Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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206 FXUS62 KRAH 062016 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 310 PM EST SAT FEB 6 2016 .SYNOPSIS...HIGH PRESSURE WILL DRIFT OFFSHORE TONIGHT. A SURFACE LOW WILL PASS OFFSHORE OF THE CAROLINA COAST SUNDAY...FOLLOWED BY AN ARCTIC COLD FRONT THAT WILL ARRIVE EARLY NEXT WEEK. && .NEAR TERM /THROUGH SUNDAY/...
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AS OF 310 PM SATURDAY... HIGH UNCERTAINTY FOR WHAT SHOULD ULTIMATELY BE A RELATIVELY LOW IMPACT EVENT TONIGHT. A CUTOFF LOW OVER THE LOW MISSISSIPPI RIVER VALLEY WILL CONTINUE TO KICK EAST TONIGHT AND THEN LIFT NORTHEAST ALONG THE SOUTHEAST COAST TONIGHT. MEANWHILE...A SURFACE LOW WILL DEVELOP OFF THE FLORIDA COAST AND THEN TRACK NORTHEAST OFF THE CAROLINA COAST...DEEPENING RAPIDLY OFF THE NC COAST ON SUNDAY. A 1030MB SURFACE HIGH OVER NORTHEAST NC WILL WEAKEN AND SHIFT NORTHEAST TONIGHT. DEEP LIFT OWING TO STRONG DCVA WITH THE UPPER LOW AND UPPER DIVERGENCE BETWEEN THE NORTHERN AND SOUTHERN STREAM BRANCHES OF THE UPPER JET WILL CAUSE PRECIP TO OVERSPREAD SE NC FROM THE SOUTH TONIGHT...AS EARLY AS 03-06Z BASED ON THE WRFARW AND HRRR. MOISTURE WILL BE SUFFICIENTLY DEEP FOR ICE-NUCLEATION...AND THE TOP DOWN METHOD SUPPORTS SNOW...OR PARTLY MELTED SNOW...DOWN THE SURFACE IN THE HEAVIER POCKETS OF PRECIP WHERE THE WETBULB PROFILE THAT IS STILL ABOVE FREEZING NEAR THE SURFACE (~1000 FT THICK). THE PREFERRED TIME APPEARS TO BE BETWEEN 09Z TO 15Z. ONE ITEM OF CONCERN IS THAT DEWPOINTS ARE CURRENTLY A LITTLE LOWER THAN FORECAST (TEENS AND MID 20S)...WHICH WOULD KEEP THE WETBULB FREEZING LINE FURTHER SOUTH THAN FORECAST AND AID IN POTENTIAL ACCUMULATION. NEAR TERM GUIDANCE CONTINUES TO KEEP THE WETBULB FREEZING LINE IN THE PIEDMONT HOWEVER. THE BIGGEST UNCERTAINTY CONTINUES TO BE THE TRACK OF THE SURFACE LOW AND NORTHWEST EXTENT OF PRECIP...WITH THE 12Z GFS STILL A WESTERN OUTLIER AND THE ECMWF CURIOUSLY WEAKER AND A LITTLE FURTHER SOUTHEAST THAN THE ENSEMBLE CONSENSUS. THE ECMWF IS ALSO THE DRIEST MODEL WITH LESS THAN A TENTH OF AN INCH ACROSS THE SOUTHERN COASTAL PLAIN. THE GFS ON THE OTHER HAND IS A FAIRLY EXTREME OUTLIER SHOWING OVER A HALF INCH AS FAR NORTH AS JOHNSTON COUNTY. THE BEST SOLUTION SEEMS TO BE 0.2" TO 0.4" SOUTH AND EAST OF A LINE FROM LAURINBURG TO WILSON. GIVEN THAT MUCH OF THIS WILL FALL AS RAIN AND THE DURATION OF A CHANGEOVER TO SNOW WILL BE LIMITED TO HEAVIER POCKETS OF PRECIP.... OUR THINKING IS THAT ACCUMULATIONS WILL BE LESS THAN AN INCH AND CONFINED TO GRASSY/ELEVATED SURFACES...THOUGH AN ISOLATED AREA WITH SLIGHTLY ENHANCED ACCUMULATIONS IS POSSIBLY. NO ADVISORY WILL BE ISSUED AT THIS TIME. OVERNIGHT