Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 221523 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1023 AM EST Mon Jan 22 2018 .SYNOPSIS... Weak high pressure at the surface and aloft early today will give way to a strong upper-level low pressure area and associated cold front moving east from the central U.S. The cold front will bring widespread rainshowers and isolated thunderstorms to the area late today and tonight, followed by colder temperatures, gusty northwest winds, and mountain snow showers by Wednesday. Temperatures will moderate to above normal again later in the week before the next frontal system arrives during the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 1023 AM EST Monday... Pockets of fog this morning are lifting or mixed out and should be gone by mid morning. The spotty WAA showers have lifted north of the forecast area this morning. Surface high pressure center continues to move into the Atlantic ocean today as the cold front in the central United States travels east. For the morning update, modified temperatures utilizing the latest surface obs, their trends and shaped towards the GLAMP for late morning into this afternoon. Raised highs up a few degrees in some locations. Adjusted cloud cover with latest satellite images and trended towards a blend of NBM and continuity. In general, cloud cover today will increase and lower. Slowed the arrival of the pre frontal showers this afternoon associated with cold front. Allowed for some moisture and the potential of showers to advance northeast along the southern Blue Ridge. More changes later this morning... As of 415 AM EST Monday... Weather conditions will deteriorate fairly rapidly today from our nice weekend weather as a deep upper low pressure area and associated cold front move toward the area from the west. The system is a full-scale cyclone with a significant snow storm on the north end and severe thunderstorms on the south end. Fortunately, neither one of these inclement conditions is expected in our region to any degree, but there are nonetheless some concerns that will need to be addressed as the weather system moves through our area later tonight and Tuesday. Through the afternoon, clouds, moisture, and winds will be on the increase across the CWA as the weather system approaches. While there may be a few sprinkles or light showers out ahead of the front during the afternoon, strong forcing should support a QLCS-type convective system, which will enter southwest VA just before sunset and translate eastward to the Piedmont by midnight. With a 65-70kt LLJ accompanying this activity, will need to monitor for convection that may be able to mix down to the surface with these gusty winds. While the area is outlooked for thunder, currently severe probabilities are not indicated in our area. It is interesting to note that each successive model run advertises slightly stronger forcing and instability as this system moves into the area, so it will need to be watched. Brooks-Craven SVR parameter has been creeping up into the 5000-10000 range and at least weak instability has been indicated for several model runs. However, there are indications that a slight "in- situ" wedge may be in place, so depending on the degree of cloud cover and light precipitation that occurs in advance, will largely determine the intensity of the main convection as it arrives later today. Brief heavy rainfall is expected with the stronger convective cells as well, but given the overall dryness and lack of meaningful precipitation in the past couple of months (very cold and dry!), do not foresee any hydro issues as this system will be moving through very quickly. All of last weeks snow cover is gone, even though the ground is still quite cold from 2+ weeks of single digit and teen temperatures. With gusty southwest winds and accompanying warm advection with 850mb temperatures around +10C, look for most areas east of the Blue Ridge to be well into the 60s today, with 50s further west for highs. Temperatures will remain above normal overnight as the true colder air will not arrive with this system until later Tuesday into Tuesday night. Thus, for today temperatures will average about 20 degrees above normal and will still be about 15 degrees above normal Tuesday morning. So at this point, despite some minor concerns with thunderstorms and gusty winds, nothing meets headline criteria. Any concerns during the forecast period will be addressed via the HWO. && .SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/... As of 345 AM EST Monday... The cold front will be pushing through the region east of the Blue Ridge across the piedmont Tuesday morning before exiting the region and taking the showers and thunderstorms with it. Will be watching the front until it is clear of the area for any embedded convective elements capable of bringing strong winds to the surface. Behind the front temperatures will be falling and upslope snow showers will develop west of the Blue Ridge aided by short wave energy streaming around the large upper trof over the eastern US. While the snow is not expected to be particularly heavy, it will be a prolonged period of show showers west of the Ridge through Wednesday night that will result in a couple of inches of accumulation at the higher elevations through the 2 day period. The low level wind field will amplify considerably behind the front and Bufkit soundings indicate efficient downward momentum transfer. This will create a prolonged period of strong, gusty winds especially west of the Blue Ridge through midweek. && .LONG TERM /FRIDAY THROUGH SUNDAY/... As of 155 PM EST Sunday... Dry weather expected into Friday as high pressure moves across the area then sets up over New England, while upper trough digs across the central and northern plains. Will start to see moisture work northeast on southwest flow late Friday into Friday night. Better threat of rain showers moves in late Saturday into Sunday ahead of slow moving front, as the front becomes parallel to the upper flow. This looks like a good chance for seeing an inch or more of rain. Colder air will be delayed until Sunday night but we could see some accumulating snow showers in the mountains per strong forcing aloft with trough. Temperatures will average above normal this period, falling back toward normal or below beyond Sunday. && .AVIATION /15Z MONDAY THROUGH FRIDAY/... As of 700 AM EST Monday... BKN-OVC VFR ceilings will prevail through much of the day as high-level moisture increases from the west in advance of a deep upper low and associated cold front currently located in the Midwest. Ceilings will mostly be between 080 and 100. Late in the day, a linear organized area, potentially a squall line or QLCS will approach from OH/TN entering the western portion of the CWA near or just before 00Z, then moving across the CWA through around 08Z in the east. This activity will be associated with IFR-LIFR ceilings and IFR visibilities, which will continue overnight. Another concern will be strong gusty winds associated with the convective activity. Wind gusts of 30-40kts at the surface are not out of the question as a strong 60-70kt LLJ traverses the area. Wind direction will be mostly SSE-SSW through the day, becoming WSW with the line of showers. Isolated thunder is possible, but not likely, so it has been left out of the TAFs. NOTAM...The ASOS at KDAN remains INOP tonight due to a power supply failure and likely wont return to service until sometime later Monday or perhaps after that. Therefore the observation remains missing at this time. Also since lower ceilings and/or patchy fog may impact the site, TAF amendments will not occur until data is once again available from the ASOS unit. This includes an addition of AMD NOT SKED in the terminal forecast at KDAN at this point. Medium confidence in ceilings through the TAF valid period. Medium confidence in visibilities through the TAF valid period. Medium to high confidence in wind speed and direction through the TAF valid period. Extended Discussion... Wind will continue to be the main problem behind the cold front later on Tuesday into Wednesday. Strong gusty northwest winds are expected behind the front Tuesday into Wednesday. VFR ceilings should return to the Piedmont by Tuesday afternoon, but MVFR ceilings with low clouds and potentially -SHSN can be expected across the westernmost sites, and possibly as far east at times as KBCB. High pressure and VFR conditions along with diminishing winds should return to the entire area by Wednesday. Dry weather including good flying conditions can be expected Thursday and Friday. && .EQUIPMENT... As of 325 PM EST Friday... NOAA Weather Radio, WXL60 (Roanoke Transmitter) which broadcasts at 162.475 MHz remains off the air. The phone company reported that the circuit line had been cut and will take until Monday January 22nd to fix it. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RAB NEAR TERM...KK/RAB SHORT TERM...MBS LONG TERM...MBS/WP AVIATION...RAB EQUIPMENT...WP

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