Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 170757 AFDILN AREA FORECAST DISCUSSION National Weather Service Wilmington OH 357 AM EDT Tue May 17 2022 .SYNOPSIS... A weak, but dry cold front will push south into the region overnight. This front will then sag south toward the Ohio River Valley on Tuesday where it will eventually stall. The weather pattern will then quickly become more active by Wednesday, with periods of showers and storms expected through the end of the work week and into the start of the next weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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A dry, weak cold front is moving through the fa early this morning. The primary result of this front will be a shift in near-surface winds out of the northwest, as well as keeping a reasonably comfortable (and generally unmodified) airmass in place for the day Tuesday. With persistent northwesterly flow aloft, model soundings show another day with steepening low-level lapse rates and even some weak instability forming. This will help with some cu development again by the afternoon, but cloud coverage should be limited as the troposphere remains fairly moisture-starved. Breezy conditions expected once again as sufficient BL mixing occurs, allowing for some periodic wind gusts of around 20-30 mph.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
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Flow aloft starts to breakdown and become more quasi-zonal Tuesday night. Models agree in a shortwave trough developing within this flow pattern across the Midwest overnight, but the timing and placement still has some differences. In our CWA, we are likely to remain dry overnight with cloud coverage increasing from the west. Due to some differences in the timing of the shortwave however, decided to keep slight chance PoPs in the grids for late Tuesday night/early Wednesday morning just touching our far western counties as some pcpn may occur ahead of the main system. Coverage in pcpn will increase late Wednesday afternoon from west to east as an MCS moves along the shortwave feature. Hi- res models such as the NAM3K/HRRR even show an MCV present in portions of Missouri/Illinois, with it beginning to lose some of its characteristics as it moves eastward into our CWA. Destabilization will help support thunderstorm potential across our entire fa, but lower instability is expected in central and west-central OH. Thus, have only kept a slight chance thunder mention near/north of I-70 for the day. The potential does exist for severe thunderstorms - mainly near/south of the OH River where the atmosphere destabilizes more and is also supported by sufficient speed shear (~30-40 kts). However, global and hi-res models seem to keep most of the instability elevated during the day, with SBCAPE struggling to build in until later in the evening. This should help limit the severe potential, but will still be something to closely monitor with additional model guidance.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
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The transition from the near term into long term period will be an active one, as will the start of the long term period, as there is an expectation for an MCS/MCV to be racing ESE through the region sometime in the Wednesday afternoon to evening time frame. This will occur, in part, due to a potent S/W translating E through the quasi- zonal/NW flow aloft that will be entrenched across the OH Vly. Guidance has come into a bit better agreement regarding the evolution of the weather situation during the day on Wednesday, although there are still plenty of questions regarding how quickly/far N low level destabilization efforts are able to evolve late in the day. It does, however, seem that most of the convective activity with the MCS -- including renewed development during the afternoon into early evening near/S of the OH Rvr -- will be primarily elevated in nature locally as the best pooling of richer LL moisture will be just off to the SW of the ILN FA across central/NW KY and s-cntrl IN by 00z. And while there is still some uncertainty regarding the latitudinal variability of the MCS/MCV, and more importantly the flanking boundary on its southern periphery, do feel like we have enough confidence to suggest that once the SHRA/TSRA moves through areas near/N of I-70, the subsidence in the wake of the complex, as well as the LL moisture boundary that will settle to the south of these areas, will yield increasingly dry conditions later into the evening Wednesday for the northern 2/3 or so of the ILN FA. Further south, however, closer to the OH Rvr, it may be a far different story. Confidence remains reasonably high in the MCS laying out a quasi W-E oriented boundary on its southern flank Wednesday evening, even as the initial MCS continues to track E. This is due, in part, to the maintenance of the convergent H8 baroclinic zone/LL moisture axis stretching from WNW to ESE across far southern IN/OH and N KY. Although the best H8 LLJ will be pulling E toward later Wednesday evening/night, there will still be some subtle convergence along the LL boundary amidst an environment of increasing LL moisture convergence/theta-e advection. And as the initial S/W energy pulls E, a better northward surge of deeper moisture will commence, yielding moisture and mass convergence along the quasi-zonal boundary. It should be noted that there are considerable