Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 211708 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 108 PM EDT THU AUG 21 2014 .SYNOPSIS...
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A STRONG UPPER LEVEL RIDGE OF HIGH PRESSURE NEAR THE GULF COAST WILL KEEP NORTHWEST FLOW IN PLACE OVER THE REGION THROUGH THE END OF THE WEEK. THIS WILL RESULT IN PERIODIC ROUNDS OF SHOWERS AND STORMS INTO SATURDAY BEFORE A COLD FRONT DROPS THROUGH FROM THE NORTH SATURDAY NIGHT. HIGH PRESSURE FOLLOWING THE FRONT SHOULD BRING DRIER AND COOLER AIR INTO THE AREA BY EARLY NEXT WEEK.
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&& .NEAR TERM /THROUGH TONIGHT/... AS OF 945 AM EDT THURSDAY... NOT A LOT OF CHANGE INTO THE AFTERNOON WITH MORNING SOUNDINGS SHOWING DEEP NW FLOW ACROSS THE REGION AND A WEAK MID LEVEL CAP ALOFT. THIS TRAJECTORY HAS ACTED TO SHIFT THE BEST LOW LEVEL THETA-E TO THE SOUTH/EAST WITH THE RESIDUAL SURFACE BOUNDARY JUST OFF TO THE NE. EXPECT THIS ALONG WITH LACK OF MUCH FOCUS IN AN INCREASING MIXED LAYER ENVIRONMENT TO LIMIT NEAR TERM CONVECTIVE DEVELOPMENT AS THE MAIN FOCUS SHIFTS TO THE NW ALONG THE CONVEYOR BELT OF IMPULSES RIDING OVER THE GULF STATES RIDGE. LATEST SHORT RANGE GUIDANCE STILL REMAINS UNCERTAIN IN THE TIMING/STRENGTH OF THE NEXT WAVE(S) THAT WILL TRAVERSE THE SOUTHERN OHIO VALLEY AND INTO THE MOUNTAINS LATER ON. HOWEVER CONSENSUS SUGGESTS THAT MAY SEE AN OLD MCV SLIP SE TOWARD THE REGION MID/LATE AFTERNOON PRECEDED BY A BROKEN BAND OF STORMS THAT COULD CROSS THE RIDGES INTO EARLY THIS EVENING. THIS SIMILAR TO THE NEW 12Z NAM IN BRINGING MORE ORGANIZED COVERAGE ACROSS THE NORTH AFTER 21Z..WITH SEVERAL OTHER SOLUTIONS HAVING A STRONGER MORE SOUTHWARD SPILLING LINE OF TSRA LATER WITH THE COMPLEX NOW OVER INDIANA. THUS KEEPING MAINLY WESTERN HIGHER CHANCE POPS WHILE TWEAKING DOWN CHANCES EAST UNTIL LATER AS BEST COVERAGE MAY NOT ARRIVE UNTIL EARLY EVENING. OTRW WILL SEE MUCH BETTER HEATING WITH ONLY THE FAR NW LIKELY TO GET CLIPPED BY EARLY CLOUDS SPILLING ACROSS WEST VA AHEAD OF A WEAKENING INITIAL WAVE. GIVEN 85H TEMPS WARMING TO AROUND 20C COMBINED WITH DOWNSLOPE AND PLENTY OF INSOLATION ELSW SUPPORTS HIGHS INTO THE 90S EAST WITH 80S WEST FOR THE MOST PART. PREVIOUS VALID DISCUSSION... IN SPITE OF THE BUSY LOOKING SYNOPSIS...NOT MUCH HAPPENING ACROSS OUR AREA EARLY THIS MORNING. THERE WAS SOME PATCHY FOG AND STRATUS...BUT A DENSE AREA OF CIRRUS MOVED OVERHEAD DURING THE OVERNIGHT LIMITING RADIATIVE EFFECTS THUS PREVENTING FOG FROM BECOMING DENSE. ANY FOG/STRATUS SHOULD QUICKLY DISPERSE AFTER SUNRISE. SHALLOW EASTERLY SURFACE WINDS THIS MORNING WILL GIVE WAY TO WEST NORTHWEST WINDS