textproduct: Cleveland

WHAT HAS CHANGED

Confidence in organized thunderstorms with a severe weather and heavy rain threat has decreased for tonight. A Wind Advisory has been issued for portions of Northeast Ohio and Northwest Pennsylvania from 12 AM to 6 PM Thursday.

KEY MESSAGES

1) After mainly light rain spreads in this evening, showers and storms are expected along a cold front late this evening into overnight tonight. Some of these storms may be severe with damaging winds the greatest concern, though the overall severe risk has trended down a little bit today.

2) Southerly winds become gusty tonight. Winds shift west- southwest on Thursday and remain gusty through the afternoon. A Wind Advisory is in effect for portions of Northeast Ohio and Northwest Pennsylvania from 12 AM to 6 PM Thursday.

3) Below normal temperatures and periodic showers are possible Thursday through early next week. The greatest chance of rain will be Sunday into Monday.

DISCUSSION

KEY MESSAGE 1... Main focus is convective potential later this evening into the overnight hours tonight along and ahead of a cold front that will cross the area. A batch of rain this evening ahead of any convection moving in from the west, along with timing late evening into the overnight, leads to considerable uncertainty regarding severe weather potential across the local area.

A decaying batch of stratiform rain from earlier convection well to our west will move east across our area late this afternoon and evening as a warm front quickly surges through from the southwest. Am not expecting any severe weather or even much (if any) lightning from this first batch this evening.

The main focus for convection will be late evening and overnight as a cold front approaches and crosses our area from northwest to southeast. As has been written in this space many times in recent days, a very impressive and dynamic system for the middle of June leading to unusually strong wind fields and shear for the summer months. A 60-70kt low-level jet will sweep across the area tonight ahead of the cold front. This will bring plenty of both bulk speed shear and low-level turning/storm relative helicity for organized convection with potential for rotating updrafts. However, as mentioned above the thermodynamic environment is much more questionable. Guidance generally suggests we'll have around 500 J/KG of uncapped (or very weakly capped) MLCAPE to work with overnight tonight with modest low- level lapse rates but no strong inversion, once we finally get the warm front through. While this is a meager amount of instability, 0-3km CAPE values in the ~50 J/KG range as suggested by most guidance are (barely) sufficient for surface based convection with at least some severe threat. Assuming we see at least a brief break between the evening rain and approaching cold front, the overall environment can support a high-shear/low-CAPE severe threat with any organized convection. If we don't see much of a break in the rain we will struggle to advect in even that modest amount instability.

In terms of if we'll see organized convection, hi-res models all generally agree that convection will lose a good amount of organization well before reaching our Northwest Ohio counties later this evening...however, some models suggest that at least scattered and mainly weak (but surface-based) convection will progress east across our area through the night as instability attempts advecting in. While the overall severe threat has trended down at least somewhat given the batch of lighter rain expected this evening, the fact that a number of models have at least some semblance of surface-based convection amid such impressive shear profiles is enough that the SPC outlook maintains a Slight Risk (level 2/5) from the I-77 corridor points west for tonight with a Marginal Risk (level 1/5) to the east. Damaging wind gusts are the most likely hazard if we see any severe thunderstorms tonight. The very strong shear profiles, low LCL heights, and marginal 0-3km CAPE can still support some tornado potential from any supercells or surging lines, but the likely lack of organized convection should keep that risk relatively lower. The environment does become supportive of very heavy rain-rates overnight, but the more disorganized depiction on many models keeps flooding potential too uncertain to issue any flood watches with this update.

The tl;dr is that some showers and thunder are likely along and ahead of the cold front tonight...arriving after 9 PM in the Toledo area and progressing east-southeast through 3-5 AM. At least an isolated severe threat, mainly in the form of damaging wind gusts, remains evident but widespread/organized severe weather is not likely. Tornadoes can't be completely ruled out, nor can locally heavy rain and flash flooding, but these appear to be secondary and overall very isolated risks.

KEY MESSAGE 2... Winds will turn gusty overnight tonight as a very strong, 60-70kt low-level jet, sweeps east across the area just ahead of the cold front tonight. These types of nocturnal jets usually don't mix down well in a warm advection regime, with the normal exception of our downslope areas along the eastern lakeshore. Downslope enhancement will be most prominent in northern Erie County PA, but can happen to at least some extent as far west as Cleveland. Some hi-res/convective allowing models also suggest the potential for convective enhancement (most likely in the form of a "wake low" as occurred to our west this afternoon, but possibly just from enhanced vertical motion in and around any convection) beneath the low-level jet. Any organized storms that may produce damaging winds would be handled by convective products, though do note there may be generally gusty winds near any weakening convection for a brief time. Generally expecting a period of 30-40 MPH wind gusts area-wide beneath the low-level jet tonight, but 45-50 MPH along the northeast lakeshore and perhaps briefly stronger anywhere else if we see any mesoscale/convective processes to enhance the gusts.

