Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 130540 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1240 AM EST SAT FEB 13 2016 .SYNOPSIS...
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ARCTIC HIGH PRESSURE WILL BUILD INTO CENTRAL NC TODAY AND SUNDAY. AN AREA OF LOW PRESSURE WILL APPROACH FROM THE WEST ON MONDAY AND CROSS THE REGION MONDAY NIGHT AND TUESDAY.
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&& .NEAR TERM /THROUGH TONIGHT/... AS OF 940 PM FRIDAY... STARTING TO FINALLY SEE BETTER WEST TO EAST CLEARING OF MOISTURE AROUND 6000-7000 FT AS A JET ON THE BACK SIDE OF THE UPPER TROUGH APPROACHES AND NORTHWEST FLOW STRENGTHENS. LOW-LEVEL MOISTURE IS STILL MORE PREVALENT ON THE COASTAL PLAIN WHERE SOME SUB-1000 FT STRATUS IS LINGERING. A PERIOD OF PATCHY FOG MAY DEVELOP IN THE SOUTHERN COASTAL PLAIN AS THE HIGHER LEVEL CLOUDS CLEARING (HINTED AT BY SREF PROBS AND KFAY/KGSB RAP SOUNDINGS)...BUT IT WOULD LIKELY BE BRIEF...PRIOR TO 06Z...WITH A NORTHWEST WIND AND COLD ADVECTION FORECAST TO SLOWLY STRENGTHEN AFTER MIDNIGHT. OTHERWISE...WHILE WE MAY SEE A SOME PATCHES OF STRATOCU DRIFT ACROSS THE AREA GIVEN ALL THE MOISTURE BANKED UPSTREAM OF THE MOUNTAINS...CLEARING SKIES AND COLD ADVECTION WILL PUSH LOWS INTO THE LOWER 20S NORTH AND WEST TO UPPER 20S SOUTH AND EAST. && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... AS OF 300 PM FRIDAY... AS EAST COAST TROUGH TRIES TO PULL OFF THE COAST...VERY STRONG COLD AIR ADVECTION WILL ENSUE BEHIND THE EXITING COASTAL SYSTEM. WITH VERY STRONG PRESSURE GRADIENT ACROSS THE AREA...COLD TEMPERATURES AND STRONG WINDS WILL BE THE FORECAST PROBLEM OF THE DAY. EXPECT WINDS TO REMAIN SUSTAINED OUT OF THE NORTH OR NORTHWEST AT 10-15 KTS WITH GUSTS OF 25-30 KTS FOR MUCH OF THE DAYLIGHT HOURS. AFTER SUNSET GUSTS WILL SUBSIDE. HIGH TEMPERATURES ONLY IN THE LOW TO MID 30S AND WITH WIND CHILL VALUES IN THE UPPER 10S TO LOW 20S FOR MUCH OF THE DAY. AS AN ASIDE...WITH THE COLD BUT ALSO DRY AIRMASS IN PLACE...MIN RH VALUES WILL DIP DOWN INTO THE LOW 20S. COMBINE THESE VALUES WITH THE HIGHER WINDS AND THERE WILL BE A SMALL INCREASE IN FIRE DANGER SATURDAY IN OUR SOUTHERN COUNTIES THAT MAY SQUEAK INTO THE LOWER 40S. SATURDAY NIGHT WILL SEE THE GUSTS SLACK OFF BUT SUSTAINED WINDS TO REMAIN UP IN THE 5 TO 10 KT RANGE KEEP THINGS MIXED A LITTLE. COMBINE THIS WITH VERY COLD EXPECTED LOW TEMPERATURES IN THE LOW TO MID TEENS...WIND CHILL VALUES SATURDAY NIGHT WILL RESIDE IN THE 5-10 DEGREE RANGE. PREPARATIONS SHOULD BE MADE NOW TO PROTECT ANYTHING SUSCEPTIBLE TO THE COLD WIND CHILLS...ESPECIALLY PETS. SOME CLOUDS WILL BEGIN TO APPROACH THE AREA LATE SATURDAY NIGHT INTO SUNDAY MORNING FROM THE WEST IN ADVANCE OF THE NEXT STORM SYSTEM. && .LONG TERM /SUNDAY THROUGH FRIDAY/... AS OF 315 PM FRIDAY... ...STORM SYSTEM LIKELY TO BRING WINTRY WEATHER THREAT SUN NIGHT/MON FOLLOWED BY HEAVY RAIN THREAT AND A FEW STORMS MON NIGHT/TUE... SUNDAY: CONTINUED CHILLY WITH THE ARCTIC HIGH PRESSURE EXTENDING FROM THE ERN GREAT LAKES DOWN THROUGH