Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 200733 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 335 AM EDT MON OCT 20 2014 .SYNOPSIS....HIGH PRESSURE CENTERED OVER NC THIS MORNING WILL MOVE OFFSHORE TODAY. A LEAD SHORTWAVE TROUGH ALOFT WILL CROSS OUR REGION TONIGHT...FOLLOWED BY A STRONGER ONE - AND PRECEDING SURFACE COLD FRONT - THAT WILL SETTLE ACROSS THE MIDDLE ATLANTIC STATES LATE TUE AND TUE NIGHT. && .NEAR TERM /THROUGH TONIGHT/... AS OF 325 AM MONDAY... A DEAMPLIFYING SOUTHERN STREAM MID-UPPER DISTURBANCE OVER WESTERN TN...AND PRECEDING AREA OF CIRRUS AT 07Z...WILL CONTINUE ENE ACROSS NC/VA THROUGH NOON. SURFACE HIGH PRESSURE CENTERED DIRECTLY OVER CENTRAL NC THIS MORNING WILL MOVE OFFSHORE TODAY...AS A STRONGER NORTHERN STREAM SHORTWAVE TROUGH AND ASSOCIATED AREA OF MAXIMUM HEIGHT FALLS ALOFT (~60 M/12 HR) AMPLIFY ACROSS THE UPPER MIDWEST AND LOWER OH VALLEY. CIRRUS ASSOCIATED WITH THE NORTHERN STREAM WAVE WILL FOLLOW QUICKLY ON THE DEPARTING HEELS OF THE ONES FROM SOUTHERN STREAM...WHILE THE LOW LEVEL RETURN FLOW ALSO PROMOTES THE ONSHORE DEVELOPMENT/ADVECTION OF AN AREA OF STRATOCUMULUS MAINLY OVER THE COASTAL PLAIN AND EASTERN PIEDMONT/SANDHILLS. TEMPERATURES WILL ALSO MODERATE IN RETURN/WARMING SW FLOW...INTO THE UPPER 60S TO LOWER 70S. TONIGHT: THE SHORTWAVE TROUGH FORECAST TO AMPLIFY FROM THE UPPER MIDWEST THIS MORNING TO THE LEE OF THE CENTRAL APPALACHIANS OVERNIGHT...WILL CAUSE A MID LEVEL CLOUD BAND AND ASSOCIATED VIRGA OR ISOLATED SPRINKLES TO MOVE EAST ACROSS CENTRAL NC BETWEEN 06-12Z. A DRY SUB-CLOUD LAYER/BELOW 10 THOUSAND FT SHOULD PRECLUDE THE OCCURRENCE OF ANY MEASURABLE PRECIPITATION. NOT AS COOL...WITH LOWS IN THE UPPER 40S TO LOWER 50S. && .SHORT TERM /MONDAY AND MONDAY NIGHT/... AS OF 235 PM SUNDAY... MONDAY...SFC HIGH WILL DRIFT EAST...COMMENCING AIR MASS MODIFICATION. LOW LEVEL RETURN EXPECTED TO BE SWLY BY AFTERNOON WITH OCCASIONAL GUSTS AROUND 15 KTS PROBABLE. LOW LEVEL THICKNESSES REBOUND ABOUT 10M FROM LEVELS OCCURRING THIS AFTERNOON. THIS YIELDS MAX TEMPS 2-3 DEGREES WARMER THAN TODAY. FACTORING IN ADDITIONAL WARMING FROM THE LOW LEVEL SW FLOW SUPPORT MAX TEMPS NEAR 70 TO THE LOWER 70S. MONDAY NIGHT...L/W TROUGH OVER THE EASTERN U.S. UNDERGOES AMPLIFICATION THANKS TO A S/W CROSSING THE GREAT LAKES INTO SOUTHERN NEW ENGLAND. THE TAILE ND OF THIS S/W WILL CROSS CENTRAL NC MONDAY NIGHT...GENERATING AREAS OF MID-HIGH LEVEL CLOUDINESS. WARM AIR ADVECTION IN THE 8000-15000FT LAYER MAY PRODUCE ENOUGH LIFT TO INITIATE SOME PRECIP BUT THE SUB CLOUD LAYER STILL QUITE DRY. THUS...EXPECT NOTHING WORSE THAN A FEW SPRINKLES...MAINLY ACROSS THE NORTH HALF...AS THIS SYSTEM CROSSES OUR REGION. VARIABLE CLOUDINESS AND A MODIFYING AIR MASS WILL RESULT IN MIN TEMPS SEVERAL DEGREES WARMER COMPARED TO TONIGHT. MIN TEMPS IN THE 40S TO AROUND 50. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/...
