Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 252340 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 740 PM EDT WED MAR 25 2015 .SYNOPSIS... LOW PRESSURE WAS OVER LAKE MICHIGAN WITH A TRAILING WARM FRONT EXTENDING SOUTH INTO THE APPALACHIAN MOUNTAINS. THIS LOW CENTER AND FRONT WILL MOVE NORTHEAST THIS EVENING INTO TONIGHT. A SECOND LOW CENTER WILL TRACK FROM THE PLAINS INTO THE NORTHEAST UNITED STATES...WHICH WILL BRING A STRONG COLD FRONT THROUGH THE REGION LATE ON THURSDAY. MUCH COLDER AIR WILL BE MOVING IN BEHIND THE COLD FRONT AND WILL RESULT IN SOME WINTRY PRECIPITATION RETURN TO AREAS WEST OF THE BLUE RIDGE. && .NEAR TERM /THROUGH THURSDAY NIGHT/... AS OF 720 PM EDT WEDNESDAY... ADJUSTED SKY GRIDS FOR LATE AFTERNOON CLEARING...BUT WILL FILL BACK IN THIS EVENING...ESPECIALLY ALONG AND EAST OF THE BLUE RIDGE. LOWERED POPS THROUGH LATE AFTERNOON...THEN INCREASED THROUGH THE EVENING AS MARINE MOISTURE TRACKS OVER THE FORECAST AREA. KEPT LIGHT RAIN...DRIZZLE...AND FOG FOR AREAS ALONG AND EAST OF THE BLUE RIDGE INTO THURSDAY MORNING. AS OF 320 PM EDT WEDNESDAY... 1030MB HIGH PRESSURE TO OUR NORTHEAST WILL CONTINUE TO WEDGE SOUTH DOWN THE EASTERN SIDE OF THE APPALACHIANS THIS AFTERNOON INTO TONIGHT. EASTERLY WINDS WERE PUSHING PLENTY OF MOISTURE INTO OUR REGION. NOT MUCH ORGANIZED LIFT FOR PRECIPITATION...THUS EXPECTING JUST SOME SPOTTY LIGHT RAIN OR SHOWERS...WITH THE WEAK ISENTROPIC UPGLIDE OVER THE CAD. WESTERN AREAS OUTSIDE THE WEDGE...PARTLY CLOUDY CONDITIONS WILL CONTINUE. IN GENERAL...DECREASED POPS TONIGHT AND SHAPED VALUES TOWARDS THE NAM. ADJUSTED CLOUD COVER TOWARDS THE CANADIAN TONIGHT...BUT THIS IS HIGHLY DEPENDENT ON THE WEDGE OR EROSION OF THE WEDGE. AS LOW PRESSURE MOVE NORTHEAST IN THE GREAT LAKES...THE WARM FRONT WILL LIFT NORTH THROUGH THE OHIO VALLEY AND MID ATLANTIC REGION. ADDED SOME DRIZZLE AND FOG TONIGHT ESPECIALLY ALONG THE BLUE RIDGE MOUNTAINS. LOW TEMPERATURES TONIGHT WILL RANGE FROM THE LOWER 40S IN THE NORTHERN MOUNTAINS TO THE LOWER 50S IN THE PIEDMONT. THE TIMING OF COLD FRONT APPEARS SLOWER WITH WAVES OF LOW PRESSURE DEVELOPING ALONG THE BOUNDARY. THE WEDGE SHOULD ERODE THURSDAY...AS SOUTHWEST WINDS BRING WARMER AIR INTO THE REGION AHEAD OF THE COLD FRONT APPROACHING FROM THE WEST. HIGH TEMPERATURES ON THURSDAY WILL VARY FROM THE LOWER 60S IN THE NORTHWEST MOUNTAINS TO THE MID 70S IN THE PIEDMONT. THESE WARM TEMPERATURES WILL HELP DESTABILIZE THE ATMOSPHERE AND ALLOW FOR A CHANCE OF THUNDERSTORMS AHEAD OF THE COLD FRONT THURSDAY AFTERNOON. THE DAY 2 CONVECTIVE OUTLOOK HAS US IN GENERAL THUNDERSTORMS WITH A MARGINAL AREA TO OUR EAST IN THE EASTERN COASTAL REGIONS OF VIRGINIA TO NORTH CAROLINA. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... AS OF 345 PM EDT WEDNESDAY... MODELS CONTINUE TO SLOW DOWN THE ARRIVAL OF THE UPPER TROUGH AND ASSOCIATED COLD FRONT...LARGELY OWING TO UPSTREAM ENERGY LAGGING BACK ACROSS THE NORTHERN PLAINS...YET TO DROP INTO THE BASE OF THE TROUGH LATER INTO FRIDAY. I WILL ADDRESS THAT ISSUE BELOW. OVERALL THE ENTIRE SYSTEM IS NEARLY 12 HOURS SLOWER TO ARRIVE INTO THE CWA THAN INDICATED A COUPLE OF DAYS AGO. THUS...THE FRONT IS JUST ARRIVING THE WESTERN BORDER OF THE CWA NEAR 00Z FRI...NOT REACHING THE EASTERN BORDER UNTIL NEARLY 12Z FRI. THIS WILL DELAY THE LIKELY/CATEGORICAL POPS AS WELL AS THE ARRIVAL OF THE COLD AIR. THE MAIN CONCERN WITH THE FRONT ITSELF WILL BE THE THREAT OF THUNDER AND ANYTHING SEVERE. SEVERE PROBABILITIES REMAIN LACK LUSTER AND THE BEST DYNAMICS REMAIN WELL REMOVED TO THE NORTH OF THE CWA AND OUT OF PHASE WITH THE BETTER THERMODYNAMICS. CAPES ARE PROGGED GENERALLY 500 OR LESS AND ALL APPRECIABLE SHEAR/LLJ ENERGY HAS TRACKED NORTH OF THE REGION BY THE TIME THE FRONTAL FORCING ARRIVES. FURTHERMORE...THE DELAY OF THE FRONT INTO THE EASTERN AREAS/PIEDMONT INTO THE COOLER EVENING HOURS WILL FURTHER REDUCE THE THREAT FOR STRONG THUNDERSTORMS. SPC HAS ONLY OUTLOOKED THE FAR EASTERN SHORE AT THIS TIME FOR ANY SEVERE THREAT. WILL CONTINUE TO MENTION SLIGHT CHC TSRA...BUT AM NOT IMPRESSED WITH THE THREAT OVERALL. MOST NOTABLE WITH THIS EVENT...WILL BE THE SHARP RETURN TO MUCH COLDER TEMPERATURES AS 850MB TEMPS PLUMMET FROM +12C AT 00Z FRI TO AS LOW AS -6C IN THE NORTHWEST AT 12Z FRI...THEN FINALLY BOTTOMING OUT AROUND -14C NORTHWEST TO -10C FAR SOUTHEAST CORNER BY 12Z SAT. THE DEGREE OF COLDNESS REALIZED AT THE SFC WILL BE LESS THAN A MONTH AGO BECAUSE OF THE HIGHER SUN ANGLE...BUT THE MUCH COLDER TEMPERATURES COMBINED WITH WIND WILL BE IN SHARP CONTRAST TO THE 60S AND 70S EXPECTED THURSDAY. LINGER POST FRONTAL PRECIPITATION...ENHANCED BY A DEVELOPING WAVE ACROSS SC/NC THU NIGHT...WILL ALLOW PRECIPITATION TO LINGER LONG ENOUGH IN THE COLD AIR TO SUPPORT RAIN SHOWERS CHANGING TO SNOW SHOWERS IN THE WESTERN MOUNTAINS WITH SOME ACCUMULATION POSSIBLE BY DAYBREAK FRIDAY. OF MORE INTEREST THROUGH THIS TIME FRAME IS THE AFOREMENTIONED DISTURBANCE ROTATING THROUGH THE BASE OF THE SHARP UPPER TROUGH AND ASSOCIATED WITH THE UPPER TROUGH AXIS MOVING OVER THE REGION FRI AFTERNOON. THIS IS A STRONG/DYNAMIC FEATURE WITH STRONG PVA. MOISTURE WILL BE LIMITED...BUT WITH STRONG CAA IN PLACE COMBINED WITH THE DISTURBANCE...A BONAFIDE AREA OF -SHSN/-SHRA APPEARS LIKELY IN ASSOCIATION WITH THIS FEATURE. THE DIFFICULTY OVER THE PAST FEW DAYS OF MODEL RUNS HAS BEEN PINPOINTING