Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 290310
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1009 PM EST WED JAN 28 2015

.SYNOPSIS...HIGH PRESSURE WILL BUILD OVER THE REGION THROUGH EARLY
THURSDAY AND THEN OFF THE SOUTHEAST COAST THURSDAY AFTERNOON.  A
COLD FRONT WILL SWEEP THROUGH THE AREA LATE THURSDAY AND THURSDAY
NIGHT. COOL HIGH PRESSURE WILL BUILD BACK IN FROM THE WEST FRIDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 10 PM WEDNESDAY...

SURFACE HIGH PRESSURE CENTERED NEAR WESTERN PA AND WESTERN NY THIS
EVENING WILL BUILD SOUTHWARD/EXTEND INTO OUR REGION OVERNIGHT. GIVEN
THE WEAK MSLP GRADIENT ACROSS THE AREA... WINDS HAVE ALREADY WENT
CALM TO LIGHT AN VARIABLE. MEANWHILE... MID LEVEL RIDGING ALOFT WILL
BUILD EASTWARD AND BE CENTERED OVER THE REGION BY 12Z THURSDAY.
GIVEN THE CURRENT POSITION OF THE MID LEVEL RIDGE WE ARE CLEAR THIS
EVENING... WITH ANY CIRRUS STILL TO THE WEST OF OUR AREA. WHILE WE
SHOULD SEE AN INCREASE IN HIGH CLOUDS EARLY THURSDAY MORNING AS THE
MID LEVEL RIDGE BUILD OVERHEAD BY DAYBREAK... THINK THE CIRRUS
SHOULD REMAIN THIN ENOUGH TO NOT HAVE A SIGNIFICANT IMPACT ON LOW
TEMPS. THUS... GIVEN THE MOSTLY CLEAR SKIES AND CALM TO LIGHT AND
VARIABLE WINDS HAVE LOWERED LOW TEMPS BY A COUPLE OF DEGREES...
WHICH IS IN LINE WITH THE COOLER SIDE OF GUIDANCE (MAV). THIS YIELDS
LOWS IN THE UPPER TEENS TO LOWER 20S. (WITH MAYBE A FEW MID 20S IN
THE URBAN CENTERS).

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
AS OF 255 PM WEDNESDAY...

THURSDAY...HIGH PRESSURE OVER THE AREA EARLY THURSDAY MORNING WILL
WEAKEN AND SHIFT SOUTHEAST OF THE SC COAST BY MIDDAY.  MEANWHILE...A PAIR OF
SHORTWAVES... ONE EMERGING OFF THE CENTRAL ROCKIES AND ANOTHER
DIVING SOUTH OUT OF THE CANADIAN ROCKIES WILL IMPACT THE REGION
THURSDAY AFTERNOON/NIGHT.  WITH THE LEAD WAVE...FORCING IS FOCUSED
ALOFT AS THE BRUNT OF THE DCVA PASSES TO OUR NORTH.  MOISTURE IS
FOCUSED IN THE MID-LEVELS...PER NAM/GFS BUFR SOUNDINGS...AND
DECREASES RAPIDLY WITH SOUTHWARD EXTENT.  WHILE THE ECMWF PRODUCES A
FEW HUNDREDTHS AREAWIDE BETWEEN 18-00Z...THE NAM/GFS/SREF SUGGEST
JUST A PASSING SPRINKLE AT BEST DURING THE AFTERNOON...AND THIS
LOOKS MOST REASONABLE. SOUTHERLY WIND WILL HELP HIGHS REBOUND
THURSDAY ESPECIALLY IN THE WEST...UPPER 40S NORTHEAST TO LOWER 50S
SOUTHWEST.

