Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 181744
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1240 PM EST THU DEC 18 2014

.SYNOPSIS...HIGH PRESSURE OVER THE MISSISSIPPI RIVER VALLEY WILL
EXTEND EASTWARD INTO THE MID ATLANTIC AND CAROLINAS ON THROUGH
FRIDAY. A LOW PRESSURE SYSTEM WILL DEVELOP ALONG THE TEXAS COAST ON
FRIDAY AND TRACK EAST ALONG THE GULF COAST ON SATURDAY...THEN MOVE
OFFSHORE THE SOUTHEAST COAST SATURDAY NIGHT INTO SUNDAY.


&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 920 AM THURSDAY...

AN ALREADY LOW AMPLITUDE TROUGH ALOFT OVER THE MID-MISSISSIPPI RIVER
VALLEY THIS MORNING WILL CONTINUE TO DEAMPLIFY AS IT SKIRTS ACROSS
THE TENNESSEE VALLEY AND VIRGINIA THROUGH TONIGHT. AN AREA OF LIGHT
RAIN MOVING ACROSS EASTERN TENNESSEE...FOCUSED NEAR THE H925-H85
FRONTAL ZONE WHERE ISENTROPIC LIFT IS GREATEST...CONTINUES TO
GRADUALLY WEAKEN WITH EASTWARD EXTENT.  EXPECT THIS TREND TO THE
CONTINUE AS THE UPPER DISTURBANCE MOVES OFF TO THE EAST-NORTHEAST
AND THE FORCING DECOUPLES.  SO NO PRECIP IS EXPECTED OVER CENTRAL
NC.  EAST OF THE MOUNTAINS...THE AIRMASS REMAINS VERY DRY WITH ALL
MOISTURE ABOVE 12K FT.   WHILE THERE IS A FAIR AMOUNT OF HIGH LEVEL
MOISTURE UPSTREAM...GUIDANCE SUGGESTS  THERE WILL PERIODS OF SUN
MIXED IN WITH THE HIGH CLOUDS (POTENTIALLY OROGRAPHICALLY ENHANCED
AT TIMES THIS MORNING. TEMPS SHOULD GET TO WITHIN A COUPLE DEGREES
OF THE CURRENT FORECAST HIGHS OF 49-55.  IF ANYTHING...THEY WILL END
UP ON THE COOLER SIDE.

SKIES WILL BEGIN TO CLEAR OFF BY EARLY FRIDAY MORNING WITH THE
PASSAGE OF THE AFOREMENTIONED MID LEVEL TROUGH. GIVEN A RATHER WEAK
MSLP GRADIENT ACROSS THE AREA WITH SURFACE HIGH PRESSURE EXTENDING
INTO THE AREA FROM THE WEST... WE SHOULD SEE LIGHT AND VARIABLE TO
CALM WINDS OVERNIGHT. THIS COMBINED WITH CLEAR SKIES WILL ALLOW US
TO COOL QUITE NICELY TONIGHT. EXPECT LOW TEMPS WILL RANGE FROM THE
UPPER 20S TO AROUND 30 (WITH MAYBE EVEN A FEW MID 20S) IN THE USUAL
RURAL COLD LOCATIONS TO THE LOWER 30S ELSEWHERE.

&&

.SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
AS OF 310 AM THURSDAY...

FRIDAY AND FRIDAY NIGHT: ANOTHER SOUTHERN STREAM DISTURBANCE IS
EXPECTED TO APPROACH THE AREA ON FRIDAY. S/W ENERGY IS EXPECTED TO
LIFT NORTHEASTWARD OUT OF THE SOUTHERN PLAINS ON FRIDAY. MEANWHILE
CENTRAL NC WILL EXPERIENCE BRIEF S/W RIDGING AGAIN ON FRIDAY IN
BETWEEN THE AFOREMENTIONED SYSTEM TONIGHT AND THE APPROACHING SYSTEM
ON FRIDAY. THIS WILL YIELD MOSTLY SUNNY SKIES... POSSIBLY BECOMING
PARTLY SUNNY BY LATE IN THE DAY AS HIGH LEVEL CLOUD COVER BEGINS TO
STREAM NORTH AND EASTWARD IN ADVANCE OF THE NEXT SYSTEM. AFTERNOON
LOW LEVEL THICKNESS VALUES ARE EXPECTED TO BE A BIT LOWER ON
FRIDAY... AROUND 5 METERS OR SO. HOWEVER... WITH MORE SUN EXPECTED
ON FRIDAY THINK WE WILL SEE SIMILAR HIGH TEMPS COMPARED TO TODAY.
THUS... EXPECT HIGH TO RANGE FROM 50 TO 55.

