CLOUDS AND
FOG MAY DEVELOP WITH CEILINGS 500-1000FT HIGHLY PROBABLE WITH POCKETS
OF 200-500FT POSSIBLE. VISIBILITY 3-5SM EXPECTED WITH AREAS OF 1-2
MILES PROBABLE.

A COLD FRONT WILL DRIFT ACROSS CENTRAL NC TUESDAY. THIS SYSTEM MAY
CAUSE AREAS OF MVFR CEILING ALONG WITH SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS. THE ISOLATED THUNDERSTORM THREAT WILL BE
HIGHEST IN VICINITY OF KFAY.

COOL HIGH PRESSURE WILL BUILD INTO CENTRAL NC FROM THE NORTHWEST. NE
LOW LEVEL FLOW MAY MAINTAIN MOISTURE IN THE LOWEST 8K FT...RESULTING
IN PERIODS OF MVFR CEILINGS AND POSSIBLY PATCHY LIGHT RAIN
WEDNESDAY...AND POSSIBLY THURSDAY. VFR CONDITIONS ANTICIPATED FRIDAY.

&&

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

&&

$$

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


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