Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 172201 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 501 PM EST Sun Feb 17 2019 .SYNOPSIS... An area of low pressure will progress into and across the area tonight with its associated frontal boundary crossing the Carolinas. After a brief break in teh wet weather Monday night into early Tuesday, the forecast turns very soggy for the remainder of the week. Tuesday night into Wednesday, enough colder air will be over the region for the strong potential for a significant winter event. && .NEAR TERM /THROUGH MONDAY/... AS OF 245 PM EST SUNDAY... Low pressure was heading eastward through central Kentucky. In advance of the low, waves of precipitation have been progressing across our area. High pressure has been anchored along the U.S. East Coast, with the precipitation over our area reinforcing the low level inversion along and just east of the crest of the Blue Ridge. The highest ridges today have been cold enough for some light icing to take place. Temperatures have struggled to climb with the region of stable rain-cooled air. On the western flanks of the forecast area, outside the influence of the cold air damming, temperatures have reached the mid-40s, and isolated thunderstorms arrived early afternoon on the southeast flanks of the approaching low. North-central sections of the forecast area remain in a Winter Weather Advisory through 700 pm for the potential for additional icing, especially along the highest ridges, and then primarily on elevated surfaces. Overnight, look for temperatures to rise slowly in advance of the approaching low and its associated surface front. Another decent plume of moisture is expected to overspread the region, with the focus for the best coverage of the heaviest rain over the central and southern sections of the area. Given this region was impacted the greatest by today`s rainfall, it will be an area to monitor for any flooding potential overnight. Have opted not to issue a Flood Watch at this time because of the localized nature of any flooding. Also, there will be an even greater potential for flooding headlines later in the week. Best not to overdo the quantity of watch headlines at this point and numb down sensitivity potentially of more substantial events later in the week. On Monday, we will be on the back side of the departing system, and winds will shift northwest and become gusty. Gusts of 30 to 40 mph will be common across the highest terrain along and west of the crest of the Blue Ridge. Gusts of 15 to 25 mph will be common across the Piedmont region. These same northwest winds will allow for drier air to erode cloud cover across the Piedmont. However, clouds will be slower to erode across the mountains thanks to an upslope component. Light precipitation in the form of light rain/drizzle or light freezing rain/drizzle will be possible across western Greenbrier County heading into the afternoon. A few flakes of snow are possible as the top of the shallow moisture layer cools to about -10C late in the day. High temperatures tomorrow will range from the low to mid 40s across the mountains with low to mid 50s across the Piedmont. && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 400 PM EST Sunday... Very active and unsettled pattern to continue through the period with significant potential for a winter storm, with both significant ice and snow accumulations possible, followed by an extended period of moderate to heavy rain events. Areal flooding and river flooding seem almost certain as we move into the mid part of the week and the weekend. The culprit will be a very active southwest flow as deep troughing remains anchored across the southwest U.S. with an endless series of vigorous embedded short waves tracking from the southwest U.S. into the south central U.S. then moving east-northeast to northeast toward the Mid-Atlantic. In essence the main storm track will be right across our area through the entire time frame. This will supply persistent cloud cover and numerous rounds of precipitation. Flooding from excessive rainfall and saturated ground will clearly be the main concern, especially as the week progresses continuing into the long term periods. Unfortunately, with a Canadian air mass lingering just to our north and meandering/oscillating back/forth across our latitude, there will be a definite concern for winter weather. That concern has solidified considerably from yesterday as the depth of cold air appears more certain and further south than indicated yesterday, which is consistent with a deeper wedge developing in response to the slow deepening trough in the south central U.S. As the warm nose from a strong southwesterly jet works its way over the shallow cold air mass later in the night/Wednesday morning, the precipitation will transition to sleet and then freezing rain. Model signals are strong for significant snow, sleet, and ice accumulations, and this could well be the most significant winter storm in terms of total accumulation since the mid-December event. With good collaboration via WPC and neighboring offices this afternoon, we concurred on the potential for winter weather with this event and have followed their snow and