Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 241437 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 1037 AM EDT WED AUG 24 2016 .SYNOPSIS... With upper level ridging over the southeastern states, warm and moist air will begin to flow into the region today. Embedded waves in the mid-level flow will bring chances for showers and storms today and Thursday, in the northern Ohio Valley and southern Great Lakes. High pressure over the Great Lakes will bring drier conditions for Friday and Saturday, before chances for storms increase slightly on Sunday and into the new week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Cluster of storms along the Illinois-Indiana border late this morning should weaken as they head east across the instability gradient. However increasing moisture along with daytime heating...albeit somewhat limited due to cloud cover...will allow for destabilization across the forecast area with CAPE over 1000 J/kg. In addition...precipitable water will increase to around 2 inches. Short wave in eastern Iowa will continue east northeast...so main forcing will pass north of the area. However...additional storms along the tail end of this system will move into the region during the afternoon. There could be sufficient instability for some stronger storms into the northwest counties. These stronger storms may produce gusty winds and locally heavy rainfall. Forecast highs look reasonable at this point.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/... The thermodynamic environment over the Ohio Valley will continue to modify from Wednesday into Thursday, with a steady stream of theta-e advection to the north of the upper ridge. 850mb temperatures are forecast to gain another 3C-4C by 18Z Thursday, and forecasts for surface temperatures have responded in kind -- no doubt, also helped by the slightly drier forecast, as will be discussed later. Interestingly, SREF plumes do not seem to be totally picking up on the warmer forecasts, and the new max temp grid for Thursday is way at the high end of the SREF spread (but in line with raw GFS/NAM projections). This allows for lower 90s in the southern third of the ILN CWA, with upper 80s elsewhere. The zone of quick WSW winds aloft will remain in place just northwest of the forecast area on Thursday, and will actually become even better established. Still, the forcing along with this feature (and a weak shortwave) will remain focused too far north for a direct impact to the middle Ohio Valley, and if anything, models have been a little more explicit in keeping drier conditions in place for Thursday. Though this shift means a lesser chance of convective debris affecting the area on Thursday morning, it`s still a possibility. That would really be the only limiting factor for instability, with SREF means (running on boundary layer temps that may actually be too low) indicating MLCAPE values of up to 2500 J/kg. Overall, the kinematic and forcing pattern looks quite similar to Wednesday, but with greater instability, and a little bit stronger shear as well. That will mean that if storms are able to propagate this far south and east, the threat for some strong storms will exist, with a primary threat of wind damage. Coverage is really the big question mark, and PoPs remain quite conservative. Until this comes into better view, it seems premature to add the threat to the HWO. As the dampening upper level wave moves east into Quebec, a very weak surface front will make some progress into the ILN forecast area on Friday, though it may never clear through the area before stalling (or washing out). The weak forcing warrants nothing more than a 20-percent chance during diurnal timing in the southern third of the forecast area, with only the northern half of the forecast area seeing a notable drop in temperatures from Thursday to Friday (and even that will only be by about 5 degrees). A slightly drier air mass, courtesy of a large area of high pressure, will settle in over the Great Lakes region on Saturday. Dry and mostly sunny conditions are expected, allowing for temperatures to increase by a degree or two from Friday, despite light wind flow and a fairly neutral advection pattern. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... For Sunday, moisture and energy spilling southeastward from Great Lakes low pressure will provide a chance of thunderstorms. Additional thunderstorms will be possible Monday when the low is forecast to drag a cold front across Ohio. A few thunderstorms may persist on Tuesday as the boundary sags gradually south to Kentucky. With a large and slow moving high in the upper atmosphere centered from the Central Appalachians to the Mid-Atlantic coast, and with mainly warm advection in the lower levels, a return to mid-summer heat is indicated. High temperatures ranging from the mid 80s to the low 90s will couple with dew points near 70 to make outdoor activities uncomfortable at best. && .AVIATION /15Z WEDNESDAY THROUGH SUNDAY/... A mid level ridge over the lower Gulf Coast states will slowly build northward through the TAF period. At the same time, embedded disturbances will rotate eastward through the Great Lakes. Return moist flow, along with the proximity of the disturbances, will bring at least a chance of showers and thunderstorms to the terminals today. Chances do not appear high at this time, but it looks like all terminals will see enough of a threat for a VCTS/CB to be employed. Southeast to south surface flow will become south later this morning around 10 to 12 knots with some local gusts in the 15 to 20 knot range by afternoon. For tonight, the latest high resolution/convection allowing models indicate that the threat for showers/storms overnight will likely be closer to the lower Great Lakes, or mainly north or northwest of the terminals. As a result, have just VFR conditions at this time. OUTLOOK...Thunderstorms possible from Thursday into Thursday night, mainly near the northern terminals. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hatzos NEAR TERM... SHORT TERM...Hatzos LONG TERM...Coniglio AVIATION...Hickman

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