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775
FXUS62 KRAH 200816
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
315 AM EST SAT DEC 20 2014

.SYNOPSIS...A FAST MOVING DISTURBANCE WILL TRACK EASTWARD ACROSS THE
REGION TODAY. WEAK HIGH PRESSURE WILL EXTEND ACROSS CENTRAL NORTH
CAROLINA SUNDAY. ANOTHER DISTURBANCE AND ASSOCIATED SURFACE LOW
PRESSURE SYSTEM WILL AFFECT OUR AREA SUNDAY NIGHT INTO MONDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 315 AM SATURDAY...

TODAY...S/W EXITING THE DEEP SOUTH EARLY THIS MORNING
PROJECTED TO CROSS NEAR OR JUST SOUTH OF CENTRAL NC LATE THIS
MORNING-EARLY THIS AFTERNOON. THIS FEATURE APPEARS TO BE ADVANCING A
LITTLE FARTHER TO THE NORTH THAN WHAT PREVIOUS MODEL RUNS HAD
DEPICTED. STILL EXPECT BULK OF LIGHT PRECIPITATION ASSOCIATED WITH
THIS FEATURE TO AFFECT MAINLY OUR SOUTHERN COUNTIES.
HOWEVER...POTENTIAL FOR SPOTTY LIGHT PRECIP TO EXTEND AS FAR NORTH
AS THE I-40 CORRIDOR BETWEEN THE TRIAD AND THE TRIANGLE THIS
MORNING. THUS HAVE ADJUSTED POPS A LITTLE HIGHER ACROSS THE NORTHERN
PIEDMONT WHILE MAINTAINING LIKELY POPS ACROSS THE SOUTH.

BULK OF LIFT ASSOCIATED WITH THE S/W WILL BEGIN TO EXIT OUR REGION
BY MID DAY-EARLY AFTERNOON. THUS SHOULD SEE PRECIP COVERAGE DIMINISH
OVER MOST OF THE PIEDMONT BY EARLY AFTERNOON. DUE TO CLOSE PROXIMITY
OF THE S/W...PRECIP MAY PERSIST WELL INTO THE AFTERNOON ACROSS THE
SANDHILLS AND SOUTHERN COASTAL PLAIN.

PARTIAL THICKNESSES OFF THE LATEST MODEL GUIDANCE IN CONJUNCTION
WITH EVAPORATIVE COOLING SUGGEST DECENT PROBABILITY OF RAIN MIXED
WITH SNOW ACROSS THE NW PIEDMONT EARLY THIS MORNING.

HIGH TEMPS TODAY DEPENDENT ON EXTENT OF PRECIP. EXTENSIVE CLOUDINESS
WILL LIMIT INSOLATION. IF PRECIP MORE WIDESPREAD THAN ANTICIPATED
ACROSS THE PIEDMONT/NORTHERN COASTAL PLAIN...TEMPS MAY STRUGGLE TO
MAKE IT OUT OF THE 30S. OVERALL...TEMPS TODAY WILL BE A SOLID 7-10
DEGREES BELOW NORMAL. MAX TEMPS GENERALLY 40-45 DEGREES.

TONIGHT...WEAK SUBSIDENCE IN THE WAKE OF THE DEPARTING S/W AND SFC
RIDGE NOSING SWD INTO OUR REGION SHOULD AID TO DIMINISH THE CLOUD
COVERAGE OVER OUR REGION. MODELS DIFFER ON EXTENT OF CLEARING WITH
THE GFS A LITTLE MORE AGGRESSIVE THAN MOST. ANY PRECIP OCCURRING AT
SUNSET ACROSS THE FAR SE SHOULD DIMINISH/DISSIPATE BEFORE 10 PM.
STILL EXPECT SOME RESIDUAL CLOUDINESS OVERNIGHT. IF GFS VERIFIES
BEST...THEN MIN TEMPS TONIGHT MAY END UP BEING 2-4 DEGREES COLDER
THAN CURRENTLY FORECAST. MIN TEMPS UPPER 20S/AROUND 30 NORTH TO THE
LOWER 30S SOUTH.

&&

.SHORT TERM /SUNDAY AND SUNDAY NIGHT/...
AS OF 315 AM SATURDAY...

SFC RIDGE EXTENDS SOUTH ACROSS THE AREA...AIDED ALOFT BY A
MINOR S/W RIDGE. THIS SHOULD PROVIDE PARTLY-MOSTLY SUNNY SKIES TO
START THE DAY. A S/W EXITING THE SOUTHERN PLAINS WILL BACK THE FLOW
ALOFT TO A SWLY FLOW AND BEGIN TO ADVANCE MID-HIGH LEVEL CLOUDINESS
FROM THE SOUTH LATE IN THE DAY. LOW LEVEL THICKNESSES IN THE 1315M-
1330M RANGE...SUPPORTIVE OF MAX TEMPS ABOUT A CATEGORY OR TWO BELOW
NORMAL. MAX TEMPS NEAR 50-LOWER 50S. IF CLOUDS ARE DELAYED ACROSS
THE SOUTH...MAX TEMPS MAY END UP BEING 2-3 DEGREES WARMER.

