Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 130408 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1208 AM EDT SAT SEP 13 2014 .SYNOPSIS... A WEAK STATIONARY FRONT WILL REMAIN SOUTH OF THE AREA THROUGH THE WEEKEND INTO EARLY NEXT WEEK. A WAVE OF LOW PRESSURE WILL RIPPLE EAST ALONG THE FRONT LATER TONIGHT AND SATURDAY BRINGING MORE WIDESPREAD RAINFALL INTO SATURDAY AFTERNOON. STRONG HIGH PRESSURE WILL FINALLY START TO BUILD INTO THE REGION FROM THE NORTH BY THE MIDDLE OF NEXT WEEK. && .NEAR TERM /THROUGH TODAY/...
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AS OF 1207 AM EDT SATURDAY... UPDATED POP AND QPF FCST GRIDS TO INCREASE RAINFALL AMOUNTS BASED ON RADAR AND GAUGE REPORTS...AND REDUCED POP FAR WEST AND NORTHEAST FOR MUCH OF THE OVERNIGHT. INCLUDED CHC THUNDER FOR SEVERAL MORE HOURS FAR SW PER LATEST MESOANALYSIS AND TRENDS IN RADAR/SAT/LTG DATA. OTHERWISE NO CHANGES AT THIS TIME TO TEMPERATURES REMAINDER OF OVERNIGHT. MAY BE A FEW AREAS OF FOG AND DRIZZLE AS WELL ESPECIALLY ON RIDGES..BUT LEFT IT LIGHT RAIN IN GRIDS FOR THOSE AREAS AS TRICKY TO DIFFERENTIATE FROM LOCATION TO LOCATION AS TRUE LIGHT RAIN SPREADS FARTHER NORTH. AS OF 955 PM EDT FRIDAY... SHOWERS CONTINUE TO PERSIST MAINLY WEST OF THE BLUE RIDGE...WHILE A FEW THUNDERSTORMS HAVE DEVELOPED SOUTH OF THE CWA IN NORTH CAROLINA. SLIGHT CHANCES OF THUNDER WAS KEPT IN THE GRIDS ACROSS NORTH CAROLINA...BUT NO OTHER CHANGES WERE MADE TO THE POPS. TEMPERATURES WERE TWEAKED A LITTLE IN RESPONSE TO THE LATEST TRENDS. THE MOIST GROUND AND LOW CLOUD CEILINGS WILL ALSO PROVIDE AREAS OF FOG AND DRIZZLE. OVERALL...IT WILL BE QUITE A WET NIGHT ACROSS THE AREA...AS PORTRAYED BY THE ABNORMALLY HIGH PRECIPITABLE WATER VALUE OF 1.67 INCHES FROM THE 00Z RNK SOUNDING. AS OF 245 PM EDT FRIDAY... UPPER LOW CLOSES OFF OVER THE UPPER MISSISSIPPI VALLEY BY THIS EVENING...THEN BEGINS TO CROSS EAST THROUGH THE GREAT LAKES TONIGHT AND SATURDAY. UPPER RIDGE REMAINS ELONGATED FROM THE SOUTHEAST COAST INTO THE SOUTHERN PLAINS. THE FORECAST AREA WILL STAY IN THE SOUTH- SOUTHWEST FLOW BETWEEN THESE TWO FEATURES. AT THE SURFACE LOW PRESSURE WILL DEVELOP ALONG A STALLED FRONT OVER MISSISSIPPI AND ALABAMA AND MOVE NORTHEAST INTO THE MID ATLANTIC REGION BY SATURDAY MORNING. SURFACE HIGH PRESSURE WILL BUILD IN FROM THE WEST ON SATURDAY. SYNOPTIC SCALE LIFT IS STRONG BY LATE TONIGHT THROUGH SATURDAY AFTERNOON WHEN FORECAST GETS INTO THE RIGHT REAR QUADRANT OF A 110 KNOT UPPER JET. THE APPROACHING SURFACE LOW WILL ENHANCE THE EAST WINDS AND LIFT ALONG THE LEE OF THE APPALACHIANS. MODELS WERE SHOWING GOOD ISENTROPIC LIFT ON THE 300K LAYER...ESPECIALLY FROM 06Z/2AM TO 12Z/8AM TONIGHT. PLENTY OF MOISTURE AVAILABLE. TOTAL PRECIPITABLE WATER VALUES ALREADY IN THE 1.5 TO 2.0 RANGE AND WILL REMAIN THAT WAY THROUGH MID DAY SATURDAY. PRECIPITATION POTENTIAL PLACEMENT SHOWED THE SOUTHERN AND EASTERN COUNTY WARNING AREAS AS A FAVORED LOCATION FOR HIGHER PRECIPITATION AMOUNTS TONIGHT INTO SATURDAY MORNING. DRIER AIR APPROACHES LATE SATURDAY IN THE NORTHERN COUNTY WARNING AREA AS THE HIGH BUILDS IN. WILL BE KEEPING TEMPERATURES MILD TONIGHT...AT OR ABOVE GUIDANCE. HIGHS TOMORROW WILL BE SUPPRESSED BY CLOUDS AND PRECIPITATION. COOLER MET LOOKS REASONABLE.
