Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 221757 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 157 PM EDT Thu Jun 22 2017 .SYNOPSIS... High pressure will remain over the southeast United States today as Tropical storm Cindy tracks north through the lower Mississippi Valley. The tropical system will cross the Tennessee Valley tonight ahead of an approaching cold front. This front passes through the Mid Atlantic region on Saturday, followed by high pressure for the beginning of next week. && .NEAR TERM /THROUGH TONIGHT/... As of 945 AM EDT Thursday...No significant changes needed with this update; essentially just modified the start time of steadier rain associated with leading edge of warm front, using a blend of the slower finer-resolution guidance. Regional radar shows rain shield generally along and south of I-40 in NC and TN. Precip shield is making slow northeastward inroads due to dry air as sampled by 12z RNK/GSO RAOBs. Should see progressively lowering/thickening clouds, but steadier rain should really hold off until about 1 PM across Smyth, Wythe, Tazewell Counties in VA and Ashe and Watauga Counties in northwest NC. Highs today should be warmest in the central VA Piedmont as these areas will stay mostly clear to partly cloudy the longest (in the mid 80s), contrasting with temps into the lower/mid 70s at most west/southwest of I-77. Previous near-term discussion issued at 245 AM follows... Staring out with a relatively dry air mass across southwest Virginia, southeast West Virginia, and northwest North Carolina this morning. Moisture increases quickly today and tonight with surface dew points rising into the mid 60s to lower 70s and precipitable water values reaching 1.5 to 2.0 inches by this evening. Models similar in arrival time of precipitation. Wide band of showers across northern Mississippi to northern Georgia will continue to move northeast and reach the Virginia-North Carolina border between 15Z/11AM and 18Z/2PM. Will be after 00Z/8PM before the bulk of the showers advance past Roanoke and Lynchburg. Not much support for thunderstorms. Highest convective available potential energy and lowest Lifted Index values will be across the piedmont of southern Virginia and northern North Carolina. Clouds will hold back heating today. Will stay close to warmer guidance for lows tonight based on the expected dew points. && .SHORT TERM /FRIDAY THROUGH SUNDAY/... As of 330 AM EDT Thursday... Remnants of Tropical Storm Cindy will bring rain into the area in two parts Thursday night into Friday morning and Friday night into Saturday morning. The main circulation with TS Cindy will move ashore along the SE TX and SW LA this morning. Out ahead of the main circulation are tropical short waves tracking across MS/AL. These short waves will move across the Tennessee Valley today, over the area tonight, then to the Mid Atlantic coast by Friday afternoon. In the wake of these waves will be a very humid air mass with dew points in the mid 60s to lower 70s. Under destructive sunshine Friday, clouds are expected to develop breaks in the afternoon which could lead to a few pop-up showers in the afternoon. For the most part, this sunshine will help temperatures climb into the lower 80s across the mountains to the upper 80s in the piedmont. A cold front will pickup the remnants of Cindy and track her across the Tennessee Valley Friday afternoon and over the forecast area Friday night into Saturday morning. The interaction of a cold front and tropical storms remnants will bring a period of heavy rain into the region. With a tropical air mass in place (precipitable water values approaching 2.0 inches) and strong dynamics, heavy rain is likely for the area, especially north of hwy 460. If storms are efficient enough, flooding is a strong possibility. However, this event will come across the area during non-diurnal hours and moving at a fairly fast pace. If models are correct, heavy rain potential will only last for 2 to 4 hours. Rainfall amounts across the mountains will range from three quarters south of hwy 460 to an inch and a half north. Amounts east of the Blue Ridge will range from a third of an inch south to three quarters of an inch north of hwy 460. The chance for severe weather is also possibly with damaging wind being the primary threat. As remnants of Cindy exit by Saturday afternoon, temperatures will rebound into the upper 70s to lower 80s west of the Blue Ridge to the upper 80s east. Dew points will drop into the 60s, which should make the day feel somewhat better. Subsidence in the wake of the storms will bring some breezy/gusty conditions to the area Saturday afternoon. Guidance starts out similar Saturday night with a cold front parked just to the southeast of the region. Lingering isolated showers will be possible across southeastern sections of the area. Front will be east of us Sunday but wave of low pressure moving northeast along it through the eastern Carolinas may send more clouds into the southern CWA with a slight threat of showers/sprinkles. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... 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 /18Z THURSDAY THROUGH TUESDAY/... As of 157 PM EDT Thursday... Initial VFR conditions first couple hours of the TAF period, but with gradually deteriorating conditions after 00z with approaching warm frontal showers. Ceilings steadily lower to MVFR from southwest to northeast. Better confidence on lower ceilings west and a little lower confidence on lower ceilings for Lynchburg and Danville. Visbys in rain generally VFR-MVFR. In addition, increasing low-level winds of up to 40 kts may produce periods of low-level wind shear after 04z, with the best chance at Roanoke, Lewisburg, Bluefield and Blacksburg. Southwest/south winds should be in the 4 to 6 kt range through overnight. 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 mid-morning. Could see an isolated shower or thunderstorm develop toward the end of the TAF period, though coverage and timing is of low confidence. Any thunderstorm that does develop has potential to produce gusty winds and heavy downpours. Winds will continue to be gusty along the ridges, leading to localized periods of turbulence in and around these. Extended Aviation Discussion... Coverage of showers and thunderstorms continue to increase later Friday afternoon but particularly into Friday night. 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 720 AM EDT Thursday... The combination of the the remnants of T.S. Cindy crossing the area in concert with the approach and arrival of a cold front may set the stage for very heavy, flood producing, rain across parts of the area Friday night into early Saturday morning. Forecast precipitable water values are around 1.75 to 2.00 inches across our region Friday and Friday night, which equates an anomaly of to +2 to +3 standard deviations above normal across the area. This type of airmass will result in efficient rainfall production and very heavy rainfall rates. The Day 2 Excessive Rainfall Outlook from the Weather Prediction Center places a Marginal risk of flash flooding across southeast West Virginia and much of southwest Virginia and northwest North Carolina, with the Slight Risk on the western edge of southeast West Virginia. The highest rainfall amounts will be over the mountains where 1 to 2 inches of rain area possible. Localized three inch amounts are not unreasonable for parts of southeast West Virginia. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS NEAR TERM...AL SHORT TERM...RCS LONG TERM...WP AVIATION...AL/AMS HYDROLOGY...DS

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