Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 280545 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1245 AM EST SAT FEB 28 2015 .SYNOPSIS...COLD HIGH PRESSURE OVER THE CENTRAL PLAINS WILL BUILD INTO THE MID ATLANTIC THROUGH SATURDAY. A COLD FRONT WILL APPROACH FROM THE NORTHWEST ON SUNDAY AND MOVE INTO THE AREA BY MONDAY. && .NEAR TERM /THROUGH SATURDAY NIGHT/... AS OF 950 PM FRIDAY... GOOD RADIATIONAL COOLING TO START THE NIGHT AS SKIES ARE CLEAR AND WINDS ARE EITHER LIGHT OR CALM. REGIONAL RAOB ANALYSIS REVEALS MODEST COLD ADVECTION IN THE LOW-LEVELS (BELOW 850MB) AS ANOTHER 1040MB HIGH IS MOVING EAST ACROSS THE MIDWEST STATES. THE NAM AND GFS BOTH SHOW RAPID MOISTENING IN THE BOUNDARY LAYER...WITH SATURATION REACHING UP TO AROUND -8C AND EVEN A LITTLE QPF VIA SOME SHALLOW FGEN WITH THE INITIAL SURGE OF COLD ADVECTION. HOWEVER...THIS IS NOT SUPPORTED BY THE LATEST RAP AND HRRR. THE STRATUS WOULD ESSENTIALLY DEVELOP OVERHEAD...SO THE LACK OF CLOUDS DEVELOPING UPSTREAM OVER VA ISNT MUCH HELP. THE MOST RECENT NAM AND GFS FORECAST SOUNDS HAVE TREND SLIGHTLY WARMER IN BOUNDARY LAYER AND SLOWER WITH THE SATURATION WHICH COULD BE AN INDICATION THAT THEY HAVE BEEN OVERDONE. SREF MEMBERS ARE PRETTY MUCH SPLIT DOWN THE MIDDLE. STILL EXPECT SOME STRATUS WITH THE NORTHEAST FLOW BUT MAYBE MORE PATCHY THAT PREVIOUSLY THOUGHT. WILL LOWER LOWS A DEGREE OR TWO BASED ON TRENDS...DIPPING TO NEAR 20 IN THE NORTHEAST AND CLOSER TO 30 IN THE SOUTHEAST. AS FOR BLACK ICE...DESPITE A DAY OF GOOD MELTING TODAY...THE POTENTIAL FOR BLACK ICE TONIGHT AND SAT MORNING IS STILL THERE FOR AREAS THAT RECEIVED THE HEAVIEST SNOW. AFTER COORDINATING WITH OFFICIALS FROM SEVERAL OF THE HARDEST HIT COUNTIES...WE HAVE DECIDED TO ISSUE AN ADVISORY FOR BLACK ICE FOR TONIGHT FOR OUR VA BORDER COUNTIES...AND FOR FORSYTH EAST TO FRANKLIN. WE WILL ALSO ISSUE AN SPS FOR THE REMAINING COUNTIES THAT GOT LESSER AMOUNTS OF SNOW TO COVER THE MORE ISOLATED NATURE OF BLACK ICE POTENTIAL. FOR SATURDAY...COOL HIGH PRESSURE WILL CONTINUE BUILDING SOUTH DURING THE DAY SATURDAY...RESULTING IN FAIR WEATHER WITH BELOW- NORMAL TEMPS. HIGHS ONLY IN THE MID 30S. LIKE TODAY...IF THERE IS LESS CLOUD COVER THAN FORECAST...THE SUN COULD HELP WARM TEMPS SEVERAL DEGREES HIGHER THAN FORECAST. SATURDAY NIGHT...FLOW IN THE 925-850 MB LAYER WILL TURN TO THE SW AND BEGIN ADVECTING MOISTURE UP INTO OUR AREA AS THE 850MB RIDGE MOVES EAST AHEAD OF THE TROUGH MOVING ACROSS THE UPPER MISS VALLEY. WITH THE SFC RIDGE AXIS HOLDING FIRMLY IN PLACE ACROSS OUR AREA... THE SUBSEQUENT OVERRUNNING AND UPGLIDE WILL RESULT IN INCREASING CLOUDS OVERNIGHT. THERE ARE VARYING SOLUTIONS RIGHT NOW REGARDING WHEN PRECIP WILL DEVELOP ACROSS OUR AREA...BUT THE PRECIP START TIME IS IMPORTANT BECAUSE IF IT STARTS EARLY ENOUGH...SAY A FEW HOURS EITHER SIDE OF SUNRISE...IT MAY BE COLD ENOUGH STILL FOR A VERY BRIEF PERIOD OF FREEZING RAIN AT THE ONSET OF PRECIP. EVEN IF THE EARLIER SOLUTIONS WERE TO VERIFY...THE QPF DURING THAT TIME WOULD BE VERY LIGHT...SO LITTLE IF ANY IMPACTS WOULD BE EXPECTED. IT`S DEFINITELY WORTH KEEPING AN EYE ON. LOWS IN THE MID TO UPPER 20S. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 240 PM FRIDAY... SURFACE HIGH PRESSURE RIDGING INTO CENTRAL NC FROM THE NORTHEAST WILL LINGER OVER THE AREA THROUGH SUNDAY...WITH CONTINUED COLD ADVECTION AND CLOUDY SKIES. HIGHS EXPECTED TO BE MAINLY IN THE UPPER 30S NW TO MID 40S SE. THE SURFACE HIGH WILL BE SUPPRESSED TO THE SOUTHEAST SUNDAY EVE/NIGHT AS A SURFACE LOW TRAVERSES THE GREAT LAKES AND ITS ASSOCIATED COLD FRONT PUSHES SE TOWARD THE REGION. RAINFALL COULD BEGIN AS EARLY AS MONDAY AFT/EVE AHEAD OF THE FRONT AS WARM MOIST SOUTHWEST FLOW ABOVE THE SURFACE OVERRUNS THE COLD AIR AT THE SURFACE...PARTICULARLY IN THE WESTERN PORTIONS OF THE AREA... ALTHOUGH THE GFS IS A BIT MORE EXCITED ABOUT THAT POSSIBILITY THAN THE ECMWF. THERE WILL HOPEFULLY BE ENOUGH WARM ADVECTION FROM THE SOUTHWEST AHEAD OF THE FRONT TO KEEP TEMPERATURES ABOVE FREEZING...AS A NON-DIURNAL TEMPERATURE CURVE IS ANTICIPATED FROM 18Z SUNDAY THROUGH 00Z TUESDAY. REGARDLESS...FORECAST SOUNDINGS SHOW ENOUGH OF A WARM NOSE ABOVE THE SURFACE AND LIMITED MOISTURE IN THE ICE NUCLEATION REGION THAT PRECIPITATION SHOULD BE ALL LIQUID. TEMPERATURES SHOULD RISE APPROXIMATELY 5 DEGREES OR SO OVERNIGHT INTO THE UPPER 30S NW TO MID 40S SE BY MONDAY MORNING. BY SUNRISE MONDAY THE COLD FRONT IS EXPECTED TO BE ON THE DOORSTEP OF CENTRAL NC...WITH THE BEST RAINFALL CHANCES ACTUALLY ENDING WELL AHEAD OF THE FRONT. THE MODELS SHOW THE RAINFALL ALONG THE MAIN AXIS OF THE FRONT DISSIPATING AS IT CROSSES THE MOUNTAINS AND THE FRONT BECOMING ORIENTED MORE WEST TO EAST THROUGH CENTRAL NC MONDAY AFT/EVE. DIFFERENCES/UNCERTAINTY IN THE TIMING AND LOCATION OF THE FRONT AS IT SETTLES SOUTH WILL RESULT IN A FAIRLY BIG MARGIN FOR ERROR IN THE MAX AND MIN TEMPS AS COLD HIGH PRESSURE BUILDS IN FROM THE NORTH BEHIND THE FRONT. FOR NOW EXPECT HIGHS AROUND 50 DEGREES NORTH TO MID 50S SOUTH AND LOWS IN THE LOW 30S NORTH TO UPPER 30S SOUTH. && .LONG TERM /TUESDAY THROUGH FRIDAY/... AS OF 310 PM FRIDAY... A COLORADO LOW IS EXPECTED TO DEVELOP OVER THE MIDWEST EARLY TUESDAY AS SURFACE HIGH PRESSURE AND NORTHWEST FLOW ALOFT LINGER OVER CENTRAL NC. THE HIGH WILL SHIFT OFFSHORE TUESDAY AFTERNOON...WITH WARM MOIST SOUTHERLY RETURN FLOW ADVECTING INTO THE REGION. SUBSEQUENTLY...THE COLD FRONT WILL LIFT NORTH THROUGH THE AREA AS A WARM FRONT...WITH THE CHANCE FOR RAIN TO ONCE AGAIN MOVE INTO THE SOUTHWEST PORTIONS OF THE AREA TUESDAY AFT/EVE AND INTO THE OVERNIGHT HOURS. ALTHOUGH CONFIDENCE IN TEMPERATURES IS FAIRLY LOW AT THIS TIME...HIGHS ARE EXPECTED TO BE IN THE MID 40S TO MID 50S FROM NW TO SE AND WILL AGAIN LIKELY BOTTOM OUT IN THE LATE EVENING BEFORE