Sunrise 6:31 AM   Sunset 8:40 PM Moonrise 4:31 AM   Moonset 6:15 PM

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FXUS61 KILN 062345 AFDILN

AREA FORECAST DISCUSSION National Weather Service Wilmington OH 745 PM EDT Mon May 6 2024

SYNOPSIS
Several rounds of showers and storms are expected through Thursday amidst a continued warm and humid pattern. Slightly cooler air will filter into the region late in the week, with slightly drier conditions also expected. However, periodic chances for showers will likely linger into the weekend.

NEAR TERM /UNTIL 6 AM TUESDAY MORNING/
A well-defined MCV moving NE through WC KY this afternoon is providing a focus for renewed development of arcing bands of SHRA, with ISO TSRA, about its center. This MCV, notable on both regional satellite and radar imagery, will migrate to near KCVG around 00z. The best potential for redevelopment of convection this afternoon/evening is likely to occur on the ern/srn flanks of this feature, mainly in far SE IN, N KY, and far srn OH through early evening.

Due to the LL flow fields around the MCV (and the relatively shallow nature of the convection), storm motion/evolution is likely to become somewhat erratic/slow-moving late afternoon, especially very close to the MCV itself. Steering- layer flow should be fairly weak, which when combined with PWATs of 1.2 to 1.4 inches and some narrow/weak instby, will once again lend itself to at least /some/ isolated heavy rain/flooding threat.
The focus for this potential should be in the aforementioned areas, potentially as far N as a line from Ripley Co IN to Ross Co OH, with the primary area of concern just south of this line.
While most areas will receive less than an inch (with very little/none near/N of I-70), some isolated/spotty 1-2 inches will be possible in N KY/far srn OH in the most persistent/slowest-moving activity. Confidence is not quite high enough to hoist a Flash Flood Watch at this juncture, but will maintain mention in the HWO.

With quite a bit of cloud cover and SHRA/TSRA activity about the region today, temps are struggling to warm (especially in comparison to observed daytime highs recently). Highs should generally top out in the lower/mid 70s, with sfc DPs nudging back into the mid 60s for most spots. SHRA/TSRA activity should become more ISO in coverage toward the evening/beyond, trending drier area-wide toward/beyond midnight.

For the overnight period, the main item of interest will be the potential for some fog and/or very low stratus to develop along a weakly-convergent axis pivoting squarely through the heart of the area overnight. The patchy fog is likely to be /most/ widespread S of I-70 and especially near the OH Rvr where the LL flow will be the weakest and the pooling of near-ground moisture is maximized.

SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/
Midlevel ridging briefly moves through the OH Vly tonight as a tremendously large/broad low migrates into the upper Midwest. On the SE flank of this stacked/occluding low, S/W energy pivoting around the basal portion of the longwave trof will eject NE into the OH Vly by Tuesday afternoon/evening. This will provide the focus for an active short-term period, with the details discussed below.

Bottom line up front... the setup for severe storms appears to have increased and become a bit more concerning given recent data trends. The main time period for severe potential locally appears to be somewhere in the vicinity of the 4 PM to 11 PM EDT window, likely maximizing between 6 PM and 10 PM.

Diving a bit further into the details, expect that a (somewhat decaying) band of convection will move into the region by mid/late morning Tuesday. This activity represents "convective leftovers" from the central plains severe weather episode expected later today. Although the activity /should/ be on a weakening trend with eastward progression closer to/into the ILN FA around/after noontime, a slightly slower arrival may mean that sufficient diurnal destabilization could occur /ahead/ of this activity, lending itself to at least some potential of SB- convection and redevelopment along the eastward-moving arc. Do think that the activity should survive long enough to enter the local area, potentially providing a focus for some redevelopment along it's trajectory through the ILN FA between about 12 PM and 4 PM. Certainly a few strong/severe storms may develop associated with this feature (providing it holds together enough), with strong/damaging winds and some small hail being the primary threat through the first half of the afternoon.

