Marine Weather and Tide Forecast for Flat Rock, OH

KEY MESSAGES
1) A linear snow squall and trailing lighter snow showers along an E'ward-moving cold front exit NE OH and NW PA by this late afternoon.

2) Primarily below-normal temperatures are expected tonight through the upcoming week.

3) Lake-effect snow develops downwind of Lake Erie tonight and persists through at least the middle of the upcoming week.

4) Outside the lake-effect snow, periodic, widespread, and accumulating snow should impact our region through the upcoming week.

DISCUSSION
KEY MESSAGE 1...
At 1:40 PM EST this afternoon, a surface cold front was located near an Erie, PA to Warren, OH to Minerva, OH line. This front will continue moving E'ward and is expected to exit the rest of our CWA by 4 PM, give or take one hour. Convergence/moist ascent along the surface cold front will continue to release weak potential instability in the lowest ~1 km AGL and result in strong/maximized ascent at a cloud temperature near -8C to -10C below cloud top temperatures in the DGZ and as surface wet-bulb temperatures hover near 0C ahead of the front. Thus, steady to heavy snow and graupel showers will persist along the surface front in our CWA and continue to prompt Special Weather Statements or Snow Squall Warnings. Light snow showers related to moist isentropic ascent aloft remain possible ahead of the front, while light snow showers are also possible for up to about two hours behind the surface cold front passage and will be associated with convergence/moist ascent along the upper- reaches of the front. Fresh snow accumulations today are expected to be 2" or less. Greatest amounts are expected in the higher terrain of NW PA, where a somewhat colder environment should allow snow to accumulate more easily.

KEY MESSAGE 2...
Behind today's cold front passage, primarily below-normal temperatures are expected tonight through Saturday, January 24th a net and deep troughing aloft, associated with an unusually- cold air mass, becomes established over eastern Canada and impacts the eastern United States during the bulk of the next seven days. At the surface, our CWA is expected to primarily reside in the cold sector based on the latest projected mid latitude cyclone track. A reinforcing Arctic front should sweep E'ward through our region on Monday before a warm front sweeps NE'ward through our region Tuesday night. Prior to the warm front passage, overnight lows are expected to be near 10F to 15F around daybreak Sunday and Monday, respectively, near 0F to 5F around daybreak Tuesday, and bottom-out near 5F to 10F Tuesday evening, before the warm front ushers-in a warmer air mass originating over the Gulf. Minimum wind chills should be mainly in the 0F to -10F range tonight through Tuesday night, but the coldest minimum wind chills (-10F to -20F) are expected around daybreak Tuesday and should eventually prompt the issuance of a Cold Weather Advisory.

On Wednesday, low-level WAA in the warm sector should contribute to highs reaching the lower to mid 30's before a strong cold front sweeps SE'ward across our CWA Wednesday afternoon and evening. Net low-level CAA behind the front is expected through the end of next week and contribute to below-normal temperatures Wednesday night through Saturday, January 24th. Additional sub- zero wind chills are possible, especially around daybreak Friday.

KEY MESSAGE 3...
Lake-effect snow (LES) should develop over and downwind of the ~1C ice-free waters of Lake Erie tonight, especially after midnight, as 850 mb temperatures tumble to near -16C behind the cold front. However, the LES is expected to be light, due in part to limited moisture between 850 and 700 mb, and primarily impact portions of western NY due to a SW'erly mean low-level flow. However, these light LES showers may skirt the lakeshore at times in our CWA, east of Cleveland, and yield snow accumulations less than one inch.

