Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 050903 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 403 AM EST THU MAR 5 2015 .SYNOPSIS...A STRONG COLD FRONT WILL PUSH SOUTHWARD THROUGH THE CAROLINAS TODAY. IN THE WAKE OF THE FRONT...ARCTIC HIGH PRESSURE WILL BUILD INTO THE AREA ON FRIDAY AND SETTLE OVER THE REGION FRIDAY NIGHT. && .NEAR TERM /THROUGH TONIGHT/... AS OF 320 AM THURSDAY... A WINTER WEATHER ADVISORY WILL BE ISSUED FOR A CHANGEOVER TO FREEZING RAIN AND SLEET ACROSS THE TRIAD TO TRIANGLE TO GOLDSBORO NORTHWARD TO THE VA BORDER... FROM 300 PM THROUGH MIDNIGHT TODAY. THE MAIN AREA OF CONCERN IS FROM THE VA/NC BORDER SOUTHWARD TO AROUND THE HIGHWAY 64 CORRIDOR WITH THE COUNTIES OF DAVIDSON...RANDOLPH...CHATHAM...WAKE...JOHNSTON... AND WAYNE ALONG THE SOUTH END OF THE ADVISORY. TIMING WOULD BE 300 PM THROUGH MIDNIGHT... WITH THE MOST ICING EXPECTED AFTER 500 PM. THE CURRENT WARM GROUND... INCREASING SUN ANGLE... TIME OF DAY... AND TEMPERATURES EXPECTED BETWEEN 300 PM AND 500 PM WOULD SUGGEST MOST IF NOT ALL ICING WOULD BE CONFINED TO ELEVATED SURFACES BEFORE AROUND 500 PM OR SO. THE NORTHERN PIEDMONT... THE NORTH EDGES OF THE TRIAD AND TRIANGLE MAY SEE SOME ICING BECOMING A PROBLEM ON BRIDGES AND OVERPASSES WELL BEFORE 500 PM IF TEMPERATURES FALL TO OR BELOW 30... WHICH IS POSSIBLE. THE LATEST DATA AGAIN CONFIRMS THE COMPLEXITY OF THIS POTENTIAL ICING EVENT. WE START THE DAY WITH TEMPERATURES AND DEW POINTS AT 50- 60 DEGREES IN THE PROPOSED ADVISORY AREA... AFTER A DAY IN WHICH HIGHS REACHED INTO THE MID 70S. WE ARE AWAITING THE INITIAL COLD FRONT (WITH COOLING INTO THE 40S NOTED OVER VA) TO ROLL SOUTH THROUGH THE REGION THIS MORNING... FOLLOWED BY THE DELAYED BUT MAIN SURGE OF MUCH COLDER ARCTIC AIR DURING THE AFTERNOON. THIS OCCURS AS A WAVE OF LOW PRESSURE IS EXPECTED TO TRACK ALONG THE INITIAL BOUNDARY (THAT WILL STALL TO OUR SOUTH THIS AFTERNOON). THIS WAVE IS DEPICTED WELL ON WATER VAPOR IMAGERY AND THE HI-RES MODELS INDICATE THIS FEATURE WILL MOVE ACROSS THE AREA FROM WEST TO EAST THIS AFTERNOON AND EVENING. QPF ON THE 0.50 TO NEARLY 0.75 SHOULD RESULT SUPPORTED BY LARGE SCALE LIFT ON THE COLD SIDE OF THE BOUNDARY AS THE WAVE TRAVERSES THE REGION. OTHER MAJOR ISSUES TO CONSIDER INCLUDE BUT ARE NOT LIMITED TO: THE FORECAST WARM NOSE ALOFT IS VERY WARM (6-9 DEGREES/C) WITH A COLD NOSE THAT LOWERS TO BETWEEN -3 TO -5 DEGREES/C DURING THE TIME WHEN THERE IS SIGNIFICANT PRECIPITATION EXPECTED (20Z-03Z) IN THE PROPOSED ADVISORY AREA. THE NAM (TAKEN LITERALLY) IS THE WARMEST BY FAR AND KEEPS ALL AREAS ALONG AND SOUTH OF ASHEBORO TO RALEIGH 33 OR 34 THROUGH 03Z/TONIGHT (END OF THE EVENT)... STRONGLY SUGGESTING ALL RAIN IN THESE AREAS. ON THE COLDEST SIDE... THE EC AND GFS INDICATE ENOUGH COOLING OF THE ENTIRE COLUMN... MID AND NEAR SURFACE LAYER TO GIVE A CHANGE TO SNOW AT RALEIGH WITH UP TO AN INCH AT 00Z... AND 2- 3 INCHES NORTH. WE WILL NOT GO WITH EITHER EXTREME SOLUTION... BUT NOTE THEM NONETHELESS. ONE APPROACH THAT