NC. WILL HAVE INCREASING CLOUDS AHEAD OF THE APPROACHING STORM... AS OUR MID LEVEL FLOW SHIFTS FROM FAST NORTHWESTERLY TO WEST-SOUTHWEST... A FUNCTION OF PACIFIC NORTHWEST ENERGY DIVING INTO AN INITIALLY FLAT/BROAD CENTRAL CONUS TROUGH CAUSING ITS AMPLIFICATION. STATISTICAL GUIDANCE STILL SUPPORTS HIGHS FROM 29 NE TO 35 SW. -GIH SUN NIGHT THROUGH TUE: OVERVIEW: CONFIDENCE IS BEGINNING TO INCREASE REGARDING THE TIMING... MOST PROBABLE PRECIP TYPE PATTERN... AND PRIMARY WEATHER THREATS FOR THE INCOMING SYSTEM. LATEST GUIDANCE SHOWS A BIT QUICKER ONSET... WITH PRECIP ARRIVING IN THE NRN/WRN CWA SUN NIGHT... AS WELL AS A SLIGHTLY EARLIER DEPARTURE ON TUE. LONGWAVE TROUGHING WILL CONTINUE TO AMPLIFY ALONG THE MISS VALLEY AS NRN STREAM ENERGY DROPS INTO ITS BASE OVER THE GULF STATES... CULMINATING IN A NARROW DEEP SHORTWAVE TROUGH TAKING ON A POSITIVE TILT AS IT SWINGS ENE INTO THE CAROLINAS. AT THE SURFACE... THE POLAR HIGH SITUATED OVER THE NORTHEAST AND MIDATLANTIC STATES SUN NIGHT CONTINUES TO PUSH STEADILY NORTHEAST AND OFFSHORE THROUGH MON... WHILE A COASTAL FRONT FORMS ALONG THE CAROLINA COAST EXTENDING BACK TO DEVELOPING LOW PRESSURE OVER THE CENTRAL GULF STATES. THIS LOW THEN TRACKS EAST THEN NE THROUGH WRN NC MON NIGHT/TUE MORNING BEFORE MOVING QUICKLY INTO THE NORTHEAST STATES... WITH A TRAILING FRONT SWEEPING THROUGH CENTRAL/ERN NC BY EARLY TUE AFTERNOON. PRECIPITATION CHANCES: THE INITIAL PROCESSES TO FORCE ASCENT SUNDAY NIGHT INTO EARLY MONDAY INCLUDING DPVA AND MOIST ISENTROPIC UPGLIDE ARE RATHER WEAK AND FOCUSED PRIMARILY ON WRN AND NRN PORTIONS OF CENTRAL NC. WILL TREND POPS UP TO LIKELY NW AND RETAIN HIGH CHANCES ACROSS THE SOUTH AND EAST SUN NIGHT INTO MON MORNING... WITH QPF FAIRLY LIGHT... UNDER A QUARTER INCH MAINLY IN THE NW. BUT THIS CHANGES QUICKLY WITH THE ADDITION OF STRONG UPPER DIVERGENCE (DUE TO IDEALLY JUXTAPOSED POLAR AND SUBTROPICAL JETS) AND VIGOROUS LOW LEVEL MOISTURE TRANSPORT EAST OF THE LOW. WILL RAMP UP POPS FURTHER TO CATEGORICAL WEST/LIKELY EAST LATE MON... THEN TO CATEGORICAL EVERYWHERE MON NIGHT THROUGH TUE MORNING... ENDING SW TO NE TUE AFTERNOON. PTYPES: USING THE TOP-DOWN METHODOLOGY WITH CONSIDERATION OF THE INITIALLY VERY COLD/DENSE NATURE OF THE SURFACE AIR MASS... THE INITIAL COLD AIR ALOFT GIVING WAY TO A WARM NOSE... AND THE STRONG LOW LEVEL WARM ADVECTION APT TO DISLODGE THIS SURFACE AIR MASS GRADUALLY FROM SE TO NW MON EVENING... EXPECT THIS TO START AS MOSTLY LIGHT SNOW WITH PERHAPS PATCHY LIGHT SLEET SUN NIGHT ACROSS THE NRN AND WRN CWA... FOLLOWED BY A SLOW STEADY TRANSITION FROM SSE TO NNW TO FREEZING RAIN/SLEET THEN TO ALL RAIN... WITH THE FAR NW COUNTIES INCLUDING THE TRIAD THE LAST TO SEE AN END TO THE WINTRY PRECIP MON EVENING. TENTATIVE ACCUMULATIONS ARE UP TO ONE TO TWO HUNDREDTHS OF AN INCH OF ICING (TRACE AMOUNTS) FOR MUCH OF THE CWA... AND SNOW TOTALS OF 1-3" NW QUARTER WITH AN INCH OR LESS ELSEWHERE... ALL OF WHICH SHOULD BE QUICKLY SWEPT AWAY BY MODERATE TO POTENTIALLY HEAVY RAINFALL LATE MON NIGHT INTO TUE