LATER THIS MORNING AND DURING THE AFTERNOON. THE LOW LEVEL WIND FLOW WILL BE FROM THE NORTHWEST TODAY...WINDS 7-14 MPH...AND GUSTY NEAR THE RIDGE CRESTS. THE DEEPER FLOW...WELL ALOFT...IS ALSO FROM THE NORTHWEST. THIS WILL TRANSPORT DEBRIS CLOUDINESS DOWNSTREAM FROM THUNDERSTORMS OVER THE MIDWEST AND OHIO VALLEY REGIONS...CLOUD LAYERS MAINLY ABOVE 10KFT. WITH WINDS OUT OF THE WEST TODAY...THIS WILL CREATE DOWNSLOPE COMPRESSIONAL WARMING AND SUBSIDENCE. DO NOT EXPECT MUCH IN THE WAY OF LOCAL STORM DEVELOPMENT DUE TO THIS DOWNWARD VERTICAL MOTION. PRIMARY AREA TO WATCH FOR THUNDERSTORM DEVELOPMENT WILL BE VCNTY OF STALLED FRONTAL BOUNDARY OVER THE OHIO VALLEY. STORMS WHICH DEVELOP VCNTY OF THIS BOUNDARY...ACROSS IL/IN/OH/KY...WILL MOVE DOWNSTREAM TOWARD THE MID ATLANTIC REGION THIS EVENING AND DURING THE OVERNIGHT TONIGHT. HIGHEST CONFIDENCE FOR STORMS THIS AFTERNOON WILL BE FROM WEST VIRGINIA INTO THE OHIO VALLEY...THE THREAT TRANSITIONING DOWNSTREAM INTO VIRGINIA AND NORTH CAROLINA TONIGHT. HELD OFF ON ANY SIGNIFICANT CHANCE OF PRECIP EAST OF THE BLUE RIDGE UNTIL AFTER 4PM. STORMS WHICH DEVELOP OVER THE OHIO VALLEY MAY BECOME ORGANIZED INTO AN MCS...MESOSCALE CONVECTIVE COMPLEX. IF THIS OCCURS...THIS COULD TRANSLATE INTO A SEVERE THREAT FOR OUR FCST AREA...THE PRIMARY THREAT BEING WIND. TEMPERATURES TODAY WILL GET A BOOST BY THE RELATIVELY STRONG DOWNSLOPE WESTERLY WIND...READINGS TESTING 90 ROA/LYH/DAN...AND WELL INTO THE 80S ACROSS THE MTNS. THE GFS MODEL INDICATES QUITE A BIT OF DEBRIS CLOUDINESS DEVELOPING IN ADVANCE OF THE STORM ACTIVITY OVER THE OHIO VALLEY...SO THIS MAY INHIBIT FULL SENSIBLE HEATING. NEVER THE LESS...LOOKING AT A WARM AFTERNOON... TEMPERATURES RESEMBLING SOMETHING MORE TYPICAL OF AUGUST. WITH CLOUDS AROUND TONIGHT...READINGS SHOULD NOT FALL MUCH BELOW 70... WITH A RANGE OF 65 TO 70 FITTING PRETTY MUCH THE ENTIRE CWA. && .SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/... AS OF 400 AM EDT THURSDAY... THIS PORTION OF THE FORECAST PERIOD CONTINUES TO OFFER AN ACTIVE WEATHER REGIME. STILL ON FRIDAY...THE AREA WILL BE BETWEEN HIGH PRESSURE TO OUR WEST AND LOW PRESSURE OFF THE COAST OF NEW ENGLAND. A BAROCLINIC ZONE OVER THE REGION ITSELF WILL LEAD TO AT LEAST ISOLATED TO SCATTERED COVERAGE OF SHOWERS AND AFTERNOON AND EVENING THUNDERSTORMS. HOWEVER...THE PRESENCE OF PERIODIC SHORTWAVE TROUGHS RIDING SOUTHEAST ALONG THIS BOUNDARY THROUGH SATURDAY WILL GIVE SOME PARTS OF OUR REGION LIKELY TO CATEGORICAL COVERAGE OF PRECIPITATION...SOME OF WHICH COULD BE LOCALLY HEAVY. THE PAST FEW DAYS...GUIDANCE HAS PRESENTED A CORNUCOPIA OF SOLUTIONS REGARDING TIMING AND TRACK OF THESE IMPULSES OVER OR NEAR OUR REGION. THE