textproduct: Cleveland

WHAT HAS CHANGED

A Heat Advisory has been issued for parts of Northwest Ohio for Wednesday. Hot and humid conditions continue on Thursday, and additional advisories may be needed for part of the area.

KEY MESSAGES

1) Occasional chances for showers and thunderstorms continue ahead of a cold front that crosses on Friday. Risks for locally heavy rain and severe weather exist, but overall confidence in organized severe weather or heavy rain is currently low.

2) Hot and humid conditions continue ahead of a cold front that crosses on Friday, with limited overnight relief. Heat index values will peak in the 90s to around 100 across much of the area Wednesday and Thursday, with slightly cooler values closer to the lakeshore in far Northeast OH and Northwest PA.

3) Generally low impact weather is expected this weekend into early next week, with a few low rain chances in the forecast.

DISCUSSION

KEY MESSAGE 1...

A typical setup for this time of year with occasional chances for convection until a cold front crosses on Friday, but with plenty of dry windows and rather low confidence in when/where the most organized rain/storm chances play out.

For this evening and tonight, weak low pressure currently over northern lower Michigan will continue to drift east into Ontario. The warm front has cleared the area, though another surface trough currently extends across western Ohio and will work east across the area through early Wednesday. Aloft, a very weak shortwave trough currently moving east out of the upper Mississippi Valley will move across the region overnight tonight into early Wednesday. Will monitor the surface trough moving east across the area along with the modest upper support that will move through later tonight for increased shower and thunder potential. There may also be a few isolated pop-up showers and storms elsewhere this evening given uncapped instability. Certainly not looking at a steady/widespread rain this evening or tonight, but given the humid airmass, instability, and various weak sources for lift suspect a good number of areas will get a shower/storm at some point. This activity may linger into the first part of Wednesday across far Northeast OH and Northwest PA before continuing to exit east.

The main concern tonight with any convection will be locally heavy rain, given near record high precipitable water values for early June, weak flow, and skinny instability profiles. However, the disorganized nature of any convection should be a limiting factor for heavy rain/flash flooding potential. Strong low-level instability and turning along the surface trough axis has led to some rotating storms in eastern Michigan this afternoon...shear and forcing are a bit weaker with southward extent into Ohio, meaning the severe weather threat should be rather minimal.

Wednesday should be a largely dry dry with minimal forcing as a narrow ridge axis builds in. Lingering northwest flow aloft across Northeast OH and Northwest PA and potential for an outflow boundary to linger in that vicinity does offer means for isolated to widely scattered storms to fire Wednesday afternoon/evening given moderate to strong instability. However, with the weak forcing activity should be limited and POPs are generally in the 20-40% range, briefly a bit higher in parts of Northeast OH and Northwest PA in the evening. Strong and deep instability profiles coupled with marginal deep-layer shear can support a severe risk in the form of damaging winds and perhaps hail if storms do develop across parts of the area, though again this is of lower confidence.

A number of models suggest potential for an organized MCS to develop upstream of our area Wednesday evening and turn southeast into the deeper instability and towards our area overnight Wednesday night. A modest west-southwest low-level jet could help maintain convection into our area if it's able to organize upstream. Activity would be on a weakening trend if it is able to enter our area, though given the humid and unstable airmass that will persist even overnight can not rule out a severe weather threat in the form of damaging winds if a robust MCS can develop upstream and move in. The SPC Day 2 outlook does include a Slight Risk (level 2 of 5) for Toledo for this potential, with a Marginal Risk (level 1 of 5) elsewhere.

A similar setup on Thursday, with the ridge axis essentially overhead but potential for activity from Wednesday night to linger into Thursday across southern/eastern portions of our area. Outside of that, there should be plenty of dry time on Thursday. Will again need to monitor for isolated to scattered convection Thursday afternoon and evening given the hot, humid, and very unstable airmass, potential lingering outflow boundaries or a lake breeze, and modest northwest flow aloft over the eastern portions of the area. While there's again low confidence in widespread/organized convection Thursday afternoon or evening, there's some severe weather potential with very impressive instability profiles. Weaker shear and the discussed lack of forcing are potential negating factors.

