Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 280823 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 322 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 SUNDAY/... AS OF 320 AM SATURDAY... ...THREAT FOR A LIGHT ICING EVENT INCREASING FOR THE NC PIEDMONT EARLY SUNDAY... TODAY...ARCTIC HIGH PRESSURE BEGINNING TO EXERT ITS INFLUENCE ON THE SENSIBLE WEATHER ACROSS CENTRAL NC AS EVIDENT BY THE SFC DEWPOINTS IN THE SINGLE DIGITS ACROSS THE NW PIEDMONT AT 07Z. THE CENTER OF THIS HIGH WILL BE OVER SOUTHERN NEW ENGLAND THIS AFTERNOON WITH THE SFC RIDGE AXIS EXTENDING DOWN INTO THE CAROLINAS. THUS EXPECT THE AXIS OF THE LOWER DEWPOINTS (TEENS) TO LIE ACROSS THE PIEDMONT/NORTHERN COASTAL PLAIN THIS AFTERNOON-EARLY EVENING. A NARROW BAND OF STRATUS CURRENTLY WORKING ITS WAY WEST-SW ACROSS THE NORTHERN PIEDMONT. MEANWHILE A THICKER MORE EXTENSIVE VEIL OF HIGH CLOUDS WAS ADVANCING EAST-NE ACROSS THE TN VALLEY/DEEP SOUTH. THUS SHOULD SEE A GRADUAL INCREASE IN MID-HIGH LEVEL CLOUDS LATER TODAY. STILL THINK THAT CLOUDS WILL BE THIN ENOUGH TO ALLOW AT LEAST MILKY SUNSHINE TO OCCUR THIS AFTERNOON. INSPITE OF MOSTLY-PARTLY SUNNY SKIES...LOW LEVEL CAA WILL RESULT IN MAX TEMPS 7-10 DEGREES COOLER THAN FRIDAY. MAX TEMPS MID-UPPER 30S NORTH TO THE LOW-MID 40S SOUTH. TONIGHT AND SUNDAY... LATEST MODEL GUIDANCE HAS TRENDED WETTER LATE TONIGHT INTO SUNDAY. THIS INCREASES THE THREAT FOR A LIGHT ICING EPISODE EARLY SUNDAY...MAINLY ACROSS THE PIEDMONT COUNTIES. TONIGHT...SFC RIDGE AXIS WILL REMAIN OVER THE REGION...MAINTAINING A SUPPLY OF COLD DRY AIR IN THE LOWEST 2-4K FT OF THE ATMOSPHERE. ABOVE THE COLD DRY STABLE LAYER...SLY FLOW WILL BE INCREASING IN RESPONSE TO THE 850MB HIGH DRIFTING OFF THE SE U.S. COAST. THIS RETURN FLOW WILL ADVECT A WARMER...MORE MOIST AIR MASS INTO THE CAROLINAS. THIS RETURN FLOW STRENGTHENS SUBSTANTIALLY AFTER 12Z SUNDAY...THUS EXPECT THE BEST UPGLIDE TO OCCUR AFTER DAYBREAK SUNDAY. STILL...MODELS HAVE A TENDENCY TO BE A LITTLE TARDY WITH RETURN FLOW EVENTS. THUS WILL INTRODUCE A SLIGHT/SMALL CHANCE POP INTO THE FORECAST FOR THE PRE-DAWN HOURS WITH THE HIGHEST POPS CONFINED TO THE SOUTHERN PIEDMONT/WESTERN SANDHILLS. PARTIAL THICKNESS TECHNIQUE INDICATES A TREND TOWARD RAIN BY DAYBREAK SUNDAY AS A DECENT WARM NOSE DEVELOPS ALOFT. HOWEVER MODEL SOUNDINGS INDICATE A SHALLOW SUB FREEZING LAYER OVER MOST OF CENTRAL NC AT DAYBREAK SUNDAY. THUS...ANY LIGHT PRECIP THAT OCCURS PRIOR TO DAYBREAK WILL LIKELY BE IN THE FORM OF FREEZING RAIN/FREEZING DRIZZLE. MIN TEMPS WILL VARY FROM THE LOWER 20S IN THE NORTHERN COASTAL PLAIN WHERE CLOUD COVERAGE WILL INITIALLY BE THINNEST TO THE UPPER 20S ACROSS THE FAR SOUTH-SW. SUNDAY...PRECIPITATION EXPECTED TO BECOME MORE COMMON AFTER DAYBREAK ACROSS THE WEST AS ISENTROPIC UPGLIDE INCREASES. THIS PRECIP FALLING THROUGH THE DRY AIR MASS IN THE SUB CLOUD LAYER