Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 260135 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 830 PM EST WED FEB 25 2015 .SYNOPSIS...
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LOW PRESSURE WILL TRACK NORTHEAST FROM THE FLORIDA PANHANDLE TO OFF THE NORTH CAROLINA COAST TONIGHT AND THURSDAY MORNING. COLD CANADIAN HIGH PRESSURE WILL FOLLOW THE STORM FRIDAY INTO SATURDAY.
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&& .NEAR TERM /THROUGH THURSDAY/...
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AS OF 830 PM WEDNESDAY... ...HEAVY SNOW DEVELOPING INTO THE TRIAD AND TRIANGLE AREAS... ...CONDITIONS WILL DETERIORATE RAPIDLY IN THE NEXT TWO HOURS... PRECIPITATION WAS RAPIDLY DEVELOPING NORTHWARD ACROSS CENTRAL NORTH CAROLINA NEAR MID EVENING. THE 00Z/GSO SOUNDING STRONGLY SUPPORTED THE CURRENT ONGOING FORECAST OF A MAJOR IF NOT CRIPPLING SNOW STORM OVER MUCH OF THE PIEDMONT INTO THE NORTHERN COASTAL PLAIN. RAIN AND SNOW WERE MIXED AT THE ONSET OF THE PRECIPITATION ALONG THE NC/SC BORDER COUNTIES WHERE TEMPERATURES WERE IN THE MID 30S. THE PRECIPITATION WAS BEGINNING AS SNOW ALONG AND NORTH OF A LINE EXTENDING FROM KANNAPOLIS AND BADIN TO SILER CITY TO RALEIGH IN THE COLDER AIR. UPSTREAM SNOW WAS FALLING AT KGSP WITH THE RAIN/SNOW TRANSITION SOUTH OF KGSP. THE GSO SOUNDING DEPICTED PLENTY OF MID LEVEL DRY AIR THAT WILL MOISTEN AND COOL SHORTLY SUPPORTING THE RAPID TRANSITION TO ALL SNOW THROUGHOUT MUCH OF THE REGION ESPECIALLY ALONG AND NORTHWEST OF A FAY TO GSB LINE. BASED ON THE OBSERVATIONS IN NORTHERN MISSISSIPPI... NORTHERN ALABAMA INTO SOUTHWESTERN NC... AND THE CURRENT MODEL PROJECTIONS... SNOWFALL RATES OF 1 TO 2 INCHES PER HOUR APPEAR LIKELY IN THE PIEDMONT SHORTLY. WE WILL TRY TO PIN DOWN THE MAIN TRANSITION ZONE (LIKELY TO BE IN THE VICINITY OF NEAR FAYETTEVILLE TO GOLDSBORO OR POSSIBLY SOUTHEAST OF THAT REGION AT LEAST EARLY ON). CURRENT FORECAST APPEARS TO HANDLE THIS SITUATION WELL AND UNLESS ADDITIONAL DATA SUPPORTS SOMETHING DIFFERENT... WE WILL MAINTAIN THE LOWER SNOW AMOUNTS IN THE SE. THE SURFACE TEMPERATURES WILL ALSO COOL RAPIDLY WITH THE ONSET OF PRECIPITATION... WITH MUCH OF THE PIEDMONT EXPECTED TO BE 28-31 DURING THE HEIGHT OF THE EVENT OVER THE PIEDMONT... AND NEAR 32 IN THE SE. PREVIOUS DISCUSSION ISSUED AS OF 340 PM WEDNESDAY... ...MAJOR WINTER STORM SET TO STRIKE CENTRAL NC WITH 6 INCHES OR MORE WET SNOW LIKELY TO FALL ACROSS MUCH OF CENTRAL NC INCLUDING THE RALEIGH AND GREENSBORO METRO AREAS... ...WINTER STORM WARNING CONTINUES FOR TONIGHT AND THROUGH MIDDAY THURSDAY FOR ALL THE PIEDMONT...NORTHERN/CENTRAL COASTAL PLAIN AND SANDHILLS AND NOW INCLUDING WAYNE COUNTY... ...WINTER WEATHER ADVISORY HAS BEEN ISSUED FOR TONIGHT AND THURSDAY FOR THE SOUTHERN COASTAL PLAIN... MODEL