Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 060555
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1255 AM EST SAT FEB 6 2016

.SYNOPSIS...HIGH PRESSURE WILL SETTLE OVERHEAD THROUGH TODAY THEN
DRIFT OFFSHORE TONIGHT. A SURFACE LOW WILL PASS OFFSHORE OF THE
CAROLINA COAST SUNDAY...FOLLOWED BY AN ARCTIC COLD FRONT THAT WILL
ARRIVE EARLY NEXT WEEK.

&&

.NEAR TERM /OVERNIGHT/...
AS OF 955 PM FRIDAY...

LITTLE CHANGE REQUIRED TO THE NEAR TERM FORECAST.

A COLD DRY AIR MASS HAS OVERSPREAD CENTRAL NC DURING THE LAST 24
HOURS AS EVIDENT BY THE 00Z GSO SOUNDING MEASURING PRECIPITABLE
WATER VALUE OF 0.12 INCHES...AND SFC DEWPOINTS IN THE TEENS TO
AROUND 20 DEGREES IN THE NW PIEDMONT. WHERE SFC WINDS HAVE
DECOUPLED...TEMPS HAVE ALREADY FALLEN INTO THE UPPER 20S-LOWER 30S.
ELSEWHERE WHERE SFC WINDS 3-5KTS CONTINUE...TEMPS WERE IN THE MID-
UPPER 30S. AS THE SFC RIDGE SETTLES OVERHEAD LATER TONIGHT...WINDS
WILL BECOME CALM PRETTY MUCH EVERYWHERE. UNDER NEARLY IDEAL
NOCTURNAL COOLING CONDITIONS (ASIDE FROM A NEARLY SATURATED TOP SOIL
OVER THE EASTERN HALF OF THE FORECAST AREA)...TEMPS BY EARLY
SATURDAY SHOULD BE IN THE 20-25 DEGREE RANGE.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY/...
AS OF 255 PM FRIDAY...

SPLIT FLOW OVER THE CONUS WILL LEAD TO A CUT OFF SOUTHERN STREAM
WAVE THAT SWINGS ACROSS THE SOUTHEAST US SATURDAY AND THEN LIFTS
ALONG THE EAST COAST ON SUNDAY...WITH A RAPIDLY DEEPENING SURFACE
LOW(TO 980MB) OVER THE GULF STREAM AND A SHARP CUTOFF OF PRECIP ON
ITS WESTERN SIDE.  HIGHS SATURDAY WILL BE IN THE UPPER 40S AND
LOWER 50S...WITH CLEAR SKIES EARLY SATURDAY NIGHT AND STRONG COOLING
FOR THE FIRST HALF OF THE NIGHT.  THE SURFACE LOW IS FORECAST TO
BEGIN TO DEVELOP AFTER 06S SUNDAY...WITH MOISTURE INCREASING RAPIDLY
OVER THE SOUTHERN COASTAL PLAIN BY 12Z. TEMP PROFILES (OR WETBULB
PROFILES) WILL BE SUB-FREEZING DOWN TO ABOUT A 1000 FT OR SO FROM
THE SURFACE...AND MODELS INDICATE SUFFICIENT MOISTURE IN THE ICE
NUCLEATION ZONE FOR CRYSTAL GROWTH AS LIFT INCREASE TOWARD 12Z
SUNDAY.  HOWEVER...BASED ON THE CURRENT FORECAST TRACK OF THE
SURFACE LOW...RH CROSS-SECTIONS FROM MULTIPLE MODELS SHOW VERY DRY
AIR NEAR AND WEST OF I-95 THAT WILL BE HARD TO OVERCOME.
SIMILARLY...AND ESPECIALLY EAST OF I-95...THE BIG QUESTIONS SEEMS TO
BE WHETHER OR NOT PRECIP RATES WILL BE HEAVY ENOUGH TO OVERCOME THE
LOW-LEVEL ABOVE FREEZING LAYER AND SUSTAIN SNOW AS THE PREDOMINATE
PTYPE. OUTSIDE OF THE STORM INDUCED NORTHERLY FLOW...THERE IS NO
REAL COLD AIR SUPPORT TO OUR NORTH....AS THE INITIAL COLD HIGH OVER
US WILL WEAKEN AND DEPART TO THE NORTHEAST ON SATURDAY. THE GFS HAS
TRENDED WESTWARD AND WETTER IN THE PAST 2 OR 3 RUNS..BUT IS A
WESTERN OUTLIER.  THE CONSENSUS SEEMS TO BE A TENTH TO A THIRD OF AN
INCH OF QPF FROM SCOTLAND COUNTY TO WILSON COUNTY. THESE LIQUID
AMOUNTS WOULD NOT LIKELY CAUSE MANY PROBLEMS AS FAR AS SNOW
ACCUMULATION GIVEN THAT PRECIP RATES WOULDNT BE THAT HIGH AND
SURFACE TEMPS WOULD BE IN THE MID/UPPER 30S AT WORST.