ice accumulations closely, namely winter storm warning criteria ice of .25 to .50 inch and snow accumulations of 4-8 inches across the north with 1-3 inches in the south. Given that this is 72+ hours out, no headlines have been issued yet, but will strongly highlight the potential in the HWO/eHWO. Current indications are that the winter weather event will transition into a flooding event through the day Wednesday and Wednesday night. Current QPF projections are in the 2-4 inch range for the Tue-Thu time frame, which is in addition to all the rain we have received over the weekend and early this week. WPC has noted that there are numerous models with strong signals for flooding across a large portion of the southeastern U.S., TN Valley, and into the southern Appalachians. Again, being that this is over 72 hours out, no headlines have been issued at this time, but areal flooding and river flooding appears likely. Please plan accordingly. Temperatures will average near normal during this period as we oscillate between the colder Canadian air mass present just to our north and the much milder air to our south. Thus, there will be some fluctuations above and below normal through the time period. Wednesday will remain below normal, but much above normal temperatures are expected as the week progresses. /Confidence in Forecast Parameters/ Temperatures - Moderate to High, Precipitation Probabilities - High, Winter Weather Potential - Moderate, Flooding Potential - Moderate to High, Winds - Moderate to High. && .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 430 PM EST Sunday... Very wet and unsettled weather continues with a positively tilted mean trough in the western U.S. and a broad subtropical ridge remaining anchored off the southeast U.S. coast. This will keep a conveyor belt of deep moisture anchored over the area along with an active baroclinic zone. Temperatures will start out below normal on Wednesday, then creep to above normal levels by the end of the week as the baroclinic zone is nudged a tad further north thanks to the peristent subtropical ridge off the southeast U.S. coast. Indications are that the baroclinic zone will slip south of the area briefly as high pressure builds to our north on Thursday, to provide a small opportunity for the heavier rain to shift south of our area. However, another significant wave emanating from the southwest U.S. trough is progged to push the baroclinic zone back north into our area Saturday with more heavy rain and flooding possible at that time. At any rate, temperatures will finally warm enough with southwest flow to erode the returning wedge, that the main focus through this period will be flooding, not winter weather. WPC days 1-7 precip outlook currently highlights areas exceeding 4" mainly in western NC, eastern TN, and southwest VA. Areawide, expect at least 2-3", with local amounts of 4-5 inches likely. Please remain abreast of the threat of flooding and river flooding with later forecasts as their is an increasing threat for areal flooding and river flooding, especially during the later half of the week. As noted above, with the region increasingly in the warm sector during this period, temperatures will average above normal and remain mostly above freezing. && .AVIATION /21Z SUNDAY THROUGH FRIDAY/... As of 1245 PM EST Sunday... Precipitation continues to stream across the area this afternoon with some breaks developing across western sections. Temperatures were slowly rising, thus fewer locations are and will continue to become candidates for freezing rain. Those ceilings that are still VFR are expected to trend to IFR/MVFR levels. Those areas already IFR/MVFR will continue that way through the afternoon, with all locations trending IFR through the overnight hours. An addition wave of rain is expected to spread across the area overnight, with the greatest concentration across the southern half of the area. In the wake of this system, winds will shift northwest and trend gusty. This will allow clouds to clear out east of the crest of the Blue Ridge tomorrow morning, with lingering sub-VFR clouds across the mountains, along with some patchy rain or freezing rain across portions of southeast West Virginia. Forecast confidence in the above scenario is moderate. Extended Aviation Discussion... Development of northwest flow behind the departing Low pressure is expected to bring improving conditions through Monday afternoon. Lingering mountain cloudiness is expected to maintain MVFR cigs across the mountains until Monday night. Brief break in the wet weather is expected Tuesday, conditions primarily VFR. Tuesday night and Wednesday another low pressure system will bring sub-VFR conditions as well as providing another opportunity for winter precipitation. A frontal boundary will remain close to the region Thursday into Friday keeping precipitation and the potential for sub-VFR conditions in the forecast. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Winter Weather Advisory until 7 PM EST this evening for VAZ018>020-023-024-034-035. NC...None. WV...None. && $$ SYNOPSIS...DS NEAR TERM...DS SHORT TERM...RAB LONG TERM...RAB AVIATION...DS

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