WILL LEAD TO EVAPORATIVE COOLING...LIKELY LOCKING IN THE SUB FREEZING SFC TEMPS OVER THE PIEDMONT FOR A GOOD PART OF THE MORNING. DUE TO TIMING UNCERTAINTY...WILL CAP POPS AT SOLID CHANCE ACROSS THE WESTERN COUNTIES TRENDING TO SLIGHT CHANCE IN THE COASTAL PLAIN. IF LATER MODEL RUNS ARE CONSISTENT...AN INCREASE IN POPS WILL BE WARRANTED AFTER DAYBREAK IN THE WEST. THE LOCKING IN OF THE SUB FREEZING TEMPS WILL CAUSE A PERIOD OF LIGHT FREEZING RAIN OVER MOST OF THE PIEDMONT SUNDAY MORNING. AT THIS TIME NOT EXPECTING ENOUGH ICE ACCRUAL TO CAUSE POWER OUTAGES BUT COULD SEE SOME SLICK ROADS...ESPECIALLY BRIDGES AND OVERPASSES. THIS WILL LIKELY WARRANT THE NEED OF AN ADVISORY IN LATER FORECAST ISSUANCE. IN THE MEANTIME...WILL HIGHLIGHT THREAT IN THE HWO. EXPECT PRECIPITATION CHANCES TO INCREASE TO LIKELY SUNDAY AFTERNOON AS UPGLIDE REACHES MAXIMUM. WILL EVENTUALLY SEE FREEZING RAIN TRANSITION TO A COLD RAIN OVER MOST OF THE PIEDMONT BY MID DAY...AND OVER THE NW PIEDMONT BY EARLY AFTERNOON. THE OVERCAST SKIES AND EXPECTED PRECIP WILL LIMIT TEMPS TO THE LOW-MID 30S OVER THE PIEDMONT COUNTIES TO THE UPPER 30S-LOWER 40S EAST OF HIGHWAY 1. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... AS OF 300 AM SATURDAY... SUNDAY NIGHT THROUGH MONDAY NIGHT: A WEAK SURFACE LOW ALONG THE COAST ON SUNDAY EVENING IS EXPECTED TO LIFT NORTHEASTWARD AWAY FROM THE AREA ON SUNDAY. MEANWHILE... A SURFACE COLD FRONT WILL APPROACH THE AREA FROM THE WEST ON SUNDAY NIGHT... WITH AN ASSOCIATED SURFACE LOW MOVING INTO THE EASTERN GREAT LAKES. BOTH THE GFS/NAM SHOW THE BEST DEEP MOISTURE SHIFTING OFF TO THE EAST OF THE AREA OVERNIGHT... WITH MID LEVEL DRYING ALOFT NOTED IN BOTH THE GFS AND NAM BUFR SOUNDINGS. THUS... WITH A LACK OF A GOOD COLD AIR SOURCE TO THE NORTH AND DRYING ALOFT TAKING PLACE... EXPECT WE SHOULD SEE TEMPS SLOWLY WARM OVERNIGHT... RESULTING IN LOW TEMPS OCCURRING DURING THE SUNDAY EVENING TIME FRAME OF THE OVERNIGHT PERIOD. EXPECT LOWS WILL GENERALLY BE IN THE MID TO UPPER 30S... WITH PERHAPS A FEW LOCATIONS ACROSS THE FAR SOUTHEAST NEAR 40 DEGREES. THE AFOREMENTIONED SURFACE COLD FRONT TO IS EXPECTED TO MOVE THROUGH THE AREA LATE MORNING INTO THE AFTERNOON... AND GENERALLY DRY. HOW FAR THE CAD BOUNDARY ERODES BEFORE THE FRONT DROPS SOUTH/SOUTHEASTWARD THROUGH THE AREA IS STILL IN QUESTION... WITH SOME LOCATIONS IN THE HEART OF THE CAD ACROSS THE NORTHWEST PIEDMONT SEEING HIGH TEMPS OCCUR AFTER THE FROPA AS THE CAD AIRMASS WOULD THEN BE SCOURED OUT (WITH POSSIBLY EVEN SOME SUN). THINK STATISTICAL GUIDANCE IS TOO HIGH FOR MONDAY... AND WENT CLOSER TO THE RAW GFS/NAM MODEL VALUES. THIS YIELDS HIGH TEMPS RANGING FROM THE UPPER 40S/NEAR 50 NORTH TO THE UPPER 50S/NEAR 60 SOUTH. SURFACE HIGH PRESSURE WILL BUILD INTO THE AREA FROM THE NORTH AND NORTHWEST ON MONDAY NIGHT USHERING IN ANOTHER DRY COLD SURFACE AIRMASS. LOWS BY