Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 161511 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1011 AM EST Tue Jan 16 2018 .SYNOPSIS... Low pressure tracking through the Great Lakes will gradually push a cold front through the Mid Atlantic region today and tonight. A front will form along the front, which will then become incorporated into a developing coastal low off of the Mid Atlantic and New England coast. High pressure builds in behind this system for Wednesday into Friday. && .NEAR TERM /THROUGH TONIGHT/... As of 1005 AM EST Tuesday... Adjusted timing of snow entering extreme southwest Virginia and southeast West Virginia this morning by an hour or so. Light snow and/or flurries will start around noon. Accumulating snow may not begin across the Mountain Empire, New River Valley and the Alleghany Highland of Virginia until 3 or 4 pm. Amounts have not changed. As of 405 AM EST Tuesday... Low pressure develops along the front in the Southern Appalachians this afternoon before tracking northeast then being absorbed into the deepening coastal low Wednesday morning. Surface and low level winds do not back ahead of the front but there will be some better convergences at 850 mb tonight. Large bulk of the lift with this system will be post frontal with the vorticity advection and minimal upper diffluence. Enough of a pressure rise and cold air advection behind the front for and increase in northwest winds from southeast West Virginia into northwest North Carolina. This will promote upslope snow showers through Wednesday morning. Timing of the onset of snow looks similar to past few model runs. Will be reaching a Lewisburg to Boone line after 12Z/7AM. HRRR, Hi- Res guidance and RAP bring leading edge into southeast West Virginia around 15Z/10AM. More of an eastward push does not occur until after sunset. Based on this timing and expected snow amounts have added another segment to the Winter Weather Advisory roughly east of Lynchburg to Martinsville. && .SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/... As of 455 AM EST Tuesday... The deep upper trough over the region at 12Z Wed will quickly lift out of the region as strong Pacific energy moves into the West Coast of the U.S. and breaks down the eastern U.S. trough. The large-scale synoptic driven light snow event will quickly exit the region by midday or early afternoon in the east. Upslope snow showers may continue or redevelop across the Alleghanys, but conditions will not remain favorable for long because of rapidly trending less favorable wind flow and upper- level ridging/zonal flow. Total snow amounts are expected to be in the 1-3 inch range for most of the CWA. The biggest story on Wednesday will be another surge of bitter cold true Arctic air. Currently there is a pocket of such centered over Kansas City where temperatures are in the 0F to -10F range. The 850mb temperatures in this pocket of Arctic air are around -24C, which rivals the coldest air we have seen in previous cold outbreaks this winter. Fortunately, by the time it arrives in our region, it has "warmed" to -18C, which should hopefully spare us the below zero temperatures we saw with the last cold outbreak. Nonetheless, we are still looking at low temperatures in the single digits west to the teens east both Wednesday and Thursday morning. Winds will be increasing during the day Wednesday and Wednesday evening as a coastal low develops off the Mid-Atlantic coast. This will drive wind chills below zero for many areas west of the Blue Ridge and to near zero for the Piedmont, more so Thursday morning than Wednesday morning, when such wind chills will be more confined to areas just west of the Blue Ridge. Given that a Winter Weather Advisory has been issued for the expected snow accumulations across the CWA, the wind chill issue has been included in the WSW for snow. Unlike previous Arctic surges the past several weeks, especially since Christmas, as noted above, the upstream Pacific energy will quickly break down the eastern U.S. trough and allow the flow to transition to zonal rather quickly. It will do so quickly enough that 850mb temperatures will moderate quickly to above zero readings in about a 24-30 hour window after bottoming out around -18C early Wednesday. This will allow a fairly rapid warmup to begin Thursday and continue into the weekend as 850mb temperatures rise to +10C or better by Saturday. Thus, temperatures will start out well below normal Wed and Thu with highs in the teens west to 20s east and lows from 0 to 10 west and 10-15 east, warming to highs in the 40s west and 50s east by Friday with lows mainly in the 20s. Expected snow cover could play havoc with low temperatures (e.g., the -11F that LYH saw a couple of winters ago when in some areas Thursday morning, but much will melt Thursday afternoon and much of the remainder by Friday afternoon, especially in the east. && .LONG TERM /SATURDAY THROUGH MONDAY/... As of 510 AM EST Tuesday... Quite a change in the overall upper atmospheric pattern during the extended will lead to a period of much above normal temperatures that will last into the first half of next week. Broad upper ridging across the southeast will expand northward and deep troughing shifts to the western U.S. 500 mb heights over our area will rise from the current 540dm range to 570dm or so by this weekend. Highs temperatures will warm well above normal into the 50s west and 60s east by early next week. Most will enjoy the milder temperatures after the bitter cold we have endured most of January as well as late December. A Pacific based system will arrive from the Midwest early next week. With 850mb temperatures in the positive double digit range, no concerns with any winter weather and on the other hand there does not appear to be enough instability for thunder yet either in our region. However, rain showers will be likely by late Monday into Monday night. Some snow showers may develop on the back side of this weather system into Tuesday as a brief surge of moderately cold air follows (850mb temps only to the -6C range). && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... As of 720 AM EST Tuesday... Ceilings have lowered to around 5000ft in western and central West Virginia with light snow. Ceilings will lower to MVFR from west to east today into tonight across southeast West Virginia, northwest North Carolin and southwest Virginia in advance of a cold front and band of light to moderate snow. Medium to high confidence on the arrival time of the snow and associated MVFR visibilities. The general trend this morning had been for the HRRR and RAP guidance to slow down the arrival of snow until after 10AM. A low will develop along the front this afternoon and evening which will expand the areal coverage of snow in the central and eastern Virginia and North Carolina. Winds will turn to the northwest behind this system bringing in much colder air. Extended Discussion... Dry air will restore conditions to VFR by Thursday under high pressure. VFR conditions should persist into the weekend with warming temperatures. Moisture will return to west Sunday night into Monday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Winter Weather Advisory until 10 AM EST Wednesday for VAZ007- 009-010. Winter Weather Advisory from 6 PM this evening to 3 PM EST Wednesday for VAZ034-035-043>047-058-059. NC...Winter Weather Advisory from 6 PM this evening to 3 PM EST Wednesday for NCZ004>006. WV...Winter Weather Advisory until 10 AM EST Wednesday for WVZ042>044-507-508. && $$ SYNOPSIS...AMS NEAR TERM...AMS/RCS SHORT TERM...RAB LONG TERM...RAB/RCS AVIATION...AMS/PM is the U.S. government's official web portal to all federal, state and local government web resources and services.