Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 250937 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 435 AM EST WED FEB 25 2015 .SYNOPSIS...AN AREA OF LOW PRESSURE WILL FORM OVER THE NORTHERN GULF OF MEXICO TODAY AND WILL THEN TRACK QUICKLY NORTHEAST...OFF THE CAROLINA COAST OVERNIGHT THROUGH EARLY THURSDAY. COLD CANADIAN HIGH PRESSURE WILL THEN BUILD INTO THE REGION FRIDAY AND INTO THE WEEKEND. && .NEAR TERM /TODAY/... AS OF 400 AM WEDNESDAY... ...WINTER WEATHER ADVISORY FOR BLACK ICE THROUGH NOON WEDNESDAY... TODAY: MID AND UPPER LOW OVER THE SOUTHWEST US WILL OPEN UP AS IT ADVANCES EASTWARD THROUGH THE SOUTHERN PLAINS AND LOWER MS VALLEY TODAY. WEAK SURFACE HIGH PRESSURE WILL EXTEND OVER THE AREA TODAY AS SURFACE LOW PRESSURE DEVELOPMENT GETS UNDERWAY OVER THE NORTHERN GOM. TOP-DOWN MOISTENING WILL INCREASE THROUGHOUT THE DAY AS FLOW ALOFT BACKS TO SWLY ALOFT...WHICH SHOULD YIELD A RATHER EXTENSIVE CIRRUS CANOPY ACROSS THE AREA TODAY...ESPECIALLY ACROSS THE SOUTHERN TIER. STRENGTHENING MID-LEVEL WARM MOIST AIR ADVECTION WILL HAVE RAIN SPREADING TO OUR SOUTHERN DOORSTOP NEAR SUNSET(21-00Z)...WITH PARTIAL THICKNESSES/THERMAL PROFILES SUGGESTING SNOW MIXED WITH RAIN ACROSS THESE SOUTHERN COUNTIES...BUT LITTLE TO NO ACCUMULATION GIVEN ABOVE FREEZING SURFACE TEMPERATURES. AFOREMENTIONED HIGH LEVEL CLOUD COVER AND MELTING OF SNOW(CURRENTLY ON GROUND)SHOULD KEEP HIGHS TODAY ON THE COOLER SIDE OF GUIDANCE. HIGHS 40 TO 45. && .SHORT TERM /TONIGHT THROUGH THURSDAY/...
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AS OF 430 AM WEDNESDAY... ...WINTER STORM WARNING HAS BEEN ISSUED FOR TONIGHT AND THURSDAY FOR ALL THE PIEDMONT...NORTHERN/CENTRAL COASTAL PLAIN AND SANDHILLS... ...WINTER WEATHER ADVISORY HAS BEEN ISSUED FOR TONIGHT AND THURSDAY FOR THE SOUTHERN COASTAL PLAIN... THERE HAS BEEN A CONTINUED SLIGHT NORTHWARD SHIFT IN GUIDANCE SINCE YESTERDAY...WHICH EQUATES TO A WETTER AND MARGINALLY WARMER SOLUTION FOR CENTRAL NC...THOUGH THE OVERALL PATTERN REMAINS UNCHANGED WITH THE DEAMPLIFICATION/ENE SHEARING OF A SHORTWAVE TROUGH FROM NEAR THE RIO GRANDE THIS MORNING TO THE MIDDLE ATLANTIC COAST BY THU MORNING. THE ASSOCIATED FORCING FOR ASCENT ATOP A PAIR OF CLOSELY-SPACED AND STRONG FRONTAL ZONES DRAPED ACROSS THE NORTHERN GOM TO A SFC LOW ABOUT MIDWAY BETWEEN CAPE HATTERAS AND BERMUDA...WILL RESULT IN THE CONTINUED DEEPENING OF A SFC LOW OVER THE NW