textproduct: Cleveland

WHAT HAS CHANGED

A Flood Watch has been issued for along and east of I-77 through 10 PM this evening. A Severe Thunderstorm Watch as been issued for most of the forecast area through 9 PM this evening. Main hazards for the severe thunderstorm watch are damaging winds and large hail.

KEY MESSAGES

1) Scattered to numerous showers and storms are expected this afternoon and evening. Some storms may turn severe with damaging winds and large hail the main hazards. Flash flooding is possible along and east of I-77.

2) Below average temperatures arrive to end the weekend and start the upcoming week. Periodic lake-enhanced rain showers will primarily impact portions of Northeast OH and Northwest PA late tonight through at least Monday night, with a few showers or storms elsewhere Sunday afternoon/evening.

3) A period of dry and quiet weather is expected the first half of the week. Scattered showers thunderstorms return Wednesday night into Thursday.

DISCUSSION

KEY MESSAGE 1... The combination of a low-level trough axis and modest warm air/ moisture advection has been fueling some thunderstorms early this morning, primarily over Lake Erie but extending southwest into parts of North Central OH as of 3 AM. While this activity is generally favored to lift east-northeast and diminish this morning, it may still be on the scope as the rest of the world awakens, particularly over and close to Lake Erie. While it may not be an entirely dry morning given this activity, greater shower and storm potential, including a risk for some strong to severe storms, awaits until the afternoon and evening hours.

Aloft, a shortwave will dig into the central Great Lakes today into tonight while taking on a neutral to slightly negative tilt. This will encourage a weak surface low to slowly deepen while drifting out of northern Michigan and into southern Ontario late today and tonight. A pre-frontal trough is still expected to cross the area this afternoon and early evening from west to east, with a strong cold front arriving in Northwest OH late this afternoon and surging southeast across the area through this evening. Large scale forcing for ascent will maximize late this afternoon and evening as a vort max rounds the base of the deepening shortwave and rotates into the northern OH/Lake Erie vicinity, though more modest forcing is evident even earlier in the day.

Showers/storms are expected to begin developing during the midday or early afternoon timeframe, with activity peaking in coverage, intensity, and organization during the late afternoon and early evening. Showers/storms are expected to exit southeast this evening with the cold front, with activity quickly transitioning to lake-enhanced showers later tonight. Activity will likely blossom along both the pre-frontal trough and a lake breeze near the northeastern shoreline near and east of the I-77 corridor this afternoon, and across Northwest OH along the cold front itself. Given the increasing forcing into the late afternoon/evening and multiple triggers for convection, it's likely that eastern portions of our area see the most widespread convection and greatest overall rain amounts, with some areas likely seeing multiple rounds in quick succession. With that said, nearly all CAMs develop fairly numerous storms along the cold front as it pushes across our western counties, so odds are that a large majority of the area will see a shower or storm this afternoon/evening on the balance.

There is some potential for both severe weather and locally heavy rain with storms this afternoon/evening, though the overall setup will not favor higher end convective hazards. Clouds and perhaps some ongoing shower/thunder activity will slow heating today, though weak to moderate, uncapped instability (1000-2000 J/KG of MLCAPE) is expected to develop through the afternoon as low-level lapse rates steepen to around 8C/km. Some pockets of dry air aloft will contribute to modest DCAPE values in the 500-800 J/KG range. These marginal thermodynamics, coupled with increasing forcing and modest deep- layer shear values of 20-30kt, can support loosely organized convection. The primary severe threat today will be locally damaging winds, most likely with any small lines or clusters that evolve but also possible with any more intense cells. Isolated large hail is also possible, mainly with any updrafts that exhibit transient rotation which is most likely within storms along/east of the pre-frontal trough where surface flow will be more backed. While the overall lower-end environment and potential for storms to quickly get "messy" and work over the atmosphere puts a lid on severe potential today, most CAMs have quite a bit of convection across our area with some organization depicted, giving the SPC confidence to introduce a Slight Risk (level 2 of 5) for severe weather for much of the area east of the I-75 corridor (and a Marginal/level 1 of 5 for I-75).

In terms of heavy rain potential, storm motions from the west- southwest will be fairly parallel to the incoming cold front, so the potential for multiple rounds and/or transient training does exist. Precipitable water values and warm cloud depths are not especially concerning for efficient rain-rates, though we will need to monitor portions of Northeast OH/Northwest PA for repeated storms or training convection that can still drop localized 2-3" rain amounts. Otherwise, area-average QPF will generally be in the 0.25-1.00" range through this evening, least across Northwest OH and greatest across Northeast OH/Northwest PA. The WPC has introduced a Marginal Risk (level 1 of 4) for excessive rainfall/localized flash flooding across Northeast OH and Northwest PA in their latest excessive rainfall outlook.

KEY MESSAGE 2... After pulling a cold front across the area this evening, the surface low and upper trough across the central/eastern Great Lakes will continue to deepen through Sunday while beginning to stack, cut-off, and slow. The system will then start to slowly fill/weaken Sunday night and Monday while drifting to the east- northeast across southeastern Canada and New England. The seasonably chilly airmass pulled in behind the cold front and lingering moist cyclonic flow behind the stacking surface low/ upper trough will give us an early taste of fall to end the weekend and start the week...including some lake-enhanced rain. 850mb temperatures will bottom out at 6-9C Sunday night into early Monday, with 700mb temperatures dipping a bit below 0C as 500mb temperatures fall to around -20C.

