Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 041852
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
250 PM EDT MON MAY 4 2015

.SYNOPSIS... HIGH PRESSURE OFF THE MID ATLANTIC COAST WILL EXTEND
INTO THE REGION THROUGH MID WEEK. AN AREA OF LOW PRESSURE WILL FORM
NEAR THE BAHAMAS DURING THE MIDDLE OF THE WEEK AND MOVE SLOWLY NORTH
TOWARD THE SOUTHEAST COAST.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 245 PM MONDAY...

HIGH PRESSURE HAS SETTLED OFFSHORE AND EXTENDS WSW ACROSS THE
CAROLINAS TODAY...WITH BUILDING HEIGHTS CONTINUING ACROSS THE
SOUTHEAST STATES.  A FEW SHOWERS DEVELOPING OVER THE MOUNTAIN SLOPES
WILL DRIFT EAST THIS EVENING IN WEAK WESTERLY STEERING
FLOW...BUT INSTABILITY IS VERY WEAK OVER THE WESTERN PIEDMONT AND IT
WILL BE HARD FOR MORE THAN JUST AN ISOLATED TO SHOWER TO SURVIVE
EAST OF THE YADKIN.  THE SHOWERS AND MOST OF THE CLOUDS WILL
DIMINISH WITH LOSS OF HEATING...LEADING TO A MOSTLY CLEAR NIGHT AND
LOWS MOSTLY IN THE MID 50S.

&&

.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
AS OF 245 PM MONDAY...

HIGH PRESSURE WILL REMAIN IN PLACE OFFSHORE OF THE CAROLINAS ON
TUESDAY.  MEANWHILE A COLD FRONT WILL MOVE INTO THE VICINITY OF THE
MASON-DIXON LINE AND A SHALLOW UPPER TROUGH OVER THE GULF OF MEXICO
WILL DRIFT EAST ACROSS THE FLORIDA. BETWEEN THESE FEATURES...THE
ONLY FORCING FOR CONVECTION WILL BE DIFFERENTIAL HEATING ALONG THE
MOUNTAIN SLOPES AND A DEVELOPING LEE TROUGH THAT SHOULD REMAIN WEST
OF THE TRIAD.  FORECAST SOUNDINGS SHOW ANOTHER DAY OF RELATIVELY
DEEP MIXING AND LITTLE POTENTIAL FOR INSTABILITY.  WHAT CONVECTION
THAT DOES FORM TO THE NORTH AND WEST WILL ENCOUNTER A NORTHEASTERLY
STEERING FLOW THAT SHOULD FURTHER HELP TO KEEP ANY SHOWERS/STORMS
WEST OF THE TRIAD.  HIGHS AGAIN IN THE LOWER 80S...MAYBE A DEGREE
WARMER THAN TODAY BASED ON A SLIGHT UPTICK IN 1000-850MB THICKNESSES
BY 5M OR SO.

ANOTHER MOSTLY CLEAR NIGHT EXPECTED ON TUESDAY NIGHT AS LINGERING
CLOUD COVER FROM CONVECTION OVER VIRGINIA SHOULD HOLD TO OUR NORTH.
SOME VERY THIN HIGH CLOUDS MAY BEGIN TO FILTER IN FROM THE SOUTH AS
A SUB-TROPICAL LOW BEGINS TO DEVELOP NEAR THE BAHAMAS.  LOWS AGAIN
MOSTLY IN THE MID-60S.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
AS OF 215 PM MONDAY...

LIKELY LOW PRESSURE DEVELOPMENT OVER THE NRN BAHAMAS DOMINATES THE
MEDIUM RANGE FORECAST. WHILE SUCH DEVELOPMENT -- AND A GENERAL DRIFT
TO THE NORTH OR NNW -- IS FAIRLY CERTAIN AT THIS POINT... ITS EXACT
MOVEMENT... STRENGTH... AND POTENTIAL FOR TROPICAL CHARACTERISTICS
REMAINS IN QUESTION.

