Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 020905 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 505 AM EDT MON MAY 2 2016 .SYNOPSIS...
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A WEAK COLD FRONT ACROSS THE OHIO VALLEY EARLY MONDAY MORNING WILL DRIFT SLOWLY THROUGH THE CENTRAL APPALACHIANS BY EARLY TUESDAY. LOW PRESSURE WILL DEVELOP ALONG THE FRONT TONIGHT AND MOVE NORTHEAST TOWARD THE MID-ATLANTIC COAST BY TUESDAY MORNING. WIDESPREAD SHOWERS AND THUNDERSTORMS WILL ACCOMPANY THESE FEATURES. FOR WEDNESDAY THROUGH FRIDAY...A DEEP UPPER LOW PRESSURE AREA WILL SAG SOUTHWARD FROM THE GREAT LAKES INTO THE APPALACHIANS KEEPING AN UNSETTLED AND UNSEASONABLY COOL WEATHER PATTERN ACROSS THE REGION.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 445 AM EDT MONDAY... AN ACTIVE 24 HOURS WEATHERWISE EXPECTED ACROSS THE CWA WITH THE MAIN CONCERNS BEING STRONG TO SEVERE THUNDERSTORMS AND LOCALLY HEAVY RAINFALL. OVERALL...EXPECTING GREATER THREAT FOR SEVERE TODAY THAN OBSERVED SUNDAY...ALONG WITH MORE WIDESPREAD RAINFALL. SYNOPTIC PATTERN FEATURES A WEAK COLD FRONT DRAPED ACROSS THE OHIO VALLEY INTO NEW ENGLAND. A SERIES OF UPPER-LEVEL IMPULSES DRAPED ATOP THE FRONT FROM THE SOUTHERN PLAINS TO NEW ENGLAND...ALL EMANATING FROM A PERSISTENT BROAD UPPER LOW IN THE SOUTHWEST U.S. OVER THE NEXT 24 HOURS...THE FRONT WILL SAG SLOWLY SOUTHWARD IN RESPONSE TO REPEATED DISTURBANCES...ADDITIONAL CONVECTION WITH COLD POOL OUTFLOW...AND A STRENGTHENING UPPER LOW ALL THE WHILE JUST NORTH OF THE GREAT LAKES REGION. BY 00Z THIS EVENING...EXPECT THE FRONT TO EXTEND FROM EASTERN TN INTO EASTERN WV AND CENTRAL MD. EXPECTING AMPLE HEATING IN ADVANCE OF THE FRONT WHICH WILL PUSH CAPES IN EXCESS OF 2000 J/KG ACROSS MUCH OF THE CWA BY MID- LATE AFTERNOON. WITH DEWPOINTS IN THE LOW 60S AND PWATS NEARING 1.5 INCH AND AT LEAST WEAK SHEAR...AND A WEAKLY DIFFLUENT UPPER DISTURBANCE APPROACHING THE AREA FROM THE SOUTHWEST...CONDITIONS APPEAR FAVORABLE FOR A FAIRLY WIDESPREAD SEVERE WEATHER EVENT. AS A RESULT...SPC HAS OUTLOOKED MUCH OF THE CWA FOR A SLIGHT RISK OF SEVERE TODAY AND TONIGHT. SHEAR/HELICITY IS NOT OVERLY IMPRESSIVE ACROSS THIS REGION...WITH THE BETTER OF SUCH LOCATED ACROSS NORTHERN VA/MD/DC AREA...WHERE SPC HAS INDICATED A 5 PERCENT RISK OF TORNADOES. MAIN THREATS IN OUR AREA...AS IT HAS BEEN THE PAST FEW DAYS...SHOULD BE HAIL AND SOME WIND DAMAGE WITH DCAPES APPROACHING 1000 J/KG BY AFTERNOON. 500MB TEMPS ARE COOLING TOWARD -20C THROUGH THE PERIOD AND THE FREEZING LEVEL IS RELATIVELY LOW. THE OTHER CONCERN WILL BE HEAVY RAINFALL WITH ANY TRAINING OF STORMS. THIS ISSUE IS ADDRESSED BELOW IN THE HYDROLOGY SECTION. MODELS IN FAIRLY GOOD AGREEMENT ON TIMING OF THE HEAVIER PRECIPITATION AND CONVECTION...GENERALLY HOLDING OFF UNTIL MID TO LATE AFTERNOON AS A SHORT WAVE MOVES INTO MIDDLE TN/NORTHERN AL. THUS...WE SHOULD SEE SHOWERS/THUNDERSTORMS INCREASING AFTER 18Z FROM THE SOUTHWEST...SPREADING NORTHEAST INTO THE CWA DURING THE LATE AFTERNOON/EVENING...SPREADING SLOWLY EAST OVERNIGHT. INDICATIONS ARE THAT CONVECTION COULD LINGER MUCH OF THE NIGHT...ESPECIALLY EAST OF THE BLUE RIDGE. THE GREATEST THREAT FOR SEVERE AND FLASH FLOODING WILL BE IN THE 22Z-04Z TIME FRAME. WITH NO WEDGE IN PLACE TODAY AND SOME INSOLATION EXPECTED...ESPECIALLY EASTERN AREAS...HAVE LEANED TOWARD THE WARM SIDE OF GUIDANCE. TEMPS SUN WERE QUITE WARM AS THE WEDGE BROKE MUCH EARLIER THAN EXPECTED...AND WITH 850MB TEMPS HOVERING NEAR +12C AGAIN TODAY...IT SHOULD BE QUITE WARM...70S WEST TO LOWER 80S EAST.