TUESDAY MORNING AREA EXPECTED TO BE IN THE UPPER 20S NORTH TO THE MID TO MAYBE UPPER 30S SOUTH. && .LONG TERM /TUESDAY THROUGH FRIDAY/... AS OF 320 AM SATURDAY... TUESDAY THROUGH FRIDAY: A 1030+ MB SURFACE HIGH... EXPECTED TO BE LOCATED ALONG THE SOUTHERN MID ATLANTIC COAST ON TUESDAY MORNING... WILL QUICKLY SHIFT EASTWARD AND OFFSHORE BY TUESDAY AFTERNOON... LEAVING A DRY SURFACE AIRMASS IN ITS WAKE. MEANWHILE... MID LEVEL RIDGING WILL BUILD ACROSS THE AREA AS THE MID LEVEL FLOW ACROSS THE CONUS BECOMES MORE AMPLIFIED... A SURFACE LOW IS EXPECTED TO DEVELOP/STRENGTHEN INVOF THE FOUR CORNERS REGION MONDAY NIGHT... WILL THEN QUICKLY LIFT EAST-NORTHEASTWARD AND INTO THE GREAT LAKES REGION BY TUESDAY EVENING... WITH ADDITIONAL ENERGY DIVING DOWN THE BACK SIDE OF THE ASSOCIATED MID/UPPER LEVEL TROUGH... AS THE FRONT BECOMING PARALLE WITH THE MID TO UPPER LEVEL FLOW BY TUESDAY NIGHT AND QUITE WET... WITH THE MID LEVEL RIDGE OVER OUR REGION TO START THE PERIOD SHIFTING EASTWARD. SOUTHERLY FLOW IN ADVANCE OF THE FRONT ACROSS CENTRAL NC WILL QUICKLY INCREASE ON TUESDAY ATOP THE COLD SURFACE AIRMASS... WITH LIKELY AN INSITU CAD WEDGE DEVELOPING AS SOME LIGHT ISENTROPICALLY DRIVEN PRECIP IS EXPECTED TO BEGIN SPREADING ACROSS CENTRAL NC BY TUESDAY AFTERNOON INTO THE EVENING. HOWEVER... WITH SURFACE HIGH LONG GONE BY TUESDAY EVENING AND SOUTHERLY FLOW INCREASING WE SHOULD SEE THE CAD WEDGE BEGIN TO RETREAT OVERNIGHT TUESDAY... WITH TEMPS LIKELY RISING OVERNIGHT. THE AFOREMENTIONED SURFACE COLD FRONT IS EXPECTED TO SLOWLY SHIFT EASTWARD AND INTO AND ACROSS THE MOUNTAINS ON WEDNESDAY... WITH THE FRONT NOW EXPECTED TO MOVE THROUGH OUR AREA ON WEDNESDAY NIGHT INTO THURSDAY MORNING (THE GFS AND ECMWF ARE NOW WITHIN ABOUT 6 HOURS OF EACH OTHER NOW... WITH THE GFS ON THE FASTER SIDE)... WITH WPC FAVORING THE SLOWER ECMWF TIMING ACROSS OUR AREA. THE MAIN SHOWER ACTIVITY (WHICH COULD BRING HEAVY RAIN AT TIMES.. ESPECIALLY ACROSS THE NORTHWEST PIEDMONT) IS EXPECTED TO GENERALLY BE ALONG AND BEHIND THE FRONT. THE GFS HINTS AT THE POTENTIAL FOR SOME SWITCH OVER TO LIGHT SNOW BEFORE PRECIP ENDS ON THURSDAY EVENING... BUT THIS IS WAY TOO FAR OUT IN TIME TO ADD ANY NON- LIQUID... WHICH WOULD PROBABLY RESULT IN LITTLE TO NO IMPACT AS WELL. COLD AIR CHASING THE PRECIP. DRY WEATHER IS EXPECTED TO SPREAD BACK INTO THE AREA BY FRIDAY. TEMPS DURING THE MEDIUM RANGE WILL BE A ROLLER COASTER... WITH HIGHS TEMPS... TUESDAY... 40S TO LOWER 50S... WEDNESDAY 60S AND 70S... THURSDAY 40S AND 50S... AND FINALLY FRIDAY BACK IN THE 40S (WITH MAYBE SOME 30S EVEN). LOWS WILL FOLLOW A SIMILAR PATTERN. HOWEVER... ALL PRECIP AS OF NOW APPEARS TO BE IN THE FORM OF LIQUID FOR THE MEDIUM RANGE. && .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...WSS SHORT TERM...BSD LONG TERM...BSD AVIATION...WSS

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