Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 010840 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 440 AM EDT WED JUL 1 2015 .SYNOPSIS... A FRONTAL ZONE WILL REMAIN DRAPED ACROSS THE AREA FOR THE NEXT SEVERAL DAYS. WAVES MOVING ALONG THIS FRONTAL ZONE WILL KEEP A CHANCE OF SHOWERS AND THUNDERSTORMS IN OUR FORECAST THROUGH THE WEEKEND. HIGH PRESSURE MOVING IN FROM THE UPPER MIDWEST ON SUNDAY MAY FINALLY NUDGE THE FRONT FAR ENOUGH TO OUR SOUTH AND EAST TO BRING SOME DRIER WEATHER TO THE REGION FOR THE FIRST PART OF NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 400 AM EDT WEDNESDAY... AN UPPER LEVEL TROF WILL REMAIN OVER THE EASTERN US AS IMPULSES OF SHORT WAVE ENERGY ROTATE THROUGH THE FLOW. THIS WILL DRIVE A LOW PRESSURE SYSTEM FROM THE GREAT LAKES REGION IN TO CANADA AND KEEP A FRONTAL ZONE MEANDERING ACROSS THE REGION. THIS WILL SERVE AS A TRIGGER FOR CONVECTION TODAY...BUT INSTABILITY AND SHEAR ARE LIMITED SO IT LOOKS LIKE GENERAL THUNDERSTORMS WILL BE THE RULE WITH STRONGER ACTIVITY CONFINED TO LOCATIONS FURTHER TO THE SOUTHWEST AS PER THE LATEST SPC DAY 1 OUTLOOK. PRECIPITABLE WATER VALUES ARE NOT EXTREME TODAY SO DO NOT ANTICIPATE ANY HYDRO ISSUES TO DEVELOP. BELIEVE ACTIVITY WILL INITIALLY EXHIBIT A DIURNAL TREND AND START TO TAPER OFF AFTER SUNSET...BUT MODEL GUIDANCE IS KEEN ON THE IDEA OF SLIDING ANOTHER IMPULSE ALONG THE FRONTAL ZONE AND INTO THE AREA LATE TONIGHT. WHILE WATER VAPOR IMAGERY DOES INDEED SUPPORT THE NOTION OF A SERIES OF SHORT WAVES...CONFIDENCE IS LOW AS TO WHETHER OR NOT ONE OF THESE WILL KICK OFF AN MCS THAT WILL BRING WIDESPREAD SHOWERS/THUNDER TO THE REGION TONIGHT. FOR NOW WILL GO WITH A WETTER SOLUTIONS AND RAISE POPS BACK UP TO HIGH CHC/LOW LIKELY WEST OF THE BLUE RIDGE IN ANTICIPATION OF AN MCS REMNANT MOVING IN. WILL HAVE TO TAKE A LOOK AT THE MESO MODELS LATER TODAY TO SEE IF THESE POPS CONTINUE TO LOOK VALID. EXPECTING TEMPS TO BE RIGHT AROUND NORMAL WITH READINGS NEAR 90 PIEDMONT/SOUTHSIDE TO LOWER 80S IN THE MOUNTAINS FOR HIGHS...COOLING TO UPPER 60S EAST/LOWER 60S WEST FOR LOWS TONIGHT. && .SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/... AS OF 415 AM EDT WEDNESDAY... BROAD TROUGHING CONTINUES THROUGH THE PERIOD WITH NUMEROUS EMBEDDED DISTURBANCES TRACKING THROUGH THE BASE OF THE TROUGH ROUGHLY ON A PERISTENT TRAJECTORY FROM THE NORTHERN PLAINS SOUTHEASTWARD THROUGH THE MO/TN VALLEY INTO THE SOUTHERN APPALACHIANS AND SOUTHEAST STATES. THIS PATTERN WILL CERTAINLY SUPPORT CONTINUED MESOSCALE CONVECTIVE COMPLEXES AS IT HAS THE PAST COUPLE OF DAYS. HOWEVER...THERE ARE SUBTLE DIFFERENCES AMONG THE MODELS AS TO THE EXACT TRACK AND TIMING OF THE PROJECTED MESOSCALE CONVECTIVE...WHICH LEADS TO LOW