Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 160000 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 700 PM EST MON DEC 15 2014 .SYNOPSIS... HIGH PRESSURE IS EXPECTED TO WEAKEN AS IT DRIFTS EAST AND OFF THE COAST BY TONIGHT. A COLD FRONT WILL CROSS THE AREA TUESDAY WITH AN OPPORTUNITY FOR SHOWERS. HIGH PRESSURE IS EXPECTED TO RETURN FOR MIDWEEK. ANOTHER LOW PRESSURE STORM APPROACHES FRIDAY AND PUSHES NORTHEAST INTO THE COMING WEEKEND. && .NEAR TERM /THROUGH TUESDAY/...
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AS OF 630 PM EST MONDAY... FORECAST TEMPS WERE RUNNING MILDER THAN CURRENT TEMPS AT 6 PM AS THE TYPICAL DUSK DROP WITH DRY AIRMASS HAS ALLOWED TEMPS TO LOWER INTO THE UPPER 30S TO MID 40S ACROSS MOST OF THE REGION...ASIDE FROM URBAN SPOTS LIKE ROANOKE AND THE HIGHER TERRAIN OF WV WHERE BLF STILL SITS AT 50. UPSTREAM...RADAR SHOWING SHOWERS MOVING EWD OFF THE CUMBERLAND PLATEAU...EXTENDING SWD TO CHATTANOOGA. FURTHER NORTH THE SHOWERS WERE MORE SCATTERED AND WEAKER. THE 18Z NAM WAS HANDLING THIS WELL...AND BASED ON LATEST TRENDS HAVE SLOWED DOWN TIMING OF SHOWERS BY ABOUT 1-2 HOURS. STILL LOOKS LIKE MEASURABLE RAINFALL AFTER MIDNIGHT INTO THE MOUNTAINS IS EXPECTED. THOUGH TEMPS FALLING INTO THE 30S...ONCE MID AND LOWER DECK FALLS IN...TEMPS WILL STEADY OUT OR RISE A FEW DEGREES. PREVIOUS VALID DISCUSSION... SURFACE HIGH PRESSURE OVER OUR REGION WILL WEAKEN AND MOVE INTO THE ATLANTIC OCEAN TONIGHT. MEANWHILE...A COLD FRONT WILL BE APPROACHING THE FORECAST AREA FROM THE WEST. DURING THE OVERNIGHT INTO TUESDAY MORNING...RAIN SPREADS EASTWARD FIGHTING DRIER AIR IN PLACE. WITH 85H TEMPERATURES OF +6 TO +10 DEG C...AND MINIMUM TEMPERATURES REMAINING ABOVE FREEZING...NOT LOOKING AT ANY PRECIPITATION TYPE ISSUES. ON TUESDAY...ONE LOBE OF UPPER TROF OVER THE GREAT LAKES REGION WILL BE OPENING UP AS IT MOVES NORTHEAST INTO NEW ENGLAND. SFC LOW WILL FOLLOW A SIMILAR PATH...WHICH KEEPS BEST DYNAMIC SUPPORT OFF TO OUR NORTHWEST...AS IT PUSHES A COLD FRONT THROUGH OUR AREA TUESDAY AFTERNOON. THE COLD FRONT WILL REACH THE MOUNTAINS BY 18Z TUESDAY AND EXIT THE CWA BY TUESDAY NIGHT. DO NOT BELIEVE THAT THERE IS ENOUGH INSTABILITY TO ADD THE MENTION OF THUNDERSTORMS TO THE PIEDMONT FOR TOMORROW AFTERNOON AT THIS TIME. HIGH TEMPERATURES ON TUESDAY WILL RANGE FROM THE MID 40S IN THE MOUNTAINS TO THE MID 50S IN THE PIEDMONT.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... AS OF 330 PM EST MONDAY... EXTENSIVE AREA OF MOISTURE BELOW 700MB ON THE WEST SIDE OF THE APPALACHIANS THROUGH WEDNESDAY MORNING. WILL MAINTAIN PRECIPITATION IN THE FAVORED UPSLOPE AREAS OVERNIGHT TUESDAY NIGHT. BUFKIT SOUNDINGS SHOWED MOISTURE WAS TOO SHALLOW FOR CRYSTAL GROWTH. BUT ONLY A SMALL AREA IN WESTERN GREENBRIER COUNTY AND THE NORTHWEST NORTH CAROLINA MOUNTAINS WAS COLD ENOUGH TO SUPPORT A CHANCE OF FREEZING RAIN. MORE LIKELY PRECIPITATION WILL BE VERY LIGHT...DRIZZLE AND POSSIBLE FREEZING DRIZZLE. WENT BELOW GUIDANCE FOR MAXIMUM TEMPERATURES ON WEDNESDAY IN THE WESTERN MOUNTAINS SINCE THAT AREA WILL BE STARTING OUT THE DAY WITH CLOUD COVER. SUBTLE...PACIFIC ORIGIN SHORT WAVE CROSSES THE TENNESSEE VALLEY AND MID ATLANTIC STATES WEDNESDAY NIGHT AND THURSDAY. ASSOCIATED JET WITH THIS FEATURE WILL PROVIDE SOME UPPER DIFFLUENCE. NO DEEP MOISTURE BUT ENOUGH FOR AMPLE MID AND HIGH LEVEL CLOUDS. WILL ADD LOW PROBABILITY OF PRECIPITATION IN FOR LATE WEDNESDAY NIGHT INTO THURSDAY. SREF GUIDANCE AND BUFKIT SUGGEST THE POTENTIAL FOR LIGHT SNOW ON THE NORTHERN EDGE OF ANY PRECIPITATION SHIELD. ANY AMOUNTS FOR RAIN OR SNOW LOOK TO BE LIGHT. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... AS OF 300 PM EST MONDAY... FOR THURSDAY EVENING...MAY SEE A FEW LIGHT RAIN SHOWERS DRIFTING ACROSS THE FORECAST REGION...POSSIBLY LIGHT SNOW OVER HIGHER RIDGES OF THE MOUNTAINS...BEFORE MIDNIGHT AS A WEAK UPPER LEVEL DISTURBANCE PASSES OVERHEAD. NO ACCUMULATIONS ARE EXPECTED. HIGH PRESSURE WILL THEN PASS ACROSS THE GREAT LAKES THURSDAY NIGHT...AND THEN BUILD SOUTHWARD ACROSS THE MID ATLANTIC ON FRIDAY TO WEDGE AGAINST THE EASTERN FACE OF THE APPALACHIANS. AS THE HIGH BUILDS IN...WE WILL NOTICE WINDS SHIFTING INCREASINGLY NORTHEASTERLY...WHICH WILL DRAW COOLER AIR INTO OUR AREA FROM NEW ENGLAND. THE OTHER MAJOR FEATURE WE WILL SEE TAKE SHAPE ON FRIDAY IS THE PASSAGE OF A LARGE UPPER LEVEL TROUGH FROM THE ROCKIES EASTWARD ACROSS THE PLAINS. THIS TROUGH WILL SUPPORT DEVELOPMENT OF A LOW PRESSURE SYSTEM ALONG THE TEXAS COAST THAT WILL PUSH EAST NORTHEAST FRIDAY NIGHT AND SATURDAY. THIS LOW PRESSURE SYSTEM WILL BE A MAJOR FACTOR IN OUR WEATHER FOR THE COMING WEEKEND...LIKELY BRINGING WINTER STORM CONDITIONS TO PORTIONS OF OUR AREA. WEATHER FORECAST MODELS ARE IN BETTER AGREEMENT WITH ONE ANOTHER TODAY CONCERNING THIS SYSTEM...BUT HAVE NOTICEABLY SHIFTED IN THE TRACK THAT THE STORM IS EXPECTED TO FOLLOW. MOST CONSISTENT OVER THE PAST COUPLE DAYS HAS BEEN THE ECMWF...AND HAVE STEERED THE LONG- RANGE FORECAST IN ITS FAVOR THIS AFTERNOON...ALONG WITH THE SIMILAR CANADIAN MODEL. HOWEVER...UNCERTAINTY STILL REMAINS AND HAVE NOT COMPLETELY BOUGHT INTO THE ECWMF/CANADIAN SOLUTIONS AS THE 15/12Z RUNS HAVE SHIFTED THE LOW EAST FROM THE PREVIOUS RUNS...WITH THE LOW NOW EXPECTED TO PASS NORTHEAST ALONG THE COAST RATHER THAN FURTHER INLAND. THE SHIFT IN TRACK KEEPS OUR AREA FURTHER AWAY FROM THE WARM AIR WRAPPING AROUND THE LOW...WHICH NOW INTRODUCES A STRONGER POTENTIAL FOR SNOW AND SLEET FURTHER EAST...POSSIBLY TO INCLUDE THE SOUTHSIDE...AS COLDER AIR IS DRAWN ACROSS OUR AREA TOWARD THE LOW CENTER. ALSO SEE A POSSIBILITY OF REDUCED PRECIPITATION FOR OUR AREA AS THUNDERSTORM ACTIVITY DEVELOPING ALONG THE GULF COAST MAY ABSORB SOME OF THE MOISTURE RIDING NORTHWARD INTO THE MID ATLANTIC. AT ANY RATE...THE FORECAST FOR THIS SYSTEM IS FAR FROM SET IN STONE...AND ADDITIONAL CHANGES/ADJUSTMENTS ARE LIKELY OVER THE NEXT COUPLE OF MODEL RUNS. THE LOW PRESSURE SYSTEM IS EXPECTED TO AFFECT OUR AREA MAINLY FROM THE PREDAWN HOURS OF SATURDAY THROUGH LATE SATURDAY EVENING. AS THE LOW MOVES AWAY SATURDAY NIGHT...WINDS WILL SHIFT NORTHWESTERLY... RESULTING IN LINGERING UPSLOPE SNOW SHOWERS ACROSS THE WESTERN RIDGES...WHILE CLEARING CONDITIONS CAN BE EXPECTED FURTHER EAST. HIGH PRESSURE WILL BEGIN TO SETTLE ACROSS OUR AREA LATE SUNDAY EVENING. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/...