MORNING. RAINFALL TOTALS AND STORM POTENTIAL: AT THIS TIME STORM TOTAL LIQUID QPF IS EXPECTED TO BE 1-2" WITH LOCALLY HIGHER AMOUNTS POSSIBLE... GIVEN THE HIGH WATER CONTENT AND STRONG LIFT MON NIGHT/TUE MORNING. BASED ON THE ANTECEDENT CONDITIONS AND SEVERAL RIVERS AND CREEKS RUNNING HIGH... A FLOOD WATCH MAY BE NEEDED FOR SOME PORTION OF THE AREA. ALSO... WHILE LAPSE RATES ARE UNLIKELY TO BE VERY IMPRESSIVE... THE STRONG AND FOCUSED LIFT POSSIBLE WITH THIS SYSTEM AND WARMING LOW LEVELS ESPECIALLY IN THE SANDHILLS AND COASTAL PLAIN MAY SUPPORT A FEW LIGHTNING STRIKES ON TUE. TEMPS: EXPECT LOWS SUN NIGHT OF 22-26. TEMPS SHOULD SLOWLY RISE MON THROUGH MON NIGHT... REACHING THE LOW 30S NW TO LOW 40S SE LATE MON... RISING TO THE MID 30S NW TO MID 40S SE MON NIGHT... AND PEAKING AT 48-56 TUE PRIOR TO FRONTAL PASSAGE. WED THROUGH FRI: WE MAY SEE A PERTURBATION SWING THROUGH THE LONGWAVE ERN TROUGH BASE ACROSS VA ON WED... BUT MODELS VARY ON THE STRENGTH AND LATITUDE OF ANY SUCH WAVE... AND REGARDLESS THE MOISTURE WILL BE LIMITED YIELDING NO IMPACTS ON CENTRAL NC OTHER THAN SOME CLOUDS ACROSS THE NORTH. OTHERWISE... THIS PERIOD WILL FEATURE A TRANSITION AWAY FROM WRN RIDGE/ERN TROUGH OVER THE CONUS... AS FLAT RIDGING BUILDS OVER THE GULF/SOUTHEAST STATES FROM THE WEST... WITH A NET RESULT OF DRY WEATHER AND NEAR TO SLIGHTLY ABOVE NORMAL TEMPS FOR CENTRAL NC. -GIH && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
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AS OF 1240 AM SATURDAY A LAYER OF SCATTERED-BROKEN STRATOCU WILL LINGER ACROSS THE NORTHERN COUNTIES THROUGH 10Z...THEN GRADUALLY DIMINISH. THE LEADING EDGE OF AN ARCTIC AIRMASS WILL OVERSPREAD CENTRAL NC THROUGH 11Z. SFC WINDS WILL GUSTS BETWEEN 20-25KTS WITH THE PASSAGE OF THE BOUNDARY. AFTER 11Z...EXPECT VFR CONDITIONS WITH FEW-SCATTERED STRATOCU. SFC WINDS WILL BE BRISK WITH GUSTS 22-27KTS HIGHLY PROBABLE FROM THE NW. THESE BRISK WINDS WILL SLOWLY SUBSIDE LATER TONIGHT. VFR CONDITIONS TO CONTINUE INTO SUNDAY THOUGH MID-HIGH LEVEL CLOUDS WILL BE INCREASING DURING THE DAY AS AN AREA OF LOW PRESSURE APPROACHES FROM THE WEST. MOISTURE AHEAD OF THIS SYSTEM WILL LEAD TO SUB VFR CEILINGS ALONG WITH PATCHES OF PRECIPITATION LATE SUNDAY NIGHT INTO MONDAY MORNING. AT ONSET...THIS PRECIPITATION MAY OCCUR AS A WINTRY MIX. THE SUB VFR CONDITIONS MAY LINGER INTO EARLY TUESDAY WITH IMPROVING CONDITIONS LATE TUESDAY INTO WEDNESDAY.
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&& .CLIMATE... HERE ARE THE RECORD LOWS AND RECORD LOW MAXIMUM TEMPERATURES FOR SAT FEB 13TH AND SUN FEB 14TH AT GSO... RDU... AND FAY: REC YR REC YR LOW LOW MAX ---------------------------------------------- GSO: 02/13 11 1955 31 1986 02/14 6 1905 22 1914 RDU: 02/13 4 1899 10 1899 02/14 -2 1899 27 1916 FAY: 02/13 14 1973 32 1955 02/14 12 1968 33 1916 && .RAH WATCHES/WARNINGS/ADVISORIES... NONE && $$ SYNOPSIS...WSS NEAR TERM...SMITH SHORT TERM...ELLIS LONG TERM...HARTFIELD AVIATION...WSS CLIMATE...RAH

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