Area Forecast Discussion
Issued by NWS Blacksburg, VA

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074 FXUS61 KRNK 220929 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 529 AM EDT Sun Oct 22 2017 .SYNOPSIS...
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High pressure will finally move east of the area by tonight. A strong cold front and upper trough will move into the region from the west late Monday, crossing the area through early Tuesday. The front will bring widespread rain followed by much cooler temperatures for the later half of the week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 515 AM EDT Sunday... The large high pressure area, both surface and aloft that has been over the region the past several days will drift east and be located just off the VA/NC coast by Monday morning. As the high moves east, a deepening upper trough will move slowly east from the Midwest and intensify, moving into the Mid-Atlantic region late Monday. Today will still be dry, although with considerable high cloud cover as it increases in advance of the deepening upper-level system. Light rain will begin to develop along the Blue Ridge in northwest NC around or shortly after midnight, then spread northeast, especially along the Blue Ridge, during the morning hours. The bulk of the rainfall will arrive after the near term period. Temperatures will still be warm today as 850mb readings hover around +15C and remain very mild tonight with increasing warm, moist southerly flow across the region. Some areas will be hard pressed to fall below 60 degrees Monday morning. High temperatures today will be mostly in the 70s, except 60s high terrain in the west.
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&& .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
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As of 215 AM EDT Sunday... The item of interest during this portion of the forecast continues to be the first substantial rainfall for the entire forecast area in over a week`s time, Monday into Tuesday. A cold front will approach the region on Monday through IN/KY/TN/AL. In advance of this feature, southeast isentropic and orographical lift, that started Sunday night, will increase through the day. The result will be the development of an increasingly expansive area of showers, with the greatest coverage across the western half of the region. Model guidance has been trending more quickly with the spread of the heaviest precipitation into the area, now most probably by the afternoon in the southwest sections. Surface wind gusts will be on the increase during the day especially at the higher elevations of the Northern Mountains of North Carolina and neighboring sections of the Mountain Empire region of southwest Virginia. Here, a few gusts may reach 40 to 45 mph by the late afternoon This same quicker guidance likewise brings the cold front into and across the area Monday night. The result will be the Monday evening time frame as the period for the heaviest precipitation in association with the front, across the north and northeastern sections of the region. A combination of weak surface based instability and substantial increase in low level shear supports isolated thunderstorms coincident to the leading edge of the cold front across the southern half of the region Monday afternoon through Monday evening. The latest Day 2 Convective Outlook by SPC places this region within a Marginal risk of severe thunderstorms with damaging winds the greatest threat. By late Monday night into Tuesday, most of the latest guidance has the front and associated precipitation east of the region. The NAM is a bit slower, with activity lingering in the east until about midday Tuesday. Our latest forecast will reflect the faster departure with a hint of lingering activity in the east Tuesday morning. By Tuesday afternoon through Wednesday night, our attention for any additional precipitation turns to the western sections of the region. Gusty northwest flow behind the front, and the approach of its parent upper level low/trough, will help maintain cloud cover and isolated to scattered showers across the preferred upslope regions of southeast West Virginia, and to a lesser extent, the neighboring first tier of counties of southwest Virginia. As colder air works its way into the area, some of these isolated rain showers may transition to isolated snow showers across this same geographical area Wednesday night. QPF numbers will be minimal at this point with little if any in the way of accumulation.
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&& .LONG TERM /THURSDAY THROUGH SATURDAY/...
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As of 415 PM EDT Saturday... All of the extended models have trended much more progressive with the upper trough, lifting it out Thursday, west to southwest flow aloft returning to the area and allow temperatures to moderate quickly. Wednesday looks like it will be the coolest day of the week, then moderating for Thursday and Friday. Models are now hinting at another upper level long wave trough for the weekend with the potential for showers and bonafide cold frontal passage. The GFS brings clouds/showers into the area as early as Saturday whereas the ECMWF is 24 hours slower holding off on any appreciable QPF until Sunday. Attm will introduce low chance threat for showers Saturday, but nothing more until models can resolve the timing.
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&& .AVIATION /09Z SUNDAY THROUGH THURSDAY/... As of 200 AM EDT Saturday... The strong high pressure area that has been over the region for the past several days will slide just to our east and just off the coast today. A strong southern stream short wave will begin to approach the region from the southwest late tonight and Monday. Extensive high clouds will overspread the area today in advance of the approaching upper trough. However, ceilings are expected to remain VFR outside of very patchy early morning fog (e.g., KLWB and KBCB) in the 09Z-13Z time frame. Most of the day, conditions will be BKN250 throughout the CWA. After 00Z, southerly flow will begin to increase in advance of the short wave and bring deeper Gulf moisture into the region from the southwest. Ceilings should begin to lower into the MVFR range, especially across northwest NC into southwest VA after 04Z, but more so after 06Z Mon. Winds will be calm to light and variable through midday, then become southeast 5-8mph with low end gusts possible in the KBLF area during the afternoon/evening. High confidence in ceilings and visibilities throughout the TAF valid period. Medium confidence in wind direction, high confidence in wind speed throughout the TAF valid period. Extended Aviation Discussion... A deep upper trough and associated strong cold front will move into the region from the west Monday night/early Tuesday with 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. MVFR showers may return by early next week. && .HYDROLOGY...
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As of 230 AM EDT Sunday... Latest model trends place the bulk of the precipitation pre- and concurrent to the approaching cold front across the area Monday afternoon and evening. The latest QPF numbers from WPC offer a solution that gives the region one to two inches of rain from early Monday morning through Monday night. Higher amounts are noted along the higher elevations along and west of the Blue Ridge from roughly Roanoke, VA southwest into the Northern Mountains of North Carolina. Amounts of two to three inches are more likely during this same time period, with amounts immediately along the crest of the Blue Ridge a little shy of four inches. The latest Day 3 Excessive Rainfall from WPC places the entire forecast area within a Slight Chance of exceeding flash flood guidance. While the expected rainfall amounts are decent, they are trending lower than the flash flood guidance provided by the corresponding RFCs. At this time, a minor flooding concern will continue to be placed in the HWO and eHWO, but no headlines will be hoisted at this time.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RAB NEAR TERM...RAB SHORT TERM...DS LONG TERM...DS/PM/RAB AVIATION...RAB/RCS HYDROLOGY...DS

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