Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 280225 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 920 PM EST SAT DEC 27 2014 .SYNOPSIS...HIGH PRESSURE OVER THE EASTERN CAROLINAS WILL MOVE OFFSHORE OVERNIGHT. A COLD FRONT WILL APPROACH FROM THE NORTHWEST ON SUNDAY... THEN PUSH SLOWLY SOUTHEAST THROUGH THE AREA MONDAY AND MONDAY NIGHT. HIGH PRESSURE WILL BUILD IN FROM THE WEST LATE TUESDAY THROUGH THURSDAY. && .NEAR TERM /TONIGHT THROUGH SUNDAY/... AS OF 920 PM SATURDAY... SATELLITE CLOUD TRENDS SUPPORT EARLIER EXPECTATIONS OF CLOUDS OVERSPREADING CENTRAL NC FROM THE WEST AND SW... WITH CLOUDS STEADILY THICKENING AND LOWERING OVERNIGHT. THIS IS EXHIBITED WELL BY A COMPARISON OF THE 00Z GSO SOUNDING WITH UPSTREAM SOUNDINGS... WITH DRY AIR NEAR 500 MB AND BELOW 700 MB AND A PW NEAR 0.6 IN AT GSO... WHEREAS UPSTREAM LOCATIONS INCLUDING THE FFC AND BMX SOUNDINGS ARE MUCH WETTER THROUGH THE COLUMN... WITH PW VALUES 1.0- 1.5 IN... OVER 200% OF NORMAL... WHICH IS POISED TO ADVECT INTO NC. THE DEEPEST MOISTURE WAS OBSERVED OVER CENTRAL/SRN AL INTO CENTRAL GA... ASSOCIATED WITH A WEAK VORTICITY MAXIMUM... AND THIS IS ALSO WHERE REGIONAL RADAR SHOWS EXPANSIVE RAIN -- SOME OF IT MODERATE -- SPREADING TOWARD SOUTH CENTRAL NC... ALTHOUGH THE NE PROGRESSION OF THIS RAIN IS HINDERED BY INITIAL EVAPORATION ON ITS NE EDGE. NEVERTHELESS... RADAR TRENDS SUGGEST THAT THE SOUTHERN HALF OF THE CWA MAY SEE MEASURABLE RAIN FIRST... SIMILAR TO THE LATEST HRRR AND WRF-ARW RUNS. WE ALSO HAVE MUCH LOWER SURFACE DEWPOINTS IN THE NORTHERN CWA (UPPER 30S) AS COMPARED TO THE SOUTHERN AND EXTREME ERN CWA (LOW 40S)... AND THESE LOWER DEWPOINTS WILL TAKE LONGER TO BE OVERCOME. BASED ON THIS... HAVE MADE MINOR ADJUSTMENTS TO RAISE POPS A BIT LATE TONIGHT OVER THE SOUTH WITH A SMALL DOWNWARD TWEAK OF POPS IN THE NORTHWEST/NORTH CENTRAL... AND NO POPS NORTHEAST OF RALEIGH OVERNIGHT. MUCH OF WHAT WILL INITIALLY BE SEEN ON RADAR IN CENTRAL NC IS APT TO EVAPORATE PRIOR TO HITTING THE GROUND... BUT STILL EXPECT A LOW CHANCE OF MEASURABLE AMOUNTS TO SPREAD INTO THE SW CWA SOON AFTER MIDNIGHT... THEN EXPAND INTO THE REST OF THE WRN AND SRN CWA AFTER 3 AM. AMOUNTS WILL BE VERY LIGHT... A FUNCTION OF THE WEAK FORCING FOR ASCENT. AS ANTICIPATED EARLIER... TEMPS FELL MOST SOON AFTER NIGHTFALL AND HAVE LEVELED OFF SOMEWHAT... AND THE ENCROACHMENT OF CLOUDS WILL FURTHER BLANKET THE CWA OVERNIGHT... LIMITING TEMP FALL. EXPECT LOWS TO RANGE FROM THE LOWER 40S (NE) TO UPPER 40S (WEST). -GIH EARLIER DISCUSSION FROM 255 PM: LATEST SURFACE ANALYSIS SHOWS AN AREA OF SURFACE HIGH PRESSURE CENTERED NEAR THE NC/SC COAST ALONG THE COASTAL CAROLINAS AND VIRGINIA. A POSITIVELY TILTED DEAMPLIFYING UPPER TROUGH ACROSS THE WESTERN PLAINS AT MIDDAY TODAY WILL CONTINUE TO SHIFT SLOWLY EAST TODAY AND TONIGHT. THE NORTHERN PORTION OF THE TROUGH ASSOCIATED WITH THE NORTHERN JET STREAM WILL SHEAR EAST INTO THE EASTERN GREAT LAKES WHILE BY LATE SUNDAY AFTERNOON. THE SOUTHERN EXTENT OF THE TROUGH IS SHARPER AND MOVES SLOWLY EAST REACHING THE ARKLATEX BY SUNDAY EVENING. THE ASSOCIATED COLD