125 FXUS61 KRLX 280919 AFDRLX Area Forecast Discussion National Weather Service Charleston WV 519 AM EDT Sat Oct 28 2017 .SYNOPSIS... A strong upper trough/low with associated cold front crosses Saturday into Sunday. High pressure early next week. Showery conditions return by mid-week, with a warming trend. && .NEAR TERM /THROUGH TONIGHT/... As of 515 AM Saturday... A cold front crossed the Ohio Valley overnight, but will take all day today to cross WV. This is because the driving upper level short wave trough minors out as it lifts out, leaving the upper level flow out of the south-southwest, ahead of a second, stronger upper level trough digging into the lower Ohio and Tennessee valleys today and tonight. A wave of low pressure forms just east of the southern appalachians this evening, in response to the digging trough, and moves up along the cold front, east of the appalachians, tonight. The front is an anafront, so dry, mild weather ahead of the front, gives way to cooler weather, and rain, behind the front later today and tonight. The leading edge of the rain, just pushing into western portions of the forecast area this morning, will move across the forecast area this morning into this afternoon. On the backside, rain will taper off across the middle Ohio Valley this afternoon and evening, but will be slow to taper farther east tonight, as the wave of low pressure moves up along the front. The rain is likely to persist all night in the mountains, as well as back into the northern WV lowlands. The mountains will have the most prolonged rainfall, on account of the wave moving up along the front tonight, which will push values up over an inch. However, PW values of only a little above an inch will keep hourly and three-hourly rates down, and the area should still be able to handle a soaking rain. Southerly winds could gust to 40 mph across the higher ridges this morning, on account of strong winds aloft ahead of the cold front. Colder air behind the front will undercut the warmer air above, so snow or sleet could mix in toward dawn Sunday. NAM-based raw and MOS temperatures were blended in with a short term consensus. Surface temperatures are forecast to drop to the mid 30s by dawn Sunday, so a freeze is not expected. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... As of 430 AM Saturday... By Sunday morning, a the frontal boundary responsible for Saturday's widespread rainfall will have slowed just beyond the eastern edges of this region with heaviest precip moving out. Meanwhile a deepening low pressure wave will be positioned to our southeast in the Carolina/Virginia Piedmont, enhancing precipitation in central and northern WV through the period. Warm mid- level air will work in aloft allowing for a brief period of freezing rain in the mountain valleys Sunday morning. A changeover to all snow comes later that afternoon as cooler air establishes through the column. Expect primarily cold rain with perhaps a few wet snowflakes elsewhere in the lowlands. Greater snowfall accumulations come Sunday night as the Piedmont region low moves into the Mid-Atlantic region to our east. Mid- level frontogenesis, isentropic lift, and upslope influences suggest a chance of mesoscale snow-banding over the central WV mountains up through south-central PA, though too many timing and position discrepancies exist at this time to take accumulation far above a blend of models. Regardless, have slightly increased total snowfall from previous forecasts to 1-3 inches generally above 2500 ft with light accumulation possible in mountain valleys and isolated amounts around 3.5 inches along highest ridges. Snow tapers off by day break as the low moves off to the northeast. && .LONG TERM /MONDAY THROUGH FRIDAY/... As of 500 AM Friday... High pressure builds in through Tuesday night, bringing dry weather, and shifts overhead early Wednesday bringing in warm southwesterly flow. Models are currently in agreement for embedded disturbances from mid-week onward, though timing and intensity differences are aplenty, so opted for more widespread PoPs. Went with a general blend of temperatures beyond Wednesday given uncertainty in the position of boundary, but a definite warming trend is on tap for this period. && .AVIATION /09Z SATURDAY THROUGH WEDNESDAY/... As of 220 AM Saturday... A cold front will cross the area overnight and Saturday, bringing wet, and much cooler weather, along with deteriorating flight categories. VFR conditions ahead of the front will give way to deteriorating conditions behind it, lagging several hours. The front was already along the Ohio River as of 06Z, but MVFR in rain will not occur at HTS until 09Z, and PKB 11Z. CRW and CKB will not see deteriorating conditions until 15-16Z, and mountain sites BKW and EKN 20-21Z Saturday. IFR is expected at CRW by Saturday afternoon, CKB Saturday evening, perhaps a bit earlier on visibility in rain both locations. IFR is expected in the mountains Saturday night on visibility and ceilings, again perhaps a bit earlier on visibility, and perhaps along the Ohio River on ceilings Saturday night. Southerly surface flow will be light south, except a bit gusty in the mountains ahead of the front through Saturday morning, and then light west to northwest behind the front, which is from right out of the gate HTS and PKB, but not until 15Z CRW, 17Z CKB, 20Z BKW and then not until 02Z Sunday at EKN. Moderate to strong south to southwest flow ahead of the front through Saturday morning, will become light northwest behind the front Saturday afternoon. FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 06Z SUNDAY... FORECAST CONFIDENCE: Medium. ALTERNATE SCENARIOS: Restrictions in rain behind the front could vary, including onset time. 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. DATE SAT 10/28/17 UTC 1HRLY 08 09 10 11 12 13 14 15 16 17 18 19 EDT 1HRLY 04 05 06 07 08 09 10 11 12 13 14 15 CRW CONSISTENCY H H H H H H M M M L L L HTS CONSISTENCY H H H M M M M L H L L L BKW CONSISTENCY H H H H H H H H H L L L EKN CONSISTENCY H H H H H H H H H M M L PKB CONSISTENCY H H H H H H M M M M L L CKB CONSISTENCY H H H H H H H H H L L L AFTER 06Z SUNDAY... Periods of IFR in rain Saturday night into Sunday, and in snow over higher elevations Sunday into Sunday night. && .RLX WATCHES/WARNINGS/ADVISORIES... WV...None. OH...None. KY...None. VA...None. && $$ SYNOPSIS...TRM/MC NEAR TERM...TRM SHORT TERM...MC LONG TERM...MC AVIATION...TRM