Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS62 KRAH 281219
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
715 AM EST SUN DEC 28 2014

.SYNOPSIS... A COLD FRONT WILL APPROACH FROM THE NORTHWEST TODAY...
THEN PUSH SLOWLY SOUTHEAST THROUGH THE AREA MONDAY AND MONDAY NIGHT.
HIGH PRESSURE WILL BUILD IN FROM THE WEST LATE TUESDAY THROUGH
THURSDAY.

&&

.NEAR TERM /THROUGH 6PM/...
AS OF 350 AM SUNDAY...

SOUTHWESTERLY FLOW CONTINUES ALOFT BETWEEN A DEEP LAYER RIDGE OVER
THE CARIBBEAN AND A POSITIVELY TILTED UPPER TROUGH EXTEDNING FROM
THE GREAT LAKES TO NORTHERN MEXICO. AN UPPER DISTURBANCE IN THE
FLOW...ALONG WITH BROAD WARM ADVECTION OVER THE SOUTHEAST...IS
FORCING AN AREA OF LIGHT TO MODERATE PRECIP ACROSS NORTHERN
ALABAMA/GEORGIA.  A FEW RADAR ECHOES ARE SHOWING UP OVER THE
SOUTHERN AND WESTERN PIEDMONT...BUT PRECIP IS MOST LIKELY STILL
EVAPORATING AS THE THE VERY DRY LAYER BELOW 5K FT (PER 00Z KGSO
RAOB) CONTINUES TO MOISTEN.  GIVEN THAT ISENTROPIC LIFT AND WARM
ADVECTION ARE EXPECTED TO WANE WITH TIME AND NORTHERN EXTENT THIS
MORNING...THE RAIN...WHILE STILL LIKELY AT MOST LOCATIONS...WILL BE
VERY LIGHT WITH QPF OF ONLY A FEW HUNDREDTHS AND POTENTIALLY ONLY A
TRACE FOR MANY.

TEMPERATURES ARE CURRENTLY IN THE UPPER 40S TO LOWER 50S...AND ARENT
LIKELY TO FALL MUCH MORE THIS MORNING.  DEWPOINTS ARE IN THE UPPER
30S AND THERE WILL BE SOME EVAPORATIONAL COOLING...BUT GIVEN THE
LIGHT QPF AND WARMER MORNING TEMPS...WILL RAISE FORECAST HIGHS A
COUPLE DEGREES...56-66 NORTHWEST TO SOUTHEAST.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/...
AS OF 345 AM SUNDAY...

TONIGHT AND MONDAY...  A COLD FRONT...WHICH IS CURRENTLY MOVING INTO
THE OHIO VALLEY REGION...WILL PUSH SOUTHEAST INTO THE AREA BETWEEN
00Z AND 06Z. MEANWHILE...A SHORTWAVE WITHIN THE UPPER TROUGH WILL
LIFT FROM TEXAS TOWARD THE SOUTHERN APPALACHIANS TONIGHT.  WHILE
DEAMPLIFYING...THIS SHORTWAVE COMBINED WITH THE RIGHT ENTRANCE
REGION OF A 150KT UPPER JET OVER THE NORTHEAST US WILL BRING ANOTHER
ROUND OF WIDESPREAD PRECIP LATE TONIGHT AND INTO MONDAY.   THE RAIN
IS EXPECTED TO SPREAD FROM WEST TO EAST AFTER MIDNIGHT TONIGHT AS A
WEAK WAVE OF LOW PRESSURE MOVES ALONG THE FRONT AS IT NEARS THE
NC/SC BORDER.  WITH BETTER FORCING/MOISTURE THROUGH A DEEPER
LAYER... RAINFALL AMOUNTS SHOULD BE HIGHER WITH THIS ROUND OF
PRECIP...AS THE GFS AND ECMWF BOTH SHOULD UPWARDS OF A QUARTER OF AN
INCH.

HIGHS OF UPPER 40S NORTH TO LOW/MID 50S SOUTH ARE LIKELY TO OCCUR
EARLY IN THE MORNING THEN FALL DURING THE AFTERNOON...ESPECIALLY
ACROSS THE NORTH AS PRECIP OVERSPREADS THE POST-FRONTAL AIRMASS AND
A WEAK COLD AIR DAMMING AIRMASS DEVELOPS.

