Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 201948 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 247 PM EST SAT DEC 20 2014 .SYNOPSIS...
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A SHORTWAVE LOW WILL EXIT THE AREA THIS AFTERNOON INITIATING A BRIEF DRYING TREND FOR SUNDAY. THE PATTERN WILL BECOME UNSETTLED AGAIN SUNDAY NIGHT AND INTO EARLY NEXT WEEK AS A LOW PRESSURE SYSTEM DEVELOPS OFF OF THE SOUTHEAST COAST AND MOVES NORTHWARD INTO THE CAROLINAS FOR THE BEGINNING OF NEXT WEEK.
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&& .NEAR TERM /THROUGH SUNDAY NIGHT/...
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AS OF 245 PM SATURDAY... TODAY AND TONIGHT: VERY LIGHT RAIN STILL FALLING ACROSS EASTERN COUNTIES THIS HOUR BUT OTHERWISE MUCH OF THE CWA IS CLEARING OUT AS FAR AS PRECIPITATION. CLOUD COVER IS A DIFFERENT STORY AS THERE IS A PATCHWORK OF CEILINGS IN THE WAKE OF THE SHORTWAVE ANYWHERE FROM VFR TO IFR. WESTERN STATIONS FOR THE MOST PART HAVE RETURNED TO VFR AND SHOULD STAY THERE THROUGH THE AFTERNOON AS DRIER AIR BEGINS TO MOVE IN BELOW 850 MB. THIS DRIER BOUNDARY LAYER SHOULD FILTER INTO EASTERN SITES OVER THE NEXT SEVERAL HOURS. AT LEAST VFR CEILINGS SHOULD HANG ON FOR THE REST OF THE DAY WHICH WILL KEEP MAX TEMPS DOWN IN THE LOW 40S. SOME NORTHERN SITES WILL NOT GET OUT OF THE UPPER 30S TODAY. OVERNIGHT TONIGHT THERE IS A LOW CONFIDENCE FORECAST REGARDING ANY POTENTIAL CLEARING. THE RESULT OF SUCH CLEARING WOULD BE A GREAT OPPORTUNITY FOR FOG IN A WINDOW GENERALLY BETWEEN 6-12Z. THIS WILL ALSO COINCIDE WITH A WINDOW OF POTENTIAL FREEZING TEMPERATURES AS THICKNESS VALUES ARE AROUND 1310 AND MOST GUIDANCE SUGGESTING LOWS TONIGHT IN THE UPPER 20S TO LOW 30S. CURRENT FORECAST SOUNDINGS SHOW THE POTENTIAL ACROSS THE NORTHERN AREAS AND ARE PRETTY FAVORABLE FOR FREEZING FOG EVEN WITH A POTENTIAL THIN BROKEN TO OVERCAST LAYER AROUND 5 KFT. COVERAGE OF THE FOG WILL MOST LIKELY BE PATCHY BUT COULD BE UPGRADED TO AREAS IN SOME LOCATIONS. IMPACTS OF THIS WILL MOST LIKELY BE INCONSEQUENTIAL BUT CAN NOT RULE OUT SOME SLICK SPOTS ON ELEVATED SURFACES...BUT IN ALL LIKELIHOOD ROADS SHOULD BE OK. SUNDAY AND SUNDAY NIGHT: TEMPERATURES WILL QUICKLY REBOUND AND THE SURFACE LAYER SHOULD DRY OUT AFTER 14Z OR SO. THE ATTENTION THEN WILL TURN TO THE EVOLVING PATTERN FOR SUNDAY WHICH WILL BE THE DEVELOPMENT OF TWO FEATURES...ONE BEING A COASTAL LOW ALONG THE SOUTHEAST COAST AND THE SECOND BEING THE DEVELOPMENT OF A CAD WEDGE ASSOCIATED WITH A HIGH PRESSURE OVER THE NORTHEAST. MOST OF THE MOISTURE ASSOCIATED WITH THE LOW WILL REMAIN SOUTH OF THE AREA...SO SUNDAY SHOULD BE DRY BUT WE WILL SEE SOME CLOUD COVER ENCROACHING FROM THE SOUTHWEST...WHICH WILL INCREASE THROUGH SUNDAY AFTERNOON. HIGHS ON SUNDAY WILL BE IN THE UPPER 40S NORTH TO LOW 50S SOUTH. ON SUNDAY NIGHT THE ISENTROPIC LIFT WILL INCREASE SIGNIFICANTLY AS THE LOW GETS CLOSER TO THE AREA AND THE WEDGE FRONT SHARPENS UP. PRECIPITATION CHANCES WILL STEADILY INCREASE OVERNIGHT FROM SLIGHT CHANCE EARLY ON TO NEAR DEFINITE BY MONDAY MORNING. SOUTHWESTERN AREAS WILL SEE THE MOST QPF BEFORE DAYBREAK...MOST LIKELY BETWEEN 0.1-0.2 INCHES. BECAUSE OF THE CLOUD COVER...LOWS WILL MODERATE A LITTLE...MID 30S TO LOWER 40S NORTHEAST TO SOUTHWEST.
