Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 051141 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 741 AM EDT SUN JUL 5 2015 .SYNOPSIS... AN UPPER LOW WILL DRIFT SLOWLY FROM EAST TENNESSEE TODAY TOWARD WESTERN PENNSYLVANIA BY LATE MONDAY BRINGING WIDESPREAD RAIN AND A FEW THUNDERSTORMS TO THE AREA TODAY THROUGH MONDAY. A COLD FRONT WILL MOVE INTO THE REGION FROM THE OHIO VALLEY BY WEDNESDAY...THEN STALL AND LIFT BACK NORTH AS A WARM FRONT LATE IN THE WEEK AS HIGH PRESSURE ALOFT BUILDS ACROSS THE SOUTHEAST STATES. SCATTERED SHOWERS AND THUNDERSTORMS WILL ACCOMPANY THE FRONT. BELOW NORMAL TEMPERATURES EARLY IN THE WEEK WILL TREND TO ABOVE NORMAL TEMPERATURES BY THE END OF THE WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 515 AM EDT SUNDAY... A CLOSED LOW WILL BE SPLITTING OFF FROM THE MEAN TROF AND SLOWLY MOVING OVER THE REGION TODAY AND TONIGHT. THIS WILL SET THE AREA UP FOR SOME WIDESPREAD RAINFALL WITH UPPER DIFFLUENCE AND DEEP E/SE FLOW WITH GOOD MOISTURE TRANSPORT GENERATING PRECIPITABLE WATER VALUES APPROACHING TWO INCHES. THANKFULLY ANTECEDENT CONDITIONS ARE NOT AS WET AS THEY COULD HAVE BEEN AND THE MOST VULNERABLE AREAS TO HYDRO CONCERNS ARE FROM THE MOUNTAIN EMPIRE REGION UP THROUGH SOUTHEAST WEST VIRGINIA...SO A FLASH FLOOD WATCH HAS BEEN POSTED FOR THOSE COUNTIES FROM LATE THIS MORNING THROUGH TONIGHT. AS THE LOW SPINS SLOWLY TO OUR WEST...WE WILL SEE A BIT OF A DRY SOT WORK IN FROM THE SOUTHWEST. SEVERAL MODELS ARE QUITE AGGRESSIVE WITH SHUTTING DOWN THE PRECIPITATION QUICKLY BUT WITH A CLOSED LOW AND DECENT SYNOPTIC SUPPORT IN PLACE WILL SHADE THINGS TOWARD THE SLOWER/WETTER SOLUTIONS. WITH A GOOD AMOUNT OF CLOUD COVER EXPECTED WE SHOULD SEE TEMPERATURES TODAY JUST A FEW DEGREES COOLER THAN YESTERDAY WITH LOW/MID 80S EAST TO LOW/MID 70S WEST. LOWS TONIGHT WILL GENERALLY BE 65 TO 70 EAST...WITH 60 TO 65 WEST. && .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/... AS OF 430 AM EDT SUNDAY... CLOSED UPPER LOW WILL BE NEAR THE VA/WV/KY BORDER INTERSECTION AT 12Z MON...DRIFTING NORTH-NORTHEAST INTO WESTERN PA BY EVENING. THE WARM ADVECTION AND HEAVIEST PART OF THE RAINFALL SHOULD BE LIFTING TOWARD THE I-64 CORRIDOR AT THE START OF THIS PERIOD...THEN INTO NORTHERN VA/WV BY AFTERNOON/EVENING. AS IT DOES SO...A BAROCLINIC ZONE WILL DEVELOP ON THE WEST SIDE OF THE UPPER LOW. SOMEWHAT OF A DRY SLOT IS EVIDENT WORKING ITS WAY INTO THE PIEDMONT AND