Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 281959 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 259 PM EST SAT FEB 28 2015 .SYNOPSIS...COLD HIGH PRESSURE WILL EXTEND INTO THE AREA FROM THE NORTH TODAY. A WEAK DISTURBANCE MOVING SOUTH TO NORTH THROUGH THE REGION WILL BRING UNSETTLED WEATHER LATE TONIGHT INTO SUNDAY. A COLD FRONT WILL CROSS THE AREA SUNDAY NIGHT INTO MONDAY. && .NEAR TERM /THROUGH SUNDAY/... AS OF 1015 AM SATURDAY... ...THREAT FOR A LIGHT ICING EVENT INCREASING FOR THE NC PIEDMONT EARLY SUNDAY... REST OF TODAY: HAVE LET THE ADVISORY FOR BLACK ICE EXPIRE ON SCHEDULE... ALTHOUGH IT MAY TAKE ANOTHER HOUR OR SO FOR SOME AREAS TO RISE ABOVE FREEZING... AND WILL COVER THIS WITH A SPECIAL WEATHER STATEMENT. OTHERWISE... MID CLOUDS (AND A FEW LOWER CLOUDS) STREAMING ACROSS THE NRN/WRN CWA ARE PROJECTED TO OVERSPREAD THE ENTIRE AREA TODAY... RESULTING IN PARTLY SUNNY TO MOSTLY CLOUDY SKIES FOR MUCH OF THE DAY... WITH AN EVENTUAL NW-TO-SE PARTIAL CLEARING TREND LATE IN THE DAY... AS SUGGESTED BY THE NAM AND CANADIAN MODELS(WHICH ARE DOING BETTER WITH THE CURRENT SKY COVER WHILE THE GFS IS DEPICTING FAR TOO MANY LOW CLOUDS IN THE TRIAD). CHILLY SURFACE HIGH PRESSURE CENTERED OVER PA WILL CONTINUE TO EXTEND SOUTHWARD INTO THE AREA TODAY... AND THIS LOW LEVEL COLD/DRY AIR ADVECTION COMBINED WITH MORE CLOUDS THAN SUNSHINE WILL HOLD MAX TEMPS DOWN AT LEAST 2-3 CATEGORIES COOLER THAN YESTERDAY... IN THE 36-43 RANGE. -GIH TONIGHT AND SUNDAY... LATEST MODEL GUIDANCE HAS TRENDED WETTER LATE TONIGHT INTO SUNDAY. THIS INCREASES THE THREAT FOR A LIGHT ICING EPISODE EARLY SUNDAY...MAINLY ACROSS THE PIEDMONT COUNTIES. TONIGHT...SFC RIDGE AXIS WILL REMAIN OVER THE REGION...MAINTAINING A SUPPLY OF COLD DRY AIR IN THE LOWEST 2-4K FT OF THE ATMOSPHERE. ABOVE THE COLD DRY STABLE LAYER...SLY FLOW WILL BE INCREASING IN RESPONSE TO THE 850MB HIGH DRIFTING OFF THE SE U.S. COAST. THIS RETURN FLOW WILL ADVECT A WARMER...MORE MOIST AIR MASS INTO THE CAROLINAS. THIS RETURN FLOW STRENGTHENS SUBSTANTIALLY AFTER 12Z SUNDAY...THUS EXPECT THE BEST UPGLIDE TO OCCUR AFTER DAYBREAK SUNDAY. STILL...MODELS HAVE A TENDENCY TO BE A LITTLE TARDY WITH RETURN FLOW EVENTS. THUS WILL INTRODUCE A SLIGHT/SMALL CHANCE POP INTO THE FORECAST FOR THE PRE-DAWN HOURS WITH THE HIGHEST POPS CONFINED TO THE SOUTHERN PIEDMONT/WESTERN SANDHILLS. PARTIAL THICKNESS TECHNIQUE INDICATES A TREND TOWARD RAIN BY DAYBREAK SUNDAY AS A DECENT WARM NOSE DEVELOPS ALOFT. HOWEVER MODEL SOUNDINGS INDICATE A SHALLOW SUB FREEZING LAYER OVER MOST OF CENTRAL NC AT DAYBREAK SUNDAY. THUS...ANY LIGHT PRECIP THAT OCCURS PRIOR TO DAYBREAK WILL LIKELY BE IN THE FORM OF FREEZING RAIN/FREEZING DRIZZLE. MIN TEMPS WILL VARY FROM THE LOWER 20S IN THE NORTHERN COASTAL PLAIN WHERE CLOUD COVERAGE WILL INITIALLY BE THINNEST TO THE UPPER 20S ACROSS THE FAR SOUTH-SW. SUNDAY...PRECIPITATION EXPECTED TO BECOME MORE COMMON AFTER DAYBREAK ACROSS THE WEST AS ISENTROPIC UPGLIDE INCREASES. THIS PRECIP FALLING THROUGH THE DRY AIR MASS IN THE SUB CLOUD LAYER WILL LEAD TO EVAPORATIVE COOLING...LIKELY LOCKING IN THE SUB FREEZING SFC TEMPS OVER THE PIEDMONT FOR A GOOD PART OF THE MORNING. DUE TO TIMING UNCERTAINTY...WILL CAP POPS AT SOLID CHANCE ACROSS THE WESTERN COUNTIES TRENDING TO SLIGHT CHANCE IN THE COASTAL PLAIN. IF LATER MODEL RUNS ARE CONSISTENT...AN INCREASE IN POPS WILL BE WARRANTED AFTER DAYBREAK IN THE WEST. THE LOCKING IN OF THE SUB FREEZING TEMPS WILL CAUSE A PERIOD OF LIGHT FREEZING RAIN OVER MOST OF THE PIEDMONT SUNDAY MORNING. AT THIS TIME NOT EXPECTING ENOUGH ICE ACCRUAL TO CAUSE POWER OUTAGES BUT COULD SEE SOME SLICK ROADS...ESPECIALLY BRIDGES AND OVERPASSES. THIS WILL LIKELY WARRANT THE NEED OF AN ADVISORY IN LATER FORECAST ISSUANCE. IN THE MEANTIME...WILL HIGHLIGHT THREAT IN THE HWO. EXPECT PRECIPITATION CHANCES TO INCREASE TO LIKELY SUNDAY AFTERNOON AS UPGLIDE REACHES MAXIMUM. WILL EVENTUALLY SEE FREEZING RAIN TRANSITION TO A COLD RAIN OVER MOST OF THE PIEDMONT BY MID DAY...AND OVER THE NW PIEDMONT BY EARLY AFTERNOON. THE OVERCAST SKIES AND EXPECTED PRECIP WILL LIMIT TEMPS TO THE LOW-MID 30S OVER THE PIEDMONT COUNTIES TO THE UPPER 30S-LOWER 40S EAST OF HIGHWAY 1.-WSS && .SHORT TERM /MONDAY AND MONDAY NIGHT/...
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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.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/...
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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.
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&& .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... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...HARTFIELD/WSS SHORT TERM...KC LONG TERM...KC AVIATION...HARTFIELD

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