Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 191839 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 239 PM EDT TUE MAY 19 2015 .SYNOPSIS... A COLD FRONT WILL MOVE ACROSS THE MID ATLANTIC REGION THIS AFTERNOON AND EVENING...TRIGGERING SPOTTY SHOWERS AND A FEW THUNDERSTORMS... WITH BETTER RAIN CHANCES EAST OF THE BLUE RIDGE. ONCE THE FRONT PASSES EAST OF THE AREA...COOLER DRIER AIR WILL FILTER INTO THE REGION FOR MID WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1100 AM EDT TUESDAY... AT 1100 AM...SURFACE COLD FRONT WAS ALIGNED ALONG THE WESTERN SLOPES OF THE APPALACHIANS. THIS FRONT WILL CROSS OVER THE MOUNTAINS EARLY THIS AFTERNOON...THEN EAST ACROSS THE PIEDMONT DURING THE LATE AFTERNOON. THE MORNING RNK/GSO SOUNDINGS WERE STILL VERY MOIST WITH PWATS 1-2 STANDARD DEVIATIONS ABOVE NORMAL. AS SUCH...EXPECTATION IS FOR SCATTERED SHOWERS/STORMS TO DEVELOP ALONG THE FRONT AS IT MOVES EAST OF THE MOUNTAINS THIS AFTERNOON. THE MEAN WIND IS A LITTLE STRONGER TODAY...FROM THE WEST AT 15-20KTS...SUGGESTING ANY ACTIVITY THAT DEVELOPS SHOULD NOT DWELL OVER ANY PARTICULAR LOCATION FOR VERY LONG. NEVER THE LESS STILL EXPECT SHOWERS WITH HEAVY DOWNPOURS UNTIL FROPA. BEST HEATING/INSTABILITY THIS AFTERNOON WILL BE ACROSS THE PIEDMONT WHERE CAPES WILL REACH 2000 K/KG AND LI`S OF M3 TO M5. AS SUCH...STRONG STORMS ARE POSSIBLE ACROSS SOUTHSIDE VA AND INTO THE PIEDMONT OF NC THIS AFTERNOON. ALL RAINFALL IS EXPECTED TO END AROUND SUNSET AS THE COLD FRONT COMPLETES ITS PASSAGE ACROSS OUR AREA. THE COLD FRONT WILL BRING MUCH DRIER AIR INTO THE AREA...RESULTING IN A NOTABLE DECREASE IN THE AMOUNT OF MUGGINESS OF THE AIR...AS WELL AS A DECREASE IN THE AMOUNT OF CLOUD COVER WHICH WILL ALLOW US TO ENTER TUESDAY NIGHT UNDER MOSTLY CLEAR SKIES. WILL ALSO SEE WIND SPEEDS INCREASE BEHIND THE FRONT...WITH THE OCCASIONAL 25 MPH GUST POSSIBLE ACROSS THE MOUNTAINS DURING THE AFTERNOON. DOWNSLOPE WINDFLOW AND THE ARRIVAL OF DRIER AIR WILL ALLOW FOR A SLIGHTLY WIDER RANGE IN TEMPERATURES THIS AFTERNOON...WITH HIGHS RANGING FROM THE UPPER 70S ACROSS SOUTHEAST WEST VIRGINIA...TO THE UPPER 80S ACROSS THE SOUTHSIDE. LOWS TONIGHT WILL BE COOLER THAN IN NIGHTS PAST...RANGING FROM THE LOW 50S WEST TO THE UPPER 50S EAST. && .SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/... AS OF 415 AM EDT TUESDAY... SURFACE HIGH PRESSURE WILL RIDGE INTO THE REGION FROM THE WEST AND NORTHWEST BEHIND THE TUESDAY COLD FRONT...BUT WILL NOT MOVE OVER THE AREA UNTIL LATE IN THE WEEK. THIS COLD FRONT WILL DRIFT SOUTH FROM CAROLINA INTO GEORGIA. A SPLIT FLOW PATTERN BEGINS TO DEVELOP WITH A DEEP COLD CORE UPPER LOW ACROSS SOUTHEAST CANADA/NORTHEAST U.S...AND YET ANOTHER UPPER LOW DRIFTING OFF THE WEST COAST INTO THE SOUTHWEST U.S. AN ELONGATED RIDGE IS EVIDENT BETWEEN THESE TWO SYSTEMS EXTENDING FROM THE MID- SOUTH/SOUTHERN PLAINS INTO