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&& .SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/...
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AS OF 345 AM EDT MONDAY... A COLD FRONT WILL PUSH EASTWARD OVER THE MID ATLANTIC...WHICH WILL BRING ANOTHER ROUND OF SHOWERS FOR MOST OF THE CWA. SOUTHSIDE VIRGINIA AND THE NORTHWEST NORTH CAROLINA PIEDMONT COULD SEE SOME CHANCES OF THUNDERSTORMS WITH LINGERING INSTABILITY PRESENT...DUE TO HIGH TEMPERATURES REACHING THE MID 70S IN THIS AREA. THE COLD FRONT FINALLY MOVES TOWARD THE COAST BY TUESDAY NIGHT...WHICH WILL ALLOW LOW TEMPERATURES TO DROP INTO THE MID 40S TO THE MID 50S. BY WEDNESDAY..A DEEP UPPER LEVEL TROUGH SHOULD APPROACH FROM HUDSON BAY IN CANADA TOWARD THE MID ATLANTIC. THE MODELS INSIST THAT THE UPPER LEVEL TROUGH WILL CLOSE OFF INTO A CUT OFF LOW DURING THURSDAY...WHILE ANOTHER CUT OFF LOW DEVELOPS ALONG THE CALIFORNIA COAST. WITH AN UPPER LEVEL RIDGE FIRMLY ENTRENCHED OVER THE PLAINS BETWEEN THE TWO LOWS...THIS OMEGA BLOCK PATTERN SHOULD BLOCK THE ATMOSPHERIC FLOW ACROSS THE UNITED STATES. DUE TO THE CLOSED LOW OVERHEAD...EXPECT GENERALLY CLOUDY SKIES...PERIODS OF SHOWERS WITH SOME PATCHY DRIZZLE AND FOG...AND BELOW NORMAL TEMPERATURES. OVERALL...IT CERTAINLY WILL NOT FEEL LIKE THE FIRST WEEK OF MAY TOWARD THE END OF THIS WORK WEEK.
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&& .LONG TERM /FRIDAY THROUGH SUNDAY/... AS OF 400 PM EDT SUNDAY... TEMPERATURES ARE EXPECTED TO TAKE A TUMBLE FOR THE END OF THE WEEK AS HIGH AMPLITUDE UPPER LEVEL TROUGH SINKS SOUTH FROM THE GREAT LAKES AND A CUTOFF LOW DEVELOPS OVER THE MID ATLANTIC REGION. 85H TEMPS OF 0 TO +5 DEG C ARE PROGGED TO BE OVER THE FORECAST AREA BY THURSDAY NIGHT...AND IF THIS VERIFIES...IT WILL SUPPRESS TEMPERATURES AT LEAST 10 TO 15 DEGREES BELOW NORMAL. AS THE UPPER LOW PASSES OVERHEAD...COLD POOL ALOFT WILL COMBINE WITH DAYTIME HEATING FOR A DAILY THREAT OF INSTABILITY SHOWERS AND CONSIDERABLE CLOUDINESS. CUTOFF LOW WILL LIKELY BE SLOW TO MOVE OUT PER BLOCKY LOOK TO THE UPPER AIR PATTERN...WITH CUTOFF LOWS ON THE WEST AND EAST COASTS AND A RIDGE UP THROUGH THE CENTRAL CONUS. UNLIKE THE LAST OMEGA BLOCK WHERE THE MID ATLANTIC ENJOYED UNSEASONABLY WARM AND DRY CONDITIONS UNDER THE UPPER LEVEL RIDGE...JUST THE OPPOSITE IS OCCURRING THIS GO ROUND. OVER THE WEEKEND THE MODELS INDICATE THE CUTOFF LOW WILL GRADUALLY DRIFT EAST TO JUST OFF THE MID ATLANTIC COAST...TEMPERATURES ALOFT MODERATING. THIS SHOULD ALLOW FOR A GRADUAL WARMING TREND WITH TEMPERATURES RETURNING TO NORMAL BY THE START OF NEXT WEEK. ATTM...WEEKEND AS A WHOLE LOOKS DRY. WE HAVE A SLIGHT CHANCE OF SHOWERS OVER THE MOUNTAINS TO ACCOUNT FOR THE INSTABILITY...BUT NOT CONFIDENT THERE WILL BE MUCH COVERAGE. && .AVIATION /09Z MONDAY THROUGH FRIDAY/... AS OF 155 AM EDT MONDAY... EARLIER SHOWERS AND THUNDERSTORMS HAVE