Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 270546 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 146 AM EDT MON APR 27 2015 .SYNOPSIS... COOL AND UNSETTLED WEATHER WILL BE IN PLACE ACROSS THE APPALACHIANS AND CENTRAL MID ATLANTIC REGION THIS WEEK... AS A COOL UPPER LOW REMAINS ANCHORED OVER THE NORTHEAST UNITED STATES. THE BEST CHANCE FOR PRECIPITATION WILL BE WEDNESDAY AND THURSDAY...AS LOW PRESSURE DEVELOPS OVER THE SOUTHEAST AND TRACKS JUST TO OUR SOUTH AND EAST...BEFORE MOVING OFF THE MIDDLE ATLANTIC COAST THURSDAY NIGHT. && .NEAR TERM /THROUGH TODAY/... AS OF 1245 AM EDT MONDAY... MINOR CHANGES TO TEMPS/SKY/WX INTO EARLY MORNING BASED ON TRENDS. MAINLY SEEING MID DECK IN THE SRN CWA AND EXPECT THE CLEARING TREND TO CONTINUE INTO MORNING. FOG IN THE RIVER VALLEYS OF WEST AND/OR PATCHY FROST TO OCCUR THRU DAWN. AS OF 330 PM EDT SUNDAY... THE WEDGE IS SLOWLY ERODING FROM THE NORTH AS LOW PRESSURE IS PULLING AWAY AND ALLOWING DRIER AIR TO WORK IN. VISIBLE SATELLITE IMAGES SHOW THE CLEARING AND OTHER BREAKS IN THE CLOUDS AND THIS IS ALLOWING THE SUN TO GIVE TEMPS A BIT OF A LATE DAY BOOST. THE CLEARING TREND IS EXPECTED TO SLOWLY CONTINUE THROUGH EARLY TONIGHT AND THIS WILL ALLOW FOR SOME CHILLY TEMPERATURES OVERNIGHT. THERE MAY BE SOME PATCHY FROST WEST OF THE BLUE RIDGE AND IN SOME LOW SPOTS ACROSS THE PIEDMONT BUT DO NOT BELIEVE CONDITIONS WILL BE WIDESPREAD ENOUGH FOR AN ADVISORY SO WILL HIGHLIGHT THIS IN AN SPS FOR AREAS WEST OF THE BLUE RIDGE. WE SHOULD BE IN FOR A BIT OF EARLY MORNING SUN TO START OFF ON MONDAY...BUT WITH A POOL OF COLD AIR ALOFT AND A VIGOROUS SHORT WAVE ROTATING AROUND THE UPPER LOW OVER THE NORTHEAST US...EXPECT CLOUDS TO BLOOM BY LATE MORNING AND A CHANCE/SLGT CHC OF SHOWERS WEST OF THE BLUE RIDGE BY THE AFTERNOON. ISOLATED THUNDER AND SOME GRAUPEL IS NOT OUT OF THE QUESTION FROM THE GREENBRIER VALLEY THROUGH THE ALLEGHANY HIGHLANDS. TEMPS TOMORROW WILL CONTINUE TO RUN BELOW NORMAL WITH HIGHS GENERALLY MIDDLE 50S WEST OF THE RIDGE TO MIDDLE 60S EAST. THE BOUNDARY LAYER WILL ALSO BE WELL MIXED SO EXPECT A GOOD NORTHWEST BREEZE TO ADD TO THE CHILL. && .SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/... AS OF 330 PM EDT SUNDAY... TWO SYSTEMS WILL BE THE PRIMARY PLAYERS IN OUR WEATHER FOR THE FIRST HALF OF THE WORK WEEK. THE FIRST IS A LARGE UPPER LOW OFF THE NEW ENGLAND COAST...AND THE SECOND IS A SOUTHERN STREAM SYSTEM THAT MOVES THROUGH THE SOUTHERN PLAINS INTO TENNESSEE VALLEY BY WEDNESDAY. WITH REGARD TO THE SECOND SYSTEM...MODEL ENSEMBLES SHOW THERE IS LOW CONFIDENCE ON THE TIMING AND STRENGTH OF THIS SYSTEM. THE 12Z GFS IS STRONGEST AND SLOWER...WHILE THE NAM APPEARS TO BE AN OUTLIER WITH ITS FASTER SOLUTION. GENERALLY FOLLOWED THE 00Z ECMWF WITH THIS SYSTEM...WHICH HAS SHOWN GOOD CONSISTENCY KEEPING THE SYSTEM CLOSED THROUGH 00Z THURSDAY. A SHORTWAVE PIVOTING AROUND THE LARGE NEW ENGLAND UPPER LOW EXITS OUR AREA TO THE SOUTH BEFORE 12Z TUESDAY. LINGERING CONVECTIVE SHOWERS UNDER THIS SYSTEM MONDAY EVENING SHOULD DIMINISH WITH THE LOSS OF HEATING. MEANWHILE...AT THE SURFACE...HIGH PRESSURE BEGINS TO NOSE INTO WESTERN PORTION OF THE FORECAST AREA EARLY TUESDAY. IF WINDS CAN SUBSIDE ENOUGH...TEMPS IN SOME OF THE HIGHER ELEVATIONS IN SE WV MAY ALLOW FOR PATCHY FROST TO FORM. TUESDAY APPEARS TO BE THE MOST TRANQUIL DAY OF THIS PERIOD...AS A WEAK SHORTWAVE RIDGE BUILDS IN ADVANCE OF THE SOUTHERN STREAM SYSTEM AND A BLEND OF