Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 011747 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1245 PM EST SUN MAR 1 2015 .SYNOPSIS...COLD HIGH PRESSURE WILL EXTEND INTO THE REGION THROUGH THIS EVENING... ALTHOUGH SOME LOW LEVEL MOISTURE WILL SPREAD INTO THE AREA FROM THE SOUTH RESULTING IN UNSETTLED WEATHER TODAY. A COLD FRONT WILL MOVE THROUGH THE REGION ON MONDAY. HIGH PRESSURE WILL BUILD INTO THE REGION LATE TUESDAY AND THEN MOVE OFFSHORE ON WEDNESDAY AS A STRONG COLD FRONT APPROACHES FROM THE WEST. && .NEAR TERM /THROUGH TODAY/... AS OF 955 AM SUNDAY... UPDATED: TEMPS ACROSS THE SOUTHERN CWA ARE INCHING INTO THE 32-33F RANGE CURRENTLY WITH WET BULBS ALSO RIGHT AT THE FREEZING MARK AND RISING... SO DESPITE ADDITIONAL BANDS OF LIGHT PRECIP TRACKING NE TOWARD THIS AREA FROM THE SW... BELIEVE WE CAN SAFELY ALLOW THE ADVISORY TO EXPIRE IN THIS AREA ON SCHEDULE. THE NCDOT HAS NOT REPORTED ANY SIGNIFICANT TRAFFIC PROBLEMS RECENTLY... HOWEVER IT MAY STILL TAKE AWHILE FOR RESIDUAL LIGHT ICE GLAZE TO MELT AND WASH OFF... SO WILL CONTINUE TO ADVISE EXTRA CAUTION. OTHERWISE... OCCASIONAL LIGHT PRECIP DRIVEN BY STRONG/DEEP MOIST UPGLIDE FROM 285K UP THROUGH AT LEAST 300K PERSISTS OVER CENTRAL NC. THIS UPGLIDE APPEARS TO BE MAXIMIZED NOW... WITH A SLOW DIMINISHING TREND THROUGH THE DAY. WILL MAINTAIN HIGH POPS... TRENDING DOWN AND OUT WEST TO EAST LATER THIS AFTERNOON THROUGH EARLY EVENING. THE OBSERVED 12Z GSO SOUNDING SHOWS WELL THE WARM NOSE ALOFT AND LOW LEVEL COLD AIR... INDICATING A CONTINUED THREAT OF FREEZING RAIN OVER THE REMAINDER OF CENTRAL NC WHERE TEMPS NOW SIT AT 28-31 WITH SUBFREEZING WET BULBS. MOST ACCRUAL HAS BEEN ON ELEVATED OBJECTS AND BRIDGES/OVERPASSES... WITH GROUND-ADJACENT ROAD SURFACES JUST WET IN MANY AREAS. WITH THE LOSS OF SUPPORT FROM THE PARENT HIGH TO PROVIDE A STEADY FEED OF LOW LEVEL COLD AIR... RESULTING IN A LIMITATION OF ICE ACCRUAL BY LATENT HEAT RELEASE... NOT ALL OF THE ADDITIONAL PRECIP WILL RESULT IN ICING... AND OUTSIDE OF THE FAR NRN SECTIONS WHERE TEMPS ARE COLDEST... MOST AREAS WILL SEE ONLY A TRACE AMOUNT OF ADDITIONAL ICING. WILL MAINTAIN THE CURRENT FORECAST SLOW TREND OF TEMPS RISING TO AT/ABOVE FREEZING FROM SOUTH/SE TOWARD THE NORTH/NW FOR THE REST OF THE DAY. NO CHANGES TO REMAINING ADVISORY AT THIS TIME. -GIH PREVIOUS DISCUSSION FROM 345 AM: TODAY...RIDGE EXTENDING FROM PARENT ARCTIC HIGH OVER THE NORTHERN MID ATLANTIC MAINTAIN A SUPPLY OF COLD DRY AIR INTO CENTRAL NC THIS MORNING. RETURN SLY FLOW ON THE BACKSIDE OF THE RETREATING 925-850MB HIGH OFF THE SE U.S. COAST ADVECTING OVER THE COLD STABLE AIR MASS AT THE SURFACE. THIS HAS RESULTED IN PATCHES OF LIGHT PRECIP TO BEAK OUT OVER OUR FAR SOUTHERN COUNTIES SHORTLY AFTER MIDNIGHT ...AND BEGINNING TO SPREAD