THURSDAY NIGHT...ON THE HEELS OF THE LEAD WAVE...THE TRAILING
SHORTWAVE...AND ASSOCIATED WEAK COLD FRONT...WILL CROSS THE CWA IN
THE 03-09Z TIME FRAME.  THE FORCING FOR ACCENT IS MUCH BETTER WITH
STRONGER DCVA AND WEAK LOW-LEVEL FRONTAL CONVERGENCE...ALL WITHIN
THE LEFT EXIT REGION OF A STRENGTHENING SPEED MAX OVER THE MID-
MISSISSIPPI VALLEY REGION.  HOWEVER...MOISTURE MAY AGAIN BE TOO
LIMITED AS THE DEEPER LAYER FLOW BECOMES WESTERLY.  A FEW ISOLATED
LIGHT SHOWERS OR SPRINKLES ARE POSSIBLE WITH FRONT...BUT MAJORITY OF
THE AREA SHOULD BE DRY. MAY SEE A FEW WIND GUSTS BEHIND THE FRONT
WITH THE INITIAL COLD ADVECTION...AS LOWS FALL INTO THE LOW TO MID
30S.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
AS OF 335 PM WEDNESDAY...

FRI THROUGH SAT NIGHT: THE MODELS ARE IN GOOD AGREEMENT REGARDING
THE AMPLIFICATION OF A PAIR OF STRONG NORTHERN STREAM SHORTWAVE
TROUGHS INTO AND OFFSHORE THE COAST OF THE MIDDLE ATLANTIC STATES ON
FRIDAY. THE ASSOCIATED SFC COLD FRONT SHOULD BE NEAR THE COAST AT
THE START OF THE PERIOD/12Z FRI...WITH STRONG CAA - OFFSET TO SOME
DEGREE BY 30 KTS OF NW DOWNSLOPE FLOW - FOR THE REMAINDER OF THE
DAY. THE RESULT WILL BE BLUSTERY NW WINDS TO AROUND 30 MPH WITHIN A
DEEPLY MIXED (~5 K FT) BOUNDARY LAYER...AND HIGHS IN THE MIDDLE 40S
TO AROUND 50 DEGREES.

1030 MB CONTINENTAL POLAR HIGH PRESSURE WILL BUILD EAST OF THE
APPALACHIANS FRI NIGHT. CONSENSUS LL THICKNESS VALUES AROUND 1280
METERS SUPPORT LOWS MOSTLY IN THE LOWER 20S...THOUGH UPPER TEENS
WILL BE POSSIBLE WHERE AND IF DECOUPLING/CALM OCCUR TOWARD DAYBREAK.

THE SFC RIDGE WILL CREST OVERHEAD SAT...THEN DRIFT OFFSHORE SAT
NIGHT. MEANWHILE ALOFT...INITIALLY NW FLOW WILL TRANSITION TO
INCREASINGLY ZONAL FLOW DOWNSTREAM OF BOTH A NORTHERN STREAM S/W
TROUGH APPROACHING FROM WESTERN CANADA AND AN EVOLVING UPPER LOW
NEAR THE BAJA. THE ZONAL FLOW WILL ALLOW ABUNDANT MID-HIGH LEVEL
MOISTURE TO STREAM EAST OVER CENTRAL NC LATE IN THE DAY AND
PARTICULARLY OVERNIGHT SAT. GIVEN THE INCREASING MOISTURE
ALOFT...LOWS WILL BE NOT BE AS COLD - MOSTLY IN THE LOWER (TO
PERHAPS MIDDLE) 30S. WHILE THE INCREASING MID-HIGH LEVEL MOISTURE
WILL LIKELY RESULT IN WIDESPREAD VIRGA BY EARLY SUN...A DRY SUB-
CLOUD LAYER IN EXCESS OF 7-8 THOUSAND FT PER MODEL CROSS SECTIONS
SUGGEST IT WILL REMAIN DRY AT THE SFC. *IF* LIFT AND MOISTURE WERE
TO INCREASE MORE QUICKLY THAN CURRENTLY FORECAST...PARTIAL THICKNESS
AND WET BULB PROFILE VALUES WOULD SUPPORT SNOW AT THE ONSET...BUT
PROSPECTS OF THAT HAPPENING ARE VERY LOW.