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&& .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... AS OF 315 AM SATURDAY... SFC RIDGE EXTENDS SOUTH ACROSS THE AREA...AIDED ALOFT BY A MINOR S/W RIDGE. THIS SHOULD PROVIDE PARTLY-MOSTLY SUNNY SKIES TO START THE DAY. A S/W EXITING THE SOUTHERN PLAINS WILL BACK THE FLOW ALOFT TO A SWLY FLOW AND BEGIN TO ADVANCE MID-HIGH LEVEL CLOUDINESS FROM THE SOUTH LATE IN THE DAY. LOW LEVEL THICKNESSES IN THE 1315M- 1330M RANGE...SUPPORTIVE OF MAX TEMPS ABOUT A CATEGORY OR TWO BELOW NORMAL. MAX TEMPS NEAR 50-LOWER 50S. IF CLOUDS ARE DELAYED ACROSS THE SOUTH...MAX TEMPS MAY END UP BEING 2-3 DEGREES WARMER. SUNDAY NIGHT...SOUTHERN STREAM S/W PROJECTED TO CROSS THE LOWER MS VALLEY AND INDUCE WEAK SFC WAVE DEVELOPMENT OFF THE SC COAST BY EARLY MONDAY. WHILE A DRY AIR SFC RIDGE WILL MAINTAIN A PRESENCE OVER CENTRAL NC...DEVELOPING SLY FLOW A FEW THOUSAND FEET ALOFT WILL INITIATE AN OVERRUNNING EVENT LEADING TO A CLASSICAL OR HYBRID COLD AIR DAMMING EVENT. AS SLY FLOW STRENGTHENS TOWARD 06Z...EXPECT RAIN TO OVERSPREAD THE REGION FROM THE SOUTH...LOCKING IN THE CAD AIR MASS. WILL START OUT WITH CHANCE POPS ACROSS THE SOUTH IN THE EVENING...RAMPING UP TO LIKELY POPS ACROSS THE SOUTH HALF AFTER MIDNIGHT...AND CHANCE POPS ELSEWHERE. IF MODEL TRENDS CONTINUE IN LATER MODEL RUNS...AN INCREASE IN POPS TO LIKELY NORTH AND CATEGORICAL SOUTH WOULD BE WARRANTED. MIN TEMPS MAINLY 35-40 DEGREES. && .LONG TERM /MONDAY THROUGH FRIDAY/... AS OF 255 AM SATURDAY... MONDAY THROUGH WEDNESDAY: A SOUTHERN STREAM S/W DISTURBANCE WILL LIFT NORTHEASTWARD OUT FROM THE GULF COAST STATES ON SUNDAY NIGHT INTO MONDAY MORNING... SPREADING WIDESPREAD RAIN ACROSS ALL OF CENTRAL NC AS ISENTROPIC LIFT RAMPS UP. WITH A 1030 MB SURFACE HIGH STILL EXPECTED TO BE EXTENDING SOUTHWARD INTO OUR AREA (AS IT EVER SO SLOWLY SHIFTS EASTWARD) EXPECT WE WILL SEE A PRONOUNCED DAMMING EVENT DEVELOP.... WITH TEMPS FALLING INTO THE MID TO UPPER 30S MONDAY MORNING ACROSS THE NORTHERN AND NORTHWEST PIEDMONT... WITH TEMPS IN THE 40S ELSEWHERE. HOWEVER... BOTH THE GFS AND ECMWF CONTINUE TO DEPICT AN ALL RAIN EVENT ACROSS THE AREA... WITH A PRONOUNCED WARM NOES AT AROUND 4-5KFT COMBINED WITH SURFACE WETBULB TEMPS IN THE MID 30S AT WORST WHEN THE PRECIP SPREADS INTO THE AREA. THE MORE SUBSTANTIAL PRECIP WILL COME TO AN END BY EARLY TO MID AFTERNOON AS THE BEST MOIST ISENTROPIC UPGLIDE BEGINS TO WANE ALONG WITH DRIER AIR ALOFT FILTERING INTO THE AREA. STILL