OVERVIEW: A BACKDOOR FRONT IS EXPECTED TO DROP SOUTHWARD TOWARD OUR
NRN BORDER BY WED MORNING... BUT LATEST GUIDANCE HOLDS THIS FRONT
(AND THE COOLER AIR BEHIND IT) JUST TO OUR NORTH... KEEPING US UNDER
THE INFLUENCE OF STACKED FLAT W-E ORIENTED RIDGING THROUGH THE LOW
AND MID LEVELS ACROSS NC EARLY WED. SUBTLE NEGATIVELY TILTED
TROUGHING ANALYZED OVER THE NE GULF THIS MORNING IS EXPECTED TO
TRACK SLOWLY ENE ACROSS FL BEFORE EMERGING OFF THE ERN FL COAST. THE
NAM INTENSIFIES THE ASSOCIATED SURFACE LOW MUCH MORE QUICKLY OVER
THE NRN BAHAMAS THAN THE GFS/ECMWF... AND THE NAM REMAINS THE
STRONGEST AS IT DRIFTS TO THE NORTH WED... WITH THE ECMWF THE
WEAKEST (MERELY AN INVERTED TROUGH WED). BY THU EVENING THE NAM/GFS
PLACE THE LOW JUST OFF HILTON HEAD SC... AND WHILE THE 00Z OP ECMWF
IS A BIT SOUTHEAST OF THIS POSITION... THE ECMWF ENSEMBLE MEAN IS
FAIRLY CLOSE TO THE NAM/GFS POSITION. THE GOOD NAM/GFS AGREEMENT
LENDS A BIT MORE CONFIDENCE IN THE GFS SOLUTION... WHICH CULMINATES
IN THE LOW TRACKING NORTHWESTWARD INTO SC THU NIGHT BEFORE BECOMING
STATIONARY (OR MEANDERING) AND WEAKENING JUST INLAND OVER THE
SOUTHEAST STATES OVER THE WEEKEND... A FUNCTION OF THE STEERING FLOW
AROUND A STRONG WRN ATLANTIC ANTICYCLONE... ALL BENEATH STRONG MEAN
EAST COAST MID LEVEL RIDGING. THE OP ECMWF ON THE OTHER HAND HOLDS
THE LOW OFFSHORE WITH A MORE NORTHEASTWARD DRIFT AND ACCORDINGLY
REMAINS STRONGER THROUGH SAT. WPC AND HPC EXPERTS ARE FAVORING A
MORE WESTWARD POSITION AS COMPARED TO EARLIER FORECASTS... A
COMPROMISE SOLUTION BETWEEN THE WESTERNMOST GFS AND EASTERNMOST
ECMWF WITH A SLIGHT LEAN TOWARD THE GFS... AND AT A SPEED SLIGHTLY
SLOWER THAN THE GFS. WHETHER THIS LOW ATTAINS ANY TROPICAL
CHARACTERISTICS IS DIFFICULT TO DETERMINE AT THIS TIME... AND ANY
SPECULATION WOULD BE JUST THAT... BUT AT LEAST SUBTROPICAL
DEVELOPMENT IS NOT OUT OF THE QUESTION GIVEN THAT WATER TEMPS JUST
NORTH OF THE BAHAMAS ARE NEAR 80 AND ABOVE CLIMATOLOGY. LATE IN THE
WEEK... TROUGHING THAT IS NOW JUST OFF THE PACIFIC NW... AND WHICH
WILL STRENGTHEN INTO A CLOSED LOW NEAR VEGAS BY FRI... WILL THEN
OPEN UP AND KICK EAST-NORTHEASTWARD THROUGH THE CENTRAL CONUS...
HELPING TO DISSIPATE AND PUSH EASTWARD ANY REMNANT LOW OVER THE
SOUTHEAST STATES.

