Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 282013 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 310 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/... AS OF 310 PM SATURDAY... ...LIGHT ICING EVENT LIKELY FOR THE NC PIEDMONT AND WRN SANDHILLS LATE TONIGHT INTO SUNDAY... OVERVIEW: WINTER IS MOST CERTAINLY NOT OVER YET. MORE WINTRY PRECIP... DRIVEN PRIMARILY BY INCREASING MOIST ISENTROPIC UPGLIDE ATOP THE COLD WEDGING SURFACE HIGH CENTERED TO OUR NE... APPEARS LIKELY TO DEVELOP AND ENTER SOUTH-CENTRAL NC LATE TONIGHT BEFORE INCREASING IN COVERAGE AND SPREADING NORTHWARD OVER THE REMAINDER OF THE PIEDMONT ON SUNDAY. SYNOPTIC PATTERN: WE`LL MAINTAIN A FAST MID LEVEL FLOW FROM THE WSW (TRENDING TO BE FROM THE WEST) OVER NC. AT THE SURFACE... THE PARENT HIGH PROVIDING THE CHILLY AIR WILL SHIFT OFF THE NORTHEAST COAST LATE TONIGHT... ALLOWING THE INVERTED TROUGH ALONG THE SE COAST AND COASTAL NC TO SHARPEN. THIS WILL CULMINATE IN A RESIDUAL STABLE COLD POOL (AND MESOHIGH) OVER THE FAR WRN PIEDMONT/FOOTHILLS OF NC/SC LATE SUN INTO SUN NIGHT. AT 850 MB... A WEAK WAVE WILL TRACK FROM NRN FL TO THE NORTH... RESULTING IN STRENGTHENING FLOW JUST ALOFT AND AN INCREASINGLY PRONOUNCED WARM NOSE IN CENTRAL NC THERMAL PROFILES. THIS WAVE WILL TRACK TO OUR NE SUN EVENING/SUN NIGHT... LEADING TO AN EVENTUAL END TO PRECIP FROM WEST TO EAST. PRECIP TIMING AND AMOUNTS: HAVE MAINLY FOLLOWED A BLEND OF THE HIGH- RESOLUTION WRF-NMM/WRF-ARW... THE HRRR... AND DOWNSCALED NAM QPF AND TIMING. EXPECT PATCHY LIGHT PRECIP TO MOVE INTO THE SRN PIEDMONT AND SANDHILLS AFTER MIDNIGHT TONIGHT... WITH LOW COVERAGE AND JUST TRACE AMOUNTS. THEN AS THE MOIST UPGLIDE DEEPENS AND STRENGTHENS... EXPECT PRECIP TO INCREASE TO AT LEAST 50-60% COVERAGE (AND THIS MAY NEED TO BE RAISED IF LATER MODEL RUNS ARE CONSISTENT) OVER THE PIEDMONT SUNDAY MORNING... SPREADING EAST OVER THE REST OF THE CWA DURING THE AFTERNOON... BEFORE ENDING WEST TO EAST SUN NIGHT. MODELS DEPICT A FAIRLY LIGHT QPF... ESPECIALLY INITIALLY OVER THE SANDHILLS UP THROUGH THE EASTERN PIEDMONT WHERE THERE WILL BE SOME MINOR DRY POCKETS ALOFT. THIS IS REASONABLE CONSIDERING THE RELATIVELY SHALLOW NATURE OF THE LIFT. EXPECT TOTAL QPF GENERALLY FROM 0.25 TO 0.40... WITH LOWER AMOUNTS IN THE SE CWA TRENDING TO THE HIGHER AMOUNTS IN THE NW CWA. PRECIP TYPE: FOLLOWING THE TOP-DOWN PTYPE METHODOLOGY... EXPECT ANY INITIAL PRECIP TO BE SOME VERY LIGHT FREEZING DRIZZLE (DUE TO SOMEWHAT DRY AIR ALOFT LIMITING ICE IN THE CLOUD)... TRENDING TO MAINLY LIGHT FREEZING RAIN OVER NRN/WRN CWA. THE ENCROACHING WARMER SURFACE AIR (AS THE COLD DOME THINS ON THE EDGES) WILL RESULT IN AN HOUR-BY-HOUR TRANSITION TO LIGHT RAIN FROM SE TO NW... WITH THE FREEZING RAIN THREAT LAST DEPARTING FROM THE TRIAD/ROXBORO AREAS LATE IN THE AFTERNOON AS WET BULBS THERE RISE TO AROUND FREEZING. AS THE SURFACE HIGH WILL BE RETREATING NE AWAY FROM THE AREA... IT WILL SLOWLY LOSE ITS GRIP ON OUR AREA AND CEASE TO PROVIDE A STEADY SOURCE OF LOW LEVEL DRY AIR THAT MIGHT ENSURE CONTINUED GLAZE BUILD- UP. SO WITH TIME... LATENT HEAT RELEASE WILL SERVE TO LIMIT ICE ACCRUAL... SUCH THAT SOME OF THE QPF IN THE LATTER HOURS