textproduct: Cleveland

WHAT HAS CHANGED

Confidence in severe weather east of I-71 has increased for this afternoon, with an SPC slight risk expected. The probability for areawide rainfall and QPF > 1" has increased Friday evening into Friday night. Confidence is increasing in a significant and long duration heat wave next week, with heat indices likely near or exceeding 100 degrees for multiple days.

KEY MESSAGES

1) There is a chance for a few strong to severe storms east of I-71 between 3 and 7 PM today.

2) Areawide rain expected Friday afternoon through Friday night. Heavy rain is possible south of US-30.

2) Significant heat and humidity builds next week, with heat indices likely exceeding 100 degrees, especially in Northwest Ohio.

DISCUSSION

KEY MESSAGE 1... An upper-level trough is moving eastward into the Great Lakes region (noted on water vapor satellite imagery), with its attendant surface low into west-central lower Michigan.

Morning convection still lingers near Youngstown area (as of ~18Z) but should exit shortly. This morning's convection left behind a slightly worked over environment, but broad southwest flow should yield quick recovery of the atmosphere. Latest mesoanalysis reveals pooling of low-level moisture and surface convergence along and in the vicinity of the I-71 corridor, which is confirmed by a building cumulus field on satellite, especially the area south of Mansfield. This is likely where we see convective initiation over the next hour or two (by 4 PM). Convection will initially begin as a broken line and shear vector angled around 45 degree to the forcing mechanism (pre- frontal trough) may actually favor keeping things clustered/multicellular initially instead of growing upscale quickly. We are also seeing additional convection developing farther west near the I-75 corridor and that may also continue to develop further.

The combination of strong deep-layer shear and modest instability expected will favor strong to severe thunderstorms with this cluster of storms. Primary weather hazard will be strong to damaging winds within the strongest storms, but large hail and a few tornado are also possible, especially if storm mode can remain a bit more discrete.

KEY MESSAGE 2... The cold front swings through tonight, stalling just south of the forecast area tonight. Low pressure that develops over the southern Great Plains and mid-Mississippi Valley moves east- northeast along this boundary and across Ohio Friday night into Saturday morning. Overall trends in synoptic features has trended just a bit farther north, with this forecast package increasing the PoP and QPF forecast, with a slightly greater risk of heavy rain and localized flooding for areas south of US-30. We'll have to monitor trends in the system because a further northward trend could yield greater impacts.

KEY MESSAGE 3... An upper-level ridge builds into the eastern CONUS next week as ensembles key in on location and strength of this feature. The 594 dam 500mb heights will be centered over the Ohio Valley, but 500mb heights will actually be most anomalous over lower Great Lakes. This will result in significant build up of heat and humidity through all of next week (at least Monday-Friday). There is high confidence in most of the area reaching multiple days of temperatures > 90 and heat indices > 100, with >50% chance of temperatures > 95 and heat indices > 105 especially along and west of I-71 (particularly the Toledo-Findlay area).

Sometimes confidence is a bit lower due to thunderstorm chances but with the positioning of the upper-level ridge, it's becoming less and less likely that storms develop at least through Wednesday.

One thing to point out is that the impacts of heat tend to increase with duration. Heat impacts will likely be at their great Wednesday onward as we see consecutive days of extreme heat and very little relief overnight (with lows in the low to mid 70s).

AVIATION /18Z Thursday THROUGH Tuesday/

Mainly VFR across the TAF sites this afternoon, with deterioration to MVFR and IFR possible in showers and thunderstorms later this afternoon and evening ahead of a cold front. Already seeing some convection developing just west of the region across Indiana, though could also see another area develop near the I-71 corridor in the next couple of hours. The highest confidence for direct shower and thunderstorm impacts is at MFD/CAK/YNG where tempo groups currently reside. Some thunderstorms could be strong to severe with wind gusts in the 40 to 45-knot range in addition to quarter-size hail.

Elsewhere, confidence in direct tsra impacts are lower, so went with a brief window of vcts at this time. Following the shower and thunderstorm threat later this evening and overnight, some patchy fog may develop, particularly east of the I-71 corridor where rain is likely to be most widespread, though confidence remains on the lower end.

Winds are generally favoring a west to southwest direction this afternoon, 8 to 12 knots. Winds will become mainly light and less than 5 knots overnight and into Friday. A lake breeze is expected to develop at CLE/ERI late Friday morning with north to northwest winds of around 8 knots.

Outlook...Non-VFR becoming more likely in showers and thunderstorms Friday night into Saturday.

MARINE

Main concern into this evening will be the threat for some stronger wind gusts associated with thunderstorms. Otherwise, generally quiet marine conditions are expected through the weekend and into early next week, though we will need to monitor wind trends on Saturday as a low pressure system slides east through the Ohio Valley. At this point, not anticipating northeast winds to exceed 15 knots. Following Saturday, mainly light east to southeast flow around 10 knots is expected through Monday.

CLE WATCHES/WARNINGS/ADVISORIES

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