Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 191334 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 934 AM EDT FRI SEP 19 2014 .SYNOPSIS... A WEAK TROUGH OF LOW PRESSURE WILL SHIFT WEST ACROSS THE MOUNTAINS TODAY AHEAD OF STRONG HIGH PRESSURE BUILDING IN FROM THE NORTH BY THIS AFTERNOON. THE HIGH WILL WEDGE SOUTH ALONG THE EASTERN SLOPES OF THE APPALACHIANS TONIGHT INTO SUNDAY KEEPING DRY WEATHER IN PLACE. A COLD FRONT SHOULD CROSS THE AREA FROM THE NORTHWEST LATER SUNDAY NIGHT INTO MONDAY FOLLOWED BY COOLER AND DRIER WEATHER INTO NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 933 AM EDT FRIDAY... THIS MORNINGS 12Z RNK SOUNDING DISPLAYED PLENTY OF LOW LEVEL MOISTURE TRAPPED BELOW THE SUBSIDENCE INVERSION WITH A EASTERLY FLOW FROM SFC UP TO 1KFT. KFCX 88D IMAGES HIGHLIGHTED A FEW SHOWERS THIS MORNING ESPECIALLY ALONG THE FOOTHILLS OF THE BLUE RIDGE MOUNTAINS. THIS ACTIVITY IS BEING SUPPORTED BY THE COMBINATION OF A WEAK SURFACE TROUGH ACROSS THE PIEDMONT AND LOW LEVEL THETA-E RIDGING EAST OF THE BLUE RIDGE. A BLEND OF THE HRRR AND HI RESW-ARW CAPTURED THIS MORNING POPS. TWO CHALLENGES FOR THIS AFTERNOON FORECAST ARE HOW FAST/DEEP CAD IS AND WHATS THE WESTERN EXTENT OF CLOUD COVER. MODEL GUIDANCE STILL SHOWS AN AXIS OF INSTABILITY ALONG THE I-77 CORRIDOR THIS AFTERNOON WITH THE WESTERN MOVING SURFACE TROUGH. INCLUDED AN ISOLATED TSRA MENTION IN NORTHWEST NORTH CAROLINA RIDGES/FOOTHILLS THIS AFTERNOON WHERE BEST LOW LEVEL CONVERGENCE LINES UP WITH THE PASSING TROUGH UNDER DECENT 85H THETA-E RIDGING. TEMPERATURES WILL LIKELY TO BE STUCK MOSTLY IN THE 60S UNDER LOW DECK AND EASTERLY FLOW. HOWEVER THE FAR WEST COULD ACTUALLY SEE READINGS PUSH INTO THE 70S GIVEN THE SLOWER WEDGING. MADE SOME MINOR ADJUSTMENTS IN TEMPERATURES...POPS AND CLOUD COVER FOR THIS MORNING INTO THIS AFTERNOON. AS OF 230 AM EDT FRIDAY... COMBINATION OF A WEAK SURFACE TROUGH ACROSS THE PIEDMONT AND LOW LEVEL THETA-E RIDGING EAST OF THE BLUE RIDGE CONTINUES TO LEAD TO ISOLATED SLOW MOVING SHOWERS IN SPOTS EARLY THIS MORNING. EXPECT THIS TO PERSIST A WHILE LONGER PER LATEST HRRR BEFORE THE DEVELOPING WEDGE STARTS TO ENHANCE FROM NE TO SW BUT A BIT SLOWER THAN EARLIER THOUGHT. THIS SHOULD START TO PRODUCE SOME SPOTTY -DZ ALONG THE EASTERN SLOPES AS SHOWERS WANE PER INCREASING STABILITY BUT LOOKS LESS THAN PREVIOUS GIVEN DRY AIR SAGGING IN FROM THE NORTH OFF MSAS. HOW FAST/DEEP ANY OF THE LOW CLOUDS CAN BANK IN ALONG THE EASTERN SLOPES KEY TO CLOUDS/TEMPS THIS AFTERNOON WITH MODELS NOW SLOWER IN INITIALLY PUSHING THE CAD SOUTH AND WEST. THIS MAY LEAD TO AN AXIS OF MODEST INSTABILITY ESPCLY ALONG THE I-77 CORRIDOR EARLY THIS AFTERNOON WHERE GUIDANCE REDEVELOPS SHRA ALONG THE WESTWARD MOVING SURFACE TROUGH. SINCE THIS IN LINE WITH CONSENSUS...BUMPED UP CHANCE POPS ACROSS NW NC...AND SW VA LATER WHILE TRIMMING ANY -DZ/-RA TO ISOLATED -SHRA BLUE RIDGE...AND LITTLE MORE THAN CLOUDS EAST-NE AS BUILDING HIGH PRESSURE START TO ENHANCE INLAND FROM THE MID ATLANTIC COAST. ALSO