textproduct: Cleveland

WHAT HAS CHANGED

Late afternoon/early evening thunderstorms have developed and have produced sporadic wind damage and hail. A Severe Thunderstorm Watch is in effect for western portions of the area until 11 PM this evening. Key Message 1 has been updated to reflect the increase in severe weather potential. Patchy fog has also been added to the forecast.

KEY MESSAGES

1.) Strong to severe thunderstorms remain possible through this evening. Damaging wind gusts, hail, and heavy rain are the primary hazards.

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...

As of about 730 PM EDT, a line of showers and thunderstorms extended from Ottawa County through northern Ashland/southwestern Medina counties with isolated to scattered storms present to the south and southwest of this line. As of now, the strongest storms are on the leading/southeastern end of this line where there is more instability to work with. Storms may produce damaging wind gusts and hail over the next couple of hours, but generally expect convection to weaken with the loss of diurnal instability over the next couple of hours, especially to the northwest where storms have trained and worked the atmosphere over. The main line of storms is following a somewhat tight instability gradient so expect showers and storms to continue a southeastward progression. A Severe Thunderstorm Watch is in effect for portions of northern Ohio through 11 PM tonight, but it's likely that some (if not all) of the watch will be gradually cleared as the severe weather risk continues to dwindle. Will need to keep an eye on hydro since storms are training a bit, although the more rural landscape and dry antecedent conditions will likely prevent a significant flooding risk.

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 /00Z Sunday THROUGH Thursday/

Scattered showers and thunderstorms are present across portions of northern Ohio, but it's possible that convection misses most TAF sites before weakening with the loss of diurnal instability. Have VCSH/PROB30 groups for terminals that may see some showers/storms early in the TAF period and will make amendments if confidence in precipitation increases at any given site. Any showers/storms could produce non-VFR conditions in heavy rainfall rates and lower ceilings. Dry weather is expected by 04Z, although inland terminals may experience MVFR/IFR conditions in low stratus/fog early Sunday morning.

Winds will become light and variable tonight before becoming north/northeast at 5 to 10 knots during the day Sunday.

Outlook...Periods of non-VFR likely in occasional showers and thunderstorms early Tuesday through Thursday.

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