Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 261730 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 130 PM EDT SUN JUL 26 2015 .SYNOPSIS... A WEAK COLD FRONT WILL DRIFT INTO THE REGION FROM THE NORTHWEST TODAY...MOVING INTO THE PIEDMONT MONDAY...THEN DRIFT SOUTH OF THE REGION TUESDAY. SCATTERED SHOWERS AND A FEW THUNDERSTORMS WILL ACCOMPANY THE FRONT. ANOTHER FRONT WILL MOVE INTO THE AREA FROM THE WEST THURSDAY...THEN STALL JUST TO THE SOUTHEAST OF THE AREA FRIDAY INTO THE WEEKEND...BRINGING A BETTER CHANCE OF SHOWERS AND THUNDERSTORMS TO THE AREA. OTHERWISE...IT WILL REMAIN WARM AND HUMID THROUGHOUT THE WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 115 PM EDT SUNDAY... SURFACE HIGH REMAINS OVER THE REGION WITH WEAK SOUTHERLY FLOW ACROSS THE PIEDMONT AND SOUTHEASTERLY FLOW ACROSS THE FOOTHILLS AND BLUE RIDGE. THE STILL EXIST AN UPPER LEVEL TROUGH WITH WEAK STEERING CURRENTS FROM THE WEST-NORTHWEST. THIS PATTERN IS SIMILAR TO YESTERDAY. EXPECT ISOLATED SHOWERS AND THUNDERSTORMS TO DEVELOP ACROSS THE MOUNTAINS...MORESO ALONG THE BLUE RIDGE...THEN DRIFT EASTWARD INTO THE FOOTHILLS AND POSSIBLY THE PIEDMONT LATE THIS AFTERNOON INTO THE EVENING. MORNING SOUNDING HAS CAPPING INVERSION AROUND 14KFT...THEREFORE ANY STORMS THIS AFTERNOON SHOULD REMAIN SHORT AND SMALL BUT COULD PRODUCE VERY LOCALIZED HEAVY DOWNPOURS AS PWATS HAVE INCREASED TO OVER AN INCH. SHOWERS WILL FADE WITH LOSE OF HEATING THIS EVENING BUT COULD LINGER UNTIL MIDNIGHT...ESPECIALLY TOWARDS LYNCHBURG...AS A WEAK WAVE TRACKS ACROSS NORTHERN VIRGINIA. AS OF 400 AM EDT SUNDAY... LATEST SATELLITE IMAGES VIA THE FOG PRODUCT SHOW LOW CLOUDS BLOOMING ALONG THE BLUE RIDGE WITH SOME VALLEY FOG ALSO DEVELOPING IN THE PRE DAWN HOURS AS A WEDGE LIKE AREA OF HIGH PRESSURE KEEPS A MOIST SOUTHERLY FLOW OF AIR ACROSS THE REGION. A SPRINKLE CAN NOT BE RULED OUT BUT THE CLOUDS AND FOG WILL BREAK UP AFTER DIURNAL HEATING BEGINS AFTER SUNRISE. BY THIS AFTERNOON A WEAK COLD FRONT WILL MOVE INTO THE REGION FROM THE NORTHWEST AND GENERATE SOME SCATTERED SHOWERS AND THUNDERSTORMS MAINLY FROM THE RIDGE WESTWARD. INSTABILITY AND SHEAR ARE LACKING SO DO NOT ANTICIPATE ANY STRONG STORMS...BUT PRECIPITABLE WATER VALUES WILL BE INCREASING SO EVEN THOUGH COVERAGE LOOKS TO BE RATHER SPARSE THOSE WHO GET WET WILL GET QUITE WET IN LOCAL DOWNPOURS. BELIEVE THERE WILL BE A TYPICAL DIURNAL BIAS TO THE