Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 011124 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 724 AM EDT FRI AUG 1 2014 .SYNOPSIS... AN UPPER TROUGH OF LOW PRESSURE WILL CONTINUE TO RETROGRADE WEST TO THE MISSISSIPPI RIVER VALLEY...AND THE CENTER OF SURFACE HIGH PRESSURE WILL SHIFT TO OUR EAST TODAY. AN UPPER DISTURBANCE TRACKING JUST SOUTHEAST OF THE AREA WILL BRING MORE IN THE WAY OF WIDESPREAD RAINFALL INTO THIS AFTERNOON. LINGERING MOISTURE IN THE WAKE OF THIS FEATURE WILL COMBINE WITH HEATING TO RESULT IN MORE SHOWERS AND STORMS OVER THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 240 AM EDT FRIDAY... UNUSUAL WIDESPREAD RAIN EVENT FOR MID SUMMER LOOKS IN STORE FOR MUCH OF TODAY AS SHORTWAVE ENERGY CURRENTLY OVER SOUTHERN S CAROLINA TRACKS NE CROSSING THE EASTERN PORTIONS OF THE CWA BY THIS EVENING. THIS WILL CONTINUE TO ENHANCE THE OVERRUNNING OF WARM/MOIST AIR ON SE FLOW OVERTOP A DEVELOPING COOL WEDGE EARLY THIS MORNING...WITH SOME DEGREE OF PRECIP SPREADING NORTH AND WEST ACROSS MUCH OF THE REGION BY 12Z. STILL APPEARS THAT THE HEAVIEST RAINFALL WILL BE ACROSS SOUTHERN SECTIONS AND ENHANCED ALONG THE SOUTHERN BLUE RIDGE BY UPSLOPE FLOW OF NEAR 2 INCH PWATS INTO THIS AFTERNOON. HOWEVER APPEARS CONVECTION ALONG THE COASTAL CAROLINAS CONTINUES TO DISRUPT THE DEEPER SE TRAJECTORY WITH MORE CONVECTIVE NATURE COVERAGE FARTHER TO THE SOUTH IN CONJUNCTION WITH THE HIGHER THETA-E AIR BEING ADVECTED ACROSS THE FRONT INTO THE N CAROLINA COASTAL PLAINS. THIS MAY HAVE ALSO CAUSED THE MODEL INIT TO BE TOO FAR WEST WITH THE CORE OF HEAVIER RAINFALL BUT EXPECT THE CURRENT AXIS TO PIVOT MORE NORTH- SOUTH ORIENTED SIMILAR TO THE LATEST HRRR AS THE WAVE HELPS SHARPEN THE TROF WHILE BACKING THE FLOW ALOFT THIS MORNING. QUESTION IS WHETHER OR NOT WILL GET ENOUGH HEAVIER RAINFALL OVER A PROLONGED PERIOD TO PRODUCE FLOOD ISSUES GIVEN DRY CONDITIONS PER LATEST FFG SHOWING 6 HOUR AMOUNTS OF 3.5-4.5 INCHES TO CAUSE FLOODING. SINCE EXPECTING MOST OF THE RAINFALL TO REMAIN MORE STRATIFORM WITH EMBEDDED HEAVIER DOWNPOURS WONT POST A WATCH OVER THE SW FOR NOW BUT EXPECT UPSLOPE MAY CAUSE A GOOD 2-3+ INCHES ALONG THE EASTERN SLOPES. BEST LIFT SPREADS NE WITH THE WAVE THIS AFTERNOON CAUSING THE SOLID AXIS OF PRECIP TO SHIFT ACROSS EASTERN/NE SECTIONS DURING THE AFTERNOON WITH SOME TAPERING TO LIGHTER SHRA WEST/SW. COULD EVEN SEE A FEW BREAKS DEVELOP FAR WEST ON THE PERIMETER OF THE COOL AIR OTRW CLOUDY AND VERY COOL TO START AUGUST. HIGHS QUITE TRICKY AS SOME SPOTS MAY SEE MORE OF A WINTER CAD EVENT WITH TEMPS ONLY RISING A FEW DEGREES AT MOST ALONG THE BLUE RIDGE WHERE KEEPING IT IN THE 60S FOR THE MOST PART. THINK SPOTS OVER THE PIEDMONT INCLUDING SW VA INTO SE WVA MAY BE ABLE TO BUMP VALUES INTO THE LOW/MID 70S ESPCLY IF THE RAINFALL DIMINISHES A BIT FASTER AND THINGS BRIGHTEN SLIGHTLY. IMPULSE EXITS THIS EVENING LEAVING THE REGION WITHIN THE RESIDUAL WEDGE BUT UNDERNEATH A CONTINUED DIFFLUENT PATTERN