LOWS WILL RANGE FROM THE LOWER 30S NORTHWEST TO MID 30S SOUTHEAST. SOME PARTIAL CLEARING ON SUNDAY WILL ALLOW TEMPS IN THE WESTERN PIEDMONT TO HIT THE 50S MARK...WITH LOW TO MID 40S OTHERWISE TO THE EAST. THE TIGHT PRESSURE GRADIENT ON THE WESTERN SIDE OF THE DEEPENING LOW (FORECAST TO DROP TO 980MB) WILL LEAD TO A STIFF 15- 20MPH NORTHERLY WIND AND GUSTS TO AS HIGH AS 30MPH IN THE COASTAL PLAIN...PER THE PREFERRED NAM/ECMWF. A TRACK CLOSER TO THE COAST LIKE THE GFS COULD LEAD TO WIND GUSTS APPROACHING 40MPH.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... AS OF 200 PM SATURDAY... REGARDLESS OF HOW CLOSE TO THE COAST A COASTAL LOW WOBBLES AS IT BOMBS OFF THE SOUTHEAST US COAST DURING THE NEXT 24-36 HOURS...THE RESULTANT DEEP CYCLONE IS FORECAST TO ACCELERATE NORTHEASTWARD AND AWAY FROM THE NC COAST SUNDAY NIGHT...IN RESPONSE TO A "KICKER" VORTEX AND ACCOMPANYING ELONGATED SHORTWAVE TROUGHS IN SHORT WAVELENGTH FLOW ALOFT...FORECAST TO PIVOT FROM THE UPPER MIDWEST TO THE TN AND LOWER MS VALLEYS THROUGH EARLY MON. AN AREA OF BROAD BUT STRONG 100-150 METER HEIGHT FALLS AND COOLING/FGEN ALOFT...AND ASSOCIATED FORCING FOR ASCENT AND POCKET OF STEEP (6.5-7.5 C/KM) 850-500 MB LAPSE RATES...WILL SUPPORT THE EASTWARD MAINTENANCE OF A BAND OF SHOWERS INTO CENTRAL NC DURING THE AFTERNOON AND EVENING. A "WARMING" DEEP LAYER SOUTHWEST FLOW...INCLUDING A SSW SURFACE BREEZE AND TEMPERATURES MONDAY AFTERNOON IN THE UPPER 40S TO MIDDLE 50S...WILL ENSURE THIS ACTIVITY WILL FALL PRIMARILY IN THE LIQUID FORM. HOWEVER...AS THE PARENT VORTEX SETTLES FURTHER SOUTHEAST AND THE ACCOMPANYING ARCTIC FRONTAL ZONE MOVES THROUGH CENTRAL NC DURING THE MID-LATE EVENING...AND AS AN INITIALLY WEAK WAVE ON THE FRONT DEEPENS OFF THE MIDDLE ATLANTIC COAST...A PERIOD OF LINGERING LOW- MID LEVEL MOISTURE MAY BRIEFLY OVERLAP WITH THE RAPIDLY COOLING BOUNDARY LAYER TO SUPPORT A BRIEF MIX OR CHANGEOVER TO SNOW NEAR THE VA BORDER BEFORE ENDING OVERNIGHT. ANY SUCH OCCURRENCE WOULD LIKELY BE TOO LATE TO INTERACT WITH ANY APPRECIABLE PRECIPITATION...SO NO IMPACTS ARE ANTICIPATED. && .LONG TERM /TUESDAY THROUGH SATURDAY/... AS OF 245 PM SATURDAY... NORTHWEST FLOW...IN A HIGHLY AMPLIFIED PATTERN CHARACTERIZED BY WESTERN NOAM RIDGING AND A MEAN TROUGH OVER EASTERN NOAM...WILL MAINTAIN A GENERALLY DRY PERIOD EAST OF THE NC BLUE RIDGE...BUT WITH A FEW OPPORTUNITIES FOR LIGHT...LEE-SIDE PRECIPITATION. WITHIN THE COLD...STEEP LAPSE RATE-BEARING...CYCLONIC FLOW ALOFT...PERIODS OF ENHANCED CLOUDINESS AND VIRGA WILL BE SUPPORTED BY A SERIES OF DISTURBANCES MIGRATING THROUGH THE BASE OF THE EAST COAST TROUGH. IF THOSE DISTURBANCES AND ENHANCED MOISTURE/LIFT ARE MAXIMIZED WITH (NEAR) PEAK DIURNAL HEATING...WITH THE RESULTANT