Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 311932 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 320 PM EDT FRI OCT 31 2014 .SYNOPSIS...
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A POWERFUL STORM SYSTEM WILL AFFECT THE AREA TONIGHT THROUGH SATURDAY NIGHT. LOW PRESSURE WILL DEVELOP OVER THE WESTERN CAROLINAS TONIGHT... THEN TRACK EAST TOWARD THE COAST SATURDAY... FINALLY TURNING NORTHEAST AND MOVING OFF THE COAST THROUGH SATURDAY NIGHT. COLD HIGH PRESSURE WILL BUILD IN FROM THE WEST SATURDAY NIGHT THROUGH MONDAY.
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&& .NEAR TERM /THROUGH SATURDAY NIGHT/...
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AS OF 320 PM FRIDAY... THIS EVENING THROUGH SAT: PRIMARY CONCERN REMAINS THE BRISK AND GUSTY WINDS EXPECTED TO DEVELOP SAT AFTERNOON... AS THE RISK OF ANY FROZEN PRECIP IN THE FAR WRN AND SW CWA CONTINUES TO DECLINE. POCKETS OF BRIEF HEAVIER RAIN ARE POSSIBLE OVER THE WRN PIEDMONT... BUT SHOULD CAUSE NOTHING MORE THAN MINOR STREET FLOODING AT MOST. OVERVIEW: HIGHLY ANOMALOUS (HEIGHTS DROPPING TO AROUND 5 STANDARD DEVIATIONS BELOW NORMAL) MID LEVEL LOW PRESSURE NOW DROPPING INTO NRN INDIANA IS STILL EXPECTED TO INTENSIFY AS IT DROPS SOUTHEAST... TO NEAR AVL BY SAT MORNING... CROSSING SC SAT BEFORE SWINGING NE OFF THE NC COAST SAT NIGHT. THE GREATEST HEIGHT FALLS WILL BE OVER SC (NEARLY 180 M IN 12 HRS)... WHILE THEY SHOULD BE MUTED BUT STILL IMPRESSIVE AT 80-120 M OVER CENTRAL/SRN NC. AT THE SURFACE... PRIMARY LOW PRESSURE JUST OFF THE NC COAST WILL MOVE NE TONIGHT... AS SECONDARY LOW PRESSURE FORMS OVER SOUTH CENTRAL NC. THIS LOW WILL TRACK EAST ALONG THE CENTRAL/ERN NC/SC BORDER REGION SAT MORNING WHILE SLOWLY DEEPENING... BEFORE MOVING E/NE OFF THE NC COAST SAT AFTERNOON/EVENING WHILE STRENGTHENING FURTHER. POPS: FOLLOWING THE CONVECTION-ALLOWING MODEL TRENDS AND EXTRAPOLATION OF EXISTING PRECIP... WILL BRING LOW CHANCE POPS INTO THE FAR WRN CWA EARLY THIS EVENING... SPREADING SLOWLY EAST WITH POPS INCREASING WEST TO EAST OVERNIGHT. GIVEN THE INTENSE DEEP LAYER FORCING FOR ASCENT... PEAK IN MID LEVEL DEFORMATION... AND STRENGTHENING LOW LEVEL MOISTURE TRANSPORT... CATEGORICAL POPS STILL LOOK GOOD FOR THE WRN AND SRN CWA FOCUSED ON LATE TONIGHT THROUGH MID AFTERNOON SAT... AS THIS IS WHERE THE DPVA WILL BE MAXIMIZED IN CONJUNCTION WITH THE GREATEST UPPER DIVERGENCE IN THE LEFT EXIT REGION OF THE DIVING JET TO OUR WEST... YIELDING DEEP AND VIGOROUS LIFT. HOWEVER... BOTH EXPLICIT AND CONVECTION-ALLOWING AS WELL AS THE SREF HAVE TRENDED TOWARD MUCH LOWER COVERAGE OVER THE NE CWA... AND BASED ON THE SLIGHTLY MORE SOUTHERLY TRACK OF THE MID LEVEL LOW AND ASSOCIATED DPVA AND UPPER DIVERGENCE... THIS TREND LOOKS REASONABLE... AND HAVE NUDGED POPS DOWNWARD IN AREAS NORTH/EAST OF THE TRIANGLE TO 30-50% THROUGH THE EVENT. WILL BE SLOW TO TAPER