Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 211956
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
255 PM EST SUN DEC 21 2014

.SYNOPSIS...HIGH PRESSURE TO THE NORTH WILL SET UP A COLD AIR
DAMMING EVENT WITH PRECIPIATION CHANCES INCREASING TONIGHT AND INTO
MONDAY AS A SURFACE LOW MOVES UP THE SOUTHEAST COAST.

&&

.NEAR TERM /THROUGH MONDAY NIGHT/...
AS OF 220 PM SUNDAY...

HIGH PRESSURE OVER THE MID ATLANTIC STATES IS SLOWLY SHIFTING
EASTWARD THIS AFTERNOON AND INTO A FAVORABLE POSITION FOR A HYBRID
COLD AIR DAMMING EVENT TO BEGIN. THIS IS KEEPING MOISTURE PENNED UP
SOUTH OF THE AREA TODAY BUT A SOUTHERN STREAM SHORTWAVE WILL BEGIN
TO CREATE SOME TROUGHING ALONG THE COAST OVERNIGHT TONIGHT INTO
MONDAY WHICH WILL HELP TO SHARPEN UP THE WEDGE FRONT ACROSS CENTRAL
NC AND SET THE STAGE FOR A WET COUPLE OF DAYS.

FOR THE REST OF TODAY EXPECT LESS CLOUD COVER EAST OF HIGHWAY ONE
WITH LINGERING MVFR CEILINGS IN THE WEST. THIS HAS BEEN TRYING TO
BURN OFF OVER THE PAST SEVERAL HOURS BUT SOME PLACES ARE STILL UNDER
GREY SKIES. THIS IS CREATING A LOT OF DIFFERENTIAL HEATING ACROSS
THE CWA AND ANY LOCALES IN THE CLEARING HAVE TEMPERATURES RISING
ABOVE FORECASTED HIGHS AND THOSE UNDER THE CLOUD COVER ARE STILL
BELOW FORECASTED HIGHS. THE END RESULT WILL BE PLUS OR MINUS 50
DEGREES DEPENDING ON LOCATION. WINDS ARE MAINTAINING A NORTHEASTERLY
COMPONENT AND WILL CONTINUE TO DO SO WITH SPEED AROUND 5 KTS.

TONIGHT...MOISTURE WILL BEGIN TO INCREASE FROM THE SOUTH AIDED BY
ISENTROPIC LIFT INCREASING OVER TOP OF THE WEDGE THAT WILL BEGIN TO
BUILD IN THIS EVENING...AND THE RIGHT ENTRANCE REGION OF AN UPPER
JET THAT IS PROGGED TO BEGIN TO MOVE OVER CENTRAL NC DURING THE LATE
NIGHT HOURS. HIGH RESOLUTION MODELS HAVE PRECIPITATION BEGINNING IN
THE SOUTHERN COUNTIES AFTER 00Z AND SPREADING NORTHWARD THROUGH THE
CWA BY ABOUT 4Z OR SO. THE ONSET OF PRECIPIATION WILL ALSO MARK THE
BEGINNING OF MVFR CEILINGS. LOW TEMPERATURES WILL RANGE FROM THE MID
30S NORTH TO LOW 40S SOUTH.

MONDAY AND MONDAY NIGHT: RAIN IS EXPECTED TO PERSIST THROUGH THE DAY
ON MONDAY AS THE SURFACE LOW MOVES NORTHWARD JUST OFF THE NC COAST.
LOW CEILINGS AT IFR LEVELS ARE EXPECTED THROUGHOUT THE DAY. WHILE
RAIN IS EXPECTED TO BE CONTINUOUS...THE QPF AMOUNTS WITH THIS SYSTEM
ARE FAIRLY LOW. ONLY EXPECT A TOTAL OF A QUARTER TO A HALF OF AN
INCH OF RAIN. WITH THE WEDGE LOCKED IN TO THE WEST AND THE COASTAL
TROUGH TO THE EAST...THERE SHOULD BE A FAIRY DECENT GRADIENT FROM
NORTHWEST TO SOUTHEAST IN THE HIGH TEMPERATURE SPREAD ON MONDAY.
HIGHS IN THE NORTHWEST PIEDMONT WILL STRUGGLE TO GET TO 40 DEGREES
WHEREAS HIGHS CLOSER TO 50 WILL BE COMMON IN THE SOUTHEAST. FOR THE
MOST PART PRECIPIATION IS EXPECTED TO END AFTER 00Z TUESDAY BUT
CONTINUED MOISTURE IN THE AREA WILL LEND ITSELF TO CONTINUING
DRIZZLE THROUGH THE NIGHT ON MONDAY. THIS WET AND COOL PERIOD WILL
ALSO LEND ITSELF TO PERIODS OF PATCHY FOG WITH THE MOST LIKELY TIMES
BEFORE SUNRISE ON TUESDAY. LOWS IN THE MID 30S TO LOWER 40S.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
AS OF 300 PM SUNDAY...

