Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 221726 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 126 PM EDT WED APR 22 2015 .SYNOPSIS... A STRONG UPPER-LEVEL DISTURBANCE WILL MOVE ACROSS THE REGION TODAY ACCOMPANIED BY STRONG...GUSTY WINDS AND SCATTERED SHOWERS AND THUNDERSTORMS. FOR THURSDAY AND FRIDAY...A DEEP UPPER LOW IN THE NORTHEAST U.S. WILL KEEP BREEZY...CHILLY CONDITIONS ACROSS THE REGION. BY THE WEEKEND...ANOTHER UPPER-LEVEL DISTURBANCE WILL BRING THE NEXT CHANCE OF SHOWERS TO THE REGION ALONG WITH CONTINUED COOL TEMPERATURES. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1025 AM EDT WEDNESDAY... SLOWED DOWN THE ARRIVAL OF SHOWERS AND SCATTERED THUNDERSTORMS THIS MORNING AND PLACED THE HIGHER POPS DURING THE AFTERNOON. ALSO ADJUSTED THE DURATION OF THE STRONGER CONVECTION WINDOW TO 3 HOURS OVER ANY PARTICULAR AREA THROUGH THE AFTERNOON BASED ON LATEST HRRR/WRF. LACK OF MOISTURE IS THE LIMITING FACTOR FOR STRONG CONVECTION THIS AFTERNOON BUT CAN NOT RULE OUT MARGINAL SEVERE CELLS WITH INVERTED-V SOUNDING AND INCREASING DCAPE VALUES. SPC HAS THE FORECAST AREA...ESPECIALLY EAST OF THE BLUE RIDGE...IN A MARGINAL OUTLOOK WITH DEEP SHEAR FOR ORGANIZED THUNDERSTORM CLUSTERS. DEW POINTS WERE IN THE 30S AND INCREASING WITH A STRONG SOUTHWESTERLY FLOW. AS OF 345 AM EDT WEDNESDAY... A POTENT ALBERTA CLIPPER LIKE SYSTEM EMBEDDED WITHIN THE BOTTOM OF A LARGE/DEEP UPPER LOW CENTERED ACROSS THE GREAT LAKES WILL BRING GUSTY WINDS AND SCATTERED SHOWERS AND A FEW THUNDERSTORMS TO THE REGION TODAY...FOLLOWED BY UNSEASONABLY COOL TEMPERATURES THURSDAY AND FRIDAY. ALTHOUGH LOW-LEVEL/SURFACE MOISTURE IS LACKING IN THE WAKE OF THE SUN-MON SYSTEM...STRONG DYNAMICS WILL OVERCOME THE LACK OF SURFACE MOISTURE AND SUPPORT ELEVATED CONVECTION. FOLLOWING THE LEAD OF THE HRRR...WHICH IS IN AGREEMENT WITH THE LARGER-SCALE MODELS...BRING SOME SCATTERED LIGHT SHOWERS INTO THE WESTERN MOUNTAINS AROUND DAYBREAK...BUT A BETTER CHANCE OF CONVECTION WITH THE ACTUAL WIND SHIFT/UPPER TROUGH LATE MORNING WEST TO LATE AFTERNOON EAST. BASICALLY LOOKING AT A 2-4 HOUR WINDOW FROM WEST TO EAST IN THE 16Z-20Z TIME FRAME OF CONVECTIVE CHANCES. GIVEN STRONG 850MB WINDS...50+ KTS THIS MORNING TO AROUND 40KTS BY AFTERNOON...AND 30-40KTS BULK LOW-LEVEL SHEAR...COMBINED WITH 850MB TEMPS NEARING 0C AND 500MB TEMPS AROUND -25C...ALONG WITH A DRY LOWER ATMOSPHERE AND INVERTED-V SOUNDING...LEADS TO HIGH POTENTIAL FOR ANY CONVECTION TO BRING STRONG WIND GUSTS DOWN TO THE SFC. THE STRONG CELLS COULD ALSO PRODUCE MARGINALLY SEVERE HAIL. THE LIMITING FACTOR WILL BE MOISTURE AND INSTABILITY WITH MUCAPE MOSTLY 200-300 J/KG AT BEST. NONETHELESS...GIVEN THE STRONG DYNAMICS NOTED ABOVE...SPC HAS OUTLOOKED MUCH OF THE CWA