AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC ISSUED BY NATIONAL WEATHER SERVICE WAKEFIELD VA 314 PM EST WED NOV 20 2013 .SYNOPSIS... HIGH PRESSURE WILL REMAIN CENTERED OVER THE NORTHEAST STATES TONIGHT WITH A RIDGE EXTENDING DOWN INTO THE MID ATLANTIC. THE HIGH SLIDES OFFSHORE THURSDAY INTO THURSDAY NIGHT. A COLD FRONT WILL APPROACH FROM THE NORTHWEST ON FRIDAY AND CROSS THE AREA ON SATURDAY. HIGH PRESSURE THEN RETURNS EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... AS OF 3 PM WEDNESDAY... LATEST SFC ANALYSIS REVEALS 1036 MB HI PRES CENTERED OVR UPSTATE NY...WITH ASSOCIATED RIDGING EXTENDING DOWN THRU THE CNTRL CAROLINAS. THIS AREA OF HI PRES WILL REMAIN IN PLACE TNGT LEADING TO LGT NE FLOW AND A WEAK COLD AIR DAMMING (CAD) SETUP. ALOFT...A WEAK MID-LEVEL RIDGE BLDS OVER THE FAR ERN CONUS AS MID-LEVEL S/W TROFS TRAVERSE THE CNTRL PLAINS AND GREAT LAKES REGIONS. RESULTANT NERLY LO-LEVEL FLOW AND CAD SCENARIO WILL LEAD TO SLGTLY BLO NORMAL TEMPS TNGT AND PATCHY -DZ OVER WRN AREAS AS THE SFC-H8 LAYER WILL BE QUITE MOIST DESPITE MARGINAL LIFT. NAM CONTINUES TO FAVOR PRECIP MORE THAN OTHER GUIDANCE...HOWEVER THE 12Z RUN HAS BACKED OFF A BIT FROM THE PREVIOUS RUN. OTHERWISE...MSTLY CLOUDY TNGT WITH LO TEMPS RANGING FROM THE MID 30S NW TO LWR 40S SE. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/... AS OF 3 PM WEDNESDAY... SHORT-TERM PERIOD STARTS OFF THU WITH THE CENTER OF SFC HI PRES OVER SRN NEW ENGLAND SLIDING OFFSHORE WHILE A RIDGE STAYS EXTENDED DOWN THRU THE MID ATLANTIC. MODELS CONTINUE TO SIGNAL FOR A WEAK CAD...MORE SO IF LIGHT PRECIP FALLS INTO THE WESTERN PIEDMONT THURSDAY MORNING. NEAR SFC NE FLOW WILL QUICKLY VEER IN THE 925-850MB LAYER TO THE S-SW...MAINTAINING A FAIRLY STRONG LOW- LEVEL INVERSION AND TRAPPING THE MOISTURE. FAVORED MAX TEMPS ON THE COOL SIDE OF GUIDANCE...ESPECIALLY IN THE NW. IF SPOTTY LIGHT PRECIP BREAKS OUT...THERE IS POTENTIAL FOR MAX TEMPS IN THE NW PIEDMONT TO REMAIN BELOW 50 DEGREES. LITTLE CHANGE IN CONDITIONS THURSDAY NIGHT WITH A SLIGHTLY BETTER CHANCE FOR SPOTTY LIGHT PRECIP. HAVE MAINTAINED A SLIGHT CHANCE FOR LIGHT RAIN FOR MOST OF CENTRAL NC THURSDAY NIGHT. HIGH TEMPS THURSDAY LWR 50S NW TO NEAR 60 SE. MIN TEMPS THURSDAY NIGHT LWR 40S FAR NORTH TO MID 40S ELSEWHERE. HIGH PRESSURE IS EXPECTED TO BE LOCATED OFF THE MID-ATLANTIC ON FRIDAY MORNING... WITH A STILL MOIST EAST TO SOUTHEASTERLY LOW LEVEL FLOW (925 MB