Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 291713 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC ISSUED BY NATIONAL WEATHER SERVICE BLACKSBURG VA 1213 PM EST THU JAN 29 2015 .SYNOPSIS...
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HIGH PRESSURE WILL MOVE OFFSHORE THIS AFTERNOON AHEAD OF A COLD FRONT THAT WILL CROSS THE AREA TONIGHT INTO FRIDAY MORNING. HIGH PRESSURE WILL BUILD IN FROM THE WEST ON FRIDAY...WHICH WILL HELP TO KEEP CONDITIONS DRY INTO THE WEEKEND.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 1027 AM THURSDAY... 15Z ANALYSIS SHOWS HIGH PRESSURE CONTINUING TO PUSH EAST OF US WHILE THE COLD FRONT OVER THE OHIO VALLEY MOVES EAST. CLOUDS WILL CONTINUE TO INCREASE ACROSS OUR AREA AS THIS PATTERN EVOLVES AND THE COLD FRONT APPROACHES. MODELS STILL SUGGESTING A FEW RAIN SPRINKLES OR LIGHT RAIN SHOWERS ARE POSSIBLE LATER TODAY IN ADVANCE OF THE FRONT...WITH THE BEST CHANCES ACROSS OUR NORTHERN AND WESTERN ZONES. LATEST HRRR SUGGESTS THE SLIGHT CHANCE POPS THIS AFTERNOON MAY NEED TO BE EXPANDED A LITTER FURTHER EASTWARD ACROSS OUR AREA...BUT EITHER WAY...ANY RAIN THAT OCCURS WILL BE VERY LIGHT WITH LOW IMPACTS. OTHERWISE...NO SIGNIFICANT CHANGES WITH THE MORNING UPDATE. PREV DISCUSSION AS OF 230 AM...OPTIMAL RADIATIONAL COOLING FOR THE NEXT COUPLE OF HOURS WHILE HIGH PRESSURE OVERHEAD CALMS WINDS AND SKIES REMAIN CLEAR. THIS WONT LAST FOR TOO LONG HOWEVER AS HIGH CLOUDS ARE BEGINNING TO MOVE IN FROM THE WEST ASSOCIATED WITH A FRONTAL SYSTEM WITH PARENT MOVING INTO THE CHICAGO AREA AT THIS TIME. THE ATTENDANT COLD FRONT...WHICH IS WEAK IS PROGGED TO CROSS CENTRAL NC LATER TONIGHT AND INTO FRIDAY MORNING. UNTIL THEN...SOUTHERLY RETURN FLOW WILL PICK UP ON THE BACK SIDE OF THE SURFACE HIGH AFTER SUNRISE WITH SOME GUSTING AROUND 15 KTS POSSIBLE...ESPECIALLY IN THE WEST WHICH IS FURTHER AWAY FROM THE CENTER OF THE HIGH. USING DRY ADIABATIC METHODS OR LOW LEVEL THICKNESSES SUGGEST TEMPERATURES IN THE MID TO UPPER 50S BUT WITH THE INCREASING CLOUD COVER...ESPECIALLY DURING PEAK HEATING THESE NUMBERS WILL BE CUT BACK TO THE UPPER 40S TO MID 50S. CANT RULE OUT SOME HIGHER TEMPS IN THE SOUTHEAST...WHERE THE EFFECTS OF THE APPROACHING SYSTEM WILL BE MOST DELAYED. AS FAR AS PRECIPITATION CHANCES ARE CONCERNED WITH THE ACTUAL FRONT...CONDITIONS ARE DRY BUT THE LATEST VERSION OF THE MODELS IS NOT QUITE AS DRY AS YESTERDAY WITH PW VALUES INCREASING TO NEAR 0.7 INCHES AS OPPOSED TO 0.5 YESTERDAY. A FIRST LOOK AT HIGH RESOLUTION CONVECTIVE MODELS ALSO SHOWS SOME VERY LIGHT PRECIPITATION IN THE NORTHWEST PIEDMONT JUST AFTER 21Z AND FADING OUT AS IT HEADS EASTWARD BEFORE PICKING UP AGAIN OFF THE COAST. FORECAST SOUNDINGS SHOW A SIMILAR STORY WITH THE BEST SATURATION IN THE TRIAD WITH LESS LIKELY CHANCES FOR RAIN SOUTH AND EAST. DESPITE BETTER CHANCES IN THE TRIAD...SATURATION