textproduct: Cleveland

WHAT HAS CHANGED

For tonight into Saturday morning, a Freeze Warning has been issued for southern Erie and Crawford Counties in PA and a Frost Advisory has been issued for most of northern OH. The advisory excludes Erie, Lorain, Medina, Summit, and Cuyahoga Counties. The potential for additional precipitation, mainly in the form of rain, has increased this evening into Saturday morning, especially along and near Lake Erie in northern OH.

KEY MESSAGES

1.) Unusually-cold air temperatures persist through this Saturday night. Frost and periodic sub-freezing air temperatures remain a concern. In addition, periodic precipitation, mainly in the form of rain, is expected through Saturday afternoon.

2.) Near-normal to above-normal air temperatures return Sunday through Tuesday night, when multiple rounds of showers and thunderstorms are possible.

3.) Below-normal air temperatures return Wednesday through Friday, May 8th. Additional periods of rain are forecast.

DISCUSSION

KEY MESSAGE 1...

Cyclonic W'erly to NW'erly flow aloft and embedded shortwave disturbances affect our region through Saturday as a mid/upper- level low drifts E'ward over west-central QC. At the surface, a high pressure ridge builds slowly from the north-central United States and vicinity. This weather pattern evolution at the surface and aloft will maintain a CAA regime and unusually-cold air temperatures across our region. Partial clearing and easing surface winds tonight will allow low temperatures to mainly reach the lower to mid 30's Saturday morning where the Freeze Warning and Frost Advisory are in effect. Elsewhere, including the Lake Erie Islands, lows in the upper 30's to lower 40's are expected as lake-effect cloud cover contributes to less nocturnal cooling. On Saturday, partly to mostly cloudy sky and peeks of sunshine should be accompanied by afternoon highs reaching only the mid 40's to lower 50's.

Widespread rain associated with moist isentropic ascent aloft, ahead of a shortwave trough axis, will continue to depart our CWA generally from west to east through this early evening. Primarily dry weather is then expected through Saturday courtesy of stabilizing subsidence accompanying the building ridge. However, moist isentropic ascent aloft, ahead of a separate shortwave trough axis, should generate isolated to scattered showers late this afternoon through early Saturday afternoon as the shortwave trough axis advances from the western Great Lakes toward western NY and western PA. A mainly NW'erly mean low-level flow of unusually-cold and sufficiently-moist air over/downwind of ~11C Lake Erie and the development of weak lake-induced instability should allow periodic lake-effect rain showers to stream generally SE'ward across portions of NW OH and especially NE OH and NW PA during this mid-evening through early Saturday afternoon before lake-effect precip ends in response to lake- induced CAPE waning via a lowering subsidence inversion. Rain should be the predominant precip type this evening into Saturday, but rain may mix with or change to wet snow at times overnight tonight into Saturday morning in the higher terrain of NE OH and NW PA. Any snow accumulations are expected to be less than 0.5" and confined to the higher terrain of NW PA.

During Saturday night, NW'erly flow aloft and dry weather are expected as a shortwave ridge builds from the western Great Lakes and the surface portion of the ridge continues to build from the west. Considerable clearing and weak or calm surface winds will contribute to significant nocturnal cooling. Accordingly, lows should reach mainly the upper 20's to mid 30's and areas of frost are expected to form around daybreak Sunday. Another Frost Advisory and Freeze Warning will be needed.

KEY MESSAGE 2...

On Sunday, the ridge at the surface and aloft will depart E'ward and allow a warm front to sweep N'ward through our region. The warm front passage is expected to be dry due to a relatively-dry low-level atmospheric column. WAA at the surface and aloft, along the backside of the ridge, will contribute to late afternoon highs reaching the mid 50's to lower 60's.

Primarily cyclonic and SW'erly to W'erly flow aloft and embedded shortwave disturbances should impact our region Sunday night through Tuesday night. At the surface, the aforementioned ridge will continue to exit generally E'ward, subtle surface trough axes, tied to the shortwave troughs aloft, will traverse our area, and a cold front should sweep SE'ward through our region Tuesday evening through Tuesday night. Periodic showers and thunderstorms are expected as weak to moderate CAPE, including elevated CAPE, is released by low-level convergence/moist ascent along the surface trough axes and cold front, and by moist isentropic ascent aloft ahead of shortwave trough axes. Ahead of the cold front, low-level WAA should be accompanied by lows reaching the 40's to lower 50's around daybreak Monday, late afternoon highs reaching the 60's to lower 70's on Monday, overnight lows reaching the 50's around daybreak Tuesday, and late afternoon highs reaching the 60's to 70F on Tuesday. Lows should reach the 40's around daybreak Wednesday as colder air overspreads our region behind the cold front.

KEY MESSAGE 3...

Cyclonic W'erly flow aloft and embedded shortwave troughs should impact the southern Great Lakes and OH Valley on Wednesday through Friday and be accompanied by primarily below-normal air temperatures. This pattern should allow net surface troughing to affect our CWA. Periodic rain showers are forecast due to moist isentropic ascent aloft, ahead of shortwave trough axes, and low-level convergence/moist ascent along surface trough axes.

AVIATION /00Z Saturday THROUGH Wednesday/

Scattered rain showers will continue to pivot east across northern Ohio this evening, resulting in potential for brief and periodic showers at Ohio terminals through later tonight or early Saturday morning. Can't rule out a few snowflakes or graupel mixing with showers given the cold air aloft, although significant impacts to visibilities due to precipitation are not expected. A period of lower stratus and patchy fog is likely east of KTOL/KFDY and south of the lakeshore early Saturday morning, during which time ceilings will likely drop to MVFR. The best chance of IFR conditions in lower stratus/fog will be at inland locations of NE OH, specifically KCAK/KYNG. Ceilings will likely improve throughout the day Saturday, although scattered to broken low-end VFR ceilings will stick around through the remainder of the TAF period.

Outlook...Non-VFR possible in scattered showers and thunderstorms late Monday through Wednesday as a cold front moves southeast across the area.

MARINE

Northwest winds of 10-15 knots this afternoon will decrease tonight. Winds back to southwesterly on Saturday night as high pressure settles south to the Ohio Valley. Winds increase to 15-20 knots by Sunday night but flow will be offshore through Monday. Winds shift to northerly behind a cold front on Tuesday night and a window of Small Craft Advisories may be needed.

CLE WATCHES/WARNINGS/ADVISORIES

OH...Frost Advisory from 2 AM to 9 AM EDT Saturday for OHZ003- 006>008-017>019-027>031-036>038-047-089. Frost Advisory until 9 AM EDT Saturday for OHZ012>014-022-023- 032-033. PA...Frost Advisory from 2 AM to 9 AM EDT Saturday for PAZ001. Freeze Warning until 9 AM EDT Saturday for PAZ002-003. MARINE...None.