POPS DOWN IN THE SOUTHEAST CWA SAT AFTERNOON... GIVEN LINGERING STEEP MID LEVEL LAPSE RATES AND GREATER DEFORMATION HERE. PTYPE AND THUNDER CONCERNS: MODELS HAVE BEEN TRENDING WARMER WITH THE BOUNDARY LAYER TEMPS IN RECENT RUNS... AND NOW SUGGEST A SMALLER CHANCE OF ANY MIXED-IN WET SNOW OVER A SMALLER AREA SAT MORNING... PRIMARILY ALONG AND SE OF A LINE FROM INT TO MEB. BUT EVEN HERE... YESTERDAY`S INDICATIONS OF A NEAR-FREEZING ISOTHERMAL LAYER WITH SATURATION WELL UP ABOVE -10C ARE LOOKING LESS CERTAIN... WITH WARMER AIR AROUND 925 MB AND LESS MOISTURE ABOVE -10C. WILL CONTINUE TO HOLD ANY MENTION OF WET SNOW OUT OF THE FORECAST... GIVEN THE VERY LOW CHANCES... HOWEVER WOULDN`T BE AT ALL SURPRISED TO SEE A LITTLE SNOW MIXED IN BRIEFLY... PARTICULARLY IF ANY INSTABILITY CAN BE ACHIEVED WHICH WOULD DRIVE UP PRECIP RATES. FORECAST MID LEVEL LAPSE RATES REMAIN STEEP... 6.5-7.0 C/KM TONIGHT SLIPPING JUST A BIT TO 6.0-6.5 C/KM SAT... BUT WITH THE POTENTIAL FOR SLIGHTLY LESS MOISTURE THROUGH THE COLUMN (PW VALUES PEAK NEAR 0.75" WHICH IS JUST NEAR NORMAL)... ANY LIGHTNING STRIKES WOULD BE FEW AND ONLY WHERE EXTREMELY SLIM INSTABILITY IS AUGMENTED BY INTENSE DYNAMIC FORCING FOR ASCENT. WINDS: IT SHOULD TAKE AWHILE FOR THE SURFACE WINDS TO PICK UP SAT... GIVEN THE INITIAL SLACK GRADIENT AS THE SECONDARY LOW FORMS OVER SOUTH CENTRAL NC. AS THIS LOW SHIFTS EAST AND OFFSHORE AND DEEPENS DURING THE DAY AND SAT NIGHT... THE RAPIDLY TIGHTENING GRADIENT SHOULD RESULT IN SUSTAINED WINDS PEAKING AT 15-20 KTS (POTENTIALLY HIGHER IN SPOTS) IN THE LATE AFTERNOON THROUGH EVENING. STILL EXPECT GUSTS OF 25-30 KTS. THIS IS JUST UNDER WIND ADVISORY CRITERIA... BUT IMPACT-WISE WE SHOULD STILL SEE LIGHT OBJECTS GETTING TOSSED AROUND AND A FEW BRANCHES COMING DOWN... ESPECIALLY CONSIDERING THAT MOST LEAVES ARE STILL ON THE TREES. WIND CHILLS MAY HOLD IN THE 30S TO LOWER 40S OVER THE WRN HALF OF THE CWA SATURDAY. TEMPS: PATTERN OF EARLIER FORECASTS TO UNDERCUT STATISTICAL GUIDANCE SUBSTANTIALLY STILL APPEARS PRUDENT... WITH A CHILLY CANADIAN-SOURCE AIR MASS MOVING IN... STRENGTHENING COLD AIR ADVECTION... STEADY PRECIP FOR A GOOD CHUNK OF THE DAY... AND ABUNDANT CLOUD COVER. BUT IT MAY TAKE AWHILE FOR THE COOLEST AND MOST DENSE AIR TO GET OVER THE MOUNTAINS... ESPECIALLY GIVEN THE SLOW/LATE FORMATION OF THE SECONDARY LOW PRESSURE WHICH WOULD RETARD CAA INITIALLY ON SAT. HAVE NUDGED HIGHS UP A DEGREE OR SO TO 46-55 WEST TO EAST... STILL WELL BELOW STATISTICAL GUIDANCE. FOR SAT NIGHT: MODEL OUTPUT INDICATES QUICKLY TAPERING RAIN CHANCES FROM NW TO SE SAT EVENING AS THE SECONDARY SURFACE LOW SHIFTS OFF THE OUTER BANKS. WILL MAINTAIN LIKELY POPS SE AND SLIGHT CHANCE AT MOST WEST FOR A FEW EARLY EVENING HOURS... FOLLOWED BY VERY LOW TO NO POPS AFTER 06Z. EXPECT GRADUAL CLEARING WEST TO EAST OVERNIGHT ONCE NW FLOW AND DOWNSLOPE DRYING TAKE OVER. THE