IN THE MODEL SOUNDINGS IS BRIEF AND CONFINED TO THE 850-700 MB RANGE WITH A LOT OF DRY AIR UNDERNEATH...SUGGESTIVE OF SPRINKLES OR VIRGA PERHAPS IF MOISTURE CANT REACH THE SURFACE. THE RESULT IS STILL VERY INCONSEQUENTIAL AS QPF AMOUNTS WOULD BE A COUPLE OF HUNDREDTHS OF AN INCH AT THE VERY BEST BUT MORE LIKELY TRACE AMOUNTS OR NOTHING. BETTER UPPER LEVEL DYNAMICS COME IN AFTER 00Z FRIDAY BUT THE SYSTEM JUST LOOKS TO DRY TO SUSTAIN ANYTHING AT THAT TIME. AFTER FRONTAL PASSAGE AROUND 6Z FRIDAY...WINDS WILL SHIFT BACK TO NORTHWESTERLY AND COLD AIR ADVECTION WILL ONCE AGAIN ENSUE. LINGERING CLOUD COVER BEHIND THE FRONT WILL KEEP LOWS WARMER...IN THE LOW TO UPPER 30S NW TO SE. AS DRY AIR WORKS IN BEHIND THE FRONT...CLOUDS MAY CLEAR OUT FOR THE LATE MORNING PERIOD...BUT THEN WRAP AROUND MOISTURE ON THE BACK SIDE OF THE EXITING SYSTEM WILL MOVE IN FROM THE NORTH AND CUT DOWN ON INSOLATION DURING PEAK HEATING. THIS MAY CAUSE A TEMPERATURE GRADIENT FROM THE NORTH TO SOUTH RESULTING IN HIGHS IN THE MID 40S TO LOW 50S. DRY CONDITIONS ARE EXPECTED AND INCREASING WINDS OF 15-20 KTS SUSTAINED WITH GUSTS OF UP TO 25 KTS COULD CAUSE SOME FIRE WEATHER CONCERNS ON FRIDAY AFTERNOON. AT THIS TIME MIN RH VALUES WILL HOVER AROUND 30%. WINDS WILL DIE OFF AFTER SUNSET AND COUPLED WITH CLEAR SKIES WILL CAUSE OPTIMAL RADIATIONAL COOLING RESULTING IN LOW TEMPERATURES NEAR 20 DEGREES FRIDAY NIGHT INTO SATURDAY MORNING.
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&& .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... AS OF 300 AM THURSDAY... SURFACE HIGH PRESSURE OVER THE TN VALLEY WILL BUILD SOUTHWARD ACROSS THE AREA ON SATURDAY...SHIFTING SOUTH AND OFF THE SOUTHEAST COAST SATURDAY NIGHT. ALOFT...WEAK SOUTHERN STREAM IMPULSES EMBEDDED IN INCREASING ZONAL FLOW ALOFT LATE SATURDAY/SATURDAY NIGHT WILL YIELD THICKENING CIRRUS LAYER THROUGH THE DAY WITH MOSTLY CLOUDY SKIES BY SATURDAY NIGHT. HIGHS WILL REMAIN BELOW NORMAL...RANGING FROM LOWER 40S NORTH TO MID/UPPER 40S SOUTH. LOWS SATURDAY NIGHT IN THE LOWER TO MID 30S. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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AS OF 300 AM THURSDAY... SUNDAY THROUGH MONDAY: MINOR MID-LEVEL IMPULSES EMANATING FROM THE UPPER TROUGH/CLOSED LOW OVER THE SOUTHWEST US...WILL INTERACT....POTENTIALLY PHASE WITH NORTHERN STREAM ENERGY DIVING SEWD WITHIN THE BROADENING CONUS TROUGH. ASSOCIATED CYCLOGENESIS WILL TRACK EASTWARD ACROSS THE LOWER MS VALLEY/MID-SOUTH ON SUNDAY...CROSSING THE SOUTHERN APPALACHIANS SUNDAY EVENING AND THEN OFF THE CAROLINA COAST BY MIDDAY MONDAY. DESPITE MODEL DIFFERENCES IN THE AMPLITUDE OF THE NORTHERN STREAM TROUGH...TIMING OF THE BETTER RAIN CHANCES INTO THE AREA ARE SIMILAR...WITH RAIN CHANCES QUICKLY RAMPING UP LATE SUNDAY AFTERNOON/EARLY EVENING...WITH CATEGORICAL POPS SUNDAY