Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 211136
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
635 AM EST SUN DEC 21 2014

.SYNOPSIS...WEAK LOW PRESSURE WILL MOVE OFF THE SOUTHEAST COAST
TONIGHT...AS HIGH PRESSURE REMAINS OVER THE AREA THROUGH SUNDAY.
ANOTHER LOW PRESSURE SYSTEM WILL MOVE ALONG THE CAROLINA COAST
MONDAY.

&&

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

TODAY...SURFACE HIGH CENTERED OVER THE EASTERN GREAT LAKES EARLY
THIS MORNING WILL DRIFT EAST ACROSS THE NORTHERN MID ATLANTIC
TODAY...AND EXTEND SWD INTO THE CAROLINAS. ALOFT A WEAK...RELATIVELY
FLAT...S/W RIDGE WILL CROSS OUR AREA. THE COMBINED EFFECTS OF THESE
TWO FEATURES SHOULD MAINTAIN DRY CONDITIONS UNTIL LATE AFTERNOON.
ABUNDANT MOISTURE IN THE LOWER LEVELS OF THE ATMOSPHERE WILL RESULT
IN WIDESPREAD CLOUDINESS OVER MOST OF THE PIEDMONT AND SANDHILLS
EARLY THIS MORNING. IN THE COASTAL PLAIN WHERE PARTIAL CLEARING HAS
OCCURRED...EXPECT LOW CLOUDS AND/OR FOG TO DEVELOP PRIOR TO
DAYBREAK. EXPECT PARTIAL CLEARING ACROSS MOST OF CENTRAL NC LATER
THIS MORNING IN RESPONSE TO WEAK SUBSIDENCE MIXING DRIER AIR ALOFT
TOWARDS THE SURFACE. MAX TEMPS THIS AFTERNOON DEPENDENT ON THIS
PARTIAL CLEARING TO ALLOW FOR BITS OF SUN...WARMING TEMPS WELL INTO
THE 40S WITH LOWER 50S POSSIBLE ACROSS THE SOUTH. IF PARTIAL
CLEARING FAILS TO MATERIALIZE...THEN MAX TEMPS WILL MOSTLY LIKELY BE
IN THE MID-UPPER 40S.

LATE THIS AFTERNOON-TONIGHT...MODEL GUIDANCE IN GOOD AGREEMENT IN
ITS DEPICTION OF A SOUTHERN STREAM S/W PROJECTED TO CROSS THE LOWER
MS VALLEY AND INDUCE WEAK SFC WAVE DEVELOPMENT OFF THE SC COAST BY
EARLY MONDAY. WHILE THE DRY AIR SFC RIDGE WILL MAINTAIN A PRESENCE
OVER CENTRAL NC...DEVELOPING SLY FLOW A FEW THOUSAND FEET ALOFT WILL
INITIATE AN OVERRUNNING EVENT...LEADING TO A CLASSICAL OR HYBRID
COLD AIR DAMMING EVENT. AS SLY FLOW STRENGTHENS OVERNIGHT...EXPECT
RAIN TO OVERSPREAD THE REGION FROM THE SOUTH...LOCKING IN THE CAD
AIR MASS. SPOTS OF LIGHT PRECIP MAY BREAK OUT PRIOR TO SUNSET ACROSS
THE FAR SOUTH BUT BEST LIFT EXPECTED TO OCCUR AFTER MID-LATE EVENING
IN THE SOUTH...AND AFTER MIDNIGHT ACROSS THE NORTH. PLAN TO ADJUST
POPS IN THIS DIRECTION...WITH LIKELY POPS ACROSS THE FAR SOUTH BY
01Z-02Z WITH SLIGHT CHANCE ACROSS THE NORTH...BECOMING CATEGORICAL
BY EARLY MONDAY ACROSS THE SOUTH AND LIKELY ACROSS THE NORTH. MODEL
PRECIP AMOUNTS NOT AS ROBUST AS 24-36 HOURS AGO WITH AMOUNTS THROUGH
SUNDAY NIGHT-EARLY MONDAY ABOUT A TENTH OF A INCH OR LESS.
INCREASING/THICKENING CLOUDS OVERNIGHT WILL AID TO MODERATE TEMPS SO
EXPECT MIN TEMPS TO OCCUR AROUND OR SHORTLY AFTER MIDNIGHT WITH
STEADY TEMPS THEREAFTER. MIN TEMPS 35-40.