Most of the area will dry out late this evening into the overnight as the cold front exits, though as cooler west- northwest flow aligns over the ~25C lake waters some lake- enhanced showers will begin developing and moving into Northeast OH/Northwest PA. A vort max and low-level trough axis will cross the region very late tonight into early Sunday, likely causing activity to peak in organization. While some lake effect showers will continue on Sunday across Northeast OH/Northwest PA, the activity will likely lose organization and intensity for several hours after the morning trough passage. Another potent vort max and low-level trough axis will drop in from the northwest late Sunday afternoon and evening, bringing another uptick in lake-enhanced shower activity over and east-southeast of Lake Erie from as far west as the Islands and Sandusky points east. There will also be an uptick in showers across the rest of the area with the trough passage late Sunday afternoon and evening. Chilly, cyclonic west-northwest flow continues through at least Monday night or early Tuesday and some lake effect/ enhanced shower activity remains likely. However, there will likely be a trend for activity to become less intense/organized later Sunday night and beyond as high pressure builds in. A possible exception is Monday night when another vort max and trough passage is hinted at. That could cause one last uptick in the lake-driven showers, especially farther east.

In terms of any hazards, instability will be deep enough over the lake for some thunder/lightning potential with the lake- enhanced activity...especially through the first half of Sunday night. The overall set-up with a somewhat shorter west-northwest fetch and some wind shifts through the event isn't overly favorable for intense, banded rainfall with a flash flood risk across the snowbelt. However, rain amounts will gradually add up (especially through Sunday evening) where lake-enhanced showers are most frequent and the potential for localized flooding will need to be kept in mind, especially if parts of Northeast OH or Northwest PA see locally heavy rain today. The heaviest rain amounts will likely occur slightly inland from the lakeshore form the Cleveland area points east-northeast. Otherwise, with cold air aloft and stronger winds towards and above 500mb, any thunderstorms with the trough passage late Sunday afternoon/ evening may produce gusty winds and/or small hail...especially over and downwind of Lake Erie.

KEY MESSAGE 3... Locations outside of any lake enhanced rain showers are expected to dry out Sunday night and remain dry into the first half of the week. Lake enhanced rain will gradually dwindle starting late Sunday night and eventually end by Tuesday as discussed above. Overall, this will lend to a tranquil first half of the week across much of the area. Temperatures will slowly rebound towards normal starting on Tuesday. Another trough is expected to dig into the Great Lakes Wednesday night and Thursday. This will likely be accompanied by another surface low and its associated fronts. Chances for showers and some storms may arrive as early as Wednesday afternoon/evening, but are most favored on Thursday with this system.

AVIATION /18Z Saturday THROUGH Thursday/

Showers and thunderstorms are expected areawide today, especially along and east of I-77 where multiple rounds of storms are likely this afternoon and evening. IFR and lower conditions with reduced visibilities are likely with any thunderstorm today.

SPC has a slight risk (level 2 of 5) of severe thunderstorms for this afternoon and evening. Strong to damaging wind gusts up to 50 knots are possible within the strongest storms, along with hail up to 1 inch in diameter. These hazards are likely to be isolated in nature and there is a low probability of impact to any terminal directly.

Scattered rain showers and MVFR ceilings may linger across Northeast Ohio and Northwest Pennsylvania tonight, becoming more reserved to Northwest Pennsylvania tomorrow.

Outlook...Non-VFR conditions will be likely Sunday through Monday morning with lake enhanced rain showers and isolated thunder possible for areas downwind of Lake Erie in Northeast Ohio and Northwest Pennsylvania.

MARINE

Marine weather conditions on Lake Erie will become rough and not ideal later tonight and continuing through late Monday. There is a round of strong storms over the central basin of Lake Erie this morning that will track eastward through Sunrise. Gusty winds up to 35 knots and isolated waterspouts could be possible with these early morning storms over the lake. A cold front will approach Lake Erie from the west late this afternoon and move across later this evening. Winds ahead of the cold front will be from the south to southwest 10 to 15 knots today and waves of 1 to 2 feet. Scattered strong to severe storms will be possible again this afternoon and evening with the frontal passage. Winds will shift around from the west to northwest tonight 15 to 20 knots and continue Sunday through Monday. Waves will increase 3 to 7 feet later tonight and those rough conditions will likely continue Sunday through Monday. Waterspouts will be very possible on Lake Erie starting tonight and lingering through Monday. Small Craft Advisories and Beach Hazard Statements for rip currents have been issued late tonight through at least Monday morning. These headlines will more than likely need to be extended later into Monday with future updates. High pressure will slowly build in Monday into Tuesday with nicer lake weather conditions returning by Tuesday. By Tuesday, winds will be westerly to southwesterly 5 to 15 knots and waves decreasing to 1 to 2 feet.

CLE WATCHES/WARNINGS/ADVISORIES

OH...Beach Hazards Statement from midnight EDT tonight through Monday morning for OHZ009>012-089. Flood Watch until 10 PM EDT this evening for OHZ011>014- 021>023-032-033-089. PA...Beach Hazards Statement from midnight EDT tonight through Monday morning for PAZ001. Flood Watch until 10 PM EDT this evening for PAZ001>003. MARINE...Small Craft Advisory from midnight tonight to 10 AM EDT Monday for LEZ144>149.