OR SO). THUS... THINK WE SHOULD START THE DAY MOSTLY CLOUDY TO OVERCAST ACROSS THE AREA... WITH POSSIBLY SOME PATCHY DRIZZLE AND/OR LIGHT RAIN ACROSS CENTRAL NC. THE BIG QUESTION IS HOW QUICKLY CAN WE ERODE THIS LOW CLOUD COVER AND SEE INCREASING SOUTHERLY FLOW ACROSS THE AREA. THE NAM IS STILL MORE AGGRESSIVE IN SHOWING IMPROVING AND WARMING CONDITIONS FOR FRIDAY (MET HI TEMP FOR RDU IS 72). WILL STILL REMAIN BELOW GUIDANCE FOR HIGHS WITH MOSTLY CLOUDY SKIES HOLDING FOR MOST OF THE DAY. THIS YIELDS HIGH TEMPS LWR 60 NW TO UPPER 60S AROUND 70 SE. THE NEXT SURFACE COLD FRONT IS EXPECTED TO CROSS THE AREA ON SATURDAY (13-17Z TIME FRAME). THE MAIN DYNAMICS ARE AGAIN EXPECTED TO PASS TO THE NORTH OF THE AREA AS A STRONG S/W CROSSES THE GREAT LAKES. LOW LEVEL FLOW IN ADVANCE OF THE FRONT IS FORECAST TO BECOME MORE WESTERLY. THUS...MODEL GUIDANCE HAS STAYED FAIRLY DRY ALONG AND BEHIND THE FRONT. POPS ARE LOW END CHANCE FOR NOW. WITH GOOD DOWNSLOPE FLOW BEHIND THE FRONT AND MAYBE EVEN SOME CLEARING LATE IN THE DAY... STILL THINK WE WILL SEE HIGH TEMPS IN THE 60S AREAWIDE. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... AS OF 3PM WEDNESDAY... SUNDAY AND MONDAY: MODELS ARE IN GOOD AGREEMENT PUSHING THE NEXT SURGE A VERY COLD AIR INTO THE REGION LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING. THE COLD FRONT WILL HAVE LIKELY PUSHED OFFSHORE BY 00Z SUNDAY AND ANY LINGERING LIGHT RAIN SAT EVENING SHOULD BE OVER THE EASTERN COASTAL PLAIN AND COAST QUICKLY MOVING OFFSHORE. AS THE 1050 MB HIGH BUILDS SOUTH INTO THE MIDWEST...STRONG CAA WILL KICK IN ACROSS THE REGION BETWEEN 06Z AND 12Z SUN. EXPECT BREEZY CONDITIONS AND RAPIDLY FALLING TEMPERATURES WITH THE SURGE PRIOR TO DAYBREAK SUNDAY. EXACTLY HOW COLD LOWS ARE SUN MORNING WILL BE DETERMINED BY EXACTLY WHEN THE COLD AIR SURGE MOVES IN. STILL...EXPECT LOWS SUNDAY MORNING AROUND 30 INTO THE LOWER 30S HOWEVER GUSTY CONDITIONS WILL MAKE IT FEEL MUCH COLDER DUE TO WIND CHILLS. BREEZY CONDITIONS PERSIST THROUGH THE DAY SUNDAY ALONG WITH STRONG CAA. DESPITE NEARLY FULL SUNSHINE HIGHS SUNDAY WILL STRUGGLE TO WARM TO NEAR 40. WINDS WILL SLOWLY DECREASE SUNDAY AFTERNOON AS THE HIGH SETTLES IN FROM NE AND THE PRES GRAD RELAXES. BY SUNDAY NIGHT/MONDAY MORNING THE HIGH WITH VERY DRY AIR AND CALM WINDS WILL BE IN PLACE ALLOWING MORNING TO DROP WELL INTO THE 20S (LOW TO MID 20S) ACROSS ALL OF CENTRAL NC. BY MONDAY SKIES WILL REMAIN