387 FXUS61 KILN 061405 AFDILN AREA FORECAST DISCUSSION National Weather Service Wilmington OH 1005 AM EDT Mon Sep 6 2021 .SYNOPSIS... High pressure will continue to move eastward across the Ohio and Tennessee valley regions today, providing generally quiet weather through Tuesday. A cold front will move through the area late Tuesday into Wednesday, bringing a chance of rain, and some slightly cooler temperatures for the rest of the week. && .NEAR TERM /THROUGH TONIGHT/... As a high pressure ridge gradually drifts eastward today, a poorly-defined cold front will move southward out of the Great Lakes and into the northern sections of the ILN forecast area. Ahead of this feature, there will be an area of enhanced westerly theta-e advection. Combined with the boundary layer convergence from the front, which is the only obvious forcing mechanism, some sprinkles are expected to develop (along with an enhanced cumulus field). Given the extremely weak QPF returns across the model suite, and the relatively dry boundary layer conditions (dewpoints in the upper 50s), measurable precipitation seems unlikely. Will maintain sprinkle forecast, but will make another assessment later this afternoon should CAMs dictate otherwise. The westerly winds today may provide some gusts up to 15-20 MPH, especially as the boundary layer mixes in the mid to late afternoon. Lower 80s are in the max temp forecast -- very close to normal. && .SHORT TERM /TUESDAY/... The surface high will be passing off to the east / southeast of the region tonight, with winds becoming light once again, but a different scenario aloft -- as 850mb theta-e continues to increase across the region on WSW flow. This will keep conditions a little cloudier and a little warmer than the previous night, with min temps in the upper 50s to around 60. On Tuesday morning, deep-layer southwesterly flow will be increasing significantly over the Ohio Valley and Great Lakes, as the gradient tightens between the departing high and a developing stacked low pressure system near Lake Superior. This southwesterly flow will quickly push the frontal boundary northward, clearing the ILN CWA into the warm sector for all of Tuesday. As moisture will still be somewhat lacking, this pattern favors deep mixing, gusty winds (25-30 MPH in the northern part of the CWA), and warm temperatures. This forecast (mid 80s) is a degree or so above the model blend, but it probably still has room to grow by another degree or two. As the model trend has continued to be for a slower frontal passage, precipitation now appears likely to hold off until after 6PM on Tuesday evening. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Long wave trough will develop over the region early in the period. Initial short wave carving out this trough will pass north of the area but give the initial push to a cold front that will be approaching at the beginning of the period. Additional energy will follow later Tuesday night into Wednesday. This will push the front all of the way through the area. Related to the timing of the mid level support, at least some of the 00Z guidance is suggesting that showers and thunderstorms that develop northwest of the area on Tuesday will be in a slow weakening state as they move into the forecast area Tuesday evening, but then the line of showers (instability will be negligible by this point) will become better defined later in the night and continuing into Wednesday. Looks like a high coverage-low QPF event. So have increased PoPs to likely. The rest of the long term is forecast to be dry. The long wave trough will slowly translate east through the rest of the week and deamplify heading into the weekend. This will allow heights to start rising and flow will become more zonal by late in the period. A short wave passing well north of the area over the weekend may push a front into the area on Sunday. There is uncertainty whether it will make it this far south, and if it does there does not appear to be enough moisture or lift to result in a chance of precipitation at this point. Temperatures will continue to be a bit below normal until the weekend when a warming trend will occur. && .AVIATION /14Z MONDAY THROUGH FRIDAY/... Aside from valley fog at KLUK this morning -- and maybe again tomorrow morning -- VFR conditions are expected through the TAF period. After a period of light winds to start the morning, westerly winds will pick up by noon, with gusts to around 16-18 knots. Cumulus clouds will increase through the day, and there appears to be a very small chance of a sprinkle or a light shower after 18Z. This chance is too small to include in the TAFs, and would have little to no aviation impact if it occurred. A few clouds may stick around overnight tonight, but VFR conditions should prevail, as winds become light heading into Tuesday morning. OUTLOOK...MVFR conditions will be possible with showers on Wednesday morning. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hatzos/Hickman NEAR TERM...Hatzos/Hickman SHORT TERM...Hatzos LONG TERM... AVIATION...Hatzos