ALOFT ON THE FRONT OF THE 5H TROF. LITTLE UPPER SUPPORT REMAINING OVERNIGHT FOR MUCH ADDED RAINFALL ESPCLY AFTER MIDNIGHT BUT LIKELY ENOUGH WEAK UPSLOPE TO KEEP LIKELY OR HIGHER POPS GOING BLUE RIDGE INTO LATE THIS EVENING. FLOW BEHIND THE DEPARTING WAVE MAY ACTUALLY TURN WESTERLY ENOUGH TO SHUT OFF SHRA WESTERN HALF LATE SO CUT POPS BACK TO MAINLY CHANCE AFTER MIDNIGHT WHEN MAY BE MORE DRIZZLE/FOG OUT EAST. CONTINUED COOL WITH LOWS LIKELY ONLY FALLING A FEW DEGREES BUT AFTER A CHILLY DAY WONT TAKE MUCH TO GET INTO THE 50S WEST AND LOW 60S EAST. && .SHORT TERM /SATURDAY THROUGH SUNDAY/... AS OF 314 AM EDT FRIDAY... A BERMUDA HIGH REMAINS OVER THE WESTERN ATLANTIC WHILE AN UPPER LEVEL TROUGH IS DRAPED OVER THE MISSISSIPPI VALLEY THIS WEEKEND. WITH THE FORECAST AREA IN BETWEEN THESE TWO SYNOPTIC FEATURES...IMPULSES WITH TROPICAL MOISTURE WILL KEEP A GOOD CHANCE FOR SHOWERS AND SCATTERED THUNDERSTORMS IN THE AREA OVER THE WEEKEND. COMPARED TO YESTERDAY...MODELS HAVE SHIFTED THE AXIS OF HEAVY STEADY RAIN EAST ALONG THE COAST. THE FORECAST AREA WILL STILL SEE A FAIR AMOUNT OF RAIN OVER THE WEEKEND...BUT WILL BE MORE CONFIDED TO THE AFTERNOON AND EVENING HOURS. DESPITE THE MODELS TRENDING DRIER...KEEP POPS THROUGH THE ENTIRE PERIOD WITH LOW CHANCE DURING NON-DIURNAL HEATING HOURS AND HIGH CHANCE-LIKELY DURING THE AFTERNOON AND EVENING. ALSO WITH THE DRIER MODEL SOLUTIONS...EDGE TEMPERATURES UP A FEW DEGREES EACH AFTERNOON. DESPITE WARMING THE FORECAST TEMPERATURES...THEY WILL REMAIN COOLER THAN NORMAL BY AT LEAST 10F FOR THE FIRST WEEKEND IN AUGUST. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... AS OF 330 PM EDT THURSDAY... MONDAY THROUGH WEDNESDAY THE TROFFING IN THE EAST FLATTENS. A SURFACE COLD FRONT COMES SOUTH THROUGH NEW ENGLAND MONDAY TUESDAY...BUT WILL ONLY MOVE SO FAR SOUTH WITH THE BOUNDARY PARALLEL TO THE UPPER FLOW. THIS WILL KEEP THE FORECAST AREA ON THE WARM UNSTABLE AIR MASS ON THE SOUTH SIDE OF THE FRONT THROUGH THURSDAY. DEEPEST MOISTURE AND BEST LIFT WILL BE FOCUSED ALONG THE COAST FRONT ACROSS THE CAROLINAS AND GEORGIA. NOT SEEING ANY ORGANIZED FORCING FOR THE COUNTY WARNING AREA. TEMPERATURES WILL BE NEAR NORMAL THROUGH THE PERIOD. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... AS OF 650 AM EDT FRIDAY... FLYING CONDITIONS WILL CONTINUE TO DETERIORATE THIS MORNING AS AN AXIS OF SHOWERS WITH EMBEDDED HEAVY RAIN SLIDES SLOWLY NORTH...LIKELY COVERING MOST OF THE REGION BY MID MORNING. MODELS CONTINUE TO SHOW THIS SCENARIO WITH WIDESPREAD RAINFALL ESPCLY BLUE RIDGE EAST INTO THIS AFTERNOON BUT DIFFER ON EXACTLY WHERE THE HEAVIEST MAY TAKE SHAPE. STILL APPEARS SOUTHERN SECTIONS RUNNING UP ALONG THE EASTERN SLOPES OF THE SOUTHERN BLUE RIDGE WILL SEE THE HEAVIEST RAINFALL INCLUDING WIDESPREAD MVFR TO IFR FOR MUCH OF TODAY...AND PERHAPS INTO THE OVERNIGHT. WESTERN LOCATIONS SUCH AS KBLF/KLWB MAY BREAK BACK OUT INTO VFR AFTER EARLY RAINFALL GIVEN DOWNSLOPE AND PASSAGE OF DEEPER MOISTURE