The greatest confidence in organized convection is likely late Thursday night into Friday along and just ahead of a strong cold front that will cross on Friday. The front is currently favored to move across our area Friday morning and early afternoon. If that works out the greatest severe potential would be to our west Thursday night and then ramp back up to our east Friday afternoon. Will continue to pin down the timing of the front, as even a modest slower trend would increase potential for severe weather in at least our eastern counties on Friday.

The airmass remains very soupy ahead of the front so locally heavy rain will remain a concern with any convection until it clears. The thinking is convection should remain disorganized or sporadic enough to continue limiting the potential for truly excessive rain amounts or flash flooding, though if any training or repeated storms occur it would become an issue.

KEY MESSAGE 2...

Dew points will remain in the upper 60s and lower 70s until the front clears on Friday, with very warm afternoon highs and mild overnight lows offering little relief. Lows through Thursday night will struggle to dip below the upper 60s and lower 70s. Highs on Wednesday will generally reach the upper 80s and lower 90s, though more clouds and some component of flow off the lake will keep extreme Northeast Ohio and Northwest PA several degrees cooler. Thursday's highs should be rather close to Wednesday's, perhaps a degree or two warmer in spots assuming there isn't more convection than expected on Thursday. Highs will begin getting knocked back on Friday as the front crosses.

Have issued a Heat Advisory for much of Northwest Ohio for Wednesday afternoon. Heat index values should top out in the upper 90s and lower 100s in the advisory counties. We may need additional advisories on Thursday for portions of the area, possibly as far east as Cleveland, though will give another day of model runs to better evaluate any convective or cloud cover wrinkles to that forecast. More clouds and a bit more marine influence in far Northeast OH and Northwest PA will keep peak heat index values in the upper 80s/lower 90s there both days. Elsewhere, peak heat index values should get well into the 90s outside of the heat advisory. Given the early season nature of the heat and lacking overnight relief, those who are without proper air conditioning, work outside, or are otherwise sensitive to the heat will want to take precautions.

KEY MESSAGE 3...

Temperatures will still be summer-like but closer to normal this weekend, with a re-enforcing shot of cooler air expected to bring below average temperatures early next week behind a Sunday cold front. Mainly dry weather is favored this weekend into early next week, but will need to monitor the expected cold front on Sunday for shower and storm chances.

AVIATION /18Z Tuesday THROUGH Sunday/

Mixed-bag of VFR and MVFR across the TAF sites this afternoon, associated with pockets of lower ceilings. Highest confidence for non-VFR vsbys over the next several hours is at TOL/FDY/ERI as there remain two areas of concern for shower and thunderstorm development. Anticipate vsbys to briefly fall to IFR with the passing showers and thunderstorms, and have these reflected as tempos in the latest update. Another wave of energy will move east through the area later this evening and overnight, though confidence in direct TAF impacts remains low. An area of low ceilings may also develop late overnight into Wednesday morning, particularly along and east of the I-71 corridor. Although MVFR ceilings are reflected in the latest update, it is possible for ceilings to trend lower towards IFR in future packages.

Winds are generally out of the south this afternoon, 10 to 15 knots with periodic gusts of 20 to 25 knots. Winds will gradually shift towards the southwest overnight, then favor a west to southwest direction by early Wednesday afternoon, around 10 knots.

Outlook...Periods of non-VFR likely in occasional showers and thunderstorms through Friday. Another period of non-VFR conditions is possible in showers and thunderstorms Sunday afternoon.

MARINE

Apart from the threat of thunderstorms into Friday, and potentially again on Sunday, mainly quiet marine conditions are expected across Lake Erie through the weekend with no headlines anticipated and flow generally offshore, south to southwest, 10 to 15 knots. Main period of concern for any stronger thunderstorms appears to be Wednesday night into Thursday as guidance is hinting at a line of convection moving west to east across the Lower Great Lakes.

CLE WATCHES/WARNINGS/ADVISORIES

OH...Heat Advisory from noon to 8 PM EDT Wednesday for OHZ003- 006>009-017-018. PA...None. MARINE...None.