textproduct: Cleveland

WHAT HAS CHANGED

The Enhanced Risk (Level 3 of 5) of severe weather for today has been removed from our forecast area. Locations along and west of the I-77 corridor remain in a Slight Risk (Level 2 of 5).

KEY MESSAGES

1) Scattered severe thunderstorms are possible across much of the area this evening into tonight. All severe weather hazards and heavy rainfall are possible.

3) Gusty non-thunderstorm winds are likely this evening through Thursday.

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

DISCUSSION

KEY MESSAGE 1... An unseasonably deep 980mb low pressure system will move east across the Great Lakes region today through early Thursday. The low will lift a warm front across the local area early this evening, followed by a cold front tonight into early Thursday morning. Showers and thunderstorms will likely develop due to isentropic lift ahead of the warm front late this afternoon into this evening with a line of strong to severe thunderstorms moving east into the area later this evening and into the overnight hours. There's still some uncertainty with timing, especially with the second round later this evening, but it appears that the second round will move into the Toledo area after 8-9 PM and into the Cleveland area after Midnight.

While a few strong to severe thunderstorms can't be completely ruled out with the first round of convection, the better chance of severe weather will arrive ahead of the cold front later tonight. The environment will be conducive for severe thunderstorms with an unseasonable 60 to 70 knot LLJ over the local area and dew points climbing into the 60s. The impressive wind field will result in ample wind shear as these storms move into the area, although instability will be pretty limited at this point. In an environment like this, however, it won't take much instability for organized convection to maintain itself. Guidance still supports a broken line of supercells congealing into more of a QLCS at some point tonight, though there's some uncertainty in where/when that will happen. Either way, storms will likely weaken as they encounter slightly more stable air in the eastern half of the area late tonight.

The best chance of severe weather will be across the western half of the area. The Enhanced Risk (Level 3 of 5) has been expanded east to the I-75 corridor and now includes the western part of the Toledo metro area, Bowling Green, and Findlay. Meanwhile, a Slight Risk (Level 2 of 5) stretches east to just east of I-77 with a Marginal Risk (Level 1 of 5) spanning from just east of I-77 into far western PA. All severe weather hazards will be on the table given the amount of shear in place, however locations generally west of I-71 have the greatest potential of seeing significant damaging wind gusts in addition to tornadoes and large hail.

Behind the warm front, PWAT values will increase to 1.75 to 2 inches, which is right around the daily maximum. The unusually high PWAT values in combination with "tall, skinny CAPE" will prime the atmosphere for heavy to torrential rainfall rates this evening into tonight. Flow may be nearly parallel to the frontal boundary which may result in some training, however storm motion will be quite fast which will help limit residence time over one location. There's quite a spread in the highest axes of QPF amongst guidance members which results in uncertainty in the locations of the greatest flooding risk. While there will probably be localized flooding (and possibly flash flooding) somewhere in the area, confidence in the location is too low to warrant a Flood Watch at this time.

KEY MESSAGE 2... Strong wind gusts are likely outside of thunderstorms tonight through much of Thursday. There will probably be a period of wind gusts to 40 to 45 mph with the best LLJ ahead of the cold front tonight. Locally higher gusts are possible, but it's possible that these gusts are largely convective. Forecast soundings also suggest that the strong wind gusts could be isolated at times due to inefficient vertical mixing. If these strong gusts end up materializing outside of thunderstorms, a Wind Advisory may be needed for tonight. Additional gusty winds are likely behind the front during the day Thursday with sustained westerly winds to 30 mph and gusts to 35 to 45 mph likely areawide. This would be the second opportunity for a Wind Advisory. As mentioned in the previous discussion, events like this typically happen during a time of year when leaves are not on trees. Leafed out trees will be more vulnerable to strong winds and sustain damage more easily, which could result in more power outages in comparison to similar similar gusts during the cold season.

KEY MESSAGE 3... Cold air advection on the back side of the low will result in scattered rain showers downwind from Lake Erie through Thursday. 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 /18Z Wednesday THROUGH Monday/

VFR conditions persist across terminals this afternoon before a deepening low pressure system glides across the Great Lakes region tonight. Initially expect rain showers to enter the I-75 corridor from the west around 20Z/Wed before isolated convection approaches around 00Z/Thu. Anticipate a similar trend from west to east, though convection will likely be weakening as it pushes towards central and eastern terminals during the overnight hours. Strong to severe thunderstorms remain possible, particularly across the western two-thirds of terminals tonight and during the overnight hours. Strong winds and a tornado will be the primary concern, though large hail is possible. Conditions are expected to fall to MVFR, isolated IFR possible, through early Thursday morning.

Southerly to southwesterly winds and gusts in showers and thunderstorms tonight will remain elevated with sustained winds 15-20 knots and gusts 25-35 knots, possibly higher in severe thunderstorms. A strong LLJ will move overhead and have introduced a brief window of LLWS before the best gusts mix down to the surface later this evening. Non-thunderstorm southwesterly to westerly winds and gusts will remain elevated behind the passing of the surface cold front through the day on Thursday.

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

MARINE

High pressure lingering over the area into this afternoon will keep fairly pleasant marine conditions present across Lake Erie with southwest winds of 10 to 15 knots. Given offshore flow, waves will remain 1-2 feet into the evening.

Very hazardous marine conditions arrive late this evening and will stick around through Thursday as a deepening low pressure system moves into the region. Associated with this low, a strong cold front is expected to push east across Lake Erie beginning near 00Z Thursday, bringing strong winds across the basin. Initial winds ahead of the cold front will be 20 to 25 knots from the south- southeast before backing to become more westerly by Thursday morning. Some winds may be as high as 30 knots at times, with locally higher still possible in any convection that develops. As the winds gain a more westerly component, wave heights will quickly increase to 4 to 6 feet in the western basin lakeshore and 6 to 8 feet across the central and eastern lakeshore. Locally higher waves up to 10 feet are possible at times, especially in the open waters. These conditions will be dangerous to small crafts and will also result in a high risk of rip currents. Swimming and boating will be dangerous on Thursday. In addition to the hazardous conditions, strong southwest winds, there is also a potential for water levels in the western basin to fall below the critical mark for safe navigation tonight into Thursday. To highlight these concerns, both a Small Craft Advisory and Beach Hazards Statement have been issued and we will continue to monitor water levels in coming forecasts. Conditions will improve across Lake Erie on Friday with northwest winds of 10 to 20 knots expected, but wave heights only climbing to 1 to 4 feet.

CLE WATCHES/WARNINGS/ADVISORIES

OH...Beach Hazards Statement from 8 PM EDT this evening through Thursday evening for OHZ003-007-009>012-089. PA...Beach Hazards Statement from 8 PM EDT this evening through Thursday evening for PAZ001. MARINE...Small Craft Advisory from 8 PM this evening to 8 PM EDT Thursday for LEZ142>144. Small Craft Advisory from 8 PM this evening to 2 AM EDT Thursday for LEZ145>149. Gale Warning from 2 AM to 6 PM EDT Thursday for LEZ145>149- 165>169.