textproduct: Cleveland

WHAT HAS CHANGED

The potential for thick wildfire smoke continues to increase tonight and Thursday, and there is growing potential for it to linger through at least Friday. Chances for showers and thunderstorms continue to increase late Friday and Saturday, but Sunday has trended dry.

KEY MESSAGES

1) Hot conditions will continue through Saturday, but the humidity will temporarily drop for Thursday and Friday leading to lower heat indices in the upper 80s to low 90s.

2) Wildfire smoke to affect the region tonight and Thursday leading to poor air quality, which could linger through Friday.

3) Periodic showers and thunderstorms are expected Friday through mid next week. The greatest potential for organized storms is late Friday and Saturday.

DISCUSSION

KEY MESSAGE 1... The center of the anomalous 600 DAM H5 ridge has shifted to a position from the corn belt through the Ohio Valley this afternoon, with satellite and water vapor loops showing a band of moisture associated with convection dropping southeastward through the northern and central Great Lakes on the northern edge of this ridge. This band of clouds and scattered showers/thunderstorms will continue to sag toward the area this evening and tonight as a weak cold frontal boundary sags across Lake Erie and NW PA and eventually through northern Ohio by Thursday morning. Strong mid-level capping is in place beneath the ridge this afternoon characterized by 700 mb temps of 12 to 14 C and a defined EML, so despite strong instability (MUCAPE over 4000 J/Kg on the latest Mesoanalysis), not sure that the weak approaching front can sufficiently breach the cap to get any convection into our area. The 12Z runs of the HREF and RRFS backed off on the thought of isolated convection early tonight, but given the instability, kept slight chance POPS in the 00 through 06Z timeframe for an isolated cell or two dropping across the lake.

Otherwise, the main impact of the weak cold frontal passage tonight will be a 5 to 10 degree drop in dew points. Air temperatures will remain hot Thursday and Friday (mid 80s to low 90s), but the brief influence of surface high pressure building into the northern and eastern Great Lakes will advect drier low-level air into the area, keeping dew points in the upper 50s to mid 60s. This will limit heat indices to the upper 80s/low 90s Thursday and Friday.

A strong mid/upper shortwave progressing from the northern Plains into the Great Lakes late Friday and Saturday will lift the frontal boundary back northward as a warm front, and this will bring the sticky air (dew points over 70 F) back into the region for Saturday to go along with one more hot day. More on that system in key message 3 below.

KEY MESSAGE 2... The most unique element of this forecast is growing concern for thick wildfire smoke tonight and Thursday, possibly lingering through Friday. Wildfires continue to burn in northern Minnesota and central Ontario Province, and visible satellite loops today have been showing the smoke plume funneling east/southeast across the northern and central Great Lakes and New England in the NW flow on the northern edge of the mid/upper ridge. The frontal boundary is helping to converge and bring this plume to the surface, and surface observations and webcams in northern Lower Michigan have shown very poor visibilities today. As the frontal boundary sags into the area tonight and Thursday, the smoke plume is expected to sag in as well. The 12Z HRRR and RRFS were more aggressive with smoke density and visibilities late tonight through Thursday night, so smoke coverage has been increased in the forecast during that time. This may support visibilities as low as 1 to 3 miles at times, as well as very poor air quality. People are encouraged to limit time outdoors Thursday. At least patchy smoke could linger Friday given a continuation of NW flow aloft, but confidence is lower beyond the time range of the HRRR and RRFS, so kept it out of the forecast Friday for now.

KEY MESSAGE 3... As mentioned above, a strong mid/upper shortwave trough will progress from the northern Plains through the Great Lakes late Friday and Saturday. This system will finally shunt the large mid/upper ridge southwest into the southern Plains and Rockies, with a strong cold frontal passage Saturday evening or Saturday night. The old frontal boundary will lift back north as a warm front Friday night and early Saturday in response to the approaching shortwave and associated surface low. As this front lifts back north, a 30+ knot low-level jet and associated strong theta e advection could trigger an MCS across the central Great Lakes Friday night. Depending on the evolution and track of this complex, some showers and thunderstorms could spill into the region Friday night and early Saturday. The more likely timeframe for organized convection will be along and ahead of the cold front Saturday evening. Moderate to strong instability is expected in the warm sector, and given what looks like a dynamic shortwave trough for mid summer (moderate to strong mid level flow), severe weather and heavy rainfall is possible. The amount of instability will be influenced by how much debris cloudiness and showers get into the area Saturday morning from the prior MCS. Given the set up, would anticipate our CWA to be included in a future severe weather outlook from the SPC for Saturday.

Canadian high pressure will bring cooler, drier, and less humid conditions Sunday and Monday, but chances for showers and storms will return late Monday and Tuesday as another cold front drops through the area. Mid/upper troughing deepening across the eastern CONUS through the middle of next week will allow progressively cooler air to build in, and temperatures will be below normal for a change.

AVIATION /18Z Wednesday THROUGH Monday/

Widespread VFR conditions persist this afternoon as high pressure continues to influence the weather in the area. As the evening progress, hazy conditions will become more widespread as smoke from Canadian wildfires begins to sink south across the area. As an inversion develops tonight, between 03-06Z on Thursday, some of the smoke will become trapped near the surface, likely reducing visibilities to at least 5-6SM, but could be lower at the northern terminals. Conditions will not improve much on Thursday with the smoke stream situated right over the area. Some hi-res models do suggest IFR visibilities possible by Thursday afternoon due to the density of smoke, but with low confidence opted to cap at MVFR visibilities and not lower. Will have to monitor upstream observations in the coming hours.

west-northwest winds of 5-10 knots this afternoon, periodically gusting up to 20 knots near the lakeshore, will weaken near sunset and becoming light overnight with overall flow shifting to be from the north. These northerly winds will increase to 5-10 knots by mid to late Thursday morning.

Outlook...Non-VFR visibility possible tonight through Thursday night due to wildfire smoke. Non-VFR likely Friday night through Saturday night in showers and thunderstorms.

MARINE

Southwest winds across Lake Erie of 5-10 knots this afternoon will diminish to 5 knots or less this evening in to the overnight hours as a weak cold front sags south across the lake. Behind this boundary, winds will become northerly at 5 to 10 knots into Thursday night, resulting in waves across the nearshore to build to 2 feet or less. A warm front will lift north late Friday into early Saturday, allowing for south- southwest winds of 10-15 knots to develop. A cold front will quickly follow late Saturday into Sunday with winds sustained at 10-15 knots but shifting to become more northerly. During this period, waves across the central basin will build to 2-4 feet, possibly needing a Small Craft Advisory for part of Sunday. An active weather pattern continues into next week, resulting in numerous wind shifts and periods of waves between 2 and 4 feet.

CLE WATCHES/WARNINGS/ADVISORIES

OH...Heat Advisory until 8 PM EDT this evening for OHZ003-006>011- 017>023-027>033-036>038-047. PA...None. MARINE...None.