MONDAY NIGHT...COLD/DRY ADVECTION WILL CONTINUE BEHIND THE FRONT
...THOUGH THE COLD AIR DAMMING AIRMASS WILL BE MAINTAINED BY SOME
SHALLOW UPGLIDE AND POCKETS OF LIGHT RAIN OF DRIZZLE.  ALL MODELS
KEEP THERMAL PROFILES ABOVE FREEZING THROUGH TUESDAY MORNING AND
SUGGEST NO TYPE ISSUES. LOWS IN THE UPPER 30S AND LOWER 40S.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
AS OF 340 AM SUNDAY...

TUE: A WELL-DEFINED SHORTWAVE TROUGH OVER WA THIS MORNING WILL
AMPLIFY ACROSS THE ROCKIES THROUGH TONIGHT...THEN DEAMPLIFY FROM THE
CENTRAL PLAINS TO THE MIDDLE ATLANTIC COAST TUE THROUGH TUE NIGHT.
THE PASSAGE OF THIS FEATURE AND ASSOCIATED GLANCING BLOW OF THE
SOUTHERN PERIPHERY OF HEIGHT FALLS ALOFT...AND ASSOCIATED FORCING
FOR ASCENT...WILL PRODUCED RENEWED LIFT ATOP A STILL-SATURATED LAYER
IN ROUGHLY THE LOWEST SEVERAL THOUSAND FT --DEEPEST NEAR THE VA
BORDER/IN CLOSEST PROXIMITY TO THE STRONGEST HEIGHT FALLS ALOFT OVER
THE MIDDLE ATLANTIC-- SUCH THAT OTHERWISE PERIODS OF DRIZZLE THROUGH
EARLY TUE WILL BECOME LIGHT RAIN DURING THE MORNING TO MIDDAY HOURS.
BEHIND THE PASSING SHORTWAVE TROUGH...NW 925-850 MB FLOW WILL
PROMOTE BOTH DOWNSLOPE FLOW AND A DISSIPATION OF THE CAD INVERSION
VIA CAA - BOTH MECHANISMS THAT SHOULD SERVE TO SCOUR THE CAD REGIME
AND PROMOTE CLEARING BY THE AFTERNOON OR EVENING. THE TIMING OF THIS
PROCESS REMAINS IN QUESTION OWING TO TIMING DIFFERENCES AMONGST NWP
GUIDANCE REGARDING THE PASSAGE OF THE SHORTWAVE TROUGH...THOUGH
THERE HAS BEEN AN OVERALL SLOWER TREND EVIDENT IN THE GUIDANCE. AS
SUCH...WILL FAVOR A SLOWER CLEARING TREND FROM WEST TO EAST SUCH
THAT TEMPERATURES LIKELY WILL NOT HAVE TIME TO RESPOND TO THE
SETTING AFTERNOON SUN...WHICH WOULD RESULT IN HIGHS ONLY IN THE
LOWER TO MIDDLE 40S. IF A FEW HOUR PERIOD OF SUN DOES MATERIALIZE...
MOST LIKELY OVER THE SOUTHERN AND WESTERN PIEDMONT DURING THE
AFTERNOON...TEMPERATURES WOULD RESPOND TO NEAR NORMAL VALUES IN THE
UPPER 40S.

TUE NIGHT-SAT: STRONG...ARCTIC HIGH PRESSURE OVER THE ROCKIES EARLY
IN THE PERIOD WILL OTHERWISE SPRAWL EAST ACROSS THE MIDDLE ATLANTIC
AND SOUTHEAST STATES...THROUGH THU...BENEATH GENERALLY WESTERLY FLOW
BETWEEN CONFLUENT BRANCHES OF THE UPPER JET...BEFORE DRIFTING
OFFSHORE AHEAD OF AN EJECTING DESERT SW (BRIEFLY) CUTOFF LOW FRI-
SAT. THE RESULT WILL BE COOL CONDITIONS --MOST NOTABLY WED AND THU
MORNINGS WHEN TEMPERATURES SHOULD DIP WELL INTO THE 20S (WITH UPPER
TEENS POSSIBLE IN OUTLYING AREAS THAT EXPERIENCE CALM) GIVEN
PROJECTED LOW LEVEL THICKNESS VALUES IN THE 1290-1300 METER RANGE.
IT WILL ALSO BE CLEAR OR MOSTLY SO DURING MOST OF THE PERIOD...WITH
THE EXCEPTION OF A PERIOD OF PASSING MID-HIGH CLOUDS IN ASSOCIATION
WITH A STRONGLY-SHEARED AND POSITIVELY-TILTED TRAILING SHORTWAVE
TROUGH DURING THE DAY WED.

