Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 220944 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 444 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 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 /09Z MONDAY THROUGH FRIDAY/... As of 1115 PM EST Sunday... Overall VFR to ocnl MVFR cloud bases to persist overnight as passing bands of strato-cu work across the region into early Monday. While VFR ceilings are likely in the east, the best chance at seeing MVFR will continue to reside over the western mountains. Visibilities are expected to remain VFR into tonight, then patchy MVFR fog is possible overnight into Monday morning. Only exception around the KLWB vicinity where warm/moist air over the colder river will make for locally dense fog/stratus with IFR/LIFR cigs/vsbys likely through daybreak on Monday. Appears VFR to hold for much of the day on Monday with a gradual increase in MVFR cigs from the south and west ahead of an upstream cold front by later in the afternoon. Looks like a few showers well ahead of the front could arrive in the west by later in the day but for now leaving out any vsby restrictions due to showers until after 00z/7PM Monday evening. South to southeast winds will also increase with speeds of 10-20 kts possible Monday afternoon, including gusts to perhaps 25 kts or higher along the western ridges near KBLF. NOTAM...The ASOS at KDAN remains INOP tonight due to a power supply failure and likely wont return to service until sometime later Monday. 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. Extended Discussion... Sub-VFR conditions are expected to overspread the area from west to east ahead of a strong cold front Monday night as a swath of showers passes across overnight into early Tuesday. In addition an embedded QLCS with isolated thunderstorms, may accompany the front overnight including a 50-60kt low level jet. Consequently, the greatest concern with these showers will be strong wind gusts, potentially of 45-50 mph or possibly even greater for a short duration in the Monday night/early Tuesday morning time frame. 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...RAB SHORT TERM...MBS LONG TERM...MBS/WP AVIATION...JH/KK/RAB EQUIPMENT...WP

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