CONVECTION SO ACTIVITY WILL BE SIMMERING DOWN AFTER SUNSET. THERE ARE INDICATIONS THAT NORTHWEST FLOW ALOFT...COURTESY OF THE UPPER RIDGE OVER THE MID SECTION OF THE COUNTRY...CONTINUES TO SEND A STEADY SUPPLY OF RELATIVELY WEAK SHORT WAVE ENERGY IN OUR DIRECTION. ANOTHER ROUND OF SHOWERS/STORMS MAY BE APPROACHING FROM THE NORTHWEST TOWARD DAYBREAK MONDAY. AT THIS TIME THERE IS TOO MUCH UNCERTAINTY IN THIS SCENARIO TO WARRANT ANYTHING MORE THAN LOW CHANCE POPS BUT IT WILL BE REEVALUATED WITH LATER MODEL RUNS AND ADJUSTED ACCORDINGLY. WARMER AIR WILL MAKE A PUSH INTO THE REGION JUST AHEAD OF THE APPROACHING FRONT SO TEMPERATURES TODAY WILL BE A FEW DEGREES WARMER THAN SATURDAY WITH READINGS FROM AROUND 90 EAST OF THE RIDGE TO THE MIDDLE 80S WEST. LOWS TONIGHT WILL BE RIGHT AROUND NORMAL WITH UPPER 60S/AROUND 70 EAST TO MID/UPPER 60S WEST. && .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/... AS OF 415 AM EDT SUNDAY... THE WEAK FRONT THAT WILL DRIFT INTO THE REGION FROM THE NORTHWEST TODAY WILL CONTINUE MOVING SLOWLY SOUTHEAST THROUGH THE AREA MONDAY. THERMODYNAMICS ARE WEAK FOR THIS TIME OF YEAR AND DYNAMICS ARE NIL WITH THIS SYSTEM. THE GFS IS VERY LACKLUSTER WITH INSTABILITY AND PRECIPITATION WITH THIS SYSTEM...WHILE THE NAM AND ECMWF DEPICT SUBSTANTIALLY MORE. LOCATION OF FRONT AND BEST CONVERGENCE NEAR THE BLUE RIDGE...PLUS POTENTIAL WEAK OUTFLOW BOUNDARY RESIDING ACROSS THIS REGION AS WELL FROM POTENTIAL DECAYING OVERNIGHT/EARLY MORNING CONVECTION ACROSS WV/WESTERN VA...SHOULD FOCUS THE BEST COVERAGE FOR CONVECTION EAST AND SOUTH OF THE BLUE RIDGE BY AFTERNOON. GIVEN THE OVERALL SCENARIO...AND SOME CREDENCE TO THE GFS...CANNOT SUPPORT POPS HIGHER THAN CHANCE LEVELS AT THIS TIME. SPC ONLY HAS GENERAL THUNDER DEPICTED FOR THE AREA. GIVEN THE OVERALL LACK OF INSTABILITY FOR MID-JULY AND RELATIVE WARM TEMPS ALOFT WITH 500MB RIDGING...THIS SEEMS VERY REASONABLE. ALL INDICATIONS ARE THAT A WEAK FRONTAL BOUNDARY WILL RESIDE SOMEWHERE ACROSS WESTERN/CENTRAL NC INTO EASTERN TN AND ESSENTIALLY WASH OUT. A STRONG SUBTROPICAL RIDGE ACROSS THE CENTRAL/SOUTH CENTRAL U.S. WILL BRIEFLY AMPLIFY INTO THE SOUTHERN APPALACHIANS WEDNESDAY. MEANWHILE...LOW PRESSURE MOVING ACROSS SOUTH CENTRAL CANADA TOWARD ONTARIO/QUEBEC...WILL PUSH A COLD FRONT INTO THE OHIO VALLEY. CONVECTION WED SHOULD BE GENERALLY PUSHED SOUTH AND WEST OF THE AREA...BUT COULD EXTEND NORTHWARD