AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 658 AM EST FRI DEC 5 2014 .SYNOPSIS...HIGH PRESSURE WILL EXTEND DOWN THE EAST COAST UNTIL AN UPPER LEVEL DISTURBANCE AND ASSOCIATED SURFACE FRONTAL SYSTEM MOVE ACROSS OUR REGION SATURDAY AND SATURDAY NIGHT. && .NEAR TERM /THROUGH TONIGHT/... AS OF 325 AM FRIDAY... HIGH PRESSURE OVER NC THIS MORNING WILL REMAIN SO TODAY. VEERING LOW- MID LEVEL WINDS...INDICATIVE OF THE WARM ADVECTION REGIME ATOP THE COOLER AND STABLE AIR ASSOCIATED WITH THE PARENT 1037 MB ARCTIC HIGH OVER THE NORTHEAST...WILL CONTINUE TO STREAM THE BRUNT OF THE LOW (MVFR RANGE) CLOUDINESS AND A PATCH OR TWO OF LIGHT RAIN...ACROSS THE WESTERN CAROLINAS...INCLUDING THE WESTERN NC PIEDMONT...TODAY. MEANWHILE...A SEPARATE AREA OF MID LEVEL CLOUDS (MOSTLY BETWEEN 8-12 K FT) ARE FORECAST TO DIMINISH WITH THE DEPARTURE OF A LOW AMPLITUDE WAVE ALOFT OFF THE MID-ATLANTIC COAST THIS MORNING. AS SUCH...A MIX OF SUN AND CONSIDERABLE HIGH CLOUDS WILL RESULT OVER MOST OF CENTRAL NC TODAY...WITH THE MORE PERVASIVE LOW CLOUDINESS HOLDING OVER THE WESTERN PIEDMONT. TEMPERATURES WILL CONSEQUENTLY DISPLAY A LARGER THAN AVERAGE RANGE...FROM AROUND 50 DEGREES NW TO NEAR 60 IN THE COASTAL PLAIN. TONIGHT: A PAIR OF CLOSELY-SPACED SHORTWAVE TROUGHS THIS MORNING... ONE OVER NW OKLAHOMA AND THE OTHER OVER NEW MEXICO...WILL TRACK EAST INTO THE CENTRAL APPALACHIANS AND TN VALLEY...RESPECTIVELY...BY SAT MORNING. WHILE THE APPROACH OF THESE FEATURES WILL CAUSE MID-HIGH CLOUDINESS TO THICKEN AND LOWER AREA-WIDE...THE DEEPER AND LOWER LEVEL MOISTENING AND LIFT...SUPPORTIVE OF AREAS OF LIGHT RAIN OR DRIZZLE...WILL BE DIRECTED INTO THE WESTERN PIEDMONT BY A LLJ ACCOMPANYING THE AFOREMENTIONED WAVES ALOFT. LOWS WILL LIKELY BE WIDE-RANGING WITH MOST IN THE MIDDLE TO UPPER 40S...BUT CALM WITHIN THE SURFACE RIDGE WILL PROVIDE AN OPPORTUNITY FOR STRONGER RADIATIONAL COOLING TO AROUND 40 DEGREES WHERE/WHEN THINNER CLOUDS PREVAIL...MOST LIKELY LATE THIS EVENING-AROUND MIDNIGHT. PATCHY FOG AND/OR VERY LOW STRATUS WILL BE POSSIBLE IN THOSE AREAS. && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... AS OF 345 AM FRIDAY... NWP GUIDANCE SUGGESTS ADDITIONAL SHORTWAVE ENERGY INITIALLY OVER THE INTERMOUNTAIN WEST WILL AMPLIFY...PHASE WITH...AND RE-ENERGIZE THE SHORTWAVE TROUGH OVER NEW MEXICO THIS MORNING. THE PHASED SHORTWAVE TROUGH IS THEN FORECAST TO FURTHER AMPLIFY FROM THE TN VALLEY TO THE SOUTH ATLANTIC COAST THIS PERIOD. ACCOMPANYING 50-80 METER/12HR HEIGHT FALLS AND SUBSTANTIAL COOLING ALOFT WILL OVERSPREAD A SOUTHWESTERLY LLJ. STRONG DIFFERENTIAL THERMAL ADVECTION WILL CAUSE RAPID STEEPENING OF 850-500 MB LAPSE RATES...COINCIDENT WITH MODEST LIFT...SUCH THAT NUMEROUS TO WIDESPREAD SHOWERS AND EVEN A FEW ISOLATED THUNDERSTORMS WILL SPREAD EAST ACROSS CENTRAL NC SAT AFTERNOON...AFTER ONGOING/CONTINUED EARLY MORNING LIGHT RAIN AND DRIZZLE OVER THE WESTERN PIEDMONT. THAT LIGHT RAINA ND DRIZZLE...AND WIDESPREAD LOW OVERCAST...WILL LIKELY KEEP THE NW PIEDMONT WEDGED IN...AROUND 50 DEGREES...WHILE AREAS TO THE EAST CLIMB WELL INTO THE 60S. THOUGH SHOWERS AND ISOLATED STORMS WILL MOVE EAST WITH THE PASSAGE OF AN OCCLUDED/COLD FRONT DURING THE EVENING...THE DEEPENING OF A SURFACE LOW AS IT MOVES OFFSHORE WILL MAINTAIN A MOIST NNE FLOW THAT WILL LIKELY RESULT IN CONSIDERABLE LOW OVERCAST AND AREAS OF LIGHT RAIN OR DRIZZLE...WHICH WILL ONLY SLOWLY EDGE EASTWARD THROUGH SUN