Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 010332 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1030 PM EST SAT FEB 28 2015 .SYNOPSIS...COLD HIGH PRESSURE REMAINS OVER THE REGION THROUGH SUNDAY. INCREASING MOISTURE WILL HELP PROVIDE FOR UNSETTLED WEATHER SUNDAY. A COLD FRONT MOVES THROUGH THE AREA MONDAY...FOLLOWED BY HIGH PRESSURE AGAIN FOR TUESDAY...BEFORE ANOTHER COLD FRONT MOVES INTO THE REGION WEDNESDAY. && .NEAR TERM /THROUGH SUNDAY NIGHT/...
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AS OF 1030 PM SATURDAY... ...A LIGHT ICING EVENT LIKELY FOR THE NC PIEDMONT AND WRN SANDHILLS LATE TONIGHT INTO SUNDAY... STRONG 1043MB HIGH CENTERED OVER THE DELMARVA HAS SUPPLIED A VERY DRY AIRMASS FOR CENTRAL NC THIS EVENING WITH DEWPOINTS WELL INTO THE TEENS. MODELS HAVE STRUGGLED WITH THE AIRMASS A BIT...WITH THE GFS AND ECMWF BEING TO COLD THIS EVENING...BUT THE WETBULB FREEZING LINE IS SUPPRESSED WELL SOUTH TO THE NC/SC BORDER. EARLY ON... RADAR RETURNS HAVE BEEN CONFINED TO CENTRAL AND EASTERN SC AND APPEAR TO BE INITIALLY DRIVEN BY WARM ADVECTION UP NEAR 700MB. DRIER AIR BELOW HAS KEPT THE PRECIP SPOTTY BUT THERE ARE SOME REPORTS OF LIGHT RAIN IS SC. WITH TIME...THE WARM ADVECTION AND ISENTROPIC LIFT WILL INCREASE ACROSS SOUTHERN AND WESTERN NC IN RESPONSE TO AN UPPER LEVEL JET CROSSING THE MID-MISSISSIPPI VALLEY REGION. DRY AIR SHOULD ALSO KEEP PRECIP SPOTTY INITIALLY...BUT THE LOW-LEVEL JET IS FORECAST TO INTENSIFY TO 40-50KT FROM THE PIEDMONT NORTH INTO VA AFTER 09Z...SO EXPECT PRECIP TO FILL IN AND QPF TO INCREASE MORE TOWARD THE 12-15Z TIME FRAME. MOISTURE NEVER REALLY REACHES ABOVE -6 TO -8C...SO WHILE BRIEF PERIODS OF SLEET ARE POSSIBLE...FREEZING RAIN WILL BE THE PREDOMINATE PTYPE. MODEL QPF RANGES A TENTH OF AN INCH THROUGH 18Z ON THE ECMWF TO UP TO A QUARTER OF AN INCH ON THE NAM. THE GFS IS OVERDONE UPSTREAM OVER GEORGIA...SO HAVE DISCOUNTED IT FOR NOW. AS YOU GO EAST...CONFIDENCE IN MEASURABLE PRECIP IS MUCH LOWER TONIGHT AS MOISTURE IS SHALLOWER...AND BY THE TIME BETTER PRECIP SPREADS EAST TOMORROW...WARMING SHOULD ALLOW TEAMS AND WETBULB VALUES TO RISE ABOVE 32 BY MID-MORNING. THE MAIN CONCERN AND CHANGE IN THE FORECAST THIS EVENING IS IN THE NORTHERN PIEDMONT AND NORTHERN COASTAL PLAIN WHERE INCREASING QPF MAY OVERLAP WITH SUB- FREEZING TEMPS FOR A LONGER PERIOD THAN PREVIOUSLY EXPECTED SUNDAY MORNING. GENERALLY STILL EXPECT A TENTH OF AN INCH OF ICE AT MOST ACROSS THE NORTHWEST PIEDMONT...BUT SOME AREAS OVER THE NORTHERN PIEDMONT COULD SEE A TENTH OF AN INCH AS WELL. GIVEN THE QUESTIONABLE MODEL PERFORMANCE AND CONSISTENCY WITH THIS EVENT SO FAR...CONFIDENCE IN THE WINTER WEATHER ADVISORY IS BEST ONLY IN THE WEST AND MUCH LOWER IN THE EAST. HAVE ELECTED TO EXPAND THE ADVISORY TO COVER ALL OF CENTRAL NC...AND WILL MESH THE NEW AREAS WITH THE PREVIOUS ADVISORY SEGMENTS...ENDING FROM NORTH TO SOUTH THROUGH THE MORNING HOURS.
