Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 190816
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
315 AM EST FRI DEC 19 2014

.SYNOPSIS...HIGH PRESSURE CENTERED OVER THE MID MISSISSIPPI RIVER
VALLEY WILL GRADUALLY EXTEND INTO THE CAROLINAS TODAY. A WEAK STORM
SYSTEM WILL DEVELOP OVER THE TEXAS GULF COAST TODAY... THEN TRACK
EASTWARD ACROSS THE SOUTHEAST STATES ON SATURDAY. WEAK HIGH PRESSURE
WILL BRIEFLY EXTEND ACROSS CENTRAL NC ON SUNDAY.

&&

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

TODAY...MID LEVEL CLOUDS ASSOCIATED WITH WEAK WARM AIR ADVECTION
ALOFT WILL DECREASE/DIMINISH EARLY THIS MORNING AS A WEAK S/W RIDGE
AND ATTENDANT SFC RIDGE (FROM PARENT HIGH OVER THE MID MS VALLEY)
BUILDS INTO THE CAROLINAS. MINOR 850MB THERMAL TROUGH WITH WEAK CAA
WILL MAINTAIN A  CHILLY AIR MASS WITH HIGH TEMPS 4-5 DEGREES BELOW
NORMAL. MAX TEMPS UPPER 40S FAR NE TO THE MID 50S SOUTHERN THIRD.

TONIGHT...A S/W LIFTING E-NE FROM THE SOUTHERN PLAINS WILL ADVANCE
EAST ACROSS THE LOWER MS VALLEY TONIGHT. WARM AIR ADVECTION AHEAD OF
THIS SYSTEM WILL INCREASE MOISTURE ACROSS OUR REGION...RESULTING IN
THICKENING CLOUD COVERAGE FROM THE WEST-SW. MODEST ISENTROPIC
UPGLIDE MAY CAUSE PATCHES OF LIGHT RAIN TO DEVELOP OVER THE FAR
WESTERN-SOUTHERN PIEDMONT PRIOR TO DAYBREAK. MIN TEMPS GENERALLY IN
THE LOW-MID 30S THOUGH SOME PLACES IN THE WEST AND SOUTHWEST WILL
SEE MIN TEMPS OCCUR SHORTLY AFTER MIDNIGHT...WITH TEMPS HOLDING
STEADY THEREAFTER DUE TO THE THICKENING CLOUDS.

&&

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

S/W CROSSING THE DEEP SOUTH EARLY
SATURDAY WILL SPREAD MOISTURE INTO CENTRAL NC. BEST LIFT THROUGH THE
COLUMN ASSOCIATED WITH SPEED CONVERGENCE AT 700MB AND MODEST
HEIGHT FALLS IN THE MID LEVELS. THE MODEL GUIDANCE HAS BEEN
TRENDING DRIER COMPARED TO 48-72 HOURS AGO WITH SOME NEAR TERM MODELS
NOW SUGGESTING LITTLE IF ANY MEASURABLE PRECIP OVER THE NORTHERN
PIEDMONT. WILL NEED TO MONITOR THE DEVELOPING RAIN SHIELD OVER THE
LOWER MS VALLEY TODAY...AND THE TN VALLEY/DEEP SOUTH TONIGHT. PER
LATEST MOISTURE PROFILES AND LIFT...FELL THAT A FEW HUNDREDTHS
PROBABLE ACROSS THE PIEDMONT SATURDAY MORNING. THUS HAVE ADJUSTED
POPS BACK INTO THE LIKELY CATEGORY OVER THE NW PIEDMONT AND
MAINTAINED A LIKELY POPS IN THE SOUTH. FOR AREAS NORTH AND EAST OF
RDU..CONTINUED CHANCE POPS. AGAIN...WHAT PRECIP THAT OCCURS WILL BE
LIGHT WITH AMOUNTS VARYING BETWEEN A TRACE TO LESS THAN A TENTH OF
AN INCH.

NAM AND GFS BUFKIT SOUNDINGS SUGGEST A BRIEF OPPORTUNITY FOR MIXED
PRECIP IN THE NW PIEDMONT AROUND DAYBREAK...COINCIDING WITH THE BEST
LIFT. THE GFS AND NAM HAVE TRENDED SLIGHTLY COOLER WITH PARTIAL
THICKNESSES SUGGESTING A RAIN/SNOW MIX POSSIBLE IN THE TRIAD AND
POSSIBLY THE ROXBORO AREAS...MAINLY WHEN HEAVIER PRECIP INTENSITY IS
OCCURRING. WHILE BULK OF PRECIP WILL BE LIQUID...CANNOT RULE OUT THE
POSSIBILITY OF SOME SNOW MIXED IN AT TIMES NORTH OF TEH I-85/40
CORRIDOR IN THE TRIAD.

