Area Forecast Discussion
Issued by NWS Blacksburg, VA

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210 FXUS61 KRNK 162100 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 400 PM EST Mon Jan 16 2017 .SYNOPSIS...
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Strong area of low pressure over the central United States will move northeast and into the Great Lakes by Tuesday. A cold front trailing south from the low will move east, and cross the Mid Atlantic Region Tuesday night.
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&& .NEAR TERM /THROUGH TUESDAY/...
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AS OF 345 PM EST Monday... Vigorous upper level low is spiraling northeast through the Central Plains and into the upper Mid-West. As of 18Z/1PM the surface low was near Kansas City with a cold front trailing south into east Texas. A warm front extended east from the low into the lower Ohio Valley. Southerly winds ahead of this system was advecting warm moist air northward from the Gulf Coast Region and into the Tennessee Valley where temperatures were in the 60s/70s. This warm air was trying to spill across the Appalachian Divide from the west, but was only making it as far east Bluefield WV...Marion VA...and Boone NC. East of the Divide, the airmass was cool and stable with temperatures in the 40s. The only exception was a sucker hole in the clouds vicinity of Martinsville...Greensboro...and Danville where temperatures squeaked into the 50s. For tonight, the cool wedge east of the divide (which covers 3/4ths of our CWA) will remain in place with stratus and areas of fog persisting through the overnight. Temperatures will change very little within this airmass. West of the divide, Tazewell and Smyth Counties, and for the higher mountain peaks (which will be above the stable air), the warming southwest winds from the Tennessee valley will keep temperatures mild through the overnight with readings not dropping much lower than 50. Models are in relatively good agreement for the mid-CONUS surface front to move east Tonight and Tuesday with deeper moisture arriving across our mountain counties by daybreak Tuesday, then overspreading the rest of the forecast area during the morning. Greatest POPs and QPF are expected across the northern CWA closer to the surface low which is headed for the Great Lakes. Rainfall amounts of a half inch or so are expected across the northern CWA with generally a quarter inch or less across the south. The cool wedge is expected to finally get displaced by Tuesday afternoon, so in spite of the increasing rain threat, temperatures should be 5 to 15 degrees warmer.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
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As of 330 PM EST Monday... A vigorous northern stream short wave will move through the upper midwest and penetrate the broad southern stream ridge over the eastern US. This will allow a surface low moving through the Great Lakes region to push a cold front through the area Tuesday night, with a good chance of precipitation mainly west of the Blue Ridge. The low level wind field will become amplified and with the passage of the cold front, cold air advection will aid downward momentum transfer and create quite windy conditions Tuesday night into Wednesday. The upper pattern will then begin to amplify substantially with a sharp southern stream ridge taking shape in the eastern US. This will allow high pressure to build over the region, and after some lingering upslope showers west of the Blue Ridge Wednesday we can expect generally quiet weather through Thursday. However by Thursday night, the ridge axis will pass to our east and allow low pressure moving up the Mississippi valley to push increasing isentropic lift over the region with the chance for precipitation increasing substantially. Despite the passage of the front on Tuesday night the air behind the front is only modestly colder, resulting in a continuation of above normal temperatures through midweek.
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&& .LONG TERM /FRIDAY THROUGH MONDAY/...
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As of 330 PM EST Monday... The upper pattern will be in a state of flux for the end of the week and through the weekend, as one closed low over the upper midwest dissipates on Friday and is replaced by a very large closed low which dominates the eastern US by Sunday night. This will keep a progression of weather system s affecting our region through Monday. First, a dissipating low pressure system moving northward into the Great Lakes region will push a warm front through the Appalachians and central mid Atlantic region with a good chance of precipitation for Friday. Then in response to the changing upper pattern, another low will develop over the mid Mississippi valley and push what appears to be a dynamic occluded front into the area on Sunday. By this time deep moist southerly flow will be well established above the boundary layer, and when coupled with the dynamics of the front has the potential to produce a significant amount of rainfall. Guidance also indicates the presence of some instability which would support a chance for some thunder in an environment of robust low level winds. This is still quite a ways off but well worth keeping an eye on in the coming days. We eventually get into the dry slot, but moisture and colder air wrapping well around the vertically stacked system will keep a good chance of rain around through Monday. Temperatures will remain well above normal through the weekend, but colder air wrapping around the vigorous low on Monday will bring temperatures down a bit west of the Blue Ridge.
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&& .AVIATION /21Z MONDAY THROUGH SATURDAY/... As of 100 PM EST Monday... Wedge of cool stable air on the east side of the Appalachians will promote low cigs, and in some areas low vsbys, through the 24 hour valid Taf pd. Cigs of 1-2kft were common just east of the Blue Ridge with cigs of 300 to 900 feet withing the vicinity of the Blue ridge in addition to IFR VSBYS. Have low confidence that the majority of the area will rise above MVFR today. Wedge in place will keep cigs down against the mountains and foothills and this will likely persist until we can get better mixing ahead a an approaching cold front later Tuesday. Until then, the expectation is for flight conditions to improve to no more that MVFR. Extended Aviation Discussion... A strong front will arrive from the west Tuesday associated with showers and widespread sub-VFR. Some actual bonafide clearing may take place behind the front on Wednesday with potential period of VFR Wednesday into early Thursday. However, this is expected to be short-lived per return of unsettled weather by weeks end as moisture returns from the southwest. No precipitation type issues are expected through the end of this week...just plain ol rain. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PM NEAR TERM...PM SHORT TERM...MBS LONG TERM...MBS AVIATION...PM

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