Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 291126 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 726 AM EDT Sat Apr 29 2017 .SYNOPSIS... High pressure offshore will maintain a warm and humid southerly flow of air across the region through the weekend. A strong cold front will move through the area Monday with showers and thunderstorms, followed by some cooler, but near seasonal temperatures through the first part of next week. && .NEAR TERM /THROUGH TONIGHT/... As of 222 AM EDT Saturday... Overall convection continues to skirt by just to the north early this morning associated with weak impulses riding along a weak front stalled near the Ohio River. May see density help drag an isolated shower or storm toward the far northwest counties early this morning, so included a token mention mainly western Greenbrier given lingering instability, otherwise keeping things dry to start. Degree of cloud cover/fog the main concern early on given debris canopy over the north this morning and potential for warm advection strato-cu to fill in across the south/east. Thus bumped up sky cover to start before seeing any leftover clouds erode by late morning as upper heights build through the afternoon in response to strong high pressure offshore. This combined with a very warm 850 mb southwest trajectory should interact with better afternoon insolation to push highs into the 80s most spots, with perhaps a few low 90s east given such a warm start. This may push record highs in spots despite lack of good downsloping per the climate section below, unless clouds are a bit more and linger longer. Heating and moist dewpoints will also allow for very strong afternoon instability although convective focus limited to mainly the higher terrain where orographics and differential heating aided by some early cloudiness could spark at least isolated storms. However most models have backed off on coverage over the west this afternoon given the cap/warmth aloft and best forcing shifting off well to the west. Think degree of heating including southwest flow along the mountains still enough for spotty coverage espcly if get an outflow or two around within the weak convergence field. Therefore keeping in low pops mainly southern Blue Ridge to start with a gradual northward shift later in the day perhaps aided by a faint wave spilling over the ridge. Expect any convection to fade shortly after loss of heating this evening given lack of much support as the main area of lift shifts back to the west with the next wave along the front. However guidance shows some instability lingering overnight in the warm/moist environment south of the residual front just to the north. This along with continued southwest flow and possibly residual outflow could keep an isolated storm or two going into the overnight but not enough to mention after midnight for now. Otherwise more patchy fog likely under partly cloudy skies early with perhaps more stratus around late. Lows mostly in the 60s although a few spots out east may struggle to fall below 70 as appears guidance too quick to drop dewpoints off late. && .SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/... As of 215 AM EDT Saturday... Sunday through Monday, expect a strengthening southerly low level jet, thanks to an increasing pressure gradient between stationary high pressure off the coast of the Carolinas and a deepening area of low pressure ejecting northeast from the Central Plains states. The low`s associated cold front is progged to cross the region on Monday. We can expect a continuation of above normal temperatures and dew points values heading into Monday thanks to the southerly jet. Although, as we experience more cloud cover and chances of precipitation, daytime highs are not expected to be as extreme as those forecast today. Sunday into early Sunday evening, convection will be primarily diurnally and orographically based. By late Sunday night, coverage is expected to start increasing again with the approach of a strong cold front. This front will cross the region on Monday with generous shear along and just in advance of it. Storms on Monday may be on the strong side with gusty winds, especially during the peak heating of the afternoon across the Piedmont. Model guidance has trended quicker with the passage of the front, so that limited shower and thunderstorm activity will still be across the far eastern sections of the area Monday evening. Tuesday night, winds become gusty from the northwest behind the front with some of the higher elevations experiencing gusts of 35 to 45 mph, with weaker gusts at lower elevations, and even weaker in the Piedmont. As drier air races into the region, anticipate skies to clear rapidly with limited cloud cover across the region on Tuesday. However, gusty winds will continue during the course of Tuesday. By Tuesday night, winds will weaken, but high level cloud cover will start to increase as a disturbance makes headway eastward through the Lower Ohio Valley. Temperatures during this portion of the forecast will be above normal, but trend cooler each day. Readings on Sunday will average 10 to 15 degrees above normal with values by Tuesday above 5 degrees above normal. && .LONG TERM /WEDNESDAY THROUGH FRIDAY/... As of 240 AM EDT Saturday... A high amplitude eastern trough gets reinforced Wednesday through Thursday. 00Z ECMWF closes off a low over the Gulf Coast states by Friday morning, while the GFS is much deeper in the northern stream. Surface boundary remains east-west oriented on Wednesday. Weak waves of low pressure will track east along the front. Will carry a dry forecast Wednesday with near normal temperatures. The 00Z ECMWF brings one of these waves and the associated probability of precipitation into the Mid Atlantic region on Wednesday night and Thursday. WPC leaned toward the ensembles in this time frame, tracking a low from the Tennessee Valley Thursday through the Mid Atlantic states on Friday. This pattern favors below normal temperatures for both of those days. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
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As of 710 AM EDT Saturday... Area remains in between deeper moisture with the front just to the northwest and return low level moisture around high pressure to the southeast early this morning. This should allow for mainly VFR conditions under high/mid clouds this morning with some patchy valley fog making for brief sub-VFR in spots mainly across the western TAF sites. Only exception likely around KDAN and perhaps KLYH where have seen MVFR low deck slide north east of the Blue Ridge. Latest Nam suggests that some of this stratus/strato-cu could linger across the south/east through mid or late morning so including a prevailing lower cig at KDAN, while leaving out at KLYH for now given uncertainty. Also could see an isolated shower work toward KLWB along the southern end of the main convective band to the north. Thus may also include a VCSH mention for a few hours pending release coverage. Combination of deeper moisture lifting back to the north and strong heating should make for a return to widespread VFR heading into this afternoon across the region. However lingering low level moisture in conjunction with the heating will result in increasing instability by mid to late afternoon. This could be enough to produce isolated mainly mountain convection but coverage at this point too iffy to make mention in any of the TAF locations. Otherwise looking at some developing CU fields with a few buildups likely under south to southwest winds at 7-15 kts with possible gusts to around 20 kts this afternoon under the strong heating. Expect any isolated evening convection to fade shortly after dark making way for overall VFR into the overnight. However more potential for patchy dense fog in spots espcly valleys late, as well as possible stratus along/east of the Blue Ridge, including any location that sees an afternoon shower today. Therefore will include brief MVFR vsbys in a few of the valleys and eastern sections where low level moisture will be a bit more widespread. Extended Aviation Discussion... High pressure should continue to linger Sunday ahead of a cold front to the west resulting in widespread VFR conditions after early fog/stratus fade. As a low pressure system approaches from the west late Sunday night, the potential for showers and thunderstorms will increase over the western mountains by early Monday. The cold front associated with this system should reach the Appalachians Monday and depart offshore by Tuesday morning. As such, expect the best chance of MVFR conditions during the frontal passage from west to east during Monday. VFR conditions return behind the front on gusty westerly winds Tuesday followed by continued good flying weather under high pressure Tuesday night into much of Wednesday. However moisture may return to the mountains by late in the day Wednesday with local MVFR possible in isolated showers by the end of the day.
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&& .CLIMATE... Potential for high temperature records to be broken Saturday, April 29, as well as record warm lows for the 29th Current record/year Roanoke89/1915 Lynchburg88/1974 Danville91/1981 Bluefield83/1996 Blacksburg83/1974 Current record/year Roanoke63/1956 Lynchburg66/1956 Danville65/1956 Bluefield63/1991 Blacksburg59/1962 && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/MBS NEAR TERM...JH SHORT TERM...DS LONG TERM...AMS/DS AVIATION...JH/JR/MBS CLIMATE...JR/WP

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