THE EXACT TRACK OF THIS SYSTEM. FORTUNATELY...ALL OF THE MODELS ARE ON BOARD WITH THIS FEATURE TODAY...WHILE THE GFS HAS BEEN DEPICTING THIS FOR SEVERAL DAYS. THE TRACK REMAINS SOMEWHAT QUESTIONABLE...THE EAST TN/SW VA/NW NC/SOUTHERN WV AREA SEEMS TO BE THE TARGET. ONCE AGAIN...AS A RESULT...HAVE DEPICTED AN AREA OF ENHANCED POPS/-SHSN/-SHRA FRI AFTERNOON/EVENING AS THIS FEATURE ROTATES THROUGH THE REGION...EVEN INTO THE PIEDMONT. SOME SNOW ACCUMULATIONS ARE POSSIBLE AS A RESULT...BUT WILL LIKELY BE CONFINED TO GRASSY AREAS AS THE ROAD SURFACES WILL BE TOO WARM. THE EXCEPTION WILL BE CONTINUED UPSLOPE AREAS ACROSS SE WV...WHERE A COUPLE OF INCHES OF SNOW ACCUMULATION WILL BE POSSIBLE BY SAT MORNING. USED A MODEL BLEND FOR TEMPERATURES THROUGH THE PERIOD AS THEY ALL LOOKED REASONABLE. MOST IMPORTANT...A HARD FREEZE IS EXPECTED IN ALL AREAS SAT AND SUN MORNING...WITH WIND CHILLS NEAR -5C ALSO POSSIBLE EARLY SAT IN THE WEST. EXPECT LOWS IN THE TEENS WEST TO MID 20S EAST BY SAT/SUN MORNING WITH HIGHS ONLY IN THE 30S AND 40S SATURDAY...STRUGGLING TO RISE ABOVE FREEZING ACROSS THE MOUNTAINS. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... AS OF 400 PM EDT WEDNESDAY... THE ARCTIC/CANADIAN HIGH WILL SETTLE OVER THE REGION LATE SAT- EARLY SUN...BRINGING THE COLDEST TEMPERATURES TO THE REGION OVERALL THAT WE HAVE SEEN IN OVER TWO WEEKS. NORTHWEST FLOW PREVAILS THROUGH MONDAY WITH AN ALBERTA PROGGED TO TRACK ACROSS THE REGION SUN-MON. THE GFS IS FASTER AND STRONGER WITH THIS SYSTEM THAN THE ECMWF...BUT GIVEN THE PATTERN IN PLACE AT THAT POINT...THE GFS FORECAST SEEMS MORE REASONABLE. POPS ARE QUESTIONABLE WITH THIS SYSTEM...SO HAVE JUST INDICATED LOW CHC POPS IN THE WEST FOR NOW UNTIL BETTER CONSENSUS IS OBTAINED FROM THE MODELS ON THIS SYSTEM. BEYOND THAT...THE UPPER FLOW BECOMES MORE ZONAL AND THE FOCUS WILL BE ON A HIGHLY KINEMATIC...PACIFIC BASED SYSTEM IN THE SOUTHERN STREAM EXPECTED TO REACH THE CWA AT THE END OF THE FORECAST PERIOD. THIS COULD BE A SEVERE WEATHER SYSTEM FOR THE SOUTHERN PLAINS TO THE SOUTHEAST STATES...BUT MORE QUESTIONABLE FOR OUR AREA. YIELDED TOWARD THE SUPERBLEND FOR POPS IN THE LAST TWO PERIODS TO BETTER AGREE WITH NEIGHBORS. HOWEVER...TIMING OF THE ARRIVAL OF WARM ADVECTION PRECIPITATION ASSOCIATED WITH THIS SYSTEM REMAINS HIGHLY QUESTIONABLE AT THIS POINT. THE ZONAL FLOW WILL YIELD TO NEAR NORMAL TEMPERATURES THROUGH THE PERIOD. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... AS OF 735 PM EDT WEDNESDAY... && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...KK NEAR TERM...KK/RCS SHORT TERM...RAB LONG TERM...RAB AVIATION...KK/RCS

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