AS THE MID LEVEL DISTURBANCE SHIFTS NORTHEASTWARD TOWARDS OUR REGION
FROM THE LOWER MS RIVER VALLEY ON FRIDAY EVENING/EARLY SATURDAY
MORNING SURFACE LOW PRESSURE WILL DEVELOP ACROSS THE NORTHERN GULF
OF MEXICO AND BEGIN TRACKING EASTWARD. AS THE SYSTEM APPROACHES
MOISTURE WILL STREAM NORTHWARD ACROSS CENTRAL NC... WITH SHALLOW
ISENTROPIC LIFT BEGINNING TO INCREASE ACROSS THE WESTERN AND
SOUTHWESTERN PORTION OF THE CWA DURING THE EARLY MORNING HOURS OF
SATURDAY. AT THE ONSET OF LIGHT PRECIP SPREADING INTO NORTHWEST
PIEDMONT WE COULD SEE A BRIEF PERIOD OF SOME SLEET MIXED IN WITH THE
LIGHT RAIN. HOWEVER... TEMPS ARE EXPECTED TO REMAIN ABOVE FREEZING
ACROSS THE WESTERN/NORTHWESTERN PIEDMONT ON SATURDAY MORNING NO
IMPACTS ARE EXPECTED. IN FACT WILL KEEP ANY MENTION OF SLEET OUT OF
THE FORECAST FOR NOW.... AS ANY OCCURRENCE WOULD BE BRIEF AND OF NO
IMPACT. LOW TEMPS SATURDAY MORNING WILL RANGE FROM THE UPPER 30S
SOUTH/SOUTHWEST TO THE LOWER 30S NORTHEAST.


&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
AS OF 347 AM WEDNESDAY...

SATURDAY...WHILE A SFC DRY AIR RIDGE AND PARENT HIGH ARE STILL IN A
FAVORABLE LOCATION TO SUPPORT A COLD AIR DAMMING EVENT
SATURDAY...THE LATEST MODEL GUIDANCE HAS TAKEN THE MID LEVEL S/W ON
A MORE SLY TRAJECTORY THAN PREVIOUS MODEL RUNS AND PARENT HIGH A FEW
MILLIBARS WEAKER THAN PREVIOUS MODEL RUNS. THIS STILL YIELDS A
HYBRID DAMMING EVENT THOUGH PRECIP AMOUNTS APPEAR TO BE LIGHTER THAN
EARLIER FORECASTS. S/W HAS RECENTLY ENTERED THE UPPER AIR RAWINSONDE
NETWORK SO THE 12Z MODEL RUN SHOULD GIVE AN INDICATION OF EVENTUAL
STRENGTH/TRACK OF THIS SYSTEM  REGARDLESS...OVERCAST SKIES AND
AREAS/WIDESPREAD LIGHT RAIN WILL RESULT IN A COLD DAMP DAY. MOS
GUIDANCE APPEARS TOO WARM AND AM RELUCTANT TO RAISE MAX TEMPS
SATURDAY FROM CURRENT FORECAST (NEAR 40 NW TO UPPER 40S FAR SE). IF
RAIN COVERAGE ENDS UP BEING SPOTTY VERSUS WIDESPREAD...THEN COULD
SEE AN ADJUSTMENT IN MAX TEMPS TO VALUES COMPARABLE TO THE NAM MOS
(MID-UPPER 40S, NEAR 50 SE).

SATURDAY NIGHT...SUBSIDENCE BEHIND THE EXITING S/W SHOULD AID TO
DIMINISH LIGHT PRECIP WITH GREATEST THREAT FOR SPOTTY LIGHT PRECIP
OVER THE SANDHILLS/SOUTHERN COASTAL PLAIN (AGAIN DUE TO THE MORE SLY
TRACK OF THE S/W). OTHERWISE CONTINUED CONSIDERABLE CLOUDINESS WITH
PATCHY DRIZZLE AND/OR LIGHT FOG. MIN TEMPS MID-UPPER 30S.

SUNDAY THROUGH WEDNESDAY...A MAJOR STORM MAY AFFECT THE SE U.S. LATE
TUESDAY INTO WEDNESDAY (INCLUDING CENTRAL NC) WITH POTENTIAL IMPACT
ON TRAVEL DUE TO HEAVY RAIN AND STRONG GUSTY WINDS.

