textproduct: Cleveland

WHAT HAS CHANGED

A Wind Advisory has been issued for Erie County, PA from 11 PM today to 11 AM EDT Tuesday for SE'erly to S'erly downslope surface winds up to 30 mph, gusting up to 55 mph.

KEY MESSAGES

1.) Multiple rounds of showers and thunderstorms are expected this evening through Wednesday night. Gusty winds are expected in Erie County, PA late this evening into most of Tuesday morning, especially along and within several miles of Lake Erie.

3.) Below-average air temperatures are expected Wednesday through this Saturday night with multiple opportunities for frost formation. A warming trend should begin this Sunday, May 3rd.

DISCUSSION

KEY MESSAGE 1... A ridge at the surface and aloft exits E'ward the rest of today through Tuesday and is followed by cyclonic SW'erly to W'erly flow aloft over our CWA. Multiple shortwave disturbances embedded in the cyclonic flow aloft will traverse our region. At the surface, a primary low downstream of a prominent shortwave trough axis will deepen as it wobbles NNE'ward from the Upper MS Valley to James Bay the rest of today through sunset Tuesday evening. Deepening of this low pressure center at the surface and aloft will contribute to the development of a S'erly to SSW'erly low-level jet of about 45-55 knots that will translate E'ward over our CWA this evening through mid-morning on Tuesday. In response to the low's track, a surface warm front should sweep NE'ward through our region between about 4 AM and midday Tuesday before a surface cold front begins to sweep E'ward across our CWA Tuesday afternoon and nears the OH/PA line by sunset Tuesday evening. Low-level WAA ahead of and behind the warm front will contribute to an unusually-mild night tonight. Lows should reach the 50's to lower 60's around daybreak Tuesday. Tuesday's highs should reach the mid 60's to mid 70's amidst persistent low-level WAA ahead of the warm front and within the warm sector, and peeks of sunshine.

SHOWERS AND THUNDERSTORMS:

Multiple rounds of scattered to widespread showers and thunderstorms are expected to traverse our region generally from SW to NE between about 5 PM today and mid-morning tomorrow as weak CAPE, including elevated CAPE, and moderate to strong deep layer bulk shear allow ongoing convection over/near IL/IN late this afternoon to persist amidst SW'erly mean mid-level flow. Additional showers and thunderstorms should develop over our region late this evening through tomorrow morning due to moist isentropic ascent along the upper-reaches of the warm front and enhanced moist isentropic ascent associated with the low-level jet amidst the aforementioned thermodynamics and kinematics. SPC has far-western portions of our CWA included in a marginal risk of severe thunderstorms capable of producing damaging straight-line convective wind gusts this evening through tonight. However, this risk appears to be very marginal due to the expectation of weak instability and the development of sizable DCIN via nocturnal cooling-related stabilization of the boundary layer this evening through daybreak tomorrow. Additional isolated showers and thunderstorms are possible late Tuesday morning through sunset Tuesday evening courtesy of low-level convergence and moist ascent along the cold front and pre-front surface trough axes, which should release weak instability amidst mainly moderate deep layer bulk shear.

WIND ADVISORY:

SE'erly to S'erly downslope surface winds up to 30 mph, gusting up to 55 mph, are expected in Erie County, PA late this evening through mid-morning on Tuesday for the following reasons: tightening of the synoptic MSLP gradient in response to the aforementioned deepening low; low-level winds increasing with height promoting mechanical mixing of the boundary layer up to ~1kft AGL, which should allow the mixing to tap into the lower-reaches of the aforementioned low-level jet. Note: multiple recent runs of the HRRR suggest the upcoming convection may be accompanied by a fairly-strong cold pool and wake low at/near the surface this evening into the predawn hours of Tuesday, and the resulting mesoscale MSLP gradient may be tight enough to generate advisory-criteria wind gusts for several hours across most of our CWA. Will let the evening shift reevaluate the potential need to expand the Wind Advisory. ----

During Tuesday night through Wednesday night, cyclonic SW'erly to W'erly flow aloft should persist over our region as a primary trough axis moves from the northern Great Plains and vicinity to the central Great Lakes. At the surface, the cold front should drift E'ward across the rest of our CWA by daybreak Wednesday as a new low develops NE'ward along the front from the Ark-La-Tex region to the Mid OH Valley. This low should then develop farther NE'ward along the front and reach southern QC by daybreak Thursday as a surface ridge builds very slowly from SK and vicinity. Additional periods of scattered showers and thunderstorms are expected Tuesday night through Wednesday as sufficient instability, including elevated CAPE, is released by the following: low-level convergence/moist ascent along the front; low-level frontogenesis resulting from low- level WAA and CAA induced by the frontal cyclone; moist isentropic ascent preceding shortwave trough axes in the cyclonic flow aloft. Lows should reach the mid 40's to lower 50's around daybreak Wednesday and be followed by daytime highs only in the 50's to lower 60's as net low-level CAA occurs behind the cold front. Isolated and lingering rain showers should end generally from west to east Wednesday night as the upper-reaches of the cold front depart and the aforementioned surface ridge builds generally from the northwest. Partial clearing, easing surface winds, and net low-level CAA should allow lows to reach the mid 30's to mid 40's around daybreak. The coldest lows may be accompanied by patchy frost formation in the valleys of interior NW PA.

