textproduct: Cleveland

WHAT HAS CHANGED

A Severe Thunderstorm Watch has been issued for the entire area through 10 PM EDT. The threat of severe storms for tonight has increased to an Enhanced Risk (level 3 of 5) across Northeast Ohio and Northwest Pennsylvania. A Flood Watch has been issued until midnight for portions of Northeast Ohio and Northwest Pennsylvania that have already received heavy rain over the last 24 hours.

KEY MESSAGES

1) Scattered to numerous severe thunderstorms are expected this evening. The primary threat will be damaging winds but large and a tornado or two are also possible. Thunderstorms will also produce heavy rain and could result in flash flooding, especially for area that have received heavy rain over the last 24 hours.

2) The threat for strong to severe thunderstorms will continue on Friday, especially across southern portions of the area.

3) Cooler and drier weather is expected for the holiday weekend.

DISCUSSION

KEY MESSAGE 1... Considerable instability has developed across the region this afternoon with ML CAPE values of 2500-3000 J/kg. An MCS is taking shape over lower Michigan and is going to be the driving feature for severe thunderstorms to affect the area this evening. A Severe Thunderstorm Watch has been issued for the entire area through 10 PM and a Flood Watch has been issued for portions of Northeast Ohio and Northwest Pennsylvania through Midnight.

The MCS is moving southeast around the periphery of the upper level ridge. A bullseye of 40-50 knots of effective shear is forecast to move from Michigan across Lake Erie towards Cleveland and the northeast lakeshore. Damaging wind gusts to 70 mph will be the primary hazard this evening, although isolated stronger wind gusts are possible, especially with bowing line segments or cold pool acceleration. Large hail and a tornado or two are also possible given the strong shear and lift in the column. Latest CAMs do indicate more of a linear feature that looks fairly progressive through the evening. In this case, the potential for training storms may be somewhat lower. Portions of Northeast Ohio received up to 2 inches of rain this morning while portions of Northwest PA and especially Erie County has received 2-5 inches of rain over the last 36 hours. This recent rainfall will lead to wet antecedent conditions and flooding or flash flooding will be faster to develop.

The southward extent of storms is less certain, especially south of Route 30 in NW Ohio. If storms can extend farther south, DCAPE values are very high in the 1200-1400 J/kg range, making downbursts very concerning.

This activity will push southeast of the area by 10 PM but a boundary will remain from lower Michigan towards Central Ohio. Additional shortwave energy is expected to round the ridge overnight and showers could continue along with scattered thunderstorms. Any thunderstorms late tonight should pose a lower threat of severe weather.

KEY MESSAGE 2... The timing and coverage of storms this evening and late tonight will have an impact on severe weather potential on Friday. One shortwave could pass early Friday morning with a second through midday on Friday. Some models indicate that southern portions of the area could destabilize again between the first and second round with a few severe thunderstorms possible on Friday, especially along and south of the Route 30 corridor. The potential for stronger storms would be a little earlier in the day, from late morning through mid-afternoon.

The cold front has trended slower to clear the local area, thus prolonging the potential for showers and thunderstorms. Another round is possible across NW Ohio on Friday night and even into Saturday now. This should shift south with time on Saturday as we finally see a cap developing with increasing subidence.

KEY MESSAGE 3... High pressure over the Great Lakes will begin to build in from the north on Saturday, firmly taking hold of the area for Sunday and Monday. A drier airmass will accompany high pressure with temperatures settling back to seasonal norms in the upper 70s to near 80 degrees.

AVIATION /18Z Thursday THROUGH Tuesday/

Challenging forecast in terms of timing multiple rounds of showers and thunderstorms that are expected to move through the region between this evening and Friday afternoon. The complex of thunderstorms currently organizing in western Lower Michigan is expected to turn ESE and move across Lake Erie this evening. This complex will impact most of northern Ohio and NW PA with torrential rain, gusty winds, and frequent lightning. Tried to tweak the timing of this with TEMPO groups, and generally expect it to impact KTOL, KCLE, and KERI between 22 and 01Z. The storms should be weaker with southward extent, but confidence is increasing that they will at least clip KFDY, KMFD, KCAK, and KYNG between roughly 00 and 02Z.

There will be a lull most of the overnight, and that should allow for at least MVFR mist in some of the typical spots (KTOL, KFDY, KMFD), but some additional showers may dive into the KTOL area late. Confidence is low on that. There is better potential for another round of activity entering NW Ohio after 16Z Friday, so started to add SHRA and VCTS to KTOL, KFDY, and KCLE after 18Z. Mainly VFR is expected outside of the mist and rounds of storms.

SW winds of 5-10 knots this afternoon will turn light S tonight then W to WNW at 5-10 knots by mid Friday morning.

Outlook... Non-VFR possible in rounds of showers/storms through Friday evening.

MARINE

Mainly quiet conditions are expected on Lake Erie through Friday outside of rounds of thunderstorms. A quasi-stationary front draped west- east across the lake this afternoon and evening will push slowly south as a cold front tonight and Friday. This will keep winds on the lake light and variable through Friday afternoon before becoming more steadily N at 5-10 knots. Stronger NE winds of 10-20 knots are expected late Friday night through Sunday as Canadian high pressure builds across the Great Lakes. This will build wave heights to 2 to 3 feet in the western and central basins at times, and we may be near Small Craft Advisory criteria. Lighter, mainly E winds, are expected Sunday night through Tuesday.

CLE WATCHES/WARNINGS/ADVISORIES

OH...Heat Advisory until 8 PM EDT this evening for OHZ003-006>008- 017>019-027>031-036>038-047. Flood Watch until midnight EDT tonight for OHZ012>014-023-089. PA...Flood Watch until midnight EDT tonight for PAZ001>003. MARINE...None.