HOPEFULLY WILL WORK OUT BEST IN THIS COMPLEX SITUATION WILL BE TO BLEND THE FORECAST MODELS WITH WHAT WE KNOW... DELAYED COLD AIR DUE TO THE PARENT HIGH NOT FAVORABLE EARLY ON... THE WARM NOSE TO NEARLY 10 DEG/C EARLY ON... AND THE INCREASINGLY COLD... COLD NOSE CENTERED AROUND 925 MB AS THE SUN SETS... AND A WINDOW OF OPPORTUNITY THAT IS NARROWING WITH TIME TO BETWEEN 21Z AND 03Z FOR THE CHANGEOVER. THE ABOVE WILL BE COMBINED WITH THE FORECAST P-TYPE NOMOGRAMS OFF THE COLDER EC/GFS WHICH SUPPORT A MIX WITH AND CHANGEOVER TO FREEZING RAIN AND SLEET... WITH EMPHASIS ON THE PLACEMENT OF THE WEB BULB ZERO LINE. THE WET BULB ZERO IS FORECAST TO REACH THE SOUTH END OF THE ADVISORY AREA AROUND 23Z-01Z OR WHEN THE MAIN SHIELD OF PRECIPITATION IS FORECAST TO GRADUALLY END. SINCE THE WARM NOSE IS EXPECTED TO BE VERY PROMINENT... SNOW IS NOT EXPECTED TO BE A MAIN ISSUE. AND... IT IS DIFFICULT TO DETERMINE THE AMOUNT OF SLEET THAT WILL REACH THE GROUND AS WELL GIVEN THE EXTENSIVE EXPECTED WARM NOSE. RAIN GRADUALLY MIXING WITH FREEZING RAIN IS EXPECTED THIS AFTERNOON WITH THIS GRADUAL MIXING EXPECTED TO BEGIN IN THE ROXBORO TO WARRENTON AREAS AROUND MID AFTERNOON... REACHING THE SOUTH END OF THE ADVISORY AREA IN THE TRIAD AND TRIANGLE BETWEEN 500 AND 700 PM AS THE TEMPERATURES EACH DOWN TO 32 OR BELOW. FREEZING RAIN THROUGH THE DAYLIGHT HOURS SHOULD BE CONFINED TO THE ELEVATED ABOVE GROUND AND ROAD SURFACES... UNTIL THE SURFACE TEMPERATURES FALL TO 30 OR BELOW. THIS MOST LIKELY WOULD OCCUR IN THE AREAS FROM ROXBORO TO WARRENTON JUST BEFORE SUNSET... AND IN THE TRIANGLE AND TRIAD AROUND SUNSET OR JUST BEYOND. DUE TO POTENTIAL MODEL ERRORS IN THE FORECAST WARM NOSE... THERE IS ALSO THE POTENTIAL FOR MORE SLEET THAN CURRENTLY ANTICIPATED. IN ADDITION... AS THE ENTIRE COLUMN COOLS FROM SUNSET TO MID EVENING... THIS WILL BE THE WINDOW OF OPPORTUNITY FOR SLEET TO BECOME PREDOMINATE IN THE ADVISORY AREA (AS THE MAIN PRECIPITATION BEGINS TO TAPER OFF). BOTTOM LINE... RAIN IS EXPECTED THIS MORNING. THEN THE GRADUAL MIX WITH FREEZING RAIN FROM THE NORTH MAINLY FROM MID AFTERNOON ONWARD AS THE SURFACE TEMPERATURES FALL TO AND THEN BELOW 32. SO THROUGH THE DAYLIGHT HOURS... THIS IS EXPECTED TO BE A RATHER MINOR WINTER WEATHER EVENT WITH MOSTLY RAIN... BUT ICING MAY BEGIN ABRUPTLY AS TEMPERATURES FALL AND NIGHTFALL SETS IN. IF MORE SLEET BEGINS TO FALL EARLIER THAN ANTICIPATED - THEN CONDITIONS WILL WORSEN EVEN BEFORE NIGHTFALL. WE WILL TRY TO ERROR ON THE SIDE OF CAUTION AND PLACE THE ADVISORY IN EFFECT BEGINNING AT 300 PM. THIS MAY ACTUALLY AID IN GETTING MOST PEOPLE OFF THE ROADS BEFORE THE TRADITIONAL RUSH HOUR. && .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... AS OF 320 AM THURSDAY... AS THE PRECIPITATION ENDS THIS EVENING...THE NEXT PROBLEM WILL BE THE BLACK ICE AND EVEN FLASH FREEZE AS IT CLEARS TONIGHT...AND TEMPS PLUMMET INTO THE 15-20 RANGE. MUCH MORE ON THIS LATER TODAY. FOR FRIDAY...BLUSTERY AND COLD...MOSTLY SUNNY. HIGHS IN THE 30S TO LOWER 40S SOUTH. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... AS OF 345 AM THURSDAY... SAT-SUN NIGHT: EXPECT MOSTLY CLEAR SKIES AND MODERATING TEMPS... (THOUGH STILL BELOW NORMAL) OVER THE WEEKEND WITH NORTHERN STREAM SHORTWAVE ENERGY CONFINED WELL NORTH TO THE GREAT LAKES/NEW ENGLAND AND SOUTHERN STREAM SHORTWAVE ENERGY CONFINED TO THE DESERT SW/WESTERN GOMEX. EXPECT HIGHS IN THE 50S SAT/SUN AND LOWS RANGING FROM THE LOWER 30S SAT NIGHT TO MID/UPPER 30S SUN NIGHT WHEN MID/UPPER LEVEL CLOUD COVER SHOULD INCREASE ACROSS THE REGION AS SOUTHERN STREAM SHORTWAVE ENERGY...ATTENDANT WAA/FGEN...AND RESULTING PRECIPITATION PROGRESS EASTWARD ALONG THE GULF COAST. MON-TUE: GIVEN A SPLIT FLOW SYNOPTIC PATTERN...CONFIDENCE IN FORECAST DETAILS DECREASES BY EARLY NEXT WEEK...PARTICULARLY WITH REGARD TO THE EVOLUTION OF SOUTHERN STREAM SHORTWAVE ENERGY PROGRESSING EAST ALONG THE GULF COAST. GIVEN THAT THE LATEST GUIDANCE IS IN CLOSER AGREEMENT ON INCREASED CLOUD COVER AND PRECIP CHANCES MON/MON NIGH...WILL INCREASE POPS AND DECREASE TEMPS IN THAT TIME FRAME. -VINCENT && .AVIATION /09Z THURSDAY THROUGH MONDAY/... AS OF 1237 AM THURSDAY... MAINLY VFR CONDITIONS...IN CONTINUED SOUTHWESTERLY FLOW AHEAD OF AN APPROACHING COLD FRONT...WILL BECOME MVFR-IFR FROM NORTH TO SOUTH WITH THE PASSAGE OF THE COLD FRONT BETWEEN 10-14Z AT NORTHERN TAF SITES...TO BETWEEN 15-19Z AT KFAY. TWO EXCEPTIONS TO THE OTHERWISE PRECEDING VFR CONDITIONS WILL BE A TEMPORARY MVFR CEILING AT KINT/KGSO FOR A BRIEF TIME THIS EVENING...AND A MEDIUM CHANCE OF IFR VISIBILITY RESTRICTIONS AND/OR CEILINGS AT KFAY OVERNIGHT...WHERE THE COMBINATION OF RADIATIONAL COOLING DURING TIMES OF LIGHTER TO OCCASIONALLY NEAR CALM WIND...WITH A RELATIVE MAXIMUM IN SURFACE DEWPOINTS OVER SE NC...WILL SUPPORT THE DEVELOPMENT OF AREAS OF FOG/LOW STRATUS. ONCE SURFACE WINDS LESSEN AND QUIT GUSTING AREA-WIDE WITHIN THE NEXT COUPLE OF HOURS IN ASSOCIATION WITH THE DEVELOPMENT OF A NOCTURNAL INVERSION...LOW LEVEL WIND SHEAR WILL ALSO BECOME PROBABLE OWING TO THE DEVELOPMENT OF A 40-50 KT LOW LEVEL JET JUST ABOVE THE SURFACE. THE PASSAGE OF THE AFOREMENTIONED SURFACE COLD FRONT WILL END THE THREAT OF LOW LEVEL WIND SHEAR...AND INSTEAD RESULT IN A STRONG POST- FRONTAL NORTHEASTERLY WIND BETWEEN 10-15 KTS...WITH GUSTS AROUND 20 KTS. WIDESPREAD RAIN AND ASSOCIATED MVFR-IFR CONDITIONS TRAILING THE PASSING COLD FRONT WILL CONTINUE THROUGHOUT THU...BEFORE RAIN CHANGES TO FREEZING RAIN AND SLEET FROM NORTH TO SOUTH THU AFTERNOON AND EVENING. OUTLOOK: AFTER LINGERING LIGHT SLEET AND MVFR CONDITIONS KRDU/KFAY/KRWI THU EVENING...PERSISTING LONGEST INTO THU NIGHT AT KFAY...VFR CONDITION ARE ANTICIPATED FOR THE NEXT SEVERAL DAYS. && .RAH WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY FROM 3 PM THIS AFTERNOON TO MIDNIGHT EST TONIGHT FOR NCZ007>011-021>028-038>043-078. && $$ SYNOPSIS...VINCENT NEAR TERM...BADGETT SHORT TERM...BADGETT LONG TERM...VINCENT AVIATION...BADGETT

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