Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 220155 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 955 PM EDT THU AUG 21 2014 .SYNOPSIS...A SERIES OF UPPER LEVEL DISTURBANCES WILL DIVE SOUTHEAST INTO OUR REGION FROM THE OHIO VALLEY AND MIDWEST. A COLD FRONT LOCATED ACROSS THE MID ATLANTIC ON FRIDAY WILL MOVE SOUTH THROUGH THE AREA OVER THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 310 PM WEDNESDAY... NORTHWEST FLOW CONTINUES ALOFT. THE PIEDMONT TROUGH IS SET UP OVER THE EASTERN PIEDMONT/COASTAL PLAIN...AND AREAS TO THE WEST HAVE SEEN MORE MIXING THAN IN THE EAST WITH MORE WESTERLY FLOW AND DRIER AIR ALOFT. MLCAPE RANGES FROM LESS THAN 1000 J/KG TO AS MUCH AS 2000 J/KG. THE CUMULUS FIELD OVER THE COASTAL PLAIN IN A BIT MORE PRONOUNCED WHERE LOW-LEVEL CONVERGENCE AND INSTABILITY OVERLAP. TO THE NORTHWEST...A SERIES OF UPPER DISTURBANCES ARE MOVING ACROSS KENTUCKY/WEST VIRGINIA. THE MEAN FLOW MAY CAUSE SOME OF THE SCATTERED CONVECTION THAT TRIGGERS FROM THIS DISTURBANCE TO MOVE SOUTHEAST INTO THE NORTHWEST OR NORTHERN PIEDMONT BY THIS EVENING. HOWEVER...THE HRRR CONTINUES TO SHOW VERY LITTLE ACTIVITY THIS AFTERNOON. EFFECTIVE SHEAR WILL INCREASE 25-30KT ACROSS THE NORTH THIS EVENING...SO IF ANY STORMS CAN GET GOING THERE...THEY WILL STAND THE BEST CHANCE OF BEING STRONG TO SEVER WITH THE LOSS OF HEATING...THE CHANCE OF SHOWERS OR STORMS WIL SLOWLY DIMINISH...THOUGH A CHANCE MAY LINGER ACROSS THE NORTH THROUGH MIDNIGHT AS CONVECTION OVER VIRGINIA EVOLVES. LOWS IN THE LOWER 70S. && .SHORT TERM /FRIDAY AND FRIDAY NIGHT/... AS OF 235 PM THURSDAY... FRIDAY WILL BE ANOTHER DAY WITH NORTHWESTERLY FLOW ALOFT...SURFACE TROUGHING IN THE EAST...AND THE POTENTIAL FOR A DISTURBANCE OR TWO TO CROSS THE AREA. THE MAIN DISTURBANCES IN QUESTION ARE LIKELY ASSOCIATED WITH CONVECTION OVER THE UPPER MIDWEST...AND ARE PROGGED TO MOVE SOUTHEAST ACROSS THE AREA LATE FRIDAY AFTERNOON. TIMING OF SUCH A FEATURE IS STILL TOUGH THIS FAR OUT...SO CONFIDENCE IN ITS ADDITIONAL SUPPORT FOR AFTERNOON CONVECTION IS LOW. DEEP MIXING IS EXPECTED AGAIN DURING THE AFTERNOON...WHICH WILL TEMPER INSTABILITY A LITTLE IN THE WEST WHERE DEWPOINTS SHOULD DROP BACK INTO THE MID 60S. THERMAL PROFILES ARE RELATIVELY SIMILAR TO TODAY...SO MLCAPE SHOULD AGAIN RANGE FROM LESS THAN 1000 J/KG IN THE WEST TO OVER 1500 J/KG IN THE EAST. A BELT OF STRONGER WESTERLIES OVER THE CENTRAL APPALACHIANS WILL LIKELY ENHANCE CONVECTION OVER VA...AND SOME OF THIS ACTIVITY MAY DRIFT SOUTH INTO THE NORTHERN PORTIONS OF THE CWA BY FRIDAY EVENING...SO WILL HAVE THE HIGHEST CHANCE POPS ACROSS THE NORTH...WHILE AREAS IN SOUTHERN PIEDMONT MAY STAY DRY. H85 TEMPS ARE FORECAST TO BE ABOVE 20C AGAIN FRIDAY AND WITH DEEP MIXING RESULTS IN MID TO POSSIBLY UPPER 90S. DEWPOINTS ARE FORECAST TO MIX OUT A LITTLE MORE IN THE EAST THAN TODAY...THOUGH ONLY SLIGHTLY...SO HEAT INDEX VALUES SHOULD AGAIN HOLD AROUND 100F IN THE SOUTHEAST. DEPENDING ON HOW MUCH CONVECTION THERE IS TO THE NORTH FRIDAY EVENING...THERE IS THE POTENTIAL FOR A WEAK EFFECTIVE FRONT INTO THE NORTHERN COASTAL PLAIN FRIDAY