Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 281053 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 653 AM EDT Sun May 28 2017 .SYNOPSIS... With warm and moist air in place, showers and thunderstorms will be possible today ahead of a cold front. Drier conditions are expected behind the front overnight, with occasional slight chances of precipitation through the first half of the week, and temperatures close to normal. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A large expanse of convection currently stretches from central North Carolina to northeastern Texas, with virtually all of the fresh development on the southern periphery, and mostly stratiform precipitation to the north. The ILN CWA is well north of even the edges of the lighter rainfall, and the vast majority of 00Z model runs support what observational analysis has been suggesting for a while now -- only very slim chances of any precipitation over the next several hours. What is setting up for this afternoon is a scenario that, out of all the convective events (or non-events) over the past several days, may be the most straightforward -- diurnal destabilization ahead of a surface trough, leading to convective development near peak heating. Will this activity be severe? It certainly appears to be a possibility, but with several caveats that will clamp down on a higher-end or more widespread risk. Destabilization will be sufficient, but not significant. Advective flow in the boundary layer will not be especially favorable -- WSW out of the lower Ohio Valley, rather than more southerly. It is uncertain if dewpoints in the ILN CWA will be able to rise more than a couple degrees from their current readings. In terms of insolation potential, while preliminary / non-operational GOES-16 imagery suggests a gradual dissipation of the blowoff clouds from the southern convection, stratocumulus is also developing -- and should continue to develop through morning. Thus, skies will probably never truly clear out today. These muted expectations translate to instability forecasts (MLCAPE) in the 1000-1500 J/kg range, and probably toward the lower end of that scale. Shear and forcing will also be sufficient, but not significant. When looking at the wind shift and theta-e gradients, it is apparent that the surface trough is not sharp, and its convergence is not especially focused. Ahead of an upper trough, there will be support for ascent, with WSW flow increasing at 500mb going into the afternoon hours. However, the stronger winds aloft do not arrive until after precipitation is expected to be ending. The result is that shear will be strong enough to support storm organization -- around 40 knots -- but it will be largely-unidirectional. Taking these factors together, storms are expected to develop ahead of the trough (mainly eastern IN / western OH) after 19Z, though the storms will be more scattered than focused. Through the peak of the diurnal cycle, there will be enough instability to support some of the storms becoming severe, with shear that will allow for some organization -- mainly in clusters and bows, though perhaps some supercell structures early in the evolution. Not sure it is possible to pick out a specific section of the ILN CWA for a greater threat than anywhere else, but this has the looks of a fairly standard slight-risk type event. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... Behind the surface trough, precipitation is expected to come to an end in the 00Z-09Z time frame, with drying conditions leading to clearing skies by Monday morning. With fast flow aloft to the south of an upper low in the northern Great Lakes, another surface trough will be moving into the ILN CWA late in the day. With a drier air mass in place, most of the precipitation will probably hold off until Monday evening. While the Sunday evening trough/front will do little to change temperatures over the region, with max temps Monday expected to be very similar to Sunday -- mid 70s to near 80. However, the big difference will be in the dewpoint temperatures -- a drop from the mid 60s to the mid 50s. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... The immediate long term period, Monday night through Wednesday, will feature a closed upper level over Ontario, which will slowly rotate east/northeast through this period. Embedded disturbances rotating around this low, complimented by weak cold fronts/trof axes, will keep a low threat for showers and thunderstorms going, mainly during the peak heating of the day. High temperatures should remain in the 70s with the coolest day occurring on Wednesday. The upper level closed low will elongate and finally shift more to the northeast such that a ridge of high pressure will build southeast into the Ohio Valley Wednesday night into Thursday. After a cool start in the lower 50s, highs should rebound into the mid and upper 70s. The remainder of the extended becomes a bit muddled as we head into next weekend. General model consensus is to bring another piece of upper level energy in the form of a closed low southeast into south central Canada by Friday and then slowly push it east across southeast Canada/northern Great Lakes through the weekend. Return moist flow around the departing high and between a slow moving frontal boundary from the north will bring the threat for showers and thunderstorms to the region. Temperatures will remain near seasonal normals for early June. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/...
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Pockets of low clouds have begun to develop across the area, with IFR ceilings now developing in spots. This may continue through the next several hours, so the TAFs have been updated for this. By late morning, ceilings are likely to lift to VFR. After that, attention will turn to chances for showers and storms during the mid afternoon into the evening hours. Where storms occur, MVFR/IFR conditions and gusty winds will be possible. However, with some questions about the amount of storms that will develop, will keep the TAF mention to VCTS. Clearing is expected behind the storms, with VFR conditions going into the overnight period. There are some indications that there may be reduced visibilities tonight, but the air mass will be drying, so this is not yet certain. OUTLOOK...No significant weather expected.
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&& .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hatzos NEAR TERM...Hatzos SHORT TERM...Hatzos LONG TERM...Hickman AVIATION...Hatzos

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