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&& .SHORT TERM /MONDAY AND MONDAY NIGHT/... AS OF 220 PM SATURDAY... THE APPROACHING UPPER LEVEL TROUGH WEAKENS AS IT MOVES THROUGH CENTRAL NC ON MONDAY. LATEST MODEL RUNS INDICATE MONDAY WILL BE MOSTLY DRY...WITH A SLIGHT CHANCE OF SOME LIGHT PRECIPITATION EARLY IN THE DAY...DRYING INTO THE AFTERNOON AS THE RAINFALL ALONG THE FRONT DISSIPATES OVER THE MOUNTAINS. THE COLD FRONT WILL TILT TO A MORE WEST TO EAST ORIENTATION AND SLIDE THROUGH THE AREA BY MONDAY EVENING. SURFACE HIGH PRESSURE WILL BUILD IN THEREAFTER AND REMAIN THROUGH MONDAY NIGHT. ALTHOUGH TEMPERATURES SHOULD RISE DURING THE DAY GIVEN GRADUALLY CLEARING SKIES AND THUS GOOD SUNSHINE...THE INCREASES WILL BE GREATEST ACROSS THE SOUTH WHERE THE FROPA HAPPENS LATER. HIGHS WILL RANGE FROM UPPER 40S ACROSS THE NORTH TO UPPER 50S IN THE SOUTH...ALTHOUGH THEY ARE HIGHLY DEPENDENT ON THE TIMING OF THE FRONT. OVERNIGHT LOWS SHOULD BE IN TEH UPPER 20S NORTH TO UPPER 30S SOUTH. && .LONG TERM /TUESDAY THROUGH SATURDAY/... AS OF 300 PM SATURDAY... TUESDAY THROUGH THURSDAY NIGHT: THE UPPER LEVEL TROUGH ASSOCIATED WITH AN UPPER LEVEL LOW OVER CENTRAL CANADA ON TUESDAY WILL EXTEND SOUTHWEST THROUGH THE INTERMOUNTAIN WEST AND INTO THE DESERT SOUTHWEST. AT THE SURFACE...THE COLORADO LOW THAT DEVELOPS ON MONDAY WILL BEGIN ITS TREK EASTWARD THROUGH THE MIDWEST MONDAY NIGHT... SLIDING NORTHEAST INTO THE GREAT LAKES ON TUESDAY. THE ASSOCIATED COLD FRONT THAT DEVELOPS WILL EXTEND FROM APPROX THE CENTRAL GREAT LAKES TO THE ARKLATEX BY LATE TUESDAY. ACROSS CENTRAL NC...THE CAD WEDGE THAT SET UP MONDAY NIGHT WILL LINGER THROUGH THE DAY TUESDAY. THE FORECAST PROBLEM FOR THIS PART OF THE FORECAST CONTINUES TO BE HIGH UNCERTAINTY IN TEMPERATURES DUE TO THE LINGERING WEDGE AND THE WARM FRONT RETREATING NORTHWARD. THE MODELS HAVE A TENDENCY TO ERODE THE WEDGE TOO QUICKLY...ESPECIALLY IF THERE IS PRECIPITATION FALLING INTO IT...SO CURRENTLY INDICATE THE WEDGE STICKING AROUND A BIT LONGER...WITH A LARGE SPREAD IN TEMPS FROM NW TO SE ACROSS THE AREA TUESDAY AND WEDNESDAY. CONFIDENCE REMAINS LOW WITH RESPECT TO TEMPS...AS ANY CHANGES TO THE WEDGE EROSION AND TIMING/POSITION OF THE WARM FRONT AS IT RETREATS NORTHWARD WILL HIGHLY IMPACT TEMPERATURES. THEY WILL HOWEVER INCREASE GRADUALLY FROM MIDNIGHT WEDNESDAY THROUGH AROUND MIDNIGHT THURSDAY AS THE WARM FRONT RETREATS NORTHWARD. SHOULD THE WEDGE BE LOCKED IN LONGER OR ERODE EARLIER CURRENT FORECAST TEMPS WOULD BE WAY OFF. TEMPS: LOW 40S NW TO MID 50S SE TUESDAYS...INCREASING TO LOW 60S NW TO LOW 70S SE ON WEDNESDAY. A NORMAL DIURNAL TEMPERATURE CURVE SHOULD RETURN WEDNESDAY NIGHT. LOWS IN THE LOW 40S NW TO LOW 50S SE. HIGHS THURSDAY MID 40S NW TO MID 50S SE. PRECIPITATION: SOME LIGHT RAIN COULD FALL INTO THE WEDGE ON TUESDAY AS WARM MOIST AIR FROM THE SOUTH ADVECTS IN OVER THE COLD AIR TRAPPED AT THE SURFACE. THIS WOULD ACT TO THEN LOCK THE WEDGE IN LONGER. THERE WILL BE A SLIGHT CHANCE TO