DURING MAX HEATING INTO THE MOUNTAINS OF NC AND FAR SW VA. BY WED NIGHT/EARLY THU MORNING...REMNANT CONVECTION COULD BE APPROACHING THE WESTERN BORDER OF THE CWA ASSOCIATED WITH THE NEW COLD FRONT. OVERALL...WED SHOULD BE A MOSTLY SUNNY...WARM/HOT DAY WITH MINIMAL PRECIPITATION. MAX/MIN TEMPS WILL AVERAGE ABOVE NORMAL THROUGH THE PERIOD WITH THE EXTENSION OF THE STRONG SUBTROPICAL RIDGE LOCATED ACROSS THE SOUTHERN PLAINS RIDGING INTO OUR REGION THROUGH MUCH OF THIS PERIOD. WED SHOULD BE THE HOTTEST DAY IN ADVANCE OF THE NEXT APPROACHING COLD FRONT. GFS GRIDDED TEMPS REMAIN WELL ABOVE THE OTHER MODELS...NOW EVEN ADVERTISING TEMPS AOA 100F INTO THE PIEDMONT WED. FEEL MAX TEMPS SHOULD GENERALLY BE 10 DEG F LESS THAN INDICATED BY THE GFS GRIDDED TEMPS. HAVE GENERALLY GONE WITH A MODEL BLEND THROUGH THE PERIOD...NUDGING UP ONE OR TWO DEGREES IN SOME AREAS AS APPROPRIATE. && .LONG TERM /THURSDAY THROUGH SATURDAY/... AS OF 430 AM EDT SUNDAY... SOME CHANGES INDICATED TO THE OVERALL UPPER ATMOSPHERIC PATTERN THIS PERIOD. THE STRONG SUBTROPICAL RIDGE RETROGRADES INTO THE SOUTHWEST U.S. AS A VIGOROUS UPPER TROUGH SHIFTS INTO THE NORTHEAST U.S. A COLD FRONT WILL MOVE INTO THE REGION FROM THE NORTHWEST THU AND SHOULD PROVE TO BE OUR NEXT BEST CHANCE FOR SHOWERS AND THUNDERSTORMS. DYNAMICS AND INSTABILITY LOOK TO BE A GOOD BIT STRONGER THAN NOTED WITH THE MON/TUE SYSTEM...SO THERE SHOULD BE BETTER COVERAGE OF SHOWERS/THUNDERSTORMS...AND PERHAPS A FEW BECOMING STRONG. THE FRONT DRIFTS TOWARD THE COAST AND INTO SOUTHERN NC/NORTHERN SC BY FRI...TAKING THE PRECIPITATION WITH IT. CONFIDENCE IN THE FORECAST BEYOND FRIDAY REMAINS LOW. HOWEVER...MODELS ARE COMING INTO BETTER AGREEMENT THAT THERE WILL NOT BE A TROPICAL SYSTEM FORMING OFF THE SOUTHEAST U.S. COAST...RATHER AN ELONGATED SW-NE TROUGH WILL DEVELOP ALONG THE OLD FRONTAL BOUNDARY FROM AL/GA NORTHEAST INTO SOUTHEAST VA AS HIGH PRESSURE ALOFT ALSO BUILDS ACROSS THE WESTERN ATLANTIC. THIS LEAVES AN OVERALL UPPER TROUGH/WEAKNESS IN THE FLOW ALOFT..IN PLACE FROM AL/GA NORTHEAST TOWARD THE MID-ATLANTIC...WITH STRONGER WESTERLIES REMAINING IN PLACE NORTH OF THE MASON-DIXON LINE. THE MAIN PROBLEM LIES IN EXACTLY WHERE WILL THIS TROUGH SET UP...AS THE BULK OF THE ASSOCIATED PRECIPITATION WILL REMAIN MOSTLY EAST OF THE TROUGH. MODEL CONSENSUS FOCUSES THE BULK OF THE ASSOCIATED RAINFALL JUST EAST AND SOUTH OF THE CWA...BUT