Area Forecast Discussion
Issued by NWS Charleston, WV

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000 FXUS61 KRLX 091427 AFDRLX Area Forecast Discussion National Weather Service Charleston WV 927 AM EST Sat Dec 9 2017 .SYNOPSIS... Digging upper trough/cold front pushes through today and tonight, and again early next week after a brief warm up on Monday. One last cold shot late week may be the last in this series. && .NEAR TERM /THROUGH TONIGHT/...
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As of 915 AM Saturday... No changes this morning. Light snow likely making it into the southern mountains near Flat Top, and into the GReenbrier Valley and Pocahontas mountains. As of 415 AM Saturday... The main weather maker in the eastern third of the CONUS remains an expansive zone of frontogenesis across the South. The extent to which this southern system effects our region is limited by dry mid- levels - chance pops featured only in Pocahontas through early afternoon. An axis of high pressure extends up the Ohio Valley, keeping us dry elsewhere. An amplified upper-level trough digging through the Great Lakes region and into the Ohio Valley kicks this Piedmont system offshore Saturday, allowing for a brief period of sct/clearing skies during the afternoon. Pressure and height falls ahead of the trough erode surface high pressure and induce southwesterly low-level flow, allowing for modest warm air advection through the early afternoon. So, have taken aftn temperatures slightly warmer with guidance - especially where clearing is favored. Cold air advection (steepening lapse rates) behind the digging trough`s accompanying cold front coincident with a low-level plume of high RH off Lake Michigan opens the door for scattered snow showers and perhaps a few convective snow squalls later Saturday afternoon through the overnight hours. Low freezing heights limit mixed precip potential, and more intense squalls would locally cool atmosphere so have opted for majority snow over other precip types during onset spare for isolated spots of mixed precip near the Tristate and Big Sandy basin. Low- to mid- level winds turn more northwesterly with the passage of the trough aloft, so upslope is enhanced across northern mountain zones from roughly 05 to 10Z Sunday morning. Most areas should see a dusting to an inch in heavier showers with 2-4 inches in the upslope areas. Strong NW winds with 30-40mph gusts are possible, especially on the ridge tops. Vsbys will lower in blowing snow and wind chills will be close to advisory criteria.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 400 AM Saturday... Snow showers will linger in the mountains on Sunday morning, but generally the day will see improving conditions with decreasing clouds as short wave pushes well to our east. Although we will see some sunshine, temperatures will stay about 10 degrees below normal. Flow shifts SW overnight on Sunday and warm air advection kicks in on Monday. Temperatures will climb back up to near normal values out ahead of another cold front. Forecast guidance is in good agreement with the cold front pushing through overnight Monday and early Tuesday morning. The initial short wave with the front may kick off a few snow showers mainly across the Northern Forecast area, but amounts with this first wave will be quite light with little to no accumulation. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 410 AM Saturday... Much colder air filters in behind the cold front on Tuesday. Deep upper trough sinks over the area Tuesday afternoon. NW flow with a fetch off Lake Michigan will advect moisture into the region. Early forecast model soundings indicate fairly unstable soundings in the low to mid levels with strong lapse rates. This could set the stage for wide spread snow shower activity from late Tuesday afternoon through early Wednesday morning. Could see some snow squall activity as well and current timing could impact the Tuesday afternoon commute. The active pattern continues through the week, with a brief break Wednesday before a clipper system pushes through late in the week. && .AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
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As of 615 AM Saturday... Intermittent VFR decks providing bkn120 for lowland sites this morning as bands of mid/high clouds associated with a strong low moving up the Atlantic coast gradually move eastward. SCT decks and clearing are possible through a small corridor also moving eastward through the late morning/early afternoon of Saturday ahead of a cold front. The cold front and digging upper level short wave trough approaching from the west will bring the return of mid and high clouds Saturday afternoon. The front and onset of precip occurs from W to E between 22Z Sat and 02Z Sun; terminals are forecast to be -shsn with the exception of HTS, where mixed precip may occur. BKW, CRW, and PKB will likely see similar timing shortly after HTS when frontal orientation w/ digging trough is taken into consideration. Winds turn westerly after frontal passage. Hi-res models agree on widespread, intermittent snow squall activity Saturday evening/overnight suggesting widespread MVFR ceilings and in some heavier cases IFR ceilings/vsbys. Though, confidence on timing and intensity is low so have opted to trend down ceilings for the final hours of the TAFs in lowland sites. Confidence on upslope snow Saturday night is high, so have included -shsn at CKB/BKW/EKN terminals. Gusty winds are also likely in any heavier squalls, especially across the higher elevations. FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 12Z SUNDAY... FORECAST CONFIDENCE: High. ALTERNATE SCENARIOS: Timing of snow squalls and front orientation may alter the timing of associated MVFR to IFR conditions, gusty winds, and snow showers. This is reflected well in consistency tables below. EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY OF WFO FORECAST TO AVAILABLE MODEL INFORMATION: H = HIGH: TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS. L = LOW: TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. UTC 1HRLY 12 13 14 15 16 17 18 19 20 21 22 23 EST 1HRLY 07 08 09 10 11 12 13 14 15 16 17 18 CRW CONSISTENCY H H H H H H H H H H H M HTS CONSISTENCY H H H H H H H H H H M L BKW CONSISTENCY H H H H H H H H H H H M EKN CONSISTENCY H H H H H H H H H H H M PKB CONSISTENCY H H H H H H H H H H H M CKB CONSISTENCY H H H H H H H H H H H M AFTER 12Z SUNDAY... Lingering MVFR/IFR conditions with upslope snow showers are possible through around 17Z Sunday. Another wave Monday night/Tuesday is forecast to have similar, squally snow showers favoring mountain terminals.
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&& .RLX WATCHES/WARNINGS/ADVISORIES... WV...None. OH...None. KY...None. VA...None. && $$ SYNOPSIS...MPK/MC NEAR TERM...26/MC SHORT TERM...MPK LONG TERM...MPK AVIATION...MC

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