CHANCE OF PRECIP ACROSS THE WEST/NORTHWEST PORTIONS OF THE AREA THROUGH WEDNESDAY MORNING... EVEN THOUGH THE MAIN PRE-FRONTAL CONVECTIVE RAINFALL REMAINS LARGELY WEST OF THE APPALACHIANS. THE LATEST 12Z ECMWF AND GFS MODEL RUNS ARE IN BETTER AGREEMENT WITH THE TIMING OF THE FROPA AND THE ASSOCIATED RAINFALL AS IT MOVES THROUGH THE AREA. THE LATEST RUNS SUGGEST THAT RAIN WILL BE LIKELY ACROSS THE WEST BEGINNING WEDNESDAY AFTERNOON...PROGRESSING THROUGH CENTRAL NC WEDNESDAY NIGHT AND THURSDAY...AND ENDING AROUND MIDNIGHT FRIDAY. THIS IS ANOTHER CASE OF THE COLD AIR CHASING THE PRECIP...AND FOR NOW EXPECT ALL PRECIP TO FALL AS RAIN...BUT THAT WILL CONTINUE TO BE MONITORED WITH SUBSEQUENT FORECAST UPDATES AS THAT PERIOD APPROACHES. FRIDAY THROUGH SATURDAY: HIGH PRESSURE WILL BUILD IN BEHIND THE FROPA THURSDAY NIGHT...REMAINING OVER THE REGION INTO THE WEEKEND. EXPECT A DRY FORECAST PERIOD FOR NOW...WITH HIGHS IN THE LOW TO MID 40S FRIDAY...INCREASING INTO THE 50S SATURDAY. LOWS FRIDAY NIGHT IN THE 20S. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... AS OF 820 PM SATURDAY... UNDER THE INFLUENCE OF MODIFIED ARCTIC SFC HIGH PRESSURE...VFR CONDITIONS WILL PREVAIL THIS EVENING. HOWEVER...THE DEVELOPMENT AND STRENGTHENING OF GENERALLY SE FLOW JUST ABOVE THE SURFACE WILL RESULT IN THE NORTHWARD DEVELOPMENT OF PRECIPITATION AND CEILINGS...INITIALLY BETWEEN 3 AND 5 THOUSAND FT...WHICH WILL SUBSEQUENTLY LOWER THROUGH MVFR-IFR RANGE TO LIFR...LATER TONIGHT THROUGH SUNDAY. THE PRECIPITATION WILL FALL MOSTLY AS RAIN AT RWI...WHERE TEMPERATURES ARE LIKELY TO CLIMB ABOVE FREEZING BEFORE PRECIPITATION ARRIVES SUN MORNING...WITH A TRANSITION FROM FREEZING RAIN TO RAIN ELSEWHERE...WITH SAID TRANSITION LIKELY TO NOT OCCUR UNTIL MID-LATE AFTERNOON AT TRIAD TAF SITES. THE STRENGTHENING AND GRADUAL VEERING OF THE FLOW FROM SE TONIGHT TO SSW ON SUNDAY...JUST ABOVE NE FLOW WITHIN A STABLE/COOL SURFACE LAYER...WILL RESULT IN LOW LEVEL WIND SHEAR CONDITIONS LATE TONIGHT THROUGH SUNDAY. THOUGH PRECIPITATION AND LOW LEVEL WIND SHEAR WILL END FROM WEST TO EAST LATE SUNDAY OR SUNDAY EVENING...LIFR CONDITIONS WILL PERSIST IN A LINGERING COLD AIR DAMMING REGIME AND ASSOCIATED SHALLOW SATURATION IN THE LOW LEVELS THROUGH 14-17Z MON. OUTLOOK: AFTER A RETURN TO VFR MON-MON NIGHT...PERIODS OF UNSETTLED CONDITIONS WITH ASSOCIATED RAIN AND SUB-VFR CONDITIONS ARE EXPECTED TUE THROUGH THU...WITH THE RELATIVELY LOWEST AND MOST PROLONGED CONDITIONS AT TRIAD TAF SITES...WHERE PROLONGED COLD AIR DAMMING WILL BE MOST PROBABLE. && .RAH WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY FROM 4 AM TO NOON EST SUNDAY FOR NCZ008>010-024>026-040-041-073>076. WINTER WEATHER ADVISORY FROM 1 AM TO 10 AM EST SUNDAY FOR NCZ077-083>086-088. WINTER WEATHER ADVISORY FROM 4 AM TO 6 PM EST SUNDAY FOR NCZ007-021>023-038-039. && $$ SYNOPSIS...DJF NEAR TERM...HARTFIELD/BLS SHORT TERM...KC LONG TERM...KC AVIATION...RAH

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