FRONT WHICH EXTENDS FROM MICHIGAN SOUTHWEST TO EASTERN TX AT MIDDAY TODAY WILL MOVE EAST REACHING EASTERN PA AND NORTHWEST GA BY LATE SUNDAY AFTERNOON. MAINLY CLEAR SKIES ACROSS CENTRAL NC THIS AFTERNOON WILL GIVE WAY TO INCREASING HIGH AND MID CLOUDINESS THIS EVENING AS MOISTURE BEGINS TO INCREASE AHEAD OF THE FRONT. WHILE HIGH AND MID LEVEL CLOUDINESS WILL THICKEN OVERNIGHT... NAM/GFS/SREF BUFR SOUNDINGS ALL NOTE THAT THE LOWER THIRD OF THE TROPOSPHERE IS SLOW TO MOISTEN OVERNIGHT UNTIL LOW LEVEL MOISTURE SURGES INTO THE REGION FROM THE SOUTHWEST TOWARD DAYBREAK SUNDAY. THE PRECIPITATION IS LARGELY DRIVEN BY ISENTROPIC LIFT AROUND THE 295K SURFACE WITH THE BEST SURGE OF LIFT SKIRTING ACROSS THE NORTHWESTERN EDGE OF CENTRAL NC AND WILL ADVERTISE LOW CATEGORICAL POPS THERE. FORCING FOR ASCENT DECREASES TO THE SOUTH AND EAST ON SUNDAY WITH LOW CHANCE POPS ADVERTISED FOR THE SANDHILLS AND SOUTHERN COASTAL PLAIN. SO SUNDAY WILL FEATURE CLOUDY SKIES ACROSS CENTRAL NC IT WONT BE WASHOUT FOR EVERYONE. MAINLY SPOTTY LIGHT RAIN IS EXPECTED TO THE SOUTH AND SOUTHEAST OF RALEIGH WITH THE MOST WIDESPREAD RAIN EXPECTED NEAR AND ESPECIALLY TO THE NORTHWEST OF INTERSTATE 85. TEMPERATURES WILL BE A LITTLE TRICKY AS THEY WILL TEND TO FALL QUICKLY THIS EVENING AFTER SUNSET BUT THE OVERNIGHT TREND WILL BE COMPLICATED BY THE INCREASING MID AND HIGH CLOUDS AND THE LIGHT SOUTHERLY STIRRING AHEAD OF THE APPROACHING COLD FRONT. WILL FORECAST LOWS IN THE MID 40S WEST TO LOWER 40S EAST. HIGHS ON SUNDAY WILL BE COMPLICATED BY TE PRECIPITATION WHICH SHOULD KEEP HIGHS IN THE MID 50S ACROSS THE NORTHWEST PIEDMONT WITH MID 60S ACROSS THE SANDHILLS AND SOUTHERN COASTAL PLAIN WHERE THE RAIN WILL BE MORE SCATTERED. -BLAES && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... AS OF 330 PM SATURDAY... SUNDAY NIGHT...DEEP SW FLOW WILL MAINTAIN A MOIST AIR MASS ACROSS CENTRAL NC SUNDAY NIGHT INTO MONDAY MORNING. A STOUT DISTURBANCE ALOFT WILL APPROACH IN THE SW FLOW LATE SUNDAY AND CROSS OUR REGION EARLY MONDAY. MEANWHILE CENTRAL NC WILL BE IN THE RIGHT ENTRANCE REGION OF A 130-150KT JET. THE ENHANCED LIFT SUPPLIED BY BOTH THE JET AND THE APPROACHING DISTURBANCE INTERACTING WITH AN ABNORMALLY MOIST AIR MASS (PRECIP WATER VALUES PROJECTED TO BE 1-1.2 INCHES) WILL CAUSE RAIN TO BECOME WIDESPREAD LATE SUNDAY NIGHT INTO EARLY MONDAY. MIN TEMPS UPPER 40S FAR NORTH TO THE LOW-MID 50S FAR SOUTH. MONDAY... WIDESPREAD RAIN WILL DIMINISH IN COVERAGE AND INTENSITY BY MID DAY-EARLY AFTERNOON AS THE UPPER LEVEL DISTURBANCE AND THE JET DEPART OUR REGION. WHILE THE MID-UPPER LEVELS OF THE ATMOSPHERE WILL DRY OUT...SW FLOW IN THE 925-850MB LAYER WILL MAINTAIN SATURATION RESULTING IN OVERCAST SKIES WITH SPOTS OF RAIN AND/OR DRIZZLE. SURFACE COLD FRONT WILL DRAG SOUTHWARD ACROSS THE REGION AS THE UPPER DISTURBANCE PULLS OUT TO THE EAST-NE. A SHALLOW COLD AIR AIR MASS WILL INFILTRATE OUR REGION FROM THE NORTH. THIS SHOULD LEAD TO FALLING TEMPS BY LATE MORNING ACROSS THE NORTH...AND THE AFTERNOON ACROSS THE SOUTH. MONDAY NIGHT INTO TUESDAY...850MB TROUGH PROJECTED TO REMAIN WEST