Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 231721 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1215 PM EST FRI JAN 23 2015 .SYNOPSIS...
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HIGH PRESSURE WILL RAPIDLY SHIFT OFFSHORE THIS AFTERNOON AS A LOW PRESSURE SYSTEM APPROACHES FROM THE SOUTHWEST. THIS STORM SYSTEM WILL TRACK JUST INLAND OF THE SOUTHEAST US COAST THROUGH TONIGHT...THEN OFFSHORE THE MIDDLE ATLANTIC AND NEW ENGLAND COAST ON SATURDAY.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 1215 PM FRIDAY... WE CAN SAY WITH 100 PERCENT CONFIDENCE NOW THAT ALL RAIN WILL FALL IN OUR CWA THROUGH THIS EVENT. THE WET BULB READINGS ARE NOW 34+ DEGREES. TEMPERATURES WILL REMAIN ABOVE FREEZING. NO PRECIPITATION TYPE ISSUES ARE EXPECTED. RAIN MAY FALL HEAVY ENOUGH LATER TODAY AND TONIGHT... MAINLY EAST OF THE TRIAD REGION... TO PRODUCE LOCAL RUNOFF ISSUES. OTHERWISE... NO HAZARDS ARE EXPECTED WITH THIS EVENT. PREVIOUS AFD ISSUED AT 900 AM... THE 12Z/GSO SOUNDING WAS WELL REPRESENTATIVE OF THE CURRENT TEMPERATURE PROFILE THROUGHOUT THE NORTHWEST PIEDMONT. THIS PROFILE IS SUPPORTIVE OF BRIEF/NUISANCE LIGHT SNOW/SLEET MIXED WITH THE RAIN AT PRECIP ONSET THIS MORNING IN THE NW PIEDMONT. HOWEVER... SURFACE TEMPERATURES ARE WELL INTO THE 30S (ABOVE FREEZING)... AND THE WET BULB TEMPERATURES ALSO JUST ABOVE FREEZING IN FORSYTH AND NW GUILFORD INTO PERSON (OUR COLDEST COUNTIES). RADAR INDICATED PRECIPITATION WAS RAPIDLY DEVELOPING OVER WESTERN NORTH CAROLINA. THE PRECIPITATION WAS FALLING AS A LIGHT MIXTURE OF SNOW/SLEET OVER THE NORTHERN MOUNTAINS AND NORTHERN FOOTHILLS... WITH A LIGHT SNOW/SLEET/RAIN MIXTURE INTO DAVIDSON/FORSYTH COUNTIES. IT IS ALONG THE LEADING EDGE OF THE PRECIPITATION SHIELD WHERE JUST ENOUGH COLD DRY AIR WAS IN PLACE OVER NW NC COURTESY OF THE 1028 MB SURFACE HIGH PRESSURE OVER PA... EXTENDING INTO NC/SC. THIS HIGH IS RAPIDLY RETREATING AND THIS IS VERY UNFAVORABLE FOR ADDITIONAL COLD DRY AIR DELIVERY INTO OUR REGION TO SUPPORT ANY SNOW/SLEET ACCUMULATION IN OUR REGION. THE WARMING ALOFT WILL SWEEP IN FROM THE SOUTH AND EAST QUICKLY TAKING TEMPERATURES INTO THE 40S AT 5K FEET THIS AFTERNOON. THIS WILL END ANY SNOW/SLEET... AND KEEP IT AS A NUISANCE ON THE LEADING EDGE OF THE EXPANDING PRECIP FIELD. ONCE WE REACH SATURATION IN THE BOUNDARY LAYER... FORECAST WET BULBS ARE TO REMAIN IN THE 33-35 RANGE TODAY. THEREFORE... BOTTOM LINE... LIGHT SNOW/SLEET/RAIN MIX AT PRECIPITATION ONSET IN THE NW AND N PIEDMONT... ROUGHLY WEST AND NORTH OF A LINE FROM DAVIDSON AND RANDOLPH COUNTIES NE TO PERSON COUNTY... NO SNOW/SLEET ACCUMULATION EXPECTED. AS THE COLUMN SATURATES WITH THE PRECIPITATION FALLING FOR 1-3 HOURS... THE PRECIPITATION WILL BE ALL RAIN WITH TEMPS EXPECTED TO HOLD NEAR THE WET BULB READINGS IN THE MID 30S THROUGHOUT THE TRIAD REGION. THIS IS SAFELY ABOVE FREEZING. THEN OVERNIGHT... TEMPS WILL REMAIN STEADY OF EVEN RISE A FEW DEGREES DUE TO THE OVERWHELMING WARMING ALOFT AND RAIN. -BADGETT PREVIOUS DISCUSSION ISSUED AT 300 AM... A POSITIVELY TILTED TROUGH OVER THE SOUTHERN PLAINS WILL CONTINUE TO MOVE EAST ACROSS THE GULF COAST STATES TODAY AND THEN BEGIN TO LIFT ACROSS THE CAROLINAS LATER TONIGHT. CYCLOGENESIS APPEARS TO BE UNDERWAY SOUTH OF NEW ORLEANS THIS MORNING... AND THIS LOW FORECAST IS TO TRACK ACROSS SOUTHERN GEORGIA AND UP THE CAROLINA COASTAL AREA TONIGHT. MODEL QPF IS RATHER HIGH TONIGHT...WITH AS MUCH AS ONE INCH IN THE WEST AND NEAR 2 INCHES EAST OF I-95...AND THIS SEEMS VERY REASONABLE GIVEN PW INCREASING TO AS MUCH AS 200 PERCENT OF NORMAL AND A PLETHORA OF 1 TO 2 INCH TOTALS ALREADY REPORTED UPSTREAM ACROSS LOUISIANA AND MISSISSIPPI. CONTEMPLATED A FLOOD WATCH GIVEN RECENT RAINFALL EVENTS AND SOIL MOISTURE...BUT WITHOUT CONVECTION THE FLOODING MAY MAY ISOLATED TO SOME OF THE SMALL CREEKS AND STREAMS THAT ARE ALREADY RUNNING HIGHER THAN NORMAL. SOME MINOR RIVER FLOODING IS ALSO POSSIBLE ON THE NEUSE AND TAR RIVERS.