ACROSS THE WESTERN PIEDMONT AT 08Z. WITH SFC DEWPOINTS SPREAD OF 12- 16 DEGREES ACROSS THE PIEDMONT AND NORTHERN COASTAL PLAIN...EVAPORATIVE COOLING SHOULD DROP SFC TEMPS TO BELOW FREEZING FOR SEVERAL HOURS ONCE THE PRECIPITATION SETS IN. OVER THE FAR SOUTH- SE...THIS TIME BELOW FREEZING SHOULD BE NO MORE THAN A COUPLE OF HOURS (IF THAT). APPEARS BEST THREAT FOR ICE ACCRUAL OF A TENTH OF AN INCH OR A LITTLE MORE WILL BE ACROSS THE FAR NORTHERN PIEDMONT/VA BORDER COUNTIES...AND INTO THE NORTHERN SECTIONS OF FORSYTH...GUILFORD AND ALAMANCE COUNTIES. ELSEWHERE...EXPECT ENOUGH ICE ACCRUAL ON EXPOSED SURFACE OBJECTS AS WELL AS BRIDGES AND OVERPASSES TO FORM A THIN GLAZE...ENOUGH TO MAKE TRAVEL HAZARDOUS IN SPOTS ACROSS THE PIEDMONT THIS MORNING. FAIRLY SUBSTANTIAL WARM NOSE ALOFT (APPROACHING 8 DEGREES C IN THE NW PIEDMONT BY LATE MORNING) MAY BE ENOUGH TO OVERCOME THE SUB FREEZING CONDITIONS AT THE SURFACE. THUS WHILE SFC TEMPS IN THE NORTHERN PIEDMONT MAY BE 31-32 DEGREES BY MID DAY...ADDITIONAL ICE ACCRUAL WILL BE SEVERELY LIMITED. PLAN TO MAINTAIN ADVISORY ACROSS THE FAR NORTH-NW UNTIL 4 PM BUT WILL ASSESS TEMP RESPONSE LATER THIS MORNING WITH A POSSIBILITY OF ENDING THE ADVISORY A FEW HOURS EARLIER. ELSEWHERE CURRENT ADVISORY END TIMES APPEAR ON TARGET. MAX TEMPS THIS AFTERNOON DEPENDENT UPON ON HOW EXTENSIVE THE PRECIP BECOMES AND WHEN IT TAPERS OFF. COUNTING ON PRECIP LINGERING THROUGH A GOOD PART OF THE AFTERNOON ACROSS THE EAST SO HAVE LOWERED TEMPS THERE A FEW DEGREES FROM PREVIOUS FORECAST. CONVERSELY...HAVE ADJUSTED MAX TEMPS UP A DEGREE OR TWO ACROSS THE WEST-SW WHERE PRECIP MAY TAPER OFF BY EARLY-MID AFTERNOON. && .SHORT TERM /TONIGHT AND MONDAY/... AS OF 345 AM SUNDAY... TONIGHT...EXTENSIVE LOW CLOUDS AND AREAS OF FOG EXPECTED WHILE A SLY SFC WIND WILL BEGIN TO STIR AS A COLD FRONT APPROACHES FROM THE WEST- NW. THESE CONDITIONS SHOULD CAUSE TEMPS TO HOLD STEADY OVERNIGHT. MIN TEMPS IN THE MID-UPPER 30S. MONDAY...SFC COLD FRONT SHOULD CROSS THE AREA IN THE MORNING. APPEARS MOISTURE DEPTH FAIRLY LIMITED TO GENERATE ANY PRECIP ACROSS THE NW BUT MAY BE ENOUGH ACROSS THE FAR SOUTH-SE TO DEVELOP A FEW PATCHES OF LIGHT RAIN. NWLY FLOW BEHIND THE FRONT WILL AID TO ADVECT A DRIER AIR MASS IN THE REGION. THIS WILL SLOWLY ERODE CLOUD COVERAGE FROM THE NW DURING THE AFTERNOON. SHOULD SEE TEMPS REBOUND INTO THE LOW AND MID 50S WITH PARTIAL SUNSHINE OVER MOST OF THE PIEDMONT BY AFTERNOON (LESS SO ACROSS THE FAR SOUTH-SE). FAVORED COOLER NAM MOS GUIDANCE VERSUS THE WARMER MOS GUIDANCE. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... AS OF 320 PM SUNDAY... MONDAY NIGHT AND TUESDAY: SURFACE HIGH PRESSURE LOCATED JUST TO THE NORTH OF CENTRAL NC AND AND MID LEVEL RIDGING EXTENDING INTO THE AREA FROM THE SOUTH WILL BOTH QUICKLY SHIFT EASTWARD ON MONDAY NIGHT INTO TUESDAY. HOWEVER... THE LINGERING COLD DRY SURFACE AIR DEPOSITED BY THE SURFACE HIGH WILL AGAIN SET THE STAGE FOR AN INSITU CAD EVENT ON TUESDAY INTO TUESDAY NIGHT... POSSIBLY LINGERING INTO WEDNESDAY MORNING ACROSS THE FAR NORTHWEST PIEDMONT. WARM MOIST AIR WILL INCREASING IN SOUTHERLY TO SOUTHWESTERLY FLOW ALOFT. GIVEN THIS AND THE LINGERING COLD SURFACE AIRMASS... WE SHOULD SEE SOME ISENTROPICALLY DRIVEN PRECIP DEVELOP TUESDAY MORNING INTO THE AFTERNOON. TUESDAY MORNING LOW TEMPS ARE EXPECTED TO BE AROUND 30 NORTH TO NEAR 40 SOUTH. MODELS CONTINUE TO BRING THE LIGHT PRECIP IN AFTER SURFACE TEMPS AND DEWPOINTS INCREASE ENOUGH TO AVOID AND NUISANCE FREEZING RAIN. HOWEVER... HIGH TEMPS WILL BE WELL BELOW NORMAL AND GREATLY AFFECTED BY THE CAD AIRMASS. MAV STATISTICAL GUIDANCE APPEARS TO BE WAY TOO WARM FOR TUESDAY... WITH THE RAW GFS TEMPS CLOSER TO MET GUIDANCE VALUES. FOR NOW WILL LOWER TEMPS FURTHER... AND THIS MAY NOT EVEN BE FAR ENOUGH. WILL WO WITH HIGH TEMPS RANGING FROM THE UPPER 30S NORTH TO NEAR 50 IN THE FAR SOUTHEAST. TUESDAY NIGHT THROUGH THURSDAY NIGHT: ANOTHER STRONG ARCTIC COLD FRONT WILL APPROACH THE REGION ON TUESDAY NIGHT... BEFORE SLOWLY MOVING ACROSS THE AREA WEDNESDAY INTO THURSDAY MORNING. THE FRONT IS EXPECTED TO BECOME PARALLE WITH THE MID LEVEL FLOW AS THE MID/UPPER LEVEL TROUGH BECOMES MORE OF A FULL LATITUDE TROUGH... WHICH APPEARS TO PHASE SOME THE THE SOUTHERN STREAM ENERGY WITH THE NORTHERN STREAM... RESULTING IN A DEEP FETCH OF SOUTHWESTERLY MID LEVEL FLOW... ALONG WITH SEVERAL SURFACE LOWS TRACKING ALONG THE FRONT FROM TIME TO TIME. MOST OF THE SHOWERS WILL BE ALONG AND BEHIND THE FRONT... MAINLY FROM WEDNESDAY MID-MORNING INTO THE AFTERNOON UNTIL LATE THURSDAY (WITH A GOOD CHANCE OF PRECIP... POSSIBLY SOME HEAVY AMOUNTS OF RAIN). IN ADDITION... MODELS HAVE TRENDED FASTER WITH SURGING THE STRONG/DEEP COLD LOW LEVEL AIRMASS INTO THE REGION. IF THIS WERE TO OCCUR... WE COULD POSSIBLE SEE SOME WINTRY P-TYPES ON THURSDAY. HOWEVER... GIVEN WE ARE STILL TALKING ABOUT DAY 5 IN THE FORECAST AND WE ARE NOW IN THE MONTH OF MARCH... WILL WAIT TO ADD ANY NON-LIQUID P-TYPE TO THE FORECAST. DRY WEATHER IS EXPECTED TO RETURN FOR AT LEAST FRIDAY. HOWEVER... THE SYNOPTIC PATTERN MAY REMAIN CONDUCIVE FOR WAVES OF LOW PRESSURE TO DEVELOP AND TRACK ALONG THE FRONT... WHICH IS EXPECTED TO BE LOCATED OFF THE CAROLINA COAST LATE WEEK INTO THE WEEKEND. THUS... WE COULD CONCEIVABLY SEE SOME PRECIP IF ONE SUCH SYSTEM DEVELOPS NEXT WEEKEND. TEMPS DURING THE MEDIUM RANGE WILL INCLUDE SOME DECENT SWINGS... WITH HIGHS TEMPS WEDNESDAY IN THE 60S AND 70S... THURSDAY 40S AND 50S (MAYBE COLDER)... WITH FRIDAY BACK IN THE 40S (WITH MAYBE SOME 30S EVEN). WE WILL SEE SOME MODERATING BY SATURDAY... GENERALLY BACK INTO THE 50S... GIVEN WE REAMIN DRY. LOWS WILL FOLLOW A SIMILAR PATTERN. AS MENTIONED ABOVE... ALL PRECIP AS OF NOW APPEARS TO BE IN THE FORM OF LIQUID FOR THE MEDIUM RANGE... OUTSIDE OF *MAYBE* A BRIEF PERIOD AS THE PRECIP ENDS ON THURSDAY. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... AS OF 1245 PM SUNDAY... PRIMARY AVIATION CONCERNS NEXT 24 HRS: CONTINUED IFR/LIFR CIGS AND MVFR/IFR VSBYS THROUGH TONIGHT... AND BORDERLINE LOW LEVEL WIND SHEAR THIS EVENING/TONIGHT. WIDESPREAD IFR/LIFR CONDITIONS PERSIST OVER CENTRAL NC TAF SITES THIS AFTERNOON... ALONG WITH PATCHES OF RAIN (FAY/RDU) OR FREEZING RAIN (RWI/INT/GSO). THIS FREEZING RAIN AT RWI/INT/GSO WILL TREND TO JUST RAIN THIS AFTERNOON... FIRST AT RWI THEN AT GSO AND INT. ALL LOCATIONS SHOULD BE JUST RAIN BEFORE 21Z. PERIODS OF RAIN WILL TAPER OFF AT INT/GSO BY 22Z THIS AFTERNOON... AT RDU BY 00Z THIS EVENING... AND AT FAY/RWI BY 04Z LATE THIS EVENING. WITH FAIRLY LIGHT SURFACE WINDS OVERNIGHT AND A MOIST GROUND... CONFIDENCE IS HIGH THAT IFR/LIFR CONDITIONS WILL HOLD THROUGH AT LEAST 12Z MON AT ALL TAF SITES. AS A WEAK FRONT DROPS SOUTHEAST INTO THE AREA MONDAY... CAUSING SURFACE WINDS TO SHIFT FROM LIGHT SW TO BE FROM THE NW... THESE LOW CLOUDS/FOG WILL SCOUR OUT GRADUALLY TO VFR BY THE 16Z-18Z MONDAY TIME FRAME AT INT/GSO... WITH LOWER CONFIDENCE IN THIS OCCURRING PRIOR TO 18Z AT RDU/RWI/FAY. LOW LEVEL WIND SHEAR THREAT REMAINS MARGINAL AND FOCUSED AFTER MIDNIGHT TONIGHT AT FAY/RDU/RWI... AS 1000-1500 FT AGL WINDS BECOME WESTERLY AT 25-30 KTS. LOOKING BEYOND 18Z MON... VFR CONDITIONS SHOULD PERSIST FROM EARLY TO MID AFTERNOON MONDAY THROUGH MONDAY NIGHT... AS THE SURFACE FRONT SETTLES ALONG THE SRN NC BORDER WHILE HIGH PRESSURE NOSES IN FROM THE NORTHWEST. HOWEVER... A DISTURBANCE ALOFT RIDING ALONG THE SURFACE FRONT WILL BRING A THREAT OF MVFR/IFR CONDITIONS STARTING LATE MONDAY NIGHT (INT/GSO) OR TUE AFTERNOON (RDU/RWI/FAY)... ALONG WITH A LLWS RISK. THESE SUB-VFR CONDITIONS SHOULD GIVE WAY TO VFR CONDITIONS AT FAY THEN AT RWI/RDU WED AS A WARM FRONT MOVES NORTHWEST THROUGH THE AREA WITH STRENGTHENING SW WINDS... BUT SUB- VFR CONDITIONS MAY HOLD IN LONGER AT INT/GSO. THIS WARM FRONT WILL DROP BACK DOWN SOUTHEAST THROUGH THE AREA AS A COLD FRONT LATE WED OR WED NIGHT... TURNING SURFACE WINDS BACK AROUND TO NORTH/NORTHEASTERLY FOR THU WITH WIDESPREAD RAIN AND SUB-VFR CONDITIONS. VFR CONDITIONS SHOULD RETURN TO NORTHERN SECTIONS (RDU/RWI/INT/GSO) BY THURSDAY NIGHT/FRIDAY. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY UNTIL 4 PM EST THIS EVENING FOR NCZ007-021>023-038-039. && $$ SYNOPSIS...RAH NEAR TERM...HARTFIELD/WSS SHORT TERM...WSS LONG TERM...BSD AVIATION...HARTFIELD

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