Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 230228 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 1028 PM EDT Mon May 22 2017 .SYNOPSIS... A ridge of high pressure will remain across the region tonight and Tuesday. Rain chances will increase as low pressure approaches the region from the southwest late Tuesday night, and then moves north through the area Wednesday. Rain showers may linger on Thursday, as the low begins to move east and cooler conditions return to the area. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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Center of surface ridge over the upper Ohio Valley this evening will move to southern New England by Tuesday morning. Its ridge axis will continue to extend into our region into Tuesday. Satellite imagery shows enhanced cirrus shield moving up from the southwest should encompass the region tonight. As a result, have increased sky percentage to allow for mostly cloudy conditions. Overnight lows will dip into the lower 50s.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Jet energy will dig south across the northern plains sharpening up a trof Tuesday and eventually carving out an upper level low over the mid MS Vly Tuesday night. Expect to see an increase in high and some mid level clouds during the daylight hours Tuesday. The digging system will delay the eastward push of deep moisture and precipitation. Expect Tuesdays highs to be close to normal, ranging from the lower 70s northwest to the mid 70s southeast. Have opted for a slower onset of precipitation with low level easterly flow. Have limited rain shower pops to chance category spreading in from the southwest Tuesday night. Expect Tuesday nights lows to be in the lower and middle 50s. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... On Wednesday morning, a deepening upper-level trough will be gradually moving southeast into the middle Mississippi Valley region, as southwesterly flow aloft becomes more established over the southeastern states. As this trough closes into a low, surface cyclogenesis is expected to occur in the lower Ohio Valley, with all models now depicting a deepening surface low rotating north through somewhere near the IN/OH/KY corner during the first half of Wednesday. Ahead of the surface low, widespread precipitation now appears likely, so PoPs have been increased to 70 percent and will likely have to go higher at some point in future forecasts. As colder air moves in aloft near the upper low, steepening mid-level lapse rates should allow for at least some instability to develop, especially on the back edge of the main precipitation area. This will allow for a chance of thunder, in a regime with forcing and cyclonic turning associated with the surface low. This may allow for a few organized storms, though marginal shear and instability values make any level of severe threat very uncertain, and differences with regards to the track of the surface low also preclude defining an area for any potential risk. The forecast is always worth a second look when assessing a deepening surface low moving through the area in the spring. Will keep the HWO blank for now, but continue to watch as additional model runs lock in the pressure patterns a little closer. A dry slot is expected to move into the area (particularly the southeastern CWA) on Wednesday evening, as additional precipitation becomes more focused in the higher theta-e air on the back side of the upper low. This will bring another area of precipitation through the ILN CWA on Thursday, as the upper low passes overhead, perhaps again providing some weak instability due to the cooler air aloft. However, there is a wider range of solutions regarding the placement of enhanced vorticity around the low on Thursday, so PoPs will be kept on the lower end until agreement improves. Both Wednesday and Thursday will see relatively cooler temperatures, with highs in the 60s both days -- below normal for late May. 12Z GFS/ECMWF runs have, interestingly, continued to trend faster going into the weekend -- not just with the departure of the upper low on Friday, but with additional precipitation chances beginning early Saturday. Beyond that, model spread remains somewhat high for the weekend forecast, as a series of shortwaves is expected to move eastward across the region in the pseudo-zonal flow. At least initially, it is likely that some sort of surface boundary will exist across the region, with greater theta-e just to the south. Though this may eventually shift northward, this pattern is one that would support multiple rounds of showers and storms within an increasingly moist air mass. Thus, there will be at least some potential for both stronger storms as well as heavy / repeated rainfall for Saturday and Sunday. Within the GEFS suite and from run- to-run of the operational ECMWF/GFS, there are still big differences in wave amplitude/timing, negating the ability to forecast the specifics. For now, lower-end PoPs will be maintained through the entire weekend (though this has been increased from the previous forecast), with slightly above normal temperatures. This may come to an end with a cold frontal passage late Sunday into Monday, leading to drier conditions to start next week. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... VFR conditions can be expected through the TAF period. The center of high pressure over the Ohio Valley this evening will move northeast to a position over southern New England by Tuesday morning. A ridge axis will still extend southwest into the region on Tuesday. Varying amounts of mid and high level clouds will stream overhead through Tuesday. Calm/light and variable winds will become east on Tuesday. OUTLOOK...MVFR ceilings and visibilities possible Wednesday into Thursday, and again Saturday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hickman/AR NEAR TERM...Hickman SHORT TERM...AR LONG TERM...Hatzos AVIATION...Hickman

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