GUIDANCE HAS TRENDED SLIGHTLY MORE NORTHERLY WITH THE TRACK OF THE DEVELOPING STORM SYSTEM AND IN FACT THE LATEST SURFACE ANALYSIS SHOWS THE SURFACE CENTER SLIGHTLY NORTH OF THE FORECAST POSITION. THIS CONTINUED TREND RESULTS IN A SLIGHTLY WARMER BOUNDARY LAYER AND HEAVIER PRECIPITATION AMOUNTS. NWP GUIDANCE IS IN RATHER GOOD AGREEMENT WITH THE MAIN FEATURES RELEVANT TO THIS FORECAST HOWEVER...SUCH A HIGH AMPLITUDE EVENT CAN BE SIGNIFICANTLY IMPACTED BY THE MOST SUBLE VARIABLES. SO WHILE CONFIDENCE IS ABOVE AVERAGE REGARDING THE OVERALL SCENARIO SEVERAL FACTORS STILL MAKE US UNEASY REGARDING OVERALL ACCUMULATION TOTALS. WITH THE LACK OF A WELL DEFINED SOURCE OF COLD AIR AND ANTECDENT TEMPERATURES TODAY WARMING INTO THE LOWER TO MID 40S...THE PRECIPITATION WILL START AS RAIN IN MOST LOCATIONS...EVEN NEAR THE VA BORDER. BUT GIVEN IMPRESSIVE PRECIPITATION RATES...DIABATIC COOLING FROM MELTING SHOULD COOL SURFACE TEMPERATURES TO AROUND FREEZING AND ALLOW THE PRECIPITATION TO CHANGE OVER TO SNOW AND BEGIN ACCUMULATING. THIS SCENARIO INHERENTLY CONTAINS SOME RISK FOR A FORECAST BUST. IN ADDITION...THE HEAVY RATES AND SHORT DURATION OF EVENT MEAN THAT EVERY HOUR COUNTS AND THAT A SLIGHT DELAY IN THE COLD AIR OR A MIXTURE WILL HAVE A SIGNIFICANT IMPACT ON STORM TOTALS. WITH A FEW OF THE MAJOR CAVEATS NOTED...CONFIDENCE IS INCREASING IN A MAJOR WINTER STORM WITH SIGNIFICANT WET SNOW OF 6 INCHES OR MORE LIKELY TO FALL ACROSS MUCH OF CENTRAL NC INCLUDING THE RALEIGH AND GREENSBORO METRO AREAS. THE GREATEST SNOW TOTALS ARE LIKELY TO FALL IN THE REGION FROM RALEIGH NORTHEAST TO THE ROANOKE RAPIDS AREAS WHERE LOCALIZED AMOUNTS APPROACHING 10 INCHES ARE POSSIBLE. VERY IMPRESSIVE SNOWFALL RATES ON THE ORDER OF 1 TO 2 INCHES PER HOUR WILL ALLOW SNOW TOTOALS TO EXPLODE AFTER MIDNIGHT. THE FORECAST IS ALSO DIFFICULT ACROSS THE SOUTHERN COASTAL PLAIN...SOUTHERN SANDHILLS AND EVEN NEAR THE SC BORDER WHERE A WARM NOSE IS EXPECTED TO BE SUFFICIENT TO CHANGE THE SNOW TO A MIXTURE OF SNOW...SLEET AN FREEZING RAIN AROUND OR JUST AFTER MIDNIGHT. SOUTH OF CLINTON...FAYETTEVILLE AND RAEFORD...SURFACE TEMPERATURES WONT FALL BELOW FREEZING AND ANY SNOW ACCUMULATION WILL FALL IN A SHORT WINDOW DURING THE LATE EVENING TO JUST AFTER MIDNIGHT WITH JUST A SLOPPY WET SNOW OR RAIN EXPECTED AFTER 200 AM OR. DRY SLOTTING WILL END THE SIGNIFICANT PRECIPITATION ACROSS THE SOUTHERN PORTION OF THE CWA AFTER 3 TO 5 AM WITH THE MAIN AREA OF PRECIPITATION CLOSER TO THE VA BORDER ENDING FROM WEST TO EAST BETWEEN 5 AND 7AM. ALL OF THE SIGNIFICANT PRECIPITATION WILL END BY OR JUST AFTER DAYBREAK ON THURSDAY. TEMPERATURES AT THAT POINT WILL HAVE REACHED THEIR COLDEST AND HAVE FALLEN TO THE 28 TO 32 RANGE. SPOTTY FREEZING RAIN AND FREEZING DRIZZLE DRIVEN BY PERSISTENT SHALLOW LOW LEVEL MOISTURE WILL CHANGE TO LIGHT FREEZING RAIN OR MIST BY AFTERNOON. HIGHS WILL STRUGGLE TO CLIMB TO THE 33 TO 36 RANGE BY LATE AFTERNOON.