THAT IS HOW THE CURRENT FORECAST APPEARS TO PLAY OUT...BUT THERE IS
STILL ENOUGH UNCERTAINTY IN THE TRACK OF THE SURFACE LOW...AS WELL AS
THE ORIENTATION OF THE UPPER WAVE AND THE ROLE OF THE KICKER
SHORTWAVE THAT DIVES THROUGH THE CENTRAL PLAINS BEHIND IT.  THE
LATTER WILL BE BETTER SAMPLED TONIGHT.  SMALL CHANGES IN THESE
FEATURES...IE THE MAIN SHORTWAVE BECOMING NEGATIVELY TILTED SOONER
AND/OR THE SURFACE LOW TRACKING A LITTLE FURTHER WEST COULD HAVE A
GREATER IMPACT.

NOT TO LEAVE OUT THE WESTERN CWA...BUT MOSTLY CLEAR TO PARTLY CLOUDY
SKIES WEST OF THE TRIANGLE  SHOULD MAKE FOR A DECENT DAY ON SUNDAY
WITH HIGHS IN THE UPPER 40S TO AROUND 50.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
AS OF 250 PM FRIDAY...

SHORTWAVE ENERGY MOVING ONSHORE BRITISH COLUMBIA TONIGHT WILL RESULT
IN RAPID AMPLIFICATION OF A LONGWAVE TROUGH OVER THE EASTERN US SUN
NIGHT/MONDAY AS IT DIGS SOUTHEAST THROUGH THE UPPER MIDWEST INTO THE
OH VALLEY AS AN UPPER LOW...ON THE HEELS OF A NEGATIVELY TILTED
SHORTWAVE PROGRESSING OFFSHORE THE SOUTHEAST COAST. THE RESULTING
LONGWAVE TROUGH IS EXPECTED TO PERSIST OVER THE EASTERN CONUS
THROUGH MID-WEEK...OR UNTIL UNIDIRECTIONAL FLOW ALOFT BECOMES
ESTABLISHED THU/FRI. LIGHT PRECIP IS EXPECTED TO OCCUR IN ASSOC/W
POTENT SHORTWAVE ENERGY ROUNDING THE SOUTHEAST PERIPHERY OF THE
AFOREMENTIONED UPPER LOW MONDAY AFT/EVE. GIVEN SOUTHWEST FLOW
THROUGHOUT THE COLUMN AND THE PRESENCE OF LOW-LEVEL WARM
ADVECTION...NO PTYPE CONCERNS ARE ANTICIPATED. EXPECT BELOW
NORMAL TEMPERATURES TUE/WED IN ASSOCIATION WITH STRONG/PERSISTENT
COLD ADVECTION AS THE LONGWAVE TROUGH SHIFTS EAST INTO THE MID-
ATLANTIC/CAROLINAS. FROM A PATTERN RECOGNITION STANDPOINT...I.E.
UPPER TROUGH AXIS NEAR/OVER THE REGION AND WESTERLY FLOW THROUGHOUT
THE LOW/MID LEVELS...DRY CONDITIONS ARE GENERALLY EXPECTED TO
PREVAIL. ONE EXCEPTION WILL BE A POTENTIAL FOR ISOLD/SCT DIURNAL
CONVECTION TUE AFTERNOON GIVEN STEEP LAPSE RATES/VERY COLD TEMPS
ALOFT AND OCCASIONAL DPVA ASSOC/W SHORTWAVE ENERGY ROUNDING THE
BASE OF THE TROUGH /UPPER LOW/ OVER THE MID-ATLANTIC. WHETHER OR
NOT CONVECTION DEVELOPS WILL HIGHLY DEPEND ON THE TIMING/MAGNITUDE OF
DPVA...AND EVEN IF CONVECTION WERE TO DEVELOP...A VERY DRY SUB-CLOUD
LAYER WOULD HAVE TO BE OVERCOME...THUS CONFIDENCE REMAINS LOW. IF
CONVECTION WERE TO DEVELOP...A SHALLOW ABOVE FREEZING LAYER IN
THE LOWEST 500-1000 FT AGL WOULD SUGGEST RAIN SHOWERS...THOUGH SOME
POTENTIAL FOR A RATE-DRIVEN CHANGEOVER TO SNOW SHOWERS WOULD BE
PRESENT. -VINCENT

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
AS OF 1255 AM SATURDAY...

VFR CONDITIONS AND LIGHT WINDS WILL PREVAIL THROUGH THE TAF
PERIOD...OWING TO HIGH PRESSURE THAT WILL BUILD ACROSS THE
APPALACHIANS THROUGH TODAY.

THE AFFECTS OF A COASTAL LOW PRESSURE WILL GRAZE MAINLY EASTERN TAF
SITES (FAY AND RWI) WITH SUB-VFR CONDITIONS AND LIGHT RAIN ON
SUNDAY. A COUPLE OF UPPER LEVEL DISTURBANCES WILL BRING ADDITIONAL
CHANCES OF LIGHT SHOWERS AND BRIEF SUB-VFR CONDITIONS TO ALL SITES
LATE MON...AND AGAIN MAINLY AT NORTHERN TAF SITES LATE TUE.

&&

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

&&

$$

SYNOPSIS...BADGETT
NEAR TERM...WSS
SHORT TERM...SMITH
LONG TERM...VINCENT
AVIATION...BADGETT


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