Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 271812 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 212 PM EDT MON APR 27 2015 .SYNOPSIS... AN UPPER DISTURBANCE MOVES ACROSS THE AREA TODAY INTO THIS EVENING KEEPING THE REGION IN A COOL AIR MASS. LOW PRESSURE OVER TEXAS WILL SHIFT EAST INTO THE GULF COAST STATES AND TN VALLEY TO BRING OUR NEXT ROUND OF RAIN BY MIDWEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 950 AM EDT MONDAY... VISIBLE SATELLITE IMAGERY SHOWS ABUNDANT SUNSHINE ACROSS THE REGION THIS MORNING WHICH IS A MOST WELCOME SIGHT AFTER SUCH A DREARY WEEKEND. HOWEVER...THE WATER VAPOR LOOP SHOWS A VIGOROUS SHORT WAVE ROTATING AROUND THE UPPER LOW ANCHORED OVER THE NORTHEAST US. THIS SHORT WAVE WILL MOVE OUT OF THE GREAT LAKES AND BE ON OUR DOORSTEP BY EARLY THIS EVENING. MOISTURE IS LIMITED BUT SHOULD BE SUFFICIENT TO COMBINE WITH LIFT OUT AHEAD OF THE SHORT WAVE AND INSTABILITY GENERATED BY STRONG SUNSHINE UNDER THE POOL OF COLD AIR ALOFT TO GENERATE SOME SHOWERS AND POSSIBLY AN ISOLATED RUMBLE OF THUNDER MAINLY ACROSS THE FAR NORTH FROM THE GREENBRIER VALLEY INTO THE ALLEGHANY HIGHLANDS. WITH THE COLD POOL ALOFT IT WOULD NOT BE SURPRISING TO SEE SOME GRAUPEL WITH SOME OF THE MORE SUBSTANTIAL SHOWERS. THE REST OF THE FORECAST AREA LOOKS TO BE IN GOOD SHAPE WITH CLOUDS DECREASING EAST OF THE BLUE RIDGE INTO THE PIEDMONT. LOW LEVEL WINDS ARE NOT VERY IMPRESSIVE BUT THE BOUNDARY LAYER WILL BE WELL MIXED THIS AFTERNOON SO STILL EXPECT BREEZY CONDITIONS AFTER THE INVERSION BREAKS LATE THIS MORNING. HIGH TEMPS WILL BE CONSIDERABLY WARMER THIS AFTERNOON THAN THIS PAST WEEKEND BUT WILL STILL BE RUNNING 10 DEGREES BELOW NORMAL. PREVIOUS DISCUSSION... TONIGHT...THIS SHORTWAVE EXITS AND SHOWERS DIMINISH OVER THE MTNS AND WINDS WILL SUBSIDE SOMEWHAT. SKIES CLEAR SO TEMPS SHOULD BE DROPPING TOWARD THE MID TO UPPER 30S MTNS...TO AROUND 40 ACROSS THE PIEDMONT. ISSUE TONIGHT WILL BE FROST/FREEZE POTENTIAL. HAVE ONLY THE HIGHEST RIDGES OF SE WV/MT ROGERS CLOSE TO 32F. WHILE A FEW POCKET OF FROST ARE POSSIBLE...THINK ENOUGH OF A GRADIENT INHIBITS FROST FORMATION. THOSE WHO LIVE IN DEEPER/SHELTERED VALLEYS WILL BE PRONE TO FROST. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... AS OF 300 AM EDT MONDAY... GFS/ECMWF WERE SIMILAR IN BRINGING THE UPPER LOW SLOWLY EAST FROM THE OK/TX AREA TUESDAY MORNING INTO THE TN VALLEY BY WED MORNING. AT THE SFC...LOW PRESSURE WILL RIDE ALONG THE GULF COAST TUE-WED...THEN SHIFT OFF THE GA COAST BY WED EVENING. WHILE THIS OCCURS A NRN STREAM TROUGH MOVES ACROSS THE GREAT LAKES AND JUST NORTH OF