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/... AS OF 320 PM WEDNESDAY... A MID-LEVEL SHORTWAVE IS FORECAST BY BOTH THE GFS AND THE NAM TO MOVE THROUGH CENTRAL NORTH CAROLINA THURSDAY EVENING...WITH ANOTHER WEAK WAVE ON FRIDAY. LOW-LEVEL MOISTURE REMAINS IN PLACE OVERALL... HIGHLIGHTED BY MODEST VALUES OF MEAN RELATIVE HUMIDITY IN THE 1000- 500MB LAYER AS SURFACE HIGH PRESSURE GRADUALLY BUILDS IN. 850MB THETA-E IS GENERALLY LOW DURING THE PERIOD WITH PRECIPITABLE WATER VALUES AT OR JUST BELOW NORMAL FOR LATE FEBRUARY...HOWEVER...VIEWING THE NAM AND GFS BUFR SOUNDINGS...AGAIN...LOW-LEVEL MOISTURE REMAINS WITH SOME MOISTURE SATURATION AT TIMES TO AT OR JUST COLDER THAN - 10C. THE GFS IN PARTICULAR PROVIDES FOR MARGINAL MEASURABLE PRECIPITATION IN THE FAR NORTHWEST PIEDMONT OVERNIGHT THURSDAY... AND THEN MAINLY ALONG AND WEST OF U.S. 1 FRIDAY SHIFTING BACK WEST AGAIN FRIDAY NIGHT INTO EARLY SATURDAY. IT IS DURING THESE PERIODS THAT BUFR SOUNDINGS FORECAST MOISTURE TO A LEVEL IN ATMOSPHERE COLDER THAN -10C. LIFT IS MARGINAL DURING THIS SHORT-TERM PERIOD...LIKELY BEST ON FRIDAY WHEN BUFR SOUNDINGS SHOW LOW-LEVEL LAPSE RATES STEEPENING AND THE COMBINATION OF 850MB CONVERGENCE AND UPPER-LEVEL DIVERGENCE IS BEST MAINLY OVER THE FAR NORTHWEST PIEDMONT OVERNIGHT THURSDAY AND ALONG AND WEST OF U.S. 1 FRIDAY. GIVEN THE LOW-LEVEL MOISTURE AND MODEST SUPPORT ALOFT WITH THE MID-LEVEL SHORTWAVES...IN ADDITION TO THE GFS VERY LIGHT QPF AND SOME NOTICE OF LIGHT PRECIPITATION OUTPUT ON THE NCEP HIGH RES NMMB...HAVE OPTED TO INCLUDE A SLIGHT CHANCE OF FLURRIES MAINLY IN THE FAR NORTHWEST PIEDMONT THURSDAY NIGHT...WITH A SLIGHT CHANCE OF SNOW SHOWERS THERE FRIDAY WHERE BUFR SOUNDINGS ESPECIALLY ON THE GFS SHOW THE LAPSE RATES STEEPENING. A SLIGHT CHANCE OF FLURRIES ELSEWHERE FRIDAY TO NEAR U.S. 1 OR SO...THEN A SLIGHT CHANCE OF FLURRIES FRIDAY NIGHT ALONG AND NORTH OF A LINE FROM ABOUT KRWI TO KAFP. BY SATURDAY MORNING...BUFR SOUNDINGS SHOW ENOUGH DRYING THAT ANY FLURRIES THAT EXIST SHOULD ONLY BE LOCATED OVER THE FAR NORTHWEST PIEDMONT. TOWARD KFAY...BUFR SOUNDINGS FROM THE GFS AND NAM DO NOT SHOW DEEPER LOW-LEVEL MOISTURE GETTING TO OR COLDER THAN -10C...SO HAVE NOT MENTIONED ANY FLURRIES THERE THIS PERIOD. CURRENTLY THINK THERE SHOULD BE LITTLE OR NO IMPACT AS THE PRECIPITATION SHOULD BE VERY LIGHT IF IT OCCURS...THOUGH STILL NOTICEABLE. SATURDAY DURING THE DAY...HIGH PRESSURE CONTINUES TO BUILD IN. AFTER LOWS THURSDAY NIGHT IN THE 20S...HIGHS FRIDAY SHOULD RANGE WITHIN A DEGREE OR THREE EITHER SIDE OF 40...CLOSE TO WHAT WOULD BE ASSOCIATED WITH THE 1000-850MB THICKNESSES. LOWS FRIDAY NIGHT IN THE UPPER TEENS TO MID 20S...A BLEND OF GUIDANCE BASED ON CONTINUED CLOUD COVER. ON SATURDAY...A LITTLE COLDER THAN FRIDAY DUE TO COLDER THICKNESSES TO START THE DAY AND THE HIGH BUILDING IN...MOSTLY MID 30S. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... AS OF 1200 PM WEDNESDAY... THE LONG-TERM SATURDAY NIGHT THROUGH WEDNESDAY IS CATEGORIZED BY SOME UNCERTAINTY IN PRECIPITATION TIMING AND TYPE...WITH AT LEAST MODEST CONFIDENCE IN MUCH WARMER TEMPERATURES DEVELOPING BY THE END OF THIS PERIOD THAN WHAT HAS BEEN OCCURRING RECENTLY. DRYING IS FORECAST FOR SATURDAY NIGHT...WITH A MID-LEVEL SHORTWAVE MOVING INTO THE CAROLINAS BY SUNDAY NIGHT. AS HEIGHTS ALOFT RISE LATE IN THE WEEKEND AND EARLY NEXT WEEK...THE 06Z GFS IN PARTICULAR AND POSSIBLY EVEN THE 12Z GFS SEEMS TO HAVE ISSUES WITH FEEDBACK SUCH THAT THE ECMWF IS PREFERRED OVERALL. IT SHOULD BE COLD TO START SUNDAY MORNING AS CLOUDS INCREASE...BUT THE GFS AND ECMWF TREND OF A LATER ARRIVAL OF MID-LEVEL VORTICITY AND OVERALL MOISTURE INCREASE SHOULD RESULT IN PRECIPITATION BEING IN THE FORM OF LIQUID BY THE TIME ANY WOULD ARRIVE LATER IN THE DAY. PARTIAL THICKNESSES AND MODEL SOUNDINGS CURRENTLY SUPPORT THIS...AND WILL HAVE A CHANCE OF AFTERNOON RAIN SUNDAY PRIMARILY TOWARD THE YADKIN RIVER FOLLOWED BY CHANCES OF RAIN OVERNIGHT...WITH SURFACE TEMPERATURES REMAINING ABOVE FREEZING AND MODEL SOUNDINGS SHOWING WARMING ALOFT AS 1000- 850MB THICKNESSES RISE AROUND 20M DURING THE NIGHT...SUGGESTING THE POTENTIAL FOR LOW TEMPERATURES EARLY SUNDAY NIGHT FOLLOWED BY STEADY OR A SLOW RISE IN READINGS LATE. A BRIEF WARMUP OCCURS MONDAY AHEAD OF A COLD FRONT THAT MOVES THROUGH CENTRAL NORTH CAROLINA LATER IN THE DAY AND AT NIGHT. STRONG HIGH PRESSURE BUILDS IN BEHIND THE COLD FRONT...AND THE PATTERN WOULD SUGGEST PRETTY CHILLY TEMPERATURES ONCE AGAIN WITH THE 1000- 850MB THICKNESSES SUGGESTING LOWS A LITTLE BELOW FREEZING. MOS GUIDANCE LOWS ARE AT LEAST ONE IF NOT MORE CATEGORIES ABOVE THIS... SO FOR NOW WILL SIMPLY UNDERCUT GUIDANCE WITH OVERNIGHT LOWS AT OR SLIGHTLY ABOVE FREEZING. CONDITIONS SHOULD DRY BRIEFLY BEHIND THE FRONT AS HIGH PRESSURE BUILDS IN...THEN UNCERTAINTY INCREASES AS THE GFS AND THE ECMWF SUGGEST MOISTURE RETURNING TO CENTRAL NORTH CAROLINA AS THE GULF OPENS BY TUESDAY INTO TUESDAY NIGHT. IF PRECIPITATION WOULD RETURN TO CENTRAL NORTH CAROLINA QUICKLY ENOUGH ON TUESDAY...PRECIPITATION TYPE CONCERNS WOULD EXIST DUE TO CHILLY THICKNESSES TO START THE DAY. BY 00Z WEDNESDAY ON THE 12Z GFS...AND FOR THE MOST PART ON THE 00Z ECMWF...THICKNESSES ARE WARM ENOUGH FOR RAIN AND BASED ON THE WARM-AIR ADVECTION AT THE TIME WOULD ANTICIPATE ANOTHER POTENTIAL NON-DIURNAL TEMPERATURE SCENARIO AS ANY COLD-AIR DAMMING ERODES. BASED ON THE PATTERN WILL ONLY NOTE A SLIGHT CHANCE OF RAIN OR SNOW EARLY ON THE SIXTH DAY IN THE WESTERN PIEDMONT WITH A CHANCE OF JUST ALL RAIN THROUGHOUT CENTRAL NORTH CAROLINA BY TUESDAY AFTERNOON. 