Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 291506 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1006 AM EST Tue Nov 29 2016 .SYNOPSIS...
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A weak front will remain just west of the area this afternoon into early Wednesday allowing a series of upper disturbances to track along the boundary. This will result in periodic rounds of rainfall this afternoon and again later tonight into Wednesday. A stronger cold front will pass through the region Wednesday night bringing drier and cooler weather for the end of the week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 950 AM EST Tuesday... Axis of heavier showers now crossing the Blue Ridge along the residual outflow from overnight and along a warm front lifting to the northeast. Decent rainfall amounts along the swath of precip with a good third to one half inch currently. Latest HRRR shifts this band, in advance of the stalled front along the western slopes, quickly east into the afternoon with most significant rainfall exiting the southeast by mid afternoon if not sooner. Cant totally rule out a rumble of thunder over the far south and east as guidance shows some weak instability under a swath of good upper diffluence within the very mild air that has advected north from overnight. However appears most convection likely to be even farther to the southeast where deeper instability will reside so leaving out mention. Otherwise bumped up pops to higher likely/categorical along the axis of rainfall as it progresses east into the piedmont through early afternoon. This should bring about a lull in all but the far southern sections where plan to leave in some low pops for late in the day once the main band slides east. Southwest winds remain quite strong aloft but currently too high to mix very strong speeds to the surface despite lack of much of an inversion where temps have warmed. Highs again appear mild, mostly 60s to even around 70 southeast, but tricky farther north where still stuck in the cool pool north of the warm front. Thus lowered highs back closer to 60 far north/west where may see a brief surge once the rain tapers per latest Met mos. Previous discussion as of 400 AM EST Tuesday... First round of much needed rainfall moving through the region early this morning. This rainfall is associated with a dampening/shearing out short wave emanating from a deep upper low centered across the Midwest. Rainfall amounts so far have all been less than an inch ranging from around 2/3rd or a letter better across northwest NC into Grayson county VA to only a few hundreths across the Piedmont. Far from a drought buster, but certainly welcome, especially with the best rainfall in the most severe drought Blue Ridge mountain forest areas. The last piece of energy from this short wave will traverse the region through the morning hours with additional light rainfall amounts, mostly from this point forward across the northern and eastern portions of the forecast area. Additional rainfall during the afternoon/evening will be limited, but cannot completely drop pops below mentionable values as broad southwest flow aloft prevails and additional upstream disturbances are on the way. As the upper low continues to move slowly east through Wednesday, a more significant and final disturbance is progged to round the base of the trough and bring another round of rainfall beginning late tonight in the west spreading further east Wednesday. With a better tap into the Gulf, this one promises to bring more beneficial rainfall to the area, but will leave further discussion on that to the next section. The GFS is fairly aggressive on instability late tonight/early Wednesday as the upper-level feature approaches and elevated thunder cannot be ruled out, but given that this is the only model indicating such and the potential for a cool, stable boundary layer, will not include thunder through this period at this time. The strong surface winds associated with the 50kt+ LLJ will shift east of the CWA during the morning hours. A few gusts toward 40kts still not out of the question through the morning hours along the higher peaks of the Blue Ridge across Bedford/Amherst, but not enough coverage to warrant a new Wind Advisory. A less impressive LLJ will approach the region from the west late tonight in association with the next short wave, but speeds look to be well below advisory criteria east of the divide and thus will not issue any further wind headlines at this point. 850mb temps surge well into the double-digit range today of +12C to +13C well north into the northeast U.S. A non-diurnal temperature trend was already under way this morning with balmy late November temperatures in the 50s and which have been rising overnight. By afternoon this will equate to temperatures well into the 60s except 50s higher mountain elevations, some 20 degrees above normal. Look for a very mild night tonight/Wednesday morning as strong southerly winds continue to transport warm/Gulf air this direction. Low temperatures Wednesday morning will be some 30 degrees above normal in the mid 50s to near 60!
