textproduct: Cleveland

WHAT HAS CHANGED

Added a low chance for showers/thunder in parts of Northwest OH late this afternoon and evening. The overall forecast for the active period Saturday into Sunday remains similar, though did expand shower chances outside of the "snowbelt" on Sunday.

KEY MESSAGES

1) Mainly dry weather is expected through early Saturday. A few showers or storms are possible across parts of Northwest and North Central Ohio late this afternoon into tonight.

2) Scattered to numerous showers and thunderstorms are expected to move across the area Saturday afternoon and evening. There is a Marginal Risk (level 1 of 5) for a few severe thunderstorms, with damaging winds and hail the main risks. Locally heavy rainfall is also possible.

3) Below average temperatures arrive for Sunday and Monday, with periodic lake-enhanced rain showers east-southeast of Lake Erie. A few isolated showers will remain possible across the rest of the area on Sunday.

DISCUSSION

KEY MESSAGE 1... Surface high pressure begins exiting to the east-northeast through the day today. A plume of higher theta-e air is expected to build across western and central OH by this afternoon and evening, allowing modest but uncapped instability to develop through the afternoon as heating occurs. A shortwave is diving out of the Upper Midwest early this morning and will swing across the area this afternoon and evening with an accompanying surface trough. Some hi-res models are depicting isolated to widely scattered convection in response. Overall, there's enough there to add a 20- 30% type chance for showers/thunder across parts of Northwest and North Central OH after 5 PM, with some activity potentially lingering through the evening and well into the night amid weak warm air advection. Modest forcing/ instability along with weak shear precludes a severe threat. The rest of the area is favored to remain dry through early Saturday. Highs will reach the upper 70s and lower 80s today, with lows tonight ranging from the mid 50s to lower 60s.

KEY MESSAGE 2... Active weather is expected Saturday afternoon and evening as a seasonably deep trough digs into the Great Lakes, allowing low pressure to gradually deepen as it tracks from Michigan into southern Ontario and drags a strong cold front through the area.

There's decent agreement that a pre-frontal trough will push east across the area Saturday afternoon, with the strong cold front itself pushing into Northwest OH late in the afternoon and pushing southeast across and then out of the area through the evening. Some large scale ascent begins spreading in ahead of the digging trough by midday/early afternoon, with the greatest support during the late afternoon and early evening as a vort max rounds the base of the digging trough and rotates into northern Ohio. It is likely that showers and storms will begin developing around midday or early afternoon along both the cold front and pre-frontal trough, along with perhaps along a lake breeze near the lakeshore from Cleveland points northeast. Activity should peak in coverage and intensity during the late afternoon and early evening hours before exiting to the southeast with the front and transitioning to lake-enhanced showers Saturday night. Overall, much of the area should see a shower or storm Saturday afternoon or evening with two rounds possible across parts of the area in quick succession.

While mid-level lapse rates will remain weak at 6.0C/km or less, some heating of a fairly moist low-level airmass (PWATs increasing to ~1.5" ahead of the cold front) should yield moderate instability (1000-2000 J/KG of MLCAPE) Saturday afternoon. Along with 20-30 knots of effective deep-layer shear and increasing forcing, this is an environment that is on the lower end of what can support organized convection with a severe weather threat. Activity along the pre-frontal trough becoming more widespread earlier in the afternoon could sap some of the thermodynamics from the atmosphere ahead of the cold front and greater forcing that arrive during the late afternoon and early evening. Given the lower-end environment and potential for pre- frontal convection to muddy the picture, the current SPC Day 2 outlook maintains a Marginal Risk (level 1 of 5) for severe weather across the entire area on Saturday. The primary threats would be marginally severe wind gusts or hail with a few stronger storms. A bit more heating and/or widespread convection holding off until later in the afternoon when the cold front and greater forcing arrive would be items that could increase the severe threat a bit from the current outlook.

