Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 261001 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 501 AM EST Fri Feb 26 2021 .SYNOPSIS... Canadian high pressure will drift eastward from the Ohio Vally and Pennsylvania today toward New England tonight allowing colder air to spread southwest down the east side of the Appalachians. Meanwhile, a series of vigorous weather systems will track northeastward from the south central U.S. bringing moisture and precipitation to the area. This precipitation will occur in the form of a wintry mix today and tonight for the mountains and rain elsewhere. Additional widespread rainfall and periods of heavy rainfall possibly leading to flooding are expected through the weekend and into early next week. && .NEAR TERM /THROUGH TODAY/... As of 445 AM EST Friday... ...Minimal Winter Weather Event Expected Today Impacting Mainly the Higher Terrain of the Western Mountains... A difficult and complex forecast in place today from the standpoint of winter precipitation. After unseasonably warm temperatures the past couple of days and lots of sunshine, we return to the winter weather problems today at least in a minimal fashion. The complexity is that confidence is low in winter precipitation type, supporting temperatures, and accumulations. Certainly this event does not rival any of the high impact events we have had in recent weeks this February. Feeling is that this is a minimal impact event at best and almost entirely confined to higher terrain, mostly above 3000 ft. Temperatures this morning are still well above freezing in most areas this morning, generally in the upper 30s to mid 40s with dewpoints in the 20s, so clearly some room for evaporative cooling as the precipitation arrives later this morning, currently moving northeast from Middle TN and northern AL/GA. However, the timing of this precipitation into the area mid to late morning allows for some additional warming this morning. Current advertised temperatures grids do not even show temperatures throughout the vast majority of the CWA, especially elevations below 2500 ft., even reaching freezing today or tonight. Even with the wedge, largely "in-situ" confidence in temperatures dropping low enough to support accumulations of snow/sleet/freezing rain across the majority of the area remains low to very low as we proceed further into the day as the precipitation spreads further northeast. With these factors in mind and mainly a rain event with temperatures above freezing, have tailored the Winter Weather Advisory to include areas only along/west of the Blue Ridge and emphasized higher elevations. Would have used elevation potion in GFE, but unfortunately it failed within GFE here, so had to include the entire county and specify the elevation in the wording. Could clearly see the WSW being cancelled early if any winter weather fails to materialize outside the highest terrain mainly in western NC, Grayson county, and southeast WV, specifically western Greenbrier county. Rain amounts today should generally be 1/2 inch or less. While this should not result in any flooding issues, it combined with all of the recent and frequent rain/snow/sleet/freezing rain events of the past month, sets the stage for a potentially significant flooding threat going into the weekend and early next week, including rivers, creeks, and streams, as FFG values are low with very saturated ground and the potential for 2-4 inches of rainfall during the weekend and early next week. /Confidence Levels in Forecast Elements/ Temperatures - Moderate to High, Precipitation Probabilities - Moderate to High, Winds - High, Winter Precipitation Threat - Low. && .SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/... As of 230 AM EST Friday... ...Heavy, potentially flooding rains possible for parts of the area this weekend into early Monday... February has been a wet month across the region with most of our climate sites ranging from around 0.50 inch to 1.25 inches above normal. Much of this precipitation fell in the form of freezing rain, sleet or snow, that helped maintain wet soil conditions as the collective snowpack gradually melted as days warmed. This weekend, we are looking at a pattern where low pressure heads eastward through the Great Lakes region all while a second low lifts northeast out of the mid-Mississippi valley into the Lower Ohio Valley. As this is transpiring, a warm front is expected to approach the area from the south on Saturday, cross region on Sunday, and stall just to our north Sunday night. As the Great Lakes low heads eastward, its associated cold front then is expected to sweep through the area Sunday night into early Monday. Southwest flow south of the warm front will increase in velocity and advect a generous amount of Gulf of Mexico moisture into the region. A look at the NAEFS Standard Anomalies