NIGHT...NECESSITATING POPS THROUGH THE OVERNIGHT HOURS. LOWS IN THE UPPER 60S TO LOWER 70S. && .LONG TERM /SATURDAY THROUGH THURSDAY/... AS OF 145 PM THURSDAY... THE LONG TERM PERIOD REMAINS CHARACTERIZED BY A BUILDING UPPER RIDGE ACROSS THE MISSISSIPPI RIVER VALLEY WITH A DEEPENING UPPER TROUGH OFF THE EAST COAST...RESULTING IN A NORTHWEST UPPER FLOW REGIME ACROSS CENTRAL NORTH CAROLINA. AT THE SURFACE...A BACKDOOR COLD FRONT WILL MOVE SOUTH THROUGH THE AREA ON SATURDAY. DEEP MOISTURE WILL REMAIN ENTRENCHED OVER THE REGION THROUGH THE FIRST HALF OF THE WEEKEND. AS SUCH...THE BEST CHANCE OF PRECIPITATION WILL BE ON SATURDAY GIVEN THE SURFACE BOUNDARY AND POTENTIAL ADDITIONAL SUPPORT FROM DISTURBANCES ALOFT WITHIN THE NORTHWEST FLOW. THE UPPER TROF AXIS SHIFTS FURTHER OFFSHORE...ALLOWING DRIER AIR TO SURGE SOUTH AT THE MID LEVELS...WITH DEEPER MOISTURE SUPPRESSED SOUTHWEST OF THE AREA SUNDAY THROUGH THE MIDDLE OF NEXT WEEK. THE UPPER RIDGE WILL SHIFT EAST TO FURTHER AID IN DAMPENING CONVECTION AS WELL...SO PRECIP CHANCES WILL BE MINIMAL FROM MONDAY THROUGH THURSDAY. LOW LEVEL THICKNESS VALUES WILL GRADUALLY FALL THROUGH EARLY NEXT WEEK AS THE UPPER TROUGH DEEPENS DOWN THE WESTERN ATLANTIC. IN ADDITION...NORTHEASTERLY SURFACE FLOW WILL PERSIST AS HIGH PRESSURE RIDGES INTO THE AREA FROM THE NORTHEAST. ALL OF THIS WILL RESULT IN BELOW NORMAL TEMPS...WITH MID 80S TO NEAR 90 DEGREES ON SATURDAY FALLING INTO THE UPPER 70S TO LOW/MID 80S SUNDAY THROUGH TUESDAY. TEMPS WILL BEGIN TO MODERATE WEDNESDAY INTO THURSDAY AS THE UPPER RIDGE SHIFTS EAST. OVERNIGHT LOWS THIS WEEKEND WILL BE IN THE UPPER 60S TO LOWER 70S...WITH MID TO UPPER 60S MONDAY MORNING AND FOR THE REMAINDER OF THE WEEK. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... AS OF 800 PM THURSDAY... 24-HR TAF PERIOD: SCATTERED SHOWERS AND STORMS WILL PERSIST THROUGH 06Z AS THEY TRACK TOWARD THE SOUTH/SOUTHEAST...THOUGH ACTIVITY IS EXPECTED TO DIMINISH IN COVERAGE AND INTENSITY THROUGH THAT TIME. SUB-VFR FOG AND/OR LOW CEILINGS ARE LIKELY TO DEVELOP OVERNIGHT ACROSS PORTIONS OF CENTRAL NC...ESP WHERE MEASURABLE RAINFALL OCCURS LATE THIS EVENING. DIURNAL CONVECTION WILL BE POSSIBLE AGAIN FRI AFTERNOON AND EVENING...WITH THE BEST CHANCE AT THE RDU/RWI TERMINALS. LOOKING AHEAD: DIURNAL CONVECTION IS EXPECTED AGAIN ON SAT... ENHANCED BY THE PASSAGE OF A BACK DOOR COLD FRONT FROM THE NORTH/NE SAT EVE/NIGHT. WIDESPREAD IFR CEILINGS ARE EXPECTED IN THE WAKE OF THE BACKDOOR COLD FRONT SAT NIGHT/SUN MORNING...POSSIBLY PERSISTING THROUGH THE DAY AND INTO SUN NIGHT. AN UNSEASONABLY AMPLIFIED SYNOPTIC PATTERN KNOWN AS AN `OMEGA BLOCK` WILL PREVAIL THROUGH THE MIDDLE OF NEXT WEEK...CENTERED OVER THE APPALACHIANS. AS A RESULT... AT THIS TIME EXPECT VFR CONDITIONS EARLY/MID NEXT WEEK...THOUGH A PERSISTENT EAST/ENE LOW-LEVEL FLOW MAY ALLOW ENOUGH MOISTURE ADVECTION FOR LOW-TOPPED SHOWER ACTIVITY AT SOME POINT. -VINCENT && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...BLAES NEAR TERM...BLS SHORT TERM...BLS LONG TERM...MLM AVIATION...VINCENT

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