Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 230114 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 914 PM EDT Thu Jun 22 2017 .SYNOPSIS...
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A warm front will lift north across the area overnight ahead of a cold front that will approach from the west on Friday. The remnants of Cindy should interact with this front as it crosses the region Friday night into early Saturday resulting in the potential for heavy rainfall and gusty winds. Much drier air will follow the front for Sunday into next week.
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As of 855 PM EDT Thursday... Swath of mainly light showers continues to edge east/northeast across the region this evening associated with an arc of vorticity aloft and a weak surface warm front. Expecting this to continue a few more hours as the main wave passes to the northwest. However some of the latest short term guidance picks up on another wave heading northeast out of TN/GA and brings more widespread rainfall by midnight and persists into the early morning hours. This despite very moist soundings appears overdone given current trends and lack of deep convection currently to the southwest. Thus will continue with low end likely pops into the overnight for rather low QPF across all except the east where expect drier mid level air to hold longer. This also while leaving out much convective mention given loss of heating and the main corridor of upward motion passing by to the north/northwest overnight. Latest blended TPW also showing the influx of deeper tropical moisture from the south overnight behind the passing wave aloft which should keep things very muggy with lows 60s to lower 70s. Previous discussion as of 347 PM EDT Thursday Warm front associated with surge of humid air on the extreme eastern periphery of Cindy`s circulation continues to gradually creep northeastward. Leading edge of warm frontal rain currently extends from central KY southeastward into the mountains of NW NC and into southeastern NC. The coarser-resolution and finer- resolution 12z NWP suite are in pretty good agreement on shifting the axis of steadiest rainfall across the western third of the forecast area, and particularly into our southwestern WV counties before shifting northeastward into the southern Shenandoah Valley and into the central VA Piedmont after midnight. Kept PoPs to Chance range from the NC foothills/Piedmont and Southside areas where guidance is generally consistent on showing more limited coverage. Rainfall amounts through tonight run from a few hundreths east to four- tenths across the Alleghany Mtns in VA/WV. Accompanying the frontal passage will be an increase in southwesterly winds along the higher ridges. Could see gusts at times reach up to 35 mph associated with an 850 mb jet of 40 kts toward Friday morning. Expectation of cloudiness should keep temperatures on the mild side this evening, and trends in MOS guidance have been for milder temperatures. Stayed away from bias-corrected temps which are too cold, opting for a raw guidance/12z MET MOS blend giving lows in the mid 60s to lower 70s. By morning, it should start feeling more humid. Warm front will have lifted northward by mid-morning Friday. However, it`s expected that sky cover will remain partly to mostly cloudy at best in the wake of the front. Wind fields will remain quite strong aloft - in fact, strengthen some as we progress toward the latter half of the day, ahead of Cindy`s remnants and the cold front moving southward. 12Z NWP guidance currently keeps much of the forecast area dry. It is highly conditional, but if greater breaks/more heating is realized could envision a few stronger storms developing in the daylight hours. I don`t think that outcome is likely - as of now, instability is progged to be very low - but it is something that will need to be closely monitored with subsequent guidance. I did keep lower end Chance PoPs around on Friday to keep the door open for that potential. While SPC`s 1730Z Day-2 Outlook shows much of the western third of the forecast area in a 5% combined severe probability, this appears to be more for the evening period. I mentioned the wind increase earlier...with 850 mb winds increasing to around 50 kts during the day, a continuation of at least breezy conditions can be expected along the ridges. While expected gusts are sub- Advisory level, minor issues possible with limbs/branches being downed by afternoon as trees are fully leafed and more vulnerable to being felled. Will highlight potential for breezy conditions in the HWO. Overall expect lots of cloud cover and humidity on the increase, with highs ranging from the mid/upper 70s to the middle 80s.