AREAS EAST OF THE BLUE RIDGE BY AFTERNOON. WIDESPREAD RAIN SHOWERS DURING THE MORNING SHOULD FOCUS MORE TOWARD THE NORTHERN AND WESTERN PART OF THE CWA BY AFTERNOON INTO THE EARLY EVENING...BEFORE TAPERING OFF IN THESE AREAS AFTER SUNSET. THE HEAVIEST RAIN DURING THE DAY SHOULD FALL ROUGHLY NEAR THE I-77 AND I-64 CORRIDORS WITH THE COMBINED EFFECT OF WARM ADVECTION RAINFALL EARLY IN THE EVENT...TRANSITIONING TO DEFORMATION RAINFALL WEST DURING THE AFTERNOON. AFTERNOON PRECIPITATION SHOULD BE LIMITED TO A FEW SPOTTY SHOWERS ACROSS AREAS EAST OF THE BLUE RIDGE WITH AN ANTICIPATED DRY SLOT IN THAT REGION. WILL HOLD ONTO LIKELY POPS ACROSS WEST MUCH OF THE DAY...WITH POPS DECREASING INTO THE SLIGHT CHANCE CATEGORY NC COUNTIES BY EVENING. QPF AFT 12Z SHOULD RANGE FROM 3/4 INCH IN THE WEST AND NORTHWEST TO 1/4 INCH IN THE SOUTHEAST PART OF THE CWA. THIS RAINFALL SHOULD NOT BE ENOUGH TO EXACERBATE ANY FLOODING PROBLEMS...BUT LATER SHIFTS WILL NEED TO EVALUATE IF THE FLASH FLOOD WATCH WILL NEED TO CONTINUE BEYOND THE CURRENT 10Z MON EXPIRATION. BY MONDAY NIGHT...THE UPPER LOW WILL HAVE MOVED FAR ENOUGH NORTH AWAY FROM THE AREA...AS WELL AS SHEARING OUT...THAT ANY ASSOCIATED RAINFALL ACROSS OUR REGION SHOULD HAVE ENDED. LOW CLOUDS AND PATCHY DRIZZLE MAY LINGER ACROSS THE MOUNTAINS...BUT NO APPRECIABLE RAINFALL IS EXPECTED. FOR TUESDAY...PROGRESSIVE FLOW ACROSS THE NORTHERN STATES WILL QUICKLY PUSH A NEW FRONTAL ZONE AND ASSOCIATED WEAK UPPER TROUGH INTO THE REGION FROM THE WEST. LINEAR ORIENTED...POTENTIALLY STRONG CONVECTION...APPEARS LIKELY WITH THIS SYSTEM. THIS ACTIVITY WILL LIKELY REACH WESTERN WV/FAR SOUTHWEST VA AND THEN DIMINISH AS IT ATTEMPTS TO CROSS THE MOUNTAINS DURING THE LESS FAVORABLE EVENING HOURS. THIS AGREES WELL WITH THE MARGINAL RISK SPC HAS ADVERTISED ON DAY 3 ENDING JUST SHY OF OUR WESTERN BORDER. OTHERWISE...MUCH OF THE DAY TUESDAY SHOULD OFFER A MINIMUM OF PRECIPITATION ACTIVITY ACROSS THE CWA...ESPECIALLY EAST OF THE BLUE RIDGE. HAVE GENERALLY ADVERTISED ONLY SLIGHT CHANCE POPS FOR AREAS EAST OF THE BLUE RIDGE WITH A WARM...MOIST ATMOSPHERE IN PLACE...BUT DYNAMICS WILL BE LIMITED AT BEST. WEDNESDAY HAS BECOME MORE PROBLEMATIC TODAY AMONG THE MODELS THAN INDICATED YESTERDAY AS A RESULT OF INCREASED SUBTROPICAL RIDGING ACROSS THE SOUTHEAST STATES. THIS ALLOWS THE TUESDAY FRONT TO DRIFT INTO THE CWA AND THEN LIFT BACK NORTH. IT SHOULD LINGER LONG ENOUGH IN THE REGION