textproduct: Cleveland

WHAT HAS CHANGED

An Extreme Cold Watch has been issued for Erie and Crawford Counties, PA for potential minimum wind chills of -20F to -30F. The watch is in effect from 1 AM to 12 PM EST this Saturday. Widespread accumulating snow, heavy at times, is still expected affect our entire region tonight through Friday evening.

KEY MESSAGES

1.) Patchy to areas of freezing fog are expected this morning. Will continue to monitor trends in NWP guidance and weather obs for the potential need of a Freezing Fog Advisory.

2.) Primarily below-normal temperatures are expected through this Monday. Widespread sub-zero minimum wind chills are still forecast this Saturday and Sunday, respectively.

3.) Periods of snow are expected tonight through this weekend. Also, gusty northwesterly winds are expected Friday afternoon into Friday night with areas of blowing snow.

4.) Temperatures should rebound to near normal values next week Tuesday and Wednesday.

DISCUSSION

KEY MESSAGE 1... Clear sky and weak or calm surface winds have allowed a surface-based layer of air to cool to supersaturation via radiational cooling in some locales. This has resulted in isolated freezing fog formation given air temperatures and surface temperatures are well below 32F in the fog. Freezing fog may expand in coverage through daybreak this morning, which may prompt the issuance of a Freezing Fog Advisory. Will continue to monitor this situation closely. Any fog is expected to dissipate via diurnal convective mixing of the boundary layer during the mid or late morning hours of today.

KEY MESSAGE 2... Net troughing aloft, associated with an abnormally-cold air mass, remains entrenched over eastern Canada. This trough will impact at least most of the eastern United States through this Monday night, including northern OH and NW PA, as the S'ward extent of the trough fluctuates. Mainly below-normal temperatures are expected to persist in our CWA. For context, our normal highs are near 35F and normal lows are near 20F this time of year. At the surface, a ridge continues to exit E'ward before two cold fronts, arguably, sweep SE'ward through our CWA on Friday. The first front should traverse our region Friday afternoon through early evening, while an Arctic front should traverse our region Friday evening. Low-level WAA on the backside of the ridge should allow our highs to reach the lower to mid 20's this afternoon. Lows should reach the 10F to 20F range this evening before readings begin to moderate somewhat around and especially after midnight, via strengthening low- level WAA. On Friday, daytime highs are expected to reach the mid 20's to mid 30's before the first cold front passage results in a slight temperature drop. Behind the Arctic front, an Arctic ridge and associated much colder air temperatures should affect our region through Monday night as the core of the ridge moves from the northern Great Plains toward New England. For example, low temperatures should reach the single digits on either side of 0F around daybreak Saturday morning and Sunday morning, respectively, when widespread sub-zero minimum wind chills are expected. A Cold Weather Advisory for northern OH and an upgrade from Extreme Cold Watch to Warning for NW PA will likely be needed overnight Friday night into Saturday morning, when the coldest wind chills (near -15F to -30F) should occur.

KEY MESSAGE 3... SNOW:

Odds favor fair weather today as the aforementioned surface ridge continues to exit E'ward. Periods of widespread snow, steady at times, are expected to overspread our region generally from northwest to southeast tonight and then persist through Friday evening due to the following: moist isentropic ascent ahead of a SE'ward-moving shortwave trough axis aloft and the release of at least weak potential instability in the lowest ~1 km AGL via convergence/moist ascent along the first cold front and especially the Arctic front. Based on trends in higher-res NWP model guidance, we are growing increasingly concerned that a narrow band of heavy graupel and/or snow will accompany the Arctic front passage Friday evening as the aforementioned frontal forcing for ascent and release of potential instability result in strong, maximized ascent at cloud temperatures near 8C to 12C below zero and amidst 0-1 km AGL mean wind speeds around 20 to 30 knots. Thus, snow squalls are a concern. The widespread snowfall is still expected to total primarily 1 to 4 inches in our CWA. The greatest totals should be focused in the higher terrain of NE OH and NW PA, where localized totals up to 5 or 6 inches are possible. This is where snow should be enhanced by moist NW'erly upslope flow for as long as several hours behind the first cold front and before the Arctic front ushers-in a much drier low/mid-level air mass. Future trends in our official forecast may prompt the issuance of a Winter Weather Advisory, especially in NE OH and NW PA.

During Friday night through this Sunday, periodic and scattered lake- effect snow (LES) showers should target our CWA amidst a NNW'erly to NW'erly mean low-level flow of sufficiently-cold/moist air over/downwind of the ice-free waters of Lake Huron and possible gaps in Lake Erie's ice cover. Given the expectation of extensive ice cover on Lake Huron and especially Lake Erie, LES intensity and amounts should be limited. Note: a shortwave trough embedded in NW'erly flow aloft may generate widespread light snow across our CWA Saturday night into Sunday. Current odds favor dry weather Sunday night through Monday night amidst stabilizing subsidence accompanying the aforementioned ridge.

WIND AND BLOWING SNOW:

NW'erly surface winds are expected to be around 20 to 25 mph sustained and gust up to 30 to 45 mph behind Friday's cold front passages. Steep low-level lapse rates and rather deep mechanical mixing of the boundary layer amidst low-level winds and CAA increasing with height will promote these gusty winds. Wind gusts should begin to subside during the wee hours of Saturday morning and ease significantly by daybreak amidst a relaxing MSLP gradient. Trends in NWP model guidance will continue to be monitored for the potential need of a Wind Advisory (peak gust criteria: 46-57 mph). Note: these NW'erly surface winds are expected to result in blowing and drifting of freshly-fallen snow.

KEY MESSAGE 4... During next week Tuesday through Wednesday, the surface ridge should exit E'ward as the ridging aloft, associated with a warmer air mass, overspreads our region from the west. Accordingly, daytime highs should reach mainly the mid 30's to lower 40's each day. Overnight lows Tuesday night should reach mainly the lower to mid 20's. Current odds favor dry weather on Tuesday courtesy of stabilizing subsidence accompanying the ridge. Periods of snow and/or rain are possible Tuesday night through Wednesday as subtle shortwave disturbances ripple generally E'ward through the ridge aloft.

AVIATION /18Z Thursday THROUGH Tuesday/

A mix bag of VFR and MVFR conditions are being observed across the area this afternoon ahead of an approaching low pressure system. Conditions should gradually deteriorate through the evening to have widespread MVFR ceilings between 2-3kft with a few light snow showers possible across the northern terminals. These conditions will further worsen to IFR and possible LIFR as widespread snow showers move into the area Friday morning. Within snow showers, visibilities will likely drop to 1SM or less, but for now opted to maintain the 1SM in the TAF given a bit of timing uncertainty. In addition, ceilings will gradually lower to less than 1kft. These conditions will persist through the remainder of the TAF period.

Winds this afternoon will persist from the southwest at 5-10 knots, gradually gaining a more westerly component Friday morning. After this TAF period, wind gusts of 20-30 knots are possible from the northwest as the cold front departs to the east.

Outlook...Non-VFR likely Friday evening as the clipper system continues to bring snow to the area. Northwest wind gusts of 30-35 knots will be possible Friday evening through Saturday morning.

MARINE

Lake Erie remains primarily ice covered and is expected to remain this way for the foreseeable future. An Alberta Clipper system brings a stout cold front Friday evening and winds becoming northwesterly approaching gale force for the central and western basins. into Saturday morning. Some compaction of ice may occur during these conditions near the shoreline.

CLE WATCHES/WARNINGS/ADVISORIES

OH...None. PA...Extreme Cold Watch from late Friday night through Saturday morning for PAZ001>003. MARINE...None.