CERTAINLY IMPACTING TO SOME EXTENT OUR SOUTHERN AND EASTERN COUNTIES...MAINLY EAST OF THE BLUE RIDGE. GIVEN THAT THERE IS SOME TROPICAL CONNECTION WITH THIS PATTERN TO THE GULF...HEAVY RAINFALL COULD OCCUR WITHIN THIS CORRIDOR OF PRECIPITATION...BUT GIVEN THE LOW CONFIDENCE...IT REMAINS ENTIRELY TOO SOON TO ADVERTISE SUCH OR LIKELY POPS AT THIS POINT. SOME MODELS...ESPECIALLY THE CANADIAN...KEEP THE BULK OF THE MEANINGFUL PRECIPITATION ALL EAST OR SOUTH OF OUR CWA THROUGH THIS PERIOD. TEMPERATURES SHOULD FALL BACK TO MORE NORMAL LEVELS FOLLOWING THE WED FRONTAL PASSAGE...THEN GENERALLY HOLD NEAR NORMAL INTO THE WEEKEND. THERE IS STILL NO INDICATION OF ANY SUBSTANTIAL COOLING THROUGH THIS PERIOD WITH ANY CANADIAN AIR MASSES REMAINING WELL NORTH OF THE AREA...500MB HEIGHTS HOVERING IN THE 588DM RANGE...AND TROPICAL MOISTURE ENTRENCHED ACROSS AT LEAST THE SOUTHEAST HALF OF THE CWA. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... AS OF 114 PM EDT SUNDAY... A HUMID BUT WEAK SURFACE HIGH PRESSURE WILL RESIDE OVER THE REGION TODAY. SOUTHERLY WINDS WILL BE LIGHT THROUGH THIS EVENING BUT COULD HELP PROMOTE SHOWERS ALONG THE BLUE RIDGE THIS AFTERNOON. WINDS ARE ALSO WEAK ALOFT BUT OUT OF THE WEST- NORTHWEST. SHOWERS EXPECTED TO GENERATE ACROSS THE MOUNTAINS THIS AFTERNOON...THEN DRIFT INTO THE FOOTHILLS THROUGH THIS EVENING. COVERAGE OF STORMS WILL BE ISOLATED AND WITH LOW CONFIDENCE WILL MENTION VICINITY SHOWERS AT BLF/LWB/BCB/ROA FOR LATE THIS AFTERNOON. DEBRIS CLOUDS MAY LINGER THROUGH MOST OF THE NIGHT BUT ANY CLEARING COULD LEAD TO FOG FORMING...ESPECIALLY IN AREAS THAT HAVE RAIN TODAY AND IN MOUNTAIN VALLEYS. THE WEAK COLD FRONT WILL DRIFT SLOWLY SOUTHEAST THROUGH MONDAY. SHOWER AND THUNDERSTORM ACTIVITY WILL BECOME MORE WIDESPREAD ON MONDAY WITH THE FRONT IN CLOSE PROXIMITY. OUTSIDE MAINLY AFTERNOON/EVENING SHOWERS AND THUNDERSTORMS AND LATE NIGHT/EARLY MORNING MAINLY VALLEY FOG...EXPECT MOSTLY VFR CONDITIONS. EXTENDED AVIATION FORECAST... MOSTLY VFR CONDITIONS EXPECTED MID WEEK AS HIGH PRESSURE RETURNS...BEFORE BETTER CHANCES FOR SHOWERS/THUNDERSTORMS RETURN LATE IN THE COMING WORKWEEK WITH THE NEXT FRONTAL BOUNDARY AND A POTENTIAL DEEP FETCH OF GULF MOISTURE. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...MBS NEAR TERM...MBS/RCS SHORT TERM...RAB LONG TERM...RAB/WP AVIATION...RCS

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