CONFIDENCE IN THE POP FORECAST AND TO A LESSER EXTENT THE TEMPERATURE FORECAST. IN ADDITION...MODELS PROJECT ASSOCIATED RAINFALL/QPF AT ALL HOURS OF THE DAY AND NIGHT...WHICH IS MOST LIKELY NOT THE SCENARIO THAT WILL PLAY OUT. GIVEN THE TIME OF YEAR...DIURNAL HEATING AND THE NORMAL DIURNAL CYCLE OF PRECIPITATION CAN BE EXPECTED DESPITE THE MODEL PROJECTIONS. IT DOES APPEAR MORE LIKELY THAT THE SOUTHWEST PART OF THE CWA HAS A BETTER CHANCE OF SEEING REPEATED MCS ACTIVITY THROUGH THE PERIOD THAN DOES THE NORTHEAST...BUT A SLIGHT CHANGE IN THE PATH/TIMING WOULD RENDER THIS THEORY LESS ACCURATE. OVERALL...THERE IS A TENDENCY FOR THE BAROCLINIC ZONE TO SHIFT SOUTH MORE INTO AL/GA/SC BY THE WEEKEND. AT THIS POINT...THE BEST DYNAMICS AND INSTABILITY APPEAR TO TRACK ACROSS THE REGION FRIDAY...WHICH CORRESPONDS WITH THE ONLY PERIOD IN WHICH SPC CURRENTLY HAS MORE THAN JUST A TINY CORNER OF THE CWA IN A MARGINAL RISK. BOTH THURSDAY AND FRIDAY THERE APPEARS TO BE SOME CHANCE FOR A REMNANT MCS TO BE DRIFTING INTO THE REGION AT DAYBREAK...WHICH LEAVES CONSIDERABLE QUESTION AS TO HOW MUCH INSTABILITY AND REDEVELOPMENT OF CONVECTION WILL TAKE PLACE LATER IN THE DAY IF CLOUD COVER...PRECIPITATION...AND COOLER TEMPERATURES LINGER. INSTABILITY PROGS ARE MEAGER AT BEST THROUGH MUCH OF THE PERIOD AND THE BEST SHEAR AXIS REMAINS TO OUR SOUTHWEST. SO OVERALL...CONFIDENCE IS QUITE LOW IN THE POP FORECAST OTHER THAN TO SAY THAT PRECIPITATION AND CONVECTION IS LIKELY WITHIN AT LEAST 12 HOUR BLOCKS EACH DAY. TRACK AND TIMING WILL ONLY BE POSSIBLE AS THESE EVENTS MOVE INTO THE NEAR TERM. FOR THIS REASON...HAVE GENERALLY CAPPED POPS IN THE 50-60 PERCENT RANGE DAYTIME AND 30-40 PERCENT RANGE NIGHTTIME...WITH THE HIGHEST POPS THROUGH MUCH OF THE TIME FRAME FOCUSED ACROSS THE SOUTHWEST...MORE LIKELY TO BE WITHIN THE PATH OF PROJECTED CONVECTIVE COMPLEXES. 850MB TEMPS HOVER IN THE +12C TO +16C RANGE NORTH TO SOUTH THROUGH MOST OF THE PERIOD. THIS...COMBINED WITH THE EXPECTED CLOUD COVER AND PRECIPITATION WILL HOLD MAX TEMPS SLIGHTLY BELOW NORMAL...BUT MIN TEMPS ABOVE NORMAL. && .LONG TERM /SUNDAY THROUGH TUESDAY/... AS OF 430 AM EDT WEDNESDAY... THE PERSISTENT UPPER TROUGH DURING THE SHORT TERM PERIOD BEGINS TO SHEAR OUT AND LIFT NORTHEAST DURING THE LONG TERM AS UPPER HEIGHTS BEGIN TO RISE IN RESPONSE TO BROAD UPPER RIDGING EXTENDING FROM THE SOUTHWEST/SOUTH CENTRAL U.S. INTO THE NORTHEAST U.S. THE TAIL END OF THE PRIOR UPPER TROUGH APPEARS DESTINED TO BECOME CUTOFF ACROSS THE SOUTHEAST STATES. THIS PERIOD SHOULD BE CHARACTERIZED BY A GENERAL DECREASE IN CONVECTION...CERTAINLY LESS MCS ACTIVITY AS THE PATTERN BECOMES CONSIDERABLY LESS FAVORABLE FOR SUCH THROUGH THE PERIOD...AND A SLIGHT INCREASE