Area Forecast Discussion
Issued by NWS Blacksburg, VA

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844 FXUS61 KRNK 170614 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 214 AM EDT SUN MAY 17 2015 .SYNOPSIS... HIGH PRESSURE OFFSHORE WILL MAINTAIN A MOIST SOUTHERLY FLOW OF AIR ACROSS THE REGION THROUGH MONDAY. A COLD FRONT WILL SLOWLY APPROACH FROM THE WEST LATE MONDAY...MOVING THROUGH THE REGION TUESDAY. COOLER...DRIER AIR WILL FILTER INTO THE REGION BY THE MID PART OF NEXT WEEK BEHIND THE FRONT. && .NEAR TERM /THROUGH TODAY/...
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AS OF 835 PM EDT SATURDAY... MAIN CORRIDOR OF CONVECTION REMAINS ACROSS THE FAR WESTERN THIRD THIS EVENING IN AN AXIS OF HIGHER CAPE UNDER A WEAK CONVERGENCE AREA ALONG THE TAIL OF ANOTHER PASSING WEAK MID LEVEL WAVE. EVENING RNK SOUNDING SHOWING THINGS QUITE SATURATED WITH MOIST PWATS AND WEAK VEERING OVERTOP RATHER STRONG INSTABILITY. THUS APPEARS AT LEAST SHALLOW CONVECTION MAY CONTINUE TO LINGER A BIT LONGER WEST AS STILL SEEING NEW DEVELOPMENT OFF OUTFLOW BANDS. THUS KEEPING LIKELY/HIGH CHANCE POPS GOING ESPCLY VA HIGHLANDS/SE WEST VA UNTIL JUST BEFORE MIDNIGHT. LATEST HRRR ALSO SHOWS SOME COVERAGE OUT TO THE BLUE RIDGE IN VIRGINIA WHERE INSTABILITY YET TO BE WORKED OVER MUCH. THEREFORE LEAVING IN SOME CHANCE POPS FARTHER EAST INTO THE EARLY MORNING HOURS BEFORE ENOUGH COOLING...AND LESS UPPER SUPPORT FINALLY CAUSES SHRA TO FADE. OTRW DEGREE OF DEBRIS CLOUDS MAKING THINGS A BIT TRICKY WITH FOG COVERAGE OVERNIGHT AS SHOULD STILL SEE RATHER WIDESPREAD FOG/STRATUS WEST WHERE HEAVY RAIN HAS OCCURRED. ELSEWHERE APPEARS PATCHY COVERAGE OUTSIDE OF AREAS THAT HAVE SEEN THE HEAVY DOWNPOURS...AND MOSTLY IN THE LOW SPOTS/VALLEYS PROVIDED A BIT OF CLEARING LATER. SOUPY ENVIRONMENT WILL ONLY ALLOW FOR GRADUAL TEMP FALLS OVERNIGHT WITH MOST SPOTS STAYING IN THE 60S EXCEPT FOR PERHAPS A FEW 50S NW VALLEYS. PREVIOUS DISCUSSION AS OF 303 PM EDT SATURDAY... SUBTROPICAL RIDGE CONTINUES FROM THE SOUTHEAST STATES INTO THE MID- ATLANTIC REGION THIS AFTERNOON INTO SUNDAY. A SOUTHERLY FLOW OF WARM AND HUMID AIR COMBINING WITH INSTABILITY AND WEAK SHORTWAVES THIS THIS AFTERNOON GENERATING SCATTERED SHOWERS AND THUNDERSTORMS. CAPES THIS AFTERNOON VARY FROM 500 TO 1K J/KG...AND LIS AROUND MINUS 1 TO MINUS 3...WITH INCREASED PWAT ABOUT AN INCH. INTERESTING TO NOTE OFF THE 18Z SPC MESOANALYSIS OF A 800 DOWNDRAFT CAPE LOCATED TO OUR NORTHEAST. AS INDICATED BY SWODY1...THE BETTER DYNAMIC AND CHANCE FOR STRONGER TO SEVERE ARE LOCATED TO OUR NORTH AND WEST. ONE CONCERN FOR THIS AFTERNOON INTO TONIGHT WILL BE THE POTENTIAL FOR LOCALLY HEAVY RAINS WITH WEAK STEERING CURRENTS LEADING TO SLOW MOVING THUNDERSTORMS...ESPECIALLY ACROSS ACROSS THE MOUNTAINS. EXPECT MOST OF THE CONVECTION TO DIMINISH THIS EVENING WITH THE LOSS OF SOLAR HEATING. CAN NOT COMPLETELY DRIER IT OUT...BECAUSE THERE IS ANOTHER UPPER DISTURBANCE ROTATING ACROSS THE REGION OVERNIGHT INTO SUNDAY MORNING. WITH LOW LEVEL MOISTURE AND LIGHT WINDS ANTICIPATE THAT AREAS OF FOG WILL FORM OVERNIGHT ESPECIALLY IN LOCATION THAT RECEIVE RAINFALL ON SATURDAY. LOW TEMPERATURE OVERNIGHT WILL BE MILD WITH READINGS FROM THE UPPER 50S IN THE MOUNTAINS TO THE MID 60S IN THE PIEDMONT. UPPER RIDGE WILL HOLD FAST THROUGH SUNDAY BUT GRADUALLY START TO FLATTEN OUT AND SHIFT EAST AS SURFACE HIGH PRESSURE CENTERED OFF THE MID ATLANTIC COAST SURFACE SINKS FURTHER TO THE SOUTH. THE DAY TWO CONVECTION KEEPS US IN GENERAL THUNDERSTORMS SUNDAY WITH BEST DYNAMICS REMAINING TO OUR WEST. THE OROGRAPHIC FORCING WILL SERVE AS THE PRIMARY MECHANISM FOR DIURNAL CONVECTION...ALONG WITH OUTFLOW BOUNDARY INTERACTIONS AND POSSIBLY SOME WEAK UPPER SHORT WAVE ENERGY. HIGH TEMPERATURES ON SUNDAY WILL RANGE FROM THE LOWER 70S IN THE MOUNTAINS TO THE UPPER 80S IN THE PIEDMONT.