GOM THIS MORNING. GUIDANCE IS THEN FAIRLY TIGHTLY CLUSTERED WITH THE TRACK OF A MILLER "A" SFC LOW ACROSS THE NORTHERN FL PENINSULA THIS EVENING AND ROUGHLY ALONG THE GULF STREAM TO JUST EAST OF CAPE HATTERAS BY 12Z THU. AS HAS BEEN NOTED IN PREVIOUS DISCUSSIONS...THE LACK OF A PARENT COLD HIGH IS ADMITTEDLY SOMEWHAT CONCERNING. AN ARCTIC SFC HIGH AT 1045 MB WILL BE CENTERED OVER SOUTHERN ALBERTA/SASKATCHEWAN AND WILL CONSEQUENTLY HAVE LITTLE INFLUENCE AT OUR LATITUDE DURING THE HEIGHT OF THE STORM TONIGHT. HOWEVER...A VERY FAVORABLE MILLER "A" CYCLONE TRACK ALONG AND JUST OFFSHORE THE SE COAST...IN CONJUNCTION WITH A PRECEDING ARCTIC HIGH THAT APPEARS TO BE JUST COLD ENOUGH DESPITE BEING IN A DRAMATICALLY WEAKENED STATE FROM A COUPLE OF DAYS AGO...BUT IS STILL CHARACTERIZED BY SFC TEMPERATURES AND DEWPOINTS MOSTLY IN THE TEENS TO 20S OVER NC THIS MORNING...WILL SUPPORT A SIGNIFICANT WINTER STORM **WITH A NARROW P-TYPE (SNOW/RAIN) TRANSITION ZONE AND DEEP NEAR FREEZING ISOTHERMAL PROFILES CHARACTERISTIC OF MILLER "A` SFC PATTERNS.** PRECIPITATION RATES...OCCASIONALLY MODERATE TO HEAVY...WILL ONLY SERVE TO ENHANCE THE DEEP NEAR FREEZING ISOTHERMAL PROFILES RIGHT ALONG THE SNOW/COLD RAIN INTERFACE...OWING TO MELTING. SURFACE TEMPERATURES ARE EXPECTED TO HOLD NEARLY STEADY IN THE 29 TO 33 DEGREE RANGE OVER THE WARNING AREA...AND 32 TO 34 DEGREES OVER THE ADVISORY AREA. DESPITE SOME MINIMAL OVERALL RISE IN THICKNESS VALUES VERSUS THE SLIGHTLY COLDER AND DRIER SOLUTIONS OF YESTERDAY...PROJECTED PARTIAL THICKNESS VALUES OVER MOST OF THE PIEDMONT AND NORTHERN COASTAL PLAIN REMAIN SQUARELY IN THE RANGE TYPICAL OF SIGNIFICANT SNOWSTORMS IN CENTRAL NC. WITH A SLIGHTLY MILDER SOLUTION COMES A SLIGHTLY WETTER ONE...LED BY A BLEND OF THE VERY SIMILAR 00Z ECMWF AND GFS...SO QPF HAS BEEN RAISED TO AROUND ONE HALF INCH OVER THE NW PIEDMONT TO AS MUCH AS ONE INCH OVER THE SOUTHERN COASTAL PLAIN. PARTIAL THICKNESS VALUES HEAVILY WEIGHTED TOWARD THE FAVORED 00Z ECMWF AND GFS...FAVORS MOSTLY SNOW OVER THE PIEDMONT AND NORTHERN COASTAL PLAIN...WITH A MIX OF SNOW AND A COLD RAIN (OR FREEZING RAIN WITH LITTLE ACCRUAL WHERE SFC TEMPERATURES OSCILLATE ABOUT THE FREEZING MARK) OVER THE ADVISORY AREA. BASED ON THE QPF NOTED ABOVE AND SNOW RATIOS OF 9-10:1 PER WHAT IS TYPICAL OF EVENTS CHARACTERIZED BY PARTIAL THICKNESS VALUES IN THE ~1285/~1535 METER RANGE...WITH SLIGHTLY LOWER RATIOS