Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 200726 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 326 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/...
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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.
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&& .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 /TUESDAY THROUGH SUNDAY/... AS OF 245 PM SUNDAY... FOR TUE-WED: A MID LEVEL VORTEX IS STILL EXPECTED TO DEEPEN OVER LK ERIE AND PUSH SSE THROUGH WRN PA TUE... THEN DROP TO THE DC VICINITY BY WED MORNING... AND WOBBLE NORTHWARD OVER THE MIDATLANTIC COAST WED/WED NIGHT. CYCLONIC SURFACE FLOW SETS UP TUE OVER CENTRAL NC WITH ABOVE NORMAL THICKNESSES AHEAD OF THE CLIPPER COLD FRONT WHICH PUSHES SOUTHEAST THROUGH THE AREA TUE EVENING... INTRODUCING COOLER AIR AS A NOSE OF CANADIAN-SOURCE HIGH PRESSURE BUILDS IN FROM THE NNW. EXPECT CONSIDERABLE MID CLOUDS TO START TUE AS THE 700 MB TROUGH SWINGS THROUGH. THESE SHOULD CLEAR OUT BY LUNCHTIME BUT WILL BE FOLLOWED BY LOWER BROKEN CLOUDS (ENHANCED BY DAYTIME HEATING AND SUBSEQUENT CONVECTIVE TOWERS) ACROSS THE NE AND EAST AS AN ELEVATED MOIST LAYER AT 850-700 MB SWEEPS IN FROM THE NORTH. WITH LITTLE OPPORTUNITY FOR ANY MOISTURE RETURN IN THE LOWER LEVELS... ANY CHANCES FOR PRECIP WITH THE DIGGING VORTEX ALOFT LOOK QUITE LOW. BUT THERE IS AN IMPRESSIVE AMOUNT OF DPVA AS STRONG VORTICITY LOBES ROTATE AROUND THE BASE OF THE LOW... WHICH MAY PARTIALLY COMPENSATE FOR THE RELATIVELY SHALLOW MOISTURE. NORTHEAST SECTIONS OF THE CWA WHERE THE HIGHER SURFACE DEWPOINTS WILL BE TEMPORALLY AND SPATIALLY JUXTAPOSED WITH THE BEST DYNAMIC LIFT MAY STILL SEE A QUICK SPRINKLE TUE EVENING/NIGHT... SO WILL LEAVE IN THE EXISTING SLIGHT CHANCE IN THE NE. THE ENERGY SWINGING THROUGH THE TROUGH BASE WILL CAUSE THE LOW TO SHIFT NE WED... AND WITH JUST WEAKER AND SHEARED VORTICITY DIVING SE OVER CENTRAL NC AND VERY LITTLE MOISTURE THROUGH THE COLUMN... WED SHOULD REMAIN DRY EVEN IN THE NE CWA... ALTHOUGH THIS AREA SHOULD SEE GREATER CLOUD COVERAGE WED. EXPECT WARM HIGHS TUE TO REFLECT THE MILD THICKNESSES... 69-75. LOWS SHOULD SLIP BACK INTO THE 40S AREAWIDE TUE NIGHT POST-FRONT... THEN EXPECT BELOW NORMAL HIGHS OF 62-67 WED AS THICKNESSES DROP BACK INTO THE 1330S... ROUGHLY 25 M BELOW NORMAL. LOWS WED NIGHT 40-45. FOR THU-SUN: THE DRY PATTERN LOOKS VERY LIKELY TO PERSIST. THE SURFACE AND MID LEVEL LOWS TO OUR NE SHIFT FURTHER NE AWAY FROM NC LATE IN THE WORK WEEK AS A PORTION OF THE CANADIAN-SOURCE HIGH BREAKS OFF OVER THE GREAT LAKES AND OH VALLEY AND BUILDS GRADUALLY TOWARD NC FROM THE WNW. LOW LEVEL WINDS REMAIN MOSTLY LIGHT FROM THE NW... AND THE DOWNSLOPE DRYING SHOULD ENSURE DECENT SUNSHINE AND MIXING. EXPECT ANOTHER BELOW-NORMAL DAY THU... WITH HIGHS IN THE MID- UPPER 60S... BUT THEN THICKNESSES ARE EXPECTED TO MODERATE HEADING INTO THE WEEKEND. THE GFS/ECMWF DIFFER WITH THEIR HANDLING OF A WEAK BUT FULL-LATITUDE MID LEVEL TROUGH OVER THE PLAINS THU. THE GFS FOCUSES ON THE NORTHERN PORTION OF THE TROUGH... DRAWING SHORTWAVE ENERGY SOUTHEAST INTO THE VORTEX OFF NEW ENGLAND AND PROGRESSING THE ENTIRE LOW/TROUGH OFF THE COAST BY SAT... FOLLOWED BY STRONG MID LEVEL RIDGING BUILDING OVER TX AND THE GULF STATES SUNDAY. THE ECMWF ON THE OTHER HAND PLACES GREATER IMPORTANCE ON THE SOUTHERN END OF THE PLAINS TROUGH... RESULTING IN A CLOSED LOW OVER ERN TX FRI WHICH THEN DROPS INTO THE NW GULF OVER THE WEEKEND. ALL OF THIS RESULTS IN TWO VERY DIFFERENT LONGWAVE PATTERNS OVER NOAM BY SUN... ALTHOUGH FOR NC... BOTH RESULT IN A FLAT LIGHT NW OR WNW MID LEVEL FLOW WITH NO MECHANISMS TO FORCE ASCENT AND NO REAL CHANCE TO GET ANY DECENT MOISTURE INTO THE AREA WITH HIGH PRESSURE DOMINATING AT THE SURFACE. AS SUCH... WILL KEEP THE FORECAST DRY... WITH TEMPERATURES CREEPING BACK UP JUST ABOVE NORMAL. -GIH && .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...HARTFIELD AVIATION...MWS

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