US. MODELS KEEP THESE TWO STREAMS SPLIT...BUT ENOUGH OF INVERTED TROUGH IN THE AREA PLUS ATLANTIC FLOW TO THROW RAINFALL INTO AREA BY TUESDAY NIGHT...AND ESPECIALLY INTO WEDNESDAY. NUDGED POPS UP AND HAVE CATEGORICAL POPS ALONG THE BLUE RIDGE SOUTH OF ROANOKE WEDNESDAY WITH HIGH CHANCE POPS FROM THE GREENBRIER VALLEY TO THE PIEDMONT NORTHEAST OF LYH. AS WE HEAD INTO WEDNESDAY NIGHT THE GFS BECOMES MORE AMPLIFIED AND STRONGER WITH THE NORTHERN LOW THAN OTHER GUIDANCE...AND THEREFORE DRIVES THE TROUGH FURTHER SOUTH AND BRINGS THE SFC LOW NE ALONG THE NC COAST. THE ECMWF MORE OPEN WILL TAKE THE LOW FURTHER OUT TO SEA. ATTM...AM COMPROMISING THE TWO AND KEEPING HIGHER POPS OVER THE SE CWA WED NIGHT. HIGHS ARE EXPECTED TO STAY BELOW NORMAL WITH WEDNESDAY APPEARING THE COOLEST...THOUGH THE ERN CWA MAY STAY MILD ENOUGH WITH MID 60S...WHILE THE BLUE RIDGE SOUTH OF ROANOKE ONLY GETS INTO THE UPPER 40S TO MID 50S...AND COULD BE COOLER IF RAIN MOVES IN FASTER. && .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 /18Z MONDAY THROUGH SATURDAY/...
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AS OF 210 PM EDT MONDAY... HIGH CONFIDENCE IN VFR CONDITIONS THROUGH THE PERIOD EAST OF THE BLUE RIDGE. SHOULD BE GOOD RAD COOLING TONIGHT BUT WITH A GOOD DRYING DAY TODAY BELIEVE PATCHY FOG WILL NOT BE AS PREVALENT AS LAST NIGHT DUE TO GOOD DRYING TODAY SO WILL NOT INCLUDE IN THE TAFS. KBCB WILL ALSO BE VFR THOUGH BEING MORE FOG PRONE WILL USE A BRIEF TEMPO FOR MVFR FOG TOWARDS DAYBREAK. KLWB/KBLF WILL BE DEALING WITH SOME LOW LEVEL MOISTURE WORKING IN FROM THE NORTH. WILL KEEP THESE SITES MVFR BUT INDICATE THE POSSIBILITY OF SOME LOWER IFR CLOUDS WITH A SCT LAYER. FOG MAY BECOME AN ISSUE AT KLWB DEPENDING ON HOW LONG CLOUDS HOLD. WOULD NOT BE SURPRISED IF NEXT SHIFT FINDS IT NECESSARY TO INTRODUCE IFR FOG AT KLWB BASED ON TRENDS EARLY TONIGHT. WINDS WILL SUBSIDE AFTER SUNSET AND REMAIN LIGHT THROUGH TOMORROW. EXTENDED AVIATION DISCUSSION... VFR CONDITIONS ARE EXPECTED BEFORE CONDITIONS WORSEN ONCE BY LATE TUESDAY NIGHT. MODELS WERE SPEEDING UP MOISTURE INTO THE AREA...ESPECIALLY SOUTH OF A BLF-DAN LINE BY WED MORNING. ATTM...THE GFS IS MOST AGGRESSIVE IN HANGING THE STORM BACK CLOSER TO THE COAST INTO FRIDAY WHICH COULD KEEP THE AREA SOCKED INTO SUB VFR WEATHER LONGER. THE ECMWF IS MORE PROGRESSIVE...AND ALL IN ALL LOOKS LIKE WED-THU ARE SUB VFR DAYS...WITH SOME IMPROVEMENT FRIDAY.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...WP NEAR TERM...MBS/WP SHORT TERM...WP LONG TERM...PH/RAB AVIATION...MBS/WP

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