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&& .SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/... As of 200 AM EST Tuesday... On Wednesday, a shortwave trough will head northeast across the region on the east side of an upper low/trough centered across the north central part of the nation. At sunrise, rain is expected across primarily the western and southwestern portion of the area. As the day progresses, coverage will translate eastward in concert with a shift eastward of the upper trough. By Wednesday evening, the shortwave trough will be exiting the eastern portion of the area with some trailing precipitation across the eastern quarter of the area. The upper systems associated 850mb trough axis will cross the area Wednesday evening, and northwest flow will commence. Although, the latest guidance suggests not the best cross barrier flow with an orientation more west-northwest. Look for scattered rain showers across the western slopes of southeast West Virginia through the overnight hours. Enough cold air may arrive by sunrise Thursday for a mix with or change over to snow showers. Thursday through Friday night, the upper low/trough near the Great Lakes region will make gradual progress eastward towards and over the Canadian Maritimes. This will keep the region under a prevailing west to northwest flow, all while an west-east oriented surface ridge axis noses into the western parts of the area. We expected flurries/sprinkles to conclude the precipitation Thursday morning across the western parts of Greenbrier County, WV. The vast majority of the area will be dry Thursday into Friday night. A disturbance within the northwest flow is expected to pass through NY/PA on Friday. While most of the energy and moisture with this system will stay north of the area, enough may make it south enough to yield scattered upslope flurries/sprinkles across western Greenbrier County Friday into Friday night. Temperatures will trend colder during this portion of the forecast. Readings on Wednesday will be 15 to 20 degrees above normal. By Friday, temperatures closer to normal for this time of year are forecast. && .LONG TERM /SATURDAY THROUGH MONDAY/... As of 330 PM EST Monday... Saturday brings possibly a transition day toward wetter conditions late weekend, but there are unresolved differences among the models in this regard. Highs near climo for early December. Still considerable divergence persisting in the model solutions for the latter part of the extended. 00Z/28 Euro came in quite wet for weekend with a deep trough located over Texas and the Gulf opening up with strong moisture return along with favorable dynamics. Latest 12z/28 operational EC run maintains similar solution with this fairly bullish scenario for additional precipitation. This in distinct contrast to last few GFS/CMC runs which keep western trough much further west, back across AZ or northern Mexico with a flat zonal flow across the east and little to no northward moisture return through Sunday. Latest PMDEPD discussion is favoring the run- to- run consistency of the GFS and maintaining high pressure over our area through Sunday and suppressing significant precipitation well to the southwest. Have raised PoPs into chance range starting early Sunday but confidence is not particularly high. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... As of 645 AM EST Tuesday... Poor aviation conditions expected through the TAF valid period. A broad upper low pressure area centered across the western Great Lakes will drift slowly east through Thursday. An initial short wave and associated cold front were moving through the region this morning with a couple of waves of light rainfall. The later area of light rain will traverse the forecast area during the morning hours, exiting to the east during the early to mid afternoon. Little additional measurable precipitation is expected during the afternoon. The next wave of precipitation, associated with the main disturbance rounding the base of the deep upper trough and originating from the southeast states, will approach the area late tonight and early Wednesday. There are some indications that there may be a period of MVFR or better cigs west of the Blue Ridge for a brief period this afternoon toward 00Z before conditions sock back in for good for the rest of the night. However, this improvement is not expected east of the Blue Ridge where south- southeast winds will hold the low-level moisture in place. Otherwise, mostly MVFR-IFR cigs through midday, becoming mostly IFR-LIFR after 00Z in DZ and FG. The next round of rain will arrive around 09Z in the west, closer to 12Z in the east. Visibilities will generally be MVFR to low end VFR through mid day, VFR during the afternoon, becoming mostly MVFR to locally IFR overnight in DZ, FG, and -RA. The strong low-level jet that traversed the area overnight has generally pushed northeast of the area and is weakening. Winds have dropped below advisory criteria. Will carry LLWS at KLWB for a couple more hours, but not include anywhere else. Winds across the Piedmont have largely decoupled showing east 3-5kts. Otherwise, mainly seeing SSE-SSW winds 5-7kts with low end gusts yet in a few places. Winds through much of the TAF valid period will be SSE-SSW 4-8kts with low end gusts by afternoon many locations, decreasing after 00Z and trending more SSE. Medium confidence in ceilings and visibilities through the TAF valid period. Medium confidence in wind speed through the TAF valid period. Medium to high confidence in wind direction through the TAF valid period. Extended aviation discussion... Improving conditions expected after the upper low and final short wave move east of the area Wednesday night. Conditions should become largely VFR east of the Blue Ridge into the weekend. Upslope clouds and potentially a weak clipper system could bring a low chance of rain or snow showers into the Alleghanys Thursday and Friday along with lingering MVFR cigs before conditions improve there as well. && .FIRE WEATHER... As of 430 AM EST Tuesday... Beneficial rainfall of 1/2 to isolated near 1 inch amounts observed across the southwest part of the forecast area, which has been the driest area with the most significant drought and forest fire conditions in recent weeks. Thus, this rainfall is very good news. Now with winds also in a diminishing trend, fire threat has been greatly reduced. Additional rainfall expected tonight/Wednesday should further alleviate any fire weather concerns in the short term. && .RNK WATCHES/WARNINGS/ADVISORIES...
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VA...None. NC...None. WV...None.
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&& $$ SYNOPSIS...JH/RAB NEAR TERM...JH/RAB SHORT TERM...DS LONG TERM...DS/PC/RAB AVIATION...AMS/MBS/RAB FIRE WEATHER...

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