&&

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

MONDAY...BEST LIFT ASSOCIATED WITH THE SOUTHERN STREAM S/W WILL
AFFECT OUR REGION MONDAY MORNING THEN LIFT NEWD OUT OF OUR AREA
MONDAY AFTERNOON. THUS...WILL ADVERTISE HIGHEST POPS IN THE MORNING
WITH DECREASING POPS IN THE AFTERNOON. AGAIN MODEL CONSENSUS HAS
DECREASED EXPECTED RAINFALL AMOUNTS COMPARED TO 24 HOURS AGO BUT
STILL EXPECT AROUND A QUARTER OF AN INCH. THE WIDESPREAD RAIN EARLY
IN THE DAY WILL AID TO LOCK IN THE CAD AIR MASS AND ASSOCIATED LOW
CLOUDS. THIS WILL RESULT IN MAX TEMPS JUST 5-8 DEGREES WARMER THAN
EXPECTED MIN TEMPS. MAX TEMPS NEAR 40 NW TO NEAR 50 FAR SE.

MONDAY NIGHT...CAD AIR MASS EXPECTED TO PERSIST MAINTAINING
EXTENSIVE CLOUDINESS WITH AREAS OF DRIZZLE OR SPOTTY LIGHT RAIN.
TEMPS USUALLY DO NOT DISPLAY MUCH DIURNAL CHANGE IN THIS TYPE OF AIR
MASS SO MIN TEMPS EXPECTED TO RANGE FROM THE MID 30S NW TO THE LOW-
MID 40S SE.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
AS OF 215 AM SUNDAY...

...WARM... WET AND RATHER WINDY SYSTEM TO AFFECT OUR REGION TUESDAY
NIGHT THROUGH CHRISTMAS EVE... THEN WINDY AND COOLER CHRISTMAS DAY...

THERE IS HIGH CONFIDENCE OF A WARM... WET AND WINDY SYSTEM WILL
AFFECT OUR REGION MID WEEK. MODELS AND ENSEMBLES AGREE IN GENERAL IN
THAT A THE MAIN SURFACE STORM TRACK WILL BE FROM THE GULF OF MEXICO
NORTHWARD THROUGH THE TENNESSEE AND OHIO VALLEY REGIONS TUE NIGHT
INTO WEDNESDAY NIGHT. THE OPERATIONAL GFS IS SLOWER/A BIT WEAKER
WITH THE MAIN SURFACE WAVE... DEPICTING A 997 MB SURFACE LOW OVER KY
18Z/WED... WHILE THE AVERAGE OF THE ENSEMBLES SUGGEST AROUND A 992
LOW OVER OR NEAR NW OHIO 12Z/WED. REGARDLESS... WITH THE STORM
HEADING UP THE WEST SIDE OF THE APPALACHIANS... OUR REGION WILL HAVE
TO DEAL WITH RESIDUAL COLD AIR DAMMING... A RETREATING
WEDGE/WARM/COASTAL FRONT... AND THEN THE MAIN COLD FRONT. TIMING OF
THESE WILL BE CRITICAL TO THE SENSIBLE WEATHER FORECASTS. THIS FAR
OUT... THESE DETAILS WILL HAVE TO BE REFINED AS THE EVENT EVOLVES.
AT THIS POINT WE WILL MAINTAIN CONTINUITY FROM OUR PREVIOUS
FORECASTS AND BLEND IN THE LATEST ENSEMBLE MEANS TO GIVE IT OUR BEST
SHOT AT EACH OF THESE FEATURES. ONE THING FOR SURE... CONFIDENCE IS
100 PERCENT IN ALL RAIN.

