871 FXUS61 KCLE 290306 AFDCLE Area Forecast Discussion National Weather Service Cleveland OH 1006 PM EST Thu Jan 28 2021 .SYNOPSIS... High pressure will build slowly east from the middle Mississippi Valley region to the central Great Lakes by Saturday morning. This high will extend from near James Bay south to the Gulf Coast states. The high will move east of the area Saturday night allowing a deepening area of low pressure to move east across the Ohio Valley Sunday and Sunday night, shifting to the east coast by Monday. A trough of low pressure will linger into Tuesday. && .NEAR TERM /THROUGH FRIDAY NIGHT/... Hi-res guidance is starting to capture the ongoing situation with the Lake Huron connected snow band focused in western NY this evening. Models continue to show a southwest movement of the moisture connection and snow band through the overnight as the 925-850mb flow veers more northerly. Made some small adjustments to pops and snow amounts here, but the general forecast thinking remains the same. Elsewhere across northeast OH, robust snow shower activity from the western Lake Erie basin has impacted the higher terrain of Medina, Cuyahoga, and Summit counties over the past several hours. This activity is not being handled well, so have raised pops for the next several hours until drier air moving over the western basin disorganizes the snow bands/showers. Original discussion... Surface high pressure currently situated from James Bay to the Gulf Coast states will slowly move east through tomorrow night. Northwest flow aloft is expected through this period with a mid- level trough moving southeast across the eastern Great Lakes region this evening and tonight, followed by a steady stream of positive vorticity over the eastern Great Lakes through much of the day Friday and perhaps into early Friday night. The result is ongoing lake effect snow across northeast Ohio and northwest Pennsylvania with a continuation of lake effect in some capacity through Friday night. The areal extent of lake effect snow is expected to decrease late tonight through tomorrow with the western periphery of the lake effect showers pushing eastward late tonight. Snow showers will be mainly reserved for northwest Pennsylvania Friday through Friday night. The best chance for heavier snow will be tonight over northwest Pennsylvania. Modeled soundings show deepening inversion heights to 8 kft and lake-induced CAPE of around 350 J/kg. Lake effect snow will be solidly embedded in the dendritic growth zone (DGZ) with at least a portion of upward vertical motion in the DGZ, though max vertical motion is expected to be just below the DGZ. Because of this, going with snow ratios of around 20:1, which will result in a light, fluffy snow. A lake effect band with a connection to Lake Huron is expected to be impacting northwest Pennsylvania, which could produce snowfall rates of up to one inch per hour and visibilities down to quarter mile. For this reason, we are forecasting 3 to 6 inches of snow (with locally higher amounts) in northwest Pennsylvania through the day Friday and a Winter Weather Advisory for northwest Pennsylvania and Ashtabula. We are anticipating this Lake Huron snow band to wobble between Chautauqua County, NY and Ashtabula County, OH, which will act to spread out the snow a bit. However, if this band wobbles less and remains more stationary in northwest Pennsylvania, snow totals for northwest Pennsylvania will likely need to be increased and and upgrade to a Lake Effect Snow Warning may be needed. Dry air and warmer temps with the surface high and upper-level ridge will allow lake effect to dwindle Friday evening and Friday night. Temperatures through the near term will be on the chilly side with day time highs in the upper 20s and night time lows in the teens. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... High pressure will be centered over Lake Erie to start on Saturday and dry conditions will be present across the area. However, things will change quickly as a strong upper trough will support a low pressure system that will move along the Ohio River on Sunday. The recent trends with this system are that the timing of the medium range models is fairly consistent with precipitation entering the southwestern portions of the area on Saturday night, spreading northeast through Sunday. Have pushed a more aggressive PoP forecast with more categorical PoPs for the region. The one thing that remains unclear is precipitation type. The ECMWF is the coldest model and suggests all snow for the forecast area and therefore higher snow accumulations. Other models suggest that a warmer layer enters ahead of the low on Sunday and there could be rain or a wintry mix across portions of the area. At this point, maintain a middle of the road forecast with all snow north and a mix in the south on Sunday, but have added about an inch of snow across the board to the forecast. Regardless, we are expecting widespread accumulating snowfall with this system and interested groups should remain weather aware for possible winter weather headlines. && .LONG TERM /MONDAY THROUGH THURSDAY/... By Monday morning, low pressure will be weakening as it enters the upper Ohio Valley as its supporting upper trough will fully transfer support to a coastal low pressure system moving up the East Coast. The surface low will slow over the region, becoming just a weak trough by Tuesday. The atmosphere should remain cold enough for snow and with residual moisture and lake enhancement and will maintain likely PoPs on Monday with lingering snow chances into Tuesday. High pressure with an upper ridge will enter on Wednesday and should allow for the one dry day of the long term forecast period. However, the progressive pattern continues and another system will enter the region for Thursday. At this point, we will be on the warm side of this system for the end of the week. Temperatures should be near normal for highs until Thursday when we could reach the upper 30s ahead of the next system. && .AVIATION /00Z Friday THROUGH Tuesday/... Low stratus will affect most of the terminals through at least the first half of the period as high pressure builds into the area. Ceilings are expected to be MVFR to low VFR, although VFR should prevail after 12Z at KFDY and KTOL. Lake effect moisture will keep low clouds around longer downwind of Lake Erie, with some SHSN possible at KCLE, KCAK, and KYNG, and a brief period of IFR conditions in SHSN at KERI before 12Z. Winds will generally remain out of the northwest through the period. Outlook...Non-VFR possible within lake effect snow showers through Friday evening. Periods of non-VFR possible in snow Saturday night through Tuesday. && .MARINE... With high pressure to the west of the lake, northwest flow will continue across the basin. With winds to 25 knots in onshore flow, will continue Small Craft Advisories for the eastern half of the lake. With the latest forecast, these stronger winds could linger a bit longer on Friday and have extended the Small Craft Advisories a bit to reflect a few more hours of stronger winds and waves. High pressure will be over the lake Friday night into Saturday and flow will be variable for a brief period before coming around to the southeast then east on Saturday afternoon and evening. Low pressure will approach on Sunday and pass south of the lake, increasing easterly flow and another round of marine headlines are expected. With the unfavorable easterly flow, there could be increases in water levels over the western basin and lakeshore flooding could be an issue as well. The low passes southeast of the area on Monday as it merges with a coastal system and winds will become more northeast on Monday and then north by Tuesday. && .CLE WATCHES/WARNINGS/ADVISORIES... OH...None. PA...Winter Weather Advisory until 10 AM EST Friday for PAZ002-003. MARINE...Small Craft Advisory until 10 PM EST Friday for LEZ148-149. Small Craft Advisory until 4 PM EST Friday for LEZ146-147. && $$ SYNOPSIS...Saunders NEAR TERM...Greenawalt/Saunders SHORT TERM...Sefcovic LONG TERM...Sefcovic AVIATION...Greenawalt MARINE...Sefcovic