textproduct: Cleveland

WHAT HAS CHANGED

A Heat Advisory has been issued from a Cleveland-Akron-Wooster- Mt Vernon line points west from Tuesday afternoon through Wednesday.

KEY MESSAGES

1) It will be humid with a couple of rain chances through midday Tuesday, but with limited overall impacts/hazards.

2) Hot and humid conditions are expected Tuesday afternoon through Thursday, with peak heat index values ranging from the mid 90s to lower 100s and limited overnight relief.

3) An unsettled pattern with multiple risks for thunderstorms is expected late Tuesday through Friday. There is considerable uncertainty regarding the timing and placement of thunderstorms, but severe weather and locally heavy rainfall are possible.

DISCUSSION

KEY MESSAGE 1... A very warm and humid Monday afternoon across the area with temperatures ranging from the upper 70s in PA to the upper 80s in Marion and dew points in the upper 60s and lower 70s. Low impact weather is expected through Tuesday morning, though do note it will be a muggy night with lows mainly staying up in the lower to mid 70s with dew points only slightly cooler than that. A weak shortwave glancing the region may continue to cause a few light showers (and perhaps a stray storm) across the area through early this evening before exiting east-southeast. Another shortwave will glance the region late tonight/early Tuesday, which will combine with ongoing warm air/moisture advection to spark some showers and possibly an isolated storm late tonight into early Tuesday. Any showers will exit to the southeast by midday Tuesday.

KEY MESSAGE 2... Meteorological fall technically starts on Tuesday, but it will not feel like it with a Heat Advisory in effect for a good chunk of the forecast area. Upper ridging will reach peak amplitude across the central and eastern U.S. Tuesday and Wednesday, before shifting southwest as troughing builds over the Northeast Thursday and Friday. A very warm and humid airmass (PWATs climbing to nearly 2.00" and 850mb temperatures topping out at 20-22C) will support what is hopefully the season's last round of excessive heat across the local area through Thursday.

High temperatures will range from the mid 80s to lower 90s on Tuesday with dew points in the low to mid 70s. Wednesday appears to be the hottest day, with highs ranging from the upper 80s to mid 90s with dew points in the upper 60s and lower 70s. Thursday will still be quite warm but trend a bit cooler farther north, with highs forecast to range from the mid 80s to lower 90s with dew points mainly in the lower 70s. There is some potential for lingering cloud cover, afternoon convection, and a lake breeze to keep far Northeast OH and Northwest PA slightly cooler on Tuesday. Convection potential does add some uncertainty for Wednesday and Thursday. Current consensus is that any lingering convection will clear early Wednesday, with any renewed activity largely holding off until after peak heating. Thursday appears to have the greatest potential for convection to keep temperatures cooler than forecast.

Arguments for the heat being hazardous/impactful include warm/ humid nights providing for limited relief, the multi-day duration, and some school buildings not having air conditioning across the area. So while forecast peak heat index values are on the lower end for a Heat Advisory and there is some uncertainty, opted for a Heat Advisory from the Cleveland- Akron area points west for Tuesday and Wednesday where confidence is overall the highest in peak heat index values nearing or reaching 100 degrees both days. We may need to expand the advisory east to include more of our eastern Ohio counties for Wednesday, but these areas look a bit cooler on Tuesday than areas farther west so left them out for now. Parts of the advisory may need to continue through Thursday, though uncertainty regarding the timing of the cold frontal passage and convective potential are too high to do that yet.

KEY MESSAGE 3... The local area will be located on the edge of a heat ridge through much of the week as a front waivers to our north through Wednesday and pushes south Thursday and Friday. This will place us in a potentially active corridor of weather for most of the week, though overall confidence in the timing and location of greater thunderstorm potential remains low. With that said, an elevated mixed layer (EML) plume will lead to steeper mid-level lapse rates atop very warm and humid low-levels, fueling moderate to very strong instability across the area from Tuesday afternoon until the cold front tries crossing Thursday into Friday. West-northwest flow aloft will also be moderately strong, providing sufficient shear for organized and potentially severe convection. Precipitable water values climbing to 1.70-2.00" in this very warm environment will also support torrential rain rates within convection and potential for heavy rain/flash flooding with any training or repeated rounds of convection through the week.

Starting with Tuesday and Tuesday night, it's possible much of the afternoon and evening hours are dry as there is a distinct lack of large-scale forcing during that time. However, there's good agreement in very strong and only weakly capped instability developing Tuesday afternoon/evening. There may be some triggers for afternoon/evening convection, mainly in the form of a lake breeze near the northeastern lakeshore and potentially a differential heating boundary left behind by morning clouds/ showers. These boundaries may support a few storms developing during the afternoon or evening, mainly across northeastern portions of our area. Greater potential for storms may arrive overnight Tuesday night into very early Wednesday morning as a shortwave glances the region, potentially sparking thunderstorms upstream that track into the local area. The greatest overall chances for storms late Tuesday and Tuesday night will be across northern portions of the area (including Lake Erie, Northeast OH, and Northwest PA) with chances diminishing to the southwest.

It currently appears that any lingering activity will exit early Wednesday, leaving a period of drier weather through the day. A shortwave will approach and move through late Wednesday and Wednesday night as the surface cold front approaches from the north. The current forecast favors potential for isolated to scattered storms to try developing late Wednesday afternoon or evening, especially along the lake breeze or any boundaries left by earlier convection, with greater potential sagging in from the north/northwest later Wednesday night. Will need to closely monitor this progression as hi-res models that run out through Wednesday (such as the 12z RRFS) do offer some potential for organized convection to arrive as early as Wednesday afternoon.

The same general pattern persists on Thursday and possibly even for Friday, though details become quite murky by then and it's possible the front clears at least parts of our area. The general theme is that unsettled weather remains in the forecast for Thursday and Friday with lingering potential for organized and potentially severe convection along and ahead of the front. The greatest concern will gradually shift towards our southwestern counties Thursday and Friday. The hope is that high pressure to the northeast presses in enough to push the front out of the area this weekend. Confidence in that scenario is not high so some lower rain chances remain in the forecast for Saturday and Sunday, especially farther south and west.

AVIATION /18Z Monday THROUGH Saturday/

Isolated rain showers with VFR conditions are possible over the next couple but should dissipate as they move southeast. Light rain showers could linger in Northwest Pennsylvania tonight but otherwise VFR is expected. Isolated to scattered showers could develop Tuesday morning approximately 11-15Z with some better chance at non-VFR occurring, though this is very low confidence at this point.

Outlook...Several rounds of thunderstorms are possible across Northeast Ohio and Northwest Pennsylvania Tuesday through Wednesday night, with a better chance at showers and storms elsewhere in the area Thursday and Thursday night.

MARINE

Broad southwest flow is expected as the warm front pushes northeast of Lake Erie, and will continue through at least Wednesday night before a cold front moves south across the lake on Thursday. There are a couple periods that winds could briefly reach 20 knots though small craft advisories are not expected at this time. Through the week, there will be multiple chances for thunderstorms, though timing if very uncertain at this point. Any thunderstorms that do occur could become strong to severe with a good chance of producing winds > 34 knots and hail > 0.75".

CLE WATCHES/WARNINGS/ADVISORIES

OH...Heat Advisory from 2 PM Tuesday to 8 PM EDT Wednesday for OHZ003-006>011-017>021-027>031-036-037-047. PA...None. MARINE...None.