378 FXUS61 KILN 130721 AFDILN AREA FORECAST DISCUSSION National Weather Service Wilmington OH 321 AM EDT Mon Sep 13 2021 .SYNOPSIS... Well above average temperatures persist today through Tuesday before the next chance for rain arrives on Tuesday night into Wednesday. Slightly above average temperatures return on Thursday through the end of the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Surface high pressure remains centered southeast of the Ohio Valley today along with slight upper level ridging overhead. Southwesterly flow around the high will result in warm, humid conditions with highs in the upper 80s this afternoon along with dew points in the 60s. A few cumulus clouds are possible during peak heating, but overall, skies should remain mostly sunny. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... Surface high pressure stays anchored southeast of the Ohio Valley tonight through Tuesday along with slight upper level riding over the area. This will result in persistent warm, humid conditions due to southwesterly winds. Forecast lows tonight are in the middle to upper 60s and forecast highs on Tuesday are in the upper 80s. By late Tuesday afternoon, clouds will likely start increasing along and northwest of I-71 as a surface front starts sinking southward toward the Ohio Valley. Have also included a slight chance of showers and thunderstorms northwest of Dayton by 8pm Tuesday evening as the front approaches. However, most, if not all, locations should remain dry through 8pm Tuesday evening. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... S/W trof axis finally begins to approach the OH Vly early in the long term period as the remnants of tropical system Nicholas meander about the northern Gulf Coast. More locally, expect that several broken bands of convection will have initiated to the NW of the ILN FA Tuesday evening before drifting SE into the local area during the late evening and overnight hours. Several weak convectively-driven pressure perturbations/waves may develop along the sagging frontal boundary, but the best LL wind field is likely to be decreasing already by late Tuesday night as the system begins to undergo a frontolytic process into the day Wednesday. What this means for us is most likely a scenario with SCT convection moving into the local area during the late evening hours Tuesday with a steady decrease both in intensity (due to diurnal stabilization) and coverage as the activity shifts SE through the heart of the overnight period. Cannot rule out an isolated strong storm during this time period, but there will be several factors working /against/ a more pronounced severe threat locally, most notably a stabilizing BL and poor LL lapse rates and, to a lesser extent, marginal deep-layer shear (0-6km bulk shear only on the order of 25-30kts coinciding with SB instby). The better shear and instby fields are not likely to be favorably overlapping to support more than an isolated severe threat, especially as LL convergence along the front gradually weakens by daybreak Wednesday as well. With this being said, could very well see maintenance of at least SCT convection through a good portion of the ILN FA through the nighttime period, even if it is slightly elevated in nature. SPC SWODY2 has placed the NW third of the ILN FA under a MRGL risk for severe storms during this period, so do think that the threat for gusty/damaging winds will be fairly isolated in nature, if one evolves at all. The sagging frontal boundary begins to slow during the daytime Wednesday, eventually washing out in the area by Wednesday night. What little LL convergence remains along the frontal boundary will likely serve as a focus for convection reinitiation, especially near/south of the I-71 corridor during the afternoon -- largely due to diurnally-driven destabilization. Once again, the better shear will remain displaced to the NW of the pool of SB instby near/south of I-71, so feel that even with SCT convection about the area Wednesday, the severe threat (locally damaging winds) will be rather isolated in nature. Diurnal convection should wane quickly Wednesday evening with the loss of daytime heating, yielding a period of quieter conditions for Wednesday night through the end of the workweek. While the overall pattern evolution during this time remains somewhat unclear, especially with the remnant low of Nicholas meandering NE into the TN Vly and along the spine of Appalachians, do feel we will once again enter a slightly quieter stretch of weather for the second half of the workweek and particularly into the upcoming weekend. There are a few uncertainties in exactly what track the remnants of Nicholas take, so there remains the potential that better moisture moves into the OH Vly by Friday with some forcing to initiate some disorganized showers and/or storms. This may eventually warrant introduction of higher PoPs, primarily during the daytime, both Friday and Saturday. However, at the very least, expect above normal temperatures during this time period (especially at nighttime when the humidity may allow for lows to be generally ~6-8 degrees above seasonal norms). This will coincide with an expansion of a midlevel ridge northeast into the OH Vly by Saturday/Sunday. && .AVIATION /07Z MONDAY THROUGH FRIDAY/... Aside from a few high level clouds moving through, clear skies are being observed across the entire Ohio Valley tonight. Mostly clear skies and VFR visibilities are expected to persist the rest of tonight and Monday. Southwesterly winds from 5-10 knots will persist the entire TAF period along with the VFR conditions. OUTLOOK...Thunderstorms possible Wednesday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Campbell NEAR TERM...Campbell SHORT TERM...Campbell LONG TERM...KC AVIATION...Campbell