DEVELOPMENT OF WEAK INSTABILITY (LESS THAN 100 J/KG)...THEN A FEW SNOW SHOWERS COULD RESULT...AMIDST AN AREA OF OTHERWISE SCATTERED FLURRIES/SPRINKLES; AND THIS SCENARIO APPEARS MOST LIKELY TUE AFTERNOON OVER THE NORTHERN PIEDMONT. THEN...AS A LEAD MID-UPPER VORTEX LIFTS AND FILLS...AND THE FLOW ALOFT BRIEFLY RELAXES/HEIGHTS RISE DOWNSTREAM OF A NEW VORTEX SETTLING OUT OF SOUTHERN CANADA...A BRIEF EPISODE OF LOW-MID LEVEL WAA AND ACCOMPANYING WEAK MSL PRESSURE FALLS/WAVE DEVELOPMENT ALONG THE FRONT MAY SUPPORT THE DEVELOPMENT OF AN AREA OF LIGHT PRECIPITATION OVER THE SOUTHEASTERN STATES/CAROLINAS FRI-SAT. HOWEVER...THERE IS CONSIDERABLE MODEL SPREAD DURING THIS TIME...AND TEMPERATURES WOULD BE ONLY MARGINALLY SUPPORTIVE FOR ANY WINTRY PRECIPITATION...IF IN THE LOW PROBABILITY EVENT THAT PRECIPITATION OCCURS AT ALL. IT WILL OTHERWISE BE A CHILLY WEEK...BUT NOT BRUTALLY SO...WITH TEMPERATURES AVERAGING ABOUT 5-10 DEGREES BELOW "NORMAL". PERHAPS THE MOST EXCITING WEATHER LURKS JUST BEYOND DAY 7...AS THE AFOREMENTIONED NEW VORTEX MIGRATES ACROSS THE GREAT LAKES AND CONSEQUENTLY SUPPRESSES THE NORTHERN STREAM/PROMOTES CONFLUENT FLOW ALOFT THAT WOULD SUPPORT THE SOUTHEASTWARD MAINTENANCE OF A 1040- 1045 MB HIGH FROM THE ARCTIC. WHILE THIS WOULD YIELD INITIALLY JUST COLD CONDITIONS FOR THE WEEKEND...AN INCREASINGLY ACTIVE SOUTHERN STREAM WOULD RAISE THE PROBABILITY OF STREAM INTERACTION...AND STORMINESS AND APPALACHIAN COLD AIR DAMMING...EARLY TO MID NEXT WEEK. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... AS OF 1245 PM SATURDAY... VFR CONDITIONS WITH A LIGHT AND VARIABLE WIND BECOMING NORTH- NORTHEASTERLY OVERNIGHT. A SURFACE LOW WILL DEVELOP OFF THE FLORIDA COAST THIS EVENING AND THEN TRACK ALONG THE SOUTHEAST COAST TONIGHT AND SUNDAY. THE LOW IS FORECAST TO DEEPEN DRAMATICALLY OFF THE NC COAST...BRINGING PRECIP AND STRENGTHENING AND STRONG NORTHERLY WINDS TO EASTERN NC. THERE IS STILL AN UNUSUAL AMOUNT OF FORECAST UNCERTAINTY IN THE NEXT 24 HOURS...BUT IT APPEARS MVFR CEILINGS AND A CHANCE OF A RAIN/SNOW MIX WILL BE GREATEST FROM KMEB/KJNX/KRWI AND EAST. FORECAST SOUNDINGS SUGGEST CEILINGS WILL REMAIN ABOVE 1000FT...MORE IN THE 2000-3000FT RANGE...EXCEPT IN THE HEAVIEST PRECIP. PRECIP WILL COME TO AN END BY SUNDAY AFTERNOON...BUT WINDS WILL CONTINUE TO GUST TO AROUND 25KT AND HIGHER TO THE EAST. OUTLOOK...A COUPLE OF UPPER LEVEL DISTURBANCES WILL BRING ADDITIONAL CHANCES OF LIGHT SHOWERS AND BRIEF SUB-VFR CONDITIONS....ALONG WITH GUSTY WINDS...LATE MONDAY... AND AGAIN MAINLY AT NORTHERN TAF SITES LATE TUESDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...SMITH NEAR TERM...SMITH SHORT TERM...2 LONG TERM...2 AVIATION...SMITH

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