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&& .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... AS OF 330 AM FRIDAY... MODELS DEPICT A BRIEF PERIOD OF MID-LEVEL DRYING AS A DRY SLOT SURGES ACROSS THE AREA LATE TONIGHT...BUT THE ARRIVAL OF THE UPPER TROUGH AND STRONGER DCVA SHOULD CAUSE PRECIP TO REDEVELOP OR REINTENSIFY EARLY SATURDAY...MAINLY ACROSS THE EASTERN HALF OF THE AREA. RAINFALL TOTALS MAY NOT BE AS HIGH WITH THE SURFACE LOW HAVING MOVED OFF TO THE NORTHEAST...BUT MODELS SHOW ANOTHER HALF INCH POSSIBLE PRIOR TO 15Z. PRECIP WILL THEN END FOR MUCH OF THE AREA AS MORE PRONOUNCED DRYING ALOFT DEVELOPS. HOWEVER... A DEFORMATION BAND EXPECTED TO DEVELOP OVER THE TENNESSEE VALLEY WILL PIVOT ACROSS AT LEAST THE NORTHERN HALF OF THE AREA AROUND MIDDAY. RAPID MID-LEVEL COOLING AND RESATURATION OF THE ICE-NUCLEATION ZONE SUGGESTS RAIN COULD MIX WITH OR CHANGE OVER TO SNOW WITHIN THIS BAND...BUT FORECAST SOUNDINGS HAVE THE LOWEST 2000 FT OF THE BOUNDARY LAYER ABOVE FREEZING AND THIS MAY BE TOO MUCH MELTING TO OVERCOME. WILL BE INTERESTING TO SEE HOW THIS UNFOLDS...THOUGH NO IMPACTS WOULD BE EXPECTED. THE BAND SHOULD DEPART THE NORTHEAST CWA BY 18Z TO 21Z...WITH CLEAR SKIES BY 00Z TO 03Z. COLD ADVECTION WILL BE RELATIVELY STRONG SATURDAY EVENING...RESULTING WIND GUSTS OF 20-25MPH FOR THE FIRST HALF OF THE NIGHT. LOWS WILL DROP INTO THE LOW TO MID 30S. -BLS SUN AND SUN NIGHT: A STRONG PACIFIC JET WILL ROUND A WESTERN CONUS RIDGE AND CAUSE AN ASSOCIATED NORTHERN STREAM SHORTWAVE TROUGH TO AMPLIFY SHARPLY FROM THE NORTHERN PLAINS TO THE CAROLINAS AND VA THROUGH SUN NIGHT. A CLIPPER SURFACE LOW WILL ACCOMPANY THE SHORTWAVE TROUGH AND CROSS THE UPPER MIDWEST AND OH VALLEY SUN AND THE CENTRAL APPALACHIANS AND MIDDLE ATLANTIC STATES SUN NIGHT. WSW LOW LEVEL FLOW AHEAD OF THE CLIPPER LOW...AND IN BRIEF SHORTWAVE RIDGING BETWEEN THIS SHORTWAVE TROUGH AND AN INTENSE CYCLONE APPROACHING NOVA SCOTIA (OUR FRI-SAT WEATHER MAKER)...WILL RESULT IN A MOSTLY SUNNY AND MILD DAY IN THE 50S TO END THE WEEKEND. THE PASSAGE OF THE SHORTWAVE TROUGH AND ASSOCIATED COLD POOL ALOFT CHARACTERIZED BY H5 TEMPERATURES AROUND MINUS 30 - AND POCKET OF MID LEVEL LAPSE RATES AROUND 7 C/KM - WILL CAUSE AN AREA OF SHOWERS TO PIVOT EAST ACROSS CENTRAL NC OVERNIGHT. ALL LIQUID IS ANTICIPATED OWING TO A 1500-3000 FT DEEP ABOVE FREEZING BOUNDARY LAYER...LOWEST AND COLDEST ONCE THE SHOWERS ARE MOVING OUT. LOWS...AND WITH CLEARING SPREADING INTO THE PIEDMONT BY DAYBREAK...WITHIN A FEW DEGREES EITHER SIDE OF 35. -MWS && .LONG TERM /MONDAY THROUGH THURSDAY/... AS OF 345 AM FRIDAY... JUST AS QUICKLY AS THE CLOUDINESS AND SHOWERS ASSOCIATED WITH THE "ALBERTA CLIPPER"/NORTHERN STREAM SHORTWAVE WAVE MOVE OUT... ADDITIONAL SHEAR VORTICITY IN FAST NW FLOW ALOFT WILL AMPLIFY INTO THE TROUGH BASE...TO