TUESDAY AND TUESDAY NIGHT... LINGERING COLD AIR DAMMING IS EXPECTED
TO BE IN PLACE OVER A GOOD PORTION OF THE PIEDMONT DAMMING REGION
12Z/TUESDAY. AN INITIAL WEAK SURFACE WAVE SHOULD BE TRACKING OFF THE
DELMARVA COAST WITH A TRAILING COASTAL FRONT INTO SE GEORGIA. THIS
COASTAL FRONT APPEARS THAT IT WILL HAVE A DIFFICULT TIME COMING
INLAND INITIALLY GIVEN THAT THE MAIN STORM TRACK AND DYNAMICS WILL
BE LIFTING NORTH (WEST OF THE MOUNTAINS) INSTEAD OF COMING EAST OR
NORTHEAST ACROSS THE MOUNTAINS. THE PRESSURE GRADIENT WILL BE
LACKING TUESDAY. HOWEVER... THE WAA PATTERN WILL INCREASE LATER
TUESDAY INTO TUESDAY NIGHT AS THE SURFACE WAVE STRENGTHENS OVER THE
TENNESSEE VALLEY AND LIFTS TOWARD OHIO BY 12Z/WED. WAA RAINS WILL BE
AIDED BY WARM FRONTAL LIFT FROM THE SOUTHEAST LATE TUESDAY NIGHT
INTO EARLY WEDNESDAY. SOME OF THE LATEST GUIDANCE SUGGESTS THE
HEAVIEST RAINS MAY FALL OVER THE WESTERN PIEDMONT INTO THE MOUNTAINS
ALONG AND NEAR THE RETREATING WARM/COASTAL FRONT. IT IS STILL
DIFFICULT TO FORECAST EXACTLY WHERE THE WARM FRONT WILL BE LOCATED
12Z/WED... BUT WHEN CLIMATOLOGY IS APPLIED TO THE GIVEN STORM TRACK
AND STRENGTH ALONG WITH THE LINGERING CAD (RETREATING SURFACE HIGH
OF 1030 MB OFF NEW ENGLAND)... THE WARM FRONT MOST LIKELY WILL BE
VERY NEAR THE SE PIEDMONT FROM CHARLOTTE TO RALEIGH EARLY IN THE DAY
WED. THE FRONT SHOULD LIFT INTO VIRGINIA DURING THE AFTERNOON. THIS
WILL LIKELY LEAD TO A LULL IN THE WARM FRONTAL RAINS AS THEY LIFT
INTO VIRGINIA WEDNESDAY AFTERNOON.

THE MAIN COLD FRONT SHOULD ARRIVE BETWEEN 00Z/06Z THURSDAY
(WEDNESDAY NIGHT)... ACCOMPANIED BY ADDITIONAL SHOWERS AND POSSIBLY
A FEW THUNDERSTORMS (IF THE LOW LEVELS CAN DESTABILIZE ENOUGH WHICH
IS IN DOUBT - GIVEN THE TIME OF YEAR. HOWEVER... SURFACE DEW POINTS
WEDNESDAY AFTERNOON IN THE WARM SECTOR SHOULD REACH 60 OR EVEN 65
SE. BREEZY TO WINDY SW FLOW AT 10-25 MPH CAN BE EXPECTED WITH TEMPS
INTO THE 65-72 RANGE. THIS WOULD STILL ONLY YIELD MUCAPES OF 100 TO
200 J/KG. IN ADDITION... THE STRONGEST LOW LEVEL JET IS EXPECTED TO
PUSH NORTHWARD INTO VA/MD BY EARLY WEDNESDAY AFTERNOON ALONG THE
RETREATING WARM FRONT. WITH THE MAIN DYNAMICS PASSING OVER THE GREAT
LAKES... THESE FACTORS WILL GREATLY LIMIT ANY SEVERE POTENTIAL WITH
THIS STORM FOR CENTRAL NC.

SENSIBLE WEATHER TUESDAY THROUGH WEDNESDAY...

