Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 290813 RRA AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 413 AM EDT WED JUL 29 2015 .SYNOPSIS...A WEAK SURFACE TROUGH WILL REMAIN OVER CENTRAL NC TODAY AS AN UPPER LEVEL RIDGE BRIEFLY BUILDS OVERHEAD. A COLD FRONT WILL APPROACH FROM THE NORTHWEST ON THURSDAY AND SINK SOUTH OF THE AREA THROUGH THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 350 AM WEDNESDAY... NORTHWESTERLY FLOW ALOFT WILL SHIFT TO A LITTLE MORE NORTHERLY TODAY AS THE CENTRAL US RIDGE BUILDS EAST IN RESPONSE TO A STRONG SHORTWAVE CROSSING THE UPPER MIDWEST. WATER VAPOR IMAGERY AND RAP H5 VORTICITY SUGGEST A COUPLE WEAK DISTURBANCES WILL DROP SOUTH ACROSS THE AREA...BUT NEITHER APPEARS TO BE VERY STRONG AND THERE SHOULDN`T BE MUCH IMPACT GIVEN THAT HEIGHTS BUILD ALOFT AND INSTABILITY WILL BE WEAK. AT THE SURFACE...A TROUGH EXTENDING SOUTH FROM THE MID ATLANTIC STATES APPEARS TO HAVE SUNK A LITTLE FURTHER SOUTH IN RESPONSE TO THE LAST EVENINGS CONVECTION NEAR THE NC-VA BORDER...NOW SITUATED FROM ROUGHLY DAVIDSON COUNTY NORTHEAST TO GRANVILLE COUNTY. THIS COULD SERVE AS AN ADDITIONAL FOCUS FROM SOME WIDELY SCATTERED CONVECTION...IN ADDITION TO CONVECTION OVER THE HIGHER TERRAIN...AND RECENT RUNS OF THE HRRR HINT AT DEVELOPMENT BY MIDDAY. IF NOTHING FORMS ON THIS BOUNDARY AND/OR IT WASHES OUT...THEN CONVECTION WILL BE FOCUS OVER THE NORTHWEST PIEDMONT AND SHOULDN`T HAVE MUCH OPPORTUNITY TO MOVE EAST GIVEN WEAK NORTHERLY STEERING FLOW. OVERALL...THE COVERAGE OF SHOWERS/STORMS IS EXPECTED TO BE LESS THAN THE PAST COUPLE OF DAYS. HIGHS SHOULD BE ABLE TO REACH THE FULL SUN POTENTIAL AS IR IMAGERY SHOWS LITTLE IN THE WAY OF UPSTREAM CLOUD COVER TO INHIBIT HEATING. HIGHS 88-93. CONVECTION SHOULD SEND A LITTLE SOONER THIS EVENING WITH LOSS OF HEATING AND NO SUPPORT FROM DISTURBANCES ALOFT. THERE IS A DISTURBANCE OVER SOUTHERN MICHIGAN THIS MORNING THAT IS FORECAST TO DIVE SOUTH LATE TONIGHT AND EARLY THURSDAY...WHICH COULD CONCEIVABLY CAUSE SOME REDEVELOPMENT OF SHOWERS...MAINLY WEST..BY EARLY THURSDAY MORNING...BUT GUIDANCE DOESN`T SHOW MUCH ACTIVITY...SO WILL LEAVE THE OVERNIGHT FORECAST DRY. LOWS WILL BE IN THE LOWER 70S. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 400 AM WEDNESDAY... A COLD FRONT...ATTENDANT TO AN OCCLUDED LOW WAY TO THE NORTH OVER CENTRAL CANADA...WILL APPROACH FROM THE NORTHWEST ON THURSDAY. THE PREFRONTAL LEE TROUGH WILL SHARPEN IN RESPONSE TO THE APPROACHING FRONT... BUT WITH INSTABILITY STILL EXPECTED TO BE RELATIVELY WEAK...MODELS ARE SURPRISINGLY DRY DURING THE DAY ON THURSDAY. THERE IS A DISTURBANCE FORECAST TO DIVE SOUTH INTO THE AREA EARLY THURSDAY...AS MENTIONED IN THE NEAR TERM DISCUSSION...AND EVOLUTION OF THIS FEATURE MAY BE WORTH WATCHING TO SEE IF/HOW IT COULD IMPACT CONVECTION INITIATION ON THURSDAY. THE FRONT WILL PUSH INTO THE AREA THURSDAY EVENING...BUT POOR DIURNAL TIMING AND FORCING LIMITED TO JUST FRONTAL CONVERGENCE SHOULD RESULT IN JUST SCATTERED CONVECTION AND NO WIDESPREAD SEVERE WEATHER. HIGHS THURSDAY HAVE THE POTENTIAL TO REACH THE LOW TO MID 90S ACROSS THE ENTIRE AREA AS THE 850MB THERMAL RIDGE SHIFTS OVER THE AREA AHEAD OF THE FRONT AND 850MB TEMPS REACH 19-20C. SOME HIGH CLOUDS ASSOCIATED WITH THE FRONTAL ZONE