SUNDAY NIGHT...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 A 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 TOWARD 06Z...EXPECT RAIN
TO OVERSPREAD THE REGION FROM THE SOUTH...LOCKING IN THE CAD AIR
MASS. WILL START OUT WITH CHANCE POPS ACROSS THE SOUTH IN THE
EVENING...RAMPING UP TO LIKELY POPS ACROSS THE SOUTH HALF AFTER
MIDNIGHT...AND CHANCE POPS ELSEWHERE. IF MODEL TRENDS CONTINUE IN
LATER MODEL RUNS...AN INCREASE IN POPS TO LIKELY NORTH AND
CATEGORICAL SOUTH WOULD BE WARRANTED. MIN TEMPS MAINLY 35-40 DEGREES.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
AS OF 255 AM SATURDAY...

MONDAY THROUGH WEDNESDAY: A SOUTHERN STREAM S/W DISTURBANCE WILL
LIFT NORTHEASTWARD OUT FROM THE GULF COAST STATES ON SUNDAY NIGHT
INTO MONDAY MORNING... SPREADING WIDESPREAD RAIN ACROSS ALL OF
CENTRAL NC AS ISENTROPIC LIFT RAMPS UP. WITH A 1030 MB SURFACE HIGH
STILL EXPECTED TO BE EXTENDING SOUTHWARD INTO OUR AREA (AS IT EVER
SO SLOWLY SHIFTS EASTWARD) EXPECT WE WILL SEE A PRONOUNCED DAMMING
EVENT DEVELOP.... WITH TEMPS FALLING INTO THE MID TO UPPER 30S
MONDAY MORNING ACROSS THE NORTHERN AND NORTHWEST PIEDMONT... WITH
TEMPS IN THE 40S ELSEWHERE. HOWEVER... BOTH THE GFS AND ECMWF
CONTINUE TO DEPICT AN ALL RAIN EVENT ACROSS THE AREA... WITH A
PRONOUNCED WARM NOES AT AROUND 4-5KFT COMBINED WITH SURFACE WETBULB
TEMPS IN THE MID 30S AT WORST WHEN THE PRECIP SPREADS INTO THE AREA.
THE MORE SUBSTANTIAL PRECIP WILL COME TO AN END BY EARLY TO MID
AFTERNOON AS THE BEST MOIST ISENTROPIC UPGLIDE BEGINS TO WANE ALONG
WITH DRIER AIR ALOFT FILTERING INTO THE AREA. STILL WE SHOULD SEE
SOME LINGERING AREAS OF LIGHT RAIN AND DRIZZLE REMAINING.

WITH A GOOD AREAWIDE QUARTER TO A HALF INCH OF RAIN EXPECTED WE
SHOULD BE ABLE TO LOCK IN THE DAMMING AIRMASS. THUS.. HAVE LOWERED
HIGH TEMPS... ESPECIALLY ACROSS THE EASTERN/SOUTHEASTERN PORTION OF
CENTRAL NC. EXPECT HIGH TEMPS TO RANGE FROM THE UPPER 30S N/NW TO
THE MID TO UPPER 40S E/SE. TEMPS MONDAY NIGHT/TUESDAY MORNING ARE
EXPECTED TO REMAIN NEAR STEADY OR EVEN SLOWLY BEGIN TO RISE A
LITTLE. THUS... WILL GO WITH LOWS RANGING FROM THE UPPER 30S TO MID
40S.

A NORTHERN STREAM DISTURBANCE WILL HAVE FORMED A DEEP TROUGH BY
TUESDAY MORNING WITH STACKED LOW PRESSURE OVER THE UPPER MIDWEST.
BOTH THE GFS AND ECMWF ARE IN GOOD AGREEMENT IN SHOWING THE DEEP
ASSOCIATED TROUGH AXIS SHIFTING EASTWARD ON TUESDAY INTO WEDNESDAY
WHILE TAKING ON MORE OF A NEGATIVE TILT... WITH THE ASSOCIATED
SURFACE FRONT (AND A POSSIBLE TRIPLE POINT LOW) MOVING ACROSS
CENTRAL NC ON WEDNESDAY MORNING INTO THE EARLY AFTERNOON (AS IT
STANDS NOW... STILL SEVERAL DAYS OUT THOUGH). QUESTIONS REMAIN AS TO
WHERE A POSSIBLE TRIPLE POINT LOW MAY FORM THOUGH... AS FINER
DETAILS LIKE THIS ARE HARD TO NAIL DOWN THIS FAR OUT IN THE
FORECAST. HOWEVER... WITH THE POTENTIAL FOR A RETREATING CAD
BOUNDARY AND STRENGTHENING LOW LEVEL WIND FIELD... WE WILL NEED TO
KEEP AN EYE ON HOW THIS SYSTEM COMES TOGETHER. THIS WOULD BE A HSLC
TYPE OF SYSTEM. GIVEN THE TIME OF YEAR IT IS QUITE HARD TO GET THE
NEEDED INSTABILITY FOR POSSIBLE SEVERE STORMS THOUGH. AS THE
EFFECTIVE FRONT APPROACHES AND MOVES THROUGH THE AREA ON WEDNESDAY
MORNING INTO THE AFTERNOON WE SHOULD SEE A BAND OF RAIN/SHOWERS
ALONG AND IN ADVANCE OF IT (WITH POSSIBLY A FEW THUNDERSTORMS)...
WITH THINGS DRYING OUT QUICKLY BEHIND THE EFFECTIVE FRONT ON
WEDNESDAY AFTERNOON.

