Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 231817 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 217 PM EDT Mon Oct 23 2017 .SYNOPSIS... An intense strong cold front will move through the region today and tonight and will move off the East Coast on Tuesday. A similar scenario will play out next weekend with a warming trend Thursday and Friday, followed by a cold frontal passage Saturday and Sunday. && .NEAR TERM /THROUGH TONIGHT/... As of 250 AM EDT Monday... GOES 16 Water vapor loops showed a short wave developing over the northern Gulf of Mexico and Florida panhandle in advance of the closed upper low moving into the western Tennessee Valley. The Florida wave reaches northwest North Carolina by 18Z/2PM and may back the low level winds and enhance what will already be healthy shear over the area. As SPC pointed out the amount of CAPE and instability is very questionable. Will have the scattered coverage of thunderstorms along the front with less potential in the pre- frontal precipitation. Will increase wind gusts today when the low level jet peaks near 70 knots from the south-southeast, with the most favorable location for strong wind from Mercer County, WV through Grayson County, VA to Watauga County, NC. All the clouds today will also limit heating but until the front goes through will have a small rise in temperatures this afternoon. Behind the front models have been consistent showing cold air advection. Upslope clouds will fill in late tonight over the mountains. Precipitable water values rise to around 1.8 inches today, which is excessively high for this time of the year. Will stay close to WPC QPF values which have been increasing every run, similar to what is shown in the synoptic guidance. Still seeing a potential for isolated flooding in the southern Blue Ridge and adjacent foothills where rainfall amounts will be the highest. Previous dry conditions will limit areal coverage, but leaf clogged storm drain may result in better chance of nuisance flooding in urban/suburban areas and high rates when the front comes through also favor an increased flooding risk. In coordination with surrounding offices, will hold off on any Flash Flood Watch and continue to highlight in the Hazardous Weather Outlook. && .SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/... As of 215 AM EDT Monday... By Tuesday morning, the influence of the front will be east of the region, and any precipitation immediately associated with it will likewise be to our east. However, the parent upper low/trough will still be to our west. The center of this upper low will be situated near the upper peninsula of Michigan with its trough axis extending south along the Mississippi River Valley. During the course of the day, these features will make slow progression eastward, still poised west of the forecast area by sunset. The bulk of the energy associated with the low is progged to remain farther north than earlier forecast. As such, our latest forecast will back down on the coverage of any associated showers in the west. At best we will now advertise isolated showers between the Northern Mountains of North Carolina and southeast West Virginia. As we progress through Tuesday night into Wednesday, the upper low/trough continues its slow progression toward/into the area. By Wednesday afternoon, the axis is progged to be overhead, while at the surface a sw-ne oriented ridge axis noses into the area from the Deep South. Moisture will be lacking, and the best dynamics will continue to north of the region. Therefore, very few, if any, showers are forecast across the western half of the region. A trend that will start on Tuesday night, and continue into at least Wednesday will be advection of colder air into the region. Tuesday night, low temperatures of the low to mid 30s will be common across the mountains with lows around 40 to the lower 40s across the Piedmont. By Wednesday night, anticipate readings about three to five degrees colder on average across the area as mostly clear clear skies are forecast, along with light winds, as the center of the surface high pressure settles overhead. High temperatures will also trend cooler. On Tuesday expect upper 50s to lower 60s across the mountains with upper 60s to around 70 across the Piedmont. On Wednesday, subtract about ten degrees from Tuesday`s numbers for the expected high temperatures. The last day of the growing season across the mountains is October 25th. While a few spots across the mountains will experience temperatures at or a little below freezing Tuesday night, the presence of cloud cover and light winds will limit the degree to which frost develops. By Wednesday night, conditions are more favorable for a frost/freeze across the mountains, but at this point, the morning of the 26th, the growing season will have ended, and thus frost will not mentioned in any forecast products or headlines. The same is not true of parts of Rockbridge County, VA. Here, and points eastward, the growing season ends November 15th. With temperatures around freezing, limited cloud cover, and light winds, patchy frost will be forecast late Wednesday night into early Thursday morning for parts of that county, including areas in and around the cities of Covington and Buena Vista. This period is still too far out it time for contemplating any headlines. Thursday into Thursday night, the center of the surface high pressure will shift east of the area. Aloft, southwest winds will start to increase in advance of an approaching upper trough across central CONUS. High temperatures on Thursday and low temperatures Thursday night will be about five degrees milder across the mountains as compared to Wednesday and Wednesday night`s readings. Highs and lows across the Piedmont will be similar to Wednesday and Wednesday night`s readings. && .LONG TERM /FRIDAY THROUGH SUNDAY/... As of 345 PM EDT Sunday... High pressure will continue build back across the southeast United States for the end of the week promoting warming temperatures through Saturday with high confidence for fair dry weather associated with sunny skies Friday. For the weekend it looks like we are going to repeat the current scenario with the development of an amplified upper level trough over the central United States which will move east pushing a cold front through the area over the weekend. The GFS is still the faster of the models bringing the front through Saturday night whereas the ECMWF is 24 hours slower holding off on any appreciable rainfall until later Sunday. Attm will maintain threat for showers Saturday through Sunday, but nothing more or less until models can resolve the timing. && .AVIATION /18Z MONDAY THROUGH SATURDAY/...
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As of 200 PM EDT Monday... A strong cold front to the west is pushing towrad the region. Conditions ahead of the front are mostly MVFR to IFR in low ceilings and reduced visibility in rain. A low level jet set up ahead of the front will create wind shear conditions this afternoon into evening. The threat does exist for thunder in this highly sheared environment to occur ahead of the front as well despite low instability. After the front passes, VFR conditions should return to the TAF locations. The front will arrive at the western border of the county warning area around 19-20Z and will exit through the east by 05-06Z. Extended Aviation Discussion... The region will be in the dry slot late Monday night and Tuesday with conditions east of the Blue Ridge improving back to VFR. In the mountains little to no improvement in expected. Much colder air comes in for Tuesday and Wednesday. Scattered showers with possible MVFR ceilings and visibilities are expected on Wednesday across the region. Upper troughing remains over the eastern United States keeping temperatures cool but with VFR flying weather.
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&& .HYDROLOGY... Localized areas through the mountains of northwest North Carolina and southwest Virginia have seen in excess of 2 inches of rain since midnight. An additional 2 to 3 inches can be anticipated before frontal passage around 8 PM this evening. && .RNK WATCHES/WARNINGS/ADVISORIES...
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VA...Flash Flood Watch until 8 PM EDT this evening for VAZ015-016. NC...Flash Flood Watch until 8 PM EDT this evening for NCZ001-002- 018. WV...None.
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&& $$ SYNOPSIS...AMS NEAR TERM...AMS/JR/PM SHORT TERM...DS LONG TERM...DS/PM AVIATION...JR/PM HYDROLOGY...JR/PM is the U.S. government's official web portal to all federal, state and local government web resources and services.