MODEL GUIDANCE FLIP-FLOPPED A BIT FOR SUNDAY INTO MONDAY WITH
GUIDANCE NOW INDICATING A NARROW DRY AIR SFC RIDGE ACROSS THE REGION
SUNDAY WITH ANOTHER S/W IN THE SOUTHERN STREAM INITIATING ANOTHER
AREA OF RAIN LATE SUNDAY INTO MONDAY. THIS SCENARIO HAS ALSO BEEN
PICKED-UP BY THE LATEST ECMWF. PARTIAL THICKNESSES SUPPORT ALL
LIQUID ACROSS THE PIEDMONT AT THIS TIME. DUE TO THE SHIFT...PLAN TO
CONFINE POPS TO JUST CHANCE AT THIS TIME LATE SUNDAY INTO MONDAY. IF
LATER MODEL RUNS MAINTAIN SOME CONSISTENCY...LIKELY POPS WARRANTED
FOR OVERNIGHT SUNDAY INTO MONDAY MORNING. WILL CONTINUE BELOW NORMAL
HIGH TEMPS SUNDAY INTO MONDAY...WITH MAX TEMPS MONDAY AS MUCH AS 7-8
DEGREES BELOW NORMAL IF RAIN MATERIALIZES.

TUESDAY INTO WEDNESDAY...AMPLIFYING L/W TROUGH IN THE NORTHERN
STREAM WILL TAP GULF MOISTURE AND STREAM IT NORTHWARD INTO THE
CAROLINAS TUESDAY INTO TUESDAY NIGHT. MODEL GUIDANCE INDICATE A
STRONG JET ROUNDING BASE OF TROUGH LATE TUESDAY NIGHT INTO WEDNESDAY
MORNING CAUSING THE TROUGH TO BECOME NEGATIVELY TILTED ACROSS THE SE
U.S. IF THIS HOLDS TOGETHER...COULD SEE A BAND OF HEAVY SHOWERS WITH
A FEW STORMS CROSS CENTRAL NC OVERNIGHT TUESDAY NIGHT INTO EARLY
WEDNESDAY. THE PARENT LOW DEEPENS SIGNIFICANTLY WEDNESDAY AND
WEDNESDAY NIGHT WITH THE POTENTIAL FOR STRONG GUSTY WINDS ACROSS
CENTRAL NC. A BRIEF BUMP UP IN TEMPS TUESDAY AHEAD OF THE STORM
SYSTEM TUESDAY FOLLOWED BY ANOTHER ROUND OF BELOW NORMAL MAX TEMPS
THOUGH TRULY FRIGID AIR NOT SEEN IN OUR REGION THROUGH CHRISTMAS.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
AS OF 1240 PM THURSDAY...

VFR CONDITIONS WILL CONTINUE THIS AFTERNOON THROUGH THE END OF THE
TAF PERIOD.  A WEEK DISTURBANCE WILL CROSS VIRGINIA THIS
EVENING...BUT THE ONLY IMPACT OVER NC WILL BE INCREASING MID/HIGH
CLOUDS....MAINLY ACROSS THE NORTHERN HALF OF THE AREA. WINDS WILL BE
LIGHT OUR OF THE NORTH-NORTHWEST...INCREASING TO 4-6KT DURING THE
DAY FRIDAY.

OUTLOOK...A LOW PRESSURE SYSTEM MOVING FROM THE GULF COAST TO THE
CAROLINA COAST FRIDAY NIGHT AND SATURDAY WILL BRING A ROUND OF SUB-
VFR CONDITIONS TO CENTRAL NC ON SATURDAY AND SATURDAY NIGHT.
HOWEVER....THIS SYSTEM MAY NOT BE AS SIGNIFICANT AS ONCE EXPECTED.
VFR CONDITIONS ARE EXPECTED TO BRIEFLY RETURN FOR SUNDAY... BEFORE
ANOTHER DISTURBANCE LIFTS NORTHEASTWARD OUT OF THE GULF... SPREADING
RAIN INTO CENTRAL NC SUNDAY NIGHT INTO MONDAY... WITH SUB-VFR
CONDITIONS.

&&

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

&&

$$

SYNOPSIS...BSD/VINCENT
NEAR TERM...BSD/BLS
SHORT TERM...BSD
LONG TERM...WSS
AVIATION...BLS


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