EAST OF THE ALLEGHANY FRONT FOR A MARGINAL RISK OF SEVERE THUNDERSTORMS CAPABLE OF PRODUCING DAMAGING WINDS GUSTS AND MARGINAL/PENNY TO QUARTER- SIZED HAIL. THIS SEEMS VERY REASONABLE GIVEN THE AMOUNT OF HAIL PRODUCED BY THUNDERSTORMS IN THE REGION MON EVENING. WILL INCLUDE MENTION IN HWO AND HAVE NOTED GUSTY WINDS AND SMALL HAIL IN ZFP. ANOTHER CONCERN TODAY IS GRADIENT WIND. ALBERTA CLIPPER SYSTEMS ARE NOTORIOUS FOR PRODUCING STRONG GUSTY WINDS...AND THIS SYSTEM TODAY WILL CERTAINLY BE NO EXCEPTION TO THIS TENDENCY. WITH STRONG MIXING...THE 40-50KT 850MB WINDS WILL BE BROUGHT DOWN TOWARD THE SURFACE QUICKLY AFTER SUNRISE...CONTINUING THROUGH THE LATE AFTERNOON. BUFKIT SOUNDINGS SHOW GOOD POTENTIAL FOR 40KT GUSTS TO MIX DOWN TO THE SFC MID-MORNING THROUGH THE AFTERNOON. TAKING THESE FACTORS INTO CONSIDERATION AND THE MOIST GROUND FROM RECENT HEAVY RAIN...HAVE OPTED TO ISSUE A WIND ADVISORY GENERALLY JUST EAST OF THE ALLEGHANY FRONT TO JUST EAST OF THE BLUE RIDGE...INCLUDING THE SHENANDOAH AND ROANOKE VALLEYS. WOULD NOT BE SURPRISED TO SEE ROA GUST TO NEAR 40 MPH AT TIMES LATER TODAY. MAX TEMPERATURES WILL BE TRICKY TODAY WITH VARIABLE CLOUDS AND DOWNSLOPE WINDS EAST OF THE BLUE RIDGE. COULD SEE QUITE A GRADIENT IN MAX TEMPS FROM JUST THE 50S IN CLOUDIER/RAINIER AREAS OF THE ALLEGHANYS TO WELL INTO THE 70S ACROSS THE PIEDMONT. WITH 850MB TEMPS DROPPING TOWARD -4C IN THE NORTH BY 12Z THU AND THE DRY ATMOSPHERE...BELOW FREEZING TEMPERATURES CAN BE EXPECTED THURSDAY MORNING...ESPECIALLY IN THE HIGHER ELEVATIONS. WIND SHOULD PREVENT FROST THU MORNING. FROST/FREEZE PROGRAM STARTS IN THE MOUNTAINS ON SATURDAY...SO NO HEADLINES YET FOR THU/FRI FROST/FREEZE. && .SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/... AS OF 330 AM EDT WEDNESDAY... EXPECT TO START THURSDAY OFF WITH AN UPPER LEVEL LOW OVER EASTERN CANADA...WHILE COOL HIGH PRESSURE IN THE LOW LEVELS OF THE ATMOSPHERE BUILDS IN FROM THE MIDWEST REGION. WEST NORTHWESTERLY WIND DIRECTION AND DRY AIR WILL RESULT IN A BROAD TEMPERATURE GRADIENT FOR AFTERNOON HIGHS...WITH LOW/MID 50S EXPECTED ACROSS SOUTHEAST WEST VIRGINIA...WHILE THE SOUTHSIDE WILL REACH THE MID 60S. A TIGHTENED PRESSURE GRADIENT WILL ALSO ENSURE GUSTY WINDS THROUGH THE DAY...WITH GUSTS REACHING 25 MPH TO 30 MPH AT TIMES ACROSS THE MOUNTAINS...SO WE CAN EXPECT WIND CHILLS WILL BE 5 TO 7 DEGREES COOLER THAN THE ACTUAL TEMPERATURE. THURSDAY NIGHT WILL ALSO BE ON THE CHILLY SIDE AS OVERNIGHT TEMPERATURES BOTTOM OUT IN THE LOW/MID 30S ACROSS THE MOUNTAINS... BELOW FREEZING IN SPOTS...WHILE THE PIEDMONT WILL FALL INTO THE MID/UPPER 30S. WIND SPEEDS ARE EXPECTED TO REMAIN GUSTY ENOUGH THROUGH THE NIGHT...AND THE AIR DRY ENOUGH...THAT FROST ACROSS THE PIEDMONT SHOULD REMAIN