SENSIBLE WEATHER: WED LOOKS DRY FOR MOST... ALTHOUGH IN THIS WEAK
FLOW REGIME... CONVECTION RESULTING FROM DIFFERENTIAL HEATING OVER
THE HIGHER TERRAIN AS WELL AS ALONG THE BACKDOOR FRONT TO OUR NORTH
MAY DRIFT INTO NRN AND NW SECTIONS LATE IN THE DAY. WILL KEEP LOW
CHANCE POPS WED IN THESE AREAS LATE AFTERNOON INTO EARLY EVENING. BY
THU AFTERNOON... FOLLOWING THE ABOVE-DISCUSSED TIMING/TRACK... WE
SHOULD START SEEING BANDS OF SHOWERS WORKING INTO THE SE CWA... WITH
CONVECTION STILL LIKELY FIRING OVER THE HIGHER TERRAIN JUST TO OUR
NW. WILL FOCUS CHANCE POPS ON THE SE AND IN THE FAR NW THU.
UNCERTAINTY GROWS EXPONENTIALLY BY FRI... BUT WITH A DECENT CHANCE
OF A WEAKER BUT STACKED LOW SOMEWHERE OVER THE INTERIOR SOUTHEAST
JUST INLAND... WILL LEAN TOWARD CLIMATOLOGICAL SHOWER/STORM
CHANCES... HIGHER SOUTH AND SE... FOR FRI AND HEADING INTO THE
WEEKEND. IF THE ECMWF IS CORRECT... WE WOULD SEE LOWER CONVECTION
COVERAGE WITH STRONGER RIDGING IN PLACE OVER THE SRN APPALACHIANS.
RAIN CHANCES SHOULD DIMINISH ONCE AGAIN SUN INTO MON WITH THE LIKELY
WEAKENING AND DEPARTURE OF ANY REMNANT LOW OVER OUR REGION... IN
RESPONSE TO THE APPROACHING TROUGH FROM THE WEST.

TEMPERATURES: LOW LEVEL THICKNESSES ARE EXPECTED TO BE SLIGHTLY
ABOVE NORMAL WED AND CONTINUE TO RISE A COUPLE OF METERS EACH DAY
THROUGH MON. SHOULD SEE HIGHS WED AROUND 80 AND LOWS WED NIGHT
AROUND 60. WITH EXPECTATIONS OF AT LEAST SOME CLOUD COVER AND
POSSIBLE SHOWERS THU ONWARD... WILL KEEP HIGHS NEAR TO SLIGHTLY
ABOVE NORMAL... TRENDING BACK TO AT LEAST A CATEGORY ABOVE NORMAL
SUN/MON AS WE SHOULD HAVE DECREASING CLOUDS AND CONVECTION COVERAGE.
ABOVE NORMAL LOWS THROUGH THE PERIOD. -GIH

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
AS OF 140 PM MONDAY...

HIGH CONFIDENCE VFR CONDITIONS THROUGH THE 24 HOUR TAF PERIOD AS
HIGH PRESSURE CENTERED OFFSHORE EXTENDS INTO OUR REGION THROUGH
TUESDAY.  SCATTERED SHOWERS ARE EXPECTED TO FORM (AND SOME ARE
ALREADY FORMING) ALONG THE MOUNTAINS TODAY...A FEW OF WHICH MAY
DRIFT EAST TOWARD THE TRIAD LATE THIS AFTERNOON.  CONDITIONS ARE
VERY FAVORABLE FOR THE SHOWERS TO VERY FAR TO THE EAST...BUT SOME HI-
RES MODELS SHOW A COUPLE SHOWERS NEAR KINT AFTER 20Z.  EVEN SO...THE
IMPACTS WILL BE SMALL IF ANY AT ALL...SO HAVE JUST INCLUDED A VFR
TEMPO AT KINT FOR THIS TAF PACKAGE.

CLEARING SKIES AND A LIGHT SOUTHWESTERLY WIND ARE EXPECTED TONIGHT
THROUGH 18Z ON TUESDAY.

OUTLOOK...VFR CONDITIONS ARE EXPECTED TUESDAY AND WEDNESDAY AHEAD OF
A FRONT THAT WILL DROP SOUTH INTO VIRGINIA BY WEDNESDAY...THEN
LIKELY REMAIN NORTH OF THE AREA AS A COASTAL LOW BEGINS TO TAKE
SHAPE OFF THE SOUTHEAST COAST LATE IN THE WEEK.  MOISTURE IS
EXPECTED TO INCREASE EACH DAY ALONG WITH THE THREAT OF EARLY MORNING
STRATUS/FOG.

&&

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

&&

$$
SYNOPSIS...BLAES
NEAR TERM...22
SHORT TERM...22
LONG TERM...HARTFIELD
AVIATION...22


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