UPPER LOW WILL SHIFT EAST OFF THE NC COAST SAT EVENING WITH HEIGHT RISES MAXIMIZED OVER SC AT 180+ M SAT NIGHT. MID LEVEL TEMPS WILL REMAIN RATHER COOL HOWEVER AS SHEARED VORTICITY STREAKING DOWN THROUGH NC ON THE WEST SIDE OF THE DEPARTING TROUGH DELAYS THE OFFSHORE KICK OF THE MEAN TROUGH UNTIL AFTER 12Z SUN... SO WE`RE LIKELY TO SEE LINGERING MID CLOUDS SAT NIGHT... CLEARING OUT OF THE WRN CWA LATE. WINDS SHOULD BE ON A STEADY DECREASING TREND OVERNIGHT BUT THE BOUNDARY LAYER WILL STAY STIRRED ENOUGH TO LIMIT FULL RADIATIONAL COOLING DESPITE THE CHILLY NATURE OF THE INCOMING AIR MASS AND ITS LOW DEWPOINTS. LOWS 33-38. A FEW OUTLYING SPOTS IN THE WRN CWA WILL LIKELY REACH 32F... BUT THIS SHOULD BE THE EXCEPTION RATHER THAN THE RULE. -GIH
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&& .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... AS OF 130 PM FRIDAY... FAIR BUT UNSEASONABLY COOL WEATHER IS EXPECTED ON SUNDAY AS HIGH PRESSURE BUILDS IN FROM THE WEST IN THE WAKE OF THE DEPARTING TROUGH. FORECAST SOUNDINGS AND CROSS SECTIONS SUGGEST A FEW LINGERING MID-LEVEL CLOUDS AT THE START OF THE DAY...BUT SKIES SHOULD BECOME MOSTLY SUNNY BY AFTERNOON GIVEN DRY NW FLOW. A LITTLE BREEZY STILL IN THE MORNING AND EARLY AFTERNOON WHILE THE HIGH IS BUILDING IN...UNTIL THE PRES GRADIENT RELAXES LATER IN THE DAY. LOW LEVEL THICKNESSES ARE PROGGED TO BOTTOM OUT ABOUT 50M BELOW AVERAGE...AROUND 1300M EARLY SUNDAY...RECOVERING TO 1315M BY LATE- DAY. THIS SUGGESTS HIGHS IN THE LOWER 50S...ABOUT 15 DEG BELOW NORMAL. HIGH PRESSURE IS THEN PROGGED TO BECOME CENTERED OVER THE CAROLINAS BY MONDAY MORNING. GIVEN THE AIRMASS IN PLACE...LIGHT WINDS UNDER THE HIGHS...AND MAINLY CLEAR SKIES...THE EXPECTATION IS STILL THERE THAT MOST OF OUR CWA WILL SEE A GROWING-SEASON-ENDING FROST OR FREEZE MONDAY MORNING. HOWEVER...WILL NEED TO KEEP A CLOSE WATCH FOR THE POTENTIAL FOR SOME OROGRAPHIC CIRRUS...GIVEN NW FLOW AND SOME MOISTURE SPILLING OVER THE MID RIDGE AXIS. WHILE CONFIDENCE IN THIS HAPPENING IS CUSTOMARILY LOW RIGHT NOW (3 DAYS OUT)...IF IT DOES MATERIALIZE...LOOKS LIKE IT WOULD BE MOSTLY ACROSS OUR FAR WESTERN ZONES...SO A DECENT FROST/FREEZE EVENT ACROSS MOST OF OUR CWA STILL LOOKS LIKELY. FOR NOW...WILL LEAVE LOWS AS-IS...RANGING FROM THE UPPER 20S WEST TO LOWER 30S EAST. && .LONG TERM /MONDAY THROUGH FRIDAY/... AS OF 130 PM FRIDAY... RIDGING AT SFC AND ALOFT WILL PROVIDE NICE WEATHER ACROSS CENTRAL NC MONDAY AND TUESDAY. THICKNESSES WILL CONTINUE MODERATING DURING THIS TIME...HOWEVER WITH THE SFC HIGH STILL CENTERED OVER US MONDAY NIGHT...LOOK FOR LOWS A COUPLE DEGREES BELOW NORMAL TUESDAY MORNING...UPPER 30S TO AROUND 40. HIGHS MONDAY AROUND 60 AND MID-UPR 60S ON TUESDAY. BY LATE TUESDAY...THE HIGH CENTER WILL MOVE OFF THE COAST...BUT THE RIDGE AXIS WILL REMAIN EXTENDED ACROSS THE CAROLINAS. WITH LOW LEVEL FLOW BECOMING MORE SWLY