MOSTLY SUBSIDED...BUT PLENTY OF CLOUD COVER LINGERS ACROSS THE MID ATLANTIC TONIGHT. WHILE CONDITIONS REMAIN VFR FOR MOST TAF SITES...THE EXCEPTION IS KBLF WHERE CEILINGS HAVE FALLEN TO LIFR ALONG WITH 1/2SM FOG. DUE TO THE MOIST GROUND FROM RECENT RAINFALL...IT SEEMS MORE LIKELY THAT MOST TAF SITES WILL DROP TO IFR DUE TO GROUND FOG. CONFIDENCE IS LOWEST FOR IFR AT KROA WHERE CLOUDS AND VISIBILITIES MAY STAY AT VFR...ALTHOUGH BRIEF MVFR CANNOT BE RULED OUT ENTIRELY. WINDS SHOULD PICK UP FROM THE SOUTHWEST DURING MONDAY...AS A COLD FRONT APPROACHES FROM THE WEST. ALL TAF SITES SHOULD IMPROVE TO VFR BY LATE MORNING...BUT EXPECT SOME BROKEN CUMULUS TO DEVELOP AS SOME SUNSHINE DESTABILIZES THE ATMOSPHERE. SHOWERS AND THUNDERSTORMS SHOULD BE ON THE INCREASE BY MONDAY AFTERNOON. SOME OF THE STRONGER STORMS MAY CONTAIN LARGE HAIL AND DAMAGING WINDS. THE THREAT FOR CONVECTION SEEMS MORE WIDESPREAD...SO A MENTION OF VCTS WAS INCLUDED AT ALL SITES. EXTENDED AVIATION DISCUSSION... THE COLD FRONT WILL STALL OVERHEAD ON MONDAY EVENING...AND WAVES OF LOW PRESSURE SHOULD TRACK ALONG THE STALLED FRONTAL BOUNDARY DURING TUESDAY. THIS PATTERN SHOULD KEEP THE MID ATLANTIC IN MVFR/IFR CONDITIONS DURING TUESDAY...BEFORE THE FRONTAL BOUNDARY IS PUSHED EASTWARD BY TUESDAY NIGHT. A DEEP UPPER LEVEL TROUGH WILL ARRIVE OVER THE MID ATLANTIC ON WEDNESDAY...AND SETTLE OVERHEAD THROUGH THE END OF THIS WORK WEEK. OVERALL...FLYING CONDITIONS APPEAR RATHER POOR FOR LATE THIS WEEK DUE TO THE LIKELIHOOD OF LOW CLOUDS...PERIODS OF SHOWERS...AND PATCHY FOG. && .HYDROLOGY...
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AS OF 500 AM EDT MONDAY... MARGINAL CONCERNS FOR FLASH FLOODING ACROSS SOUTHEAST WV TODAY. THIS REGION HAS SEEN ANYWHERE FROM 1.0 TO 2.0 INCHES OF RAIN THE PAST COUPLE OF DAYS. ANOTHER 1.O TO 2.0 INCHES OF RAIN EXPECTED THERE TODAY...WITH LOCALLY HIGHER AMOUNTS IN THUNDERSTORMS THIS AFTERNOON/EVENING. THE HEAVIEST RAINFALL OVER THE PAST 2 DAYS HAS BEEN ACROSS GREENBRIER AND FAR WESTERN SUMMERS AND MERCER COUNTIES. THERE APPARENTLY WERE SOME ISSUES WITH FLOODING IN NORTHEAST GREENBRIER COUNTY LATE SUNDAY. RAINFALL AMOUNTS ON AVERAGE EAST OF THE ALLEGHANY FRONT HAVE BEEN LESS AND ANTECEDENT CONDITIONS ARE DRIER. IN AGREEMENT WITH WFO RLX...HAVE DECIDED TO GO AHEAD AND ISSUE A FLASH FLOOD WATCH FOR GREENBRIER FOR MID- AFTERNOON THROUGH THE OVERNIGHT HOURS. LATER SHIFTS MAY FEEL THE NEED TO EXPAND EASTWARD IF FUTURE CONDITIONS WARRANT...BUT DO NOT FEEL THAT IT IS WARRANTED NOW BASED ON ANTECEDENT CONDITIONS. .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...FLASH FLOOD WATCH FROM 2 PM EDT THIS AFTERNOON THROUGH TUESDAY MORNING FOR WVZ507-508.
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&& $$ SYNOPSIS...RAB NEAR TERM...JH/RAB SHORT TERM...PW LONG TERM...PM AVIATION...PW

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