THE NORTHERN PLAINS/SOUTH CENTRAL CANADA. A STRONG SHORT WAVE WILL BE DRIFTING SOUTHWEST ON THE BACK SIDE OF THE NORTHEAST U.S. UPPER LOW AND AT THE BEGINNING OF THE PERIOD WILL BE LOCATED ACROSS THE WESTERN GREAT LAKES. CONSEQUENTLY...THE RESPITE FROM THE CLOUDS AND PRECIPITATION WILL BE BRIEF AS THIS SHORT WAVE INTERACTS WITH THE STALLED FRONT TO OUR SOUTH...PULLING MOISTURE BACK NORTHWARD AS THE UPPER FLOW TRENDS INCREASINGLY ZONAL ACROSS THE REGION ALONG THE BASE OF THE NORTHEAST U.S. UPPER LOW. MID/HIGH CLOUDS WILL BE ON THE INCREASE DURING THE AFTERNOON WEDNESDAY WITH STRONG UPSTREAM PVA EVIDENT IN ADVANCE OF THE SHORT WAVE. TEMPERATURES WILL BE MUCH CLOSER TO SEASONAL NORMALS WED THAN IN PREVIOUS DAYS...BUT THE MAIN DIFFERENCE WILL BE THE MUCH LOWER DEWPOINTS/HUMIDITY LEVELS AS PWATS DROP WELL BELOW 1.0 INCH. MODELS ARE STILL NOT IN AGREEMENT ON THE TRACK/TIMING/OR THE IMPACT OF THIS SYSTEM ON THE CWA...WITH THE GFS REMAINING A FAR SOUTHERN OUTLIER TAKING MOST ALL OF THE ASSOCIATED MOISTURE SOUTH OF THE CWA...WHILE THE NAM/CANADIAN ARE AT THE OTHER END OF THE SPECTRUM SHOWING SUBSTANTIAL QPF APPROACHING AN INCH AND SPREADING AS FAR NORTH AS THE MD/PA BORDER. WPC CONTINUES TO LEAN TOWARD THE 12Z ECMWF/ECMWF ENSEMBLE FORECAST FROM YESTERDAY...AND THUS SO WILL I AS THE GFS REMAINS A CLEAR OUTLIER AMONG THE MODEL SOLUTIONS. WITH THIS SCENARIO...HAVE BROAD BRUSHED HIGH CHANCE POPS WELL NORTH AND WEST INTO THE CWA BEGINNING THU MORNING...CONTINUING INTO THE EAST DURING THE AFTERNOON. THE SHORT WAVE MOVES FAIRLY QUICKLY AND SHOULD BE EXITING THE AREA IN THE 00Z-06Z TIME FRAME FRIDAY. ANOTHER QUESTION THAT REMAINS DURING THIS TIME FRAME IS THE THREAT FOR THUNDER. AGAIN...WITH THE EXCEPTION OF THE GFS...ALL OF THE OTHER MODELS CONTINUE TO POKE A NOSE OF INSTABILITY AROUND 18Z NORTHWARD TOWARD KDAN. BUT BY FAR...THE BETTER INSTABILITY REMAINS SOUTH IN THE WFO RAH CWA. SPC HAS BROUGHT THE GENERAL THUNDER LINE INTO THE FAR SOUTHEAST CORNER OF THE CWA...WITH A MARGINAL THREAT INTO THE WFO RAH/MHX CWAS. THIS AGREES WITH MY THINKING AND CONTINUES TO SUPPORT A SLIGHT CHC OF THUNDER THU AFTERNOON IN THE DANVILLE/CASWELL AREA...AGAIN THINKING THAT THE BETTER THREAT WILL REMAIN FURTHER SOUTH...MOSTLY ON THE SOUTH/EAST SIDE OF THE ASSOCIATED SFC LOW NEAR THE SC/NC BORDER. TEMPERATURES THU WILL BE BELOW NORMAL...ESPECIALLY ACROSS THE PIEDMONT WITH HIGHS ONLY IN THE UPPER 60S TO LOWER 70S IN THE CLOUDS AND RAIN. FRIDAY...THE LARGE SURFACE HIGH ACROSS THE CENTRAL PLAINS SHIFTS EAST UNDER A SLOWLY PROGRESSIVE UPPER AIR PATTERN...KEEPING THE UPPER LOW IN THE NORTHEAST U.S...THE ELONGATED RIDGE JUST TO OUR WEST...AND THE UPPER LOW IN THE SOUTHWEST U.S. CREEPING SLOWLY INLAND FOR CONTINUED ROUNDS OF THUNDERSTORMS/SEVERE WEATHER ACROSS THE CENTRAL U.S. INTO THE WEEKEND. FOR US...THE COOLEST/DRIEST CONDITIONS SHOULD FINALLY