SUN THROUGH MON: THE MODELS HAVE TRENDED FLATTER WITH THE NORTHERN
STREAM S/W TROUGH (REFERENCED ABOVE) AS IT AMPLIFIES INTO THE MIDDLE
ATLANTIC STATES THROUGH SUN NIGHT OR MON. THE ASSOCIATED SFC LOW
REFLECTION IN RECENT NWP RUNS IS CONSEQUENTLY MUCH WEAKER AND MORE
SUPPRESSED THAN EARLIER FORECASTS. REGARDLESS OF WHETHER OR NOT THE
GUIDANCE TRENDS BACK TOWARD A STRONGER SYSTEM LIFTING UP WEST OF THE
APPALACHIANS...THE HIGHEST RAIN CHANCES WILL STILL BE SUNDAY NIGHT
IN EITHER SCENARIO. BEFOREHAND...SUNDAY SHOULD BE A CLOUDY DAY FOR
CENTRAL NC...WITH RAIN CHANCES INCREASING FROM TOP-DOWN SATURATION
OVER MAINLY THE WESTERN AND NORTHERN PIEDMONT...AND WITH HIGHS WELL
BELOW FULL SUN VALUES - MOSTLY IN THE MIDDLE 40S TO AROUND 50
DEGREES. THE FLATTER/WEAKER SFC SOLUTIONS DO HAVE RAMIFICATIONS ON
PRECIPITATION CHANCES AND TEMPERATURES FOR MON...HOWEVER...SUCH THAT
THE BULK OF THE DAY WOULD BE DRY BEHIND THE SYSTEM GIVEN THE LATEST
MODEL TRENDS...WITH CAA-DRIVEN TEMPERATURES IN THE MIDDLE 40S TO
AROUND 50 DEGREES.

MON NIGHT THROUGH WED: BENEATH HEIGHT RISES ALOFT BEHIND THE
DEPARTING NORTHERN STREAM S/W TROUGH...POST-FRONTAL...CONTINENTAL
POLAR HIGH PRESSURE WILL BUILD OVERHEAD MON NIGHT-TUE...THEN DRIFT
OFFSHORE TUE NIGHT-WED. MEANWHILE ALOFT...THE EVOLVING UPPER LOW
NEAR THE BAJA IS FORECAST TO EJECT AND TRACK ACROSS THE SOUTHERN
US...WITH ACCOMPANYING SFC LOW DEVELOPMENT FROM THE GOM TO THE
SOUTHEAST US COAST...THROUGH MID WEEK. THE RESULT WILL BE INCREASING
PRECIPITATION CHANCES IN CENTRAL NC...INTO THE SLIGHT TO CHANCE
RANGE...BY EARLY WED. PROJECTED PARTIAL THICKNESS VALUES WOULD
SUPPORT JUST A CHILLY RAIN.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
AS OF 705 PM WEDNESDAY...

24 HOUR TAF PERIOD: VFR CONDITIONS WILL CONTINUE THROUGH THE 24
HOUR TAF PERIOD.

SURFACE HIGH PRESSURE WILL BUILD INTO THE AREA THIS EVENING... THEN
SLIDE TO THE SOUTH AND EAST OF THE REGION ON THURSDAY AS A COLD
FRONT APPROACHES CENTRAL NC FROM THE WEST. THIS WILL YIELD CLEAR
SKIES THIS EVENING INTO THE OVERNIGHT... WITH LIGHT AND VARIABLE TO
CALM WINDS. MID AND HIGH LEVEL CLOUDS WILL BEGIN TO INCREASE ACROSS
THE AREA ON THURSDAY... WHILE SURFACE WINDS BECOME SOUTH TO
SOUTHWESTERLY IN ADVANCE OF THE FRONT... WITH POSSIBLY SOME GUSTS
DURING THE AFTERNOON IN THE 15 TO 20 KT RANGE (HIGHEST PROBABILITY
OF SEE SOME WIND GUSTS TO 20 KTS WILL BE AT KGSO/KINT).

OUTLOOK: A MOSTLY DRY COLD FRONT WILL MOVE THROUGH THE AREA THURSDAY
NIGHT.  A BRIEF PERIOD OF MVFR CEILINGS MAY ACCOMPANY THE FRONT.
BREEZY NORTHWESTERLY WINDS WILL FOLLOW ON FRIDAY.  THE NEXT PERIOD
OF WIDESPREAD SUB-VFR CONDITIONS WILL LIKELY COME LATE SUNDAY INTO
MONDAY.


&&

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

&&

$$

SYNOPSIS...HARTFIELD
NEAR TERM...BSD
SHORT TERM...BLS
LONG TERM...MWS
AVIATION...BSD/BLS


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