Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 201750 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 150 PM EDT WED AUG 20 2014 .SYNOPSIS...A SERIES OF UPPER LEVEL DISTURBANCES IN NORTHWEST FLOW ALOFT WILL CROSS THE REGION THIS WEEK. A BACK DOOR COLD FRONT IS FORECAST TO SLIP INTO THE AREA OVER THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1015 AM WEDNESDAY... THE OVER ALL WEATHER PATTERN STILL CONSISTS OF RELATIVELY WEAK NORTHWESTERLY FLOW ALOFT AND A BROAD TROUGH AT THE SURFACE. IS SLOWLY ERODING THIS MORNING...THOUGH AREAS NORTH OF HWY 64 ARE STILL ENSHROUDED IN STRATUS. UPSTREAM...AN UPPER LEVEL TROUGH MOVING THROUGH THE CENTRAL APPALACHIANS IS AIDING A BROKEN LINE OF SHOWERS AND STORMS...WHICH HAS ACTUALLY HELD TOGETHER PRETTY WELL ON THE SOUTHERN END NEAR THE BLUE RIDGE. THE WEAK VORT LOBE WITH THIS TROUGH WILL CROSS THE CWA THIS AFTERNOON. LINGERING STRATUS WILL DELAY BETTER DESTABILIZATION...BUT RADAR TRENDS SUGGEST THE SHOWERS AND STORMS MAY HOLD TOGETHER THROUGH AT LEAST THE TRIAD AREA INITIALLY. WITH ADDITIONAL HEATING...FORECAST SOUNDINGS GIVE 1000- 1500 J/KG MLCAPE THIS AFTERNOON...THOUGH THE NAM/GFS VALUES ARE VERY SENSITIVE TO HIGHER/LOWER DEWPOINTS. IN FACT...THE NAM FORECAST SOUNDINGS AT KINT/KGSO HAVE A DEWPOINT OF 70F AND MLCAPE OVER 2000 J/KG THIS AFTERNOON. THIS SEEMS OVERDONE GIVEN SREF CONSENSUS. ALSO ACCOMPANYING THE AFOREMENTIONED SHORTWAVE IS A RIBBON OF EFFECTIVE DEEP SHEAR OF UP TO 30KT...SO IF CONVECTION CAN REINTENSIFY OVER THE PIEDMONT BY EARLY AFTERNOON...A FEW STRONG TO SEVERE STORM CLUSTERS COULD BE POSSIBLE. WILL INCREASE POPS OVER THE NORTHWEST PIEDMONT THROUGH MIDDAY...WITH A CHANCE ACROSS THE NORTH THIS AFTERNOON AND A SLIGHT CHANCE ACROSS THE SOUTH. HIGHS IN THE UPPER 80S TO LOWER 90S. LOWS TONIGHT IN THE UPPER 60S TO LOWER 70S. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 245 AM WEDNESDAY... LITTLE CHANGE ON THE SYNOPTIC PATTERN ON THURSDAY. CENTRAL NC WILL REMAIN POISED TO SEE VORT DISTURBANCES EMBEDDED IN THE NW FLOW ALOFT AS THE UPPER LOW OVER THE GREAT LAKES WEAKENS THROUGH THE DAY AS IT MOVES EAST INTO THE NE US. AT THIS TIME...CAN NOT FIND A DISCERNIBLE FEATURE THAT WOULD SUPPORT MORE THAN ISOLATED SLIGHT CHANCE POPS THURSDAY/THURSDAY NIGHT...IN FACT...500MB HEIGHTS ACTUALLY INCREASE OVER THE AREA ON THURSDAY...WITH ASSOCIATED SUBSIDENCE/WARMING ALOFT POSSIBLY SUPPRESSING CONVECTION TO A POINT WHERE IT COULD END UP BEING ONE OF THE LEAST CONVECTIVELY ACTIVE DAYS OF THE WEEK. AS FAR AS TEMPERATURES...BOTH THE EC AND GFS INDICATE H8 TEMPERATURES WILL WARM TO 22C...WHICH SHOULD SUPPORT HIGHS THURSDAY SOLIDLY IN THE MID 90S. LOWS THURSDAY NIGHT IN THE LOWER 70S. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... AS OF 145 PM WEDNESDAY... THE INITIAL LONG TERM PERIOD REMAINS CHARACTERIZED BY A BUILDING UPPER RIDGE ACROSS THE MISSISSIPPI RIVER VALLEY WITH AN UPPER TROUGH/CLOSED LOW OFF THE NORTHEAST COAST...LEAVING CENTRAL NC UNDER NORTHWEST UPPER FLOW INTO EARLY NEXT WEEK. A BACKDOOR FRONT WILL MOVE ACROSS THE AREA LATE FRIDAY THROUGH SATURDAY...WHICH WILL PRODUCE OUR BEST CHANCE OF PRECIPITATION DUE TO LOW LEVEL LIFT FROM THE COOL AIR ADVECTION POTENTIALLY AIDED BY MODEST UPPER LEVEL SUPPORT. OUTSIDE OF THE SLIGHTLY INCREASED CONFIDENCE IN THIS EARLY WEEKEND PERIOD... PRECIP CHANCES HINGE ON MESOSCALE DISTURBANCES ALOFT WITHIN THE NORTHWEST FLOW...WHICH ARE JUST ABOUT IMPOSSIBLE TO FORECAST THIS FAR IN ADVANCE. AS SUCH...WILL MAINTAIN SMALL CHANCE POPS THROUGH MONDAY...AFTER WHICH THE UPPER RIDGE AXIS SHIFTS EAST ENOUGH TO DAMPEN PRECIP CHANCES. HEIGHTS AND LOW LEVEL THICKNESSES PEAKING FRIDAY ARE INDICATIVE OF HIGHS REACHING THE MID 90S OVER MUCH OF THE AREA. THESE HEIGHTS FALL AS THE UPPER TROF DEEPENS ALONG THE EAST COAST CONCURRENT WITH COOL AIR ADVECTION BY LATER SATURDAY IN UNIFORM LOW LEVEL NORTHEAST FLOW. HIGHS WILL BE IN TRANSITION SATURDAY...FROM MID 80S NORTH TO 90 SOUTH...AND BOTTOMING OUT IN THE UPPER 70S TO LOWER 80S SUNDAY AND MONDAY AS DAMMING SETTLES DOWN THE EAST COAST. MORNING LOWS INITIALLY IN THE LOWER 70S SATURDAY MORNING WILL GRADUALLY FALL INTO THE LOW TO MID 60S BY TUESDAY MORNING. THE UPPER RIDGE AXIS WILL SHIFT EAST ON TUESDAY...WITH DRIER AIR AND GRADUAL MODIFICATION OF THE AIR MASS IN PLACE. HIGHS TUESDAY WILL BE MOSTLY IN THE LOW TO MID 80S...WARMING TO MOSTLY MID 80S ON WEDNESDAY. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... AS OF 145 PM WEDNESDAY... MORNING STRATUS LIFTED TO VFR MOST PLACES PRIOR TO 17Z...THOUGH A FEW LOCATIONS ARE STILL REPORTING MVFR CEILINGS. INCREASING INSTABILITY AND AN APPROACHING WEAK UPPER DISTURBANCE SHOULD LEAD TO SCATTERED SHOWERS AND STORMS AGAIN THIS AFTERNOON...THOUGH THERE IS STILL NEAR TERM UNCERTAINTY AS TO WHERE SHOWERS AND STORMS WILL BE FOCUSED. BASED ON LATEST ANALYSIS IT APPEARS AREA FROM KGSO/KINT TO KFAY WILL BE MOST FAVORED...AND THERE ARE ALREADY SOME SHOWERS DEVELOPING JUST TO THE SOUTHWEST OF KFAY. OUTSIDE OF THE SHOWERS AND/OR STORMS...VFR CONDITIONS ARE EXPECTED TO PREVAIL. TONIGHT...LIGHT WINDS AND SOME CLEARING MAY LEAD TO LOW CLOUDS AND FOG BY THURSDAY MORNING...THOUGH FORECAST SOUNDINGS DONT SHOW AS MUCH POTENTIAL AS IN PREVIOUS NIGHTS. IF LOW CLOUDS OR FOG DEVELOP...IFR/LIFR CONDITIONS WOULD BE ANTICIPATED. OUTLOOK... EARLY MORNING STRATUS/FOG...ALONG WITH AFTERNOON SHOWERS AND STORMS WILL BE POSSIBLE EACH DAY THIS WEEK. A BACKDOOR COLD FRONT WILL MOVE INTO THE AREA OVER THE WEEKEND...WHICH MAY BRING ANOTHER PERIOD UNSETTLED WEATHER FOR PORTIONS OF THE AREA. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...BLS NEAR TERM...CBL/BLS SHORT TERM...CBL LONG TERM...MLM AVIATION...BLS

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