NEAR AND JUST OFFSHORE THE COAST OF THE CAROLINAS...THROUGH WED MORNING. TYPICAL MEDIUM RANGE TIMING AND AMPLITUDE DISTANCES BECOME MAGNIFIED DURING THIS TIME...WITH THE 00Z ECMWF REPRESENTING THE SOUTHERNMOST - AND CONSEQUENTLY RELATIVELY WETTEST FOR CENTRAL NC - SOLUTIONS FOR THE PERIOD MON-TUE. BASED ON A PREFERRED SLIGHTLY LESS AMPLIFIED/MORE NORTHWARD CONSENSUS OF MODEL CLUSTERING REPRESENTED WELL BY THE 00Z GFS...THE RELATIVE HIGHEST PROBABILITY OF PRECIPITATION (IN THE CHANCE RANGE) SHOULD BE CENTERED TOWARD THE NORTHEAST PIEDMONT WITH THE ARRIVAL OF THE LEAD SHEAR VORTICITY AND POSSIBLE INTERACTION WITH A LOW LEVEL MOIST AXIS OVER EASTERN NC THROUGH MON NIGHT. ANY PRECIPITATION THAT WERE TO FALL AFTER DARK MON...AFTER TEMPERATURES PEAK IN THE UPPER 40S TO LOWER 50S...WOULD BE IN THE FORM OF LIGHT SNOW OWING TO STRONG DEEP LAYER COOLING MON NIGHT - A CASE OF "THE COLD AIR CHASING THE MOISTURE". TRAILING SHEAR VORTICITY WILL CARVE THE TROUGH OFF THE COAST OF THE CAROLINAS TUE-TUE NIGHT. ASSOCIATED RE-STEEPENING OF THE LAPSE RATES ALOFT...AND LIFT/MOISTENING OF THE COLUMN...WILL RESULT IN YET ANOTHER SLIGHT TO CHANCE OF RAIN SHOWERS - OR SNOW SHOWERS WHERE/IF THE SUB-CLOUD LAYER FULLY WET-BULBS AND THEORETICALLY "MELTS OUT" A PROJECTED 1500-2000 FT ABOVE FREEZING BOUNDARY LAYER. THE REMAINDER OF THE LONG TERM WILL BE DRY AND CHILLY... PARTICULARLY WITH RESPECT TO LOWS BOTH WED AND THU MORNINGS...AS MODIFIED ARCTIC HIGH PRESSURE DRIFTS OVERHEAD IN THE WAKE OF THE TROUGH AXIS MOVING AWAY FROM THE NC COAST. && .AVIATION /18Z FRIDAY THROUGH TUESDAY/...
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AS OF 1215 PM FRIDAY... AVIATION CONDITIONS FURTHER DETERIORATE TO LIFR-IFR...THROUGH THE AFTERNOON AND EVENING. IN ADDITION...THE ARRIVAL OF AN EAST SOUTHEASTERLY TO SOUTHERLY LOW LEVEL JET AT 2000 FT...ATOP MUCH LIGHTER EASTERLY WINDS AT THE SURFACE...WILL PROMOTE A GOOD CHANCE OF LOW LEVEL WIND SHEAR CONDITIONS AT EASTERN TERMINALS THIS EVENING. PERIODS OF RAIN AND DRIZZLE...AND LIFR CONDITIONS...WILL CONTINUE OVERNIGHT...AS THE LOW PRESSURE SYSTEM TRACKS JUST INLAND OF THE COAST OF THE CAROLINAS. OUTLOOK: RAIN WILL LINGER THROUGH MIDDAY SAT...WHILE CEILINGS AND VISIBILITIES GRADUALLY RISE THROUGH MVFR RANGE...TO VFR BY AFTERNOON...AS THE LOW PRESSURE SYSTEM TRACKS UP THE MIDDLE ATLANTIC COAST AND AWAY FROM CENTRAL NC. A COUPLE OF UPPER LEVEL DISTURBANCES WILL BRING A RENEWED CHANCE OF BRIEF SUB-VFR CONDITIONS AND RAIN SHOWERS TO THE AREA SUN NIGHT-MON NIGHT...THE LATTER OF WHICH COULD MIX WITH OR CHANGE TO LIGHT SNOW AS COLDER TEMPERATURES ARRIVE BY MON EVENING.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...MWS NEAR TERM...BADGETT SHORT TERM...BLS/MWS LONG TERM...MWS AVIATION...MWS/BADGETT

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