During the daylight hours of Sunday through the daylight hours of Tuesday, the mean low-level flow of sufficiently-cold/moist air over the relatively-warm, ice-free lake waters should vary between mainly SW'erly and WSW'erly as multiple shortwave troughs traverse the Lake Erie region generally from west to east, 850 mb temperatures waver between -15C and -22C amidst greater/deeper low-level moisture, which will yield greater lake-induced instability and likely yield a strong lake-induced thermal surface trough over the ice-free lake waters, which should keep the mean low-level flow at least somewhat backed.
Thus, steadier to heavy LES is expected to primarily impact portions of western NY during the aforementioned time period.
However, during Monday through Monday evening, the above- mentioned Arctic front passage and attendant shortwave trough passage should allow mean low-level flow to veer to W'erly for a time and allow LES to impact far-NE OH and NW PA for at least several hours. As a result, our latest official snowfall forecast calls for 1-5" of fresh LES accumulation along/near the lakeshore from Lake County, OH through Erie County, PA between 7 AM Sunday and 7 PM Tuesday. We will continue to monitor trends in NWP model guidance closely.

The thermodynamic environment should remain favorable, overall, for additional Lake Erie LES Tuesday night through this Saturday. However, as the warm sector briefly overspreads the Lake Erie region overnight Tuesday night into Wednesday, there should be a brief hiatus from the LES as ice-free lake surface to 850 mb temperature differences shrink to less than 13C for a time. Exact mean low-level flow direction and LES placement, intensity, and amounts are less certain Tuesday night through this Saturday, but the more-reliable GEM and ECMWF models suggest shortwave trough passages will be accompanied by mean low-level flow varying between mainly SW'erly and W'erly. Thus, LES may impact our primary snowbelt counties and vicinity at times. Note: surface winds over Lake Erie should remain strong enough through the upcoming week to prevent the lake from freezing-over completely.

KEY MESSAGE 4...
Outside of the LES, periods of widespread snow should impact our region Sunday night into Monday due to low-level convergence and moist ascent along the Arctic front and moist isentropic ascent aloft, ahead of the accompanying shortwave trough axis.
This widespread snow should total 2" or less. Additional periods of widespread snow, outside the aforementioned LES, should impact northern OH and NW PA Tuesday night through Saturday due to moist isentropic ascent ahead of shortwave trough axes, moist isentropic ascent along the upper-reaches of the warm front Tuesday night, and low-level convergence/moist ascent along Wednesday's cold front. Additional snow accumulations should occur, but exact amounts are uncertain at this juncture.

AVIATION /18Z Saturday THROUGH Thursday/
The main focus through 20 or 21z will be a band of snow showers and squalls along a cold front, extending from near HZY to CAK and moving east at about 30kt. Brief LIFR vsby and a quick accumulation of snow is accompanying these snow showers and squalls, along with wind gusts up to 35kt. MVFR ceilings linger for a few hours behind the front, before either scattering out or rising to VFR into this evening. MVFR ceilings may return Sunday morning. South-southwest winds ahead of the front are turning more west-southwest and 10-15kt with gusts 20-25kt behind the front. Winds will lose their gustiness this evening, outside of ERI where gusts will continue longer into the night.

Outlook...Non-VFR possible in snow showers Sunday night into Monday.
Non-VFR may linger in lake effect snow across Northeast Ohio and Northwest Pennsylvania Tuesday through Wednesday.

MARINE
Ice coverage continues to expand across the western basin of Lake Erie. Hazardous marine conditions across the central and eastern basins will persist into next week as multiple systems move across the Great Lakes.

Confidence is increasing for a combination of Gales and freezing spray Monday into Tuesday across the central and eastern basin of Lake Erie as a clipper slides east through the Great Lakes, ushering in west to southwest winds of 30 to 35 knots. In addition, this system will extend an arctic front across the region, with lake air temperatures over ice- free areas expected to drop into the low teens. If trends continue, a Gale Watch appears likely in the next forecast cycle.

Following this system, southwest winds will remain elevated, around 25 knots, into Wednesday. Winds should gradually subside to 20 knots or less and begin to favor a west direction by Thursday.

CLE WATCHES/WARNINGS/ADVISORIES
OH...None.
PA...None.
MARINE...Small Craft Advisory until 7 AM EST Monday for LEZ146>149.