Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 201656 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1256 PM EDT SUN JUL 20 2014 .SYNOPSIS...
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A WEAK WEDGE OF HIGH PRESSURE WILL REMAIN OVER THE AREA THIS AFTERNOON BEFORE SLIDING OFF THE MID ATLANTIC COAST OVERNIGHT. A RESIDUAL WEAK FRONTAL BOUNDARY AND UPPER DISTURBANCE ACROSS THE CAROLINAS WILL LIFT SLOWLY NORTH INTO THE REGION EARLY NEXT WEEK. THIS WILL RESULT IN CONTINUED UNSETTLED WEATHER INTO MID WEEK AHEAD OF A STRONGER COLD FRONT THAT IS EXPECTED TO ARRIVE ON THURSDAY.
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&& .NEAR TERM /THROUGH TONIGHT/... AS OF 930 AM EDT SUNDAY... WEAK WEDGE OF COOL AIR REMAINS IN PLACE EARLY THIS MORNING BUT NOT AS STRONG AS SATURDAY GIVEN LACK OF RE-ENFORCING PRECIP...WITH EVEN SOME BREAKS SHOWING UP JUST WEST OF THE NEW RIVER VALLEY. THIS MAY ALLOW FOR A PERIOD OF SUNSHINE ESPCLY FAR SW VA INTO SE WVA WHERE LACK OF LOW CLOUDS BEFORE THE FAINT SHORTWAVE NOW WEST OF THE MOUNTAINS SLIDES EAST LATER IN THE DAY AND CAUSES CLOUDS/SHRA TO FILL BACK IN. LATEST GUIDANCE ALSO SHOWS SOME WIDELY SCTD SHRA/TSRA DEVELOPMENT MOUNTAINS WITH THIS FEATURE ESPCLY AFTER 18Z WHEN MODELS INDICATE SOME MODEST 1000-1500 J/KG CAPE OVER THE FAR WEST. THEREFORE CUT BACK ON POPS TO INIT BASED ON CURRENT RADAR TRENDS AND ADDED IN A BIT MORE TSRA I-77 CORRIDOR LATER ON PER LATEST HRRR AND NCEP WRF. CANT TOTALLY RULE OUT ISOLATED -TSRA SE PIEDMONT BUT APPEARS LACK OF MUCH INSTABILITY AND BETTER LIFT REMAINING SOUTH CLOSER TO THE OLD FRONT SHOULD PRECLUDE MUCH MORE THAN SHOWERS AT THIS POINT. OTRW KEEPING SLIGHT TO CHANCE POPS WITH HIGHEST ENDING UP FAR WEST LATER ON AND LEAST ACROSS THE NE UNDER THE WEAKENING WEDGE. EVEN WITH SOME SUN...COOLER MET MOS TEMPS STILL LOOK BEST SO KEPT VALUES CLOSE TO THE CURRENT FORECAST WHICH KEEPS MOST IN THE 70S...ALTHOUGH THE NW NC BLUE RIDGE SPOTS MAY STRUGGLE IN THE 60S MOST OF THE DAY. PREVIOUS VALID DISCUSSION... UPPER LEVEL TROUGH OVER THE EASTERN U.S. WILL REMAIN IN PLACE TODAY AND TONIGHT WITH WEAK RIDGING FROM NEW ENGLAND CONTINUING TO MAINTAIN A WEAK EASTERLY LOW-LEVEL WIND COMPONENT INTO THE MID- ATLANTIC AND CENTRAL APPALACHIANS PRODUCING SUBTLE COOL-AIR DAMMING. WITH VERY LITTLE FORCING EXPECTED AT THE SURFACE AND ALOFT THERE SEEMS TO BE LITTLE OBVIOUS TRIGGER FOR SHOWER ACTIVITY BUT THE AIR MASS