INCLUDED AN ISOLATED -TSRA MENTION NW NC RIDGES/FOOTHILLS WHERE BEST LOW LEVEL CONVERGENCE LINES UP WITH THE PASSING TROUGH UNDER DECENT 85H THETA-E RIDGING. OTRW CLOUD COVER AND TEMPS THE MAIN ISSUES ESPCLY BLUE RIDGE WHERE LIKELY TO BE STUCK MOSTLY IN THE 60S UNDER LOW DECK AND EASTERLY FLOW. HOWEVER COULD ACTUALLY SEE READINGS PUSH INTO THE 70S FAR WEST GIVEN THE SLOWER WEDGING...AS WELL AS OVER THE SOUTH/EAST IF CAN GET MORE SUNNY BREAKS AS MOISTURE STARTS TO DECREASE FROM THE EAST LATE. SURFACE RIDGING STRENGTHENS FROM THE NE OVERNIGHT HELPING PUSH THE RESIDUAL AXIS OF MOISTURE FARTHER WEST WHICH SHOULD BRING AN END TO POPS DURING THE EVENING. BANKED UP LOW LEVEL MOISTURE THOUGH LIKELY TO REDEVELOP OR PERSIST BLUE RIDGE WHERE LOTS OF LOW CLOUDS/FOG POSSIBLE. APPEARS AREAS OVER THE EAST/SE FROM HIGHWAY 29 EAST COULD SEE SOME CLEARING AS MOISTURE GETS PINCHED FARTHER WEST AHEAD OF THE DRIER EASTERLY FLOW. OTRW VARYING DEGREE OF CLOUDS FROM THE BLUE RIDGE WEST WITH LOWS MAINLY IN THE 50S PER LATEST SIMILAR MAV/MET MOS.
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&& .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... AS OF 300 AM EDT FRIDAY... THE HIGH PRESSURE CENTER THAT WAS OVER NEW ENGLAND WILL MOVE OUT INTO THE ATLANTIC OVER THE WEEKEND. HOWEVER...THIS RIDGE WILL REMAIN WEDGE BACK OVER THE MID ATLANTIC AND SOUTHEASTERN STATES INTO SATURDAY NIGHT. A GULF STREAM DISTURBANCE WILL HELP KEEP THIS WEDGE IN THE AREA AND ALSO PROVIDE SUBSIDENCE TO KEEP THE FORECAST AREA DRY SATURDAY. THESE DISTURBANCE WILL HAVE MOST OF ITS RAIN FALLING ON ITS EASTERN FLANK AS DRY AIR IS ENTRAINED INTO THE WESTERN SIDE. THIS DISTURBANCE WILL TRACK TO THE NORTHEAST AND WILL REMAIN OFFSHORE THROUGH THE WEEKEND. MODELS HAVE SPED UP THE TIMING OF THE NEXT FRONTAL PASSAGE FROM MONDAY TO SUNDAY. THIS FRONT STILL LOOKS LIKE A TYPICAL FALL FRONTAL PASSAGE WITH RAIN FALLING ALONG WESTERN SLOPES...LOSING THEIR INTENSITY MOVING TO THE BLUE RIDGE. THIS PRECIPITATION MAY THEN JUMP THE FOOTHILLS AS A WEAK LINE OF CONVECTION DEVELOPS OVER THE PIEDMONT WHERE A LEE TROUGH WILL RESIDE SUNDAY AFTERNOON. THE NAM AND ECM LOOK SIMILAR WITH KEEPING BULK OF THE RAIN OVER THE MOUNTAINS. THE GFS PROGRESSIVELY MOVES THE FRONT AND RAINFALL ACROSS THE ENTIRE FORECAST AREA...DISREGARDING DOWNSLOPE. THE FORECAST DID NOT DISCREDIT THE GFS...BUT MORE WEIGHT WAS PLACED WITH THE NAM/ECM FOR SUNDAY. SATURDAY TEMPERATURES WILL RUN WARMER THAN NORMAL WITH UPPER 70S TO LOWER 80S. AREAS NOT SEEING RAIN UNTIL LATER IN THE DAY SUNDAY SHOULD HAVE TEMPERATURES IN THE LOWER TO MID 80S. WESTERN SLOPES SHOULD HAVE RAIN FALLING BY THE AFTERNOON AND MAY SEE HIGHS IN THE MID 70S SUNDAY. && .LONG TERM /MONDAY THROUGH THURSDAY/... AS OF 200 PM EDT THURSDAY... THIS PERIOD IS SHAPING UP TO BE DRY AND SEASONAL. ANOTHER SHORTWAVE DROPS SOUTHEAST ACROSS THE TN VALLEY MONDAY AND COULD BRING ISOLATED SHOWERS TO THE ENTIRE AREAS AS FLOW BACKS ALOFT SOME. THEN HIGH PRESSURE ACROSS THE MIDWEST PUSHES EAST OVER THE MID ATLANTIC TUE- WED. TEMPS BEHIND THIS SYSTEM EARLY NEXT WEEK WILL COOL DOWN SOME...BUT NOT LOOKING AS CHILLY AS EARLIER THOUGHT...WITH 8H TEMPS +10-12C. HIGHS WILL RUN FROM THE 60S WEST TO 70S EAST...WITH LOWS MAINLY IN THE 40S...WITH SOME 50S ACROSS THE PIEDMONT. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/... AS OF 650 AM EDT FRIDAY... CIGS CONTINUE TO SLOWLY LOWER THROUGH MVFR ALONG AND EAST OF THE BLUE RIDGE EARLY THIS MORNING AS THE WEDGE STARTS TO SPILL WESTWARD. THIS MAY LEAD TO AN AREA OF IFR CIGS ESPCLY AROUND KBCB/KROA EAST TO KLYH THIS MORNING INCLUDING PATCHY -RA/-DZ. OTHER HEAVIER SHOWERS JUST TO THE WEST OF KDAN SHOULD STAY MOSTLY OUT OF THE KDAN VICINITY WHILE FEEDING NORTH UP TOWARD KROA SO INCLUDING SOME PREVAILING LIGHT RAIN/DRIZZLE OR VCSH MENTION OVER THE EAST THIS MORNING. CIGS REMAIN MORE VARIABLE TO THE WEST WITH MOSTLY VFR TO HIGH END MVFR EXPECTED A WHILE LONGER AT KBLF/KLWB BEFORE SHOWING SOME IMPROVEMENT LATER THIS MORNING INTO THE AFTERNOON. SOME ADDED SHOWER DEVELOPMENT POSSIBLE MAINLY MOUNTAINS THIS AFTERNOON BUT COVERAGE TOO WIDELY SCATTERED TO INCLUDE IN ANY OF THE TAF LOCATIONS FOR NOW. DEGREE OF LOW CIGS REMAINS IN QUESTION DURING THE AFTERNOON WITH POTENTIAL TO SEE OTHER THE WESTERN AND EASTERN PERIMETER SITES IMPROVE TO VFR WHILE STAYING STUCK IN MVFR OR WORSE ALONG THE BLUE RIDGE UNTIL LATE. FOR NOW WILL KEEP THE SCENARIO OF SEEING A SLOW RISE IN CLOUD BASES MOST SPOTS THIS AFTERNOON WITH MOST AT LEAST GETTING INTO BRIEF VFR. EAST WINDS AT 7-12 KTS TODAY WITH POSSIBLE LOW END GUSTS IN USUALLY FAVORED SOUTHEAST WIND AREAS...SUCH AS KBLF. CIGS MAY LOWER AGAIN THIS EVENING PENDING DEGREE OF EROSION/COVERAGE HEADING INTO LATE THIS AFTERNOON SO TRENDING BACK TOWARD MVFR FROM THE BLUE RIDGE EAST EARLY TONIGHT BEFORE DRYING FROM THE EAST OCCURS. OTRW ANOTHER ROUND OF LOW CIGS IN FOG AND STRATUS LIKELY LATER TONIGHT INTO EARLY SATURDAY WITH SOME ADDED PATCHY FOG LIKELY IN THE VALLEYS SUCH AS KLWB/KBCB BY MORNING. EXTENDED AVIATION DISCUSSION... WEDGE SHOULD ERODE FAIRLY QUICKLY SATURDAY IN RESPONSE TO AN UPSTREAM TROUGH. SOME LOW CLOUDS MAY LINGER THROUGH THE MORNING ALONG WITH PATCHY FOG...BUT OVERALL VFR CONDITIONS EXPECTED SAT. A FRONTAL SYSTEM WILL APPROACH SUN WITH -SHRA AND PERHAPS AN ISOLD TSRA WEST OF THE ALLEGHANY FRONT. INSTABILITY IS QUITE LIMITED AND SO IS DEEP MOISTURE. WITH A POSSIBLE TROPICAL SYSTEM DEVELOPING OFF THE COAST AT THE SAME TIME...WE MAY BE IN A STRONG SUBSIDENCE AREA AND SEE LITTLE MORE THAN -SHRA OR SPRINKLES EAST OF THE ALLEGHANY FRONT. EXPECT MOSTLY VFR-PERIODS OF MVFR CIGS SUN-EARLY MON AS THE TROUGH MOVES THROUGH. HIGH PRESSURE BUILDS IN FOR THE FIRST HALF OF NEXT WEEK WITH DRY NW FLOW. THUS...EXPECT MOSTLY VFR CONDITIONS THROUGH THE PERIOD WITH LOCAL EARLY MORNING MVFR-IFR FOG CONDITIONS. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/KK NEAR TERM...JH/KK SHORT TERM...RCS LONG TERM...WP AVIATION...JH/KK/RAB

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