Storm motion will be from the west-southeast Saturday afternoon and evening, fairly parallel to the advancing cold front. The thermodynamics don't look overwhelmingly conducive for efficient rain rates, but given the potential for some spots to see two rounds of storms and/or a bit of training we'll need to monitor for locally heavier rain Saturday afternoon/evening. Area- average QPF of generally 0.25-0.75" is expected with this system, but locally up to 2-3" amounts are feasible if there's any training or repeated rounds given the environment.

Highs on Saturday will generally be in the upper 70s or lower 80s, though it will briefly feel more muggy as dew points climb into the mid-upper 60s for a few hours ahead of the cold front.

KEY MESSAGE 3... As the calendar creeps towards September and a 2-3 standard deviation 500mb trough digs over the Great Lakes, the airmass behind Saturday evening's cold front will feel like an early taste of fall. In fact, over Lake Erie water temperatures that average slightly warmer than 25C at the moment, 850mb temps tumbling to 7-10C and with 500mb temperatures of -17 to -20C Sunday into Monday will support lake-enhanced rain showers as moist cyclonic flow aligns out of the west-northwest behind departing low pressure. A bit of thunder will remain possible with more robust activity. The coverage/intensity of any lake- enhanced showers will be maximized with any trough passages and lull between troughs. There is some agreement in a trough passage in the vicinity of Sunday morning. Confidence lowers beyond that, though there are hints that another trough or two may cross between Sunday evening and early Monday. Lake-enhanced showers should gradually decrease and begin shifting east- northeast up the lake shore late Sunday night and Monday as low pressure gradually exits and as ridging builds in, though there remains some disagreement over how quickly that happens.

As is traditionally the case with west-northwest flow, lake- enhanced rain will be most frequent and intense from the Cleveland metro area points east-northeast across the higher terrain of the "snowbelt" of Northeast OH and Northwest PA. Some activity off the lake will be possible as far west as Sandusky at times, especially through Sunday when moisture is deepest. Outside of the lake-enhanced showers it will be mainly dry, though the colder air aloft and any trough passages may encourage a few hit/miss showers across the entire area, mainly through Sunday evening. Building ridging should allow areas outside of lake-enhanced showers to dry out Sunday night and Monday.

Highs will range from the upper 60s to mid 70s Sunday and Monday, coolest across Northeast OH and Northwest PA. Overnight lows will dip into the 50s for much of the area, with some 40s Monday night if we see sufficiently clear/calm conditions.

High pressure should bring at least a couple days of quieter weather once it completely builds in early next week.

AVIATION /06Z Friday THROUGH Tuesday/

Mainly VFR conditions and fair weather skies are expected for this TAF update. There may be some patchy light MVFR fog at FDY and MFD this morning between 09z and 12z. Otherwise, there are no other impacts expected for aviation weather through the next 24 hours. Winds will be light from the east 5 to 9 knots becoming southeast towards the end of the TAF period or by this evening.

Outlook...Non-VFR expected in showers and thunderstorms on Saturday. Non-VFR conditions may continue Saturday night into Sunday in lake enhanced showers and storms across Northeast Ohio and Northwest Pennsylvania.

MARINE

Marine weather conditions will nice today on Lake Erie with a light northeast to easterly winds 5 to 10 knots and waves of 1 to 2 feet. A low pressure system and cold front will approach the eastern Great Lakes on Saturday. Winds will become southerly to southwesterly 10 to 15 knots Saturday and waves 1 to 3 feet. Behind the cold frontal passage, northwest winds will increase 15 to 20 knots late Saturday night into Sunday and waves will increase 2 to 4 feet. A Small Craft Advisory may be needed for Saturday night through Sunday. There may be some rip current potential as well for the later half of the weekend and some beach hazard statements may also be needed. There will also be the potential for some waterspouts on Sunday with colder air aloft moving over the warmer lake water. High pressure will build in on Monday and Tuesday. Winds on Monday will be 5 to 15 knots from the west with waves 1 to 3 feet. Calmer wind and waves are expected by Tuesday underneath the high pressure system.

CLE WATCHES/WARNINGS/ADVISORIES

OH...None. PA...None. MARINE...None.