Area Forecast Discussion
Issued by NWS Blacksburg, VA

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613 FXUS61 KRNK 220747 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 347 AM 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 245 AM EDT Thursday... 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 SATURDAY/... 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. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... As of 130 PM EDT Wednesday... There are notable model differences during this portion of the forecast. 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. Where the models differ is the Sunday into Monday time period. Both models offer solutions of a reinforcing cold front sweeping through the area Monday, however, that concludes the similarities. The GFS, for the most part, offers very limited moisture associated with the feature. Its European counterpart offers a wetter solutions. This wetter solution is the result of this guidance bringing a shortwave trough eastward the Tennessee Valley along the first cold front, that interacts with the second cold front, producing a generous coverage of showers across the area late Sunday night and through the day on Monday. Our forecast during this time frame will represent a blended solution that offers the potential of showers, but not to the degree done so by the European solution. On Tuesday, both the GFS and ECMWF hint at a shortwave trough heading eastward through the Great Lakes region into New England. Both keep the bulk of the energy and moisture north of our region. Our forecast will reflect at best some isolated showers across far northern sections of the forecast area. High pressure and dry weather is forecast for Wednesday. Temperatures during this portion of the forecast will start around near normal and trend to slightly cooler than normal by Wednesday. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... As of 140 AM EDT Thursday... VFR conditions today with increasing high clouds and ceilings lowering throughout the day. Exception is some patchy fog in southern Virginia early this morning, including at KLYH. Timing on the arrival of deep moisture and precipitation has slowed down on the models. Guidance currently had showers reaching KBLF and KBCB after 8PM this evening. Have ceilings lowering to MVFR at KBLF after 21Z/5PM, with medium confidence on this timing. Extended Aviation Discussion... Ceilings lower to MVFR Thursday evening into Friday with first surge of showers advancing SW to NE. More sub-VFR conditions through at least early Saturday with periods of moderate to heavy rain. Less threat of showers Saturday evening into Sunday so mainly VFR after Saturday morning, but fog Sunday morning is possible. Scattered MVFR thunderstorms possible Monday. && .HYDROLOGY... As of 320 PM EDT Wednesday... 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 Thursday night into early Saturday morning. An analysis of the 00Z/8PM NAEFS Standardized Anomalies of precipitable water around 1.75 to 2.00 inches across our region during the Thursday night through Friday night time period, which equates an anomaly of to +2 to +3 sigma across the area. Mean integrated water vapor transport is forecast to have an anomaly around +4 to +6 during this same time period. A review of the NAEFS Probabilities place a 50 to 70 percent of extreme maximum of precipitable water over southeast West Virginia mid-day Friday with 25 to 50 percent across a generous portion of the remainder of the area. The Day 3 Excessive Rainfall Outlook from the Weather Prediction Center places a Marginal risk of flash flooding across our region, with the slight chance on the western edge of our West Virginia Counties. WPC QPF numbers across our region during the Thursday through Saturday morning time period has roughly 0.50 to 1.25 across the Piedmont, with the highest amounts on the western parts of this region. Across the mountains, 1.25 to 1.75 is the average. Higher amounts near 2.00 inches are forecast across some of the higher peaks across the Mountain Empire region of southwest Virginia into the Northern Mountains of North Carolina. Western Greenbrier County, West Virginia is forecast to have some of the greatest amounts during this time period with totals around 2.50 inches possible. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS NEAR TERM...AMS SHORT TERM...RCS LONG TERM...DS AVIATION...AMS/KK/WP HYDROLOGY...DS is the U.S. government's official web portal to all federal, state and local government web resources and services.