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AS OF 634 PM EST MONDAY... WE WILL SEE A HIGH VFR CIGS THIS EVENING WITH CIRRUS SPILLING IN TWO WAVES. THE 2ND WAVE WILL BE THE UPPER TROUGH MOVING TOWARD THE REGION WITH CIGS STARTING TO LOWER TO LOW END VFR IN THE MTNS BY MIDNIGHT...WITH SHOWERS MOVING TO BLF/LWB IN THE 06-09Z TIME FRAME. THE 18Z NAM WAS MORE AGGRESSIVE WITH LOWER CIGS THAN THE OTHER MODELS...AND TEND TO BELIEVE BASED ON UPSTREAM OBS IN THE TENNESSEE VALLEY WHERE CIGS ARE DROPPING TO 1500 FT. WILL BRING BLF/LWB/BCB DOWN TO MVFR CIGS AND VSBYS IN THE 07-09Z TIME FRAME WITH ROA/LYH GETTING TO HIGH END MVFR VSBYS/CIGS IN THE 13-15Z TIME FRAME. DANVILLE WILL BE FURTHER AWAY FROM THE AXIS OF DEEPER MOISTURE AS THE FRONT MOVES ACROSS SO NOT EXPECTING ANYTHING UNDER 3KFT...THOUGH A PERIOD OF MVFR VSBYS WITH SHOWERS A GOOD POSSIBILITY BY LATE MORNING. SPED UP THE PREVIOUS FORECAST ABOUT AN HOUR OR TWO...THINKING THE SHOWERS WILL CLEAR THE MTNS...BY MIDDAY/EARLY AFTERNOON AND WITH MORE SCATTERED NATURE EAST THINK PRECIP WILL SLIP NORTHEAST AFTER 18Z. WINDS WILL STAY SOUTHEAST TO SOUTH AND LIGHT THIS EVENING...GRADUALLY SHIFTING TO THE SW AHEAD OF THE FRONT BY LATE MORNING...THEN SHIFTING TO THE WEST AT BLF/LWB BY 20Z...BUT NOT EXPECTING IT TO TURN WEST INTO ROANOKE AND POINTS EAST TIL THE TAIL END OF THIS TAF PERIOD. WINDS WILL PICK UP SOME WITH GUSTS TO 20-25 KNOTS IN THE BCB/BLF AREA IN THE AFTERNOON. MEDIUM CONFIDENCE IN VISIBILITIES...CEILINGS AND WINDS DURING THE PERIOD. EXTENDED DISCUSSION... UPSLOPE MOISTURE WILL KEEP SOME SUB VFR CIGS AT BLF PERHAPS LWB TUESDAY NIGHT INTO THURSDAY MORNING BEFORE DRIER AIR PUSHES IN. EXPECT VFR EAST...THOUGH BCB COULD SEE SOME MVFR CIGS TUESDAY NIGHT/WED MORNING. ANOTHER FAST MOVING UPPER LEVEL SYSTEM SLIDES ACROSS THURSDAY THOUGH BULK OF MOISTURE WILL BE ABOVE 3KFT...THOUGH SOME SUB VFR CIGS ARE EXPECTED SOUTH OF A BLF-DAN LINE. GOING TO FRIDAY INTO SATURDAY THE THREAT OF A WINTER STORM LOOMS FOR THE SOUTHEAST AND MID ATLANTIC AS LOW PRESSURE FORMS ACROSS THE GULF COAST STATES AND MOVES ALONG THE SOUTHEAST STATES/COAST FRIDAY NIGHT INTO SATURDAY. AT THIS TIME...AVIATION INTERESTS WILL NEED TO MONITOR THIS SITUATION AS LATER FORECASTS BECOME AVAILABLE. THIS COULD HAVE A HIGH IMPACT FOR TRAVEL OVER THE WEEKEND...FROM THE SOUTHERN APPALACHIANS AND CAROLINAS NORTH TO THE MID ATLANTIC.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...KK/PM NEAR TERM...KK/WP SHORT TERM...AMS LONG TERM...NF AVIATION...KK/PM/WP

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