Area Forecast Discussion
Issued by NWS Wilmington, OH

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271 FXUS61 KILN 211926 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 326 PM EDT Sun May 21 2017 .SYNOPSIS... A cold front will move east through the region early this evening offering scattered showers and thunderstorms. High pressure will build in for the beginning of the week offering drier and cooler conditions. Another system will approach the Ohio Valley at midweek, bringing chances of rain back into the area. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... Mid level low pivoting north through the western Great Lakes as s/w rotates around its east side. Associated surface cold front pushing east through eastern IN. Scattered showers and thunderstorms were developing across eastern Indiana/western Ohio in the marginally unstable airmass ahead of this cold front. This front will push east across ILN/s FA this evening offering chance pops for showers and perhaps a rumble of thunder. Rain chances to end with the passage of this front. Latest visible imagery shows dry slot across southern IL and western IN. Expect decreasing clouds with sfc high pressure beginning to nose in overnight. Drier air and clearing will provide cooler temperatures overnight. Expect lows from near 50 west to the mid 50s east. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Elongated mid level low to work through the northern Great Lakes with surface high pressure building into Ohio Monday afternoon. This high will offer drier conditions and temperatures a little below normal. Expect to see a good deal of sunshine with mainly just some thin high level clouds during the day. Mondays highs to range from the upper 60s north to the lower 70s south. Surface high pressure will shift east with mid level flow backing southwest. Mid and high level clouds will increase overnight with dry conditions continuing. Expect lows Monday night in the mid and lower 50s. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Surface high pressure will be departing the region to the east on Tuesday, as the upper level flow pattern begins to amplify over the region. Spawned from an upper low moving from northern Ontario to northern Quebec, a secondary upper trough (and eventually a closed low) will move south through northern Mississippi Valley region, as southwesterly flow aloft becomes more established over the southeastern states. Caught somewhat between these two features, the ILN CWA will remain dry for the first part of the day. There remains decent model agreement that most of the southern stream moisture will remain near and east of the Appalachian mountains, so attention for the middle Ohio Valley will turn to the forcing just ahead of the low, which will result in gradually increasing precipitation chances from Tuesday afternoon through Wednesday morning. There is also confidence in some degree of surface cyclogenesis in the region on Wednesday, with the greatest chances for precipitation being just ahead of this feature, mainly during the first half of Wednesday. Instability appears limited in the cooler air mass associated with the upper low, so while thunder chances are not zero, they will be low (and maybe limited to diurnal timing). Though Tuesday should be able to reach the lower 70s (especially if there are clearer skies ahead of the incoming system), a cool-down is expected for Wednesday, with the warmest conditions (mid to upper 60s) across the eastern half of the CWA (and lower 60s in the west). 12Z GFS/ECMWF runs have, interestingly, trended faster with the progression of the upper low -- keeping rain chances around for Thursday, but leaving Friday mostly dry. Will compromise this with the previous forecast (and a desire to not go too fast with the departure of an upper low) by allowing PoPs to continue into Friday morning for the eastern half of the CWA. Though Thursday will remain similar in temperature to Wednesday, fairer weather conditions will allow for a notable increase in temperatures on Friday. Model spread is quite high for the weekend forecast, giving low confidence in the specifics. A very brief period of ridging is expected to move across the Ohio Valley on Friday, before a series of shortwaves in the pseudo-zonal flow begin to affect the region on Saturday and Sunday. Within the GEFS suite and from run-to-run of the operational ECMWF/GFS, there are insurmountable differences in wave amplitude/timing. For now, low PoPs will be maintained through the entire weekend, with slightly above normal temperatures. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... Scattered showers and thunderstorms were developing across eastern Indiana in the marginally unstable airmass ahead of a surface cold front. This front will push east across the TAF sites this afternoon offering MVFR CIGs and scattered thunderstorms. With the cold front passage winds will shift to the west and conditions will improve to VFR late this afternoon across the western taf sites and early evening in the east. Surface high pressure to build in from the west becoming centered over the region Monday afternoon. This high will provide drier air and VFR conditions. OUTLOOK...MVFR ceilings possible Wed and Thurs. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...AR NEAR TERM...AR SHORT TERM...AR LONG TERM...Hatzos AVIATION...AR is the U.S. government's official web portal to all federal, state and local government web resources and services.