textproduct: Cleveland

WHAT HAS CHANGED

There is now an Enhanced Risk for severe thunderstorms Saturday afternoon and evening across Northeast Ohio and Northwest Pennsylvania, driven by straight-line wind potential.

KEY MESSAGES

1) A few showers and storms may move across the area this evening and tonight. Greater potential for thunderstorms is expected Saturday afternoon and evening. Some storms will be severe on Saturday, with damaging winds the main risk.

2) Very warm temperatures persist through Saturday as humidity increases. A cold front brings cooler weather for Sunday.

3) Showers and storms are likely Monday night and Tuesday.

4) Smoke continues to produce poor air quality and reduced visibility across the area, but will exit to the east tonight into Saturday morning.

DISCUSSION

KEY MESSAGE 1... An upper-level shortwave trough and associated surface low pressure will dive east-southeast across the Great Lakes and into New England Saturday and Saturday night. A warm front will lift east-northeast across the local area tonight ahead of the system, followed by a cold front Saturday evening.

The initial chance for showers/storms will be this evening and tonight with the warm frontal passage across the area. Large- scale forcing is rather lacking tonight, but the combination of the front, an increase in low-level warm air/moisture advection, and an unstable airmass moving in behind the front should fuel at least some hit/miss activity that moves east across the area through the night. Aside from moderate instability spreading in tonight, not much supports a severe threat in our area with any storms along the warm front. Precipitable water values will surge to over 2.00" with the warm frontal passage so any thunderstorms will have impressive rain-rates, but coverage and organization looks limited enough to avoid flash flood concerns.

We'll break into the open warm sector by Saturday morning, which should allow any showers/storms with the warm front to exit east early in the day. The greatest potential for storms will be late in the day as the cold front approaches and moves through. That said, the combination of heating/destabilization of a humid and uncapped airmass and continued modest low-level warm air/moisture advection may be enough for at least a few isolated to widely scattered showers/storms to develop in our area in the open warm sector by late morning or early afternoon. Hi-res models currently suggest a subtle low-level trough axis may focus more numerous/organized pre-frontal storm activity near southeastern portions of our area (i.e. Canton-Youngstown- Meadville) during the early-mid afternoon. The greatest forcing arrives during the late afternoon/early evening with cold front as the shortwave passes through the region and spreads the right-entrance quadrant of an upper jet streak across the area, bringing the most widespread/organized storm potential. Storms should quickly exit to the south late Saturday evening/night, though a trailing trough dropping off the lake a few hours behind the front may bring scattered showers with it.

In terms of severity of storms on Saturday, mid-level lapse rates will be weak (generally <6.0C/km) though this will be offset by strong heating of a very humid airmass, leading to strong instability (2000-3000+ J/KG of MLCAPE) by mid to late afternoon. Pockets of mid-level dry air atop the moist, strongly heated low-levels will contribute to fairly large DCAPE values of 900-1200 J/KG. Deep-layer shear will initially be weak, but does increase to 30-40kt by the late afternoon and evening as the shortwave makes its closest pass. Flow will be rather unidirectional, leading to rather modest amounts of effective storm relative helicity in the 100-150 m2/s2. Any pre- frontal storms will likely initially be cellular before gradually growing into small clusters or lines, with storms along the cold front itself expected to develop just to our north (or across northern portions of our area) and quickly grow into clusters or lines.

Damaging winds will easily be the most probable/widespread severe hazard in that environment, with organized swaths of more widespread wind damage possible with clusters or lines that take shape. Given the favorable environment and hi-res models continuously showing widespread, fairly organized convection, the SPC has increased our threat of damaging winds to "Enhanced" (level 3 of 5). The potential for significant gusts (over 75 MPH) is fairly low given somewhat marginal amounts of shear, but can't be entirely ruled out if we see a more robust bow echo evolve across Northeast OH or Northwest PA. Any initial cells ahead of the front may pose an isolated risk for large hail given the strong instability, especially if shear increases enough for a supercell or two play out. The amount of shear is marginal for a tornado threat, but there is just enough 0-3km bulk shear for a QLCS-type tornado threat with bowing lines, especially across Northeast OH and Northwest PA. Any sustained supercell would of course also need to be monitored for tornado potential, though confidence in that scenario is lower. Given the very warm and moist environment, locally heavy rainfall will also be a concern. Storm motions of 30-40 MPH (on average) should limit flash flooding potential given our drier ground. However, if any locations see repeated or perhaps brief training storms a very localized flash flood threat can't be fully ruled out. The peak severe threat is generally expected to occur between 3 PM and 9 PM from northwest-southeast across the area.