MORNING. LOWS AGAIN MOSTLY IN THE LOWER TO MIDDLE 40S. && .LONG TERM /SUNDAY THROUGH THURSDAY/... AS OF 300 AM THURSDAY... CONFIDENCE REMAINS BELOW AVERAGE IN THE EXTENDED AS MODELS CONTINUE TO EXHIBIT RUN-TO-RUN INCONSISTENCIES REGARDING THE INTERACTION OF MULTIPLE SHORTWAVES OVER THE CENTRAL TO EASTERN US. SUNDAY/SUNDAY NIGHT... A COLD FRONT WILL PUSH EAST ACROSS THE AREA SATURDAY NIGHT...WITH SKIES AT LEAST PARTIALLY CLEARING ON SUNDAY AS CANADIAN HIGH PRESSURE OVER THE GREAT LAKES NOSES SOUTH INTO THE AREA. THICKNESSES DROP BACK TOO AROUND NORMAL BEHIND THE FRONT...WITH HIGHS ACCORDINGLY IN THE LOW TO MID 50S...COOLEST TO THE NORTHEAST. A SECONDARY SURGE OF COOLER/DRIER AIR SHOULD ARRIVE BY SUNDAY NIGHT WITH LOW DIPPING WELL INTO THE 30S....THOUGH WE SHOULD BEGIN TO SEE A FAIR AMOUNT OF MID AND HIGH CLOUDS AHEAD OF THE NEXT SYSTEM. BEYOND SUNDAY NIGHT...AN ASSORTMENT OF WAVES MOVING THROUGH THE WESTERN US WILL INTERACT OVER THE CENTRAL US BY MONDAY AND ULTIMATELY LEADS TO CYCLOGENESIS OFF THE EAST COAST BY TUESDAY. HOWEVER...THIS IS WHERE MODELS HAVE VARIED IN SOLUTIONS...WITH THE ECMWF HAVING BEEN CONSISTENTLY THE MORE AMPLIFIED/CLOSER TO THE COAST AND WETTER OPTION. BUT...THE LATEST ECMWF (00Z) RUN FLIPPED BACK TO SHOWING THE SHORTWAVE/FRONT BEING MORE PROGRESSIVE...WHICH IN TURN WOULD KEEP A WEAKER LOW FURTHER OFFSHORE...AT LEAST UNTIL IT BEGINS TO INTERACT WITH A STRONGER WAVE THAT DIGS ACROSS THE UPPER MIDWEST AND THEN CLOSES OFF OVER THE MID-ATLANTIC STATES ON TUESDAY. THE PROBLEM IS THAT THE GFS SHOWS VERY LITTLE WAVE INTERACTION AND MUCH LESS AMPLIFIED SYSTEM THAT CROSSES THE UPPER MIDWEST ON TUESDAY. FROM THIS...THE BEST OPTION SEEMS TO BE TO HAVE SLIGHTLY HIGHER (BUT STILL LOW) POPS OVER THE EASTERN CWA MONDAY NIGHT INTO TUESDAY...WITH CLOUDS CLEARING OUT ON TUESDAY. MONDAY WILL BE THE COOLEST DAY GIVEN NORTHEASTERLY FLOW AND ROBUST CLOUD COVER...THOUGH HIGHS WILL BE AT OR BELOW NORMAL FOR MOST OF THE WEEK. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... AS OF 655 AM FRIDAY... AN AREA OF MOIST UPGLIDE WILL RESULT IN CONTINUED PREVAILING MVFR CEILINGS...WITH TEMPORARY IFR CEILINGS AND MVFR VISIBILITY RESTRICTIONS IN LIGHT RAIN...THROUGH AROUND 16Z...BEFORE A LIFTING AND SCATTERING TO VFR THIS AFTERNOON. THE EASTERN EDGE OF THE MVFR LEVEL CEILINGS MAY BRUSH KRDU WITH AN OCCASIONAL MVFR CEILING THROUGH 14-15Z...WITH VFR CONDITIONS EXPECTED OTHERWISE AND ELSEWHERE. IFR-MVFR CONDITIONS AND AREAS OF LIGHT RAIN OR DRIZZLE ARE EXPECTED TO RETURN TO TRIAD TERMINALS AFTER 06Z...IN A REGIME OF INCREASING UPGLIDE AND MOISTURE TRANSPORT APPROACHING FROM THE WEST. PATCHY FOG AND/OR VERY LOW STRATUS WILL BE APT TO DEVELOP ELSEWHERE...BUT CONFIDENCE REGARDING LOCATION...IF IT INDEED EVEN DEVELOPS...IS BELOW AVERAGE. OUTLOOK: SUB-VFR CONDITIONS...AND SHOWERS AND ISOLATED THUNDERSTORMS...WILL SPREAD EAST ACROSS CENTRAL NC ON SAT...IN ASSOCIATION WITH A FRONTAL SYSTEM. NORTHEASTERLY LOW LEVEL FLOW BETWEEN THE DEPARTING FRONTAL SYSTEM AND HIGH PRESSURE FORECAST TO BUILD INTO THE EASTERN US WILL THEN LIKELY MAINTAIN MVFR CEILINGS AT EASTERN SITES EARLY SUN...BEFORE A RETURN TO VFR SUN AFTERNOON. THE VFR MAY BE SHORT-LIVED...HOWEVER...AS ENE FLOW SPREADS MVFR LEVEL MOISTURE BACK INTO CENTRAL NC SUN NIGHT-MON. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. &&
Posted on: Fri, 05 Dec 2014 13:52:02 +0000
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