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&& .SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/... AS OF 210 PM EDT FRIDAY... NEXT SHORTWAVE TROUGH PASSES SATURDAY EVENING LEAVING THINGS ABOUT STATUS QUO WITH A DEEP AXIS OF MOISTURE TO THE SE...WEAK HIGH PRESSURE WEDGED IN FROM THE NORTH...AND LOW LEVEL MOISTURE ACROSS THE REGION. NEXT SERIES OF IMPULSES ALOFT LOOK PRETTY WEAK SATURDAY NIGHT INTO SUNDAY NIGHT WITH WIND FIELDS ABOVE THE WEDGE TURNING FROM MORE UPSLOPISH SATURDAY NIGHT/EARLY SUNDAY TO A MORE SOUTH/SW COMPONENT BY SUNDAY NIGHT. THIS IN ADVANCE OF ANOTHER MORE SUBSTANTIAL 5H SHORTWAVE TROUGH THAT WILL APPROACH LATE MONDAY INTO MONDAY NIGHT. THIS MAKES POPS IFFY EARLY ON WITH BEST LIFT SHIFTING TO THE SE WHILE PWATS LOWER FROM NORTH TO SOUTH BEFORE REBOUNDING AHEAD OF THE UPSTREAM WAVE MONDAY/MONDAY NIGHT. APPEARS BEST CHANCES WILL BE ALONG AND SOUTH OF HIGHWAY 460 SATURDAY NIGHT INTO SUNDAY NIGHT WITH ISOLATED POPS TO JUST CLOUDS UP NORTH. LATEST 12Z ECMWF HAS EVEN LESS COVERAGE WITH MORE CLOUDS/DRIZZLE THROUGH SUNDAY NIGHT ESPCLY SOUTH/SW INCLUDING THE SOUTHERN BLUE RIDGE. THUS APPEARS ANY SIGNIFICANT RAINFALL MAY BE EVEN LESS PER LATEST FORECAST WPC QPF PENDING LATER RUNS. DEEPER MOISTURE SHOULD RETURN BACK NORTH TO SOME DEGREE MONDAY INTO MONDAY NIGHT...AND AS DIFFLUENCE INCREASES AHEAD OF THE NEXT MID LEVEL FEATURE EXPECT SHOWERS TO COVER MUCH OF THE REGION BY LATE MONDAY WITH ISOLATED THUNDER POSSIBLE SW PER WEAK FORECAST CAPES. APPEARS SHOWERS WILL DIMINISH FROM NW TO SE LATER MONDAY NIGHT IN ADVANCE OF THE ACTUAL SURFACE FRONT THAT WILL BE NEARING THE MOUNTAINS LATE. THUS HIGHEST CHANCE POPS LATE MONDAY-MONDAY EVENING THEN DECREASING AFTER MIDNIGHT. CLOUDS AS WELL AS THE LINGERING WEDGE TO KEEP TEMPS ON THE COOL SIDE WITH LOWS CLOSER TO THE MAV MOS AND HIGHS SUNDAY MORE IN LINE WITH THE CHILLY MET MOS. MAY GET A BUMP IN HIGHS MONDAY AS THE FLOW TURNS MORE SW AND SOME BREAKS PERHAPS DEVELOP SO PUSHED MOST INTO THE 70S. && .LONG TERM /TUESDAY THROUGH FRIDAY/... AS OF 130 PM EDT FRIDAY... BROAD UPPER TROUGH WILL GRADUALLY DEEPEN ACROSS THE EASTERN STATES NEXT WEEK ALLOWING A LARGE AREA OF HIGH PRESSURE TO THE NORTH TO EVENTUALLY WEDGE SOUTH ALONG THE MOUNTAINS BY NEXT WEEKEND. THIS SHOULD PROMOTE MAINLY DRY WEATHER ALONG WITH BELOW NORMAL TEMPS THROUGH MUCH OF THE PERIOD. HOWEVER AHEAD OF THIS DRIER AIR...WILL HAVE A WEAK COLD FRONT RIDING ACROSS THE CWA FROM THE NW TUESDAY THAT SHOULD FINALLY PUSH MOST DEEPER MOISTURE TO THE SOUTH AND EAST TUESDAY NIGHT. TIMING OF THIS DRYING ALONG WITH WHETHER OR NOT ANOTHER WAVE RIDES UP THE BOUNDARY ACROSS THE SE...AS SUGGESTED BY A FEW GFS ENSEMBLE MEMBERS...REMAINS IN QUESTION. THIS FRONTAL PASSAGE ALONG WITH THE RESIDUAL MOISTURE AXIS BEING JUST OFF TO THE EAST SUGGESTS THE NEED TO KEEP IN SOME LOW POPS TUESDAY FOR NOW...THEN