WE SHOULD SEE SOME LINGERING AREAS OF LIGHT RAIN AND DRIZZLE REMAINING. WITH A GOOD AREAWIDE QUARTER TO A HALF INCH OF RAIN EXPECTED WE SHOULD BE ABLE TO LOCK IN THE DAMMING AIRMASS. THUS.. HAVE LOWERED HIGH TEMPS... ESPECIALLY ACROSS THE EASTERN/SOUTHEASTERN PORTION OF CENTRAL NC. EXPECT HIGH TEMPS TO RANGE FROM THE UPPER 30S N/NW TO THE MID TO UPPER 40S E/SE. TEMPS MONDAY NIGHT/TUESDAY MORNING ARE EXPECTED TO REMAIN NEAR STEADY OR EVEN SLOWLY BEGIN TO RISE A LITTLE. THUS... WILL GO WITH LOWS RANGING FROM THE UPPER 30S TO MID 40S. A NORTHERN STREAM DISTURBANCE WILL HAVE FORMED A DEEP TROUGH BY TUESDAY MORNING WITH STACKED LOW PRESSURE OVER THE UPPER MIDWEST. BOTH THE GFS AND ECMWF ARE IN GOOD AGREEMENT IN SHOWING THE DEEP ASSOCIATED TROUGH AXIS SHIFTING EASTWARD ON TUESDAY INTO WEDNESDAY WHILE TAKING ON MORE OF A NEGATIVE TILT... WITH THE ASSOCIATED SURFACE FRONT (AND A POSSIBLE TRIPLE POINT LOW) MOVING ACROSS CENTRAL NC ON WEDNESDAY MORNING INTO THE EARLY AFTERNOON (AS IT STANDS NOW... STILL SEVERAL DAYS OUT THOUGH). QUESTIONS REMAIN AS TO WHERE A POSSIBLE TRIPLE POINT LOW MAY FORM THOUGH... AS FINER DETAILS LIKE THIS ARE HARD TO NAIL DOWN THIS FAR OUT IN THE FORECAST. HOWEVER... WITH THE POTENTIAL FOR A RETREATING CAD BOUNDARY AND STRENGTHENING LOW LEVEL WIND FIELD... WE WILL NEED TO KEEP AN EYE ON HOW THIS SYSTEM COMES TOGETHER. THIS WOULD BE A HSLC TYPE OF SYSTEM. GIVEN THE TIME OF YEAR IT IS QUITE HARD TO GET THE NEEDED INSTABILITY FOR POSSIBLE SEVERE STORMS THOUGH. AS THE EFFECTIVE FRONT APPROACHES AND MOVES THROUGH THE AREA ON WEDNESDAY MORNING INTO THE AFTERNOON WE SHOULD SEE A BAND OF RAIN/SHOWERS ALONG AND IN ADVANCE OF IT (WITH POSSIBLY A FEW THUNDERSTORMS)... WITH THINGS DRYING OUT QUICKLY BEHIND THE EFFECTIVE FRONT ON WEDNESDAY AFTERNOON. HIGHS ON TUESDAY WILL BE TRICKY AND DEPEND ON HOW MUCH THE CAD BOUNDARY RETREATS. FOR NOW WILL GO WITH HIGHS IN THE UPPER 40S NW TO AROUND 60S SE. TEMPS BY WEDNESDAY MORNING WILL NOT FALL MUCH... WITH LOWS WEDNESDAY MORNING IN THE UPPER 40S NW TO MID 50S SE/E. TEMPS ARE EXPECTED TO WARM WEDNESDAY AHEAD OF THE FRONT INTO THE UPPER 50S NW TO THE UPPER 60S E. WEDNESDAY NIGHT THROUGH THURSDAY: WE SHOULD SEE RAPID CLEARING ON WEDNESDAY NIGHT AND CONTINUING FOR THE REST OF THE WEEK... WITH A RETURN TO QUITE WEATHER. LOWS THURSDAY MORNING ARE EXPECTED TO BE IN THE 30S... WITH HIGHS THURSDAY AND FRIDAY AFTERNOONS IN THE 50S. WE COULD BE A BIT BREEZE ON THURSDAY AS MODELS ARE SHOWING THE POTENTIAL FOR SUSTAINED WINDS OUT OF THE WSW IN THE 14 TO 20 MPH RANGE... WITH MAYBE SOME GUSTS OF UP TO 25 MPH. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... AS OF 1240 PM SATURDAY... 24 HOUR TAF PERIOD: A REAL VARIATION IN AVIATION CONDITIONS OUT THERE THIS AFTERNOON DEPENDING ON WHERE YOU ARE. IN GENERAL PRECIPIATION HAS ENDED WEST OF HIGHWAY 1 BUT EAST OF HIGHWAY 1 SOME LINGERING RAIN/SNOW SHOWERS WILL CONTINUE FOR THE NEXT COUPLE OF HOURS AS A SHORTWAVE SYSTEM MOVES EASTWARD. IN THE WAKE OF THE PRECIPIATION CONDITIONS RANGE ANYWHERE FROM VFR TO IFR WITH A LOT OF VARIATION IN BETWEEN. THEREFORE IT WILL BE A LOW CONFIDENCE FORECAST THROUGH THE AFTERNOON WITH SOME IMPROVEMENT IN CONFIDENCE LATER IN THE TAF PERIOD. AFTER PRECIPITATION WRAPS UP BY 21Z OR SO...THERE IS SOME QUESTION TO WHETHER OR NOT CLOUD COVER WILL SCATTER OUT. IT MAY DECREASE A BIT IN COVERAGE BUT MORE LIKELY BROKEN CEILINGS WILL PREVAIL...MAINLY BETWEEN 5-6 KFT. THE DEGREE OF CLEARING WILL SET THE STAGE FOR ANOTHER LOW CONFIDENCE FORECAST OVERNIGHT AND THAT IS IN REGARDS TO WHETHER OR NOT WE WILL SEE SOME FOG. THIS WILL BE MOST LIKELY AT KINT...KGSO AND POSSIBLY KRDU AS WELL. THE TIMING IS A LITTLE UNCERTAIN BUT A BIG WINDOW OF 6-12Z WOULD COVER MOST OF THE POSSIBLE TIMING. THERE IS STILL A THIN LAYER OF MOISTURE AT 6KFT DURING THE OVERNIGHT HOURS THAT COULD KEEP BROKEN TO OVERCAST CEILINGS AROUND OVERNIGHT. DESPITE THIS...FORECAST SOUNDINGS STILL CALL FOR SATURATION AT THE SURFACE. IN ADDITION...THE DEGREE OF CLEARING WILL ALSO AFFECT TEMPERATURES. ENOUGH OF A CLEARING COULD RESULT IN SOME FREEZING FOG...MAINLY BETWEEN 9-12Z AT THE THREE SITES MENTIONED BEFORE. AGAIN THIS IS A LOW CONFIDENCE FORECAST BUT THERE IS ENOUGH OF AN INDICATION TO PUT FOG IN THE TAFS AND MENTION THE POSSIBILITY OF FREEZING FOG IN THE DISCUSSION. FURTHER SOUTH AND EAST FOG IS NOT AS LIKELY BUT CANNOT BE RULED OUT. AFTER SUNRISE THINGS CALM DOWN AND CONDITIONS SHOULD FOR THE MOST PART RETURN TO VFR WITH SOME LINGERING MVFR CEILINGS POSSIBLE ON SUNDAY AFTERNOON. WINDS WILL BE LIGHT OUT OF THE NORTHEAST AROUND 5 KTS. LONG TERM: UNSETTLED PATTERN FOR THE BEGINNING OF NEXT WEEK WILL RESULT IN SOME ADVERSE AVIATION CONDITIONS POSSIBLE FOR MONDAY THROUGH WEDNESDAY BEFORE CLEARING OUT AND RETURNING TO VFR FOR CHRISTMAS DAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...ELLIS NEAR TERM...ELLIS SHORT TERM...WSS LONG TERM...BSD AVIATION...ELLIS

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