AND A THICKENING CANOPY OF CIRRUS WITH ENHANCED SW FLOW ALOFT OVER US...LOWS WEDNESDAY MORNING WILL BE WARMER...IN THE MID-UPR 40S. THE NEXT NORTHERN STREAM SHORT WAVE WILL BEGIN APPROACHING OUR REGION DURING THE DAY WEDNESDAY AND IT`S ASSOC COLD FRONT CROSSING CENTRAL NC LATE THURSDAY. THUS...WEDNESDAY WILL SEE INCREASING CLOUDINESS AND WARMING NICELY AHEAD OF THE FRONT...BUT REMAINING DRY. THE BEST CHANCE FOR ANY RAIN WITH THIS SYSTEM WILL BE ON THURSDAY ALONG AND JUST AHEAD OF THE FRONT...BUT MOISTURE PROFILES ACROSS OUR AREA ARE MODESTLY MOIST AT BEST...SO FOR NOW...WILL KEEP POPS LIMITED TO 20 PERCENT OR LESS ON THURSDAY. HIGHS CLIMBING ABOVE NORMAL (AROUND 70) FOR WEDNESDAY AND THURSDAY. RIGHT NOW...NEXT FRIDAY LOOKS TO BE BREEZY AND COOLER IN THE WAKE OF THE FRONT...WITH DECREASING CLOUDINESS THROUGH THE DAY. HIGHS COOLING BACK DOWN TO NEAR OR BELOW NORMAL FOR WEEKS END. && .CLIMATE... RECORD LO-MAX TEMPERATURES FOR NOVEMBER 1ST LO-MAX RDU 50/1925 GSO 45/1925 FAY 48/1988 && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... AS OF 1255 PM FRIDAY... PATCHES OF MVFR STRATOCU WILL LINGER AT INT/GSO DURING THE FIRST COUPLE OF HOURS OF THIS TAF FORECAST PERIOD... BUT THEN CIGS SHOULD LIFT TO VFR PRIOR TO 20Z. OTHERWISE... AT RDU/RWI/FAY... VFR CONDITIONS WILL DOMINATE THROUGH 00Z. WE`RE CURRENTLY IN GENERALLY TRANQUIL WEATHER BETWEEN LOW PRESSURE OFF THE OUTER BANKS AND A POWERFUL STORM SYSTEM OVER SW MI THAT WILL DIVE SOUTH THEN SE... CROSSING THE CAROLINAS LATE TONIGHT THROUGH SAT. CIGS ARE EXPECTED TO DROP TO MVFR ONCE AGAIN AT INT/GSO WITH PATCHY RAIN BETWEEN 00Z AND 02Z... FOLLOWED BY A DROP TO IFR/LIFR CIGS AND MVFR/IFR VSBYS IN STEADY RAIN MOST LIKELY STARTING 02Z-04Z THIS EVENING. EXPECT THESE SUB-VFR CONDITIONS (DOWN TO MVFR IN PATCHY RAIN THEN TO IFR/LIFR WITH MORE STEADY RAIN) TO SPREAD EAST INTO RDU BETWEEN 04Z AND 08Z TONIGHT... AND INTO RWI/FAY BETWEEN 08Z AND 12Z SAT MORNING. CIGS MAY REBOUND A BIT SAT MORNING BUT MVFR OR IFR CONDITIONS ARE LIKELY TO STILL PREVAIL AT ALL SITES AFTER 12Z SAT. CONCERN FOR BRISK GUSTY WINDS WILL INCREASE TOWARD THE END OF THE TAF VALID PERIOD... AFTER 13Z SAT... WHEN SURFACE WINDS MAINLY FROM THE NORTH WILL START TO INCREASE TO SUSTAINED 15-20 KTS GUSTING TO 25-30 KTS. LOOKING BEYOND 18Z SAT: STRONG GUSTY SURFACE WINDS WILL CONTINUE SAT AFTERNOON AND EVENING AS THEY SHIFT FROM NORTH TO NORTHWEST AS THE LOW STRENGTHENS OFF THE COAST. CIGS EXPECTED TO GRADUALLY RISE TO VFR AS RAIN CHANCES TAPER OFF AT INT/GSO 21Z-00Z AND 23Z-04Z SAT EVENING AT RDU/RWI/FAY... WITH WINDS DECREASING SLOWLY LATE SAT NIGHT INTO SUN MORNING. VFR CONDITIONS WILL THEN HOLD UNDER COLD HIGH PRESSURE THROUGH WED. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...HARTFIELD SHORT TERM...NP LONG TERM...NP CLIMATE...CBL AVIATION...HARTFIELD

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