textproduct: Cleveland

WHAT HAS CHANGED

Based on latest QPF trends from the NBM and WPC, upgraded the Winter Storm Watch to a warning for Ottawa, Sandusky, and Hancock Counties in NW OH. This warning is in effect from 7 PM Saturday to 7 AM EST this Monday. Based on the same QPF trends and coordination with WFO's Northern Indiana and Detroit, the Winter Storm Watch remains in effect for Lucas and Wood Counties for 7 PM Saturday to 7 AM this Monday. This is where forecast confidence in widespread warning-criteria, storm-total snowfall of at least 6 inches remains fairly low. Here is the latest info on the other weather alerts:

- Cold Weather Advisory for wind chills as cold as -17F remains in effect for all of our northern OH and NW PA counties until 7 AM Saturday. - The Winter Storm Warning for the remainder of our CWA (i.e. from Erie, Huron, Seneca, and Wyandot Counties, OH and points east) takes effect at 7 PM Saturday and is scheduled to end from west to east between 10 AM and 1 PM this Monday.

KEY MESSAGES

1) Periods of snow are expected through late next week. Biggest concern remains the upcoming winter storm tomorrow night through Monday morning.

2) Below-normal temperatures persist today through Friday, January 30th. Daily sub-zero wind chills are expected.

DISCUSSION

KEY MESSAGE 1... Aloft, a deep longwave trough associated with an unusually-cold air mass persists over eastern Canada and at least most of the eastern United States, including the Great Lakes and OH Valley, through Friday, January 30th. Based on the latest mid-latitude cyclone track, our region is expected to remain in the cold sector and experience below-normal air temperatures through late next week (see Key Message 2 for further details). Primarily fair weather is expected through early Saturday evening as a strong Arctic surface high pressure ridge slides generally E'ward across the Great Lakes and vicinity. Behind a recent Arctic front passage, light lake-effect snow (LES) showers and self-destructive sunshine-related snow showers are expected to stream generally SE'ward across NW PA, NE OH, and vicinity through this early evening. These snow showers should dissipate around sunset as the boundary layer stabilizes via nocturnal cooling and significant low-level dry air advection on the synoptic scale. Any additional snow accumulations are expected to be less than one inch.

Based on the projected evolution of the subtropical and polar front jet streams and embedded jet streaks, and shortwave troughs embedded in the above-mentioned longwave trough aloft, a primary surface low should develop along the northwestern Gulf coast on Saturday and then wobble NE'ward across the Lower MS Valley to near the Upper OH Valley by sunset Sunday evening. Simultaneously, this low should deepen, overall, amidst MSLP falls associated with focused divergence aloft/tropospheric ascent in the left-front quadrant of a jet streak. As the low pressure system's warm conveyor belt, including eventual TROWAL, undergoes isentropic ascent aloft while tapping into abundant moisture over the Gulf and southern Gulf Stream, widespread snow will overspread our region generally from south to north and reach the surface via the wet-bulb effect Saturday evening through about mid-morning on Sunday. Widespread snow will then persist through sunset Sunday evening. The snow is expected to be moderate to heavy at times, with snowfall rates up to a half inch to one inch per hour at times, since isentropic ascent and ascent tied to frontogenetical convergence in the TROWAL, respectively, are expected to be moderate to strong and maximized in a cloudy DGZ about 1 km deep at times.

As the left-front quadrant of the aforementioned mid/upper-level jet streak translates farther NE'ward Sunday night through Monday, a coastal surface low should form and deepen near Long Island and Nantucket as the previous surface low dissipates near the Upper OH Valley. Simultaneously, the coastal low will become the dominant surface low and deepen further as it wobbles NE'ward to Atlantic waters south of Nova Scotia. Accordingly, the warm conveyor belt, including TROWAL, and associated moist isentropic ascent and frontogenetical forcing for ascent will weaken over our region while translating generally E'ward. Thus, lingering snow should weaken and exit generally E'ward overnight Sunday night through early Monday afternoon. Note: given the extensive ice cover on Lake Erie, any lake-enhancement of snow in the CAA regime on the backside of the low pressure system should be limited. As of 3 PM EST Friday, our latest storm-total snowfall forecast calls for 5 to 12 inches of snow accumulation. Greatest amounts are expected toward the southeast in our CWA based on the projected evolution of the weather pattern at the surface and aloft, including surface low and TROWAL.

During the rest of Monday through Friday, periodic snow is expected due, in part to moist isentropic ascent preceding shortwave trough axes embedded in cyclonic and primarily W'erly to N'erly flow aloft. Limited LES may occur downwind of mainly ice-covered Lake Erie, amidst a primarily W'erly to NW'erly mean low-level flow of sufficiently-cold/moist air. Additional snow accumulations should occur, but exact amounts are uncertain at this juncture.

KEY MESSAGE 2... Partially clear sky and weak surface winds accompanying the aforementioned Arctic ridge will promote efficient radiational cooling late this afternoon through daybreak Saturday, when widespread lows of 0F to -10F are expected amidst net low-level CAA. Wind chills as cold as -10F to nearly -20F are forecast through daybreak. On Saturday, the development of weak low- level WAA ahead of the above-mentioned low pressure system should contribute to afternoon highs reaching the upper single digits to nearly 15F. Between sunrise Saturday morning and midnight Saturday night, wind chills should fluctuate between roughly -10F and 5F. Continued below-normal air temperatures and daily sub-zero minimum wind chills are expected Saturday night through Friday.

AVIATION /00Z Saturday THROUGH Wednesday/

Skies will continue to clear across the majority of the area tonight, although some broken 3500-5000 ft AGL clouds may hang around at KERI through the overnight hours. VFR is expected areawide with a broken cirrus deck moving into the region mid to late afternoon Saturday. Any snow is expected to remain to the south of the local area through 00Z Sunday. Winds will be out of the northwest at around 5 to 10 knots this evening before becoming light and variable overnight. East/northeast winds will develop Saturday afternoon with wind speeds likely reaching 5 to 10 knots across north-central and northwestern Ohio by early evening.

Outlook...Widespread snow spreads moves in from the south Saturday night, before tapering off Monday morning. Snow will be moderate in intensity through the event but high snowfall totals are expected. Non-VFR with lake effect snow showers will be possible in Northeast Ohio and Northwest Pennsylvania into Tuesday and again on Wednesday.

MARINE

Westerly winds of 20-25 knots on the east end of Lake Erie will decrease tonight as high pressure builds over the region. Some freezing spray is likely is ice free areas this evening but ice continues to expand on Lake Erie. Northeasterly winds of 10-20 knots return on Saturday night through Sunday as a winter storm tracks through the Ohio Valley. Southwesterly winds ramp up to 30 knots on Tuesday, then veer to northwesterly Tuesday night. A bitterly cold airmass settles in behind this system for much of next week and Lake Erie is expected to become mostly ice covered.

CLE WATCHES/WARNINGS/ADVISORIES

OH...Cold Weather Advisory until 7 AM EST Saturday for OHZ003- 006>014-017>023-027>033-036>038-047-089. Winter Storm Watch from Saturday evening through Monday morning for OHZ003-006. Winter Storm Warning from 7 PM Saturday to 7 AM EST Monday for OHZ007-008-017. Winter Storm Warning from 7 PM Saturday to 10 AM EST Monday for OHZ009>014-018>023-027>033-036>038-047-089. PA...Cold Weather Advisory until 7 AM EST Saturday for PAZ001>003. Winter Storm Warning from 7 PM Saturday to 1 PM EST Monday for PAZ001>003. MARINE...None.