textproduct: Cleveland

WHAT HAS CHANGED

No significant changes from the previous forecast.

KEY MESSAGES

1) Showers and thunderstorms are likely Monday night through Tuesday. Storms may be severe Tuesday afternoon and evening, but there is uncertainty.

2) Brief warm up Monday and Tuesday followed by a longer period of cool temperatures and low humidity mid to late week.

DISCUSSION

KEY MESSAGE 1... The mid/upper trough over the Great Lakes tonight will briefly lift Monday ahead of an unseasonably strong shortwave diving from Manitoba into the northern Great Lakes. This shortwave will continue to dive through the central and eastern Great Lakes Tuesday. As this occurs, the Canadian high at the surface will shift off of the Mid Atlantic coast Monday as a deepening surface low progresses across northern Ontario and through northern Quebec Tuesday and Tuesday night.

Return low-level flow and developing warm air advection Monday will strengthen Monday night as a warm front lifts east and northeast across the region. An impressive 110-120 knot H3 jet streak rounding the base of the diving shortwave will support a 35-45 knot low-level jet in the western Great Lakes Monday night, and this strong moist, theta e advection and isentropic ascent ahead of the warm front should ignite and sustain a nocturnal MCS. This period is starting to come into the range of CAMS, and most dive the most organized portion of this MCS across Illinois and Indiana along the instability/theta e gradient. This makes sense given that the low-levels will still be dry and stable in northern Ohio and NW PA, however, elevated instability advecting into our region overnight should still generate some showers and thunderstorms. Severe weather will not occur with this Monday night elevated convection, but locally heavy downpours are possible.

The main show associated with this unusually dynamic mid summer system still looks to be Tuesday afternoon and evening ahead of the strong cold front that will drop south across the region. The aforementioned impressive jet streak will shift across southern Ontario Tuesday afternoon as the axis of the shortwave crosses the southern Great Lakes and Ohio Valley. This will support strong ascent across northern Ohio, NW PA, and the Lake Erie region beneath the right entrance of this jet streak, leading to strong forcing along and ahead of the cold front. In most cases, this would be a clear cut set-up for an organized, severe line of convection in the form of a QLCS. The continued uncertainty lies with the Monday night and early Tuesday morning convection. The aforementioned elevated convection Monday night, as well as remnants from the upstream MCS activity, will likely leave cloud cover and outflow boundaries across our region Tuesday morning. Many times in the past, this has caused the new convection to initiate along these outflow boundaries and differential heating boundaries in southern and eastern portions of the CWA, and then the convection matures mainly south and east of our area. This very well may be the case Tuesday. The SWODY3 Enhanced Risk with 45% wind over the southern and eastern fringe of the CWA looks reasonable at this time given the potential for convection to mature to the south and east Tuesday afternoon, with lower probabilities farther north and west. This will continue to be monitored closely since the dynamics of this system and surge of warmth and humidity ahead of it could support a more widespread threat if the frontal timing slows at all or if less convection impacts the area Monday night/Tuesday morning. Regardless of intensity or organization, there will be scattered showers and thunderstorms around much of Tuesday, so maintained likely to categorical POPS.

Most areas will dry out rapidly behind the cold front Tuesday night, but deep mid/upper longwave troughing across the Great Lakes in the wake of the system and associated cold air advection and cyclonic flow will likely support additional lake-effect and lake enhanced rain showers in far NE Ohio and NW PA through Wednesday until broad Canadian high pressure builds in by Wednesday night.

KEY MESSAGE 2... The warm air advection developing Monday as the surface high departs to the east will allow temperatures to warm back into the low/mid 80s, except upper 70s in NW PA. Despite the warmer air temperatures, humidity will remain comfortable as dew points stay mainly in the 50s. This will change Monday night and Tuesday as deeper low-level moisture in the warm sector surges into the area. This will bring 70+ degree dew points back into the area for Tuesday, and this combined with temperatures in the mid/upper 80s will support heat indices around 90. For those who don't like the heat and humidity, the cooler weather will make an abrupt return behind the cold front Tuesday night as the deep mid/upper trough and strong Canadian high take up residence across the Great Lakes the rest of the week. This will support a longer period of below normal temperatures, with highs mainly in the low/mid 70s Wednesday and Thursday, gradually warming Friday through the weekend. However, humidity will remain comfortable.

AVIATION /18Z Sunday THROUGH Friday/

Overall VFR conditions will continue through the next 24 hours. Skies will be mostly clear but very hazy at times. Lingering wildfire smoke across the area will result in 5sm to 6sm haze through the time period. Winds will start out from the north 5 to 10 knots this afternoon becoming light and variable tonight. A light southerly flow of 5 knots will return by Monday morning.

Outlook...Pockets of non-VFR likely in showers and thunderstorms Monday night through Tuesday. Some thunderstorms Tuesday afternoon and evening may contain strong wind gusts. Residual non-VFR possible on Wednesday on rain showers across the eastern half of the area.

MARINE

Good marine conditions are expected on the lake this afternoon through Monday with winds around 10 knots or less and waves 1 to 2 feet. The next period of concern for rough marine conditions and marine headlines will be on Tuesday. Southwest winds will increase 15 to 25 knots ahead of a cold front. Rough marine conditions will continue into Wednesday as winds shift towards the northwest behind the front around 20 knots and waves of 3 to 5 feet. In addition, strong to severe thunderstorm wind gusts are possible across Lake Erie Monday night into Tuesday ahead of the front.

CLE WATCHES/WARNINGS/ADVISORIES

OH...None. PA...Air Quality Alert until midnight EDT tonight for PAZ001>003. MARINE...None.