Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 281047 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 645 AM EDT TUE JUL 28 2015 .SYNOPSIS...A SERIES OF PERTURBATIONS ALOFT INTERACTING WITH A MOIST AND UNSTABLE AIR MASS WILL TRIGGER SCATTERED THUNDERSTORMS...MAINLY DURING THE AFTERNOON AND EVENING HOURS...THROUGH THE REMAINDER OF THE WORK WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 400 AM TUESDAY... NORTHWESTERLY FLOW ALOFT CONTINUES DOWNSTREAM OF THE SOUTHERN PLAINS CENTRAL U.S. RIDGE...WITH NUMEROUS ILL-DEFINED DISTURBANCES STREAMING ACROSS THE CENTRAL AND SOUTHERN APPALACHIANS. MOISTURE RECOVERY ALSO CONTINUES IN EARNEST AS PW HAS RECOVERED TO NEARLY 2 INCHES IN THE PAST 24 HOURS...WITH SOUTHEASTERLY FLOW BETWEEN A RIDGE AXIS ALONG THE MID-ATLANTIC COAST AND AN INVERTED TROUGH OFF THE SOUTHEAST COAST. DEWPOINTS IN THE LOWER 70S THIS MORNING AREN`T FORECAST DROP MUCH TODAY GIVEN WEAK BOUNDARY LAYER FLOW/MIXING...WHICH SHOULD YIELD SLIGHTLY BETTER INSTABILITY THAN YESTERDAY...WITH MLCAPE OF 1000-2000 J/KG PROJECTED ACROSS THE WESTERN/NORTHERN PIEDMONT AND LESSER AMOUNTS TO THE SOUTHEAST. DIFFERENTIAL HEATING..ALONG WITH THE AFOREMENTIONED DISTURBANCES ALOFT AND A WEAK LEE TROUGH WILL BE THE PRIMARY TRIGGERS...WHICH AGAIN FAVORS THE NORTHERN/WESTERN PIEDMONT FOR AFTERNOON STORMS THAT WILL HAVE A PRIMARY THREAT OF HEAVY RAIN AND LOCALIZED FLOODING GIVEN WEAK STEERING FLOW. HIGHS 89-94. PERSISTENCE WOULD SUGGEST STORMS MAY CONTINUE TO PERCOLATE ON OLD OUTFLOW BOUNDARIES THROUGH MIDNIGHT...STAYING CONFINED TO THE PIEDMONT. LOWS WILL AGAIN BE IN THE LOWER 70S. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... AS OF 400 AM TUESDAY... THE CENTRAL U.S. RIDGE WILL BE SUPPRESSED A BIT ON WEDNESDAY BY A SHORTWAVE CROSSING THE GREAT LAKES...LEADING A LITTLE MORE NORTHERLY FLOW ALOFT OVER OUR AREA AND LESS IN THE WAY OF UPPER DISTURBANCES TO ENHANCE CONVECTIVE COVERAGE. FORECAST SOUNDINGS CONTINUE TO SHOW SLIGHTLY BETTER INSTABILITY OVER WESTERN NC AND MOST NWP FAVORS THE WESTERN HALF OF CENTRAL NC FOR AFTERNOON CONVECTION...THOUGH NORTHERLY STEERING FLOW MAY LIMIT THE BEST COVERAGE TO THE FAR WESTERN PIEDMONT. WEAK MID-LEVEL FLOW WILL CONTINUE TO LIMIT THE SEVERE WEATHER THREAT. HIGHS WILL BE BE WITH A DEGREE OR TWO OF TODAY`S VALUES...89-94. LOWS WEDNESDAY NIGHT IN THE LOWER 70S. && .LONG TERM /THURSDAY THROUGH MONDAY/... AS OF 415 AM TUESDAY... THE MODELS ARE IN GOOD AGREEMENT REGARDING THE EVOLUTION OF TWO DOMINANT FEATURES DURING THE MEDIUM RANGE - A SUB-TROPICAL RIDGE FORECAST TO RETROGRADE FROM THE SOUTHERN PLAINS AND MID-MS VALLEY WEST TO THE FOUR CORNERS REGION...AND A MID-UPPER LOW FORECAST TO LIFT FROM THE NORTHERN ROCKIES TO THE SOUTHERN TIP OF HUDSON BAY. BOTH ARE FORECAST TO THEN BECOME ANCHORED OVER THOSE RESPECTIVE LOCATIONS THROUGH THE PERIOD. AT THE BASE OF THE UPPER LOW OVER HUDSON BAY...A LONGWAVE TROUGH WILL BECOME