TO THE EAST SO WENT CLOSER TO THE LESS PESSIMISTIC GFS THERE. ELSW STAYING CLOSER TO THE LOWER CIGS SUGGESTED BY THE NAM BY THIS AFTERNOON GIVEN EASTERLY FLOW ONCE THINGS BECOME SATURATED THIS MORNING. ALSO PERIODS OF MVFR VSBYS LIKELY ESPCLY FROM THE MOUNTAINS EAST INTO THE AFTERNOON...WITH POSSIBLE IFR AT TIMES IN HEAVIER RAIN/FOG NEAR THE BLUE RIDGE...INCLUDING LOCATIONS SUCH AS KBCB/KROA. DESPITE THE EXODUS OF THE WAVE THIS EVENING...LINGERING WEDGE AND DIFFLUENCE ALOFT LIKELY TO KEEP AT LEAST SOME SPOTTY RAIN/DRIZZLE AROUND WHICH MAY HOLD MVFR TO IFR CIGS ALONG WITH FOG IN PLACE UNTIL EARLY SATURDAY MORNING. OTRW WILL HAVE WIDESPREAD IFR CONDITIONS FROM THE BLUE RIDGE EAST OVERNIGHT WITH MVFR AT KBLF AND LIFR LATE AT KLWB DUE TO DENSE FOG. EXTENDED AVIATION DISCUSSION... THE BROAD UPPER TROUGH OF LOW PRESSURE WILL LINGER ACROSS THE EASTERN UNITED STATES THROUGH SUNDAY CONTINUING TO RETROGRADE FROM THE EASTERN/CENTRAL GREAT LAKES TO THE WESTERN GREAT LAKES BY THE WEEKEND. FOR SATURDAY AND SUNDAY...THE AIR MASS WILL SLOWLY BECOME WARMER AND MORE UNSTABLE. SCT SHRA/TSRA EXPECTED AGAIN SATURDAY WITH ONLY LIMITED INSTABILITY EVIDENT. FOR SUNDAY...BETTER CHANCE OF TSRA WITH BETTER INSTABILITY ACROSS MUCH OF THE CWA...SW FLOW ALOFT...AND INCREASING MOISTURE LEVELS. THUS...BRIEF PERIODS OF MVFR-IFR CIGS/VSBYS EXPECTED IN SHRA/TSRA SATURDAY AND MORE LIKELY SUNDAY AFTERNOON. SOME DRYING WITH A RETURN TO OVERALL VFR POSSIBLE MONDAY INTO TUESDAY AS ANOTHER WEAK COOL FRONT SWEEPS IN FROM THE NW AND TAKES MOST MOISTURE TO THE SE OF THE REGION. && .HYDROLOGY... AS OF 330 AM EDT FRIDAY... STEADY LIGHT TO MODERATE RAINFALL WILL SPREAD SLOWLY NORTH THROUGH THE MORNING WITH PERIODS OF HEAVY RAIN POSSIBLE FROM THE SOUTHERN BLUE RIDGE...FOOTHILLS EAST ACROSS THE PIEDMONT. RAINFALL TOTALS OF 1-3 INCHES IS EXPECTED ALONG THE ENHANCED UPSLOPE REGIONS OF THE BLUE RIDGE AND FOOTHILLS MAINLY SOUTH OF ROANOKE WITH A GOOD 1-2 INCHES ELSW OVER THE PIEDMONT SECTIONS OF NORTHWEST NORTH CAROLINA INTO SOUTHSIDE VIRGINIA BY THIS AFTERNOON. GIVEN THE VERY DRY ANTECEDENT CONDITIONS OF LATE AND THE OVERALL LACK OF HEAVIER RAINFALL RATES...WIDESPREAD FLOODING OR FLASH FLOODING IS NOT EXPECTED BUT LOCALIZED SMALL STREAM AND POOR DRAINAGE FLOODING COULD OCCUR ESPCLY WHERE HEAVIER DOWNPOURS ARE REALIZED. RAINFALL TOTALS SHOULD QUICKLY TAPER OFF HEADING INTO FAR WESTERN VIRGINA AND SE WEST VIRGINIA WHERE ONLY UP TO A HALF INCH LOOKS POSSIBLE WITH AN INCH OR MORE LIKELY IN AREAS AROUND LYNCHBURG. && .EQUIPMENT... THE NOAA WEATHER RADIO AT WYTHEVILLE VA...WZ2500...BROADCASTING ON A FREQUENCY OF 162.450 MHZ...IS OFF THE AIR. TECHNICIANS ARE WAITING ON DELIVERY OF PARTS TO MAKE REPAIRS. THE EARLIEST THE RADIO WILL BE WORKING AGAIN IS LATER TODAY. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/NF NEAR TERM...JH SHORT TERM...RCS LONG TERM...AMS AVIATION...JH/NF/WP HYDROLOGY...JH EQUIPMENT...DS

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