Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 282041 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 341 PM EST Mon Nov 28 2016 .SYNOPSIS...
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A series of weather systems will bring warm and breezy conditions to the region, along with periods of widespread rainfall, for the next 2 days. Rain will develop ahead of a cold front tonight through early Tuesday, followed by a low pressure system moving out of the lower Mississippi valley with more rainfall on Wednesday. Cooler high pressure will then build in with dry weather expected for the end of the work week and into the weekend.
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&& .NEAR TERM /THROUGH TUESDAY/...
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As of 330 PM EST Monday... Satellite imagery continues to show thickening clouds over the region, and returns on radar have yet to reach the ground. But its only a matter of time before we saturate and get some decent precipitation going ahead of the front approaching from the west. Believe orographic effects will generate showers along the Blue Ridge ahead of the main body of showers with the front, but much of the region will wait until later tonight for the onset of precipitation. It looks like a solid shot for precipitation west of the Ridge, but guidance varies a bit on the integrity of the precipitation shield to the east and will go with the trend shown in the meso models and taper shower activity off during the afternoon. Not overly impressed with convective potential as mid/upper lapse rates are modest and any CAPE is of the long/skinny variety. While an embedded rumble of thunder is possible, will leave this out of the forecast for now. Rainfall amounts of 1 to 1.5 inches can be expected with this shot of precipitation along the southern Blue Ridge through Tuesday, but amounts up to one half inch will be more common elsewhere. The big concern through tomorrow will be the very strong low level southerly jet ahead of the front. While the core of strongest winds will slide by to our west, we will still be within the broad energized wind field and some very string gusts are expected. This being a warm advection scenario gusts will have trouble reaching the surface, and once precipitation begins and lapse rates become less steep downward momentum transfer will be limited. Will continue the current wind advisory form the northwest mountains of NC up through the Mountain Empire of VA as this is a favored area for high winds in this type of regime, but other locations from the Blue Ridge westward will also be quite windy through tonight above roughly 3500 feet MSL. As the strongest winds pull away late tonight, the high wind threat will diminish by daybreak Tuesday. Temperatures look to be rising overnight so expect an early low in the mid 40s to lower 50s, with temperatures by daybreak Tuesday about 5 to 10 degrees warmer. Highs Tuesday will then generally be in the mid/upper 60s.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
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As of 330 PM EST Monday... Initial round of precipitation will be winding down late Tuesday with front over eastern VA. Still looking for a 2nd wave of precipitation to develop in response to strong shortwave rounding the base of upper midwest closed low. Have kept high chance pops in overnight but increasing to likely by Wednesday morning. Heaviest rainfall appears to be during the day Wednesday with WPC and various model blends suggesting a range between 0.75 to 1.50 inches across the CWA. No issues expected with p-type as warm advection pushes h85 temps into +10 to +12C and none with hydrology as these amounts will be insufficient to overcome the incredibly dry antecedent conditions. Precip event winds down into Thursday with cooler and drier air working in behind the front. Expect a wide range in high temps during the day with 40F to 60F SE. Could be brief changeover to snow in the favored upslope areas but not impressive at all in terms of wind, cold advection and pressure rises for this activity. H85 temps only fall off into upper 20s in far NW to mid-30s SE.
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&& .LONG TERM /FRIDAY THROUGH MONDAY/...
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As of 330 PM EST Monday... Friday looks dry and seasonable with highs low 40s NW to low 50s SE and a Saturday possibly a transition day toward wetter conditions late weekend. 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.
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&& .AVIATION /21Z MONDAY THROUGH SATURDAY/... As of 1225 PM EST Monday... Expect VFR tafs early in the period with a rapid trend to MVFR/IFR conditions tonight as a front approaches from the west. Expect precipitation with lower cigs to spread in from west to east, but some showers will develop in upslope southeast flow along the southern Blue Ridge ahead of the main precipitation. However, a bigger concern is the low level jet ahead of the front with a core in excess of 70kts. The main thrust of the jet will brush our area as it ride up to our east, but the overall wind field is broad and there will be a sharp increase in low level winds overnight. Will include a mention of wind shear due to speed at KBLF and KLWB since they are closest to the core of highest winds, but a significant increase in low level wind speed can be expected at sites through tonight. Believe once precipitation sets in and lapse rates become less steep this will act to limit downward momentum transfer so will indicate higher winds before onset of precipitation. This will have to be monitored closely since a slower arrival of precipitation will create a larger window for higher winds to mix down, and any discreet convective elements may also be more efficient in mixing winds down. With a lot of flow parallel to the front, it will be in no hurry to clear the region and may well end up stalling out in our vicinity. This will allow poor flight conditions to linger through the end of the TAF period, though winds will be lessening as the core of stringer winds aloft pulls off to the north. Extended aviation discussion... Initial wave of rainfall will exit late Tuesday with leftover sub-VFR conditions in place before a more significant batch of rain arrives later Tuesday night and continues into Wednesday evening. This likely to keep widespread sub-VFR ceilings and visibilities in place until a cold front passes through the region early Thursday. Drier air behind the front should result in a return to VFR east of the mountains while upslope sub-VFR cigs likely linger across the southeast West Va locations, where rain or snow showers appear possible. Broad northwest flow looks to keep this scenario in place on Friday as well with upslope driven sub-VFR cigs western mountains and mainly VFR to the east. && .FIRE WEATHER...
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As of 330 PM EST Monday... Wind gusts at the higher elevations elevation will be increasing and become very strong with values approaching 50 mph especially at locations above 3500 ft. At lower elevations, gusts on the order of 20 to 25 mph will be more common. Areas east of the crest of the Blue Ridge will experience minimal gusts. Wind gusts are expected to diminish with the onset of precipitation as lapse rates become less steep and limit downward momentum transfer. Relative humidity values will be steadily increasing and be well above 50 percent by this evening, and remain well above 50 percent through midweek. A series of weather systems will bring widespread wetting rainfall to the region during the next 2 days. Rain will develop ahead of a cold front tonight through early Tuesday, followed by a low pressure system moving out of the lower Mississippi valley with more rainfall on Wednesday. Total rainfall through midweek is expected to be in the 2 to 3 inch range along the southern Blue Ridge into the mountains of North Carolina, but amounts of 1 to 1.5 inches will me more common elsewhere.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...Wind Advisory until 7 AM EST Tuesday for VAZ007-009-015. NC...Wind Advisory until 7 AM EST Tuesday for NCZ001-018. WV...Wind Advisory until 7 AM EST Tuesday for WVZ042. && $$ SYNOPSIS...MBS NEAR TERM...MBS SHORT TERM...PC LONG TERM...PC AVIATION...MBS/RAB FIRE WEATHER...MBS

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