ESTABLISHED ACROSS THE EASTERN UNITED STATES. MEANWHILE IN THE LOW LEVELS...A COLD FRONT RELATED TO THE PROGRESSION OF THE AFOREMENTIONED UPPER LOW/TROUGH AXIS ACROSS THE GREAT LAKES/TOWARD HUDSON BAY WILL SETTLE EAST OF THE APPALACHIANS LATE THU-FRI...THOUGH OVERNIGHT DIURNAL TIMING OF THE FRONTAL PASSAGE IN CENTRAL NC SUGGESTS COVERAGE OF ASSOCIATED SHOWERS AND STORMS SHOULD BE SCATTERED AT BEST...WITH THE RELATIVELY GREATER COVERAGE OVER THE NORTHERN AND NW PIEDMONT DURING THE EVENING. THE MODELS INDICATE THE FRONT --AND PLUME OF DEEP TROPICAL MOISTURE CHARACTERIZED BY PRECIPITABLE WATER VALUES AOA TWO INCHES-- WILL THEN BECOME QUASI-STATIONARY OVER THE SOUTHEAST US...WHILE A SECONDARY FRONT APPROACHES FROM THE NORTH AND SETTLES INTO THE MIDDLE ATLANTIC STATES EARLY-MID NEXT WEEK. DESPITE RELATIVELY GOOD AGREEMENT IN THESE MASS FIELDS...THERE REMAINS MIXED SIGNALS REGARDING THE PROBABILITY OF PRECIPITATION OVER CENTRAL NC FRI THROUGH EARLY NEXT WEEK. THE OVERALL CONFIGURATION OF A TROUGH ALOFT IN THE EASTERN US WOULD SUPPORT ABOVE AVERAGE CHANCES OF PRECIPITATION...BUT THE SUPPRESSION OF THE LOW LEVEL FRONTAL ZONE JUST TO THE SOUTHEAST OF CENTRAL NC WOULD FOCUS THE BRUNT OF THE SHOWERS AND STORMS OVER THE SOUTHEASTERN PART OF THE STATE. WITH THIS IN MIND...HAVE CUT BACK (BY ABOUT 25%) WPC POP...WHICH YIELDS GENERALLY SLIGHT TO CHANCE POP...HIGHEST SOUTHEAST AND MAXIMIZED DURING THE AFTERNOON AND EVENING...WITH THE EXPECTATION THAT NORTHERN AND NW PIEDMONT LOCATIONS MAY ULTIMATELY SEE VERY LITTLE RAINFALL...IF ANY...FRI-SAT. THE MODELS INDICATE THE THE TROPICAL MOISTURE LURKING OVER THE SOUTHEAST MAY THEN GET DRAWN NORTH AND ENTRAINED INTO THE LARGER SCALE TROUGH BY SUN-MON...AT WHICH TIME THE PROBABILITY OF SHOWERS AND STORMS ARE EXPECTED TO INCREASE THROUGHOUT CENTRAL NC. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/... AS OF 645 AM TUESDAY... SUB-VFR VSBYS AT KRWI WILL QUICKLY IMPROVE THIS MRONING AND VFR CONDITIONS WILL PREVAIL FOR MUCH OF THE TAF PERIOD. A FEW WEAK DISTURBANCES IN THE NORTHWESTERLY FLOW ALOFT COMBINED WITH INCREASING MOISTURE AND INSTABILITY WILL TRIGGER SCATTERED STORMS THIS AFTERNOON. WHILE AN ISOLATED STORM CANNOT BE RULED OUT AT ANY TAF SITE...MODEL GUIDANCE AND THE OVERALL WEATHER PATTERN SUPPORT A HIGHER PROBABILITY...AND THUS INCLUSIONG IN THE TAF...AT KGSO AND KINT FOR THIS AFTERNOON. OTHERWISE...SOME AREAS OF SUB-VFR VSBYS WILL BE POSSIBLE AGAIN LATE TONIGHT...WITH THE HIGHEST CONFIDENCE AT THE OFTEN FOG PLAGUED TERMINAL AT KRWI. OUTLOOK: EARLY MORNING STRATUS AND/OR FOG WILL BE POSSIBLE WEDNESDAY AND THURSDAY WITH AFTERNOON STORMS...MAINLY WEST...EACH DAY. A COLD FRONT WILL THEN MOVE INTO THE AREA ON FRIDAY...POTENTIALLY STALLING OVER EASTERN NC THIS WEEKEND. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...22 SHORT TERM...22 LONG TERM...26 AVIATION...22

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