Messages
Hot, humid, and hazy conditions continue.
Showers and thunderstorms are forecast to develop Friday and continue into the weekend, bringing a risk for localized flash flooding and gusty winds.
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Revised in 8 passages since the 1:42 PM discussion. See every revision.
Discussion
Mid level ridge axis situated northwest to southeast across the region will sag slowly south tonight and break down/ weaken. As such, a very moist airmass has begun to encroach into the Ohio Valley region on Thursday. This has acted to raise Tds even more so than yesterday, resulting in some very muggy conditions. Have continued the Special Weather Statement for hot and humid conditions through Thursday evening. CAMs still indicate some isolated thunderstorm activity primarily south of I-70 today, so have kept a low end chance of rain in the grids.
Wildfire smoke from the northern US/Canada will continue to wrap through the larger flow and into the Ohio Valley. the high-res rapid-refresh model smoke modeling suggests that near surface smoke will primarily remain across northern Ohio today before percolating southward on Friday. It's not unheard of for temperatures to be impacted a couple of degrees from a thick column of smoke, as insolation is inhibited, so have tweaked daily highs down a couple degrees accordingly for Friday, though kept Tds as is, given the moist airmass.
Even with the smoke and increasing cloud cover, muggy conditions are expected to continue through the weekend with scattered thunderstorms.
KEY MESSAGE 2) Showers and thunderstorm chances are reintroduced to the forecast on Friday and Saturday as midlevel flow becomes more northwesterly and shortwaves move through the larger flow. As previously mentioned, moisture from the Gulf will surge into the Ohio Valley, increasing precipitable water to 2+ inches, which is well above the 90% percentile and nearing climatological maximums. This moist airmass will be present both Friday and Saturday, allowing for a saturated column as well as surface Tds in the low to mid 70s.
On Friday, the first weak shortwave will move through the flow, sparking showers and thunderstorms Friday afternoon into late evening. An instability gradient will exist from west to east, with more robust instability building in from the west southwest. Scattered thunderstorms are expected to develop beginning Friday afternoon and continuing through the evening hours. Shear is nearly non-existant but DCAPE will be over 900 J/kg and MLCAPE will 1500 J/kg+. Given that and the high precipitable water, storm motions will be very slow and water loaded storms may quickly collapse, producing instances of gusty winds. Localized heavy rainfall may result in isolated flooding issues.
A larger shortwave will then pivot through the flow Saturday into Sunday, dragging a surface low pressure system through the northern Great Lakes region. The associated cold front will sag into our area Saturday afternoon into the overnight hours, bringing additional thunderstorm chances.
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