THE OVERHEAD WILL REMAIN QUITE MOIST WITH PWATS HOLDING NEAR 1.5 INCHES ACROSS MOST OF THE CWA...00Z/20 RAOB FROM KRNK HAD 1.48 INCHES WHICH IS ABOUT THE 75TH PERCENTILE FOR DATE IN JULY...ALSO RIGHT AT THE CLIMATOLOGICAL MAXIMA FOR THE YEAR. THAT SAID THE QUESTION REMAINS WHETHER WE CAN DEVELOP ANY CONVECTION AT ALL TODAY AND THAT MAY DEPEND ON SOME BREAKS IN THE PERSISTENT OVERCAST. BEST CHANCES FOR ANY SHOWERS OR EVEN A THUNDERSTORM TO DEVELOP WILL BE IN FAR WEST WHICH WILL BE LESS UNDER THE INFLUENCE OF THE WEDGE. MODEL CAPES FROM ARW_RNK REACH 1000 J/KG BY LATE AFTERNOON AT BLUEFIELD SO PUT ISOLATED THUNDER CHANCES IN THE WEST ALONG WITH CHANCE POPS GENERALLY FROM BLUE RIDGE WESTWARD AND ONLY SLIGHT CHANCE EAST. BEST SYNOPTIC FORCING FOR PRECIPITATION WILL BE WELL SOUTH OF OUR CWA IN ASSOCIATION WITH SHORT-WAVE AND WEAK LOW DOWN ALONG THE GULF COAST. SOME OF THIS ACTIVITY MAY REACH OUR SOUTHERN COUNTIES BUT AMOUNTS SHOULD BE QUITE MODEST...GENERALLY UNDER 0.25 INCHES ON A MEAN AREAL BASIS. TEMPS TRICKY AS WELL TODAY WITH CLOUDS/JULY SUN GAME IN FULL SWING. USED MODEL BLEND BUT A FEW HOURS OF EXTRA HEATING COULD PLAY HAVOC WITH CURRENT MID-70S WEST TO LOW 80S EAST FORECAST. && .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/... AS OF 430 AM EDT SUNDAY... FOCUS THROUGH THIS PERIOD WILL EVOLVE AROUND A PERSISTENT TROUGH ALONG THE SOUTHEAST U.S. COAST LEFT BEHIND FROM THE CURRENT UPPER TROUGH AS IT LIFTS OUT. WITH TIME...THIS SYSTEM ASSUMES A PSEUDO TROPICAL CHARACTERISTIC AND DRIFTS SLOWLY NORTHWESTWARD AS A MAMMOTH UPPER RIDGE BUILDS ACROSS THE WESTERN U.S. AND RIDGES EASTWARD TOWARD THE GREAT LAKES WHILE ANOTHER UPPER RIDGE AMPLIFIES IN THE WEST ATLANTIC. THIS WILL FORCE THIS FEATURE TO RETROGRADE FROM THE GA/SC COAST NORTHWESTWARD TOWARD THE SOUTHERN APPALACHIANS THROUGH THE PERIOD. FINALLY...THE LONG RANGE MODELS HAVE COME INTO REASONABLY GOOD AGREEMENT ON THE EVOLUTION AND TRACK OF THIS SYSTEM. AS THIS SYSTEM DRIFTS NORTHWEST TOWARD THE REGION DURING THE FIRST HALF OF THE WEEK...PWS WILL RISE TO NEAR 2.0 INCHES. THIS ALONG WITH INCREASING HEAT AND INSTABILITY SHOULD SUPPORT AN INCREASE IN DIURNAL CONVECTION. THE BEST CHANCES FOR SUCH SHOULD REMAIN FOCUSED ACROSS NW NC/FAR SW VA WHERE MOIST SOUTHEAST UPSLOPE FLOW WILL BE ENHANCED ALONG THE BLUE RIDGE. EXPECT SCATTERED DIURNAL CONVECTION AREA WIDE...WITH NUMEROUS AFTERNOON/EVENING SHRA/TSRA ACROSS NW NC AND