Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS62 KRAH 070256 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 955 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/...
-- Changed Discussion --
AS OF 955 PM SATURDAY... SATELLITE TRENDS AND 00Z UPPER AIR ANALYSIS DEPICT A MID-UPPER LEVEL LOW CROSSING THE DEEP SOUTH/NORTHERN GULF WITH A WELL DEFINED A BAROCLINIC LEAF NOTED ALONG THE SOUTHEAST U.S. COAST. AREAS OF LIGHT-MODERATE RAIN HAVE DEVELOPED SINCE 00Z OVER THE COASTAL PLAIN OF SC...IN RESPONSE TO INCREASING UPPER DIVERGENCE ASSOCIATED WITH THE APPROACHING UPPER LOW. THE RAIN SHIELD OBSERVED EARLY THIS EVENING FITS MOST CLOSELY WITH THE 12Z ECMWF MODEL VERSION. BASED ON OBSERVED TRENDS SINCE 21Z...STARTING TO HAVE MORE CONFIDENCE IN THE 12Z ECMWF VERSUS THE MUCH WETTER GFS SOLUTION. THE INITIAL WAVE OF PRECIP WILL CROSS INTO SOUTHERN NC PRIOR TO MIDNIGHT. DUE TO THE BONE DRY SUB CLOUD LAYER...EXPECT THIS BATCH OF PRECIP TO EVAPORATE BEFORE REACHING THE SURFACE...AND GO MORE TOWARD MOISTENING THE LOWER LAYERS. THE APPROACH OF THE UPPER LEVEL SYSTEM WILL CAUSE AN AREA OF LOW PRESSURE...ANALYZED AT 02Z OFF THE EAST FLORIDA COAST...TO STRENGTHEN AND LIFT NEWD. STILL APPEARS THAT THIS SFC LOW WILL REMAIN FAR ENOUGH OFFSHORE TO LIMIT THE WINTRY THREAT FOR CENTRAL NC. IN ADDITION...WHILE LOW LEVEL NLY FLOW WILL INCREASE IN CONJUNCTION WITH THE DEEPENING LOW OFFSHORE...THE NLY FLOW WILL NOT ADVECT/SUPPLEMENT A FRESH BATCH OF COLD AIR INTO CENTRAL NC. THUS...IN ORDER TO GET WINTRY PRECIPITATION...WILL NEED TO DEPEND UPON: 1.) EVAPORATIVE COOLING IN THE SUB CLOUD LAYER TO COOL TEMPS TO AT OR BELOW FREEZING; 2.) INCREASE PRECIP RATES. WITH SFC WET BULB TEMPS CURRENTLY ABOVE FREEZING ACROSS OUR SOUTHERN COUNTIES...THIS MECHANISM WILL DO LITTLE TO CHANGE PRECIP TO A WINTRY CHARACTER. THUS..WILL NEED TO DEPEND UPON ENHANCED PRECIP RATES TO BRING WINTRY PRECIP TO THE SURFACE. WITH THE BEST LIFT PROJECTED TO BE ALONG AND EAST OF I-95...THIS MECHANISM MAY BE REALIZED OVER OUR FAR SE-EASTERN COUNTIES. PER PARTIAL THICKNESSES AND MODEL SOUNDING DEPICTION...EXPECT THE LIGHT RAIN TO BECOME MIXED WITH SNOW. DURING TIMES OF MODERATE-BRIEFLY HEAVY PRECIP RATES...COULD SEE P-TYPE BECOME MORE SNOW THAN RAIN WITH SOME ACCUMULATION ON GRASSY AREAS. WITH SFC TEMPS ABOVE FREEZING AND ANTECEDENT GROUND TEMPS RELATIVELY WARM (MID 40S-NEAR 50)...EXPECT ANY SNOW/SLUSH THAT ACCUMULATES TO MELT RELATIVELY QUICKLY. THUS EXPECT THIS SYSTEM TO BE A RELATIVELY NON-EVENT WITH LITTLE/NO IMPACT TO TRAVEL. ANY ACCUMULATION TO BE A HALF INCH OR LESS. AT THIS TIME...APPEARS BEST CHANCE FOR WINTRY MIX TO OCCUR BETWEEN 08Z-14Z....AND MAINLY CONFINED TO LOCATIONS EAST OF HIGHWAY 1...AND MORE SO ALONG AND EAST OF I-95. AFTER 14Z...PRECIP RATES WILL BE DECREASING...LIMITING WINTRY MIX. AS THE AIR MASS WARMS DIURNALLY...EXPECT PRECIP TO BECOME ALL RAIN BY MID DAY-EARLY AFTERNOON. INCREASING CLOUD COVER WILL LIMIT THE COOLING OF TEMPS OVERNIGHT EXPECT WHERE AREAS OF PRECIP OCCUR. THUS TEMPS WILL HOLD STEADY FOR THE MOST PART NORTH AND WEST OF RDU. AS PRECIP EXPANDS ACROSS THE SE COUNTIES...TEMPS WILL FALL INITIALLY WHEN PRECIP STARTS THEN STABILIZE...BUT REMAIN ABOVE FREEZING. EXPECT THE RAIN SHIELD TO LIFT TO THE EAST-NE SUNDAY AFTERNOON...EXITING THE COASTAL PLAIN BY MID-LATE AFTERNOON. POTENTIAL FOR PARTIAL SUN TO OCCUR WHICH SHOULD BOOST TEMPS THERE TO AROUND 50. PRECIP/CLOUDS WILL LIMIT TEMP RECOVERY...RESULTING IN MAX TEMPS IN THE 40S...NEAR 40 IN THE FAR EAST-SE.
-- End Changed Discussion --
&& .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 /00Z SUNDAY THROUGH THURSDAY/... AS OF 625 PM SATURDAY... THROUGH THE 24 HOUR TAF PERIOD: VFR CONDITIONS WILL REMAIN ACROSS MOST OF CENTRAL NC THROUGH 07/06Z...THEN CIGS WILL QUICKLY LOWER SOUTH OF A KAFP-KRDU-KHNZ LINE AS LOW PRESSURE TAKES SHAPE OFF THE SE COAST. WHILE CONFIDENCE REMAINS LOW IN TERMS OF PRECIP TYPE...WE ARE FAIRLY CERTAIN THAT AT LEAST A MIXTURE OF RAIN/SNOW WILL DEVELOP FROM SOUTH TO NORTH AND PERSIST ALONG AND SOUTH OF THE AFOREMENTIONED LINE DURING THE 07/07Z TO 07/12Z TIME FRAME...AND LINGER THROUGH MUCH OF THE DAYTIME HOURS SUNDAY. DURING THIS TIME...LOOK FOR CIGS AND VSBYS TO FALL TO LOW-MVFR OR IFR. WITH DEEPENING LOW PRESSURE OFFSHORE...BY 07/08-11Z...WINDS WILL BECOME N- NE AND INCREASE TO 12KT WITH GUSTS AOA 20KT. THIS WILL PERSIST MUCH OF THE DAY SUNDAY. 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...WSS SHORT TERM...2 LONG TERM...2 AVIATION...RAH/SMITH

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.