Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 110000 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 700 PM EST Tue Jan 10 2017 .SYNOPSIS... Low pressure will deepen and move northeast into the Great Lakes tonight as high pressure moves off the southeast coast. A warm front will lift north across the region tonight into Wednesday. Another low will form in the Rockies on Wednesday which will track northeast through Thursday. This will result in milder temperatures and occasional rain for our area through the end of the week. && .NEAR TERM /THROUGH WEDNESDAY/...
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As of 657 PM EST Tuesday...Freezing rain advisory for light ice accretion and slippery road/sidewalks for eastern Greenbrier County in West Virginia and most of our northern tier of Virginia counties remains valid. However with this update I did opt to make a few changes to PoPs/Wx and hourly T`s, as well as a rather short-lived (over next 3-5 hrs) reduction in dewpoints. Lingering CAD/ridge continues to impart a cool and dry thermal and moisture profile early this evening, with temperatures hovering mainly in the mid/upper 30s with dewpoints largely in the teens. Accordingly, 2-m wet-bulb temperatures are all below freezing. These conditions precede strong pre-frontal warm advection regime with composite radar revealing a solid line of showers along a cold front now extending into eastern KY and OH. This is currently well-handled by preponderance of CAM model output; however, only the HRRR shows any appreciable eastward advance along/east of the Blue Ridge overnight. So I`ve increased PoPs for areas west of the Blue Ridge toward the Likely/Categorical range but reduced them to some extent east. Dewpoints do stand to surge from south to north particularly late evening/midnight as low- level flow veers to south/southeast and taps into higher moisture airmass now developing over the Carolinas (Td`s observed in the mid 20s- 30s). In the near-term, however, anticipate there being some wet-bulb cooling by a couple degrees before temperatures steadily rise on/after midnight. While temperatures as precipitation begins elsewhere should be mild enough for rain, it sets the stage for areas of light freezing rain along our northern counties. Timing of cessation of freezing rain around 1 am still appears reasonable. Still don`t feel amounts will be anything more than a few hundreths but that is all it can take to cause travel problems. Lows tonight should occur rather early in the 30s before steadily rising overnight. Previous near-term discussion issued at 332 PM follows... Posted a freezing rain advisory across the north this evening until 1 AM Wednesday morning. High pressure will slide east into the Atlantic ocean tonight into Wednesday. A southwest flow on the backside of the high will push warm air into our region. Used a non-diurnal temperature trend tonight. As precipitation begins...there may be a brief period when evaporative cooling as the air mass saturated lowers temperatures but the overall trend will be steady or rising tonight into Wednesday morning. Highres models like the HRRR and Hiresw-arw East showed the arrival of precipitation this evening between 23Z/6PM and 03Z/10PM. There is still enough cold air at the onset of the precipitation for freezing rain for northern portions of forecast area including the Alleghany Highlands, Greenbrier County, Rockbridge and Amherst counties. If the model temperature profiles are correct, by 1 or 2 AM temperatures across the area will be above freezing mark. Rain will spread southeast and continue for the rest of tonight into Wednesday morning. Any ice accumulations will be less than a tenth of an inch. Expect areas of fog tonight where dew points rise above freezing over the snow cover. On Wednesday, the upper level pattern will transition to a split flow regime with a closed low sinking over the Baja peninsula and weak southern stream ridging over the southeast. This will keep the Appalachians in a warm and moist southwesterly flow aloft. The warm front will continue traveling north resulting in clouds and chance of rain. Temperatures will be quite tricky as precipitation and lingering snow cover will want to lock in some cool in-situ wedging as thickness values surge. High temperatures should vary from around 40 degrees in the colder locations to the lower 50s in the southwest mountains.
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&& .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... AS OF 330 PM EST Tuesday... Noticeably milder as we head through this period with southwest flow aloft and increasing heights. However, will see less sunshine and some rain at times. One batch will be moving across and out of the forecast area Wed night, as piece of energy and low level jet move across the Central Appalachians. Best chance will be north of I-64 with less in the southeast. Thursday will be mainly dry through frontal boundary will be situated from Lake Erie, southwest to the southern Plains Thursday morning and should approach the Central Appalachians by Thursday evening. Will advertise low chance pops WV to slight chance as far east as I-81. Not changing much into Friday with threat of showers increasing late Thu night into Friday with front pushing southeast to the Carolinas. Models overall showing best lift/forcing splitting with deeper moisture swing south into the TN valley and dynamics racing north toward New England. May be a case where the WV mountains to NC mountains will have the higher threat of showers while the southeast maintains low chance. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... .AS OF 320 PM EST Tuesday... Expect this period to stay milder than normal though strong high moving across New England Saturday will keep it cool/damp, with sfc front/low situated from the KY/TN area southwest to Texas. This frontal boundary will stay in the vicinity of our area into Monday then lift northward as a warm front into the Northeast by Tuesday as strong upper low pushes east and north into the Plains. The southwest flow aloft will keep the moisture streaming in and will see temps about 10-20 degrees above normal early next week. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
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As of 657 PM EST Tuesday... VFR conditions through the next 3 hrs with developing low- level wind shear as southwesterly winds increase to near 45 kts. Flight categories then start to deteriorate, with a gradual VFR/MVFR as frontal boundary lowers ceilings and brings light rain especially western TAFs. Potential for slick runways at LWB due to initial freezing rain. As dewpoints begin to climb to values above freezing over at least a light cold snowpack, potential for MVFR fog to develop over the snow is possible and feel the best chance at this would be at DAN. South winds 6-11 kts should predominate with gusts to 25 kts at BLF through overnight. Precipitation into early Wednesday may prove spotty at best. However as southern end of frontal boundary sags southward but still hangs around by late in the day Wednesday ceilings will begin to lower to an eventual IFR/LIFR. South winds on Wednesday 4-8 kts eventually become light and variable by late Wednesday afternoon. Extended Aviation Discussion... Moisture returns back north Wednesday night ahead of a stronger frontal system and associated low pressure to the west. This likely to maintain areas of sub-VFR within lower cigs and patchy rain showers Wednesday evening into Wednesday night before seeing improvement back to VFR on Thursday ahead of the next front. This second frontal system will work its way into the region Friday into Saturday, maintaining the threat for additional sub- VFR in low cigs along with light rain and/or drizzle. Unsettled weather will continue into early next week.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...Freezing Rain Advisory until 1 AM EST Wednesday for VAZ019-020- 024-035. NC...None. WV...Freezing Rain Advisory until 1 AM EST Wednesday for WVZ507. && $$ SYNOPSIS...AMS/KK NEAR TERM...AL/KK SHORT TERM...MBS LONG TERM...WP AVIATION...AL/AMS/KK

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