HIGHS ON TUESDAY WILL BE TRICKY AND DEPEND ON HOW MUCH THE CAD
BOUNDARY RETREATS. FOR NOW WILL GO WITH HIGHS IN THE UPPER 40S NW TO
AROUND 60S SE. TEMPS BY WEDNESDAY MORNING WILL NOT FALL MUCH... WITH
LOWS WEDNESDAY MORNING IN THE UPPER 40S NW TO MID 50S SE/E. TEMPS
ARE EXPECTED TO WARM WEDNESDAY AHEAD OF THE FRONT INTO THE UPPER 50S
NW TO THE UPPER 60S E.

WEDNESDAY NIGHT THROUGH THURSDAY: WE SHOULD SEE RAPID CLEARING ON
WEDNESDAY NIGHT AND CONTINUING FOR THE REST OF THE WEEK... WITH A
RETURN TO QUITE WEATHER. LOWS THURSDAY MORNING ARE EXPECTED TO BE IN
THE 30S... WITH HIGHS THURSDAY AND FRIDAY AFTERNOONS IN THE 50S. WE
COULD BE A BIT BREEZE ON THURSDAY AS MODELS ARE SHOWING THE
POTENTIAL FOR SUSTAINED WINDS OUT OF THE WSW IN THE 14 TO 20 MPH
RANGE... WITH MAYBE SOME GUSTS OF UP TO 25 MPH.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
AS OF 105 AM SATURDAY...

AN UPPER LEVEL DISTURBANCE ADVANCING EAST ACROSS THE
DEEP SOUTH WILL PASS SOUTH OF CENTRAL NC LATER THIS MORNING THROUGH
EARLY AFTERNOON. THIS WEATHER SYSTEM WILL INCREASE CLOUDINESS ALONG
WITH PATCHES OF LIGHT RAIN OVER OUR REGION BY DAYBREAK. EXPECT
CEILINGS TO LOWER TO THE 4000-6000FT LAYER WITH SCATTERED PATCHES OF
STRATOCU WITH CEILINGS 1500-2500FT POSSIBLE BY LATE MORNING THROUGH
THE AFTERNOON...MAINLY SOUTH OF HIGHWAY 64. THIS THREAT FOR LOWER
CEILINGS WILL AFFECT THE KFAY TERMINAL. SURFACE WINDS WILL BECOME
NELY WITH SUSTAINED WINDS AOB 10KTS.

WEAK HIGH PRESSURE WILL BUILD INTO CENTRAL NC FROM NORTH TONIGHT AND
SUNDAY...MAINTAINING MOSTLY VFR CONDITIONS.

A STRONGER UPPER LEVEL DISTURBANCE AND ASSOCIATED SURFACE LOW
PRESSURE SYSTEM WILL BRING A HIGH PROBABILITY OF ADVERSE AVIATION
CONDITIONS TO CENTRAL NC SUNDAY NIGHT INTO MONDAY. WIDESPREAD
MVFR/IFR CEILINGS AND AREAS OF RAIN ARE EXPECTED. THESE CONDITIONS
WILL SPREAD NORTH INTO SOUTHERN SECTIONS OF CENTRAL NC SHORTLY AFTER
SUNSET SUNDAY THEN CONTINUE NORTHWARD SUNDAY NIGHT.

A DECENT TO HIGH THREAT FOR MVFR CEILINGS WILL LINGER MONDAY NIGHT
INTO TUESDAY AS THE LOW LEVEL AIR MASS REMAINS MOIST. A STRONG COLD
FRONT WILL APPROACH TUESDAY NIGHT AND CROSS THE REGION WEDNESDAY.
GUSTY SLY WINDS ARE EXPECTED AHEAD OF THE FRONT TUESDAY NIGHT ALONG
WITH HEAVY SHOWERS AND POSSIBLY A THUNDERSTORM OR TWO. THE FRONT
WILL CROSS THE AREA WEDNESDAY WITH BLUSTERY WESTERLY WINDS EXPECTED
IN ITS WAKE.

&&

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

&&

$$

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




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