163 FXUS61 KRNK 110540 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 140 AM EDT Thu Oct 11 2018 .SYNOPSIS... Wet weather is expected tonight and especially Thursday as Hurricane Michael moves through the southeast U.S. A cold front will cross the area by Thursday evening and shift Michael well offshore. A period of gusty northwest winds is expected in the mountains and foothills Thursday afternoon and evening. Cooler high pressure builds in to start the weekend. && .NEAR TERM /THROUGH TODAY/... As of 830 PM EDT Wednesday... Impressive surge of pre-heavy rains into the forecast area, and not associated with Michael. Current tropical connection is to a stream of moisture off the southeast Atlantic Coast, remnants of an old upper low that got sheared out under the subtropical ridge by way of the Bahamas. Never the less this has resulted in excessive rainfall for parts of northwest North Carolina into southwestern Virginia near Galax and Hillsville and western Pulaski County with upwards of 5 inches of rain. There have been numerous reports of stream flooding and road closures, in addition to a landslide near North Wilkesboro North Carolina. This particular area of heavy rain is beginning to wane, however, concern now is that we have now "primed the pump" for what could turn out to be a life threatening flash flood situation for areas which will now experience more heavy rain from the remnants of Hurricane Michael during the day Thursday. In addition, some of the larger Rivers, particularly the New River will have to digest some of this initial rain runoff with forecasts likely to be much higher than forecast. The River Forecast Center is scrambling to assess the situation and a new forecast for Galax and Radford are forthcoming. As we progress through the night, expectation is for there to be a break in the heavy rain as we await the heavy rain associated with Michael's closest approach. For the latest on Michael's intensity and forecast track information, please refer to the latest advisories from the National Hurricane Center. Michael is forecast to essentially track northeast through Georgia overnight then into the Carolinas and southern VA Thursday, its northeast turn aided by a strong cold front which is now working its way through the Mississippi River Valley. Michael's interaction with this cold front is expected to lead to an expected westward spatial expansion of Michael's heavy rain shield Thursday, and this has essentially played out in today's 12z NWP guidance. Expected local impacts for the region include the following: (1) Heavy rain, potential flash flooding and rises along smaller streams and creeks to mainstem rivers. Heaviest rains should occur through Thursday before clearing west-east Thursday late afternoon into Thursday evening in the east. (2) Post-Michael gusty to potentially damaging northwest winds Thursday afternoon into early morning Friday from the Blue Ridge, the immediate foothills counties and back westward to include the I- 81 corridor. Heavy rains should begin to progress northeastward starting earliest in the mountains of NW NC and the mountain empire around early Thursday morning, and then continue north and northeast the NC/VA Piedmont, Southside starting Thursday mid-morning and continuing into central VA by late morning. Area averaged rain forecast (in addition to what fell Wednesday evening) ranges from an inch to inch and a quarter in southeast WV and Tazewell County, 1.5-2 inches across the I-81 corridor into central VA, and then 2 to 5 inches across the southern Blue Ridge, the NC Piedmont/foothills and into Southside. These values closely resemble WPC's latest rain outlook...which has now expanded the potential for excessive rainfall farther north and west due to the pre-Michael Wednesday evening rain deluge. Localized higher amounts are still possible, particularly just northwest of the center of Michael's center track. Overall confidence on rain totals is moderate to high on where the greatest rain totals will be observed, but is lower on exact magnitudes. See the Hydro section for more detail. As heavy rain begins to skirt eastward Thursday late afternoon into early Friday, focus will then shift toward strong and gusty northwest winds across the NC/VA mountains and into the immediate foothills areas. Of concern is that saturated ground in conjunction with this rain will lead to an environment which will make weak/dead trees easier to be felled. Very strong pressure rises and north- northwesterly 850 mb jet of 40-50 kts off the GFS will likely support a period of 45-50 mph wind gusts Thursday late afternoon into evening in these areas. To avoid any potential concern with confusing messaging with what really is more of a non-tropical wind hazard, haven't issued any wind headlines as yet in collaboration with NWS GSP, but it's quite likely that at least impact-based wind headlines will be needed at some point for the potential for tree/powerline damage and hazardous travel through mountain passes such as I-77/Fancy Gap. Have opted to message in the HWO for now. May also need to consider such headlines for the Piedmont as well but have highest confidence in the mountains. Forecast confidence is overall moderate on the heavy rain and flood threat, and is moderate to high on the post-Michael wind threat. && .SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/... As of 330 PM EDT Wednesday... Focus Friday will be on post tropical storm conditions with rush of wind and cooler temperatures in the wake of Michael. Primary wind flow will be out of the northwest with dewpoints tanking into the 30s/40s as cool/dry October airmass finally makes an entrance. Temperatures Friday and into the weekend will resemble something closer to the climatological norm...a change that will stun folks into making an about-face for a jacket for outdoor activities. Weekend as a whole looks relatively dry with a couple of disturbances moving up through the Ohio Valley promising to cast a few clouds and possible showers to the WV mountains. In general, the upper air pattern will begin to shift into a Fall pattern, with broad troughing over the eastern 2/3rds of the country this weekend, trending toward a much deeper long wave trough by the middle of next week. During the transition, first in a series of short waves will pass through the base of the trough, the first wave being the remnants of the Pacific Hurricane Sergio which will pass through the Ohio Valley Sunday. The wave that follows Monday will be of Canadian origin. