Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 010502 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 102 AM EDT MON SEP 1 2014 .SYNOPSIS... THE REGION WILL STAY BETWEEN A LARGE HIGH PRESSURE SYSTEM OVER THE SOUTHEAST UNITED STATES AND A COMPLEX LOW PRESSURE SYSTEM CROSSING THE GREAT LAKES. DISTURBANCES PASSING BETWEEN THESE TWO FEATURES WILL COMBINE WITH HEAT AND HUMIDITY TO RESULT IN PERIODIC CHANCES OF SHOWERS AND STORMS INTO EARLY WEEK. A COLD FRONT FINALLY ARRIVES FROM THE NORTH WEDNESDAY INTO THURSDAY. && .NEAR TERM /THROUGH TODAY/... AS OF 102 AM EDT MONDAY... MADE SOME MINOR ADJUSTMENTS IN POPS AND TEMPERATURES FOR THIS MORNING. SHAPED POPS THIS MORNING TOWARDS A BLEND OF RAP AND HRRR. MORE CHANGES LATER THIS MORNING. AS OF 920 PM EDT SUNDAY... MAIN AXIS OF MOISTURE CONVERGENCE LIES FROM MD-CENTRAL WV. MAIN UPPER IMPULSE THAT WAS OVER TN EARLIER HAS WEAKENED AS HAVE THE SHOWERS UPSTREAM. OVERNIGHT NOT REALLY SEEING MUCH AS AIRMASS STABILIZES. WILL KEEP THE HIGHER POPS OVER THE WV MTNS INTO FAR SW VA...AS ANOTHER WEAK IMPULSE EDGES CLOSER TO THE MTNS BY DAWN. OTHERWISE EXPECT MID DECK OF CLOUDS TO REMAIN IN THE WESTERN HALF OF THE CWA WHILE THE EAST CLEARS SOME TOWARD MORNING. OVERALL FOG THREAT IS PATCHY BUT COULD GET DENSE OUT EAST IF IT CLEARS OUT ENOUGH. NO OTHER MAJOR CHANGES TO THE FORECAST THROUGH DAWN. PREVIOUS VALID DISCUSSION... SHORTWAVES WILL BE EXITING BY EARLY MONDAY LEAVING THE REGION IN DECENT WEST/SW FLOW ALOFT BUT WITHOUT MUCH FORCING WELL IN ADVANCE OF THE NEXT UPSTREAM 5H TROF/COLD FRONT TO THE NW. FORECAST SOUNDINGS SHOW QUITE A DEEP WESTERLY FLOW WHICH RESULTS IN DRYING ALOFT/LOWERING PWATS ESPCLY WEST MONDAY AFTERNOON AND A LEE TROUGH ACROSS THE PIEDMONT. MOST GUIDANCE SOLUTIONS SHOW A LACK OF MUCH CONVECTION IN THIS REGIME WITH ANY FOCUS PROVIDED BY OROGRAPHICS DUE TO WESTERLY CONVERGENCE AND PERHAPS LATE DAY LOW LEVEL BACKING SE. THUS WILL LEAVE IN SOME LOW POPS MAINLY WEST AS APPEARS A SUBTLE WAVE ALOFT COULD SNEAK THROUGH AROUND THE TIME OF MAX HEATING. OTRW EXPECT WEAK LAPSES...LACK OF DEEP INSTABILITY AND EASTERN DOWNSLOPE TO LIMIT OVERALL COVERAGE WITH MUCH OF THE DAY LIKELY DRY AFTER EARLY MID DECK/FOG ERODE. COULD BE ONE OF THE WARMEST DAYS SEEN IN A WHILE WITH 85H TEMPS PUSHING +21C OVER DECENT DOWNSLOPE AND UNDER AMPLE AFTERNOON SUN. THIS WOULD SUPPORT SOME MID 90S PIEDMONT...WITH UPPER 80S/LOW 90S BLUE RIDGE... AND LOW/MID 80S WESTERN