GRADUALLY RISING OVERNIGHT TO POTENTIALLY THE LOW 50S NW TO AROUND 60 DEGREES SE AT SUNRISE WEDNESDAY. THE MODELS STILL DIFFER QUITE A BIT WITH REGARD TO THE TIMING OF THE FRONT...AND GIVEN THE HABIT OF THE GFS TO BE A BIT ON THE FAST SIDE...WILL LEAN TOWARD THE SLOWER SIDE OF THE FROPA TIMING AND THE ASSOCIATED PRE-FRONTAL RAINFALL. THE GFS BRINGS PRE-FRONTAL CONVECTION INTO THE NW PIEDMONT AS EARLY AS WEDNESDAY AFTERNOON...WHILE THE ECMWF HOLDS OFF UNTIL AFTER MIDNIGHT THURSDAY. HIGHEST CHANCES WILL START AROUND 00Z THURSDAY IN THE NW AND END AROUND 00Z FRIDAY IN THE SE AND DRYING OUT EVERYWHERE BY FRIDAY AFTERNOON (AS OF THE LATEST RUNS). TEMPS CONTINUE TO BE LOW CONFIDENCE AS THEY WILL DEPEND STRONGLY ON THE TIMING OF THE FRONT...BUT WITH THAT BEING SAID HAVE HIGHS WED IN THE UPPER 50S NW TO LOW 70S SE. LOWS WED NIGHT AND HIGHS THURSDAY PROBABLY A BIT TOO COOL...LOW 40S NW TO AROUND 50 DEGREES SOUTH AND UPPER AROUND 50 DEGREES NW TO UPPER 50S SE...RESPECTIVELY. EXPECT A COOL BUT DRY PERIOD THU NIGHT INTO FRIDAY...LOWS IN THE MID 20S TO AROUND 30 DEGREES AND HIGHS UPPER 40S TO AROUND 50 DEGREES. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... AS OF 1245 AM SATURDAY... DEVELOPING NE LOW LEVEL FLOW WILL CAUSE A DECK OF STRATOCU TO PROGRESS SWWD ACROSS SECTIONS OF THE NORTHERN COASTAL PLAIN AND THE NORTHERN PIEDMONT OVERNIGHT. BY 10Z...THE STRATOCU WILL LIKELY BE BANKED UP AGAINST THE BLUE RIDGE AND EXTEND BACK INTO THE TRIAD REGION. THIS STRATOCU DECK SHOULD DIMINISH IN VICINITY OF THE TRIAD BY 14Z-15Z. OTHERWISE EXPECT VFR CONDITIONS AND A BRISK NE SFC WIND THIS MORNING WITH OCCASIONAL GUSTS 15-18KTS BETWEEN 10Z-18Z. THIS FLOW WILL DEPOSIT A COLD DRY AIR MASS ACROSS THE REGION TODAY...LINGERING INTO EARLY SUNDAY. AN AREA OF LOW PRESSURE WILL APPROACH FROM THE SOUTHWEST LATE TONIGHT INTO SUNDAY. SLY FLOW A FEW THOUSAND FEET ABOVE THE COLD STABLE AIR MASS AT THE SURFACE WILL PULL WARM MOIST AIR INTO THE REGION. THIS WILL CAUSE WIDESPREAD LOW CLOUDS TO DEVELOP ALONG WITH A AREAS OF LIGHT PRECIPITATION. WITH NEAR SURFACE TEMPS EXPECTED TO BE NEAR OR SLIGHTLY BELOW FREEZING...THE PRECIPITATION WILL LIKELY START OUT AS FREEZING RAIN SUNDAY MORNING THEN TRANSITION TO RAIN AS SFC TEMPS WARM TO ABOVE FREEZING BY MID DAY-EARLY AFTERNOON. THE FREEZING PRECIPITATION WILL LAST LONGEST OVER THE NORTHERN PIEDMONT...AND THE LEAST IN VICINITY OF KFAY. A COLD FRONT WILL CROSS THE REGION MONDAY...FOLLOWED BY AN AREA OF HIGH PRESSURE AND ITS ASSOCIATED VFR CONDITIONS. ANOTHER LOW PRESSURE SYSTEM WILL CAUSE ANOTHER PERIOD OF SUB VFR CONDITIONS LATE TUESDAY INTO WEDNESDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY FOR BLACK ICE IN EFFECT THROUGH 10 AM EST THIS MORNING FOR NCZ007>011- 021>026-041. && $$ SYNOPSIS...RAH NEAR TERM...RAH/BLS SHORT TERM...KC LONG TERM...KC AVIATION...WSS

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