FAR SW VA THROUGH THE PERIOD. CONSEQUENTLY...HAVE ADVERTISED HIGH CHC TO LOW LIKELY POPS IN THESE AREAS THROUGH THE PERIOD DURING THE AFTERNOON HOURS. FOR MUCH OF THE AREA THIS WILL RESULT IN INCREASING CHANCES OF BENEFICIAL RAIN...BUT SLOW MOVING/TRAINING THUNDERSTORMS...ESPECIALLY ACROSS THE MOUNTAINS TERRAIN OF NW NC/FAR SW VA COULD BECOME MORE PROBLEMATIC AS THE WEEK PROGRESSES. ALTHOUGH INSTABILITY WILL BE HIGH...DYNAMICS/SHEAR ARE WEAK. HOWEVER...AN ISOLATED PULSE SEVERE WITH STRONG WIND GUSTS COULD NOT BE COMPLETELY RULED OUT THROUGH THE PERIOD ANYWHERE IN THE CWA FOR THAT MATTER. 850MB TEMPS WILL BE ON THE INCREASE AS HEIGHTS ALOFT RISE AS WELL. HOWEVER...INCREASING DEWPOINTS/PWS AND PERSISTENT TROUGHINESS ACROSS THE REGION WILL TEMPER ANY EXCESSIVE HEAT AND SHOULD KEEP MOST AREAS IN THE 80S FOR HIGHS...70S IN THE MOUNTAINS...NEAR 90 ACROSS THE PIEDMONT. WEDNESDAY WILL BE THE WARMEST DAY IN ADVANCE OF THE FRONT/UPPER TROUGH APPROACHING FROM THE NORTHWEST. && .LONG TERM /THURSDAY THROUGH SATURDAY/... AS OF 445 PM EDT SATURDAY... UPPER RIDGE IS FORECAST TO REMAIN OVER THE WESTERN CONUS THROUGH THE LONG TERM...WITH A PERSISTENT UPPER TROUGH OVER THE EASTERN CONUS. A STRONG SHORT WAVE TRACKS FROM SOUTH CENTRAL CANADA ATOP THE UPPER RIDGE TOWARD THE GREAT LAKES. THIS DRIVES A FRONTAL SYSTEM INTO THE EASTERN U.S. AND OUR REGION BY THURSDAY. ECMWF/GFS ARE IN REASONABLE AGREEMENT ON THE PROGRESSION AND TIMING OF THESE FEATURES. THE FRONT SHOULD PUSH JUST SOUTH OF THE AREA BY FRI...ALTHOUGH AT THIS TIME OF YEAR THERE IS ALWAYS SOME UNCERTAINTY AS TO HOW FAR SOUTH THE FRONT WILL GO BEFORE STALLING. THE STRENGTH OF THE NORTHWEST FLOW ALOFT IN OUR REGION OWING TO THE STRONG UPPER RIDGE OUT WEST SHOULD SUPPORT THE FRONT PUSHING SOUTH OF THE CWA AT A MINIMUM. THE GREATEST CHANCE FOR SHOWERS/STORMS WILL BE THURSDAY AND THERE IS SOME CHANCE THAT THE LINGERING PSEUDO TROPICAL SYSTEM ACROSS THE CENTRAL/SOUTHERN APPALACHIANS AND ASSOCIATED MOISTURE COULD ENHANCE SHRA/TSRA CHANCES ALONG THE FRONT. FRIDAY STILL LOOKS LIKE A DRY DAY WITH THE FRONTAL BOUNDARY SOUTH OF THE CWA. MOISTURE COULD RETURN TO WESTERN AREAS BY SAT...BUT HAVE KEPT POPS LOW AT THIS POINT WITH TOO MUCH UNCERTAINTY ON ANY UPSTREAM NW FLOW DISTURBANCES. AFTER A VERY WARM DAY WED...THURSDAY WILL BE A TRANSITION DAY WITH THE FRONTAL PASSAGE...FOLLOWED BY A 4 TO 7 DEGREE DOWNWARD TREND IN TEMPERATURES FOR FRIDAY AND SATURDAY. USED A GFS/ECMWF MOS MODEL BLEND THROUGH THE PERIOD. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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AS OF 1235 PM EDT SUNDAY... WEDGE WILL CONTINUE TO KEEP LOWER MVFR CIGS LOCKED IN OVER THE WESTERN LOCATIONS THIS AFTERNOON WITH GRADUAL IMPROVEMENT TO VFR UNDER SOME BREAKS IN THE EAST. EXPECT MOST SHOWERS TO REMAIN CONFINED TO THE KBLF/KLWB AREAS THIS AFTERNOON WITH PERIODS OF MVFR POSSIBLE INCLUDING AN ISOLATED -TSRA AS WEAK INSTABILITY DEVELOPS AND A WEAK WAVE ALOFT CROSSES. OTRW OTHER THAN A VICINITY MENTION...KEEPING SHRA OUT OF THE TAFS THE REST OF THE AFTERNOON UNDER A LIGHT SE WIND. IMPULSE PASSES TO THE NORTH LATER TONIGHT WHICH SHOULD HELP TAPER OFF ANY SIGNIFICANT LEFTOVER SHRA OVER THE WEST OVERNIGHT. HOWEVER CONTINUED SE FLOW COMBINED WITH DEEP MOISTURE BETWEEN THE SFC-7H WILL CAUSE CIGS TO AGAIN LOWER...WITH WIDESPREAD MVFR EXPECTED ESPCLY AFTER MIDNIGHT. COULD ALSO SEE PERIODS OF IFR/LIFR AT KLWB AND ALONG THE BLUE RIDGE WHERE SOME PATCHY -DZ AND FOG POSSIBLE. ISOLATED SHRA MAY TEND TO LIMIT LOWER CLOUD FORMATION ACROSS THE SE AS WELL AS AROUND KBLF WHERE WILL SEE WEAK DOWNSLOPING. WAVE TO THE SOUTH WILL CAUSE THE FLOW TO TURN MORE EASTERLY ON MONDAY ALLOWING THE WEDGE TO ENHANCE A BIT MORE. THIS MAY KEEP AT LEAST MVFR CIGS AROUND ESPCLY BLUE RIDGE WEST INTO THE AFTERNOON BUT EXPECT MOST SHOWERS TO BE CONFINED TO SOUTHERN AREAS MAINLY KTNB-KUKF TO KDAN. MORE BREAKS ALONG WITH VFR EXPECTED A BIT SOONER ACROSS THE NORTH ALONG THE KLWB-KLYH CORRIDOR BY MONDAY AFTERNOON WITH A MIX OF MVFR/VFR AT KBCB/KROA TO KBLF LIKELY. EXTENDED AVIATION DISCUSSION... UPPER SYSTEM IN THE BASE OF THE FADING SE TROUGH WILL WEAKEN AND LIFT NORTH TUESDAY INTO WEDNESDAY IN ADVANCE OF AN APPROACHING COLD FRONT FOR THU. THIS WILL RESULT IN MORE WIDESPREAD DIURNAL CONVECTION EACH DAY WITH EARLY FOG IN SPOTS GIVING WAY TO BRIEF VFR...THEN PERIODIC MVFR IN CLOUDS/SHRA EACH AFTERNOON/EVENING. A COLD FRONT LOOKS TO PUSH THROUGH ON THURSDAY WITH BETTER COVERAGE OF MVFR/IFR PRODUCING SHOWERS AND STORMS. IMPROVED AVIATION CONDITIONS ARE EXPECTED FRIDAY BEHIND THE FRONT WITH CLEARING SKIES AND LITTLE TO NO PRECIPITATION...EXPECT POSSIBLY KDAN.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/PC NEAR TERM...JH/PC SHORT TERM...RAB LONG TERM...PM/RAB AVIATION...JH/PC/RAB

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