WHILE MEDIUM RANGE GUIDANCE DIVERGES WITH RESPECT TO THE EJECTION OF
THE AFOREMENTIONED DESERT SW LOW AND ASSOCIATED APPROACH OF THE NEXT
FRONTAL SYSTEM...THE OVERALL PATTERN (WITH TIMING DIFFERENCES TO BE
WORKED OUT) WOULD RESULT IN A LOW TRACK TO THE NW OF CENTRAL NC AND
AN ASSOCIATED WARM FRONTAL PASSAGE IN RETURN FLOW AROUND THE
DEPARTING AND MODIFIED ARCTIC HIGH --TIMING MOST LIKELY FRI NIGHT-
SAT FAVORED (DUE TO TYPICAL FAST BIAS IN NWP WITH SW CUTOFFS) AS
DEPICTED BY THE SLOWER EC AND EC MEAN. IF SHOWERS OCCUR WITH THE
PASSAGE OF THE WARM FRONT...MOST LIKELY OVER THE WESTERN PIEDMONT...
AN IN-SITU DAMMING EVENT WOULD EVOLVE INTO THE EARLY PART OF THE
WEEKEND...IN A PATTERN OTHERWISE SUPPORTIVE OF WARMING TEMPERATURES
OVER THE SE CONUS. AS SUCH...TEMPERATURES ON SAT ARE APT TO DISPLAY
A WIDER THAN AVG RANGE OVER CENTRAL NC...WITH MARKEDLY COOLER
TEMPERATURES OVER THE NW PIEDMONT.

&&

.AVIATION /12Z SUNDAY THROUGH WEDNESDAY/...
AS OF 715 AM SUNDAY...

SO FAR THIS MORNING...THE WIDESPREAD RAIN APPROACHING NC FROM THE
SOUTHWEST HAS BEEN VERY SLOW TO MAKE IT NORTH OF THE NC/SC
BORDER...LIKELY OWING TO A VERY DRY LOW-LEVEL AIRMASS OVER NC.  IN
THE 12-15Z TIME FRAME...THE POTENTIAL FOR MVFR CEILINGS WILL BE
GREATEST ACROSS THE SOUTHERN PIEDMONT AND SANDHILLS...INCLUDING THE
KFAY TERMINAL.  PRECIP SHOULD EVENTUALLY SPREAD FURTHER NORTH AND
HAVE MORE IMPACT ON MORE TERMINALS ACROSS CENTRAL NC...WITH MVFR
AND/OR IFR CEILINGS POSSIBLE...AT LEAST TEMPORARILY...BY THIS
AFTERNOON.  CONFIDENCE IS HIGHEST IN MVFR CONDITIONS AT KGSO AND
KINT.

EXPECT THE LIGHT RAIN TO THEN BE INTERMITTENT LATER THIS AFTERNOON
AS A LULL DEVELOPS...WITH A PERIOD OF VFR CONDITIONS POSSIBLE BEFORE
A COLD FRONT PUSHES INTO THE AREA FROM THE NORTH TONIGHT BETWEEN
ROUGHLY 00Z AND 06Z.  MEANWHILE...ANOTHER UPPER LEVEL DISTURBANCE
WILL CROSS THE AREA...CAUSING SOUTHERLY FLOW TO INCREASE AND ANOTHER
ROUND OF WIDESPREAD RAIN AND SUB-VFR CONDITIONS TO DEVELOP AFTER
MIDNIGHT.

WINDS WILL BE 5-10KT OUT OF THE SOUTHWEST TODAY...TURNING TO
NORTHWESTERLY AND THEN NORTHERLY BEHIND THE FRONT TONIGHT.

LOOKING AHEAD: LOW CEILINGS...ALONG WITH SOME PERIODS OF LIGHT RAIN
OR DRIZZLE WILL LINGER THROUGH MONDAY NIGHT...WITH CONDITIONS
EXPECTED TO IMPROVE LATE TUESDAY AND CONTINUE THROUGH MIDWEEK.

&&

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

&&

$$

SYNOPSIS...BLS
NEAR TERM...BLS
SHORT TERM....BLS
LONG TERM...MWS
AVIATION...BLS


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.