THE BIAS CORRECTED MET/NAM MOS WAS USED FOR HIGHS. WE START TO EXPERIENCE THE EFFECTS OF THE SOUTHERN STREAM SYSTEM TUESDAY NIGHT AND WEDNESDAY AS CLOUDS TUESDAY NIGHT AND LIGHT RAIN ARRIVES AS EARLY AS WEDNESDAY MORNING IN THE NW NC MOUNTAINS. WE COULD POTENTIALLY SEE A BIG DROP OFF IN TEMPS IN THE NORTHERN PORTION OF OUR FORECAST AREA EARLY BEFORE CLOUDS ARRIVE LATE TUESDAY NIGHT. WITH DEW POINTS IN THE 40S...IT MAY TAKE SOME TIME FOR THE ATMOSPHERE TO SATURATE TO ALLOW RAIN TO REACH THE GROUND. WEAK UPSLOPE FLOW SHOULD HELP FOCUS THE LIGHT PRECIP FROM THE SOUTHERN BLUE RIDGE INT THE NW NC MOUNTAINS AND FOOTHILLS WEDNESDAY. KEPT HIGH TEMPS BELOW GUIDANCE WITH EXPECTED WIDESPREAD CLOUDINESS. && .LONG TERM /THURSDAY THROUGH SUNDAY/... AS OF 330 PM EDT SUNDAY... WHILE THERE ARE STILL DIFFERENCES IN TIMING...THE LONG RANGE MODELS SHOW A SIMILAR SOLUTION OF LIFTING THE DEEP EASTERN U.S. TROF TO THE EAST AND SLOWLY BUILDING AN UPPER RIDGE ACROSS THE OHIO VALLEY BY THE END OF THE WEEKEND. THE GFS APPEARS OVERDONE AND TOO FAR NORTH WITH ITS PLACEMENT OF THE AXIS OF HEAVY RAIN IN OUR FORECAST AREA. OBVIOUSLY THIS WILL NEED TO BE MONITORED...BUT LEANED TOWARD THE ECMWF AND CANADIAN SOLUTIONS OF KEEPING THE AXIS OF HEAVIEST RAIN CLOSER TO THE FORECAST POSITION OF THE SFC LOW IN THE SOUTHERN CAROLINAS. WRAP AROUND MOISTURE WILL KEEP CLOUDS...MUCH COOLER THAN NORMAL TEMPS...AND LIGHT PRECIP THROUGH THURSDAY AND THURSDAY NIGHT. WITH THE DEEPENING COASTAL SFC LOW...AND PASSING OF A WEAK UPPER VORT LOBE ON THE WEST SIDE OF THE UPPER TROF AXIS...BUMPED UP WINDS LATE THURSDAY AND FRIDAY...BUT NOTHING THAT APPEARS TO WARRANT HEADLINES ATTM. AS THE DEEP SFC LOW CONTINUES TO MOVE NORTHEAST...WE SHOULD FINALLY SEE SOME CLEARING FRIDAY...THEN TEMPS CLOSER TO AVERAGE FOR EARLY MAY BY THE WEEKEND. && .AVIATION /06Z MONDAY THROUGH FRIDAY/... AS OF 125 AM EDT MONDAY... HIGH PRESSURE ENTERING FROM THE NORTH SENDING DRIER AIR SOUTH INTO THE REGION. SHOULD SEE ANY MID CLOUDS IN THE DANVILLE VICINITY CLEAR OUT THIS MORNING. ISSUE WILL BE ANY FOG OVER THE RIVER VALLEYS...WITH WET GROUND. BUT THE DRIER AIR WILL WORK TO RACE THE TEMPS SUCH THAT DEWPOINT DEPRESSION WILL STAY ENOUGH TO PREVENT DENSE FOG AT LEAST AT TAF SITES. WILL HAVE MVFR AT LYH/DAN/LWB AND BCB AT TIMES EARLY...TEMPO OVER BCB/LWB FOR IFR. CONFIDENCE IS MEDIUM OF THIS OCCURRING. ANY FOG WILL BE GONE AFTER 12Z WITH NW WINDS PICKING UP A BIT. SOME GUSTS TO 25 KTS POSSIBLE AT ROA/BCB. NW FLOW AND EMBEDDED SHORTWAVE WILL BRING CLOUDS INTO THE MTNS BY MIDDAY/EARLY AFTERNOON. CANNOT RULE OUT A SHOWER OVER BLF/LWB BUT COVERAGE IS LOW TO KEEP OUT OF TAFS. KEPT THINGS VFR THROUGH THE DAY INTO THIS EVENING. WINDS WEAKEN TONIGHT THOUGH THE HIGHER TERRAIN COULD SEE SOME GUSTS OVER 15 KTS. EXTENDED AVIATION DISCUSSION... VFR CONDITIONS ARE EXPECTED THROUGH EARLY WEDNESDAY BEFORE CONDITIONS WORSEN ONCE AGAIN WEDNESDAY AFTERNOON INTO THURSDAY...AS A LOW PRESSURE SYSTEM PASSES ACROSS THE SOUTHEAST STATES. CONFIDENCE IS GROWING THAT THIS SYSTEM WILL RESULT IN RAIN INTO MOST OF THE FORECAST ALONG WITH SUB VFR CIGS/VSBYS. SO MUCH DISCREPANCIES IN THE MODELS ATTM FOR FRIDAY THAT WX COULD BE CLEARING OUT ECMWF OR SUB VFR WITH SFC LOW SITUATED OVER THE MID ATLANTIC COAST. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...MBS NEAR TERM...CF/MBS/WP SHORT TERM...PH LONG TERM...PH/RAB AVIATION...MBS/RCS/WP

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