COME FRIDAY AS THE CANADIAN HIGH DRIFTS ACROSS OH/PA. MINIMUM TEMPERATURES SHOULD BE IN THE 40S AND 50S...BUT WITH THE LATE MAY SUN STILL EXPECT NEAR NORMAL AFTERNOON TEMPERATURES IN THE 60S AND 70S. 850MB TEMPS WILL ONLY BE IN THE +5C TO +7C RANGE ACROSS THE CWA. && .LONG TERM /SATURDAY THROUGH MONDAY/... AS OF 430 AM EDT TUESDAY... SPLIT FLOW WILL REMAIN ACROSS THE U.S. THROUGH THE WEEKEND WITH AN UPPER LOW ANCHORED OFF THE NORTHEAST U.S. COAST A BROAD...HIGHLY DIFFLUENT UPPER LOW DRIFTING EASTWARD INTO THE CENTRAL U.S. MORE THUNDERSTORMS AND SEVERE WEATHER IN THAT REGION OF THE COUNTRY INTO NEXT WEEK. FOR OUR REGION OF THE COUNTRY...EXPECT A DRY WEEKEND WITH SEASONABLY MILD TEMPERATURES...LOWS IN THE 40S AND 50S AND HIGHS MOSTLY IN THE 70S TO NEAR 80 ACROSS THE PIEDMONT. MOISTURE...WARMTH...AND HUMIDITY ARE POISED TO RETURN BY EARLY NEXT WEEK AS THE UPPER RIDGE SHIFTS EASTWARD OVER OUR AREA AND THE UPPER LOW ACROSS THE NORTHEAST U.S. SHIFTS INTO THE NORTHERN ATLANTIC. A BAROCLINIC ZONE WILL DEVELOP ACROSS THE OH VALLEY EASTWARD INTO THE NORTHERN MID-ATLANTIC LATE IN THE WEEKEND AND DRIFT SLOWLY SOUTHWARD INTO OUR REGION DURING THE FIRST HALF OF THE WEEK AS THE UPPER RIDGE BREAKS DOWN AND SHIFTS SLIGHTLY WEST TOWARD THE MID-SOUTH. INSTABILITY WILL CREEP UPWARD EACH DAY THROUGH THE PERIOD...WITH DIURNAL THUNDERSTORMS BECOME MORE LIKELY WITH EACH DAY THROUGH THE FIRST HALF OF THE WEEK...FIRST IN THE MOUNTAINS AND I-64 CORRIDOR NORTHWARD...CREEPING TOWARD SOUTHSIDE AND THE VA/NC PIEDMONT BY MONDAY AND TUESDAY. THE BAROCLINIC ZONE WILL DRIFT INTO THE REGION TUESDAY/WEDNESDAY WITH EVEN GREATER CHANCES OF WIDESPREAD CONVECTION ACROSS THE ENTIRE CWA. TEMPERATURES AND HUMIDITY READINGS WILL RETURN TO ABOVE NORMAL LEVELS. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... AS OF 200 PM EDT TUESDAY... SCATTERED SHOWERS/STORMS OVER THE AREA THIS EVENING WILL DISSIPATE BY SUNSET. A MUCH DRIER AIRMASS WILL ADVECT INTO THE FORECAST AREA OVERNIGHT AND WEDNESDAY. THIS DRY AIRMASS WILL PREVENT DEEP CONVECTION WEDNESDAY. ASIDE FROM THE SHOWER ACTIVITY THIS EVENING ANTICIPATING MAINLY VFR THROUGH THE VALID TAF PERIOD. SOME OF THE MODELS INDICATE THAT A SHALLOW LAYER OF MOISTURE MAY GET TRAPPED UP AGAINST THE WEST SIDE OF THE APPALACHIANS LATE TONIGHT. THIS MAY RESULT IN A PERIOD OF LOW STRATUS 4-8FT AGL VCNTY OF KBLF EARLY WEDNESDAY MORNING. ANY LOW CLOUD THAT DOES FORM SHOULD DISSIPATE QUICKLY WEDNESDAY MORNING. EXTENDED AVIATION DISCUSSION... AN UPPER LEVEL DISTURBANCE WILL LIKELY BRING SOME MVFR CEILINGS AND SHOWERS BACK INTO THE AREA THURSDAY...MOVING OUT FRIDAY MORNING...WITH VFR CONDITIONS RETURNING FRIDAY AFTERNOON AND SATURDAY. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...NF NEAR TERM...NF/PM SHORT TERM...RAB LONG TERM...KK/RAB AVIATION...PM

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