OF OUR REGION UNTIL MID DAY TUESDAY. THIS SUGGEST A CONTINUATION IN EXTENSIVE CLOUDINESS AND PATCHY LIGHT RAIN/DRIZZLE THROUGH THE MAJORITY OF MONDAY NIGHT. PASSAGE OF 850MB TROUGH AND ENSUING W-NW FLOW IN ITS WAKE ALONG WITH SUBSIDENCE WILL AID TO DISSIPATE CLOUD COVERAGE WEST-TO-EAST TUESDAY AFTERNOON. LOW LEVEL COLD AIR ADVECTION WILL RESULT IN A SMALLER THAN NORMAL DIURNAL TEMP RECOVERY. MIN TEMPS MID-UPPER 40S NORTH TO LOWER 40S SOUTH. MAX TEMPS TUESDAY MID 40S NORTH TO NEAR 50 SOUTH. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... AS OF 330 PM SATURDAY... WEDNESDAY THROUGH SATURDAY... A BROAD UPPER LEVEL TROUGH WILL COVER THE BULK OF THE U.S. THIS PERIOD WITH A CLOSED UPPER LEVEL LOW PROJECTED TO EDGE SLOWLY EAST ACROSS THE SW U.S-SOUTHERN ROCKIES. MODEL GUIDANCE TRADITIONALLY HAVE TROUBLE TIMING THE MOVEMENT OF THESE CLOSED LOWS INT EH SW. USUALLY...SLOWER IS BETTER. FOR CENTRAL NC...EXPECT DRY CONDITIONS THROUGH AT LEAST FRIDAY AND POSSIBLY INTO SATURDAY WITH TEMPS BELOW NORMAL AT MID WEEK...MODERATING TO NEAR NORMAL LEVELS BY THE WEEKEND. A S/W WILL CROSS THE MID ATLANTIC LATE WEDNESDAY-WEDNESDAY NIGHT...ACCOMPANIED BY A DRY SFC FRONT PASSAGE. FLOW BEHIND THIS FEATURE WILL REINFORCE THE COOL AIR IN PLACE. MAX TEMPS WILL AVERAGE 4-6 DEGREES BELOW NORMAL WEDNESDAY-FRIDAY WHILE OVERNIGHT LOWS IN THE 20S WILL BE COMMON. TIMING DIFFERENCES IN THE MODELS BY NEXT WEEKEND PLAY HAVOC WITH PRECIP CHANCES AND TEMP FORECAST. PERSISTENT WLY FLOW SHOULD LEAD TO MODIFICATION OF THE AIR MASS...LEADING TO TEMPS AT OR ABOVE NORMAL. IF PRECIP DELAYED UNTIL LATE SATURDAY OR SATURDAY NIGHT...POTENTIAL FOR TEMPS TO BE WELL ABOVE NORMAL. && .AVIATION /00Z SUNDAY THROUGH WEDNESDAY/... AS OF 630 PM SATURDAY... 24-HOUR TAF PERIOD: FAIRLY CONFIDENT THAT VFR CONDITIONS WILL PREVAIL THROUGH AT LEAST MIDNIGHT TONIGHT...AS CLOUD COVER CONTINUES TO INCREASE FROM THE WEST-SOUTHWEST. WILL SEE LOWERING CIGS FROM MIDNIGHT THROUGH SUNRISE SUNDAY AS THE RAIN APPROACHES FROM THE WEST- SOUTHWEST. THERE IS POTENTIAL FOR CIGS BELOW 1000 FT TO DEVELOP AFTER 10Z AS THE RAIN MOVES INTO THE AREA...BUT FOR NOW WILL KEEP THOSE CLOUDS SCATTERED WITH GENERALLY MVFR/IFR CIGS AND VISBYS THROUGH THE DAY SUNDAY. THE BEST SUPPORT FOR PRECIPITATION WILL OCCUR ACROSS NORTHWESTERN NC (KINT AND KGSO) WITH THE AMOUNT... DURATION AND LIKELIHOOD OF PRECIP DECREASING TOWARD THE SOUTHEAST. AVIATION CONDITIONS WILL LIKELY BE A LITTLE BETTER BUT STILL REDUCED TO THE EAST AT KRDU AND KRWI AND SHOULD BE BETTER FURTHER SOUTH AND EAST AT KFAY. WINDS WILL BE MAINLY SOUTHWEST AT 5-10 KTS THROUGH THE PERIOD. -KC LOOKING AHEAD: ANOTHER AREA OF RAIN ASSOCIATED WITH THE COLD FRONT AND A SURFACE WAVE MOVES ACROSS THE AREA LATE SUNDAY NIGHT AND MONDAY. LINGERING LOW CLOUDS AND DRIZZLE WILL CONTINUE MONDAY NIGHT INTO TUESDAY BEFORE CONDITIONS IMPROVE LATER TUESDAY WITH FAIR WEATHER EXPECTED ON WEDNESDAY. -BLAES && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...HARTFIELD/BLAES SHORT TERM....WSS LONG TERM...WSS AVIATION...KC/BLAES

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