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&& .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... As of 347 PM EDT Thursday... Forecast remains wet with remnants of Cindy shifting along a cold front. Models in general agreement in pooling higher rainfall amounts from southern Kentucky into central/northern WV. This has not changed too much from previous solutions, except for keeping most of our area out of the bullseye for torrential rains. This is still iffy depending on how fast the Cindy remnants catch up to the front. Forcing per models still suggests potential for further south track from Bristol to Lewisburg. Per WPC guidance and models will keep higher totals over the far west/northwest. Up to 2 inches of rain expected northwest of a line from JKL-BKW-HSP. Along/east of the Blue Ridge appears less with average amounts of one-quarter to three-quarters. Still not out of the woods if the banding of convection moves further south with heavier rates. Does appear the rain will start pulling out Saturday, so time frame of worst wx looks to be midnight Friday night to mid morning Saturday. Another potential issue Friday night is the strong low level jet depicted by models of 50-60 kts rolling across Southeast WV/Sw Va. Since we will be socked in with rain/clouds, expect only gusts to 30 to 40 mph at best along higher ridges above 3000 ft. Still if the ground becomes saturated, it would not take as much wind to down a weak-rooted or dead tree. Still may hang onto a few showers/storms across southside Va into NW NC Saturday afternoon, then have it dry Sat night into Sunday. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... As of 125 PM EDT Thursday... Fairly quiet wx this period with cooler temperatures as 5h trough digs across the eastern U.S. A few shortwaves in the Monday-Tuesday time frame may fuel a few showers, but overall it looks dry. Toward Thursday the upper trough exits to the east with shortwave ridging building across the Appalachians. Highs and lows Monday- Wednesday should run 5 to 10 degrees below normal, then edge close to normal by Thursday. && .AVIATION /01Z FRIDAY THROUGH TUESDAY/... As of 655 PM EDT Thursday... VFR conditions to start across the taf sites will deteriorate from southwest to northeast overnight as the column continues to saturate with light rain pushing in from the southwest. Latest guidance looks overdone in quickly taking cigs down below MVFR across much of the region before midnight given current dry air aloft in place. Thus delayed the lowering of cigs into sub-VFR until overnight while keeping vsbys more VFR per only very light rain across the region. However did TEMPO in some lower vsbys for a possible period of heavier rainfall toward midnight as a wave passes by to the northwest. Also potential to see locations along/west of the Blue Ridge lower into IFR with LIFR along the ridges. In addition, increasing low- level winds of up to 40 kts may produce periods of low- level wind shear after midnight across the mountains. Warm front should clear the forecast area early Friday morning, with related rain showers lifting into northern VA. Slow improvement to BKN/OVC VFR ceilings expected by late morning into early afternoon. Could see an isolated shower or thunderstorm develop toward the end of the TAF period, though coverage and timing is of low confidence. Therefore leaving out added convection during Friday afternoon for now based on latest models showing most showers remaining to the west until after the valid taf period. Extended Aviation Discussion... Coverage of showers and thunderstorms continue to increase later Friday evening but particularly Friday night as the combination of Cindy and a cold front slide across. Sub- VFR conditions should be the rule during this period with showers and thunderstorms, which may be heavy at times. A few stronger storms could produce gusty winds. West to east clearing anticipated through mid-day Saturday with VFR conditions and a wind shift to northwest. VFR conditions appear to continue until Monday afternoon with possible VFR/MVFR conditions northwestern terminals Monday night/Tuesday associated with a upper-level disturbance. && .HYDROLOGY... As of 345 PM EDT Thursday... Rainfall forecast/models/ensemble river forecasts suggests greater threat for flooding will be west and north of our forecast area. Average rainfall amounts of 1 to 2 inches expected from the NC mountains to Mountain empire of SW VA to southeast WV with 2 to 3 inches further west into the KY/TN/OH corridor. Not seeing enough signals to warrant a watch, but given efficient rainfall rates, any convective elements or training will increase the threat. In summary, based on models looking wet, but still not high enough confidence in a flood/flash flood watch. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH NEAR TERM...AL/JH SHORT TERM...WP LONG TERM...WP AVIATION...AL/AMS/JH HYDROLOGY...WP is the U.S. government's official web portal to all federal, state and local government web resources and services.