Once we get past about 3-4 PM or so, the environment is going to become increasingly conducive to redevelopment of convection (initially back to the W in IL/IN), with a conditionally- volatile setup very possible given rapid destabilization in the wake of early afternoon activity. There are still a few uncertainties in just /how much/ redevelopment occurs across IL/IN mid/late afternoon before it overspreads the local area late afternoon through the evening. Nevertheless, a strongly unstable environment (courtesy of SB/MLCAPE in excess of 2000J/kg) should develop within a decently-wide corridor (nudging in from the SW past 21z). This will occur amidst an environment with plenty of forcing and ascent, good midlevel lapse rates (supporting robust updraft development/strength), and good deep- layer speed shear. A H5 jet speed max will nose to the NE into the OH Vly by late afternoon/evening, eliciting an elongated and subtly-curved hodograph from the sfc to about H5. There is some directional shear in the BL as well, but the "fly-in-the-ointment," so to speak, is the backing of winds in the upper levels within the H2-H5 layer, producing an anticyclonic curvature to the end of the hodograph. This depicts a likely scenario that is conducive to discrete/cellular activity (perhaps with splitting supercells), with some clustering possible. In addition to the large to very large hail threat, the primary concern would be if sfc winds are able to back immediately ahead of the convection, especially between about 21z-03z, creating local enhancements to the 0-1km/0-3km SRH fields. This backing appears most probable/favorable near/N of I-70, suggesting the tornado potential is slightly greater in these areas than further S toward/S of the OH Rvr with the LL flow remains more veered. Given the sufficient overlap between a strongly-unstable environment, good forcing/ascent, and good deep-layer shear, all hazards are in-play Tuesday late afternoon/evening, with the greatest tornado threat likely to focus near/N of I-70 in a slightly more conducive environment with the somewhat backed LL/sfc flow. And although storm motions should be fairly quick, cannot completely rule out some brief heavy rain/flooding, especially in areas that have received significant rain over the past few days. Have adjusted HWO wording to reflect this latest thinking.

The coverage of storms should be on a decreasing trend from W to E toward midnight/beyond, with quieter conditions briefly returning late Tuesday night in the wake of evening convection.

LONG TERM /WEDNESDAY THROUGH MONDAY/
Forecast calls for active weather as numerous moisture-laden systems are expected on a southwest to west upper flow.

Period begins Wednesday with a strengthening cluster of short wave energy triggering a surface low that will move toward Ohio from the west. Favorable moisture and lift will aid convective development, while a tight pressure gradient causes breezy conditions.
Thunderstorms are nearly certain during Wednesday afternoon and evening, continuing Wednesday night as the low progresses to Northern Ohio. Organized and enhanced by the strong wind fields and supported by ample instability, some storms may be severe and produce heavy rain. As the low moves east on Thursday, coverage of convection will decrease along with the severe threat.

A few showers may occur in residual moisture on Friday. A fast moving low tracking to the Great Lakes could trigger more showers and storms on Saturday. Low chances for showers and storms will be maintained Sunday and Monday as weak short waves encounter a marginally unstable environment.

Temperatures will exhibit fluctuations that will follow changes in geopotential heights and low level advection and insolation patterns.
Highs are forecast to remain above normal on Wednesday in warm advection ahead of the first low, with highs ranging from the upper 70s to mid 80s. As geopotential heights drop and the low level flow turns northwest, readings slide to the upper 60s to around 80 on Thursday. Further reduction in geopotential heights and continued cold advection will provide highs mainly in the 60s Friday through Sunday, with lows in the 40s. A rebound to the 70s is indicated for Monday under rising heights and increasing insolation.

AVIATION /00Z TUESDAY THROUGH SATURDAY/
Still some scattered shower activity around the area this evening. Brief MVFR VIS/CIGs will be possible with these showers. This activity will continue to become more isolated over the first few hours of the TAF.

Overnight, low-level flow will saturate and winds will be weak, supporting descending CIGs from VFR to IFR/LIFR into 12Z. Given the weak winds, IFR VIS is also likely, especially where rain occurred earlier today.

Light/variable flow overnight will calm before going more southerly and increasing to around 10-15kts past 15z Tuesday. A band of SHRA/TSRA should approach from the W toward 18z (CVG/LUK/DAY/ILN) Tuesday and continue eastward toward CMH/LCK by around 20Z. Additional showers and thunderstorms are expected behind this line through the remainder of the TAF.

OUTLOOK...Thunderstorms will be possible Tuesday afternoon and evening and then again late Wednesday into Wednesday night.
MVFR/IFR CIGs are possible Wednesday night into early Thursday and again on Friday.

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

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