Area Forecast Discussion
Issued by NWS Blacksburg, VA

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753 FXUS61 KRNK 182337 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 737 PM EDT Sun Mar 18 2018 .SYNOPSIS... High pressure over the region this evening will drift east overnight as a complex storm system approaches our region from the west on Monday. This system will initially bring rain to the region Monday into Tuesday, but wintry precipitation is possible by Tuesday night and Wednesday. Cold high pressure follows this system with drier weather for the end of the week. && .NEAR TERM /THROUGH MONDAY/...
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As of 720 PM EDT Sunday... Warm afternoon temperatures are slow to fall this evening as high clouds invade the celestial dome. However, some clearing is expected north of hwy 460 for radiational cooling to drop temperatures into the low to mid 30s overnight. Across the south, upper 30s to lower 40s are likely with more cloud cover. With very dry low levels, slowed the arrival of light rain along the North Carolina High County until the early morning hours Monday. As of 230 PM EDT Sunday... Drier air continues to work into the region from the north aided by high pressure that remains bridged to the north/east late this afternoon. Expect this trend of overall clear skies outside of the far southwest counties to linger into the evening before the ridge weakens and the flow aloft quickly turns back light southerly tonight. This should begin to bring the residual moisture axis to the south back northeast overnight but to what extent in question as the low level upslope component looks quite weak/shallow into early Monday. Most guidance has also backed off on rainfall coverage overnight with most only showing some light rain across the NC mountains and perhaps along the I-77 corridor into West Va late. Thus have delayed/trimmed pops back some to mainly after midnight with clouds over the southwest redeveloping this evening before surging back northeast overnight. This longer period of clear skies likely to allow temperatures to fall a bit more given lower dewpoints, and be near freezing across the east and north, where if some rain arrives around daybreak could see some spotty light freezing rain mainly Greenbrier Valley. Otherwise tweaked lows down some with steady/rising values late as clouds increase. Warm front to the southwest to gradually lift northeast toward the region by later Monday as low pressure tracks east across portions of the northern TN valley in the afternoon. Models again struggling with the northward extent of deep moisture into a developing low level wedge per high pressure to the north. Most again suggest coverage to be light/spotty until mid/late afternoon given such shallow low level moisture beneath a dry layer aloft, where more of a southwest trajectory will exist between 85h-7h per latest forecast soundings. Also a weak impulse passing to the south along the rear of a passing southern jet max may tend to cut off northward extent of deep moisture early Monday before better lift arrives from the south later in the day. Therefore trimmed back pops espcly to start while keeping a gradual expanse in likelys or higher pops espcly south during the afternoon. Otherwise cloudy and cooler under a low level easterly breeze with highs mostly 50s, except some 40s possible Blue Ridge, and near 60 far west per favored Met mos.
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&& .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 330 PM EDT Sunday... Lots of active weather to cover through the midweek. Expect convective development upstream Monday night at the nose of the 850mb low level jet, supported by a vigorous short wave associated with a vigorous short wave moving out of the midwest. Believe convection will encounter a developing wedge over the Appalachians and become elevated with modestly steep lapse rates aloft. Severe threat will reside off to our south and west, but expect a good dose of widespread rainfall with embedded thunder Monday night across the region. QPF amounts look quite healthy which may create some local hydro issues but widepspread problems are not currently expected. Will be monitoring later model runs to see if anything changes to further elevate hydro concerns. Will also be keeping an eye on how layer thickness values behave Monday night to see how much support there will be for wet snow north of Interstate 64. It currently appears that significant accumulating snow is much more likely just off to our north but some accumulation appears likely for portions of the Alleghany Highlands into Greenbrier county WV. However, it looks to be a tight gradient so any small fluctuations can result in big changes for snow potential Monday night in the north. Tuesday through Wednesday will see significant pieces of short wave energy carve out a broad full latitude trof over the eastern US. This will allow the focus of low pressure at the surface to short to the mid Atlantic coast while a solid wedge remains over the Appalachians. Overall flow in the wedge and around the coastal lows will reinforce cold air over the region aided by dynamic cooling. This will create a thermal profile favoring a progressive change in ptype toward wet snow. So after the first low moves through Monday night and pulls away early Tuesday, the next significant short wave generates another coastal low by Tuesday night with the potential for accumulating snow across the Appalachians and central mid Atlantic region into Wednesday. This is yet another very complex system to affect the region this winter and there is a good amount of uncertainty in potential accumulations. Diurnal effects from heating will also play a role in accumulations during the day on Wednesday. Dynamic forcing lingers with some additional light snow Wednesday night along with upslope enhancement west of the Blue Ridge. High pressure then builds in with fair weather as flurries dissipate west of the Ridge Thursday morning. Needless to say temperatures will be well below normal through the period. && .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 330 PM EDT Sunday... The upper pattern will be fluctuating and progressive through the weekend. A collapsing ridge builds in form the west on Friday, followed by a period of low amplitude quasi zonal flow before a broad western trof/eastern ridge takes shape for the first part of next week. As would be expected this will keep our weather active through the weekend. Friday starts off with fair weather but low pressure moving rapidly through the Ohio valley will bring a good chance of precipitation back to the forecast by late in the day and continuing into Saturday morning, and this could be in the form of snow west of the Blue Ridge. Expect some improvement to begin later on Saturday but upslope snow showers will persist west of the Blue Ridge into early Sunday morning. Then by later on Sunday a warm front spreads precipitation back into the region from the southwest. Low to medium confidence on specific timing/location of precipitation through the period, but the overall flavor of things will be unsettled. Temperatures will gradually moderate and be near seasonal normals for the weekend. && .AVIATION /23Z SUNDAY THROUGH FRIDAY/...
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As of 730 PM EDT Sunday... VFR under light and variable winds will continue across the TAF sites through the night. VFR conditions will be fairly short- lived, however, as moisture ahead of an approaching storm system from the west results in MVFR ceilings returning Monday morning for most locations especially over the mountains. Any light rainfall appears to stay mainly south and west of the terminals until later Monday morning or afternoon at the earliest, with vsby restrictions dropping to MVFR by late afternoon/evening. Warm front lifts north ahead of a storm system to the west later Monday with deteriorating conditions in rain/showers and low ceilings across the region later Monday afternoon and overnight. Isolated thunder will also be possible Monday night as the core of this system swings across. Extended Aviation Discussion... As the low pressure system heads offshore on Tuesday night, precipitation wrapping along the western periphery of this system could bring a period of snow showers, MVFR/IFR conditions, and gusty north to northwest winds on Wednesday. Drier air should finally bring conditions back to VFR by Thursday as high pressure builds from the northwest.
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&& .EQUIPMENT... As of 340 AM EDT Sunday... The Mount Jefferson NWR remains off the air and will likely be sometime next week before it is operational again. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/PH NEAR TERM...JH/RCS SHORT TERM...MBS LONG TERM...MBS AVIATION...JH/PH/RCS EQUIPMENT...JH is the U.S. government's official web portal to all federal, state and local government web resources and services.