OFFERINGS BY THE 00Z/8PM MODEL RUNS ARE NOT MATCHING EXACTLY...BUT THEY CONTINUE TO POINT TOWARDS A CONSENSUS THAT THEIR EARLIER COUNTERPARTS ALSO HAD BEEN NOTING. FRIDAY AFTERNOON INTO FRIDAY EVENING...OR OVERNIGHT...IS A TIME WORTH WATCHING FOR ONE SUCH MORE ORGANIZED CLUSTER OF SHOWERS AND STORMS IMPACTING THE AREA. THE FOCUS FOR LOCATION IS THE WESTERN AND NORTHERN PARTS OF THE REGION. ANOTHER TIME TO WATCH IS DURING THE AFTERNOON ON SATURDAY. A BACKDOOR COLD FRONT WILL HAVE STARTED TO ENTER THE REGION AND PROGRESS TO THE WESTERN PARTS OF THE AREA BY THE AFTERNOON. ITS POSITION THERE WILL ADD A GREATER FOCUS TO COVERAGE OF SHOWERS AND STORMS DURING THE PEAK HEATING OF THE DAY. ONCE WE PROGRESS INTO SATURDAY NIGHT...AND THROUGH SUNDAY NIGHT...THIS BACKDOOR COLD FRONT WILL HAVE CONTINUED ITS PUSH WESTWARD THROUGH ALL...OR MOST OF THE REGION. MODEL CONSENSUS PLACES IT ALONG A N-S ORIENTATION FROM ROUGHLY THE GREAT SMOKY MOUNTAINS NORTH INTO THE COAL COUNTRY OF EASTERN KENTUCKY. THIS TRANSITION WILL PLACE MOST OF OUR REGION WITHIN A MOIST LOW LEVEL EASTERLY FLOW THAT WILL KEEP THE AREA STABLE...SOCKED IN WITH CLOUDS...COOLER...WITH EITHER LIGHT RAIN OR DRIZZLE....ESPECIALLY SUNDAY INTO SUNDAY NIGHT. THE EXCEPTION TO THIS RULE MAY BE AREAS SUCH AS TAZEWELL...RICHLANDS...AND MARION VIRGINIA. THIS AREA MAY BE UNDER...OR CLOSE ENOUGH TO THE FRONT...FOR MILDER TEMPERATURES...A BIT OF INSTABILITY...WITH SHOWERS AND A FEW STORMS. TEMPERATURES THROUGH THE PERIOD WILL TREND COOLER DURING THE PERIOD...ESPECIALLY BY SUNDAY. ON SUNDAY HAVE GONE WITH HIGH TEMPERATURES AROUND 10 DEGREES BELOW GUIDANCE FOR MOST LOCATIONS. THE EXCEPTION BEING CLOSER TO RICHLANDS WHERE THE FORECAST WILL REFLECT NUMBERS AROUND GUIDANCE. && .LONG TERM /MONDAY THROUGH WEDNESDAY/... AS OF 300 PM EDT WEDNESDAY... LARGE UPPER RIDGE BUILDS FROM THE LOWER MISSISSIPPI VALLEY. 500 MB HEIGHTS OVER THE FORECAST AREA BEGIN TO RISE ON TUESDAY WITH THE RIDGE CENTERED OVER THE TENNESSEE VALLEY. SURFACE HIGH PRESSURE WILL BE OVER NEW ENGLAND AND WEDGED DOWN THE APPALACHIANS THROUGH TUESDAY. BY THURSDAY A STRONG BERMUDA HIGH WILL BE IN PLACE. CHALLENGING TO TIME SHORT WAVES COMING OVER THE TOP OF THE RIDGE. WPC WAS FAVORING A BLEND OF ENSEMBLE GFS AND ECMWF THROUGH THE PERIOD. THIS KEEPS FORECAST AREA IN A PERSISTENT CHANCE OF PRECIPITATION THROUGH MONDAY NIGHT. AT THIS TIME WILL BE EMPHASIZING SUNDAY NIGHT AS THE BEST CHANCE IN THIS TIME FRAME. WILL BE WARMING UP CLOSER TO ABOVE NORMAL TEMPERATURES ASSOCIATED WITH THE UPPER RIDGE ON WEDNESDAY. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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AS OF 1245 PM EDT THURSDAY... OVERALL VFR TO PREVAIL THROUGH MUCH OF THE AFTERNOON UNDER WEAK HIGH PRESSURE AND NW FLOW ALOFT. WILL GRADUALLY SEE CU FIELDS INCREASE AS WELL AS ISOLATED CONVECTION FROM WEST TO EAST BUT THINKING CIGS TO REMAIN VFR OUTSIDE OF ANY WESTERN SHRA/TSRA. APPEARS BEST CHANCE AT SEEING A TSRA EARLY WILL BE AROUND KBLF WITH UPSTREAM COVERAGE APPROACHING...AND THEN MID/LATE AFTERNOON AT KLWB. FARTHER EAST...LOTS OF UNCERTAINTY IN HOW FAR ANY ISOLATED EARLY COVERAGE MIGHT GET AND THEN WHETHER OR NOT SOMETHING MORE ORGANIZED DEVELOPS OVER WV/OH AND TRANSLATES SE...CROSSING MUCH OF THE REGION THIS EVENING. LATEST GUIDANCE KEEPS THE MAJORITY TO THE WEST AND NORTH PER LACK OF CONSOLIDATION OF SHRA/TSRA. FOR NOW PLAN TO KEEP AT LEAST A TEMPO MENTION FOR A PERIOD OF MVFR IN TSRA FOR THE WV TERMINALS BETWEEN 19-21Z/3-5PM THEN INTO THE VA TERMINALS BETWEEN 21-24Z/5-8PM. GUSTY WINDS ALSO POSSIBLE WITH ANY OF THE STORMS PER INVERTED V TYPE SOUNDINGS SO INCLUDED MENTION. EXPECT WILL GET A BREAK IN STORMS BY MIDNIGHT FOR THE MOST PART BEFORE ANOTHER IMPULSE APPROACHES EARLY FRIDAY IN THE INCREASING NW FLOW ALOFT. SHOULD AGAIN SEE AREAS OF MVFR/IFR IN FOG PENDING DEGREE OF CLOUD COVER LATE WITH THE WORST CONDITIONS AGAIN AT KLWB AND ANY SPOT THAT SEES A DOWNPOUR THROUGH THIS EVENING. GIVEN THE STRONGER FLOW ALOFT...ADDED SHRA COULD DEVELOP BEFORE DAWN WEST AND STREAM SE ESPCLY ALONG THE KBLF-KDAN CORRIDOR FRIDAY MORNING SO INCLUDED A VCSH IN THOSE LOCATIONS FOR NOW. ELSW APPEARS LOTS OF MVFR/VFR STRATO-CU CIGS UNDER MID DECK WHICH SHOULD SLOWLY ERODE INTO VFR DURING THE AFTERNOON AFTER EARLY FOG FADES. EXTENDED AVIATION... UPPER LEVEL DISTURBANCES WILL BE MOVING THROUGH PERIODICALLY AND INTERACTING WITH A STATIONARY FRONT OVER THE AREA FOR THE NEXT FEW DAYS...RESULTING IN PERIODS OF SHOWERS AND THUNDERSTORMS. DUE TO THE HIGH MOISTURE CONTENT OF THE AIR...EXPECT STRATUS AND FOG DURING THE OVERNIGHT PERIODS WITH AREAS OF MVFR/IFR MOST PRONOUNCED BETWEEN MIDNIGHT AND 9AM EACH DAY. MODELS ARE INDICATED THAT A DEEPER EASTERLY SORT OF WIND FLOW WILL SETUP FOR THIS UPCOMING WEEKEND. THIS SUGGEST THAT LOW CIGS MAY PERSIST EVEN DURING THE DAYTIME PERIODS...SATURDAY AND SUNDAY...WITH WIDESPREAD MVFR CONDITIONS ACROSS THE AREA THIS WEEKEND DUE TO MOISTURE BANKING UP AGAINST THE EAST SIDE OF THE APPALACHIANS. BETTER PUNCH OF DRY AIR WITH HIGH PRESSURE BUILDING IN FROM THE NE MAY BE ENOUGH WITH MIXING/HEATING TO ALLOW FOR INCREASING VFR MONDAY INTO TUESDAY UNDER MAINLY DRY CONDITIONS.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH NEAR TERM...JH/PM SHORT TERM...DS LONG TERM...AMS AVIATION...JH/PM

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