ISOLATED AT BEST. FOR FRIDAY...MOSTLY CLEAR SKIES WILL CONTINUE...WITH HIGH CLOUDS STARTING TO BUILD IN DURING EARLY EVENING. HIGH PRESSURE WILL PASS ACROSS THE APPALACHIANS...MAKING FOR LIGHTER WIND SPEEDS THROUGH THE DAY. WITH THE UPPER LOW SHIFTING OVER THE CANADIAN MARITIMES AND WEAK UPPER LEVEL RIDGING APPROACHING FROM THE MISSISSIPPI VALLEY... WE CAN EXPECT SLIGHTLY WARMER AFTERNOON TEMPERATURES AREAWIDE... ALBEIT STILL SEVERAL DEGREES BELOW NORMAL FOR LATE APRIL. WITH HIGH PRESSURE PASSING TOWARD THE COAST LATE FRIDAY EVENING...WE WILL SEE OUR WINDS SHIFT EASTERLY...DRAWING COOLER AIR OFF THE ATLANTIC. RAIN CHANCES WILL ALSO INCREASE TOWARD DAWN SATURDAY AS ANOTHER LOW PRESSURE SYSTEM ADVANCES EAST ACROSS THE CENTRAL PLAINS. RAIN WILL OVERSPREAD OUR AREA BY EARLY SATURDAY AFTERNOON. WITH WINDFLOW OFF THE ATLANTIC AND WIDESPREAD RAIN/CLOUD COVER...DO NOT ANTICIPATE MUCH WARMING THROUGH THE DAY...AND THEREFORE EXPECT HIGH TEMPERATURES TO HOLD IN THE 50S AREAWIDE...WHICH IS SEVERAL DEGREES BELOW FORECAST GUIDANCE. COOL TEMPERATURES AND STABILITY OFFERED BY THE HIGH TO OUR EAST ALSO LIMITS THE POTENTIAL FOR THUNDERSTORM ACTIVITY...ALTHOUGH A RUMBLE OF THUNDER OR TWO REMAINS POSSIBLE ALONG THE WESTERN RIDGES. RAINFALL WILL BECOME MORE SHOWERY IN NATURE LATE SATURDAY NIGHT AS THE LOW PRESSURE SYSTEM PASSES EAST OF THE APPALACHIANS...MOVING OFFSHORE BY DAWN SUNDAY. && .LONG TERM /SUNDAY THROUGH TUESDAY/... AS OF 415 AM EDT WEDNESDAY... A BACK DOOR COLD FRONT WILL ARRIVE SUNDAY...BRINGING COOLER DRIER AIR INTO THE REGION FOR THE AFTERNOON INTO MONDAY. A STRONGER SURFACE WAVE TRACKS ACROSS THE TENNESSEE VALLEY TO THE CAROLINA MONDAY NIGHT INTO TUESDAY. THIS WAVE WILL HAVE MORE MOISTURE AND DYNAMICS TO BRING SOME HEAVY RAIN AND STRONG STORMS TO THE REGION. TEMPERATURES THROUGH THE PERIOD WILL REMAIN COOLER THAN NORMAL WITH UPPER 50S TO LOWER 60S ACROSS THE MOUNTAINS TO MID TO UPPER 60S EAST. && .AVIATION /18Z WEDNESDAY THROUGH SUNDAY/... AS OF 130 PM EDT WEDNESDAY... BROAD UPPER TROUGH CENTERED OVER THE GREAT LAKES WILL CONTINUE TO DOMINATE THE WEATHER ACROSS THE EASTERN U.S. THROUGH THE PERIOD. MAIN FOCUS THIS AFTERNOON WILL BE ON A STRONG SHORT WAVE PROGGED TO TRACK THROUGH THE BASE OF THE TROUGH ACROSS OUR REGION THIS AFTERNOON. WINDS WILL BE THE MAIN ISSUE THIS AFTERNOON...WITH A STRONG GRADIENT AND LOW LEVEL JET PERSISTING INTO THIS EVENING. MANY LOCATIONS WILL SEE SW-W WINDS 15-25KTS WITH GUSTS 30-40KTS IN THE 18Z-23Z TIME FRAME...VEERING MORE TO THE WNW AFTER 00Z BEHIND THE SHORT WAVE AND DECREASING INTO THE 10-15KTS WITH GUSTS 20-25KTS OVERNIGHT ACROSS THE MOUNTAINS. CIGS EXPECTED TO REMAIN MAINLY VFR...BOTTOMING OUT MOSTLY IN THE 040-050 RANGE...EXCEPT IN UPSLOPE AREAS BLF-LWB WHERE