textproduct: Cleveland

WHAT HAS CHANGED

Frost and Freeze alerts remain in effect for all of northern OH and NW PA until 8 AM EDT this morning. Frost formation is still expected inland from Lake Erie, especially around daybreak this morning, as lows settle into the lower to mid 30's in many locations inland from the lake. 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.

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

3) An overall warming trend is expected on Friday through Tuesday, May 19th.

DISCUSSION

KEY MESSAGE 1... A high pressure ridge at the surface and aloft crests E'ward across our region today. Dry weather is expected as stabilizing subsidence accompanies the ridge. Net low-level WAA develops across northern OH and NW PA today as our region becomes located along the western flank of the ridge. Highs late this afternoon are expected to reach the upper 50's to near 70F as cloud cover increases amidst moist isentropic ascent, ahead of a trough axis aloft that will continue to approach from the north-central United States and vicinity. The coolest highs are expected over and within several miles of ~54F Lake Erie since a favorable thermodynamic environment and weak synoptic MSLP gradient should promote lake breeze development late this morning through early evening.

The ridge at the surface and aloft exits E'ward tonight through Wednesday night as the aforementioned trough aloft overspreads our region and its axis moves from the Upper Midwest to near Lake Ontario and the central Appalachians. The attendant surface 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 between about daybreak and early evening on Wednesday. Behind the cold front, a surface ridge builds from the Upper Midwest 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 tonight. Abundant cloud cover associated with the low pressure system and a faster cold front passage than expected previously should limit daytime highs to the upper 50's to lower 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, although a few locations in interior NE OH may have lows reach the upper 30's around daybreak Friday morning. Daytime highs on Friday should reach only the upper 40's to mid 50's in NW PA and the 50's to mid 60's in northern OH.

KEY MESSAGE 2... Periods of rain, steady to heavy at times, are expected tonight through Wednesday due to the following: isentropic ascent along the upper-reaches of the warm front tapping into abundant moisture originating over the Gulf and especially the southern Gulf Stream; 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. SPC has a marginal risk of severe thunderstorms capable of producing straight-line wind damage that clips far-eastern portions of our CWA Wednesday afternoon and early evening. However, this risk appears to be very marginal given the expectation that abundant cloud cover will limit diurnal destabilization of the boundary layer, which in turn will limit the magnitude of low-level lapse rates and DCAPE, respectively.

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 and isentropic ascent 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 west.

KEY MESSAGE 3... An overall warming trend is expected this Friday through Tuesday, May 19th 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 in the 60's to lower 70's on Friday followed by daily highs mainly in the 80's this weekend through Monday. Tuesday, May 19th may be slightly cooler with highs in the mid 70's to lower 80's as the next cold front approaches from the northwest and results in increased potential for showers and thunderstorms, and greater cloud cover as a result. More specifically, periodic showers and thunderstorms are possible Friday night through Tuesday the 19th, but 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, multiple shortwave troughs embedded in the primarily SW'erly flow aloft and attendant surface trough axes traverse our region, and the aforementioned cold front approaches northern OH and NW PA, eventually.

AVIATION /18Z Tuesday THROUGH Sunday/

Pleasant aviation conditions are being observed across the area this afternoon as high pressure lingers over the region. By this evening however, conditions will begin to diminish as a low pressure system moves east into the Great Lakes region, moving a warm front north late this afternoon, followed by a cold front overnight. Ahead of the cold front, a strong LLJ will push northeast, increasing winds from the south-southeast to 12-16 knots across the area with gusts up to 25 knots. The strongest gusts should remain along and west of I-71. Near 02Z, showers will begin to move into NW OH, spreading east overnight. Widespread showers are expected ahead and along the front with ceilings and visibilities possibly diminishing to MVFR at times. There is a non-zero potential for thunder, however given the diurnally unfavorable timing, confidence is very low at this point.

As the front drifts east overnight, conditions will gradually dry out with the exception of eastern terminals where some lake enhanced showers will linger through the end of the period. MVFR ceilings will become more widespread behind the departing front with ceilings generally between 2-3kft. In addition, behind the front, winds will become west- northwesterly and remain elevated in the 12-15 knots range, gusting up to 25 knots. These winds are expected to persist through the end of the period.

Outlook...Non-VFR possible with lingering rain and low ceilings through Thursday. Non-VFR may return in scattered rain showers and thunderstorms late Friday into Saturday.

MARINE

Light easterly flow will be present on the lake today ahead of a warm front. This front will lift over the lake this afternoon and southwesterly flow will overtake the lake and increase. Offshore flow over the western basin will exceed 20 kts at times and a Small Craft Advisory has been issued. Low pressure will move southeast through the Great Lakes region on Wednesday, steering flow to the west, while maintaining elevated speeds. This low will extend a cold front across the lake on Wednesday night, allowing for northwest flow to become favored. This onshore flow will be in the 15 to 20 kt range and should allow for waves to reach 4 ft for the central and eastern basins and an expansion of the Small Craft Advisory is likely. 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. A warm front will cross the lake on Friday night into Saturday, allowing for 10 to 15 kts of offshore flow.

CLE WATCHES/WARNINGS/ADVISORIES

OH...None. PA...None. MARINE...Small Craft Advisory from 10 PM this evening to 10 PM EDT Wednesday for LEZ142-143. Small Craft Advisory from 10 PM this evening to 10 AM EDT Thursday for LEZ144-145.