Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 200510 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 110 AM EDT MON APR 20 2015 .SYNOPSIS... LOW PRESSURE OVER WESTERN KENTUCKY WITH A WARM FRONT EXTENDING EAST AND COLD FRONT TRAILING SOUTHWARD FROM THE LOW WILL LIFT NORTHEAST TONIGHT INTO MONDAY. A COLD FRONT CROSSES THE REGION ON MONDAY...THEN HIGH PRESSURE BUILDS IN FOR TUESDAY. && .NEAR TERM /THROUGH TODAY/... AS OF 100 AM EDT MONDAY... HEAVY RAIN HAS MOVED NORTH OF THE AREA...THEREFORE THE FLOOD WATCH HAS BEEN CANCELLED FOR THE ENTIRE AREA. PREVIOUS DISCUSSION... AS OF 333 PM EDT SUNDAY... A WARM FRONT TO OUR SOUTH WILL LIFT NORTH THIS EVENING AND CROSS THE FORECAST AREA TONIGHT. DEEPER MOISTURE AND HIGHER PWATS WILL INCREASE IN THE WARM ADVECTION WITH THE NORTHWARD ADVANCE OF THE FRONT. THE REGIONAL RADAR IMAGE SHOWED WIDESPREAD CONVECTION ACROSS THE MID ATLANTIC REGION SOUTHWARD TO THE SOUTHEAST US. THERE ARE SOME CONCERNS OF STRONG CONVECTION ACROSS GEORGIA THIS AFTERNOON MAY TAKE SOME OF THE MOISTURE AWAY FROM OUR AREA. OUR LOCAL RNK WRFARW...HIRESW-ARW...NAM AND GFS WAIT UNTIL AFTER 00Z BEFORE BRINGING IN HEAVIER CONVECTION THIS EVENING...WHILE HRRR AND ECMWF ARE A LITTLE FASTER WITH TIMING. THE HRRR AND HIRESW-ARW LIFTS THE PRECIPITATION NORTHEAST WITH MOST OF RAIN PULLING OUT BY 06-08Z. USED A BLEND OF HRRR AND NAM FOR POPS...TAPERING POPS BACK AFTER 06Z TONIGHT INTO MONDAY MORNING. NOT EXPECTING ANY STRONG THUNDERSTORMS THIS AFTERNOON INTO TONIGHT WITH CLOUD COVER HINDERING INSTABILITIES. HOWEVER...THE LOW LEVEL JET INCREASING TO 50-60 KNOTS FROM THE SOUTHEAST WILL RESULT IN STRONG UPSLOPE AND ISENTROPIC LIFT. THE STRONG WINDS THROUGH A DEEP LAYER WILL PROVIDE LARGE HELICITY VALUES LATE THIS AFTERNOON INTO THIS EVENING. THE DAY ONE CONVECTIVE OUTLOOK (SWODY1) PLACED A MARGINAL (5 PERCENT CHANCE OF WIND) ACROSS SOUTHWEST PORTION OF CWA. PLAYED LOW TEMPERATURES CLOSE TO ADJMAV WITH READINGS FROM THE UPPER 40S IN THE NORTHWEST MOUNTAINS TO AROUND 60 DEGREES IN THE PIEDMONT. A WARM...MOIST AND UNSTABLE AIRMASS EXPECTED MONDAY. THE ATMOSPHERE WILL DESTABILIZE AHEAD OF THE APPROACHING COLD FRONT WITH SHOWERS AND THUNDERSTORMS DEVELOPING MONDAY. INITIALLY CUT BACK POPS CLOSER TO NAM FOR MONDAY MORNING...THEN INCREASED TO LIKELY BY MONDAY AFTERNOON. SPC CONTINUES OUR SLIGHT RISK FOR MONDAY ACROSS MOST OF OUR CWA. THIS IS SUPPORTED BY THE DYNAMIC ENVIRONMENT WITH HEALTHY SHEAR AND DECENT CAPES AROUND 2K. IT WILL ALSO BE QUITE BREEZY WITH EFFICIENT DOWNWARD MOMENTUM TRANSFER IN A WELL MIXED BOUNDARY LAYER. THE FRONT SHOULD BE CLEARING MONDAY NIGHT. HIGH TEMPERATURES MONDAY WILL RANGE FROM THE MID 60S IN THE MOUNTAINS TO THE LOWER 80S IN THE PIEDMONT. && .SHORT TERM /TONIGHT THROUGH WEDNESDAY/... AS OF 345 PM EDT SUNDAY... TAIL END OF COLD FRONT AND ASSOCIATED CONVECTION WILL BE EXITING THE AREA JUST AFT 00Z. HOWEVER...A BROAD UPPER TROUGH...ALMOST WINTERLIKE PATTERN CONTINUES TO EVOLVE AND DEEPEN ACROSS THE GREAT LAKES WITH