IN TEMPERATURES. THE INCREASE IN MAX TEMPS...ESPECIALLY...WILL BE A RESULT OF THE ENHANCED UPPER RIDGING...500MB HEIGHTS RISING INTO THE 588-590DM RANGE AND INEVITABLY POCKETS OF 850MB TEMPS +20C TO +21C APPEARING...ESPECIALLY ACROSS THE PIEDMONT. THIS WILL ALLOW SOME MAX TEMPS IN THE LOW 90S TO REAPPEAR ACROSS THE SOUTHEAST...E.G. KDAN. ALTHOUGH HEIGHTS ARE RISING AND THERE IS LESS POTENTIAL FOR MESOSCALE COMPLEXES...WEAK NORTHWEST FLOW ALOFT PERSISTS AND WILL STILL SUPPORT A THREAT FOR CONVECTION. HOWEVER...POPS MORE IN THE 20-40 PERCENT RANGE APPEAR MORE REASONABLE DURING THIS PERIOD THAN THE 50-60 POPS ADVERTISED THROUGH MUCH OF THE SHORT TERM. && .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/... AS OF 155 AM EDT WEDNESDAY... CONVECTIVE ACTIVITY HAS EXITED THE REGION...LEAVING GENERALLY VFR CONDITIONS AT TAF SITES. HOWEVER...EXPECT LOW LEVEL MOISTURE TO BE RUNNING UP THE WESTERN SLOPES ON NW FLOW AS LOW PRESSURE PULLS THROUGH THE GREAT LAKES REGION. THIS WILL LIKELY BRING SOME MVFR CIGS TO KBCB AND KBLF. KLWB SEEMS TO FIND A WAY TO FOG IN AND WITH LIGHT FOG ALREADY AT THE STATION AFTER SOME PRECIPITATION THIS EVENING...WILL FORECAST LIFR CONDITIONS TOWARD DAYBREAK THOUGH IF CLOUD COVER DEVELOPS EARLY AND SHUTS OFF THE COOLING THIS MAY BE OVERDONE. WILL GO WITH MFVR FOG AT KLYH SINCE THEY HAD A GOOD DOSE OF RAIN BUT WILL STAY WITH UNRESTRICTED VSBYS AT KROA AND KDAN. ANY FOG/STRATUS WILL BE BURNING OFF AFTER DAYBREAK. A FRONTAL BOUNDARY WILL THEN REMAIN DRAPED OVER THE AREA AND HELP GENERATE SOME VFR CIGS AND ANOTHER ROUND OF SHRA/TSRA WEDNESDAY AFTERNOON. DO NOT HAVE A LOT OF CONFIDENCE IN TIMING OR LOCATION OF ANY CONVECTIVE DEVELOPMENT SO WILL KEEP TAFS DRY AND SEE IF LATER MESO MODEL RUNS CAN COME TO A CONSENSUS. WINDS WILL BE ON THE LIGHT SIDE WITH SOME LOW END GUSTS WEDNESDAY AFTERNOON. EXTENDED AVIATION DISCUSSION... THE REGION WILL BE IN A GENERAL NORTHWEST FLOW PATTERN THROUGH SATURDAY. WHILE ISOLATED TO SCATTERED SHOWERS AND STORMS CANNOT BE RULE OUT ANY OF THESE DAYS...THE BEST POTENTIAL WILL BE ON THURSDAY...THEN AGAIN LATER FRIDAY...FOLLOWED BY A THIRD POTENTIAL INCREASE IN COVERAGE ON SATURDAY AS SEPARATE SHORTWAVE TROUGHS PROGRESS TROUGH THE NORTHWEST FLOW. VFR CONDITIONS ARE EXPECTED FOR MOST OF THE AREA MUCH OF THE TIME. THE EXCEPTIONS WILL COME AS TEMPORARY DECREASES WITHIN ANY HEAVIER RAIN SHOWERS OR THUNDERSTORMS...AND THEN LATE AT NIGHT AND EARLY MORNING DUE TO RIVER OR MOUNTAIN VALLEY FOG...ESPECIALLY IN AREAS THAT RECEIVED PRECIPITATION THE DAY BEFORE. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...MBS NEAR TERM...MBS SHORT TERM...RAB LONG TERM...RAB AVIATION...JH/MBS

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