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 400 PM EDT Wednesday... October finally feels like, October. A large scale upper trough is forecast to reside over the eastern 2/3rds of the country the entire week, amplifying by mid-week as series of short waves digging south from Canada resulting in a fairly extensive cold intrusion to much of the central and eastern CONUS. Model consensus is for some unseasonably cold air (yep summer to winter) to overtake areas which were basking in unseasonable warmth, and in some cases extreme enough to permit the frozen form of precipitation across the upper Mid-West and Great Lakes into parts of New England where 850 mb temps plunge low enough to support snow. For the central Mid-Atlantic it will certainly feel like October, if not favor some November sort of temperatures which would be permissible for frost formation for parts of the forecast area...especially the mountain valleys. Precipitation chances appear somewhat limited, but there will be opportunities for showers associated with each passing shortwave trough, Monday favoring a day for showers, and then again toward mid week. Monday might actually turn out to be a little wetter than forecast, models trending toward some over-running associated with a frontal passage. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... As of 130 AM EDT Thursday... Looking at poor flying conditions through at least late Thursday afternoon until TS Michael and attendant front move across. At the moment patchy areas of light rain/drizzle with some embedded moderate showers streaming northward across the region. While in the lull expect ceiling and at times vsbys to trend IFR or worse. As we get closer to 12z rain shield associated with Michael heads north from the Carolinas and will see all sites receive rain, but heavier rain will be along and east of BCB/ROA. Heavy downpours and increasing winds will keep poor flying conditions. As we head toward 00z, will start to see drying out from the southwest to northeast and expect all taf sites to improve to VFR. Winds will stay gusty from the northwest from Thu afternoon through the end of the period at most sites, where some gusts over 30kts possible across DAN. Confidence is above average for sub-VFR most of the period, but lower how strong winds are and clearing to VFR. Extended Discussion... Strong northwest winds will be common Thursday night and Friday in the wake of Michael along with areas of mountain turbulence. VFR on Friday along with diminishing winds Friday night. Generally VFR anticipated over the weekend. Another front arrives Monday with possible sub-VFR cigs/vsbys with showers. && .HYDROLOGY... As of 900 PM Wednesday... An fetch of deep tropical moisture from along the southeast Atlantic Coast has resulted excessive rainfall for parts of the northwest Piedmont and mountains of northwest North Carolina and into the head waters of the New River and New River Valley of southwestern Virginia. All of Wednesday's heavy rain was in advance of Hurricane Michael. Hourly rates for most of the day Wednesday were less than an inch in an hour, but spiked around sunset with some of the rain cores jumping off the chart with rates of 4 inches an hour. This resulted in Flash Flooding from Wilkes County NC to near Galax Virginia and areas along the I-81 corridor west of Radford. A large swath of this rain has fallen within the headwaters of the New River and will likely result in a significant rise along the NEW at Galax and Radford. Please monitor the latest forecast, as we will be adjusting these forecasts based on the latest guidance from the river forecast center. Going forward, through the overnight, this first round of heavy rain, not directly associated with Hurricane Michael, is expected to wane, resulting in a lull in rainfall overnight. The coverage and intensity is expected to increase again on Thursday late morning/early afternoon with the approach of what is expected to be (by that time) Tropical Storm Michael. Weather forecast models are still indicating some variability in rainfall amounts depending on the track and speed at which the storm pushes across the Carolinas, but the most likely scenario still indicates QPF of 2 to 5 inches across the Southside of Virginia and the Piedmont of North Carolina, where the flash flood watch continues, and in addition to the rain which fell Wednesday. The highest end of this range falls in the Dan River basin where guidance already suggests moderate flooding is the most likely occurrence. But shifts in QPF will heavily affect forthcoming river forecasts and both minor or major are also possible depending on how much and where it falls. 1 to 2 inches of rain seems most likely across the upper Roanoke, James, Greenbrier where minor flooding may become a reality. Another 1 to 2 inches in the upper New River may would be problematic in that it may cause more than just minor flooding. Again, modest shifts in the rainfall pattern could substantially affect these river forecasts, so remain attentive. And for areas which have already received more than 4 inches of rain from Wednesday evenings deluge, the impacts from flash flooding could be life threatening. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Flash Flood Watch through this evening for VAZ009-012-015. Flash Flood Watch from 6 AM EDT this morning through late tonight for VAZ013-014-016-017-022-032-033-043-044-058. Flash Flood Watch from 11 AM EDT this morning through late tonight for VAZ023-024-034-035-045>047-059. NC...Flash Flood Watch through this evening for NCZ001-002-018-019. Flash Flood Watch from 6 AM EDT this morning through late tonight for NCZ003>006-020. WV...None. && $$ SYNOPSIS...AL NEAR TERM...AL/PM SHORT TERM...PM LONG TERM...PM AVIATION...PM/WP HYDROLOGY...PC/PM