convectively-driven uncertainties regarding not only the placement of renewed convection Wednesday night, but also the potential coverage of such development. A stronger afternoon/early evening MCS/MCV may be enough to shunt the best convergent axis completely S of the ILN FA for Wednesday night, rendering a solution in which most of the local area trend drier during this period. A weaker midday MCS/MCV, however, is not likely to augment the placement and orientation of said axis quite as much, suggesting that the renewed convective activity late Wednesday evening may be squarely across the southern third of the ILN FA. Or it could be any number of scenarios even between the two laid out here. The primary takeaway is that confidence is high in a corridor of renewed TSRA activity late Wednesday evening into early nighttime, in which heavy rain and localized flooding will be the primary concerns, but lower in exactly where this may set up. Training storms with very efficient rain rates may translate into pockets of very heavy rain during this period. As of right now, this is favored near and south of a corridor from near the vicinity of Ripley Co IN to Pike Co OH, although confidence in exact location remains quite low at this time. The WNW-ESE oriented axis of TSRA Wednesday night, wherever that may actually line up, will gradually weaken/dissipate during the predawn hours as the LL convergence weakens and the axis shifts S subtly. This will commence a brief window -- perhaps on the order of 12 to 18 hours or so -- in which the LL and deep-layer shear weakens considerably over the region. This will coincide with the best pooling of LL moisture pivoting across southern parts of the region, perhaps even S of the immediate ILN FA through the first half of the day on Thursday. Again, latitudinal variations exist in where the instby axis will drift, but it seems plausible at this juncture that locales N of the OH Rvr will remain in a relatively stable regime through midday as the instby builds further S across KY. But by Thursday evening, however, the LL wind fields will once again be on the increase from the W/SW as the moisture boundary pivots about the region and begins to make a more concerted movement N. This will coincide with broad/large-scale height rises, which should help keep a cap in place for most spots, or even keep any renewed convection slightly elevated in nature. There remains a signal, however, for some convective redevelopment along the northward-advancing frontal boundary late Thursday evening. Model soundings vary on whether this is likely to be surface-based or slightly elevated. But the overlap of LL instby and better deep-layer shear may re-establish itself Thursday evening into early night before the area becomes more solidly warm-sectored by daybreak Friday. Considerable questions remain at this juncture in whether the lift will be enough to 1) generate convection as the boundary moves N, and 2) whether it will be slightly elevated due to an intruding warm bulge aloft, making the threat highly conditional. If it does in fact evolve to be more surface-based, a strong to severe storm potential may also evolve Thursday evening into early Thursday night across the central part of the ILN FA as this boundary pivots N. Friday will offer the only real quiet day of the stretch, with warm and humid conditions early before a tightening pressure gradient allows for an uptick in S winds, yielding an increasingly well-mixed environment toward the afternoon. Do think we will mix down sfc DPs fairly well Friday afternoon into the evening as S winds at around 20 MPH and gusts to around 30-35 MPH will be possible at times, especially near/W of I-71. Highs will top out in the upper 80s to maybe lower 90s, depending on afternoon/early evening DP trends. Guidance has come into better agreement regarding timing of the front coming through the region more to during the day/evening Saturday, which would suggest another warm and humid day for most spots locally with the slightly slower timing than was previously indicated. The overlap of instby and shear parameter spaces suggest that a severe weather episode may also be possible Saturday afternoon into Saturday night across parts of the ILN FA, depending on exact timing. Will hold off for now on in-depth discussions regarding this potential until details come into a bit better focus. Cooler/drier air settles into the region in the post-frontal environment for Sunday into early the next week.
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&& .AVIATION /07Z TUESDAY THROUGH SATURDAY/... Skies remain mostly clear overnight even with a dry cold front passing through. Winds not expected to deviate from the west- southwest flow for majority of the night, remaining around 5 kts or less. Winds will eventually switch towards the northwest Tuesday after sunrise, increasing in magnitude with diurnal heating/mixing. Northwesterly gusts of 20-25 kts will be possible through the late afternoon hours Tuesday. VFR conditions expected through the period. There will be some ~6000 ft CIGs that develop with diurnal heating on Tuesday. Tuesday night, cloud coverage will increase from the west (generally mid-level clouds). OUTLOOK...Thunderstorms possible at times Wednesday into Thursday and again Saturday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hickman NEAR TERM...Clark SHORT TERM...Clark LONG TERM...KC AVIATION...Clark

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