Area Forecast Discussion
Issued by NWS Blacksburg, VA

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719 FXUS61 KRNK 222321 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 721 PM EDT Sun Oct 22 2017 .SYNOPSIS... A strong cold front will move through the region late Monday preceded by a period of heavy rain, then cooler temperatures for mid week. A similar scenario will play out in the extended forecast with a warming trend Thursday through Saturday, followed by a cold frontal passage late next weekend associated with showers, and cooler temperatures to close out October. && .NEAR TERM /THROUGH MONDAY/...
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As of 715 PM EDT Sunday... Only minor updates this evening to temperatures and dew points. The timing of rain to entering NW NC after midnight then spreading north by sunrise remains the same. Models are showing a strong low level jet that could warrant a wind advisory across the Mountain Empire of SW VA and the NW NC mountains overnight. However, guidance does not bring these strong winds to the surface as column becomes very saturated. Elevations above 3500 feet may see wind gusts up to 45 mph during the morning hours Monday. As of 300 PM EDT Sunday... An active period of weather is expected in the near term period, as water vapor satellite imagery shows an elongated upper trof from the upper Mississippi Valley southward to the Gulf Coast. Water vapor imagery is also indicating the first signs of a wave forming along this trof in northeast Oklahoma which the short range models strengthen, and lift northeast as a dynamic negatively-titled trof late on Monday. Low level moisture is beginning to return to the area with mid to upper 50 dew points nosing into the piedmont early this afternoon. Many of the high-res models, including the HREF, bring stratus and light precipitation, especially in the southern Blue Ridge, after 03Z tonight on easterly upslope flow. Trended toward the warmer guidance for lows tonight, especially in the mountains, but longer period of radiational cooling east of the Blue Ridge may allow temps to fall near guidance. Good surge of moisture, with PWATS projected to be 1.5 - 1.7 inches surges into our area in advance of the approaching upper level system. These values would make the top 15 for the month of October at BCB and exceed 200% of normal. With the cold front not passing until after 00Z...expect 8-12 hours of upslope precipitation especially in NW NC, where SREF plumes show a wide range of precip amounts from 1.25 to 5 inches. With dry antecedent conditions and fairly fast movement to the precipitation expected, will not issue any flood/flash flood headlines, but minor flooding is expected. Another concern for Monday is the threat for isolated tornadoes and locally damaging winds. While instability is minimal, 0-6KM Bulk shear values are expected to be greater than 50 kts on Monday. Models are also in good agreement in developing a meso-low to our south, and lifting it into western Virginia late Monday afternoon/early evening, enhancing low level helicity values. Will continue to address the threats for minor flooding and isolate tornadoes/wind damage in the HWO and briefing slides. Breaks in the clouds in the eastern portion of the forecast area (DAN/LYH) may allow temps to exceed guidance, but went near guidance elsewhere for highs.
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&& .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 330 PM EDT Sunday... Heavy rain will end by midnight Monday night followed by partial clearing as the cold front moves east of the forecast area. Initial post frontal environment will bring some cooling and drying, but a more substantial drop in thickness will not take place until late Tuesday and Tuesday night associated with the upper level trough. This suggests Tuesday will remain relatively mild, especially east of the Blue Ridge where temperatures may test 70 degrees with some sunshine. Cold air advection associated with the upper trough will be more prominent across the mountains west of the Blue Ridge Tuesday afternoon, and then areawide for Tuesday night into Wednesday. Model soundings indicate very little moisture aloft for precip Tuesday except for maybe the far west. From Tuesday night into Wednesday and Wednesday night, forecast attention will be focused around a cold upper level trough which will be passing overhead with 85h temps of minus 2 to plus 2 deg C. Any lingering moisture with the trough will be mainly confined to the mountains west of the Blue ridges with lingering low level cloudiness and potential for some sprinkles or flurries depending on the boundary layer temperature at the time. QPF numbers are minimal, a trace to a few hundredths, so not expecting anything measurable with respect to snow. && .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 345 PM EDT Sunday... High pressure will build back across the southeast United States for the end of the week promoting warming temperatures Thursday through Saturday with high confidence for fair dry weather associated with sunny skies both Thursday and Friday. For the weekend is 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 /00Z MONDAY THROUGH FRIDAY/...
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As of 720 PM EDT Sunday... VFR conditions will prevail through midnight, but flying conditions will rapidly deteriorate after 05Z (1 AM EDT) with IFR clouds and vsbys due to showers arriving south of a line from BLF-ROA after midnight, then advancing north to included mountain sites (BLF-BCB-ROA-LWB) by sunrise. Showers will expand in coverage during Monday morning with IFR to MVFR vsbys and cigs persisting through the day. Low level wind shear (WS020/16035KT) maybe an issue across the mountains between midnight and noon. High confidence in ceilings and visibilities throughout the TAF valid period. Extended Aviation Discussion... A deep upper trough and associated strong cold front will move into the region from the west Monday night/early Tuesday with sub- VFR conditions in rain/showers along with increasing wind. Colder, blustery, unsettled weather with perhaps largely MVFR conditions across the mountains will linger through the later half of next week. MVFR showers may return by early next week.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PM NEAR TERM...PH/RCS SHORT TERM... LONG TERM...PM AVIATION...RCS

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