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AS OF 335 AM MONDAY... A STRONG SHORTWAVE DIVING THROUGH THE UPPER TROUGH OVER THE EASTERN US...AND CROSSING NC TUESDAY NIGHT...WILL CLOSE OFF INTO AN UPPER LOW OFF THE DELMARVA ON WEDNESDAY. BENEATH THE UPPER LOW...STEEP TROPOSPHERIC DEEP LAPSE RATES WILL SUPPORT SOME VERY WEAK INSTABILITY...BUT THE LACK OF ANY APPRECIABLE MOISTURE WILL KEEP MOST OF THE AREA FREE OF PRECIP. SLIGHTLY HIGHER DEWPOINTS AND MARGINALLY BETTER MOISTURE OVER THE NORTHERN COASTAL PLAIN SHOULD LEAD TO A MORE PRONOUNCED CUMULUS FIELD...WHERE AN ISOLATED SHOWER OR FEW SPRINKLES MAY BE POSSIBLE. HOWEVER...TO PROSPECTS ARE TOO LOW TO INCLUDE IN THE FORECAST FOR WEDNESDAY. HIGHS WILL BE NOTICEABLY COOLER WITH THICKNESSES DROPPING TO NEAR 1330M WEDNESDAY MORNING...WHICH SHOULD YIELD LOW TO MID 60S. SIMILAR THICKNESS VALUES THURSDAY MORNING SUGGEST LOWS WILL BE MOSTLY IN THE UPPER 30S TO MID 40S. THE LOW WILL THEN SLOWLY MEANDER NORTHEAST ALONG THE MID-ATLANTIC COAST THROUGH THE END OF THE WEEK...AS HIGH PRESSURE SETTLES AND LINGERS OVER THE OHIO/TENN VALLEYS. BETWEEN THESE FEATURES...DRY WEATHER IS EXPECTED THROUGH THE PERIOD WITH NORTHWEST FLOW REMAINING IN PLACE. THE GFS AND ECMWF HAVE BEEN INDICATING A SHORTWAVE WILL MOVE FROM THE NORTHERN PLAINS TOWARD THE SOUTHEAST US BY THE WEEKEND...THOUGH THERE HAS BEEN A LOT OF DISAGREEMENT REGARDING THE AMPLITUDE OF THE WAVE AND ITS FINAL DESTINATION. THE 00Z/20TH ECMWF...WHICH HAD BEEN SHOWING THE WAVE CUTTING OFF OVER THE DEEP SOUTH...NOW SHOWS A MORE PROGRESSIVE WAVE THAT SWINGS ALL THE WAY THROUGH THE REGION AND OFFSHORE BY SUNDAY...A SOLUTION THAT IS MORE LIKE PREVIOUS GFS RUNS. THE SENSIBLE IMPACTS OF THIS WAVE APPEAR TO BE MINIMAL AS THE AIRMASS OVER NC WILL BE QUITE DRY AND STABLE...WITH JUST A SLOW TREND IN TEMPS BACK TOWARD NORMAL THROUGH THE WEEKEND.
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&& .AVIATION /06Z MONDAY THROUGH FRIDAY/... AS OF 220 AM MONDAY... CIRRUS AND CALM WILL PREVAIL THROUGH MID-MORNING...FOLLOWED BY A DEVELOPING SSW SURFACE WIND THAT WILL BECOME OCCASIONALLY GUSTY INTO THE MID-UPPER TEENS KTS MAINLY AT KINT/KGSO DURING THE MIDDAY-EARLY AFTERNOON HOURS. THE RETURN FLOW WILL ALSO RESULT IN THE ONSHORE DEVELOPMENT/ADVECTION OF AN AREA OF STRATOCUMULUS...THE WESTERN EDGE OF WHICH WILL PRODUCE SCATTERED TO BROKEN CLOUD BASES AROUND 3500- 4000 FT AT KFAY AND KRWI THIS AFTERNOON AND EVENING. OUTLOOK: THE DEVELOPMENT OF AN UPPER LOW OVER THE MIDDLE ATLANTIC STATES...AND ASSOCIATED PASSAGE OF A SURFACE COLD FRONT LATE TUE... WILL RESULT IN A CHANCE OF SHOWERS TUE-WED...MAINLY FROM KRDU AND KRWI NORTHEAST TOWARD THE CHESAPEAKE BAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...WSS LONG TERM...BLS AVIATION...MWS

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