OF THE EVENT WILL SIMPLY RUN OFF. THAT SAID HOWEVER... BASED ON FORECAST SURFACE WET BULB TEMPS AND BUFR SOUNDINGS... IT APPEARS THAT THERE WILL BE A DEEP ENOUGH SURFACE COLD LAYER TO SUPPORT A LIGHT GLAZING OVER MUCH OF THE WESTERN TWO-THIRDS OF THE CWA... WITH THE GREATER AMOUNTS (PERHAPS AT OR JUST OVER A TENTH OF AN INCH) OVER THE CLIMATOLOGICALLY-FAVORED NW CWA. TEMPERATURES: READINGS WILL FOLLOW AN ATYPICAL TREND THROUGH SUNDAY NIGHT. EXPECT LOWS TONIGHT OF 23-33... HIGHS SUNDAY OF 32-39 WEST OF I-95 AND MAINLY 40S EAST OF I-95... AND LOWS SUN NIGHT 32-44... ALTHOUGH TEMPS SUN EVENING/NIGHT SHOULD BE STEADY OR PERHAPS RISE A COUPLE OF DEGREES OVERNIGHT AS THE RESIDUAL COOL POOL STARTS TO MIX OUT IN THE FACE OF INCREASING WSW FLOW ALOFT LATE. -GIH && .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 /18Z SATURDAY THROUGH THURSDAY/... AS OF 1235 PM SATURDAY... PRIMARY AVIATION CONCERNS NEXT 24 HRS: CIGS DROPPING TO MVFR AND IFR STARTING LATE THIS EVENING (SOUTH) INTO THE EARLY OVERNIGHT HOURS (NORTH)... WITH POTENTIAL LOW LEVEL WIND SHEAR DEVELOPING. SURFACE HIGH PRESSURE CENTERED TO OUR NORTH NEAR BALTIMORE WILL CONTINUE TO NOSE SOUTHWARD INTO CENTRAL/WRN NC THROUGH THIS EVENING. EXPECT NO MORE THAN A DECK OF VFR MID CLOUDINESS THROUGH THE 03Z (FAY) TO 06Z (RDU/RWI) TIME FRAME... WITH VFR VSBYS. A DEVELOPING INVERTED TROUGH NEAR THE COAST COMBINED WITH A SURGE OF MOISTURE FROM NRN FL SPREADING NORTHWARD INTO WRN/CNTRL NC OVERNIGHT WILL BRING A GROWING RISK OF PRECIP LATE... SPREADING IN FROM SOUTH TO NORTH... WITH LIGHT PRECIP AFFECTING FAY FIRST THEN MOVING INTO INT/GSO/RDU AREAS LATE TONIGHT. RWI MAY NOT SEE MUCH IF ANY PRECIP UNTIL NEAR 18Z SUNDAY OR LATER. CIGS WILL LOWER TO MVFR THEN RAPIDLY TO IFR LATE TONIGHT INTO EARLY SUN MORNING... WITH A GOOD CHANCE OF LOW LEVEL WIND SHEAR ESPECIALLY AT FAY STARTING AS EARLY AS 09Z. CONFIDENCE IS HIGH IN IFR OR LIFR CIGS AFTER 10Z-12Z SUNDAY. FREEZING RAIN IS THE MOST LIKELY PRECIP TYPE AT INT/GSO LATE TONIGHT THROUGH SUNDAY... WITH FREEZING RAIN CHANGING TO RAIN AT RDU... AND BRIEF FREEZING RAIN CHANGING EARLY TO RAIN AT FAY. GLAZING OF ICE IS MOST LIKELY AT INT/GSO... LESS SO AT RDU/FAY. LOOKING BEYOND 18Z SUNDAY... IFR/LIFR CONDITIONS WILL HOLD THROUGH THE REST OF SUNDAY WITH PRECIP SPREADING ENE INTO RWI. EVEN IF LLWS CRITERIA ARE NOT STRICTLY MET... WINDS AT ALL SITES WILL BE INCREASING WITH HEIGHT FROM THE SW THROUGH THE LOWEST 2-3 KFT... MAKING HANDLING OF SOME AIRCRAFT CHALLENGING. PRECIP ENDS EARLY SUNDAY EVENING BUT LIFR CLOUDS EXPECTED TO LINGER THROUGH SUNDAY NIGHT... THEN ERODE FROM THE TOP MONDAY AS A COLD FRONT SWEEPS THROUGH FROM NW TO SE. HIGH PRESSURE BUILDS IN FROM THE NORTH LATE MON THROUGH MON NIGHT... THEN ANOTHER APPROACHING STORM SYSTEM WILL BRING A GOOD CHANCE OF SUB-VFR CIGS EARLY TUE THROUGH TUE NIGHT. MAY SEE A BREAK TO MVFR OR VFR CIGS WED... BUT YET ANOTHER STORM SYSTEM IS POISED TO BRING INCREASING WINDS WED THEN MORE SUB-VFR CONDITIONS AND PRECIP WED NIGHT/THU. -GIH && .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 SHORT TERM...KC LONG TERM...KC AVIATION...HARTFIELD

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