textproduct: Cleveland

WHAT HAS CHANGED

A Winter Weather Advisory for widespread snow accumulations of 3 to 5 inches has been issued for Erie and Crawford Counties in NW PA. The advisory is in effect from 10 AM tomorrow to 7 AM EST Thursday.

KEY MESSAGES

1) Below-normal temperatures, overall, persist through Tuesday, January 27th. Daily sub-zero minimum wind chills are forecast this Friday through next Tuesday. Saturday appears to be the coldest day.

2) Periods of accumulating snow are expected in our region overnight tonight through early next week.

DISCUSSION

KEY MESSAGE 1... Primarily below-normal temperatures are expected through next Tuesday, as net and deep troughing aloft, associated with an unusually-cold air mass, persists over eastern Canada and impacts at least most of the eastern United States, including the Great Lakes and OH Valley. At the surface, our CWA is expected to primarily reside in the cold sector based on the latest projected mid latitude cyclone track. However, a warm front is still expected to sweep NE'ward through our region tonight and be followed by the E'ward passage of a strong cold front Wednesday evening through the predawn hours of Thursday morning. A stronger, reinforcing cold front is expected to sweep SE'ward through the Lake Erie region and Upper OH Valley this Friday.

Prior to the warm front passage ushering-in a warmer air mass originating over the Gulf, lows should bottom-out near 5F to 10F with wind chills as cold as 0F to around -5F this evening. Temperatures should then moderate to mainly the lower teens to mid 20's by daybreak Wednesday as strong low-level WAA follows the front. On Wednesday, low-level WAA in the warm sector should contribute to highs reaching the lower to upper 30's before the aforementioned strong cold front passage. Below-normal high and low temperatures are then expected Wedneday night through this upcoming Tuesday. For example, low temperatures should reach the single digits below 0F in many northern OH and NW PA locales around daybreak Saturday. Sub-zero minimum wind chills will likely be a daily occurrence this Friday through Tuesday. Forecast trends will continue to be monitored for the need for additional cold weather alerts.

KEY MESSAGE 2... Primarily fair weather is expected through this evening as an Arctic ridge exits E'ward and a SW'erly mean low-level flow directs lingering Lake Erie lake-effect snow (LES) into portions of western NY. However, the LES may brush the lakeshore periodically in Erie County, PA, but any snow accumulations will be less than 1". Otherwise, multiple shortwave disturbances embedded in primarily W'erly to NW'erly flow aloft will affect our region tonight through next week Tuesday. Widespread snow is expected to reach the surface via the wet-bulb effect and traverse our region generally from west to east from about midnight tonight through Wednesday afternoon as moist isentropic ascent occurs along the upper-reaches of the aforementioned warm front and ahead of a shortwave trough axis. The snow should be steady to heavy at times, especially during Wednesday morning through early afternoon, as a SW'erly jet of 40 to 55 knots at/near 925 to 850 mb enhances the isentropic ascent and results in moderate to strong, maximized ascent in a cloudy DGZ about 1 to 2 km thick. Note: a surface-based melting layer should develop in the warm sector and become deep enough for rain to mix with snow at times Wednesday afternoon into early evening, especially well-south in our CWA.

During Wednesday night, the strong cold front passage should be preceded by additional moist isentropic ascent-related snow and accompanied by one or multiple bands of snow showers, steady to heavy at times, as low-level convergence and moist ascent along the front release at least weak potential instability in the lowest ~1 km AGL. Behind the front, a sufficiently-cold/moist cyclonic W'erly to WSW'erly mean low-level flow over/downwind of the ~1C ice-free waters of Lake Erie will permit renewed development of LES. This LES is expected to impact the primary snowbelt of NE OH and NW PA at times, especially along/near the lakeshore east of Cleveland due to frictional surface convergence. The LES should be heavy at times as deep low-level moisture promotes greater lake-induced instability. Fresh snow accumulations through daybreak Thursday are expected to be mainly a coating to 3 inches in northern OH and 3 to 5 inches in NW PA. However, localized totals of 4 inches are possible in the higher terrain of the primary snowbelt of NE OH.

During Thursday through Thursday night, odds favor fair weather in most of our CWA as a surface ridge noses NE'ward into our region. However, Lake Erie LES will persist amidst a favorable thermodynamic and kinematic environment, and should impact the primary snowbelt of NE OH and NW PA periodically as mean low- level flow varies between SW'erly and W'erly due to shortwave trough passages. On Friday, the passage of the stronger, reinforcing cold front may be accompanied by at least isolated snow showers, heavy at times, due to the same aforementioned reasons as Wednesday night's front passage. The front's passage will cause LES to shift from generally east of Lake Erie to generally southeast of the lake, where LES should then persist into Friday night. Thus, LES should eventually impact the entire snowbelt of NE OH/NW PA and vicinity. The LES should be steady to heavy at times Thursday through Friday night amidst periods of greater low-level moisture and lake-induced instability, respectively. Our latest snowfall forecast for the daylight hours of Thursday through Friday night calls for 1 inch or less outside the LES and 1 to 6 inches in the primary snowbelt; greatest amounts farther to the northeast.

Additional periods of accumulating snow are possible this weekend due, in part to moist isentropic ascent ahead of additional shortwave trough axes. Accumulations remain uncertain at this juncture. Favorable thermodynamics and kinematics should allow LES to persist, but all of the following are uncertain: evolution of mean low-level flow direction and ice cover on Lake Erie; LES placement, intensity, and amounts. Note: surface winds should remain strong enough to prevent Lake Erie from freezing over completely through early next week.

AVIATION /18Z Tuesday THROUGH Sunday/

Southwest winds will continue their gradual decrease at the surface to below 10kts by tonight, for a brief period of time anyways as high pressure builds in from the south. The pressure gradient increases again with the approach of a low pressure system from the west with a warm front and a cold front towards the end of the TAF period/18Z Wednesday. Ceilings lower to MVFR in precipitation after 12Z, and light snow develops with visibilities to IFR at times. Winds gust again 20-30 kts out of the southwest after 10Z Wednesday.

Outlook...Non-VFR in lake effect snow impacting northeast Ohio and northwest Pennsylvania Wednesday night through Friday. Areawide light snow is possible on Saturday.

MARINE

No Small Craft Advisories will be issued while the nearshore areas are predominantly ice covered, so this will be the case going forward for now. Ice covers the western third of Lake Erie, and for only the open water zones roughly from Cleveland east remain ice free. Offshore winds 20-30kts become southwesterly Wednesday through Thursday at 20-30kts, so the ice free open water areas will have a range of 3-6ft waves to contend with through Friday night. Lingering heavy freezing spray concerns east of Willowick are expected to cease by this late evening in response to continued easing of winds. Thus, the Heavy Freezing Spray Warning is now in effect until 10 PM this evening for U.S. waters east of Willowick.

The nearshore ice is not fastened to the shoreline, so it is possible that this ice in the central and eastern basins gets pushed around slightly into open water areas in the offshore winds.

CLE WATCHES/WARNINGS/ADVISORIES

OH...None. PA...Winter Weather Advisory from 10 AM Wednesday to 7 AM EST Thursday for PAZ001>003. MARINE...Heavy Freezing Spray Warning until 10 PM EST this evening for LEZ147>149-167>169.