Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 261401 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 1001 AM EDT Wed Apr 26 2017 .SYNOPSIS... Southerly flow will result in warm and dry weather today. A cold front will push across the region on Thursday with high pressure briefly building in behind the front. Conditions will become unsettled over the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Satellite imagery shows a band of cirrus moving into the western parts of the area. This will move across the region by mid afternoon with clear skies for the remainder of the day. Winds will continue to increase and become gusty. Forecast highs look reasonable at this point. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Embedded s/wv in the flow will eject from the southern Plains to the middle Mississippi River Valley tonight. As this occurs, low pressure will ripple along the cold front, eventually lifting north into the western Great Lakes. This will allow the cold front to approach the region tonight. Skies will start out mostly clear this evening/early morning with clouds increasing from the west. Low level moisture convergence in the form of a strong 850 mb low level jet will bring showers and embedded thunderstorms to our western CWFA between 09Z and 12Z. On Thursday, embedded s/wv will move into the western Great Lakes while the cold front advances east across the forecast area. Instability will have waned by Thursday morning, and not a lot of uptick in instability is expected as clouds increase and the front moves into the eastern forecast area by 18Z. Although a strong low level jet will exist initially, the low level 0-3 km shear vector is mainly parallel to the forecast orientation of the precipitation. This does not bode well for much in the way of bowing segments. Finally, with the s/wv passing north by afternoon, convection will become more scattered as it advances into our eastern CWFA. Thus, the threat for severe storms will remain marginal/isolated as in agreement with SPC SWODY2. After a warm start in the lower to mid 60s, temperatures will have a muted warming trend given some CAA by afternoon and cloud cover. Highs will range from the upper 60s west to the mid 70s east. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... A shortwave and cold front will be pulling northeast of the region on Thursday evening, leading to gradually (though partially) clearing skies. With this front and shortwave glancing through the region, rather than ushering in a major change in air mass, temperature recovery in southerly flow on Friday should be strong -- and in fact, it could end up warmer than Thursday due to the lack of rain. As height rises occur on Friday into Saturday, with ridging becoming established across the southeastern states, another big wave in the pattern will begin to develop over the central plains. As this occurs, 00Z models have been more insistent on a strengthening and re-positioning of the old frontal boundary, leading to significant frontogenesis over the Ohio Valley on Saturday. With a tightening theta-e gradient across the region, this front will likely act as a focus for shower and thunderstorm development -- perhaps as soon as Friday afternoon, but especially going into Friday night and Saturday. Most of the precipitation is expected to be focused along and north of the front, where surface-based instability will be limited, but elevated instability will allow for convection. Where model solutions begin to diverge is on potential drying south of the boundary in the warm sector, as well as on specific timing or magnitude of any waves of showers/storms during this time frame. There remains strong agreement in the general pattern for Sunday into Sunday night, with deepening low pressure at the surface and aloft ejecting from the plains into the Great Lakes, driving a strong cold front through the Ohio Valley. It looks mostly certain that the ILN CWA will end up completely in the warm sector within a regime of deep and strengthening southerly flow, before precipitation becomes more likely in the second half of the day. Of concern is the inconsistency with which the placement and strength of the upper low has been handled -- both from model to model and even within the GEFS solutions, which diverge most significantly from Sunday morning onward. For this reason, no attempt at a specific forecast for hazards will be made at this juncture. With that said, depending on how the pattern ends up working out, some threat for heavy rain and severe weather could occur. With flow looking mostly-meridional, that could certainly be one limiting factor for a severe threat, but the magnitude of the flow will offset that to a degree. Behind this front, as opposed to the Thursday system, there will be a notable change in air mass -- and strong cold advection that will likely lead to wind gusts in the 30-40 MPH range. Something to add to the HWO once this gets a little closer in the forecast cycle. Temperatures appear likely to remain above normal through the weekend, though the very sharp temperature gradient currently forecast for Saturday results in lower-than-normal confidence there. Sunday could be very warm, especially if the drier warm sector solutions verify, and most notably in the southeastern ILN CWA -- with mid 80s in the forecast and possibly some room for that to move. Behind the front on Monday, there will be a significant drop in temperatures -- a difference of around 20 degrees from Sunday. This forecast will continue to undercut the general model blend, coming closer to raw GFS/ECMWF numbers for Monday. No signs of significant weather on Tuesday or Wednesday, with some gradual warming expected in pseudo-zonal flow. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... For today, mid level ridge shifts east while a cold front moves east into the western Great Lakes and middle/lower Mississippi River Valley. Only some SCT cirrus is expected. Southerly winds will increase through 18Z and will become locally gusty between 20 and 25 knots. For tonight, an embedded disturbance will eject from the southern Plains into the middle Mississippi River Valley. This will perturb an area of low pressure on the cold front to our west which will begin to make inroads east as the low ripples northward toward the western Great Lakes. Showers and embedded thunderstorms are expected along and ahead of the front in an axis of low level moisture convergence and upper level support. These showers and embedded storms will move toward the western terminals toward 12Z. Winds will stay locally gusty overnight as the pressure gradient tightens. With a strong low level jet, non-convective LLWS is expected to develop overnight. OUTLOOK...MVFR ceilings and visibilities along with a chance of thunderstorms on Thursday. MVFR ceilings and visibilities with a chanced of thunderstorms again Friday night through Sunday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hickman NEAR TERM... SHORT TERM...Hickman LONG TERM...Hatzos AVIATION...Hickman

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