Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 201800 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 200 PM EDT FRI MAY 20 2016 .SYNOPSIS... Low pressure over the lower Mississippi Valley will deepen and move northeast into the Tennessee Valley today and tonight. At the same time, another low develops off of South Carolina and tracks northeast along the coast. By Sunday, these systems transition to a strong low well off of the New Jersey coast. && .NEAR TERM /THROUGH TONIGHT/... As of 1250 pm EDT Friday... Light rainfall continues to make steady, but slow, progress toward and into our region. Most of the activity was still scattered near the NC/SC border with limited progression into our immediate area. The earlier update to slow the progress has not been slow enough. The update this afternoon will reflect approximately a four hour slow down compared to the previous. This update not only recognizes the trends of the area radars, but is in alignment with the new 12Z/8am runs of both the GFS and NAM, as well as the 14Z/10am run of the HRRR. With less than expected precipitation across the region, temperatures naturally have been climbing more quickly. The update will reflect about a three to five temperature increase in the high temperatures for most locations compared the prior forecast. As of 950 am EDT Friday... Looking at the latest radar trend and the latest updates of the HRRR and RNK WRF ARW guidance, have made some adjustments to the timing of the arrival of precipitation into the area today. Have delayed the push of the likely probabilities into the southwest portion of the region to the middle of the afternoon. Also, have maintained no precipitation, or at best, a slight chance of light rain in the northeast portion of the area. Arrival time in this region being the later portion of the afternoon. As of 430 AM EDT Friday... Low pressure will develop over the Tennessee Valley today. This will enhance a wedge of high pressure over the forecast area as a second low forms off the Carolina coast. Models were in good agreement spread clouds northeast across the region followed by rain. Have slowed the onset of the rain in the northern and eastern county warning area until late afternoon. Best forcing and isentropic list as well as strong upslope will be from 00Z/8PM through 06Z/2AM. 850MB southeast low level jet increases to around 40KTS which will enhance the upslope and precipitation amounts on the eastern slopes of the Blue Ridge. Have raised wind speeds and gusts in the western downslope area overnight. Expect the smallest rise in temperatures in the southwest county warning area, especially once the rain begins. Took a blend of guidance for lows tonight. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 330 am Friday... A Miller B type system expected with parent low weakening over the Ohio Valley and the energy is transferred to the coastal low. The upper level trough will move out of the Great Lakes and push the moderate to heavy rain east of the area Saturday. The challenge in the forecast is how long does it rain hard before the secondary low becomes the primary low Saturday afternoon, pulling bulk of the precipitation out to sea. Several shortwaves will rotate around the upper trough generating scattered convection afternoon into Saturday evening. High temperatures Saturday will range from the upper 50s in the northern mountains to the lower 70s in the Piedmont. We may see warmer than expected temperatures Saturday depending on when the bulk of the rain exits. The Coastal surface low lifts northeast along the coast Saturday night. The upper level trough will pivot over the region Saturday night, keeping the chance for rain showers especially over the mountains. A few showers may overcome northwest flow and push east of the Blue Ridge overnight. Low temperatures Saturday night will drop into the mid 40s in the mountains to the mid 50s in the Piedmont. Cold pool remains over the region Sunday and with afternoon heating, scattered showers and isolated thunderstorms are possible into the evening. Sunday afternoon high temperatures will remain below normal with readings from lower 60s in the west to the lower 70s in the east. The upper trough becomes a closed low Sunday night off the Mid Atlantic coast. As the low moves away, the chance of rain will decrease with our area in a subsidence region. The locations of this feature is similar on both the ECMWF and GFS. Low temperatures on Sunday night into Monday morning will generally be from the mid 40s in the west to the lower 50s in the east. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 330 AM EDT Friday... An upper level low in the vicinity of the Mid Atlantic will keep a chance for showers and a few afternoon thunderstorms in the area Monday. If this low wobbles offshore, the area will be in the subsidence zone and with high pressure building east, the chance for rain will decrease for a few days. Once this low departs, upper level ridging will increase, which means warmer temperatures are on the way. However, with warmer temperatures, the threat for thunderstorms will increase which looks to begin Wednesday. The threat of convection may hang around through the end of the week. Temperatures will moderate to near normal on Monday, then above normal for the remainder of the workweek. && .AVIATION /18Z FRIDAY THROUGH THURSDAY/...
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As of 135 pm EDT Friday... Through Saturday afternoon an upper trough of low pressure will approach the area. A generous stream of moisture will be advected north through the area in advance of this system overtop of an existing lee side wedge of high pressure. The associated surface low pressure will enter the western parts of the area by mid-day Saturday. VFR conditions exist still generally along and north of a KBLF- KROA-KLYH line. South of this line, MVFR clouds and a few pockets of light rain were progressing into the region. As the remainder of the afternoon progresses, look for the MVFR ceilings to continue spreading north with pockets of light rain. Visibilities for the most part will remain VFR. This evening and overnight, look for a broad area of rain to overspread the region. Visibilities will trend to MVFR with ceilings trending to IFR at most locations. Conditions will start to improve late tonight as the heaviest rain moves northeast, out of the region. Saturday morning, most visibilities will be in the VFR range by 14z/10am. Ceilings for the most part will improve only to MVFR through the end of the TAF forecast period. Scattered light rain showers will be possible across primarily the western parts of the area, and an isolated thunderstorm or two cannot be ruled out toward the end of the TAF forecast period. Extended discussion... Saturday afternoon, scattered showers and isolated thunderstorms will still be possible, mainly in the west. VFR visibilities are forecast except for brief sub-VFR conditions under any heavier showers or storm. Ceilings will improve to VFR in the east, but remain mainly MVFR in the west. Saturday night into Sunday night, mainly VFR conditions are expected along with isolated to scattered showers under the passing upper level trough axis. Northwest upslope flow may maintain some MVFR ceilings in the west. Surface gusts of 20 to 25 kts will be possible across the mountains during this time frame. 850 mb winds are progged to increase to 25 to 35 kts, and gradually veer northwest to north. On Monday, winds will start to decrease as the center of the upper low continues to exit the region. Isolated showers will still be possible, especially in the east, related to this feature. Monday night through Tuesday, expect mainly VFR conditions as high pressure settles over the area. Wednesday into Thursday, anticipate a return of scattered light precipitation, and pockets of sub-VFR conditions, returns to the area as a frontal boundary establishes itself north of the region.
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&& .HYDROLOGY... As of 450 AM EDT Friday... Consistent forecast from the models and the Weather Prediction Center with one to two inches of rain expected across the forecast area from this afternoon through late in the day Saturday. A bulk of this precipitation will fall this evening into Saturday morning. There is still a potential that this longer duration rainfall will lead to localized minor flooding along streams and creeks. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS NEAR TERM...AMS/DS SHORT TERM...KK LONG TERM...KK AVIATION...DS HYDROLOGY...AMS is the U.S. government's official web portal to all federal, state and local government web resources and services.