ELEVATIONS IF CAN GET A TEMP JUMP AFTER A WARM START IN THE MORNING. && .SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/... AS OF 230 PM EDT SUNDAY... WITH WEAK HIGH PRESSURE BUILDING IN FROM THE SOUTH...EXPECT TO HEAD INTO LATE MONDAY NIGHT WITH MOSTLY CLEAR SKIES AND LIGHT WINDS. AS SUCH...WOULD NOT BE SURPRISED TO SEE PATCHY FOG DEVELOP IN SOME OF THE MOUNTAIN VALLEYS EARLY MORNING...WHICH WILL BURN OFF QUICKLY SHORTLY AFTER 9 AM. DURING TUESDAY AFTERNOON...SHOWER AND THUNDERSTORM ACTIVITY WILL INCREASE AS AN UPPER LEVEL TROUGH AND ASSOCIATED COLD FRONT APPROACH FROM THE WEST. ACTIVITY WILL START OFF ACROSS THE MOUNTAINS...SPOTTY AT FIRST DUE TO THE WESTERLY DOWNSLOPE FLOW...AND THEN WILL SPREAD EAST ACROSS THE PIEDMONT DURING THE EVENING AS THE UPPER LEVEL ENERGY SHIFTS EAST. LIGHT WINDS AND WARM TEMPERATURES ALOFT WILL LIMIT INSTABILITY...AND BELIEVE STRONG THUNDERSTORMS WILL BE ISOLATED AND SHORT LIVED. SHOWER AND THUNDERSTORM ACTIVITY WILL THEN DIMINISH THROUGH THE NIGHT WITH THE LOSS OF HEATING. BY WEDNESDAY MORNING...WILL HAVE A WEAK BOUNDARY SITUATED ACROSS OUR AREA...WHICH WILL EXHIBIT LITTLE MORE THAN A SHIFT IN WIND DIRECTION FROM ONE SIDE TO THE OTHER AS THE TRULY COOLER AND DRIER AIR WILL REMAIN WELL NORTH OF OUR AREA. REGARDLESS...THE LOW LEVEL CONVERGENCE ALONG THE BOUNDARY WILL BE ENOUGH TO TRIGGER ANOTHER ROUND OF SPOTTY SHOWERS AND THUNDERSTORMS DURING THE AFTERNOON AND EVENING. BETTER CHANCES FOR RAINFALL WILL BE FOUND SOUTH OF HIGHWAY 460. TEMPERATURES HEADING INTO THE MIDDLE OF THE WEEK WILL BE WARMER THAN NORMAL THANKS TO UPPER LEVEL RIDGING ACROSS THE SOUTHEAST STATES. LOOK FOR HIGHS TO RANGE FROM THE LOW/MID 80S ACROSS THE MOUNTAINS... TO THE LOW/MID 90S ACROSS THE SOUTHSIDE. OVERNIGHT LOWS WILL RANGE FROM THE MID 60S WEST TO THE LOW 70S EAST. && .LONG TERM /THURSDAY THROUGH SUNDAY/... AS OF 345 PM SUNDAY... A WEAK BOUNDARY WILL REMAIN SITUATED ACROSS THE AREA ON THURSDAY... PROVIDING THE LOW LEVEL FOCUS FOR SHOWERS AND THUNDERSTORMS... MAINLY SOUTH OF HIGHWAY 460. ACTIVITY IS EXPECTED TO REMAIN WIDELY SCATTERED DUE TO THE UPPER LEVEL RIDGE ACROSS THE SOUTHEAST STATES BUILDING NORTH...HELPING TO LIMIT INSTABILITY. HIGH PRESSURE WILL PASS ACROSS NEW ENGLAND...ALLOWING WINDS TO SHIFT EASTERLY THROUGH THE DAY...AND THEN SOUTHEASTERLY DURING THE EVENING. AN APPROACHING UPPER LEVEL TROUGH AND ASSOCIATED COLD FRONT WILL TRIGGER SCATTERED SHOWERS AND THUNDERSTORMS