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&& .SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/... AS OF 300 PM EDT SATURDAY... MODELS CONTINUE TO BE IN GOOD AGREEMENT DURING SHORT TERM PERIOD IN MAINTAINING A SOUTHEASTERN UPPER RIDGE AMPLIFYING INTO THE BLACKSBURG FORECAST AREA THROUGH MONDAY NIGHT BEFORE BEING GRADUALLY FLATTENED BY A SHORT WAVE TROF EXPECTED TO MOVE EAST THROUGH THE GREAT LAKES ON TUESDAY. WITH THE UPPER RIDGE HOLDING UNTIL TUESDAY...SLOWLY INCREASING HEAT AND HUMIDITY ON LIGHT SOUTHWESTERLY FLOW ALONG THE PERIPHERY OF THE UPPER RIDGE WILL CONTINUE TO SUPPORT DEVELOPMENT OF MAINLY DIURNALLY- DRIVEN SHOWERS AND THUNDERSTORMS...MOST NOTABLY IN THE MOUNTAINS WHERE THETA-E VALUES WILL BE THE HIGHEST...AND WHERE LOCALIZED FORCED ASCENT AND DIFFERENTIAL HEATING DUE TO OROGRAPHIC INFLUENCES WILL BE MAXIMIZED TO PUNCH THROUGH WEAK MID-LEVEL CAPPING INVERSION. FORECAST SOUNDINGS CONTINUE TO MAINTAIN RELATIVELY WARM TEMPERATURES IN THE MID LEVELS OF THE ATMOSPHERE ALONG WITH WEAK SHEAR INTO TUESDAY...SUCH THAT SEVERE WEATHER THREAT EVEN UP THROUGH FRONTAL PASSAGE ON TUESDAY APPEARS TO BE EXTREMELY LIMITED. CORFIDI VECTORS YIELD A SLOW...BUT SUFFICIENTLY PROGRESSIVE MOTION SUCH THAT UNLESS TRAINING ALONG AN OUTFLOW BOUNDARY AND/OR ANCHORING ON A OROGRAPHIC POINT OCCURS...FLASH FLOODING THREAT SHOULD ALSO REMAIN MINIMAL DESPITE PRECIPITABLE WATER VALUES GRADUALLY CLIMBING UP TO AND MAXING OUT IN THE 1.6 - 1.8 INCH RANGE SUNDAY INTO MONDAY. PASSAGE OF SHORT WAVE TROF AND ATTENDANT COOL FRONT LATER TUESDAY SHOULD SHOULD BRING AN END TO THREAT FOR SCATTERED SHOWERS/STORMS BY/DURING TUESDAY EVENING AS COOL ADVECTION IN WEST...AND DOWNSLOPING EAST OF THE BLUE RIDGE TAKES OVER...SETTING THE STAGE FOR DRIER AND SLIGHTLY COOLER WEATHER LATER TUESDAY NIGHT INTO THE FIRST PART OF THE LONGER TERM PERIOD. TEMPERATURES THROUGH THE PERIOD WILL CONTINUE TO BE LARGELY GOVERNED BY EXTENT OF CLOUD COVER AND INFLUENCE OF CONVECTIVE OUTFLOW BOUNDARIES...BUT NOT EXPECTED TO BE THAT FAR OFF CLIMATOLOGICAL NORMALS AREA-WIDE. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... AS OF 300 PM EDT SATURDAY... SURFACE HIGH PRESSURE BUILDING IN FROM THE NORTHWEST SHOULD MAINTAIN DRY AND SLIGHTLY COOLER WEATHER FOR THE BLACKSBURG FORECAST AREA WEDNESDAY INTO AT LEAST THURSDAY MORNING. APPROACH OF YET ANOTHER SERIES OF NORTHERN STREAM IMPULSES EXPECTED TO SUFFICIENTLY BUCKLE/BACK UPPER FLOW AGAIN IN THURSDAY/FRIDAY TIMEFRAME TO SUPPORT THE DEVELOPMENT OF WIDELY SCATTERED SHOWERS OR ISOLATED THUNDERSHOWERS...MAINLY ACROSS THE SOUTHWESTERN VA INTO THE MOUNTAINS OF NW NC WHERE RETURN FLOW AND THETA-E WILL BE A BIT HIGHER. OTHERWISE...ANOTHER RETURN TO DRIER WEATHER LOOKS TO BE IN THE OFFING BY NEXT SATURDAY AS PASSAGE OF NORTHERN STREAM WAVES SUFFICIENTLY DEEPENS/REESTABLISHES UPPER TROF OVER NEW ENGLAND...SUPPORTING SURFACE HIGH PRESSURE THAT WILL SLIDE SOUTHEAST INTO NEW ENGLAND AND WEDGE SOUTHWESTWARD INTO THE MID ATLANTIC STATES. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/...
