textproduct: Cleveland

WHAT HAS CHANGED

A Frost Advisory remains in effect for inland Ashtabula, Trumbull, and Mahoning Counties in NE OH and Crawford and southern Erie Counties in NW PA until 8 AM EDT this morning. Our low temperature forecast has trended colder for Tuesday morning. A Frost Advisory or Freeze Warning will likely be need for most of our CWA. The rest of the forecast is essentially unchanged.

KEY MESSAGES

1.) Below-average temperatures, overall, are expected through this Thursday night. Frost remains a concern this morning and overnight tonight into Tuesday morning.

2.) Unsettled weather, including periodic thunderstorms, returns Tuesday evening through Thursday.

3.) A warming trend is expected on Friday through Monday, May 18th.

DISCUSSION

KEY MESSAGE 1... A high pressure ridge at the surface and aloft builds from the north-central United States and vicinity through tonight and then crests E'ward across our region on Tuesday. Mainly dry weather is expected as stabilizing subsidence accompanies the ridge. Net low-level CAA persists through tonight, which will contribute to continued below-average temperatures. Highs late this afternoon are expected to reach only the 50's to lower 60's. Mainly clear sky, weak or calm surface winds, and low humidity accompanying the ridge will promote efficient radiational cooling this evening through daybreak Tuesday, when lows are expected to reach the lower to mid 30's across much of our CWA, inland from Lake Erie. Frost formation is expected in NW PA and much of northern OH, inland from the lake. Many of our zones will likely require a Frost Advisory or Freeze Warning. Will let the day shift reevaluate this potential. As our region becomes located along the western flank of the ridge at the surface and aloft on Tuesday, net low-level WAA will develop across northern OH and NW PA. Even so, increasing cloud cover amidst moist isentropic ascent, ahead of a trough axis aloft that will approach from the Upper Midwest and vicinity, will contribute to highs reaching the upper 50's to upper 60's. This increasing cloud cover may produce sprinkles over and very near Lake Erie around sunset Tuesday evening.

The ridge at the surface and aloft exits E'ward Tuesday night through Wednesday night as the aforementioned trough aloft overspreads our region as its axis moves from the Upper Midwest to near Lake Ontario and the central Appalachians. At the surface, the attendant low should wobble ESE'ward from the northwestern Great Lakes to northeastern NY, which should allow a surface warm front to sweep NE'ward across our CWA Tuesday night before a surface cold front sweeps E'ward through our region Wednesday through Wednesday night. Behind the cold front, a surface ridge builds from the north-central United States through Thursday night, while the mid/upper-level portion of this ridge should begin to build from the west by Thursday night.

Net low-level WAA ahead of the warm front and within the warm sector will contribute to overnight lows reaching the upper 40's to mid 50's Tuesday night. Abundant cloud cover associated with the low pressure system should limit daytime highs to the lower to mid 60's on Wednesday, ahead of the cold front. Net low-level CAA behind the cold front should contribute to lows reaching the 40's around daybreak Thursday and Friday, respectively. Highs should reach only the 50's to lower 60's late Thursday afternoon.

KEY MESSAGE 2... Periods of rain, steady to heavy at times, are expected Tuesday night through Wednesday due to the following: isentropic ascent along the upper-reaches of the warm front tapping into abundant moisture originating over the southern Gulf Stream and Gulf; convergence/moist ascent along the surface cold front; moist isentropic ascent along the upper-reaches of the cold front. Occasional thunderstorms are expected Tuesday evening through early Wednesday evening as weak CAPE, including elevated CAPE, is released by the aforementioned lifting mechanisms. During Wednesday night into early Thursday, precip is expected to transition to lake-enhanced/effect rain over and generally southeast of Lake Erie, especially central and eastern portions of the lake, as a primarily NW'erly mean low-level flow of sufficiently-cold/moist air becomes established over/downwind of the ~12C lake, at least weak lake-induced CAPE forms, and the seeder-feeder process occurs at times amidst a sufficiently- cold/moist low/mid-level atmospheric column ahead of shortwave trough axes embedded in the aforementioned trough aloft. Between daybreak and nightfall on Thursday, lingering lake-effect rain showers should end from west to east and give way to dry weather region-wide by Thursday night as lake-induced CAPE wanes via low-level dry air advection and a lowering subsidence inversion accompanying the ridge that will build from the north-central United States and vicinity.

KEY MESSAGE 3... A warming trend is expected this Friday through Monday, May 18th as our region becomes located within a net low-level WAA regime, along the western flank of the aforementioned ridge at the surface and aloft. Moderating temperatures should include daytime highs moderating from the 60's and 70's on Friday to the 80's on Monday. Periodic showers and thunderstorms are possible daily, especially during the afternoon through early evening hours, as a low-level return flow of moist air originating over the Gulf becomes established, the boundary layer destabilizes via daytime heating each day, and multiple shortwave troughs embedded in the primarily SW'erly flow aloft and attendant surface trough axes traverse our region.

AVIATION /06Z Monday THROUGH Friday/

VFR conditions are expected to persist through the TAF period. An initial round of mid-level clouds will exit to the east this morning and allow for just some high cirrus during late morning hours. Some lower VFR ceilings may return during the afternoon with some moisture between 4 and 8 kft pushing south through the airspace. High ceilings will return by evening with diurnal cooling eliminating the afternoon cumulus field. Winds during the period will be light at 10 kts or less. Wind direction will be variable overnight before settling on a northerly component for Monday.

Outlook...Non-VFR expected in showers and thunderstorms late Tuesday through Wednesday with lingering rain and low ceilings through Thursday. Non-VFR may return in scattered rain showers and thunderstorms on Friday.

MARINE

High pressure will continue building from the northwest today and allow for light northerly flow on the lake. This high will shift east on Tuesday and allow for light easterly flow on the lake. The main window for lake impacts will be from Tuesday night through Thursday with a low pressure system moving through the region. This system will enter the northwest Great Lakes on Tuesday afternoon and extend a warm front across the lake on Tuesday night. Strong southwest flow is expected to develop over the lake on Tuesday night with 15 to 25 kts of flow and a Small Craft Advisory may be needed. The low will move southeast toward the lake on Wednesday and allow for westerly flow of 10 to 20 kts across the basin. This low will extend a cold front across the lake on Wednesday night and 15 to 20 kts northwest flow will become favored behind the feature. These elevated northwest winds will continue into Thursday. With the stronger onshore flow, some elevated waves of 3 to 4 ft are possible and there is a non-zero chance for a Small Craft Advisory, especially if winds trend higher. High pressure will enter the region for Thursday night into Friday. Northerly flow will trend lighter for Thursday night before shifting to light southerly flow for Friday.

CLE WATCHES/WARNINGS/ADVISORIES

OH...Frost Advisory until 8 AM EDT this morning for OHZ014-023-033. PA...Frost Advisory until 8 AM EDT this morning for PAZ002-003. MARINE...None.