WEDNESDAY TO SERVE AS A FOCUS FOR SCATTERED IF NOT NUMEROUS CONVECTION DURING AFTERNOON HEATING. TEMPERATURES SHOULD REMAIN BELOW NORMAL WEST OF THE BLUE RIDGE MONDAY WITH WIDESPREAD CLOUDS AND RAIN. HOWEVER...EAST OF THE BLUE RIDGE SOME INSOLATION IS EXPECTED DURING THE AFTERNOON AND WE SHOULD SEE MAXIMUM TEMPERATURES CLOSER TO NORMAL IN THOSE AREAS. MAXIMUM TEMPERATURES FINALLY REACH ABOVE NORMAL LEVELS IN MUCH OF THE CWA TUESDAY WITH INCREASED AMOUNTS OF SUNSHINE AND SOUTHWEST SURFACE FLOW. WESTERN AREAS WILL SEE MAXIMUM TEMPERATURES CLOSER TO NORMAL AGAIN WEDNESDAY WITH CLOUDS AND PRECIPITATION. MINIMUM TEMPERATURES WILL AVERAGE WELL ABOVE NORMAL THROUGH MUCH OF THE PERIOD...THANKS TO CONTINUED HIGH MOISTURE CONTENT AND DEWPOINTS. && .LONG TERM /THURSDAY THROUGH SATURDAY/... AS OF 500 AM EDT SUNDAY... EXTENDED PERIOD TRENDING WARMER...BUT STILL SOMEWHAT UNSETTLED. MODELS...TO VARYING DEGREES...ADVERTISING AN INTENSIFYING UPPER RIDGE ACROSS THE SOUTHEAST STATES INTO THE MID-ATLANTIC. THE GFS/CANADIAN ARE STRONGEST WITH THE UPPER RIDGE...THE ECMWF IS THE WEAKEST...KEEPING A MORE ACTIVE WESTERLY FLOW ACROSS THE REGION. AT ANY RATE...INSTABILITY WILL BE GREATER THAN IN RECENT DAYS. AT THIS POINT...IT APPEARS THAT THURSDAY SHOULD OFFER THE BEST CHANCE FOR WIDESPREAD CONVECTION...BUT CONDITIONS SHOULD BECOME MORE UNFAVORABLE FOR WIDESPREAD ORGANIZED CONVECTION THROUGH THE END OF THE WEEK INTO THE WEEKEND WITH UPPER RIDGING TAKING HOLD OF THE REGION FROM THE SOUTH. THIS SHOULD PUSH THE MORE ACTIVE BAROCLINIC ZONE INTO OH/PA/MD/NJ. WILL NEED TO WATCH LATER TRENDS OF THE MODELS TO MAKE SURE THIS TREND CONTINUES...AS OPPOSED TO SHIFTING THE BAROCLINIC ZONE FURTHER SOUTH AND WITH NORTHWEST FLOW ALOFT...SHOULD THE UPPER RIDGE DRIFT FURTHER WEST AND REMAIN LESS AMPLIFIED THAN CURRENTLY INDICATED. WITH THE UPPER RIDGING...WE WILL HAVE TO START TALKING ABOUT HIGHS IN THE 90S AGAIN ACROSS THE PIEDMONT. HUMIDITY LEVELS WILL BE HIGH WITH DEWPOINTS NEAR 70...SO WILL NEED TO WATCH APPARENT TEMPERATURES IN THOSE AREAS TOWARD MID-WEEK. NEEDLESS TO SAY...TEMPERATURES APPEAR DESTINED TO ABOVE NORMAL LEVELS THROUGH MUCH OF THE PERIOD. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... AS OF 730 AM EDT SUNDAY... POOR AVIATION CONDITIONS EXPECTED THROUGH THE TAF VALID PERIOD. AN WEAK CLOSED UPPER LOW WILL DRIFT SLOWLY NORTHEAST FROM THE EASTERN TN VALLEY TOWARD WESTERN PA THROUGH THE TAF VALID PERIOD. WIDESPREAD RAIN AND A FEW THUNDERSTORMS WILL ACCOMPANY THIS SYSTEM...WITH THE BEST COVERAGE AND DURATION ACROSS THE WESTERN SITES...INCLUDING KLWB AND KBLF. THUNDERSTORMS SHOULD BE CONFINED TO PIEDMONT AREAS WHERE SOME HEATING IS POSSIBLE DURING THE AFTERNOON LEADING TO ENOUGH INSTABILITY TO SUPPORT ISOLD TSRA. FOR NOW...HAVE ONLY INCLUDED TSRA AT KDAN. LOW CIGS AND VSBYS EXPECTED TO PREVAIL THROUGHOUT MUCH OF THE TAF VALID PERIOD AS AN EASTERLY FLOW EVOLVES IN RESPONSE TO THE UPPER LOW TRACKING TO OUR WEST. CIGS WILL LOWER INTO THE MVFR RANGE EAST OF THE BLUE RIDGE AND MVFR-IFR RANGE WEST OF THE BLUE RIDGE BY EARLY AFTERNOON...WITH RAIN SPREADING INTO THE AREA HELPING TO LOWER THE CIGS FURTHER BY AFTERNOON/EVENING INTO THE IFR CATEGORY MOST AREAS...PERHAPS EVEN LIFR BCB/BLF/LWB. AT THIS POINT...RAIN IS EXPECTED TO OVERSPREAD THE ENTIRE AREA BY 18Z...LINGERING IN THE WEST THROUGH THE END OF THE TAF VALID PERIOD. LOW CLOUDS...FOG...AND DRIZZLE WILL LIKELY LINGER IN THE EAST OVERNIGHT AFTER THE HEAVIER RAIN DRIFTS NORTH OF THE AREA. WINDS ENE-ESE THROUGH MOST OF THE TAF VALID PERIOD 4-7KTS...EXCEPT SE AT BLF IN THE SAME SPEED RANGE. MEDIUM CONFIDENCE IN CIGS AND VSBYS THROUGH THE TAF VALID PERIOD. LOW CONFIDENCE IN TSRA POTENTIAL THROUGH THE TAF VALID PERIOD. MEDIUM TO HIGH CONFIDENCE IN WIND SPEED AND DIRECTION THROUGH THE TAF VALID PERIOD. EXTENDED AVIATION DISCUSSION... POOR AVIATION CONDITIONS TO CONTINUE INTO NEXT WEEK...BUT WINDOWS OF OPPORTUNITY FOR VFR CONDITIONS INCREASE TUE. UPPER LOW/TROUGH WILL MOVE INTO WESTERN PA BY MONDAY EVENING. MEANWHILE...A COLD FRONT WILL APPROACH FROM THE OH VALLEY BY WED. THIS LEAVES A VERY UNSETTLED/WET PATTERN ACROSS THE REGION THROUGH MOST OF THE PERIOD. TUE THROUGH THE DAY OFFERS THE BEST CHANCE FOR SEVERAL HOURS OF VFR...ESPECIALLY EAST OF THE BLUE RIDGE. EXPECT WIDESPREAD LATE NIGHT/EARLY MORNING LOW CLOUDS/FOG WITH IFR-LIFR CIGS/VSBYS. OVERALL...CONDITIONS SHOULD IMPROVE TO MVFR- VFR OUTSIDE SHRA/TSRA ACTIVITY DURING THE AFTERNOONS. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...FLASH FLOOD WATCH FROM 11 AM EDT THIS MORNING THROUGH LATE TONIGHT FOR VAZ007-009-010-012. NC...NONE. WV...FLASH FLOOD WATCH FROM 11 AM EDT THIS MORNING THROUGH LATE TONIGHT FOR WVZ042-043-507-508. && $$ SYNOPSIS...MBS NEAR TERM...AMS/MBS SHORT TERM...RAB LONG TERM...PM/RAB AVIATION...AMS/MBS/RAB

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