Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 171917 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 215 PM EST WED DEC 17 2014 .SYNOPSIS...
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HIGH PRESSURE CENTERED OVER THE UPPER MISSISSIPPI VALLEY WILL GRADUALLY EXTEND INTO THE REGION TONIGHT AND FRIDAY. A STORM SYSTEM WILL DEVELOP OVER THE TEXAS GULF COAST FRIDAY... THEN STRENGTHEN AS IT TRACKS ACROSS THE SOUTHEAST STATES SATURDAY INTO SUNDAY.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 215 PM WEDNESDAY... LATEST SURFACE ANALYSIS SHOWS A 1032MB SURFACE HIGH PRESSURE SYSTEM CENTERED OVER THE UPPER MISSISSIPPI VALLEY THAT EXTENDED INTO MUCH OF THE SOUTHEAST U.S.. A WEST TO NORTHWEST LOW/MID FLOW BEHIND THE DEPARTING TROUGH HAS RESULTED IN A WEAK LEE TROUGH OVER THE FOOTHILLS/WESTERN PIEDMONT OF THE CAROLINAS AND VIRGINIA. LARGE SCALE SUBSIDENCE HAS RESULTED IN SUNNY SKIES EAST OF THE MOUNTAINS WITH THE EXCEPTION OF A FEW THIN CIRRUS CLOUDS. HIGH CLOUDS WILL INCREASE SOMEWHAT OVERNIGHT AS ENERGY LOCATED ACROSS TX/OK THIS AFTERNOON BEGINS TO LIFT EAST AND SHEARS OUT. NOT SURE HOW OPAQUE THE CLOUDINESS WILL BE BUT WE SHOULD BE ABLE TO SEE THE WANNING CRESCENT MOON FOR MOST OF THE OVERNIGHT WITH MAINLY CLEAR SKIES. GUIDANCE TEMPS IN GOOD AGREEMENT AND WILL FORECAST LOWS IN THE 31 TO 36 RANGE. -BLAES
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&& .SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
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AS OF 215 PM WEDNESDAY... MID LEVEL RIDGE AXIS APPROACHES EARLY ON THURSDAY AND GIVES WAY TO A SOUTHERN STREAM SHORTWAVE TROUGH THAT SLIDES BY ACROSS THE OH VALLEY AND THE MID ATLANTIC THURSDAY NIGHT. EXPECT FAIR WEATHER DURING THE PERIOD WITH A FAIRLY THICK VEIL OF HIGH AND ESPECIALLY MID LEVEL CLOUDINESS. GUIDANCE...ESPECIALLY THE GFS HAS BEEN HINTING AT SOME LIGHT PRECIP MAKING IT ACROSS THE MOUNTAINS INTO THE WESTERN PIEDMONT ON THURSDAY. RECENT RUNS HAVE BACKED OFF THIS AND WE EXPECT A DRY PERIOD AND HAVE LOWERED POPS. WITH A GOOD DEAL OF CLOUD COVER...HIGHS ON THURSDAY WILL SLOWLY REACH THE 48 TO 55 RANGE. LOOK FOR LESS VARIABILITY IN LOWS ON THURSDAY NIGHT WITH LINGER MID AND HIGH CLOUDS...LOWS SHOULD RANGE BETWEEN 32 AND 36 DEGREES. -BLAES
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&& .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 318 AM WEDNESDAY... FRIDAY...SFC RIDGE PROJECTED TO EXTEND NW-SE ACROSS THE REGION FROM A PARENT HIGH (1025MB +/-) OVER THE LOWER OH VALLEY. MEANWHILE ALOFT...WEAK S/W RIDGE WILL CROSS THE REGION. EXPECT THE DAY TO START OUT SUNNY/MOSTLY SUNNY BUT SHOULD SEE AN INCREASE IN HIGH LEVEL CLOUDINESS LATE IN THE DAY...ESPECIALLY WESTERN PIEDMONT...IN RESPONSE TO S/W TROUGH AND ATTENDANT SURFACE LOW DEVELOPING WELL TO OUR SW. LOW LEVEL THICKNESSES CLOSE TO NORMAL WHICH SUGGEST HIGH TEMPS AROUND 50 NORTH TO LOW-MID 50S SOUTH. FRIDAY NIGHT...CLOUDS WILL CONTINUE TO THICKEN/LOWER THROUGH THE NIGHT. ENOUGH ISENTROPIC UPGLIDE EXISTS SHORTLY BEFORE DAYBREAK TO INCLUDE A MENTION OF SPOTTY LIGHT RAIN OVER THE SW TWO-THIRDS OF THE CWA. PARTIAL THICKNESSES HOVERING IN VICINITY OF THE RAIN/FREEZING SECTOR OF THE WINTER P-TYPE NOMOGRAM OVER THE NW PIEDMONT. HOWEVER...MODEL GUIDANCE HAD BEEN TRENDING WARMER AND THE FREEZING LEVEL FAIRLY ELEVATED (6000-8000FT). WHILE