Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 050036 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 736 PM EST WED MAR 4 2015 .SYNOPSIS...A STRONG COLD FRONT WILL CROSS CENTRAL NC LATE TONIGHT AND EARLY THURSDAY. ARCTIC HIGH PRESSURE WILL BUILD OVER THE REGION BEHIND THE FRONT FRIDAY AND SATURDAY. && .NEAR TERM /THROUGH THURSDAY NIGHT/... AS OF 305 PM WEDNESDAY... MODELS ARE IN RELATIVELY GOOD AGREEMENT IN THE TIMING OF SFC COLD FRONT WITH AN INITIAL WEAK WAVE OF LOW PRESSURE INTO THE AREA BETWEEN 06Z-12Z. SOUTHWESTERLY LOW TO MID LEVEL FLOW..BEHIND THE COLD FRONT BISECTING THE AREA AT 12Z WILL SUPPORT ANA-FRONTAL PRECIP BAND ON THE COOL SIDE OF THE BOUNDARY...ALONG A LINE FROM ALBEMARLE TO SANFORD TO WILSON...MAKING FOR A MESSY MORNING COMMUTE FOR THE TRIAD AND TRIANGLE. EXPECT QUITE A SHARP NORTH-SOUTH CONTRAST IN TEMPERATURES...RANGING FROM LOWER 40S TO LOWER 60S. THURSDAY AND THURSDAY NIGHT: THE GFS AND NAM HAVE COME INTO BETTER WITH THE TIMING OF THE COLD AIR SURGING SOUTH INTO THE AREA...WITH THE GFS TRENDING TOWARDS THE SLOWER/LESS AGGRESSIVE NAM. P-TYPE: LOW-LEVEL COLD AIR SURGING SOUTHWARD OUT OF VIRGINIA WILL INITIALLY SUPPORT A CHANGEOVER FROM RAIN TO A FREEZING RAIN/SLEET MIX AS MID-LEVEL COOLING(STRONG WARM NOSE)LAGS BEHIND. THEN AS THE MID-LEVEL COOLS AND A SUBSTANTIAL/DEEP LOW-LEVEL COLD NOSE DEVELOPS (-6C)...PRECIP COULD END AS MOSTLY SLEET WITH MODELS INDICATING A .10 TO .20 INCHES OF LIQUID EQUIVALENT CENTERED OVER THE CENTRAL PIEDMONT-NORTHERN AND CENTRAL COASTAL PLAIN BETWEEN 05/00Z AND 05/06Z. ICE AMOUNTS ARE ALWAYS DIFFICULT TO ASCERTAIN ANYTIME THERE IS A LONG DURATION IN THE MIXED SLEET/FREEZING RAIN REGIONS OF THE NOMOGRAM. ULTIMATELY THE PREDOMINATE P-TYPE IN THIS EVENT COULD LARGELY BE DETERMINED BY PRECIP RATES...WITH MORE SLEET IN THE HEAVIER PRECIP BANDS PROMOTING ENHANCED COOLING ALOFT. COULD SEE AS MUCH AS 0.10 TO 0.15 OF AN INCH OF FREEZING RAIN ALONG AND NORTH OF HIGHWAY 64 IS POSSIBLE...WITH SLEET AMOUNTS OF AROUND 0.50" POSSIBLE. ANY ICE ACCRUAL WILL BE CONFINED MAINLY TO ELEVATED SURFACES OWING TO WARM PAVEMENT TEMPERATURES FROM TODAYS +70 DEGREE READINGS. TIMING: USING A BLEND OF THE GFS AND NAM...THE CHANGE-OVER FROM RAIN TO FREEZING RAIN/SLEET LOOKS TO OCCUR BETWEEN 21Z NEAR THE VIRGINIA BORDER TO 00Z ACROSS THE CENTRAL PIEDMONT/COASTAL PLAIN(ROUGHLY ALONG AND NORTH OF HIGHWAY 64). WHILE THE CHANGE-OVER SHOULD CONTINUE TO SURGE SOUTHWARD INTO THE SANDHILLS/SOUTHERN PIEDMONT/SOUTHERN COASTAL PLAIN BETWEEN 00 TO 06Z...SUFFICIENT COOLING TO SUPPORT FROZEN PRECIP APPEARS TO SHORT TO ALLOW ANY APPRECIABLE ACCRUAL BEFORE PRECIP ENDS. SINCE ANY P-TYPE CONCERNS WILL BE DURING LATE 2ND/EARLY 3RD PERIOD...PREFERENCE IS TO HOLD OFF ON ISSUING ANY ADVISORIES AT THIS TIME