HIGH TEMPS SATURDAY DEPENDENT UPON EXTENT OF PRECIP SATURDAY AND
WHETHER PRECIP DOES DIMINISH SATURDAY AFTERNOON. HAVE ADJUSTED MAX
TEMPS UP A DEGREE OR TWO.

HAVE LEANED TOWARD A DRIER FORECAST FOR SATURDAY NIGHT AS SUBSIDENCE
IN THE WAKE OF THE DEPARTING S/W SHOULD END THE THREAT OF PRECIP
ACROSS THE REGION BY LATE SATURDAY...AND MORE SO SATURDAY EVENING
WITH SOME DECREASE IN CLOUDS POSSIBLE AFTER SUNSET. IF ENOUGH
CLEARING OCCURS...MAY SEE POCKETS OF FOG DEVELOP AFTER MIDNIGHT. IN
ANTICIPATION OF SOME PARTIAL CLEARING...HAVE LOWERED MIN TEMPS A FEW
DEGREES FROM THE PREVIOUS FORECAST (LOW-MID 30S).

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
AS OF 320 PM WEDNESDAY...

...VERY ACTIVE PATTERN DEVELOPING OVER THE LONG TERM PERIOD...

BEHIND THE DEPARTING SOUTHERN STREAM SHORT WAVE TROUGH...SHORT WAVE
RIDGING MOVES INTO THE CAROLINAS ON SUNDAY AS HIGH PRESSURE CENTERED
OVER THE EASTERN GREAT LAKES AND MID ATLANTIC EXTENDS INTO THE
REGION. THE NEXT SOUTHERN STREAM WAVE WHICH MOVES ONSHORE ACROSS CA
ON FRIDAY REACHES THE WESTERN GULF OF MEXICO ON SUNDAY NIGHT. LOOK
FOR INCREASING AND THICKENING CLOUDS ON SUNDAY WITH HIGHS IN THE
UPPER 40S TO LOWER 50S. PRONOUNCED ISENTROPIC LIFT WHICH DEVELOPS
AHEAD OF THIS SYSTEM SUNDAY EVENING ACROSS THE SOUTHEAST...SPREADS
INTO THE CAROLINAS AFTER MIDNIGHT AND PERSISTS FOR MUCH OF MONDAY
MORNING. EXPECT A BROAD AREA OF RAIN WITH THIS SYSTEM AND HAVE
INCREASED POPS. TEMPERATURES SUNDAY NIGHT WILL FALL INTO THE MID 30S
ACROSS THE NORTHERN PIEDMONT AND THE UPPER 30S ELSEWHERE...THESE
TEMPERATURES ALONG WITH A PRONOUNCED WARM NOSE AND WET BULB ZERO
VALUES HOLDING ABOVE FREEZING SHOULD PRECLUDE AND PTYPE ISSUES.

A SURFACE LOW DEVELOPING IN THE NORTHEAST GULF OF MEXICO WILL MOVE
NORTHEAST ALONG THE CAROLINA COAST MONDAY AFTERNOON AND FURTHER
OFFSHORE MONDAY NIGHT. PRECIPITATION SHOULD BECOME MUCH MORE
SCATTERED AND LIGHT MONDAY NIGHT INTO TUESDAY AS THE STRONGEST
FORCING ABATES BUT WIDESPREAD CLOUDINESS AND SMALL RAIN CHANCES
WILL PERSIST AS A MOIST AIR MASS LINGERS ACROSS THE AREA.

