Area Forecast Discussion
Issued by NWS Blacksburg, VA

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677 FXUS61 KRNK 290513 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 113 AM EDT Sat Apr 29 2017 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH TODAY/... As of 1127 PM EDT Friday... Forecast was updated to increase sky cover a little over the northwest as outflow from upstream convection pushes eastward in stronger westerly upper flow. A couple questions overnight will be fog and shower/thunderstorm threat. The latest hi-res models and 00z synoptic models still trying to develop showers further southeast toward our area than what is currently indicated on radar. The airmass is still unstable, but at the same time already getting night time subsidence which can squelch thunderstorms. Based on upstream conditions and track of line of convection should see this stay upstream of us most of the night with some showers possible at times reach Southeast WV, but overall looks isolated. Corfidi vectors suggest convection to mainly stay along/north of the Ohio River into Western PA. As for fog will see less than last night but with dewpoints in the mid 50s to mid 60s, moist ground and lighter winds along the river valleys, think will see at least fog in the river valleys overnight, mainly patchy to patchy dense. Otherwise not much change to the temps with lows running 15-20 degrees above normal in the lower to mid 60s, with some upper 50s mountains. These lows are more typical of late June into July. Previous forecast discussion from early evening... Forecast looks to remain on track. Thunder in western Greenbrier later tonight looks even less favorable than earlier anticipated as showers currently pushing toward the region are having trouble clearing the terrain. Made slight adjustments up for overnight lows as temps are not falling as fast as previously forecast and newer guidance is trending warmer. As of 215 PM EDT Friday... Satellite imagery showing a Cu field mainly east of the mountains with some cirrus over the top, but the radar is quiet and expect it to remain that way into tonight. There is some uncertainty as to the chances for showers/thunderstorms tonight mainly along and north of the Interstate 64 corridor as convection develops upstream and slides along a warm front. The majority of guidance is keeping the frontal boundary and associated convection to our north, but some meso guidance has the convection clipping the northern portion of the area. Believe the most likely scenario is for the warm front and convection to remain to our north, but an outflow boundary from this convection will sink into the region and may trigger a showers or thunderstorm in a small time window around Midnight. Will use some low chance POPs extreme north for a 3 to 4 hour period around Midnight to cover this and keep an eye on trends to see if fine tuning is needed. Conditions tomorrow will be quite unstable in the hot and humid airmass but there is significant capping aloft. In the absence of synoptic forcing to break the cap, will have to rely on orographic effects/differential heating to enhance convergence and do not expect this to be overly effective. So aside from some slight/low chance POPs for a shower/storm late in the day mainly in the mountains, expecting a dry day. Temperatures will be quite summer-like with lows tonight in the mid/upper 60s east to upper 50s/around 60 west. Highs on Saturday will be near 90 east to mid/upper 80s west. Since this our first taste of real warmth, make sure air conditioning units are clear of debris before turning them on, and be sure to take frequent hydration breaks when outdoors on Saturday. && .SHORT TERM /TONIGHT THROUGH MONDAY/... As of 215 PM EDT Friday... Large upper ridge off the southeast coast through Sunday night. Low pressure tracks across Missouri on Sunday with a warm front extending into Pennsylvania and a cold front over the central and southern Mississippi Valley. This puts the Mid Atlantic region well into the warm sector. No organized lift or forcing so will keep probability of precipitation low through Sunday night. Models still showing some differences with the timing of the cold front on Monday. Will keep the highest probability of precipitation on Monday along with a mention in the Hazardous Weather Outlooks of strong to severe thunderstorms threat due to a 50-60 knot low level jet. Minimum temperatures will be mild on Sunday night with increasing moisture and mixing from a south wind ahead of the front. Have stayed just above MAV guidance for lows Sunday night. Front will not be reaching the foothills and piedmont until Monday afternoon and evening. This should give enough time, depending on the cloud cover from upstream, for heating ahead of the front. Raised maximum temperatures east of the Blue Ridge on Monday. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... As of 215 PM EDT Friday... Upper low moves through the Great Lakes on Monday night and high amplitude eastern trough in reinforced Tuesday 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 becomes east-west oriented on Tuesday and Wednesday. Weak waves of low pressure will track east along the front. will carry a dry forecast Tuesday through 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 day. && .AVIATION /05Z SATURDAY THROUGH WEDNESDAY/...
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As of 105 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 tonight. This should allow for mainly VFR conditions into the overnight before seeing some patchy fog/stratus develop across the valleys including possible influx of lower cigs across the southeast due to advection of the low level moisture. This mainly shown via the latest Nam which appears likely overdone but given satellite trends in seeing low clouds over eastern NC will include more MVFR cigs around KDAN along with patchy fog into early Saturday morning. Otherwise given more mixing and increase in high clouds from the northwest will cut back on dense fog coverage around KBCB/KLWB/KLYH and run with more of a TEMPO nature toward daybreak at this point. Any thunder overnight at KLWB is still possible, but will likely pass far enough to the north as the latest HRRR and most other solutions keep coverage training farther north but something to watch as a weak wave passes. Unstable conditions will exist tomorrow as temperatures and dew points will be more reminiscent of summer rather than of April, however a strong cap should suppress most convective development. If there will be any thunder it will likely be very isolated and terrain induced, therefore would only be in the higher elevation. Due to the isolated nature of this convection, has for the time being not been mentioned in the TAFs. Winds will be generally light and southerly during the TAF period. Extended Aviation Discussion... High pressure should build off the Southeast coast during this weekend. Other than the potential for MVFR/IFR morning fog at the usual river valley locations, VFR conditions should prevail Saturday and Sunday. As a low pressure system approaches from the west late Sunday and Sunday night, the potential for afternoon showers and thunderstorms will increase. The cold front associated with this system should reach the Appalachian Mountains by Monday and depart offshore by Tuesday morning. As such, expect the best chance of MVFR conditions during the frontal passage.
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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/yearForecast Roanoke89/191589 Lynchburg88/197489 Danville91/198189 Bluefield83/199685 Blacksburg83/197485 Current record/yearForecast Roanoke63/195666 Lynchburg66/195664 Danville65/195666 Bluefield63/199165 Blacksburg59/196262 && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/MBS NEAR TERM...JR/MBS/WP SHORT TERM...AMS LONG TERM...AMS AVIATION...JH/JR/MBS CLIMATE...JR/WP

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