SO THAT FURTHER MODEL TRENDS CAN BE EVALUATED WITH THE 00Z/05 MODEL PACKAGE. CLEARING FROM NW TO SE AND INTRUSION OF ARCTIC AIR INTO THE AREA WILL SUPPORT COLD OVERNIGHT LOWS IN THE 20S WHICH WILL LIKELY LEAD TO BLACK ICE DEVELOPMENT ACROSS THE AREA THURSDAY NIGHT/FRIDAY MORNING. A WINTER WEATHER ADVISORY MAY BE NEEDED FOR BLACK ICE && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... AS OF 305 PM WEDNESDAY... LOW LEVEL COLD AIR ADVECTION FRIDAY WILL RESULT IN ANOTHER DAY OF WELL BELOW NORMAL TEMPS. THICKNESSES AVERAGE CLOSE TO 50M BELOW NORMAL...SUGGESTIVE OF MAX TEMPS CLOSE TO 20 DEGREES BELOW NORMAL. WITH PLENTY OF SUN AND AN INCREASING SUN ANGLE SHOULD SEE TEMPS RECOVER AT LEAST 15-18 DEGREES FROM MORNING LOWS INSPITE OF THE LOW LEVEL CAA. FAVOR THE COOLER MET GUIDANCE WHICH SUPPORTS MAX TEMPS IN THE MID-UPPER 30S. COLDEST NIGHT EXPECTED MOST LOCATIONS FRIDAY NIGHT AS 850MB THERMAL TROUGH CROSSES REGION IN THE EVENING AND SFC RIDGE SETTLES DIRECTLY OVERHEAD. MIN TEMPS 15-20 DEGREES FROM RDU AND AREAS NORTH AND EAST...TO THE LOWERS 20S FAR WEST-SW. MILDER CONDITIONS ANTICIPATED SATURDAY AS SFC RIDGE DRIFTS SLOWLY EAST. WITH PLENTY OF DRY AIR AND A DEVELOPING LOW LEVEL WEST-SW FLOW...SHOULD SEE A DIURNAL TEMP RECOVER OF 30-35 DEGREES ACROSS THE AREA. MAX TEMPS NEAR 50 FAR NE TO THE MID 50S SW. POTENTIAL FOR MAX TEMPS TO BE A FEW DEGREES WARMER...AS 850MB WLY FLOW HAS A TENDENCY TO WARM US UP GREATER THAN EXPECTED IN THESE DRY AIR MASSES. SATURDAY NIGHT...WLY FLOW ALOFT MAY FILTER SOME HIGH CLOUDS OVER THE REGION BUT THE LOWER LEVELS WILL REMAIN DRY. A LINGERING LIGHT SW SFC FLOW WILL AID TO KEEP TEMPS FROM FREE-FALLING AFTER SUNSET. MIN TEMPS NEAR 30 NORTH TO LOWER 30S SOUTH. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... AS OF 305 PM WEDNESDAY... MODERATING TEMPERATURES WILL CONTINUE INTO EARLY NEXT WEEK AS MILD HIGH PRESSURE BUILDS EAST ACROSS THE SOUTHERN OHIO VALLEY. MEANWHILE...FAST...CONFLUENT...NEAR ZONAL FLOW ALOFT WILL MAINTAIN SEPARATION BETWEEN THE NORTHERN AND SOUTHERN STREAMS...WITH THE MORE MOISTURE LADEN SOUTHERN STREAM SUPPRESSED ACROSS THE DEEP SOUTH. THIS WILL RESULT IN MOSTLY SUNNY SKIES SUNDAY AND MONDAY. HIGHS SUNDAY WILL REACH MAINLY MID 50S. ON MONDAY...AFTER A MORNING LOW AROUND 40...HIGHS WILL CLIMB TO NEAR NORMAL...WITHIN A DEGREE OR SO OF 60. SLOW EJECTION OF A SOUTHERN STREAM SHORT WAVE ACROSS THE SOUTHERN CONUS/NORTHERN GULF IS EXPECTED EARLY NEXT WEEK. AS THIS WAVE MOVES EAST...THE GRADUAL DEEPENING OF A MID LEVEL TROF OVER THE MIDWEST WILL INITIALLY BEGIN TO BULGE THE SOUTHERN STREAM NORTHWARD INTO THE SOUTH ATLANTIC STATES MONDAY NIGHT. THUS EXPECT INCREASING MID/HIGH CLOUDINESS MONDAY NIGHT WHICH WILL OFFSET RADIATION TO MAINTAIN HIGHS OF AROUND 60 ON TUESDAY