TUESDAY:
MID-LEVEL DRY AIR AND THE ABSENCE OF DISCERNIBLE
FORCING...ASIDE FROM WEAK SOUTHERLY UPGLIDE...DOWNSTREAM OF THE
DEEPENING TROUGH WILL KEEP MEASURABLE RAIN CHANCES LOW ACROSS
CENTRAL NC DURING MUCH OF THE DAY ON TUESDAY. DESPITE A LACK OF
PRECIP...SHROUD OF LOW CLOUDS WILL HELP TO KEEP THE LINGERING COLD
AIR WEDGE LARGELY IN PLACE ACROSS CENTRAL NC. MEASURABLE RAIN
CHANCES WILL RETURN BY THE LATE AFTERNOON/EVENING WITH THE
RESURGENCE OF WARM MOIST ADVECTION AND LOW-LEVEL CONVERGENCE ALONG
THE NORTHWARD RETREATING WEDGE FRONT. TEMPERATURES TUESDAY DURING
THE DAY WILL REMAIN THE 40S THROUGHOUT MUCH OF THE DAY...THE
EXCEPTION WILL  BE ACROSS THE FAR SE ZONES WHERE NEARBY WEDGE/WARM
FRONT COULD ALLOW TEMPERATURES TO WARM INTO THE LOWER 50S LATE IN
THE DAY.


TUESDAY NIGHT THROUGH WEDNESDAY NIGHT:

SOGGY...BREEZY...AND POSSIBLY STORMY CONDITIONS...

AHEAD OF THE AMPLIFYING UPSTREAM LONGWAVE TROUGH AND ATTENDANT SFC
COLD FRONT...DEEP GULF MOISTURE FEED WILL TRANSPORT ANOMALOUSLY HIGH
PWATS OF 1.5-1.7" INTO THE REGION...WHICH WOULD RANK IN THE 99TH
PERCENTILE(HIGHEST OBSERVED PWAT DURING THE MONTH OF DEC AT KGSO
BASED ON THE RADIOSONDE DATABASE WHICH DATE BACKS TO 1948 IS 1.59"-
12/21/1991). STRENGTHENING RIGHT ENTRANCE JET REGION COUPLED WITH
THIS STRONG MOISTURE FLUX CONVERGENCE WILL RESULT IN CATEGORICAL
POPS AND A WIDESPREAD SOAKING RAIN OF 1-2"...HEAVY AT TIMES TUESDAY
NIGHT AND INTO CHRISTMAS EVE MORNING. ONCE THE WARM FRONT LIFTS
NORTHWARD INTO THE VIRGINIA...THERE WILL LIKELY BE A LULL IN PRECIP
UNTIL THE ARRIVAL OF THE COLD FRONT AND ATTENDANT BAND OF SHOWERS
AND POSSIBLY EMBEDDED THUNDER THROUGH THE AREA BETWEEN 00-06Z
THURSDAY...WHICH IS A BIT SLOWER THAN YESTERDAYS TIMING.

SEVERE POTENTIAL: EVALUATING SEVERE POTENTIAL IN A LOW CAPE-HIGH
SHEAR ENVIRONMENT IS ALWAYS DIFFICULT...EVEN AT CLOSER TIME SCALES
OF 6-12 HOURS...MUCH LESS AT THE CURRENT TIME SCALE OF 3 TO 4 DAYS.
THE LULL IN PRECIP DURING MUCH OF THE DAYTIME HOURS...MAY ALLOW FOR
SOME MODEST HEATING...ESPECIALLY FROM THE US 1 CORRIDOR
EASTWARD...WHICH COULD LEAD TO BETTER DESTABILIZATION THAN MODEL
CURRENTLY SHOW(100-200J/KG MUCAPE). WEAK LAPSE RATES ALOFT OF 5.0-
5.5 C/KM ALONG WITH THE MAIN DYNAMICS PASSING OVER THE GREAT
LAKES...WILL LIMIT WIDESPREAD SEVERE POTENTIAL...BUT GIVEN
IMPRESSIVE DEEP LAYER SHEAR CANNOT RULE OUT ISOLATED SEVERE STORM AT
THIS TIME.