NUMEROUS SPOKES OF PVA/SHORT WAVES REMAINING UPSTREAM. THIS LEAVES THE REGION...ESPECIALLY THE MOUNTAINS...WITH A VERY UNSETTLED PATTERN. AT A MINIMUM...EXPECT VARIABLE CLOUDINESS. TIMING OF EMBEDDED DISTURBANCES WILL BE THE KEY TO THE TIMES FOR THE BETTER CHANCES OF SHOWERS. FOR SEVERAL DAYS...THE GFS HAS INSISTED ON A SIGNIFICANT DISTURBANCE MOVING THROUGH THE REGION WED WITH WIDESPREAD -SHRA AS A RESULT. THE OTHER MODELS REMAIN LACKLUSTER WITH THIS FEATURE...BUT DO SUGGEST AT LEAST SOME SMALL CHANCE WITHIN THIS TIME FRAME. GIVEN THE UNSETTLED NATURE OF THE PATTERN WITH UPSLOPE FLOW AND VERY DIFFICULT TO TIME UPPER DISTURBANCES...CANNOT REALLY DROP POPS AT ANY TIME. BEST FOCUS THROUGH THE PERIOD WILL REMAIN WEST OF THE BLUE RIDGE...AND ESPECIALLY ACROSS THE MOUNTAINS OF WV/FAR SW VA. IN ADDITION...ENOUGH INSTABILITY SUGGESTED WITH COLD AIR ALOFT...TO INTRODUCE ISOLD TSRA WITH THE WED DISTURBANCE AS WELL. 850MB TEMPS DROP TO NEAR 0C ACROSS THE NORTHERN PART OF THE FORECAST AREA BY WED...BUT THE BETTER COLD ADVECTION COMES IN THE EXTENDED PERIOD BEHIND THE WED DISTURBANCE. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... AS OF 400 PM EDT SUNDAY... BROAD UPPER TROUGH REMAINS IN PLACE AND DOMINATES THE EXTENDED FORECAST...GRADUALLY SHIFTING FURTHER ESE LATE IN THE PERIOD. THIS KEEPS THE REGION IN AN UNSTABLE/UNSETTLED NORTHWEST FLOW WITH NUMEROUS EMBEDDED SHORT WAVES. MODELS VARY CONSIDERABLY AS TO THE TIMING AND PLACEMENT OF THESE DISTURBANCES...BUT ENOUGH AGREEMENT THAT POPS CANNOT BE DROPPED REALLY AT ANY TIME THE OVERALL TREND IS TO PUSH THE BETTER MOISTURE FURTHER SOUTH OF THE REGION AS THE WEEK PROGRESSES AND 850MB TEMPS DROP BELOW 0C IN THE NORTHERN COUNTIES. THE ENTIRE PERIOD SHOULD FEATURE BELOW NORMAL TEMPERATURES WITH LOW CHC POPS...HIGHEST ACROSS THE MOUNTAINS AND TOWARD THE SOUTHERN COUNTIES...WITH THE NORTHERN PIEDMONT THE DRIEST. ALTHOUGH TEMPERATURES WILL BE BELOW NORMAL THROUGHOUT THE PERIOD...NO REAL CLEAR CONCERN AT THIS POINT FOR FROST/FREEZE BECAUSE OF CYCLONIC FLOW AND CLOUDS. && .AVIATION /05Z MONDAY THROUGH FRIDAY/... AS OF 110 AM EDT MONDAY... BULK OF THE RAIN IS HEADING NORTH OF THE AREA WITH THE WIND BECOMING SOUTHWESTERLY. VISIBILITIES WILL IMPROVE QUICKLY AS LIGHT RAIN TRACKS TO THE NORTH BY 08Z...THEN CEILINGS WILL LIFT TO VFR WITHIN A COUPLE OF HOURS AFTER...DEFINITELY BY 12Z MONDAY. SHOWERS AND THUNDERSTORMS WILL MOVE ACROSS THE REGION MONDAY AFTERNOON...FOLLOWED BY A COLD FRONT. PRESSURE RISES BEHIND THE FRONT WILL BRING BREEZY AND GUSTY WESTERLY WINDS TO THE AREA INTO MONDAY NIGHT. EXTENDED AVIATION... VFR RETURNS LATER MONDAY NIGHT AND TUESDAY WITH HIGH PRESSURE BUILDING IN BEHIND THE FRONT WITH A DRIER AIRMASS. THEN THE NEXT CHANCE OF MVFR CONDITIONS AND PRECIPITATION WILL BE IN THE MOUNTAINS ON WEDNESDAY AND THURSDAY. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...AMS/KK NEAR TERM...KK/RCS SHORT TERM...RAB LONG TERM...RAB AVIATION...AMS/KK/RCS

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