1000-850MB THICKNESSES ON THE 12Z GFS AND 00Z ECMWF ARE QUITE WARM WEDNESDAY...APPROACHING 1380M ON THE LATEST GFS AND ONLY SLIGHTLY COOLER ON THE 00Z ECMWF...SUCH THAT... WITH SHOWERY CONDITIONS IN A MOIST AIR MASS AND A SOUTHWEST FLOW ALOFT...HIGH TEMPERATURES COULD POSSIBLY REACH THE 60S THROUGHOUT CENTRAL NORTH CAROLINA WITH SOME TEMPERATURES PUSHING 70F ESPECIALLY OVER PARTS OF THE SANDHILLS AND SOUTHERN COASTAL PLAIN. && .AVIATION /21Z WEDNESDAY THROUGH MONDAY/... AS OF 1255 PM WEDNESDAY... FOR THE 18Z VALID TAF PERIOD...HIGH CONFIDENCE IN VFR CONDITIONS FOR THE REST OF THIS AFTERNOON DETERIORATING QUICKLY TO IFR AND SUB-IFR CONDITIONS THIS EVENING...CONTINUING OVERNIGHT. GUIDANCE SUGGESTS PRECIPITATION MOVING SOUTHWEST TO NORTHEAST INTO AND ACROSS CENTRAL NORTH CAROLINA FROM VERY LATE THIS AFTERNOON THROUGH THIS EVENING... WITH PRECIPITATION ACROSS THE AREA BY 03Z. MODEL SOUNDINGS FROM THE NAM AND GFS SUGGEST WHATEVER LIQUID PRECIPITATION THERE MAY BE TO START CHANGING QUICKLY TO SNOW...WITH ENOUGH WARMING ALOFT THAT A PRECIPITATION TYPE OF SNOW AND SLEET IS QUITE POSSIBLE AT KRDU AND KRWI. AT KFAY...THE ABOVE FREEZING DEPTH IS A LITTLE HIGHER AND LIGHT RAIN MAY LINGER A LITTLE LONGER AT THE START BEFORE A TRANSITION TO SNOW...SLEET...AND FREEZING RAIN...WITH THE NAM MODEL MOST SUGGESTIVE OF WARMTH ALOFT FOR FREEZING RAIN AND MAINLY FOR A COUPLE OR THREE HOURS CENTERED AROUND 06Z. DRYING ALOFT VERY LATE TONIGHT INTO THURSDAY MORNING SUGGEST PRECIPITATION CHANGING TO FREEZING DRIZZLE OR DRIZZLE...WITH IFR CONDITIONS CONTINUING IN LOW CLOUDS. VARIABLE WINDS THIS AFTERNOON BECOME NORTH-NORTHEAST AND NORTHEAST THIS EVENING AS LOW PRESSURE GETS CLOSER AND MOVES NORTHEAST ALONG THE ATLANTIC COAST. BEYOND THE 18Z VALID TAF PERIOD...CONFIDENCE DIMINISHES IN IMPROVEMENT FROM IFR CONDITIONS...WITH AVIATION INTERESTS BEING PREPARED FOR THE LIKELIHOOD OF SUB-VFR CONDITIONS THROUGH THURSDAY NIGHT ALBEIT WITH A FEW PERIODS OF VFR CONDITIONS POSSIBLE MAINLY THURSDAY NIGHT. SUB-VFR CONDITIONS REMAIN POSSIBLE IN LOW CLOUDS THROUGH FRIDAY WITH A GREATER LIKELIHOOD OF VFR CONDITIONS FOR FRIDAY NIGHT. VFR CONDITIONS EXPECTED SATURDAY WITH CLOUDS INCREASING AND LOWERING FOR SUNDAY...THEN SUB-VFR CONDITIONS LIKELY FOR SUNDAY NIGHT INTO MONDAY ALONG WITH CHANCES FOR PRECIPITATION. && .RAH WATCHES/WARNINGS/ADVISORIES... WINTER STORM WARNING UNTIL NOON EST THURSDAY FOR NCZ007>011- 021>028-038>043-073>078-083-084. WINTER WEATHER ADVISORY UNTIL NOON EST THURSDAY FOR NCZ085-086- 088-089. && $$ SYNOPSIS...BADGETT NEAR TERM...BADGETT/BLAES SHORT TERM...DJF LONG TERM...DJF AVIATION...DJF

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