COOL AND CLOUDY TUESDAY WITH SOME LIGHT DRIZZLE. THEN A CHANCE OF
RAIN AGAIN IN TEH AFTERNOON IN THE SW. HIGHS IN THE MID 40S TO MID
50S (PROBABLY NOT UNTIL TUESDAY EVENING). PERIODS OF RAIN... SOME
HEAVY TUESDAY NIGHT INTO WEDNESDAY MORNING. RAIN ENDING FROM THE
SOUTH BY AFTERNOON. THEN SHOWERS AND A SLIGHT CHANCE OF
THUNDERSTORMS AGAIN IN THE MID TO LATE AFTERNOON (NW)... LATE
AFTERNOON AND EVENING ELSEWHERE.  BECOMING WINDY AND WARMER FROM THE
SOUTH TUESDAY NIGHT INTO WEDNESDAY (NW ZONES LATEST TO SEE WARMING).
TEMPS RISING LATE WITH READINGS MID 50S TO MID 60S BY 12Z/WED NW TO
SE. HIGHS WEDNESDAY IN THE MID 60S TO LOWER 70S. SHOWERS TAPER OFF
QUICKLY FROM THE WEST WEDNESDAY NIGHT. CLOUDY WITH LOWS IN THE 40S
TO LOWER 50S.

THURSDAY THROUGH SATURDAY... THE PRESSURE GRADIENT WILL REMAIN TIGHT
THURSDAY WITH A GUSTY W-NW WIND AT 15-25 MPH. HIGHS GENERALLY IN THE
50S WITH PARTLY TO MOSTLY SUNNY SKIES. FRIDAY SHOULD BE DRY WITH
ANOTHER COLD FRONT EXPECTED TO AFFECT THE REGION BY LATE FRIDAY
NIGHT AND SATURDAY WITH A CHANCE OF RAIN SHOWERS. LOWS 35-40. HIGHS
55-62.

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
AS OF 635 AM SUNDAY...

WIDESPREAD MVFR/LOW END VFR CEILINGS WILL PERSIST THROUGH MID-LATE
MORNING ACROSS MUCH OF THE PIEDMONT AND SANDHILLS. OVER THE COASTAL
PLAIN...PARTIAL CLEARING MAY OCCUR. THE KRWI IS ON THE EDGE OF THE
THIS CLEARING WHICH MAY LEAD TO PERIODS OF VFR/HIGH END MVFR
CEILINGS.

MODEL GUIDANCE SO FAR THIS MORNING HAS NOT VERIFIED WELL WITH THE
CURRENT STRATOCU DECK OVER THE REGION. THIS LEADS TO LOW CONFIDENCE
THAT WE WILL SEE APPRECIABLE CLEARING LATER THIS MORNING-THIS
AFTERNOON. CURRENT THINKING IS THAT A BROKEN DECK OF STRATOCU WILL
PERSIST INTO THE AFTERNOON WITH CEILINGS 3500-4500 FT. ANY CLEARING
THAT OCCURS WILL LIKELY BE SHORT-LIVED.

A DEVELOPING LOW PRESSURE SYSTEM OVER THE NORTHERN GULF WILL BEGIN
TO LIFT NE ALONG THE GA-SC COAST TONIGHT. THIS WEATHER SYSTEM WILL
SPREAD ADDITIONAL MOISTURE INTO CENTRAL NC LATER TODAY AND TONIGHT.
THIS WILL LEAD TO A DETERIORATION OF AVIATION CONDITIONS WITH
WIDESPREAD MVFR/IFR CEILINGS AND AN EXPANDING AREA OF LIGHT RAIN.
THE ADVERSE AVIATION WEATHER CONDITIONS WILL PERSISTS INTO MONDAY
MORNING.

THE RAIN WILL DIMINISH MONDAY AFTERNOON-MONDAY NIGHT THOUGH
EXTENSIVE CLOUDINESS EXPECTED TO PERSIST.WILL LIKELY SEE WIDESPREAD
IFR CONDITIONS MONDAY NIGHT DUE TO LOW CLOUDS AND FOG/DRIZZLE.
ANOTHER LOW PRESSURE SYSTEM WILL AFFECT CENTRAL NC LATE TUESDAY INTO
WEDNESDAY...BRINGING A ROUND OF HEAVY SHOWERS AND POSSIBLY A FEW
THUNDERSTORMS. IMPROVING SKY/WEATHER CONDITIONS CHRISTMAS DAY BEHIND
AN EXITING COLD FRONT. SFC WINDS WILL BECOME BREEZY WEDNESDAY
THROUGH CHRISTMAS DAY WITH WIND GUSTS 30-35KTS PROBABLE.

&&

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

&&

$$

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


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