Marine Weather and Tide Forecast for Withamsville, OH

NEAR TERM /UNTIL 6 PM THIS EVENING/
No significant changes made with the morning update. Low clouds will likely limit high temperatures today, so have continued to shave a degree or two off the National Blend's solution. Latest HRRR continues to show development of showers and storms this afternoon...
with general movement toward the northwest. A very moist column leads to SBCAPE around 1000J/kg despite meager surface heating, with the sounding leaning in the direction of a heavy rain threat vs. any severe weather threat. Will need to monitor localized flood potential based on back-building storms or repeated rounds over any single location.

SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/
The overnight hours heading into Wednesday morning are likely to be mostly dry, though some scattered showers under the upper low could still occur -- some low end PoPs will be kept in the forecast.

On Wednesday, the low will be in the process of opening into a wave, with the axis shifting east of the ILN CWA by mid-day. Despite this, the environment will remain moist and somewhat unstable -- so even in the absence of forcing, diurnal convection is again likely to occur.
Will keep PoPs a little lower than Tuesday, owing to the weaker forcing. Hazardous weather appears unlikely as of now, though there would likely remain a low-end isolated threat for heavy rain. Highs should be a couple degrees warmer than Tuesday, generally in the mid 70s.

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/
Wednesday night, the surface pressure pattern begins to finally lose the final remnants of the surface low pressure associated with the upper level closed low that had lingered for several days over the Ohio Valley. High pressure to the east and a surface low pressure digging into the northern and central Plains provides light southeasterly flow into Thursday morning. Overnight low temperatures largely remain in the lower 60s with some mid and upper 50s in the far east (Scioto Valley).

Severe potential (Round 1): Thursday afternoon, mid-level ridging builds over the Ohio Valley, supporting above normal temperatures in the low to mid 80s. Some cloud cover likely limits temperatures a few degrees as warm air advection aloft increases over the region, causing more cloud cover. During the evening hours, the low pressure and trough remain well to the northwest of the region, located across the upper Midwest (Minnesota & Wisconsin). This presents a challenge regarding the overall strength of the forcing over the local area.
Steep mid-level lapse rates and surface dewpoints in the upper 60s provides a pool of moderate to high instability, but a forcing mechanism to push surface air through the warm air advection inversion is lacking. Some height falls support broad ascent, which may be enough to trigger elevated convection across Illinois and Indiana. Throughout the evening, this activity will attempt to enter the local forecast area, with highest chances across the far west, especially the northwest and north. Steep mid-level lapse rates and strong shear support the potential for strong updrafts and large hail. Damaging winds may also be a threat, but widespread activity doesn't appear likely at this time.

An occluded cold front moves through the area Thursday night into Friday morning, with some uncertainty as to how far south it advances
This brings us into the uncertainty for Friday

Severe potential (Round 2): Friday morning, the same occluded low pressure is still positioned over the upper Midwest, sliding slowly eastward into the Great Lakes region by the evening. Depending on its location, the ability for more moisture-charged air to move northward is highly dependent. NBM probabilities for at least 1000 J/kg of MLCAPE and at least 40 knots of bulk shear continues to increase for Friday afternoon and evening. This is directly tied to a pool of upper 60s dewpoints that moves northward, back into the local area, behind the Thursday night/Friday morning cold front. If the moisture is able to return, a shortwave trough advancing through the southern periphery of the trough will initiate the second potential severe threat. Given the location of the shortwave, favorable moisture and strong shear, there appears to be a higher severe weather potential Friday when compared to Thursday. As the most aggressive solution, the 00Z GFS depicts a "higher-end" scenario with a well organized MCS targeting areas from south central Indiana into the southern Ohio.

Uncertainty: Comparing the aggressive solutions to the less concerning outcomes reveals the placement of the primary trough over the Midwest is critical. Returning air mass scenarios always carry very low confidence because convectively driven cold pools and/or cold front almost always resolve farther south, making it difficult for moist air to return north. Trends to monitor will be the eastward advancement of the trough Friday evening. The farther east, the more challenging it will be for moisture to return northward. The shortwave trough will still provide the potential for showers and thunderstorms, but the potential for widespread severe impacts would be lower. The most recent 00Z ECMWF ENS trended slightly slower (farther west) with the trough, but still isn't as slow as the GEFS.

Whatever occurs Friday night will ultimately provide a push of moisture south of the region for the weekend. The trough will continue its eastward progression across the Great Lakes with weakly amplified jet stream flow over the Ohio Valley. Lower chances for showers/thunderstorms are forecast for the weekend, with much of the activity focused to the south and east. Temperatures are more seasonable Sunday and Monday before the next ridge builds in Tuesday.

AVIATION /18Z TUESDAY THROUGH SUNDAY/
Convective initiation has occurred across the region as of the 18Z issuance with isolated coverage. Based on the latest high-resolution guidance, coverage is likely to increase through late afternoon before starting to decrease heading into the evening. A few of these storms may contain heavy rates of rainfall, so have visibility restrictions included accordingly.

Outside of a few showers, the overnight will be comparatively quiet.
Winds will continue to be very light under the broad upper low.
In the moist environment, ceilings are expected to drop to MVFR levels by morning.

OUTLOOK...Thunderstorms are possible Wednesday afternoon, then again at times from Thursday night through Saturday. MVFR ceilings are possible Wednesday morning.

ILN WATCHES/WARNINGS/ADVISORIES
OH...None.
KY...None.
IN...None.