CLOSER TO 6-8:1 NEAR THE RAIN/SNOW LINE...SNOWFALL ACCUMULATIONS ARE EXPECTED TO RANGE FROM 3 TO 6 INCHES OVER THE WARNING AREA...WITH LOCALLY HIGHER AMOUNTS OF 6 TO 8 INCHES POSSIBLE...TO 1 TO 3 INCHES OVER THE ADVISORY AREA...WHERE AGAIN...PARTIAL THICKNESS AND SFC TEMPERATURE VALUES MARGINALLY ABOVE FREEZING WILL SUPPORT A MIXING WITH OR CHANGEOVER TO A COLD RAIN BETWEEN MIDNIGHT AND 5 AM. THE APPROACH OF A WEAK CLIPPER LOW AND ATTENDING SHORTWAVE TROUGH WILL CAUSE THE LINGERING STRATUS LAYER AND ASSOCIATED MOSTLY CLOUDY SKIES TO PRODUCE OCCASIONAL DRIZZLE OR FREEZING DRIZZLE...AFTER LINGERING LIGHT SNOW...OWING TO A LOSS OF SATURATION ALOFT/IN THE ICE NUCLEATION ZONE - BUT WITH MINIMAL ADDITIONAL IMPACT. CHILLY TEMPERATURES IN THE LOWER TO MIDDLE 30S.
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&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... AS OF 340 AM WEDNESDAY... SHORTWAVE DISTURBANCES EMBEDDED IN THE CONTINUED SWLY FLOW ALOFT AND LINGERING LOW-LEVEL MOISTURE OWING TO WHAT WILL LIKELY BE A MOIST SNOW COVER GROUND(AT LEAST FOR THE NORTHERN TWO-THIRDS OF THE FORECAST AREA)...WILL RESULT IN RATHER EXTENSIVE CLOUDINESS INTO SATURDAY. COMBINATION OF THIS CLOUD COVER...SNOW COVER AND THE ARRIVAL OF ANOTHER FRESH SUPPLY OF ARCTIC AIR INTO THE REGION LATE THURSDAY NIGHT AND INTO FRIDAY...AS A STRONG +1040MB CANADIAN SURFACE HIGH BUILDS OVER THE REGION...WILL SUPPORT TEMPERATURES WELL BELOW NORMAL(15-20 DEGREES FRIDAY AND SATURDAY. DRY WITH HIGHS IN THE MID 30S NORTH TO POSSIBLY LOWER 40S SOUTH...WITH SATURDAY BEING THE COLDEST DAY OF THE TWO. LOWS IN THE 20S...WITH SOME TEENS SATURDAY NIGHT. FLOW ALOFT FLATTENS OUT TO ZONAL BY SUNDAY WHILE MODERATING CANADIAN HIGH STARTS TO SHIFT OFF THE MID-ATLANTIC COAST AS A SW-NE ORIENTED FRONTAL ZONE STRETCHING FROM THE SOUTHERN PLAINS INTO THE OHIO VALLEY MOVES SLOWLY EASTWARD. MODELS HAVE SLOWED DOWN THE ONSET OF WAA/SOUTHERLY RETURN FLOW AND RESULTANT PRECIP INTO THE AREA LATE SUNDAY AFTERNOON/EVENING...BY WHICH TIME AIRMASS LOOKS TO HAVE MODERATED ENOUGH TO SUPPORT ALL RAIN. IT THEN LOOKS LIKE A WET PERIOD SUNDAY NIGHT THROUGH EARLY NEXT WEEK AS THE AFOREMENTIONED FRONT SETTLES SOUTHWARD INTO AREA...EVENTUALLY RETURNING NORTHWARD AS A WARM FRONT WITH CAD IMPLICATIONS TUESDAY/TUESDAY NIGHT AS HIGH PRESSURE OVER THE GREAT LAKES/NEW ENGLANDS NOSES SOUTH INTO THE AREA. PARTIAL THICKNESSES CURRENTLY SUGGEST ALL RAIN FOR NOW...BUT WILL CONTINUE TO MONITOR. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... AS OF 155 AM WEDNESDAY... 24-HR TAF PERIOD: MVFR CIGS ... FALLING CURRENTLY INTO THE IFR RANGE... HAVE DEVELOPED ACROSS THE SOUTHWESTERN HALF OF CENTRAL NC... WITH KGSO/KINT/KFAY NOW EXPERIENCING SUB-VFR CONDITIONS. EXPECT THE SUB-VFR CIGS TO OOZE EASTWARD THIS MORNING DURING THE PRE- DAWN HOURS... AT LEAST REACHING KRDU. IF STRATUS DECK DOES NOT REACH KRWI... THEN EXPECT WE SHOULD AT LEAST SEE SOME SUB-VFR VISBYS DEVELOP... POSSIBLY INTO THE IFR/LIFR RANGE. WRT THE AFOREMENTIONED STRATUS DECK... EXPECT CIGS TO LOWER WITH POSSIBLE IFR/LIFR CIGS AND VISBYS WITHIN A COUPLE HOURS OF DAYBREAK. BOTH THE GFS AND NAM SOUNDINGS SHOW ANY SHALLOW CIGS/VISBYS/MOISTURE MIXING OUT QUICKLY AFTER DAYBREAK. THUS... EXPECT ANY SITES THAT ARE AFFECTED BY THE SUB-VFR CIGS/VISBYS SHOULD LIFT/MIX OUT BY AT LEAST MID MORNING. VFR CONDITIONS AND LIGHT/VARIABLE WINDS WILL OTHERWISE PREVAIL THROUGH AROUND 00Z. CIRRUS (18-25 KFT AGL) WILL MOVE INTO THE REGION BY EARLY AFTERNOON...WITH CEILINGS LOWERING TO 5-10 KFT BY 00Z THU. AN AREA OF MODERATE TO HEAVY SNOW WILL MOVE INTO CENTRAL NC IN THE 00Z-03Z TIME FRAME.... POSSIBLY MIXING WITH RAIN AT KFAY. AS THE SNOW MOVES INTO THE AREA EXPECT IFR/LIFR CONDITIONS TO QUICKLY DEVELOP (CIGS/VISBYS). LOOKING AHEAD: ADVERSE AVIATION CONDITIONS IN THE FORM OF IFR/LIFR CEILINGS/VISBYS ASSOCIATED WITH SNOW (INT/GSO/RDU/RWI) OR RAIN/SNOW (FAY) WILL CONTINUE DURING THE EARLY MORNING HOURS OF THURSDAY... WITH SIGNIFICANT SNOW ACCUMULATION EXPECTED AT NORTHERN TERMINALS. SUB-VFR CEILINGS WILL LIKELY PERSIST IN THE WAKE OF THE COASTAL LOW PRESSURE SYSTEM DURING THE DAY THU. VFR CONDITIONS MAY RETURN FOR A PERIOD ON FRI...THOUGH INTERMITTENT SUB-VFR CONDITIONS WILL BE POSSIBLE FRI INTO THE WEEKEND IN ASSOC/W THE UNSETTLED PROGRESSIVE SYNOPTIC PATTERN IN PLACE. && .RAH WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY UNTIL NOON WEDNESDAY FOR NCZ007>011-024>028- 040>043-076>078-085-086-088-089. WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO NOON EST THURSDAY FOR NCZ078-085-086-088-089. WINTER STORM WARNING FROM 6 PM THIS EVENING TO NOON EST THURSDAY FOR NCZ007>011-021>028-038>043-073>077-083-084. && $$ SYNOPSIS...CBL NEAR TERM...CBL SHORT TERM...RAH LONG TERM...CBL AVIATION...BSD/VINCENT

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