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AS OF 200 AM EDT SUNDAY... RADAR INDICATES ONLY A FEW LINGERING SHOWERS ACROSS THE AREA THIS MORNING. OVERALL...SHOWER ACTIVITY THROUGH LATE MORNING WILL REMAIN MINIMAL...HOWEVER EXPECT TO SEE LIGHT RETURNS PASS ACROSS FROM TIME TO TIME. PATCHY FOG AND LOW CEILINGS WILL AGAIN BE THE MORE SIGNIFICANT ISSUE OVERNIGHT...MORE SO ACROSS THE MOUNTAINS AND ESPECIALLY IN AREAS WHICH RECEIVED SIGNIFICANT RAINFALL ON SATURDAY. FOG WILL BURN OFF QUICKLY AFTER 9 AM WITH STRONG DAYTIME HEATING...AND LOW CEILINGS WILL GRADUALLY LIFT AND TRANSITION TO STRATOCU THROUGH THE REMAINDER OF THE MORNING. FOR SUNDAY...LOOKING FOR ANOTHER ROUND OF SCATTERED SHOWERS AND THUNDERSTORMS SIMILAR TO WHAT OCCURRED ON SATURDAY...WITH CONVECTION DEVELOPING ALONG THE MOUNTAIN RIDGES BEGINNING AS EARLY AS 17/16Z. SHOWERS AND THUNDERSTORMS WILL BECOME SCATTERED TO NUMEROUS ACROSS THE MOUNTAINS DURING MID/LATE AFTERNOON...WITH WESTERLY FLOW PUSHING SOME OF THIS ACTIVITY EAST ACROSS THE PIEDMONT DURING LATE AFTERNOON INTO THE EVENING. STORMS WILL AGAIN BE SLOW MOVING AND CAPABLE OF PRODUCING LOCALLY HEAVY RAINFALL FOR PROLONGED PERIODS OF TIME. AS SUCH...LOOKING AT THE POTENTIAL OF LOCALIZED MVFR/IFR CONDITIONS WITHIN THE HEAVIER RAINSHAFTS... REDUCING VISIBILITIES TO A FEW HUNDRED FEET AT TIMES. CONVECTION WILL START TO WANE TOWARD SUNSET WITH THE LOSS OF HEATING...BUT EXPECT SHOWERS AND A FEW THUNDERSTORMS TO REMAIN ON THE RADAR AS LATE AS 18/04Z. MEDIUM TO HIGH CONFIDENCE IN CEILINGS...VISIBILITIES AND WINDS DURING THE TAF PERIOD. EXTENDED AVIATION DISCUSSION... LATE NIGHT/EARLY MORNING FOG AND ASSOCIATED IFR-LIFR VSBYS/CIGS ARE HIGHLY LIKELY SUNDAY NIGHT INTO MONDAY GIVEN THE SOUPY ATMOSPHERE IN PLACE. LATE MONDAY INTO TUESDAY...A COLD FRONT MOVES THROUGH. THUNDERSTORMS SHOULD BE MOST NUMEROUS IN COVERAGE AND STRONGEST IN INTENSITY DURING THIS TIME FRAME FOR ALL AREAS...ENDING FROM THE WEST DURING TUESDAY. LONGER PERIODS OF MVFR CIGS/VSBYS APPEAR LIKELY MONDAY-TUESDAY. BEHIND THE COLD FRONT...DRIER/COOLER CONDITIONS ARE EXPECTED WED-THU WITH MOSTLY VFR CONDITIONS AS HIGH PRESSURE SLIDES IN FROM THE NW.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...RAB NEAR TERM...JH/KK SHORT TERM...WERT LONG TERM...WERT AVIATION...JH/NF

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