SATURATION AND SIGNIFICANT LIFT NOTED IN THE FAVORED ICE NUCLEATION REGION OF THE ATMOSPHERE...LOW LEVEL AIR MASS CURRENTLY APPEARS TOO WARM FOR ANY WINTER P-TYPE AT THE ONSET OF THE PRECIP. WORSE CASE SCENARIO WOULD BE SOME WET SNOWFLAKES MIXING WITH THE RAIN WHEN THE PRECIP RATES ARE MODERATE/BRIEFLY HEAVY. MIN TEMPS GENERALLY MID 30S. SATURDAY...SFC DRY AIR RIDGE AND PARENT HIGH IN FAVORABLE LOCATION TO SUPPORT A COLD AIR DAMMING EVENT SATURDAY. THE NEAR SURFACE NE FLOW WILL ADVECT A COOL AIR MASS INTO OUR REGION. MEANWHILE 850- 700MB FLOW WILL PULL WARM GULF MOISTURE OVER THE COOL STABLE NEAR SURFACE AIR MASS RESULTING IN WIDESPREAD RAIN. LIFT APPEARS BEST IN THE MORNING THROUGH EARLY AFTERNOON WITH LIFT WANING IN THE WEST BY MID AFTERNOON. THE COOL SFC AIR MASS COMPOUNDED BY THE RAIN WILL HOLD TEMPS AT OR BELOW 40 DEGREES ACROSS THE NW PIEDMONT...AND IN THE 40S PRETTY MUCH ELSEWHERE. SATURDAY NIGHT...AREAS OF RAIN WILL GRADUALLY TAPER TO SPOTTY LIGHT RAIN WITH AREAS OF DRIZZLE AS MAIN LIFT MOVES AWAY FROM OUR REGION AS S/W DAMPENS TO OUR EAST. LOW LEVEL AIR MASS EXPECTED TO REMAIN NEARLY SATURATED SO WILL LIKELY KEEP LOW CLOUDS ALL NIGHT. MIN TEMPS MID-UPPER 30S. SUNDAY THROUGH TUESDAY...L/W TROUGH TO OUR WEST AMPLIFIES THIS PERIOD AS A SUBSTANTIAL S/W DIGS ON THE BACK SIDE OF THE TROUGH. THIS WILL MAINTAIN A SW FLOW ALOFT OVER CENTRAL NC. WITH A LACK OF A MECHANISM TO SCOUR OUR THE CAD AIR MASS AND CONTINUED SW FLOW ALOFT...COULD SEE A SET UP FOR A PERIOD OF CLOUDINESS SUNDAY THROUGH TUESDAY ACROSS CENTRAL CN WITH PATCHES OF LIGHT RAIN AND/OR DRIZZLE SUNDAY AND POSSIBLY INTO MONDAY. MAY SEE SOME IMPROVEMENT LATE MONDAY INTO TUESDAY THOUGH MAY BE TRADING IN LOW CLOUDS FOR A DECK OF MID-HIGH LEVEL CLOUDS. OVERALL EXPECT MORE CLOUDS THAN SUN THIS PERIOD. HIGH TEMPS WILL AVERAGE 3-5 DEGREES BELOW NORMAL WHILE MIN TEMPS WILL AVERAGE NEAR OR SLIGHTLY ABOVE NORMAL (TYPICAL FOR CLOUDY CONDITIONS). && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... AS OF 115 PM WEDNESDAY... HIGH CONFIDENCE IN FAVORABLE AVIATION CONDITIONS THROUGH THURSDAY... WITH VFR CONDITIONS DOMINATING AND WEAK LOW LEVEL WINDS. HIGH THIN CLOUDS NOW OVER THE AREA WILL SLOWLY THICKEN AND LOWER THROUGH THURSDAY... AS MID LEVEL CLOUDS BEGIN TO SPREAD IN FROM THE WEST... DUE TO STRONG UPPER LEVEL WINDS FROM NRN MEXICO ACROSS TX AND THE GULF/SOUTHEAST STATES. BUT CIGS WILL REMAIN VFR THROUGH THE TAF VALID PERIOD AS SURFACE HIGH PRESSURE EXTENDS OVER THE AREA. LOOKING BEYOND 18Z THU... VFR CONDITIONS WILL HOLD THROUGH FRI EVENING WITH PERIODS OF MID AND HIGH CLOUDS AND VFR VSBYS... BUT POOR AVIATION CONDITIONS ARE EXPECTED FROM SAT THROUGH MON. A STORM SYSTEM WILL FORM OVER THE TX GULF COAST LATE FRI... WITH LOW PRESSURE STRENGTHENING AS IT TRACKS EAST ACROSS THE SOUTHERN GULF STATES SATURDAY... TO ALONG OR JUST OFF THE SOUTHEAST COAST SAT NIGHT AND SUN. WIDESPREAD RAIN WITH SUB-VFR CONDITIONS APPEAR LIKELY FROM EARLY SAT MORNING (POTENTIALLY BEFORE DAYBREAK) THROUGH SAT. RAIN WILL TAPER TO PATCHY LIGHT DRIZZLE FOR SAT NIGHT THROUGH AT LEAST SUN NIGHT WITH SUB-VFR CONDITIONS PERSISTING. LOW CIGS COULD HOLD THROUGH MON AS WELL. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...BLAES NEAR TERM...BLAES SHORT TERM...BLAES LONG TERM...WSS AVIATION...HARTFIELD

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