WILL SPREAD ACROSS THE AREA BUT CURRENTLY DO NOT LOOK WIDESPREAD OR THICK ENOUGH TO IMPACT HIGHS. LOWS THURSDAY NIGHT WILL BE MOSTLY IN THE LOW TO MID 70S...ESPECIALLY INT HE SOUTHEAST WHERE THE FRONT WILL ONLY SLOW REACH BY FRIDAY MORNING. && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 410 AM WEDNESDAY... FORECAST RATIONALE REMAINS GENERALLY UNCHANGED FROM PREVIOUS DAYS. THE MODELS REMAIN IN GOOD AGREEMENT REGARDING THE PERSISTENCE OF AN EASTERN CONUS TROUGH FORECAST TO DEVELOP DURING THE NEAR AND SHORT TERM...COINCIDENT WITH THE RETROGRESSION OF A SUB-TROPICAL RIDGE FROM THE SOUTHERN PLAINS AND MID-MS VALLEY WEST TO THE FOUR CORNERS REGION. MEANWHILE IN THE LOW LEVELS...THE MODELS AGREE THAT A COLD FRONT RELATED TO A POTENT UPPER LOW OVER SOUTHERN MANITOBA THIS MORNING WILL BE INVOF THE I-95 CORRIDOR FRI MORNING...THEN DRIFT SOUTHEAST THROUGH THE COASTAL PLAIN THROUGH THE MIDDAY-AFTERNOON HOURS. THIS GRADUALLY DIFFUSING BOUNDARY WILL BE THE FOCUS FOR SHOWERS AND STORMS CENTERED OVER THE EASTERN CAROLINAS FRI-SUN...WHILE A DRIER AIR MASS BOTH AT THE SURFACE AND ALOFT SETTLES ACROSS THE WESTERN... AND MUCH OF THE CENTRAL PART...OF NC. AS THE PREVIOUS SHIFT NOTED...ANY NORTHWESTWARD SHIFT IN THE FRONTAL POSITION AND ASSOCIATED AXIS OF TROPICAL MOISTURE --CHARACTERIZED BY PRECIPITABLE WATER VALUES AOA TWO INCHES-- WOULD RESULT IN A WETTER WEEKEND FOR PARTICULARLY EAST-CENTRAL NC. THOUGH MODEL SPREAD INCREASES BY THE EARLY-MIDDLE OF NEXT WEEK...THE MODELS TO VARYING DEGREES HAVE HINTED THAT THE TROPICAL MOISTURE MAY GET DRAWN NORTH/INCORPORATED INTO THE LONGWAVE TROUGH BY LATE SUN-MON...AT WHICH TIME THE PROBABILITY OF SHOWERS AND STORMS ARE MORE LIKELY TO INCREASE THROUGHOUT CENTRAL NC. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... AS OF 145 AM WEDNESDAY... CONVECTION FROM LAST EVENING DIMINISHED A FEW HOURS AGO...LEAVING JUST CONVECTIVE DEBRIS CLOUDS AT OR ABOVE 6K FT DRIFTING SOUTHEAST ACROSS THE AREA. THE CRUX OF THE CLOUD COVER APPEARS TO BE MOVING SOUTH OF THE AREA AND SOME DRIER AIR ALOFT IS MOVING IN FROM UPSTREAM...WHICH SHOULD ALLOW SOME AREAS OF SUB-VFR VSBY TO DEVELOP. BASED ON EARLIER RAINFALL...KINT AND KGSO SHOULD RUN THE BEST CHANCE OF IFR OR LIFR VSBYS...AND KGSO HAS ALREADY REPORTED A PERIOD OF 1/2SM VSBY WITH PARTIAL CLEARING. CONFIDENCE IS ONLY MEDIUM AT THE MOMENT...BUT THERE IS SOME SUPPORT FROM THE HRRR MODEL. EXPECT MAINLY MVFR VSBYS AT OTHER SITES...THOUGH THE OFTEN FOG PRONE KRWI MAY SEE LOWER VSBYS AS WELL. AN UPPER LEVEL RIDGE WILL BRIEFLY BUILD OVER THE REGION TODAY AND MAY LIMIT STORM COVERAGE MORE SO THAN IN PRIOR DAYS. AS SUCH...WILL NOT MENTION THUNDER IN THE CURRENT TAF...BUT CHANCES WILL BE GREATEST AT KGSO AND KINT ONCE AGAIN. OUTLOOK...A COLD FRONT WILL APPROACH FROM THE NORTHWEST ON THURSDAY...WITH SOME PREFRONTAL CONVECTION POSSIBLE THURSDAY AFTERNOON. THE FRONT WILL THEN PUSH THROUGH THE AREA THURSDAY NIGHT AND SETTLE SOUTH OF THE AREA ON FRIDAY. IF THIS FRONT DOES PUSH ALL THE WAY THROUGH THE AREA...THEN VFR CONDITIONS WILL BE MUCH MORE LIKELY FOR THE UPCOMING WEEKEND. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...22 NEAR TERM...22 SHORT TERM...22 LONG TERM...26 AVIATION...22

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