NIGHT...CUTTING OFF FROM WEST TO EAST MORNING MONDAY AS THE MID- LEVEL DRY SLOT SPREAD EAST. CURRENT MODELS PROJECT A SOLID 0.50-1.0" ACROSS THE AREA...WITH SOME HIGHER AMOUNTS POSSIBLE IF THE MORE AMPLIFIED--WETTER GFS VERIFIES. NO P- TYPE CONCERNS. HIGHS BOTH DAYS IN THE 40S NORTH TO AROUND 50 SOUTH. LOWS SUNDAY NIGHT IN THE MID TO UPPER 30S NORTH TO LOWER-MID 40S SOUTH. MONDAY NIGHT THROUGH WEDNESDAY: CONTINENTAL POLAR HIGH PRESSURE WILL BUILD INTO THE AREA MONDAY NIGHT AND INTO TUESDAY IN THE WAKE OF THE UPPER LEVEL TROUGH LIFTING OUT OF THE AREA. IF PROJECTED LOW-LEVEL THICKNESSES VERIFY...STRONG CAA MONDAY NIGHT WILL SUPPORT LOWS TUESDAY MORNING IN THE TEENS ACROSS MUCH OF THE AREA...WITH HIGHS TUESDAY AFTERNOON STRUGGLING TO WARM INTO THE 40S. MODEL SPREAD REMAINS HIGH WITH THE EASTWARD EJECTION OF THE AFOREMENTIONED UPPER TROUGH/LOW OVER THE SOUTHWEST US. WHILE THE EC SUGGEST THIS SYSTEM COULD BRING PRECIP CHANCES BACK INTO THE AREA LATE TUESDAY NIGHT AND INTO WEDNESDAY...THE GFS AND CANADIAN SUPPRESS THE SYSTEM WELL TO OUR SOUTH...MAINTAINING DRY CONDITIONS THROUGH LATE WEEK. GIVEN THE UNCERTAINTY HAVE LIMITED POP TO SLIGHT/SMALL CHANCE.
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&& .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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AS OF 1202 PM EST THURSDAY... 24 HOUR TAF PERIOD: BANDS OF HIGH AND MID CLOUDS WILL CONTINUE TO SWEEP EAST THIS AFTERNOON AHEAD OF AN APPROACHING COLD FRONT JUST WEST OF THE MOUNTAINS. CEILINGS MAY LOWER BELOW 8K FEET ACROSS THE WESTERN SITES LATE THIS AFTERNOON AS A DEEPER BAND OF MOISTURE SWINGS EAST AND WEAKENS. THUS WILL CONTINUE MEDIUM TO HIGH CONFIDENCE OF VFR CONDITIONS THROUGH THE TAF PERIOD AS THIS FRONT SLIDES ACROSS THE FROM THE WEST TONIGHT. THERE IS A SLIGHT CHANCE THAT CEILINGS COULD APPROACH MVFR LEVELS BETWEEN 03Z-08Z/10PM-3AM BUT IFFY AND MAINLY WEST OF KRDU AT THIS POINT. SOUTH TO SOUTHWEST WINDS MAY ALSO GUST TO BETWEEN 15-20 KTS THIS AFTERNOON BEFORE RELAXING AGAIN AFTER SUNSET. MAYBE A SPRINKLE OR LIGHT SHOWER IN THE TRIAD AHEAD OF THE FRONT DURING THE LATE AFTERNOON/EARLY EVENING TIMEFRAME. THE PASSING COLD FRONT WILL BRING A SHIFT IN WINDS TO THE WEST/NORTHWEST AFTER MIDNIGHT FOLLOWED BY GUSTY NORTHWEST WINDS FOR MUCH OF THE DAY ON FRIDAY. APPEARS SUSTAINED NORTHWEST WINDS OF 15-22 KNOTS LIKELY WITH GUSTS TO 25-30 KNOTS OR PERHAPS HIGHER NEAR THE END OF THE VALID TAF PERIOD. LONG TERM: SUB-VFR CONDITIONS WILL BE POSSIBLE WITH A LOW PRESSURE SYSTEM THAT WILL CROSS THE AREA LATE SUNDAY INTO MONDAY. VFR CONDITIONS WILL PREVAIL ON TUESDAY AS HIGH PRESSURE BUILDS EAST BEHIND THIS SYSTEM.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...JH/ELLIS NEAR TERM...-/ELLIS SHORT TERM...CBL LONG TERM...CBL AVIATION...JH/ELLIS

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