Area Forecast Discussion

WHAT HAS CHANGED

The severe weather potential late this afternoon and evening has decreased, but a few scattered thunderstorms are still expected to redevelop in the wake of the first round.

KEY MESSAGES

1.) A few scattered thunderstorms will redevelop late this afternoon and evening as a cold front crosses the region. An isolated cell or two could produce damaging winds, but additional severe weather is generally not expected.

2.) After a brief cool down Sunday, heat will build next week. The combination of air temperatures and humidity may cause heat indices to exceed 100 by Thursday and Friday.

DISCUSSION

KEY MESSAGE 1...

The Mesoscale Convective System (MCS) that produced the swath of severe winds late this morning and early this afternoon along and south of U.S. 30 has exited southeast of the region. A second line of convection that impacted southern portions of Ashtabula County and Crawford County, PA has also slid east and southeast of the area. This early day convection has thrown a big wrench in the severe weather forecast for late this afternoon and evening.

Visible satellite loops show rapid clearing behind the earlier convection, and this is allowing temperatures to recover quickly back to around 80 degrees. Recovery will continue this afternoon, with temperatures in the low to mid 80s still on the table by 20Z, especially in NW and north central Ohio. Upstream dew points of around 70 F should advect ENE into the area from Illinois and Indiana ahead of the cold front, and this rich low-level moisture combined with the heating should allow for about 1500 J/Kg of MLCAPE by late afternoon. The problem is that the earlier convection has laid down multiple outflow boundaries, so the most widespread and organized redevelopment of new convection will likely occur south and east of the CWA. There is certainly low-level convergence taking place along the cold front from southwest Ontario back to northern Indiana and central Illinois, and visible satellite loops show agitated cumulus, but feel that the new convection that moves into our area late this afternoon and evening will be widely scattered. Effective bulk shear of around 40 knots could support an isolated, organized updraft or two capable of producing damaging winds, but additional severe weather is generally not expected. The latest HREF and RFS are on board with this idea in showing widely scattered showers and thunderstorms developing and sliding E/SE across the region through the evening, so lowered POPS to be more in the chance range since the most widespread convection already occurred.

Any lingering showers will quickly exit by Midnight tonight, setting up a dry night with decreasing humidity. Patchy fog is possible where locally heavy rain occurs, but confidence in that is low.

KEY MESSAGE 2...

The first official heat wave of the season is likely next week (temperatures greater than or equal to 90 for 3 or more consecutive days). After a brief cool down Sunday as the mid/upper trough axis digs through the eastern Great Lakes and Northeast U.S. and Canadian high pressure at the surface builds across the Great Lakes, an upstream mid/upper ridge will build eastward from the Plains. This ridge will become strongest across the eastern CONUS Thursday through Saturday ahead of a mid/upper trough swinging from the northern Rockies through the northern Plains.

Expect high temperatures to warm into the mid/upper 80s Monday then low 90s Tuesday as dew points increase. This will yield heat indices well into the 90s Tuesday. An old cut off low/shortwave ejecting out of the southern Plains and into the Great Lakes region late Tuesday into Wednesday will lead to greater coverage of convection and cloud cover, so temperatures Wednesday should briefly back off into the mid/upper 80s. However, expect the hottest conditions Thursday and Friday as the ridge axis strengthens overhead and SW flow deepens. Temperatures solidly into the low 90s and dew points in the low 70s will yield heat indices potentially over 100 degrees Thursday and Friday. The NWS HeatRisk map shows widespread major impacts Wednesday through Saturday due to the cumulative effects, so heat headlines may be needed late in the week.

Widely scattered convection will continue in the hot and humid airmass Thursday and Friday, but a potential for more organized convection may occur Saturday as the upstream trough and associated cold front start to break the heat.

AVIATION /18Z Saturday THROUGH Thursday/

An initial round of showers and storms have moved through the terminals during the early afternoon hours. Some residual MVFR remains at KCAK and KYNG with some trailing stratiform rain. Meanwhile, a low cumulus field is developing in Northwest Ohio with some intermittent MVFR ceilings at KTOL and KFDY. This field is ahead of the main cold front that may bring another round of showers and storms to the region this evening into tonight. Any convection should be isolated to scattered and sub-severe and have some loose PROB30 mentions this evening for any redeveloping storms but overall confidence is low for impacts. Behind this next round of convection, conditions will trend to dry with improving ceilings. Winds will be light and generally westerly with some shift to the north for Sunday. Some fog/mist will be possible where rain occurred this afternoon, mainly KMFD, KCAK, and KYNG.

Outlook...Periods of non-VFR likely in occasional showers and thunderstorms Monday night through Wednesday.

MARINE

Strong southwest flow continues over the eastern half of Lake Erie this afternoon ahead of a cold front. Elevated waves will persist through this evening and the Small Craft Advisory and Beach Hazards Statement can continue through 8 PM. The cold front will cross the lake tonight and winds will shift to the north with light onshore flow. This light north wind will continue through Sunday. A warm front will approach the lake for Monday and shift winds to the east. This front will cross the lake for Tuesday and southerly offshore flow will be favored. Southwest flow will be favored on Wednesday and Thursday with the lake in the warm sector of a low pressure system. Winds may increase to 15 to 20 kts during afternoon hours with the best mixing. Overall, not expecting any marine headlines after tonight.

CLE WATCHES / WARNINGS / ADVISORIES

OH...Beach Hazards Statement until 8 PM EDT this evening for OHZ012- 089. PA...Beach Hazards Statement until 8 PM EDT this evening for PAZ001. MARINE...Small Craft Advisory until 8 PM EDT this evening for LEZ147>149.