DRIER TUESDAY NIGHT-FRIDAY PER LATEST ECMWF. CANT TOTALLY RULE OUT ISOLATED SHOWERS MIDWEEK OVER THE SOUTH PER ANOTHER PASSING SHORTWAVE BUT IFFY GIVEN DRY AIR AND LATEST MODEL TRENDS. THUS PLANNING TO KEEP THE END OF THE WEEK MOSTLY DRY OUTSIDE OF AN ISOLATED SHOWER MENTION FAR SOUTH-EAST WEDNESDAY-EARLY THURSDAY. HIGHS MAINLY MID 60S TO AROUND 70 WEST AND 70-75 EAST WITH LOWS MOSTLY 50S...EXCEPT FOR A FEW COOLISH 40S IN THE VALLEYS GIVEN THE SURFACE RIDGE AXIS ABOUT OVERHEAD. && .AVIATION /04Z SATURDAY THROUGH WEDNESDAY/... AS OF 745 PM EDT FRIDAY... IFR-LIFR CIGS AND MVFR-IFR VSBYS THROUGH MUCH OF THE TAF VALID PERIOD...AT LEAST THROUGH 18Z SAT. STATIONARY FRONT ACROSS NC WILL REMAIN IN PLACE THROUGH THE WEEKEND...THEN GRADUALLY SHIFT SOUTH INTO EARLY NEXT WEEK. UPPER FLOW IS NEAR ZONAL WITH A SERIES OF EMBEDDED DISTURBANCES. SFC HIGH PRESSURE BRIDGING OVER THE MIDWEST ACROSS PA TOWARD THE NORTH MID-ATLANTIC COAST...CREATING FAVORABLE WEDGE ENVIRONMENT. EXTENSIVE ISENTROPIC/OVERRUNNING EVEN EXPECTED OVERNIGHT AS DEEP MOISTURE RIDES UP AND OVER THE SHALLOW LAYER OF COOL AIR NORTH OF THE STALLED FRONTAL BOUNDARY. THIS WILL PROMOTE LOWERING OF CIGS/VSBYS FROM SW-NE OVERNIGHT...MANY OF WHICH ARE ALREADY IN THE MVFR-IFR RANGE. THE BETTER CHANCE FOR RAIN COMES LATE TONIGHT/SATURDAY MORNING AS A SHORT WAVE MOVES TOWARD THE REGION FROM THE MIDWEST. AT OTHER TIMES...EXPECT WIDESPREAD -DZ AND BR. AS WINDS SHIFT TO THE NW 4-6KTS BEHIND THE PASSING UPPER SHORT WAVE SAT IN THE 18Z-20Z TIME FRAME...CIGS SHOULD IMPROVE TO MVFR AND VSBYS MVFR-VFR. PRIOR TO THIS TIMES...WINDS MOSTLY ENE- ESE 5-7KTS. MEDIUM TO HIGH CONFIDENCE IN CIGS THROUGH THE TAF VALID PERIOD. MEDIUM TO HIGH CONFIDENCE IN VSBYS THROUGH THE TAF VALID PERIOD. MEDIUM CONFIDENCE IN WIND DIR THROUGH THE TAF VALID PERIOD...HIGH CONFIDENCE IN WIND SPD THROUGH THE TAF VALID PERIOD. EXTENDED AVIATION DISCUSSION... CLOUDS WILL LINGER...EVEN AFTER THE -RA ENDS SUNDAY...BUT OVERALL CONDITIONS SHOULD BE MOSTLY MVFR...WITH LESS IFR OR WORSE CIGS/VSBYS. BEYOND SUNDAY...BROAD UPPER TROUGH DEVELOPING ACROSS THE NORTHERN STATES...WITH THE RNK CWA ON THE SOUTHERN EDGE OF THIS BROAD UPPER TROUGH...LEADING TO PRIMARILY CONTINUED ZONAL FLOW. LATEST MODEL TRENDS BEGINNING TO FAVOR POTENTIAL CHANGE TO A MORE NW FLOW ALOFT AS THE WEEK PROGRESSES...WHICH SHOULD ATTEMPT TO PUSH THE PESKY DEEP MOISTURE FURTHER SOUTH AWAY FROM THE REGION. OVERALL...EXPECT MVFR CONDITIONS TO PERSIST INTO MONDAY AS AFOREMENTIONED UPPER TROUGH BRINGS MORE CLOUDS AND SHOWERS TO THE REGION. HOWEVER...THIS WILL NOT BE A WEDGE SETUP LIKE CURRENT SITUATION...SO OVERALL IMPROVED CONDITIONS EXPECTED COMPARED TO CURRENT. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/PM NEAR TERM...AMS/PW/RAB/SK SHORT TERM...JH LONG TERM...JH AVIATION...MBS/RAB

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