Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 200850 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 450 AM EDT Fri Oct 20 2017 .SYNOPSIS... High pressure will continue to keep our weather pattern dry heading into and through the weekend. A potent cold front will approach and cross the region Monday into Tuesday, bringing a return of showers and gusty winds to the region. Drier weather returns to the area by the middle to end of next week. && .NEAR TERM /THROUGH TONIGHT/... As of 200 AM EDT Friday... Surface high pressure was centered over eastern KY/TN. A broad upper level ridge was positioned from the Florida Panhandle northwest into the Upper Mississippi River Valley. Today into tonight, the center of the surface high will shift east and be situated over the Delmarva Peninsula by Saturday morning. The upper ridge also will have shifted east a couple hundred miles so that its axis will be overhead, just slightly east of the region. The result will be another day and night of very limited cloud cover and no precipitation. The one change will be a trend towards slightly milder temperatures as both geopotential heights increase across the area and 850mb temperatures inch up about 0.5 to 1.0 deg C more as compared to those of Thursday. We are expecting another morning with some short-lived patchy fog and stratus mainly in the mountain and river valley regions. Any fog and low clouds that do manifest themselves this morning are expected to have mixed out by the mid to late morning. High temperatures today will range from the low to mid 70s across the mountains with mid to upper 70s across the Piedmont. Low temperatures tonight will range from around 40 degrees to the mid 40s across the mountains to the mid to upper 40s across the Piedmont. && .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... As of 410 AM EDT Friday... A strong 590dm+ upper ridge will be anchored over the region Saturday with 850mb temperatures hovering in the +14C to +16C range. Expect a continuation of abundant sunshine and well above normal temperatures with afternoon max temperatures on the order of 10+ degrees above normal. Although Sunday will still be warm, Saturday will be the last really warm day with near full sunshine. Lows will be in the 40s and 50s with high temperatures in the 70s, close to 80 across the Piedmont. For Sunday, the axis of the upper ridge will slowly shift off the coast as the combination of a southern stream closed low moving out of the Arklatex region and a northern stream digging trough continue to amplify the flow across the eastern U.S. Given the increasing meridional and digging/developing nature to the upper flow, the approaching weather systems will be slow as the upper ridge trudges eastward. The net result will be a continuation of an unseasonably warm day Sunday. Clouds will be on the increase, but do not expect any precipitation to arrive yet during the day Sunday. Afternoon temperatures will continue to average about 10 degrees above normal, despite the increased cloud cover. Morning low temperatures will be well above normal, mostly in the 50s. During the day Monday, the southern stream system will move into the southeast U.S., while the northern stream system digs into the Midwest. This morning`s model runs show these remaining as two distinct separate systems, with the southern system containing the bulk of the deeper moisture, instability, and shear. Overnight Monday into Tuesday morning, the increasingly negatively titled upper trough or perhaps closed low (per GFS) will begin to lift northward into the Mid-Atlantic. Expect a marked increase in showers and rainfall as this occurs. Healthy rainfall amounts of 1-2 inches will be possible by Tuesday morning daybreak, especially along the southern Blue Ridge. The threat for severe weather with this system late Monday night/early Tuesday is definitely non-zero as a 50kt 850mb LLJ traverses the region with a strong upper jet and upper diffluence. While instability is not impressive, enough CAPE exists given strong low-level shear to have some concern for severe thunderstorms during the late night/early morning hours. The favored mode would appear to be a embedded QLCS, with the greatest concern across the NC Foothills, Piedmont, and into Southside Virginia. Clouds and precipitation will keep temperatures down Monday, but given no change yet in the air mass, temperatures will still run 5-10 degrees above normal, especially minimum temps with cloud cover and much higher than normal PWATS/dewpoints. && .LONG TERM /TUESDAY THROUGH THURSDAY/... As of 435 AM EDT Friday... A deep trough will evolve across the eastern U.S. Wednesday as the aforementioned southern stream and northern stream energy phase together, most likely along or near the Mid-Atlantic coast. The bulk of the heavier precipitation and any threat for severe weather in our area will occur Tuesday morning before shifting well east/northeast of our area. A dry slot will quickly spread into the region from the southwest by afternoon/evening, confining the better threat for showers to the western mountains at that time. On Wednesday, the upper trough will begin to shift east of the region, but keep cold advection and upslope across the region. This will result in some continued threat for showers across mainly the Alleghanys southward into the western mountains of NC. Possibly early in the morning, low-level temperatures and thickness values will support a mix of rain/snow in the higher terrain, but nothing supports any accumulation or much QPF at this time. With regard to the remainder of the period, namely Thursday, all of the extended models have trended much more progressive with the upper trough, lifting it out of here as quickly as Thursday as another fast moving trough moves across the northern U.S. West to southwest flow aloft will return to the area and allow temperatures to begin to moderate by the end of the week. Temperatures Tuesday will still average above normal as the front/cooler air mass moves slowly across the area under the high amplitude/parallel flow aloft. Wednesday will be a rather chilly raw day, especially across the mountains where rain/snow showers and gusty northwest winds are expected as the upper trough reaches its deepest point. Thursday will see an end to the precipitation and a moderation in temperatures as the upper trough quickly lifts out of the region. Look for minimum temperatures in the 50s Tuesday dropping into the 30s by Thursday. Maximum temperatures will still be above normal Tuesday in the 50s and 60s west to the lower 70s east, albeit with somewhat of a non-diurnal trend as temperatures fall during the afternoon behind the front. Wednesday will be the coldest day overall with clouds, showers, gusty northwest winds, and CAA. Look for highs in the 40s west to the lower 60s east with lows in the 30s west to the 40s east. Thursday, with greater amounts of sunshine, after a chilly morning with lows largely in the 30s, afternoon temperatures will warm into the 50s west to the 60s east. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... As of 130 AM EDT Friday... Mainly VFR conditions are expected through the 24 hour TAF forecast period concluding at 06Z/2AM Saturday thanks to high pressure remaining over the region. The exception to this rule will be some IFR/MVFR fog/stratus development later tonight into early Friday morning mainly with in the mountain and river valley regions. Any sub-VFR conditions will improve to VFR by the mid to late morning Friday. Extended Aviation Discussion... High pressure will remain over the region through Sunday with generally VFR conditions expected, outside the usual late night/early morning patchy river and mountain valley fog. A deep upper trough and associated strong cold front will move into the region from the west by Monday promising a period of sub-VFR conditions in rain/showers along with increasing wind. Colder, blustery, unsettled weather with perhaps largely MVFR conditions across the mountains will linger through the later half of next week as an upper trough cuts off across the central Appalachians. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...DS NEAR TERM...DS/JH SHORT TERM...RAB LONG TERM...RAB/WP AVIATION...DS/JH/MBS/RAB

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