Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 211933 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 333 PM EDT THU AUG 21 2014 .SYNOPSIS... 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. && .NEAR TERM /THROUGH FRIDAY/... AS OF 235 PM EDT THURSDAY... DESPITE DECENT INSTABILITY OVER THE REGION THIS AFTERNOON...CONVECTION REMAINS LIMITED VIA WESTERLY WINDS ALOFT AND LOWER THETA-E UNDER FAINT LOW LEVEL RIDGING OVER THE MOUNTAINS. HOWEVER DECENT NW FLOW ALOFT REMAINS IN PLACE WITH ANOTHER UPSTREAM MID LEVEL WAVE APPROACHING FROM OHIO WHICH IS CURRENTLY PRECEDED BY A WEAK OUTFLOW DRIVEN BAND OF SHRA/TSRA. MODELS REMAIN INCONSISTENT IN WHERE TO BRING BEST COVERAGE OF STORMS INTO THIS EVENING BUT APPEARS SOME CONSENSUS ON SPILLING THE CURRENT MCS FEATURE INTO WEST VA THROUGH SUNSET BEFORE IT FADES WITH LOSS OF HEATING. THUS WILL MAINTAIN LOW LIKELY TO HIGH CHANCE POPS FAR NW THIRD GIVEN MORE MORE EAST THAN SE MOVEMENT OF THIS FEATURE...WITH A QUICK DROPOFF IN CHANCES HEADING EAST INTO THE DOWNSLOPING. THIS IMPULSE QUICKLY PASSES/WEAKENS AFTER SUNSET GIVING WAY TO INCREASING NW FLOW ALOFT AHEAD OF ANOTHER SHORTWAVE ROUNDING THE RIDGE LATE. ALTHOUGH FOCUS WILL BE LIMITED AFTER LOSS OF HEATING...SOME CONCERN WITH DEGREE OF LEFTOVER INSTABILITY AND SOME ADDED TSRA DEVELOPMENT AFTER MIXING FADES ESPCLY IF COVERAGE IS LESS EARLY ON. THIS SUPPORTS HOLDING ON TO SOME LOW POPS INTO THE EARLY MORNING HOURS BEFORE INCREASING AGAIN OVER THE WEST TOWARD DAYBREAK AHEAD OF THE NEXT SYSTEM. SOME PATCHY FOG AROUND BUT MAINLY IN THE VALLEYS GIVEN CURRENT MIXING/WARMTH AND OVERNIGHT CLOUDS. OTRW LOWS MAINLY IN THE 60S BUT PERHAPS ONLY LOW 70S EAST IF CLOUDS PERSIST. NEXT WAVE SLIDES DOWN THE RESIDUAL BOUNDARY FRIDAY WITH A POSSIBLE FADING MCS ON THE DOORSTEP ACROSS THE NW EARLY ON BEFORE IT WEAKENS CROSSING THE RIDGES. HOWEVER CONFIDENCE LOW ON THIS OUTCOME GIVEN GUIDANCE UNCERTAINTY BUT DOES APPEAR BETTER COVERAGE IN ORDER ESPCLY NW EARLY AND THEN AGAIN IN THE AFTERNOON AS MAY SEE MORE WIDESPREAD CONVECTIVE BANDS FORM ALONG RESIDUAL OUTFLOW PENDING TIMING. VERY STRONG NW JET ALOFT FOR LATE AUGUST WOULD SUPPORT MORE LINEAR BOWING TYPE STORMS WITH POTENTIAL FOR SOME OF THIS COVERAGE TO CROSS THE BLUE RIDGE DESPITE THE DEEP DOWNSLOPE COMPONENT IF CAN GET ENOUGH BREAKS TO ENHANCE AFTERNOON INSTABILITY. HOWEVER MODELS REMAIN DRIER WITH MORE DEBRIS CLOUDS AROUND IN THE MORNING...AND A MIXED OUT SCENARIO IN THE AFTERNOON WHICH WOULD AGAIN LIMIT POPS TO THE NORTH/NW. THUS TRENDED IN THAT DIRECTION WITH LIKELYS EXTREME NW AND CHANCE ELSW. HIGH TEMPS REMAIN QUITE IFFY AS WARM ENOUGH ALOFT TO ZIP INTO THE 90S EAST GIVEN MORE SUN WHILE COULD GET STUCK IN THE 70S FAR WEST IF SHRA ARRIVES EARLIER AND PERSISTS. FOR NOW USED A BLEND OF THE MAV/MET MOS WITH SUPPORT FROM THE EARLIER SLIGHTLY COOLER EC 2 METER VALUES. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... AS OF 245 PM EDT THURSDAY... SYNOPTIC SCALE PATTERN CHANGING TO A HIGH AMPLITUDE TROF IN THE WEST AND RIDGE IN THE EAST. BY SUNDAY THE 591 DM CENTER OF THE 500 MB RIDGE IS OVER THE TENNESSEE VALLEY. BEST PUSH OF THE COLD FRONT AND DEEPER MOISTURE TO THE SOUTHWEST WILL BE SATURDAY NIGHT AND SUNDAY. UNTIL THEN FORECAST AREA REMAINS IN BAROCLINIC ZONE WITH THE BEST PROBABILITY OF PRECIPITATION DEPENDENT ON UPSTREAM STORMS AND TIMING OF SHORT WAVES. WILL HAVE HIGHEST PROBABILITY OF PRECIPITATION IN FOR FRIDAY NIGHT. AS HIGH PRESSURE BUILDS IN...A SURFACE LOW TRACKS DOWN THE EAST COAST. BY SATURDAY THE LOW WILL BE OVER THE CAROLINA COAST WHICH WILL HELP BRING SURFACE AND LOW LEVEL WINDS OVER THE FORECAST AREA AROUND TO THE EAST. THIS LOW MOVES WELL OFFSHORE AS THE WEDGE STRENGTHENS ON SATURDAY NIGHT AND SUNDAY. SINCE FORECAST AREA WILL BE WELL INTO THE WEDGE ON SUNDAY HAVE KEPT MAXIMUM TEMPERATURES BELOW MOST GUIDANCE. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... AS OF 1130 AM EDT THURSDAY... SURFACE HIGH PRESSURE WILL BE IN A FAVORABLE LOCATION OVER NEW ENGLAND TO WEDGE WELL DOWN THE EAST SLOPES OF THE APPALACHIANS SUNDAY NIGHT AND MONDAY. SUPPORT FOR THE WEDGE WEAKENS BY TUESDAY. HIGH PRESSURE WILL REMAIN OVER THE FORECAST AREA THROUGH WEDNESDAY. WEDNESDAY NIGHT AND THURSDAY A COLD FRONT WILL APPROACH THE AREA. LARGE 500 MB RIDGE ALOFT WILL COVER MUCH OF THE LOWER MISSISSIPPI VALLEY ACROSS THE EASTERN UNITED STATES THROUGH THE PERIOD. THE DEEPEST MOISTURE SHIFTS SOUTHWEST OUT OF THE FORECAST AREA ON MONDAY AND TUESDAY. WILL HAVE THESE DAYS DRY IN THE FORECAST. THE CHANCE OF PRECIPITATION RETURNS TO THE AREA ON WEDNESDAY AND THURSDAY AHEAD OF THE FRONT. EXPECT MAXIMUM TEMPERATURES TO BE WARMEST ON WEDNESDAY AND THURSDAY WITH THE WEDGE GONE AND MORE POTENTIAL TO MIX DOWN WARM 850 MB TEMPERATURES. && .AVIATION /20Z THURSDAY THROUGH TUESDAY/... 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. && .EQUIPMENT... THE ASOS AT LYNCHBURG (LYH) VA REMAINS PARTIALLY INOP DUE TO A BOARD FAILURE. PARTS WILL LIKELY NEED TO BE ORDERED WITH THE RETURN OF COMPLETE SERVICE UNKNOWN AT THIS TIME. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH NEAR TERM...JH SHORT TERM...AMS LONG TERM...AMS AVIATION...JH/PM EQUIPMENT...JH

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