for precipitable water show values reaching the 1.00 to 1.25 inch range, or plus two sigma, from Saturday morning through Sunday night. The area with the most prolonged period of plus two sigma is over the southwestern sections of the region -- including parts of the Mountain Empire region and New River Valley sections of southwest Virginia and the Northern Mountains and Foothill region of North Carolina. Our latest forecast will have around two to three inches of rain over the area during the period of Saturday through Sunday night. We will need to watch for potential flooding first in the short term, especially Sunday night with heavier rain showers associated with the passage of the cold front. In a somewhat later time period, mainstream river flooding may be possible, especially within the more reactive headwaters region of the Tennessee River, including the Clinch and Holston Rivers. Monday into Monday night, cooler and drier high pressure will build into the region. Lingering scattered showers will be possible after daybreak Monday across mainly southern and eastern sections of the region. Temperatures during this portion of the forecast will average around five degrees above normal on Friday, around ten degrees above normal on Saturday and Sunday. Confidence in the above scenario is moderate to high on the general synoptic pattern transition. Specifics on rainfall amounts and location of the highest amounts are still a question mark, but signs are pointing to our southwest sections for the highest totals. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 230 PM EST Thursday... A cold front will move south into the Carolinas Monday morning. From there, guidance still remains divided on an early week system that could slip in from the southwest, bringing in an opportunity of mixed precipitation whilst cold air lingers. On the other hand, some guidance wants to park high pressure overhead and keep us dry through mid-week. For now, opted with blended guidance that reflects the first option with precipitation moving in. Following that system, a weak frontal passage is possible Thursday, but looks to lack deep moisture with it. Temperatures through the period will run warmer than normal. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... As of 100 AM EST Friday... ...Increasingly Poor Aviation Conditions Expected Today... VFR conditions are expected to persist through most of the night with increasing mid/high clouds in a BKN-OVC fashion, all generally AOA 100. Lower clouds will begin to develop and advect northward after daybreak, mostly in the 025-050 range. Isentropic lift along a developing baroclinic zone and southwest flow aloft will spread light rain into the region by mid to late afternoon from the southwest. At this point, temperatures and sounding profiles support mostly rain at the TAF sites, with any winter precipitation generally confined to the higher elevations. A brief period of sleet is possible in the western higher terrain, but mostly expecting just rain and fog going into the evening and overnight hours. IFR ceilings and visibilities will develop toward sunset. The heavier rainfall moves out of the area after 03Z leaving low clouds, drizzle, and fog with generally IFR to LIFR conditions in place throughout much of the CWA. Winds will veer to the northeast and east overnight as high pressure slides eastward across OH/PA into the northeast, setting up a favorable wedge pattern. Winds will become more southeast west of the Blue Ridge by afternoon and increase in speed with low end gusts developing across much of the area during the afternoon/evening. /Confidence in Forecast Elements/ Ceilings - Moderate to High, Visibilities - Moderate to High, Winds - Moderate to High, Winter Precipitation Threat - Low. Extended Aviation Discussion... Prolonged periods of sub-VFR flight conditions will persist through the weekend. A frontal boundary/baroclinic zone will persist from southwest to northeast across the area with a moist Pacific-based southwest flow aloft. Numerous waves of low pressure moving along the front, bringing periods of precipitation, mostly in the form of rain. The rain will persist into early next week, with the heaviest rainfall expected Sunday into Monday. Some improvement in conditions is possible by Tuesday. .RNK WATCHES/WARNINGS/ADVISORIES... VA...Winter Weather Advisory from 1 PM this afternoon to 7 AM EST Saturday for VAZ011-014-018>020-023-024. Winter Weather Advisory until 10 PM EST this evening for VAZ007-009-010-012-013-015>017. NC...Winter Weather Advisory until 10 PM EST this evening for NCZ001-002-018. WV...Winter Weather Advisory from 1 PM this afternoon to 7 AM EST Saturday for WVZ042>044-507-508. && $$ SYNOPSIS...RAB NEAR TERM...RAB SHORT TERM...DS LONG TERM...DS/RCS AVIATION...RAB

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