CIGS MAY DROP INTO THE 020-030 RANGE DURING THE AFTERNOON. STRONG DYNAMICS ASSOCIATED WITH THIS SHORT WAVE MAY OVERCOME THE SFC DRYNESS AND RESULT IN ELEVATED CONVECTION THIS AFTERNOON WITH BRUNT OF THE STRONGEST CONVECTION EXITING THE AREA BY 22Z. WITH A 50-60KT WESTERLY LLJ ASSOCIATED WITH THE SHORT WAVE...ANY CONVECTION COULD BRING THESE STRONG WINDS DOWN TO THE SFC. MODEST INSTABILITY WILL ALSO BE CAPABLE OF SUPPORTING SMALL HAIL IN THE STRONGER STORMS... ESPECIALLY CONSIDERING THE VERY COLD TEMPERATURES ALOFT. LOW CONFIDENCE FOR KEEPING VCTS AT BLF/LWB/BCB/ROA/ AS PREFRONTAL SHOWERS HAVE TRACKED ACROSS THE AREA. SOUTH OF HWY 460 AND INTO THE PIEDMONT (LYH/DAN) WILL HAVE A BETTER THREAT OF VCTS WITH ABUNDANT SUNSHINE AND INCREASING MOISTURE. HOWEVER...LOW LEVEL SHEAR MAY BE TO STRONG FOR ORGANIZED THUNDERSTORM TO DEVELOP. MEDIUM TO HIGH CONFIDENCE IN CIGS AND VSBYS THROUGH THE TAF VALID PERIOD. MEDIUM TO HIGH CONFIDENCE IN WIND SPD/DIR THROUGH THE TAF VALID PERIOD. LOW CONFIDENCE IN THUNDER POTENTIAL. EXTENDED AVIATION DISCUSSION... FRONT WILL EXIT TONIGHT WITH HIGH PRESSURE BUILDING INTO THE REGION FROM THE WEST THU-FRI. SOME GRADIENT REMAINS BETWEEN DEPARTING FRONT AND HIGH TO THE WEST THURSDAY AND POSSIBLY FRIDAY...SO GUSTY WINDS WILL REMAIN MAINLY DURING THE DAYTIME. OVERRUNNING CLOUDS WORK INTO THE AREA FRIDAY AHEAD OF A WARM FRONT. BY SATURDAY...ENOUGH MOISTURE TO ALLOW FOR SHOWERS AND MVFR WITH BEST FORCING ACROSS THE CAROLINAS. THIS WILL BE POSSIBLE INTO SUNDAY MORNING BEFORE THE SYSTEM EXITS AND SOME IMPROVEMENT IN CIGS STARTS TO OCCUR LATER SUNDAY. && .FIRE WEATHER... AS OF 345 AM EDT WEDNESDAY... DESPITE ALL OF THE RAIN SUN-MON...FUELS DRIED OUT CONSIDERABLY TUE WITH THE GUSTY WEST WINDS. SEVERAL AREAS ACROSS THE MOUNTAINS HAVE ALREADY SEEN 10-HR FUELS DROP TO 7 PERCENT DURING MIN RH TIMES. CLOUDS AND SCATTERED SHOWERS WILL BE ON THE INCREASE TODAY...BUT WINDS WILL BE AN EVEN BIGGER ISSUE THAN TUE...SO AREAS THAT DO NOT SEE ANY WETTING RAIN WILL CONTINUE TO DRY. MIN RH VALUES WILL DROP TO NEAR 30 PERCENT IN THE WARMER/DRIER PIEDMONT AREAS...BUT THIS IS JUST WHEN SCT SHRA/TSRA COULD DRIFT INTO THIS REGION. DEEPER SOILS ARE WET...SO MAIN PROBLEM WILL BE WITH FINE FUELS. DAY SHIFT MAY NEED TO CONSIDER A FIRE DANGER STATEMENT IN SOME AREAS EAST OF THE ALLEGHANY FRONT IF SHOWER COVERAGE DOES NOT MATERIALIZE. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...WIND ADVISORY UNTIL 7 PM EDT THIS EVENING FOR VAZ007-009>020- 022>024-033>035. NC...WIND ADVISORY UNTIL 7 PM EDT THIS EVENING FOR NCZ001-002-018. WV...NONE. && $$ SYNOPSIS...RAB NEAR TERM...RAB/RCS SHORT TERM...NF LONG TERM...NF/RCS AVIATION...RCS FIRE WEATHER...RAB/WP

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