KEY MESSAGE 2... Cyclonic W'erly to NW'erly flow aloft and embedded shortwave trough axes should impact our region on Thursday through Saturday night as the aforementioned surface ridge continues to build slowly from the northern and central Great Plains, and vicinity. This weather pattern evolution at the surface and aloft will maintain an unusually-cold air mass across northern OH and NW PA. Daytime highs should reach mainly the upper 40's to upper 50's daily on Thursday through Saturday. Overnight lows should reach mainly the lower 30's to lower 40's around daybreak Friday, Saturday, and Sunday, respectively. Will continue to monitor the potential for additional frost formation and the need for a Frost Advisory or Freeze Warning. Note: isolated rain showers may develop during the late morning through early evening hours of Friday and Saturday due to self- destructive sunshine and low- level convergence/moist ascent along subtle surface trough axes attendant to the shortwave troughs aloft. During the late morning and early evening hours, the atmospheric column may be cold enough for a few wet snowflakes to mix with the rain.

On Sunday, the surface ridge should build in earnest from the west as a shortwave ridge aloft does the same. Current odds favor dry weather courtesy of stabilizing subsidence accompanying the ridge. Clearer sky and greater daytime heating should allow late afternoon highs to reach the mid 50's to mid 60's.

AVIATION /18Z Monday THROUGH Saturday/

VFR across the board this afternoon and early evening. A weakening batch of rain (and perhaps a little bit of thunder, especially towards FDY and MFD) will spread west to east across the area late this evening and overnight. Most terminals can expect up to a few hours of rain with at least some transient MVFR with heavier rain...brief IFR is not ruled out. The odds of thunder at a given terminal are still too low for inclusion, but will monitor trends and adjust as needed if confidence increases. Rain exits east late tonight into early Tuesday morning, with a few lingering lighter showers and likely more widespread MVFR ceilings ahead of an approaching cold front that will sweep through late morning through the afternoon Tuesday.

South-southeast winds of 10-17kt with a few gusts to 25kt are expected through early evening. Winds, gusts, and wind shear potential become less clear for several hours later this evening into the overnight. There's high confidence in a 45-55kt southerly low-level jet sweeping east across all terminals between about 0-9z as surface winds remain south-southeast. It is on the fence for if low-levels will become stable enough for true low-level wind shear at times, or if it will remain a bit more unstable and gusty. TAFs carry both LLWS and some gusts across the board, either way it will be rough in the low-levels while taking off and landing. A brief period of stronger south- southeast wind gusts is possible early Tuesday morning behind the departing rain, especially at ERI where gusts over 40kt are likely for a few hours. Winds gradually veer more south- southwest while remaining a bit elevated and gusty into Tuesday.

Outlook...Non-VFR ceilings continue until a cold front sweeps through on Tuesday. Non-VFR likely again in showers and thunderstorms on Wednesday.

MARINE

South-southeast winds become strong tonight into early Tuesday behind a warm front, with 15-25kt sustained winds expected and some higher gusts to 35kt possible, especially along the eastern lakeshore. Waves will be largest in the open waters, but the strong offshore flow can pose a hazard to smaller craft even in the nearshore. A Small Craft Advisory kicks in at 8 PM this evening for all nearshore waters. Winds shift more west- southwest on Tuesday behind a cold front that will cross the lake during the late morning through mid-afternoon hours. Winds will be strongest through early Tuesday morning, but may be elevated at times until the cold front clears the lake later Tuesday afternoon. Mainly light winds are then expected for the remainder of the week, though a brief period of elevated 15-20kt north-northeast winds are possible on Wednesday as weak low pressure tracks through the Ohio Valley.

CLE WATCHES/WARNINGS/ADVISORIES

OH...None. PA...Wind Advisory from 11 PM this evening to 11 AM EDT Tuesday for PAZ001-002. MARINE...Small Craft Advisory from 8 PM this evening to 4 PM EDT Tuesday for LEZ142>149.