Winds turn more west-southwest very late tonight and Thursday behind the cold front. Winds aloft gradually weaken behind the cold front but remain fairly strong (30-40kt at 925mb, 35-45kt at 850mb) until early-mid afternoon as mixing heights quickly increase with daytime heating. These winds will mix down much more efficiently before dropping off late Thursday afternoon and evening. Am expecting fairly widespread 35-45 MPH type wind gusts on Thursday, up to 50 MPH closer to the eastern lakeshore.

Have gone ahead with a Wind Advisory for a handful of counties in far Northeast OH and Northwest PA, as this area will see some downslope enhancement to the wind tonight and will likely see some of the stronger wind gusts on Thursday. Toyed with an advisory elsewhere for various reasons, though confidence in widespread/coherent advisory-level gusts tonight is not there outside of the downsloping and gusts tomorrow may also end up holding a bit below criteria away from the eastern lakeshore. Still, we can start seeing minor tree damage and isolated power outages with ~40 MPH gusts when trees are fully leafed out, so people should be prepared for gusty winds and some minor impacts even outside of the advisory. If forecast gusts tick up any more we may need to expand the advisory into more of the area given possible impacts.

KEY MESSAGE 3... Cold air advection and a trailing low-level trough axis on the back side of the low will result in isolated to scattered rain showers Thursday into Thursday evening, especially downwind of Lake Erie. From there, dry weather is expected before rain chances return Sunday afternoon through Monday. Temperatures will generally remain a little bit below normal over the next several days with highs in the 70s expected. Lows will drop into the 50s Thursday night through Saturday night.

AVIATION /00Z Thursday THROUGH Monday/

An area of rain showers with embedded TSRA will work east across the region through 09Z as strong low pressure moving east through the Great Lakes brings a cold front through the area. Low confidence with TSRA impacts at any given terminal, so opted to continue PROB30 mention for the windows of best TSRA potential at each terminal. MVFR ceilings will be common with the SHRA with IFR possible in any TSRA.

Strong LLJ will push east across the area ahead of the low through 09Z. Have opted to remove LLWS mention from TAFs with well mixed soundings and gusts out of the southwest in the 25-35 kt range expected. After a brief lull in gusts around 12Z, west winds could gust again around 30 kts for the second half of the period behind the cold front.

Outlook...Periodic showers and thunderstorms with non-VFR will continue through Friday.

MARINE

Hazardous marine conditions arrive this evening as deepening low pressure moves across the Great Lakes region. Ahead of the surface cold front, southerly winds increase to 20-25 knots before becoming southwesterly at 30-35 knots behind the cold front late tonight. Have issued a Gale Warning for the central and eastern basins as confidence in 35 knot southwest gales has increased. The Gale Warning remains in effect from 2 AM Thursday through 6 PM Thursday. Wave heights in the nearshore waters are expected to build to 3 to 5 feet in the western basin and up to 6 to 8 feet across the central and eastern basins. A Beach Hazards Statement for a high risk of rip currents remains in effect across all lakeshore counties. Additionally, there is also a Low Water Advisory for the western basin from 4 AM to 4 PM Thursday as water levels are expected to fall below the critical mark of 13 inches in the strong southwesterly flow.

Marine conditions are expected to improve across Lake Erie on Friday as winds turn northwest at 10-20 knots with wave heights generally of 2-4 feet. An additional issuance of a small craft advisory may be needed to cover the onshore flow late Thursday night into Friday morning for the central and eastern basins.

CLE WATCHES/WARNINGS/ADVISORIES

OH...Beach Hazards Statement through Thursday evening for OHZ003- 007-009>012-089. Wind Advisory from midnight tonight to 6 PM EDT Thursday for OHZ011>014-089. PA...Beach Hazards Statement through Thursday evening for PAZ001. Wind Advisory from midnight tonight to 6 PM EDT Thursday for PAZ001-002. MARINE...Small Craft Advisory until 8 PM EDT Thursday for LEZ142>144. Low Water Advisory from 4 AM to 4 PM EDT Thursday for LEZ142>144-162>164. Small Craft Advisory until 2 AM EDT Thursday for LEZ145>149. Gale Warning from 2 AM to 6 PM EDT Thursday for LEZ145>149- 165>169.