textproduct: Cleveland

KEY MESSAGES

1) A line of severe thunderstorms will move across the area this evening, with most of the storms in the 4 to 9 PM window. A few scattered storms are possible this afternoon ahead of the line. Main hazard is damaging winds and heavy rainfall, but isolated tornadoes and hail up to quarter size are possible.

2) Additional showers and thunderstorms are likely Monday night and Tuesday. Storms may be strong to severe, primarily on Tuesday.

3) Cooler and less humid Sunday and Monday, brief return to heat and humidity Tuesday, then more significant cooling the rest of the week.

DISCUSSION

KEY MESSAGE 1... A very active summer evening is on tap as a strong cold front crosses the region and interacts with a hot, moist, and unstable airmass to bring widespread strong to severe thunderstorms. Early afternoon satellite and water vapor loops show a significant mid/upper shortwave trough digging into the southern Great Lakes with an associated 1000 mb surface low NE of Georgian Bay. This shortwave will swing through the eastern Great Lakes this evening, with the left exit of a 90+ knot H3 jet streak and somewhat negatively tilting trough deepening the low to 990 mb by tonight as it lifts toward the Canadian Maritimes. The trailing cold front looks to progress southeastward across Lake Erie, northern Ohio, and Northwest PA between 21 and 03Z this evening. Forecast soundings have shown little to no capping in the warm sector today, and convective temperatures have already been reached with air temps in the upper 80s to around 90 and dew points in the low to mid 70s. Heating of this very moist low-level airmass is resulting in MLCAPE values pushing 3000 J/Kg and surface based CAPE as high as 5000 J/Kg. This has already initiated convection in NW PA and along and south of the U.S. 30 corridor where a weak surface boundary has locally enhanced convergence. This convection is primarily a locally heavy rain risk, but an occasional downburst is possible given steep low-level lapse rates of 7.5 to 8 C/Km.

The main show will come immediately along and ahead of the cold front where strong forcing for ascent will trigger a QLCS in southern Lower Michigan and Ontario Province. This line will propagate southeastward across Lake Erie and much of northern Ohio and NW PA this evening, with the greatest risk for severe weather in the 20 to 01Z (4 to 9 PM window). Mid-level flow will strengthen as the front approaches, with deep layer (0-6 Km) bulk shear increasing to around 35 knots. This combined with the impressive aforementioned thermodynamics will be more than sufficient for organized, sustained updrafts. The orientation of the deep layer shear vector is somewhat parallel to the expected orientation of the line overall. This may cause parts of the line to sag across the area and backbuild a bit, leading to a sneaky heavy rain risk since PWATs will be nearing 2 inches, but the overall threat remains damaging winds. Any parts of the line that can orient more N to S will be more normal to the deep layer and 0-3 Km shear vectors, and this will cause those portions of the line to surge out and bow. Where these surges occur will have the most widespread damaging winds, with pockets of 70+ mph possible. Mid-level dry air (DCAPE around 1200 J/Kg) will further air in downdraft strength and associated wind risk. The surges/bows combined with low-level (0-1 Km) shear marginally favorable at 15-20 knots could support a couple of brief QLCS tornadoes. Finally, any embedded areas of rotation will help to sustain taller updrafts for pockets of hail, but high freezing levels should keep the largest stones around quarter size.

The convection will quickly exit the area by Midnight tonight, with dry conditions the rest of the night through Monday as Canadian high pressure builds across the Great Lakes.

KEY MESSAGE 2... After a quick shot of Canadian high pressure Monday, another strong mid/upper shortwave will dive from the Upper Midwest Monday night through the southern and eastern Great Lakes Tuesday as a longwave trough and associated closed low deepen across the Great Lakes and Northeast CONUS. This continues to look like another dynamic system for mid summer with the potential for severe weather Tuesday ahead of the strong cold front as a deepening surface low lifts up toward Hudson Bay. However, the timing, location, and evolution of the Tuesday storms remain uncertain because a low-level jet Monday night will probably initiate convection (possibly an MCS) upstream along a retreating warm front. This activity could linger Tuesday morning and disrupt the heating, as well as put down outflow boundaries that could cause new convection to initiate southeast of our area. Maintained high POPS for showers and thunderstorms Monday night and Tuesday afternoon, but details will need to be worked out. Rapid drying is expected Tuesday night in most areas, although showers could linger in NE Ohio and NW PA into Wednesday due to the deepening mid/upper trough and associated cool air aloft/cyclonic flow across the warm lakes.

KEY MESSAGE 3... Mid/upper troughing across the Great Lakes and Northeast CONUS Sunday and Monday combined with Canadian high pressure at the surface will bring cooler, less humid air, with highs in the mid 70s to around 80 Sunday and low to mid 80s Monday. This will set up a refreshingly cool night Sunday night, with lows in the mid 50s to around 60. A brief surge of heat and humidity will return ahead of the significant shortwave Tuesday, as a warm front lifting across the area Monday night and Tuesday morning brings 70+ F dew points back into the area. However, the cooling behind the cold front Tuesday night looks even more significant as the deep trough/upper low takes up residence over the Great Lakes. This will drop highs into mainly the 70s Wednesday through the end of the week, with lows in the 50s.

AVIATION /00Z Sunday THROUGH Thursday/

A cold front was located over Lake Erie, northeast to southwest. Northwest winds were present across southeast Michigan and Ontario. Most of the convection was south of the taf sites. However, there was a line showers and embedded thunderstorms located from KCLE to Kelleys Island and movement was not perpendicular to the line but southeast. As a result, will carry a tempo group for TS at KCLE and VCTS at KMFD. Have removed TS from KTOL and KFDY this evening. The cold front will move southeast with northwest winds behind the front. This will create a short period of low level windshear at KCAK and KYNG 00Z through 02z. Cold front will push through all taf sites by 03Z with shifting to the north behind the cold front around 10 knots. VFR conditions are expected for all taf sites after 04z through Sunday 00Z.

Outlook...Non-VFR possible with haze/smoke on Sunday and Monday. Non- VFR becoming more likely in showers and thunderstorms Monday night through Tuesday. Some thunderstorms Tuesday afternoon and evening may contain strong wind gusts. Residual non-VFR possible on Wednesday on rain showers across the eastern half of the area.

MARINE

Rough marine conditions will continue across Lake Erie this afternoon as southwest winds of 15 to 25 knots develop ahead of a cold front. Winds will shift towards the north behind the front later this evening and overnight, 15 to 20 knots, before diminishing to less than 10 knots by Sunday afternoon. No changes in this this package with the Small Craft and Beach Hazards for the central basin, and maintain zones west towards the Islands, mainly for cold air advection later this evening and overnight.

On Tuesday, rough marine conditions will arrive with southwest winds of 15 to 25 knots ahead of a cold front. Headlines are likely Tuesday through Wednesday as winds shift towards the northwest behind the cold front, around 20 knots.

Strong thunderstorm wind gusts are expected across Lake Erie this afternoon and evening ahead of a cold front.

CLE WATCHES/WARNINGS/ADVISORIES

OH...Beach Hazards Statement through Sunday morning for OHZ009-010. Beach Hazards Statement through Sunday morning for OHZ011-012- 089. PA...Beach Hazards Statement until 10 PM EDT this evening for PAZ001. MARINE...Small Craft Advisory until 8 AM EDT Sunday for LEZ144-145. Small Craft Advisory until 8 AM EDT Sunday for LEZ146>148. Small Craft Advisory until 10 PM EDT this evening for LEZ149.