ACROSS THE REGION ON FRIDAY AND SATURDAY. THE COLD FRONT WILL MOVE ACROSS OUR AREA SATURDAY NIGHT...USHERING IN COOLER AND DRIER CANADIAN HIGH PRESSURE. TROPICAL AIR WILL REMAIN ACROSS THE AREA THROUGH THE END OF THE WEEK. AS SUCH...EXPECT WARM AND MUGGY CONDITIONS...WITH TEMPERATURES HOLDING SLIGHTLY ABOVE NORMAL. COOLER TEMPERATURES WILL ARRIVE WITH THE COLD FRONT AT THE END OF THE WEEK. && .AVIATION /06Z MONDAY THROUGH FRIDAY/... AS OF 725 PM EDT SUNDAY... TOOK SHOWERS OUT OF THE LWB TAF THIS EVENING. STILL CANNOT RULE OUT A SHOWER INVOF BLF/LWB OVERNIGHT BUT THE CHANCES ARE LIMITED. OTHERWISE...OVERNIGHT THE OVERALL THREAT OF SHOWERS WILL FADE WITH A SCT/BKN MID DECK LINGERING. FOG CHANCES ARE GOOD BUT THE MID DECK SHOULD LIMIT HOW FAR DOWN VSBYS DROP. WILL KEEP MOST TAF SITES NO WORSE THAN MVFR OVERNIGHT WITH LWB DROPPING OCCASIONALLY TO IFR AFTER 10Z. LAST MID LEVEL WAVE WILL PASS TO THE NW BY EARLY MONDAY LEAVING THE AREA IN BETWEEN THIS FEATURE AND THE NEXT UPSTREAM COLD FRONT. DEEP WESTERLY FLOW COMBINED WITH LACK OF FOCUS AND DECENT MIXING SHOULD INHIBIT MUCH CONVECTION DURING MONDAY ESPCLY IF EARLY MID DECK PERSISTS. THIS SUPPORTS GOOD FLYING CONDITIONS FOR MUCH OF MONDAY AFTER EARLY LOW CLOUDS/FOG FADE WITH ONLY ISOLATED CONVECTION LIKELY. EXTENDED DISCUSSION... UPPER TROUGH AND ITS ASSOCIATED COLD FRONT WILL APPROACH FROM THE NORTHWEST TUESDAY WITH SIMILAR ISOLATED SHOWERS/STORMS EXPECTED DURING THE DAY AHEAD OF THE BOUNDARY. FRONT SETTLES CLOSER TUESDAY NIGHT INTO WEDNESDAY...WHEN BETTER COVERAGE OF SHRA/TSRA IS EXPECTED...AND THEN ACROSS THE SOUTH THURSDAY WHERE THE BOUNDARY STALLS. HOWEVER LOW CONFIDENCE ON THE TIMING AND SOUTHWARD POSITION OF THE BOUNDARY AT THIS POINT. THUS APPEARS MAINLY VFR ON TUESDAY...WITH PERIODS OF MVFR WEDNESDAY-THURSDAY IN MORE ORGANIZED MAINLY AFTERNOON/EVENING CONVECTION...AND MVFR/IFR UNDER EARLY MORNING FOG IN THE VALLEYS AND WHERE EARLIER HEAVY RAIN OCCURRED. FRONT WASHES OUT TO THE SOUTH OF THE AREA FRIDAY WITH MORE DIURNAL NATURE SHOWERS AND STORMS...OTRW VFR. && .EQUIPMENT... AS OF 730 AM EDT FRIDAY ... THE VISIBILITY SENSOR AT KDAN...DANVILLE REGIONAL AIRPORT...WILL BE OUT OF SERVICE UNTIL FURTHER NOTICE. A PART HAS BEEN BACK-ORDERED. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...AMS/JH NEAR TERM...JH/KK/WP SHORT TERM...NF LONG TERM...NF AVIATION...AMS/JH/WP EQUIPMENT...AMS

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