IN A WEAK CAD CONFIGURATION DESPITE THE MODESTLY BUILDING HEIGHTS ALOFT. HAVE LOW CONFIDENCE IN THE DETAILS IN THE LONGER RANGE GIVEN POOR MODEL CONSENSUS AS TO WHEN AND WHERE WE MIGHT EXPECT SURFACE DEVELOPMENT AND ATTENDANT MOISTURE ADVECTION INTO THE AREA. THE GFS SOLUTION IS MUCH FASTER...WITH STRONG OVERRUNNING AS EARLY AS TUESDAY NIGHT...WHILE THE ECMWF DELAYS DEVELOPMENT OF A SURFACE LOW UNTIL THURSDAY. AT THIS POINT WILL MAINTAIN ONGOING SLIGHT LOW CHANCES OF RAIN TUESDAY AND WEDNESDAY WITH HIGHS IN THE LOW TO MID 60S AS WE WAIT FOR BETTER MODEL CONSENSUS. THE HIGH TEMPERATURES WILL BE HEAVILY DEPENDENT ON THE POTENTIAL IN-SITU DAMMING...AND THE EARLIER GFS SOLUTION WOULD RESULT IN HIGHS BEING CONSIDERABLY COOLER...ESPECIALLY ON TUESDAY. && .AVIATION /00Z THURSDAY THROUGH MONDAY/...
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AS OF 735 PM WEDNESDAY... MAINLY VFR CONDITIONS...IN CONTINUED SOUTHWESTERLY FLOW AHEAD OF AN APPROACHING COLD FRONT...WILL BECOME MVFR-IFR FROM NORTH TO SOUTH WITH THE PASSAGE OF THE COLD FRONT BETWEEN 10-14Z AT NORTHERN TAF SITES...TO BETWEEN 15-19Z AT KFAY. TWO EXCEPTIONS TO THE OTHERWISE PRECEDING VFR CONDITIONS WILL BE A TEMPORARY MVFR CEILING AT KINT/KGSO FOR A BRIEF TIME THIS EVENING...AND A MEDIUM CHANCE OF IFR VISIBILITY RESTRICTIONS AND/OR CEILINGS AT KFAY OVERNIGHT...WHERE THE COMBINATION OF RADIATIONAL COOLING DURING TIMES OF LIGHTER TO OCCASIONALLY NEAR CALM WIND...WITH A RELATIVE MAXIMUM IN SURFACE DEWPOINTS OVER SE NC...WILL SUPPORT THE DEVELOPMENT OF AREAS OF FOG/LOW STRATUS. ONCE SURFACE WINDS LESSEN AND QUIT GUSTING AREA-WIDE WITHIN THE NEXT COUPLE OF HOURS IN ASSOCIATION WITH THE DEVELOPMENT OF A NOCTURNAL INVERSION...LOW LEVEL WIND SHEAR WILL ALSO BECOME PROBABLE OWING TO THE DEVELOPMENT OF A 40-50 KT LOW LEVEL JET JUST ABOVE THE SURFACE. THE PASSAGE OF THE AFOREMENTIONED SURFACE COLD FRONT WILL END THE THREAT OF LOW LEVEL WIND SHEAR...AND INSTEAD RESULT IN A STRONG POST- FRONTAL NORTHEASTERLY WIND BETWEEN 10-15 KTS...WITH GUSTS AROUND 20 KTS. WIDESPREAD RAIN AND ASSOCIATED MVFR-IFR CONDITIONS TRAILING THE PASSING COLD FRONT WILL CONTINUE THROUGHOUT THU...BEFORE RAIN CHANGES TO SLEET FROM NORTH TO SOUTH THU AFTERNOON AND EVENING. OUTLOOK: AFTER LINGERING LIGHT SLEET AND MVFR CONDITIONS KRDU/KFAY/KRWI THU EVENING...PERSISTING LONGEST INTO THU NIGHT AT KFAY...VFR CONDITION ARE ANTICIPATED FOR THE NEXT SEVERAL DAYS.
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&& .CLIMATE... RDU GSO FAY 03/06: RECORD LOW MAX 32-1901 34-1960 34-1960 MIN 11-1960 5-1960 19-1960 && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...RAH NEAR TERM...CBL SHORT TERM...WSS LONG TERM...MLM AVIATION...RAH CLIMATE...CBL

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