textproduct: Cleveland

WHAT HAS CHANGED

Forecast confidence continues to increase that lake-effect snow will develop downwind of Lake Erie tonight, become significant and oscillate on Sunday through at least Tuesday, and primarily impact portions of western NY. However, what remains much more uncertain is whether the lake-effect snow will shift into northwest PA and far-northeast OH for a relatively prolonged period of time and yield at least advisory-criteria snow accumulations. This uncertainty precluded the issuance of a Winter Storm Watch for any of our snowbelt counties with this forecast update.

KEY MESSAGES

1) Light snow showers may persist through this early evening.

2) Below-normal temperatures are expected tonight through the upcoming week with dangerous wind chills of -10 to -20 possible Monday into Tuesday.

3) Lake-effect snow develops downwind of Lake Erie tonight periodically impacting the primary snowbelt of Northeast Ohio and Northwest Pennsylvania Sunday night and through the week.

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

DISCUSSION

KEY MESSAGE 1... A few light snow showers will be possible for the next few hours this evening and will be associated with convergence/moist ascent along the upper-reaches of the front. A light dusting of snow is possible but otherwise no additional accumulations are expected.

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. As for daily daytime high temperatures, those should reach the 15F to 25F range Sunday and Monday respectively, and only the 10F to 20F range Tuesday.

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 /06Z Sunday THROUGH Thursday/

A stratus deck with ceilings around 2-5 kft lingers across much of the area, generally along and east of I-77. A few light snow showers may be possible underneath this stratus, mainly in the far eastern portion of eastern Ohio and into Northwest Pennsylvania. Dry air builds in and should see stratus dissipate by sunrise Sunday morning.

A low pressure system moves into the western and northern Great Lakes by Sunday afternoon, with cloud cover increasing and ceilings lowering Sunday night, followed by snow from west to east after 03Z. MVFR ceilings and IFR visibilities are expected.

Southwest winds around 10 knots continue through the TAF period, with occasional gusts to 20 knots.

Outlook...Light snow expected areawide Sunday night into Monday with lake effect snow across Northeast Ohio and Northwest Pennsylvania Monday night into Tuesday. Light snow expected Wednesday, followed by lake effect snow across Northeast Ohio and Northwest Pennsylvania Wednesday night into Thursday.

MARINE

Strong west-southwest winds of 20-30kt will continue through this evening behind a cold front. Small Craft Advisories remain posted for central and eastern nearshore zones where there is less ice. Also added a Low Water Advisory for the western basin until 1 AM/6z Sunday, as the water level at Toledo quickly dropped to 7 inches below Low Water Datum this afternoon with brisk west-southwest winds continuing through the evening, offering potential for the level to dip below the critical mark of 9 inches below datum. Some freezing spray is likely tonight into Sunday, with a brief window where heavy freezing spray is possible in the central basin late tonight into early Sunday. The expected coverage and duration of heavy freezing spray is too low to warrant a Heavy Freezing Spray warning at this time, though mariners should plan on at least some freezing spray.

Winds remain southwest overnight into Sunday though will subside slightly to 15-25 knots. An Arctic cold front will cross the lake on Monday as deepening low pressure tracks through the northern Great Lakes and into Ontario and Quebec. South-southwest winds ahead of the front will ramp up to 20-30kt late Sunday night, shifting west- southwest and increasing to 30-40kt with gusts to 40-50kt on Monday behind the front. Posted a Gale Watch for the entire lake starting at 8 AM/12z Monday, expiring at 8 PM/0z across the western basin and 1 AM/6z Tuesday elsewhere. The watch is a bit more marginal across the western basin, though it will be close either way. Sustained winds to 40kt with gusts of 45-50kt are looking increasingly likely across the central and eastern basin, with peak wave heights where open waters remain of up to 15 feet towards the east end. Heavy Freezing Spray Warnings will be needed to start the week in conjunction with the gale, and low water issues are likely on the west end. The next system will move through the Great Lakes Wednesday into Thursday with another period of elevated winds.

Ice cover is expected to expand east out of the western basin over the next several days given very cold temperatures. The gale-force winds expected on Monday will likely cause significant drifting of ice on the lake. Rapid ice development, and shifting of existing ice, may pose navigational difficulties on the lake.

CLE WATCHES/WARNINGS/ADVISORIES

OH...None. PA...None. MARINE...Low Water Advisory until 1 AM EST Sunday for LEZ142>144- 162>164. Gale Watch from Monday morning through Monday evening for LEZ142>144-162>164. Gale Watch from Monday morning through late Monday night for LEZ145>149-165>169. Small Craft Advisory until 7 AM EST Monday for LEZ146>149.