Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 070010 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 710 PM EST SAT FEB 6 2016 .SYNOPSIS... WEAK HIGH PRESSURE WILL REMAIN OVER THE AREA INTO TONIGHT. A STORM SYSTEM DEVELOPING OFF THE SOUTHEAST COAST WILL MOVE NORTHEAST BUT PASS WELL TO THE SOUTH AND EAST OF THE AREA SUNDAY INTO SUNDAY NIGHT. A SECOND AREA OF LOW PRESSURE WILL MOVE SOUTHEAST ACROSS THE MOUNTAINS FROM THE NORTHWEST EARLY NEXT WEEK...RESULTING IN MUCH COLDER TEMPERATURES ALONG WITH SNOW SHOWERS FOR MONDAY THROUGH WEDNESDAY. && .NEAR TERM /THROUGH SUNDAY/... AS OF 230 PM EST SATURDAY... UPPER LOW ALONG THE NORTHERN GULF COAST EARLY TONIGHT LOOKS TO HEAD EAST AND QUICKLY HELP DEEPEN SURFACE LOW PRESSURE HEADING NORTH OFF THE FLORIDA COAST TO ALONG THE GULF STREAM BY MORNING. THIS SHOULD CONTINUE TO FAN HIGH/MID CLOUDS NORTH ACROSS THE REGION WITHIN THE SW FLOW ALOFT EARLY ON BEFORE THE SYSTEMS START TO PHASE AND ATTEMPT TO LEAN DEEPER MOISTURE BACK INLAND. HOWEVER HOW FAR TO THE NW THIS OCCURS REMAINS IFFY GIVEN SUCH DRY AIR IN PLACE AND DEVELOPING SURFACE-7H NORTHERLY FLOW EAST OF THE BLUE RIDGE. LATEST GUIDANCE KEEPS THE MAJORITY OF THE PRECIP WITHIN A TIGHT DEFORMATION ZONE ON THE BACK OF THE COASTAL LOW JUST TO THE SE THROUGH 12Z. HOWEVER THE GFS/CMC DO TOUCH THE FAR CORNER OF THE PIEDMONT WITH A FLURRY/SPRINKLE WHILE THE HRRR AND LOCAL RNK-WRF LOOK A BIT MORE OMINOUS IN BRINGING PRECIP JUST SOUTH OF THE CWA LATE. SINCE THESE STILL APPEAR TO BE OUTLIERS ATTM WILL ONLY BEEF UP CLOUDS SE LATE TONIGHT BUT STAY DRY FOR NOW PENDING LATER TRENDS. OTRW WILL RUN WITH A PC FORECAST OVERALL FOR HIGH CLOUDS THIS EVENING...THEN BECOMING MOSTLY CLOUDY SE THIRD OVERNIGHT. LOWS AGAIN DEPENDENT UPON THE CLOUD CANOPY AS GIVEN LOW DEWPOINTS COULD QUICKLY FALL BACK INTO THE 20S SOONER. THUS GOING ON THE COLDER SIDE OF MOS OVERALL WHICH STILL SUPPORTS LOW/MID 20S MOUNTAINS TO AROUND 30 SE. SURFACE LOW RAPIDLY DEEPENS HEADING ALONG THE GULF STREAM SUNDAY AS THE UPPER LOW CATCHES UP AND HELPS SLOW THE SYSTEM DOWN. GUIDANCE AGAIN DEPICTS AN INTENSE BUT VERY COMPACT SYSTEM OFFSHORE WITH A TIGHT GRADIENT BETWEEN CLOUDS AND DEFORMATION PRECIP ON THE NW SIDE OUT EAST. HOWEVER STILL APPEARS THAT BETWEEN DRY AIR IN PLACE AND SOME EASTWARD BOOT VIA THE NEXT UPSTREAM SHORTWAVE KICKER THAT MOST DEEP MOISTURE SHOULD AGAIN STAY JUST TO THE SOUTH AND EAST SUNDAY MORNING BUT SOMETHING STILL TO WATCH. THEREFORE PLAN TO STAY DRY WITH MORE SUN WEST AND CLOUDS GIVING WAY TO MORE SUN DURING THE DAY EAST AS THE MID DECK CANOPY SLOWLY FADES AND SHIFTS EAST. WINDS MAY TURN GUSTY AS WELL SUNDAY OUT EAST ON THE PERIMETER OF THE CYCLONE WHILE OVERALL WARMING ALOFT TAKES PLACE. THIS SUPPORTS HIGHS BACK INTO THE 40S WEST AND PERHAPS SOME 50S JUST IN THE LEE OF THE BLUE RIDGE ON THE EDGE OF THE EASTERN CLOUD SHIELD PENDING HOW FAST IT EXITS. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/... AS OF 225 PM EDT SATURDAY... AN UPPER LEVEL SHORT WAVE TROUGH IN THE SOUTHERN STREAM WILL CROSS OVER THE CAROLINAS ON SUNDAY NIGHT...WHICH WILL SPIN UP AN INTENSE LOW PRESSURE SYSTEM OFF THE COAST. THE MODELS KEEP THE CWA DRY...BUT SOME CLOUD COVER MAY LINGER OVER THE PIEDMONT. AS THE COASTAL LOW EXITS ON MONDAY...A BROAD UPPER LEVEL TROUGH IN THE NORTHERN STREAM WILL DIG SOUTHWARD FROM THE GREAT LAKES TOWARD THE MID ATLANTIC. A POTENT CLIPPER SYSTEM ALONG THE LEADING EDGE OF THIS TROUGH SHOULD PROVIDE LIGHT SNOW WEST OF THE BLUE RIDGE DURING MONDAY. THE 12Z ECMWF SEEMS TOO SLOW WITH THE PROGRESS OF THE CLIPPER SYSTEM AND THE APPROACHING ARCTIC AIR...WHILE THE 12Z GFS MAY BE TOO BULLISH WITH QPF. PRECIPITATION TYPE BECOMES MORE PROBLEMATIC IN THE PIEDMONT...AS FLURRIES BEGIN OVER THE PIEDMONT BEFORE CHANGING TO RAIN WITH TEMPERATURES RISING INTO THE 40S. THE RAIN WOULD CHANGE BACK TO FLURRIES BY MONDAY EVENING AS TEMPERATURES DROP. THE BROAD UPPER LEVEL TROUGH WILL BE OVERHEAD BY TUESDAY...AS A DEEP ARCTIC AIR MASS SPILLS OVER THE CWA. WITH 500 MB HEIGHTS APPROACHING 520 DAM AND MODEL SOUNDINGS PORTRAYING A NEARLY SATURATED CLOUD LAYER UP TO -30 C FROM MONDAY EVENING THROUGH MOST OF TUESDAY...THE UPSLOPE SNOW MACHINE WILL BE HUMMING AT FULL POWER ALONG THE WESTERN SLOPES. WINTER WEATHER HEADLINES APPEAR LIKELY FOR THESE AREAS DURING MONDAY AND TUESDAY...SO IT HAS BEEN MENTIONED IN THE HWO. AREAS TO THE EAST MAY STILL A FEW FLURRIES FLYING IN THE NORTHWEST WIND...BUT NO ACCUMULATION WILL BE REALIZED AFTER THE CLIPPER SYSTEM DEPARTS OFFSHORE BY MONDAY NIGHT. TEMPERATURES WERE HELD BELOW MOS GUIDANCE THROUGHOUT THIS PERIOD DUE TO PERSISTENT COLD AIR ADVECTION. ONE LAST CONCERN COULD BE THE WIND CHILL ON TUESDAY NIGHT...AS THESE VALUES MAY DIP INTO THE SINGLE DIGITS WEST OF THE BLUE RIDGE BY DAWN...AND POSSIBLY HIT ZERO ALONG THE WESTERN SLOPES. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... AS OF 245 PM EST SATURDAY... A DEEP ARCTIC AIR MASS SHOULD REMAIN ENTRENCHED OVER THE MID ATLANTIC DURING WEDNESDAY AND THURSDAY. PERSISTENT NORTHWEST FLOW SHOULD KEEP THE UPSLOPE SNOW MACHINE IN ACTION THROUGH WEDNESDAY ALONG THE WESTERN SLOPES...BUT THE PIEDMONT SHOULD STAY DRY FROM THE DOWNSLOPE FLOW. ALTHOUGH THE SNOWFALL THREAT WILL DECREASE LATER IN THE WORK WEEK...THE THREAT FOR LOW WIND CHILL VALUES WILL INCREASE. THE LONG RANGE MODELS PROJECT THAT THE WIND CHILL VALUES SHOULD APPROACH WIND CHILL ADVISORY CRITERIA OF -5 F IN THE WESTERN MOUNTAINS ON EARLY WEDNESDAY MORNING...AND EVEN LOWER TO -10 F BY THURSDAY MORNING. WITH LOW TEMPERATURES DIVING INTO THE TEENS AND UPPER SINGLE DIGITS AND A DECENT NORTHWEST BREEZE...THE WIND CHILL THREAT IS WORTHY ENOUGH TO NOTE IN THE HWO. TEMPERATURES SHOULD MODERATE A LITTLE BY FRIDAY AS THE UPPER LEVEL TROUGH PUSHES EASTWARD...BUT THE MODELS SIGNIFICANTLY DIVERGE BEYOND THIS POINT. THE 12Z GFS TRIES TO DEVELOP ANOTHER BAND OF LIGHT SNOW FROM A SUBTLE SHORT WAVE DURING FRIDAY AFTERNOON THROUGH SATURDAY MORNING...BUT THE 12Z ECMWF KEEPS ANY MOISTURE FURTHER TO THE SOUTHEAST AND OUT OF THE CWA. WITH SO MUCH UNCERTAINTY AT THIS POINT...ONLY SLIGHT CHANCE TO LOW CHANCE POPS WERE INTRODUCED. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... AS OF 700 PM EST SATURDAY... VFR CONDITIONS ARE EXPECTED THROUGH THE TAF VALID PERIOD. A DEEP COASTAL LOW PRESSURE SYSTEM WILL BE DEVELOPING WELL TO OUR SOUTHEAST THROUGH THE PERIOD...THEN TRACKING NORTHEAST OFF THE SC/NC COAST. THIS SYSTEM WILL SPREAD SOME MID/HIGH CLOUDS ACROSS AREAS ALONG AND EAST OF THE BLUE RIDGE THROUGH THE PERIOD...ESPECIALLY OVERNIGHT/EARLY SUNDAY...BUT ANY CIGS BELOW 100 ARE EXPECTED TO REMAIN EAST OF THE RNK TAF SITES. TO THE WEST...A DEEPENING LOW WILL BE TAKING SHAPE ACROSS THE WESTERN GREAT LAKES AND MOVING SOUTHEAST. HOWEVER...THIS SYSTEM WILL NOT APPROACH OR IMPACT THE RNK CWA UNTIL JUST BEYOND THE TAF VALID PERIOD...ALTHOUGH MID/HIGH CLOUDS WILL BE APPROACHING WESTERN AREAS TOWARD THE END OF THE TAF VALID PERIOD. NO PRECIPITATION IS EXPECTED AT ANY TAF SITES THROUGH THE TAF VALID PERIOD. THE AIR MASS IS EXTREMELY DRY...SO VISIBILITIES WILL REMAIN VFR. WINDS WILL REMAIN CHAOTIC THROUGH THE PERIOD AS THE REGION FALLS BETWEEN THE DEEPENING COASTAL LOW AND THE SYSTEM APPROACHING FROM THE WEST. A GENERAL TENDENCY TOWARD NNW-NNE WINDS CAN BE EXPECTED EAST OF THE BLUE RIDGE SEEING INFLUENCE FROM THE DEVELOPING COASTAL LOW...WHILE LIGHT/VARIABLE TO LIGHT SW WINDS CAN BE EXPECTED WEST OF THE BLUE RIDGE. WEST OF THE BLUE RIDGE...SPEEDS SHOULD BE MOSTLY 7KTS OR LESS THROUGH THE TAF VALID PERIOD. TO THE EAST...POTENTIAL FOR 8-12KTS WITH GUSTS TO 20KTS KDAN-KLYH LATE TONIGHT THROUGH SUNDAY AFTERNOON IN RESPONSE TO THE COASTAL LOW. MEDIUM TO HIGH CONFIDENCE IN CIGS THROUGH THE TAF VALID PERIOD. HIGH CONFIDENCE IN VFR VSBYS THROUGH THE TAF VALID PERIOD. MEDIUM CONFIDENCE IN WIND SPEED/DIRECTION THROUGH THE TAF VALID PERIOD. EXTENDED DISCUSSION... FOR MONDAY INTO MID WEEK...A STRONG UPPER LEVEL LOW PRESSURE SYSTEM WILL SINK SOUTHWARD FROM THE GREAT LAKES AND UPPER MIDWEST. AN ASSOCIATED COLD FRONT WILL CROSS THE REGION MONDAY FOLLOWED BY A SECOND SURGE OF ARCTIC AIR TUESDAY. NORTHWEST WINDS WILL INCREASE WITH AN INFLUX OF VERY COLD AIR AND DEEP UPSLOPE MOISTURE. SNOW SHOWERS WILL BEGIN MONDAY AND CONTINUE THROUGH WEDNESDAY EVENING RESULTING IN VISIBILITY RESTRICTIONS ACROSS THE MOUNTAINS IN ADDITION TO LOW CIGS. THIS SHOULD RESULT IN A PROLONGED PERIOD OF MVFR TO IFR AT KBLF/KLWB AND POTENTIAL PERIODS OF MVFR AT KBCB/KROA. ACCUMULATING SNOW IS LIKELY IN THE MOUNTAINS WEST OF THE BLUE RIDGE. FLURRIES MAY OCCUR AS FAR EAST AS THE PIEDMONT WHERE INTERVALS OF VFR TO MVFR CIGS WILL ALSO OCCUR. CONDITIONS SHOULD BRIEFLY RETURN TO MAINLY VFR LATER WEDNESDAY NIGHT ACROSS THE REGION BEFORE POSSIBLY RETURNING TO SUB-VFR AGAIN OVER THE MOUNTAINS DURING THURSDAY WITH ANOTHER WEAK PASSING UPPER IMPULSE. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/PM NEAR TERM...JH SHORT TERM...PW LONG TERM...PW AVIATION...JH/PM/RAB

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