TEMPERATURES VERY CHALLENGING WITH HIGH BUST POTENTIAL...DEPENDENT
ON EVOLUTION/TIMING/LOCATION OF THE RETREATING WEDGE FRONT INTO THE
CLIMATOLOGICALLY FAVORED AREA ACROSS THE FAR NW PIEDMONT TUESDAY
NIGHT AND INTO THE DAY ON WEDNESDAY. EXPECT TEMPERATURES TO STEADILY
WARM AFTER MIDNIGHT TUESDAY NIGHT...WITH THE EXCEPTION BEING ACROSS
THE NW PIEDMONT...WHERE TEMPS COULD HOLD NEARLY STEADY. LOWS RANGING
FROM LOWER 40S NW TO MID 50S SE. WARM SECTOR SHOULD OVERSPREAD MUCH
OF THE AREA BY WEDNESDAY AFTERNOON...WARMING INTO THE 60S ACROSS THE
PIEDMONT...AND POSSIBLY LOWER 70S ACROSS THE SANDHILLS/SOUTHERN
COASTAL PLAIN. RAPID CLEARING AND COOL AIR ADVECTION WILL COMMENCE
CHRISTMAS EVE EVENING/NIGHT WITH LOWS CHRISTMAS MORNING IN THE UPPER
30S NW TO LOWER/MID 40S SE.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
AS OF 255 PM SUNDAY...

DEEPENING SURFACE LOW LIFTING NEWD INTO SE CANADA WILL RESULT IN
BREEZY CONDITIONS ON CHRISTMAS DAY. OTHERWISE DRY WITH SEASONABLY
MILD TEMPERATURES CONTINUING INTO FRIDAY AS HIGH PRESSURE BUILDS IN
FROM THE NORTHERN GULF.

MODEL SPREAD BEGINS TO INCREASE DRAMATICALLY LATE FRIDAY THROUGH THE
WEEKEND...WITH THE EC MUCH DEEPER WITH THE NEXT MID/UPPER LEVEL
TROUGH...RESULTING IN YET ANOTHER WET AND UNSETTLED PERIOD NEXT
WEEKEND. MEANWHILE...THE LESS AMPLIFIED GFS INDICATES QUASI-ZONAL
FLOW ACROSS SOUTHEAST US WITH DRY CONDITIONS THROUGH THE WEEKEND.
WILL INDICATE SLIGHT CHANCE POPS UNTIL BETTER AGREEMENT IS REACHED.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
AS OF 130 PM SUNDAY...

FORECAST IS EASIER TO MANAGE TODAY AS THE BEST CONDITIONS WILL BE
THIS AFTERNOON AND THEN FOLLOWED BY A HIGH CONFIDENCE FORECAST OF
CONDITIONS DETERIORATING AFTER DARK AND INTO THE OVERNIGHT HOURS
DOWN TO FIRST MVFR AND THEN IFR LEVELS WHERE THEY WILL REMAIN FOR
THE REMAINDER OF THE TAF PERIOD. ADVERSE CONDITIONS ARE ASSOCIATED
WITH A LOW PRESSURE SYSTEM DEVELOPING OFF OF THE SOUTHEAST COAST
THAT WILL BRING AN INFLUX OF MOISTURE FROM THE SOUTH. THIS WILL BE
IN THE FORM OF RAIN AS TEMPERATURES WILL REMAIN ABOVE FREEZING
THROUGHOUT THE EVENT. WHILE THERE MAY BE POCKETS OF SOME MVFR
VISIBILITIES...IFR CONDITIONS WILL PRESENT IN THE FORM OF LOW
STRATUS. PRECIPITATION WILL START JUST AFTER 00Z IN THE SOUTH AND
PUSH NORTHWARD UNTIL ALL SITES ARE UNDER THE PRECIP SHIELD JUST
AFTER 4Z GIVE OR TAKE. THE ONSET OF PRECIPITATION SHOULD ALSO MARK
THE ONSET OF MVFR CONDITIONS AND THEN LATER ON DOWN TO IFR NEAR
DAYBREAK MONDAY. WINDS WILL BE 5-10 KTS OUT OF AN EAST NORTHEASTERLY
DIRECTION FOR MUCH OF THE TAF PERIOD. CONDITIONS ARE NOT EXPECTED TO
RECOVER BEFORE 18Z MONDAY.

LONG TERM: LOW CEILINGS ARE EXPECTED TO REMAIN WELL INTO MIDWEEK AS
CONTINUOUS UNSETTLED WEATHER AFFECTS THE AREA THROUGH WEDNESDAY
NIGHT. THIS WILL BE CHARACTERIZED BY PERIODS OF RAIN...FOG AND
POSSIBLY A THUNDERSTORM. CONDITIONS SHOULD RETURN TO VFR FOR
CHRISTMAS DAY WITH SOME AFTERNOON GUSTY WINDS POSSIBLE.

&&

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

&&

$$

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


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