Conditions will be most favorable to organized, severe convection with the cold front late Saturday afternoon/evening. While confidence in some severe weather occurring is rather high across our area, there is some uncertainty regarding a more widespread severe threat. A solution such as that presented by the 12z HRRR/3km NAM in which pre-frontal convection is more limited would support the more widespread severe threat advertised in current outlooks and is currently the favored solution. However, if pre-frontal convection becomes more widespread earlier (such as the ARW WRF shows) that could limit the overall amount of severe weather somewhat.

KEY MESSAGE 2... After lows ranging from the upper 60s to mid 70s tonight, highs will reach the upper 80s and lower 90s on Saturday as dew points surge into the lower 70s. Peak heat index values will largely remain under Heat Advisory criteria of 100F, though will reach the mid to upper 90s across much of the area, especially along and west of the I-71 corridor. Those with outdoor plans will want to keep hydration/cooling in mind. A nice airmass change behind the front, with lows dropping well into the 60s by Sunday morning as highs on Sunday range from the mid 70s to lower 80s.

KEY MESSAGE 3... A potent shortwave and associated surface low is expected to pass just north of the Great Lakes Monday night and Tuesday, pushing a cold front across the local area Tuesday or Tuesday night. Showers and thunderstorms are expected as the cold front approaches and crosses the area. While any potential for severe weather or flooding will come down to finer details that aren't clear yet at this range, this does look to be a fairly dynamic system (for July) with some shear to work with.

KEY MESSAGE 4... The entire area continues to observe air quality ranging from unhealthy to hazardous due to wildfire smoke this afternoon, with visibilities mainly between 1 and 3 miles. Smoke is expected to gradually exit from west to east through tonight as the warm front lifts through. It will likely take until some point Saturday morning to fully clear Northwest PA. Once the smoke clears, a bit of smoke may return behind the cold front Sunday into Monday. However, some rain occurring in the interim where the fires are happening plus most of the smoke across the Great Lakes getting cleared out over the next day or two should lead to any smoke that returns Sunday or Monday being notably less dense/impactful than what we've seen the last two days.

AVIATION /18Z Friday THROUGH Wednesday/

Dense smoke will maintain IFR visibilities at all terminals through late afternoon before gradually improving from west to east this evening and tonight, but it will take until daybreak Saturday morning to complete clear out of KERI. Otherwise, isolated to scattered showers and thunderstorms will develop ahead of a warm front this evening and push east overnight. Confidence is low on any cells impacting a particular terminal, but they should be in the vicinity of KTOL and KFDY in the roughly 23 to 03Z timeframe and be in the vicinity of KCAK, KYNG, and KERI in the roughly 05 to 10Z timeframe. Any shower or thunderstorm could produce brief heavy rain and MVFR or lower if it impacts a terminal. Dry and VFR conditions are expected much of the morning through the early afternoon until thunderstorms develop after the TAF period ahead of a cold front.

Light and variable winds the rest of this afternoon and evening will turn S to SW tonight, with SW winds increasing to 15-25 knots by late Saturday morning through the afternoon.

Outlook...Non-VFR expected in showers and thunderstorms ahead of a cold front Saturday afternoon and evening. A few storms could be strong to severe with strong wind gusts approaching 50 knots.

MARINE

Light and variable winds on Lake Erie early tonight will turn SW and quickly increase to 15-20 knots by daybreak Saturday behind a warm front. SW winds will increase to 15-25 knots by Saturday afternoon, especially in the central and eastern basins, so a Small Craft Advisory has been issued from 14Z Saturday through 00Z Sunday. The SW direction will keep the highest waves in the open waters, with nearshore waves in the 3 to 5 foot range from Avon Point to Ripley. Winds will turn N behind a cold front Saturday night and gradually decrease to 10-15 knots late, becoming NE at 5-10 knots Sunday. Winds will quickly come around to SW at 5-10 knots Sunday night and Monday, with SW winds increasing to 15-25 knots Monday night and Tuesday ahead of another cold front, which will build waves to 3 to 5 feet. Small Craft Advisories will likely be needed again at that time. Winds will turn NW behind the front for Tuesday night and Wednesday while gradually decreasing.

Visibilities will gradually improve on the lake this evening and tonight from west to east as the smoke plume starts to move out, but extended the Dense Smoke Advisory from Avon Point to Buffalo through Midnight. Additionally, a line of strong to severe thunderstorms could bring locally high winds to 50 knots late Saturday afternoon and early evening as it progresses southeastward across the lake.

CLE WATCHES/WARNINGS/ADVISORIES

OH...Air Quality Alert until midnight EDT tonight for OHZ003- 006>009-017>019-027>032-036>038-047. PA...Air Quality Alert until midnight EDT tonight for PAZ001>003. MARINE...Dense Smoke Advisory until 4 PM EDT this afternoon for LEZ142>149-162>169.