Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 281150 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 750 AM EDT SUN SEP 28 2014 .SYNOPSIS... HIGH PRESSURE CENTERED OVER OR REGION WILL SLOWLY MOVE EAST TODAY INTO TONIGHT. LOW PRESSURE DEVELOPING ALONG THE CENTRAL GULF COAST WILL MOVE NORTHEAST TONIGHT INTO MONDAY...BRINGING WIDESPREAD CLOUD COVER TO THE REGION FOR THE FIRST HALF OF NEXT WEEK ALONG WITH THE POTENTIAL FOR RAIN. && .NEAR TERM /THROUGH TONIGHT/... AS OF 325 AM EDT SUNDAY... A RIDGE AT THE SURFACE AND ALOFT WILL WEAKEN AND SLIDE EAST WITH THE MID-UPPER LEVEL FLOW BECOMING SOUTHWEST. THIS FLOW ALOFT WILL ADVECT MOISTURE NORTHWARD FROM A DEVELOPING GULF LOW PRESSURE. PATCHES OF MORNING LOW CLOUDS AND FOG WILL LIFT BY LATE MORNING. OTHERWISE... THIS MORNING WILL START OUT MOSTLY SUNNY...THEN TREND TOWARD INCREASING HIGH CLOUDS AS THE AFTERNOON WEARS ON. LEANED HIGH TEMPERATURES THIS AFTERNOON CLOSE TO THE ADJMAV WITH READINGS FROM THE LOWER 70S IN THE MOUNTAINS TO AROUND 80 DEGREES IN THE PIEDMONT. DEEPER MOISTURE THAT HAS BEEN SUPPRESSED TO OUR SOUTHWEST BY THE HIGH PRESSURE CENTER WILL BEGIN TO MOVE BACK NORTH TONIGHT. TRIMMED BACK POPS TONIGHT THROUGH 06Z...THEN INCREASED POPS AFTERWARDS AND SPREAD RAIN NORTHWARD MONDAY MORNING. THE CHALLENGE REMAINS ON THE HOW FAR NORTH DOES THE RICHEST MOISTURE TRAVEL AND THE EXACT TRACK OF SLOW MOVING SHORTWAVE BEING EJECTED OUT OF A GULF DISTURBANCE. THE TRACK OF THIS SHORTWAVE AND WARM MOIST AIR OVERRUNNING INSITU WEDGE WILL DETERMINE RAIN AMOUNTS DURING THIS EVENT. OVERNIGHT LOW TEMPERATURES WILL VARY FROM THE LOWER 50S IN THE MOUNTAINS TO THE LOWER 60S IN THE PIEDMONT. && .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/... AS OF 415 AM EDT SUNDAY... MODEL RUN-TO-RUN CONSISTENCY REGARDING THE TRACK OF THE LOW PRESSURE AREA ALONG THE CENTRAL GULF COAST...THE ASSOCIATED MOISTURE...AND ITS TRACK REMAIN PROBLEMATIC. ALL MODELS HAVE TRENDED FURTHER SOUTH WITH THE MAIN SHIELD OF PCPN AND HEAVIER RAINFALL. THE GFS HAS MADE THE MOST DRAMATIC SHIFT SOUTH WITH THE MOISTURE AND QPF...WHILE THE CANADIAN REMAINS VERY DRY...FOCUSING NEARLY ALL OF THE QPF/PCPN ACROSS THE SOUTHEAST STATES. THE ECMWF/NAM HAS ALSO TRENDED DRIER...BUT REMAIN THE FURTHEST NORTH AND WETTEST. WPC LEARNING TOWARD THE ECMWF...SO THIS FORECAST DID AS WELL. THIS WILL RESULT IN LIKELY TO CATEGORICAL POPS SPREADING INTO THE NC MOUNTAINS/PIEDMONT...TAPERING TO SLIGHT CHC POPS ACROSS THE FAR NORTHERN COUNTIES. THE BEST TIME FRAME FOR RAIN REMAINS IN THE 12Z MON TO 18Z MON TIME FRAME...SHIFTING TO THE SOUTHEAST COUNTIES IN THE 18Z MON TO 00Z TUE TIME FRAME. STORMTOTAL QPF HAS BEEN REDUCED SIGNIFICANTLY FROM EARLIER ADVERTISED...FOR EXAMPLE FROM AROUND 2 INCHES IN THE NW NC MOUNTAINS/FOOTHILLS TO AROUND 3/4 INCH. THIS IS IN LINE WITH WPC LATEST 1-3 DAY QPF WHICH HAS ALSO SHOWN A REDUCTION ON THE ORDER OF MAGNITUDE ACROSS THE SOUTHEAST STATES