671 FXUS62 KRAH 201117 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 620 AM EST SUN JAN 20 2013 .SYNOPSIS... HIGH PRESSURE OVERHEAD THIS MORNING WILL DRIFT SOUTHWARD LATER TODAY...AHEAD OF A WEAK COLD FRONT THAT WILL MOVE THROUGH THE AREA THIS EVENING. A MUCH STRONGER ARCTIC COLD FRONT WILL CROSS THE REGION MONDAY NIGHT. && .NEAR TERM /THROUGH TONIGHT/... AS OF 300 AM SUNDAY... A S/W CROSSING THE NORTHERN GREAT LAKES AND SOUTHERN ONTARIO/QUEBEC TODAY WILL PROPEL A WEAK 850-700MB TROUGH ACROSS CENTRAL NC LATER TODAY AND THIS EVENING. LOW-MID LEVEL FLOW AHEAD OF THIS TROUGH WILL VEER FROM SW-W THIS MORNING TO W-NW LATE TODAY. IN SPITE OF PRESENCE OF TROUGH...AIR MASS LACKS ENOUGH MOISTURE TO GENERATE ANYTHING MORE THAN A FEW CLOUDS. THIS MAINLY WLY FLOW COUPLED WITH A MODIFYING AIR MASS SHOULD BOOST TEMPS TODAY 5-6 DEGREES WARMER THAN SATURDAY'S HIGH TEMPS. HIGH TEMPS MID 50S NW TO LOWER 60S SE. TONIGHT...WEAK CAA WILL OCCUR IN WAKE OF DEPARTING LOW-MID TROUGH. SKIES REMAIN MOSTLY CLEAR DUE TO LACK OF MOISTURE TRANSPORT INTO THE REGION. MIN TEMPS 31-36. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... AS OF 300 AM SUNDAY... MONDAY-MONDAY NIGHT...AN AMPLIFYING UPPER TROUGH OVER THE GREAT LAKES INTO NEW ENGLAND WILL DRIVE AN ARCTIC COLD FRONT TOWARD CENTRAL NC MONDAY...SWEEPING ACROSS THE AREA MONDAY EVENING. AHEAD OF THE BOUNDARY...A RELATIVELY DRY AIR MASS AND A WLY FLOW WILL RESULT IN MOSTLY SUNNY SKIES AND TEMPS CLOSE TO NORMAL FOR MID JANUARY. AS THE BOUNDARY GETS CLOSER IN THE AFTERNOON TIGHTENING THE PRESSURE GRADIENT...COULD SEE GUST WLY SURFACE WINDS. FRONTAL PASSAGE MONDAY EVENING NOTED BY WINDS VEERING TO THE NNW AND INCREASING TO 10-15 MPH WITH GUSTS AROUND 20 MPH...ESPECIALLY AFTER MIDNIGHT WITH THE PASSAGE OF 850MB TROUGH. MIN TEMPS BY EARLY TUESDAY MID 20S N-NW TO NEAR 30 SE. THE WIND COMBINED WITH THE COLD TEMPS WILL DRIVE WIND CHILLS VALUES DOWN INTO THE TEENS. -WSS TUESDAY AND TUESDAY NIGHT: ARCTIC HIGH PRESSURE WILL BUILD INTO THE REGION ON TUESDAY AND SETTLE ACROSS THE AREA ON TUESDAY NIGHT. THIS WILL LEAD TO SOME OF THE COLDEST TEMPS OF THE SEASON SO FAR. HOWEVER... WHILE AFTERNOON LOW LEVEL THICKNESS VALUES ARE EXPECTED TO BE WELL BELOW NORMAL... EXPECT 20 TO 25 KTS OF DOWNSLOPE FLOW IN A FAIRLY DEEP MIXED LAYER WILL HELP OFFSET SOME OF THE COLD AIRMASS FILTERING INTO THE AREA (ALONG WITH MOSTLY SUNNY SKIES... WITH ONLY THE THREAT OF SOME MID TO HIGH CLOUDS IN THE FAST CYCLONIC FLOW ALOFT). THUS.. WILL GO WITH HIGH TEMPS RANGING FROM THE MID 30S NORTH TO LOWER 40S SOUTH... WHICH IS IN LINE WITH VALUES DERIVED FROM THE IN HOUSE DRY ADIABATIC SCHEME AND COOLER MET GUIDANCE. LOWS TUESDAY ARE EXPECTED TO BE THE COLDEST OF THE SEASON SO FAR... GENERALLY IN THE TEENS... TO AROUND 20 IN THE URBAN AREAS AS THE SURFACE RIDGE AXIS SETTLES OVER THE AREA. HOWEVER... THE LATEST GFS AND NAM SHOW AT LEAST SOME POTENTIAL FOR SOME MID AND HIGH LEVEL CLOUD COVER... MAINLY ACROSS NORTHERN PORTIONS OF THE AREA. IF THIS CLOUD COVER IS REALIZED THEN LOW TEMPS COULD BE A CATEGORY OR TWO TO WARM ACROSS THESE AREAS. FOR NOW WILL MAINTAIN CONTINUITY WITH PREVIOUS FORECASTS AND GO WITH FORECAST LOW TEMPS MENTIONED ABOVE. -BSD && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... AS OF 310 AM SUNDAY... THE DEEP TROUGH ALOFT WILL BEGIN TO SHIFT TO THE EAST OF THE AREA MIDWEEK... WHILE A QUICK MOVING S/W MOVES FROM THE PACIFIC NORTHWEST INTO THE PLAINS AND MIDWEST WEDNESDAY THROUGH THURSDAY NIGHT AND MERGES WITH WEAK SOUTHERN STREAM ENERGY. THIS SYSTEM IS EXPECTED TO QUICKLY PROGRESS EASTWARD AND SEND A COLD FRONT INTO/THROUGH OUR AREA ON FRIDAY/FRIDAY NIGHT... ALONG WITH CHANCES FOR PRECIP. MODELS DIFFERENCE WITH REGARD TO THE TRACK OF THE PRIMARY SURFACE LOW AND POSSIBLE DEVELOPING WEDGE AIRMASS ACROSS OUR AREA. THE ECMWF TAKES THE DEVELOPING SURFACE LOW FROM THE CENTRAL AND SOUTHERN PLAINS INTO THE OHIO VALLEY... WITH THE GFS SHOWING A FURTHER SOUTH TRACK ACROSS OUR AREA. WE WILL NEED TO KEEP A CLOSE EYE ON THIS SYSTEM AS THE POTENTIAL FOR POSSIBLY SOME TYPE OF WINTER WEATHER MAY EXIST ACROSS AT LEAST NORTHERN PORTIONS OF THE AREA.... ESPECIALLY IF THE GFS VERIFIES. FOR NOW THOUGH WILL KEEP ALL PRECIP IN THE LIQUID CATEGORY GIVEN THE TIMEFRAME AND MODEL DIFFERENCES. FOR POPS WILL GO WITH A SLIGHT CHANCE OF POPS THURSDAY NIGHT/FRIDAY MORNING ACROSS THE NORTHWEST (WHICH COULD BE PROBLEMATIC IF A SOLUTION SIMILAR TO THE GFS WERE TO VERIFY... POSSIBLE LIGHT FREEZING PRECIP AT ONSET ACROSS THE NORTH/NORTHWEST FRIDAY MORNING). THE MAIN TIMEFRAME LOOKS TO BE FRIDAY INTO FRIDAY NIGHT FOR THE BEST PRECIP CHANCES. THUS... WILL RAISE POPS TO SOLID CHANCE FOR THIS TIMEFRAME. EXPECT PRECIP TO END IN A WEST TO EAST FASHION ACROSS CENTRAL NC FROM MIDNIGHT TO DAYBREAK SATURDAY. AS THE SURFACE FRONT AND POSSIBLE STRENGTHENING SECONDARY SURFACE LOW DEVELOPS AS THE FRONT MOVES TO THE EAST OF THE AREA... WE COULD POSSIBLY SEE THE PRECIP END AS SOME SNOW ACROSS THE NORTH/NORTHEAST. FOR NOW WILL KEEP ALL LIQUID THOUGH. COLDER AND DRY CONDITIONS ARE EXPECTED TO RETURN ON SATURDAY. HIGH TEMPS DURING THE EXTENDED ARE EXPECTED TO GENERALLY RUN BELOW NORMAL (WITH POSSIBLY A QUICK SHOT OF ABOVE NORMAL TEMPS ACROSS THE SOUTHEAST AHEAD OF THE SURFACE FRONT ON FRIDAY... WITH LOW TEMPS NEAR TO SLIGHTLY BELOW NORMAL. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... AS OF 620 AM SUNDAY... HIGH CONFIDENCE OF VFR CONDITIONS ACROSS CENTRAL NC TODAY. HIGH PRESSURE OVER THE CAROLINAS WILL DRIFT SOUTHWARD. THE CIRCULATION AROUND THIS WEATHER SYSTEM WILL RESULT IN WLY SURFACE WINDS ACROSS CENTRAL NC LATE THIS MORNING THROUGH THE AFTERNOON HOURS WITH SUSTAINED SPEEDS 10KTS OR LESS. A WEAK COLD FRONT WILL DRIFT SOUTH ACROSS CENTRAL NC LATE TODAY AND THIS EVENING. SINCE THE AIR MASS IS QUITE DRY...LITTLE IN THE MANNER OF CLOUDS WILL ACCOMPANY THE FRONT. THE PASSAGE OF THE FRONT WILL BE NOTED BY SURFACE WINDS VEERING TO THE NNW WITH SUSTAINED SPEED OF 7KTS OR LESS. THERE IS A HIGH PROBABILITY OF VFR CONDITIONS MONDAY THROUGH THURSDAY. A STRONG COLD FRONT WILL CROSS CENTRAL NC MONDAY EVENING. NW WINDS BEHIND THIS FRONT WILL BE 10-15KTS WITH GUSTS AS HIGH AS 25 KTS. THESE BRISK CONDITIONS WILL PERSIST INTO TUESDAY. SINCE MOISTURE IS LIMITED...JUST A FEW CLOUDS ARE EXPECTED WITH THE FRONT. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...WSS/BSD LONG TERM...BSD AVIATION...WSS