CLEAR AND CONDITIONS CALM. AFTERNOON HIGH WILL WARM SLIGHTLY COMPARED TO SUNDAY BUT REMAIN IN THE MID 40S. THE LACK OF WIND AND FULL SUN WILL MAKE CONDITIONS FEEL A BIT WARMER COMPARED TO SUNDAY. TUESDAY AND WEDNESDAY: THE SURFACE HIGH MOVES OFFSHORE TUE AS MODELS DEVELOP AND AREA OF LOW PRESSURE OVER THE NORTH CENTRAL GULF. MODELS DIFFER WITH THE HANDLING OF THIS SYSTEM IN THE EXTENDED...BUT DO AGREE THERE WILL BE INCREASING MOISTURE WITH THE SOUTHERLY FLOW LATE TUE INTO WED. HOW THE SYSTEM PHASES/INTERACTS WITH THE RELOADING NORTHERN STREAM TROUGH ACROSS THE EAST U.S. WILL HAVE GREAT IMPACTS ON THE FORECAST FOR TUESDAY INTO WEDNESDAY ACROSS THE REGION... WITH POSSIBLY A COASTAL SYSTEM AND A GOOD CHANCE OF RAIN/SHOWERS. EXPECT CONTINUED BELOW NORMAL TEMPS DURING THIS TIME... WITH INCREASING ODDS FOR PRECIP FROM LATE TUE INTO EARLY WED. THE NEXT COLD AIR SURGE WILL MOVE IN FROM THE NW BEHIND THIS SYSTEM WED NIGHT. && .AVIATION /20Z WEDNESDAY THROUGH MONDAY/... AS OF 2PM WEDNESDAY... AN AREA OF HIGH PRESSURE WILL MAINTAIN ITS INFLUENCE ACROSS CENTRAL NC THROUGH EARLY FRIDAY. WHILE VFR CONDITIONS CAN BE EXPECTED THROUGH EARLY AFTERNOON. WIDESPREAD BKN045 WILL PERSIST FROM RDU EAST ACROSS THE COASTAL PLAIN. EAST- NORTHEAST IN THE FLOW LEVELS IS MAINTAINING NE WINDS AT THE SURFACE AROUND 10KT WHILE EAST TO SE WINDS AT 4KFT IS ADVECTING MOISTURE FROM THE ATLANTIC. THIS MID LEVEL MOISTURE IS SPREADING TO RDU BUT SHOULD REMAIN EAST OF GSO AND INT THROUGH THE AFTERNOON. LATER TONIGHT WILL SEE AN INCREASE THREAT FOR A BROKEN TO OVERCAST DECK TO OCCUR WITH LOW END MVFR CEILINGS WITH A A PERIOD (2-4 HOURS) OF IFR CEILINGS BETWEEN 09Z- 13Z. SOME LIGHT DRIZZLE WILL ALSO BE POSSIBLE FOR JUST A BRIEF PERIOD AROUND DAYBREAK. FOR THURSDAY INTO THURSDAY NIGHT...MVFR- LOW END VFR CEILINGS BETWEEN 2500-3500FT WILL LIKELY OCCUR. THESE CEILINGS MAY PERSIST INTO FRIDAY. LOOKING AHEAD...A COLD FRONT WILL APPROACH FROM THE NW LATE FRIDAY AND CROSS CENTRAL NC SATURDAY. THIS FRONTAL SYSTEM WILL BRING A THREAT FOR SHOWERS...ESPECIALLY SATURDAY AFTERNOON WITH CONTINUED MVFR CONDITIONS DUE TO CEILINGS. COLDER AND DRIER AIR WILL OVERSPREAD THE REGION SATURDAY NIGHT INTO SUNDAY LEADING TO VFR CONDITIONS. IT WILL BE BREEZY SUNDAY WITH FREQUENT GUSTS 20-25KTS. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. &&
Posted on: Wed, 20 Nov 2013 21:44:34 +0000
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