FROM 4 INCHES TO LESS THAN 1 INCH ACROSS NORTHERN GA THROUGH WESTERN SC/NC. OUR CURRENT AMOUNTS STILL SLIGHTLY HIGHER THAN WPC IN NW NC AND FAR SW VA. WE MAY ONLY SEE VERY LIGHT -RA OR -DZ ACROSS OUR NORTHERN COUNTIES WITH THIS EVENT. TEMPERATURES MON WILL REMAIN COOL TO MILD UNDER THE CLOUDS AND RAIN...WITH A REVERSE GRADIENT FROM NORMAL...NAMELY COOLEST IN THE PIEDMONT TO WARMEST ACROSS GREENBRIER/BATH COUNTY REGION. FOR TUE-WED...GULF COASTAL SYSTEM EXITS OFF THE SC/NC COAST...TAKING LARGELY AN ENE RATHER THAN A NE TRACK. DRIER AIR WILL WORK ITS WAY INTO THE REGION FROM THE NORTHWEST. THIS PERIOD INITIALLY APPEARS DRIER THAN THOUGHT YESTERDAY WITH CONSIDERABLY LESS WEDGE POTENTIAL THROUGH EARLY WED THAN PREVIOUSLY THOUGHT. HOWEVER...LEANING TOWARD THE ECMWF SOLUTION...A WEAK SHORT WAVE TRACKS AROUND AN UPPER RIDGE LOCATED OVER THE GREAT LAKES AND SINKS DOWN INTO THE DELMARVA REGION WED. THE ECMWF IS DEPICTING LIGHT QPF WITH THIS FEATURE AND A SUBSEQUENT WEDGE DEVELOPMENT...OF WHICH THE GFS IS ALSO ON BOARD. HAVE INTRODUCED SOME VERY LOW/SLIGHT CHC POPS ACROSS THE PIEDMONT/NORTHERN COUNTIES IN ASSOCIATION WITH A POTENTIAL BACKDOOR COLD FRONT AND THE UPPER TROUGH...AND THEN INTRODUCED -DZ FROM UPSLOPE ALONG THE BLUE RIDGE AND TOWARD THE ALLEGHANY FRONT MOVING TOWARD THE BEGINNING OF THE LONG TERM WITH A WELL ESTABLISHED EAST FLOW AT THIS POINT. TEMPERATURES TUE-WED SHOULD REMAIN NEAR SEASONAL NORMALS WITH NO SIGNIFICANT CHANGE IN AIR MASS INDICATED THROUGH THE PERIOD...YET ABUNDANT CLOUD COVER TO TEMPER THE OTHERWISE RATHER WARM 850MB TEMPS HOVERING AROUND +15 TO +16C. && .LONG TERM /THURSDAY THROUGH SATURDAY/... AS OF 430 AM EDT SUNDAY... AS NOTED ABOVE...A WEDGE AIR MASS WILL BE IN PLACE ONCE AGAIN BY EARLY THU WITH ABUNDANT CLOUDS AND PATCHY -DZ EXPECTED...ESPECIALLY THROUGH UPSLOPE AREAS OF THE BLUE RIDGE AND ALLEGHANYS INTO FAR SW VA. THIS PATTERN WILL REMAIN IN PLACE UNTIL FRI WHEN A STRONG COLD FRONT APPROACHES THE REGION FROM THE WEST. A RATHER DEEP ASSOCIATED UPPER TROUGH PROMISES TO BRING SOME OF THE COLDEST AIR OF THE SEASON TO THE REGION IN ITS WAKE. A NARROW LINE OF SHOWERS AND A FEW THUNDERSTORMS WILL ACCOMPANY THE FRONT AS IT MOVES THROUGH THE REGION FRI AFTERNOON/EVENING. INSTABILITY IS MARGINAL BUT SHEAR IS QUITE DECENT. IF THE WEDGE CAN BE ERODED QUICKLY ENOUGH...FRI COULD END UP BEING THE WARMEST DAY OF THE WEEK WITH STRENGTHENING SOUTHWEST FLOW AND WARM ANTECEDENT 850MB TEMPS. MUCH COLDER TEMPERATURES AND A PATTERN MORE TYPICAL OF WINTER WILL FOLLOW IN ITS WAKE FOR THE WEEKEND. HOWEVER...MODEL CONSISTENCY ON HOW FAR SOUTH THE 0C 850MB ISOTHERM WILL REACH HAS BEEN POOR...SO NOT CONVINCED JUST YET THAT THIS WILL BE COLD ENOUGH TO PRODUCE A FROST OR FREEZE BY SUN. TEMPERATURES WEDNESDAY SHOULD BE WARMER THAN EARLIER EXPECTED GIVEN THE LACK OF A WEDGE AIR MASS AT THAT POINT. HOWEVER...THU SHOULD PROVIDE THE REGION WITH NEAR TO SLIGHTLY BELOW NORMAL TEMPERATURES AS THE WEDGE DEVELOPS AND STRENGTHENS. AS NOTED ABOVE...FRI HAS THE POTENTIAL TO BE A WARM DAY...NEARING 80 ACROSS THE PIEDMONT...BUT HIGHS WILL DROP BACK INTO THE 60S PIEDMONT AND 50S MOUNTAINS OVER THE WEEKEND BEHIND THE STRONG COLD FRONT...POTENTIALLY EVEN COOLER. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... AS OF 740 AM EDT SUNDAY... VFR CONDITIONS EXPECTED THROUGH MUCH OF THE TAF VALID PERIOD UNTIL DEEPER MOISTURE SPREADS NORTHEAST FROM THE DEVELOPING LOW PRESSURE AREA ALONG THE GULF COAST. THROUGH ROUGHLY 06Z TONIGHT...EXPECT VFR CIGS WITH JUST BKN-OVC250 THROUGH MUCH OF THE REGION. A FEW SC/CU MAY DEVELOP DURING THE DAYTIME...BUT SPARSE BL MOISTURE SHOULD LIMIT THE EXTENT OF THIS. PATCHY DENSE FOG AT MANY SITES THIS MORNING...BUT MOST NOTABLY LWB AND BCB. AS WAS THE CASE YESTERDAY...THIS SHOULD BURN OFF QUICKLY AS DRIER/WARMER AIR QUICKLY MIXES DOWN FROM ALOFT. THUS...ANY LIFR-IFR CIGS/VSBYS IN BR/FG SHOULD IMPROVE QUICKLY TO VFR BY 14Z IF NOT SOONER. DO NOT EXPECT A REPEAT OF RADIATIONAL FOG MON MORNING BECAUSE OF DENSE MID/HIGH CLOUDS AT A MINIMUM. OVERNIGHT...CLOUDS WILL LOWER BUT SHOULD REMAIN VFR MOST OF THE NIGHT. IN THE 08Z-12Z TIME FRAME...SOME MVFR CIGS MAY DEVELOP FROM BLF-BCB SOUTHWESTWARD AS MOISTURE SPREADS NORTHEAST. THE MODELS HAVE TRENDED DRIER WITH THE GULF COAST SYSTEM TAKING A MORE EASTWARD TRACK AS OPPOSED TO NORTHEAST. THUS...-RA SHOULD BE SLOW TO SPREAD INTO THE REGION AND MAY NOT REACH ANY OF THE TAF SITES PRIOR TO 12Z. FOR NOW...HAVE ONLY INCLUDED -RA AT ROA AND -DZ AT BLF/BCB. WINDS WILL BE CHAOTIC AND LIGHT AS WEAK HIGH PRESSURE DRIFTS THROUGH THE REGION TODAY. THROUGH THE TAF VALID PERIOD...WIND SPEEDS SHOULD REMAIN LESS THAN 7KTS. HIGH CONFIDENCE IN CIGS THROUGH 08Z MON...THEN MEDIUM CONFIDENCE. MEDIUM TO HIGH CONFIDENCE IN VSBYS THROUGH THE TAF VALID PERIOD. MEDIUM TO HIGH CONFIDENCE IN WIND SPD...LOW CONFIDENCE IN WIND DIR THROUGH THE TAF VALID PERIOD. EXTENDED AVIATION DISCUSSION... WIDESPREAD SUB-VFR CONDITIONS WILL SPREAD ACROSS THE REGION MONDAY AS THE UPPER DISTURBANCE TRACKS NORTHEAST FROM THE GULF AND ACROSS THE SOUTHEAST STATES. MVFR-IFR CIGS CAN BE EXPECTED ACROSS MUCH OF THE REGION MON. SOME IMPROVEMENT CAN BE EXPECTED TUE- WED...BUT THERE IS ALSO GOOD POTENTIAL FOR LOW LEVEL EASTERLY WIND FLOW TO PERSIST OFF OF THE ATLANTIC OCEAN IN THE WAKE OF THE EARLY WEEK SYSTEM...PROMOTING CONTINUATION OF LOW CIGS/VSBYS IN STRATUS...FOG...AND DRIZZLE THROUGH THE LATER HALF OF THE WEEK. A STRONG COLD FRONT IS PROGGED TO MOVE THROUGH THE REGION LATE IN THE WEEK WITH A GOOD CHANCE OF SHOWERS AND COOLER WEATHER...BUT UNTIL THAT TAKES PLACE...WE MAY BE LOOKING AT AN EXTENDED PERIOD OF FAIRLY POOR AVIATION CONDITIONS NEXT WEEK. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...KK NEAR TERM...KK SHORT TERM...RAB LONG TERM...RAB/RCS AVIATION...KK/NF/RAB

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