AN IMPRESSIVE NORTHERN STREAM SHORTWAVE TROUGH DIVES INTO THE
MIDWEST ON TUESDAY AND TUESDAY NIGHT CARVING OUT A HIGH AMPLITUDE
LONG WAVE TROUGH DEVELOPS ACROSS THE MISSISSIPPI VALLEY TUESDAY
NIGHT AND BECOMES NEGATIVELY TILTED ON WEDNESDAY AS IT BROADENS AND
REACHES THE EAST COAST. BOTH THE DETERMINISTIC GFS AND ECMWF ARE
VERY SIMILAR WITH THIS PATTERN. AT THE SURFACE...A STRONG SURFACE
CYCLONE DEVELOPS ACROSS THE GREAT LAKES ON TUESDAY INTO WEDNESDAY
WITH A STRONG COLD FRONT PROGGED TO MOVE ACROSS THE CAROLINA ON
TUESDAY NIGHT AND EARLY WEDNESDAY. THIS PATTERN WILL SUPPORT STRONG
AND GUSTY WINDS AHEAD OF AND BEHIND THE COLD FRONT WITH A PERIOD OF
WIDESPREAD RAIN AND PERHAPS A FEW THUNDERSTORMS ASSOCIATED WITH THE
FRONT. THE DEEP LAYER FLOW ATTENDANT TO THE FRONT IS VERY STRONG
WITH A SOUTHWEST WIND OF AROUND 40KTS PROGGED AT 1 KFT NEAR RDU ON
WEDNESDAY MORNING AND A WESTERLY WIND OF 40 KTS FORECAST AT RDU AT
1.5 KFT WEDNESDAY NIGHT. BOUNDARY LAYER INSTABILITY IS LIMITED BUT
BOTH THE GFS AND THE ECMWF SUGGEST A NARROW WINDOW FOR BOUNDARY
LAYER DESTABILIZATION AHEAD OF THE FRONT. THE IMPRESSIVE WIND FIELD
COMBINED WITH 700-500 MB LAPSE RATES APPROACHING 7 AS NOTED BY THE
GFS...LEADS TO AN ELEVATED SHERB VALUE THAT SUGGESTS SOME HIGHER
IMPACT HSLC CONVECTION IS POSSIBLE. THE PRECIPITATION QUICKLY ENDS
BEHIND THE FRONT WEDNESDAY AFTERNOON WITH DRY WEATHER EXPECTED FOR
CHRISTMAS DAY. HIGHS ON TUESDAY WILL RANGE FROM THE LOWER 50S IN THE
TRIAD TO NEAR 60 ACROSS THE SOUTHERN COASTAL PLAIN. TEMPERATURES
SHOULDN`T FALL MUCH TUESDAY NIGHT WITH THE CLOUDS AND STRONG
SOUTHERLY FLOW. RAISED MINS ABOVE GUIDANCE TO THE MID 40S TO AROUND
50. HIGHS WEDNESDAY WILL RANGE FROM 50 IN THE TRIAD TO NEAR 60 IN
THE SOUTHEAST WITH CHILLIER MAXES IN THE MID 40S TO NEAR 50 EXPECTED
FOR CHRISTMAS DAY. -BLAES

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
AS OF 1255 AM FRIDAY...

HIGH PRESSURE CENTERED OVER THE LOWER OH VALLEY WILL GRADUALLY
EXTEND INTO CENTRAL NC LATER TODAY AND EARLY THIS EVENING. WHILE
PATCHES OF MID LEVEL CLOUDS WILL CROSS THE REGION THROUGH 12Z...VFR
CONDITIONS WILL PERSIST. FEWER CLOUDS ANTICIPATED LATER THIS MORNING
THROUGH THE AFTERNOON WITH LIGHT AND VARIABLE SURFACE WINDS.

A LOW PRESSURE SYSTEM WILL ADVANCE TOWARD CENTRAL NC LATER TONIGHT
AND CROSS THE REGION SATURDAY. AREAS OF LIGHT RAIN WILL DEVELOP
TOWARD DAYBREAK SATURDAY AND CROSS CENTRAL NC SATURDAY MORNING
THROUGH EARLY AFTERNOON. THE LIGHT RAIN FALLING THROUGH THE LOWER
LEVELS OF THE ATMOSPHERE WILL AID TO MOISTEN THIS LEVEL...LEADING TO
THE POTENTIAL FOR PATCHES OF MVFR CEILINGS...MAINLY IN THE 14Z-20Z
SATURDAY TIME FRAME. WINDS EXPECTED TO REMAIN LIGHT AND VARIABLE.

VFR CONDITIONS EXPECTED SATURDAY NIGHT INTO SUNDAY AS WEAK HIGH
PRESSURE EXTENDS ACROSS THE AREA. ANOTHER LOW PRESSURE SYSTEM...THIS
ONE STRONGER THAN THE SATURDAY SYSTEM...WILL BEGIN TO AFFECT CENTRAL
NC SUNDAY NIGHT INTO SUNDAY...LEADING TO A PERIOD OF WIDESPREAD
MVFR/IFR CEILINGS AND AREAS OF RAIN. THE RAIN WILL DIMINISH ACROSS
THE REGION BY MONDAY NIGHT THOUGH MVFR/IFR CEILINGS WILL PERSIST
MONDAY NIGHT INTO TUESDAY.

&&

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

&&

$$

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



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