Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 201957 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 357 PM EDT Mon Aug 20 2018 .SYNOPSIS... Surface low pressure will track northeast from the mid Mississippi Valley across the Great Lakes Tuesday. Showers and thunderstorms will overspread the area ahead of an approaching warm front. Precipitation will continue tonight and Tuesday as a cold front sweeps east across the area. In the wake of the cold front, a much cooler and more comfortable airmass will move into the area, bringing dry weather through the remainder of the work week. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... Mid level low evident on WV imagery over IA/MO border. This low to open up and track into the Great Lakes overnight. Axis of convection associated with warm advection arm/isentropic lift pivoting into southwest Ohio. This arc of convection to pivot northeast though ILN/s FA through early evening. Boundary layer CAPE values of 1000-1500 j/kg feeding these storms with bulk shear of 25 to 30 kts. DCAPE values around 1000 j/kg ahead of these storms. A few of the stronger updrafts will have the potential to produce strong to severe winds mainly over the western counties early. Models solutions continue to highlight an axis of precipitable water values in excess of 2 inches. So along with wind, some of the storms will likely contain heavy rainfall. HWO product accurately describes the weather threats. Have increased pops to categorical to account for this early convective band. Expect a general lull (decrease in coverage) in convective activity until favorable forcing re-develops late tonight when a low level jet comes into play. By this time instability is marginal with blyr instby of less than 1000 j/kg. Have pops ramp back up late tonight to account for this enhanced forcing. Expect mild lows from the upper 60s to around 70. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Low level jet with enhanced convergence ahead of initial sfc front/trof will lead to a good chance for showers and thunderstorms late tonight into Tuesday morning. Have likely pops early. Linger these likely pops into Tuesday aftn over the east, where airmass has a better chance to destabilize. Even in the east cloud cover should limit instby to 1000-1500 J/kg. Better chance for severe east of ILN/s area but can not rule out a damaging wind event or two in the far east. Highs to range from the upper 70s northwest to the lower 80s southeast. Secondary front/trof to pivot through the area Tuesday evening. This will keep the threat for showers and perhaps a thunderstorm with marginal instby over the area. Drier air will begin to advecting into the area but clouds will be slow to scatter out. Expect lows from near 60 northwest to the mid 60s southeast. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... At the start of the extended forecast period on Wednesday morning, a mid-level trough will be in place across much of the eastern half of the CONUS, with surface high pressure beginning to move eastward from the plains states. The trough will move east and allow for broad ridging to build into the Ohio Valley by Thursday morning, with the surface high entering the region. By Friday, ridging will be more firmly established over the Appalachians, with the surface high moving off the mid-Atlantic coast. This pattern supports a typical gradual warming trend through the second half of the week, with the air mass remaining relatively dry. It is a typical pattern perhaps more likely to occur a month or so from now, but it will provide a period of below-normal temperatures on Wednesday, Thursday, and Friday. Starting out with highs in the lower to upper 70s on Wednesday, temperatures by Friday will have adjusted upward only slightly -- upper 70s to lower 80s. The weather pattern will continue to adjust over the weekend, switching to more of a warm-advection and potentially stormy scenario. On Saturday morning, there will be an increase in southerly flow into the Ohio Valley, as a mid-level trough positions itself just upstream of the region. This will support the development of precipitation on Saturday -- right now appearing to favor the early part of the day. Admittedly there is good agreement in the last two runs of both the GFS/ECMWF on timing, but this is a change from yesterday, so PoPs will be kept in the 20-30 percent range until this solution gains a little more temporal continuity. There is high confidence in a ridge settling into the southeastern states through the rest of the weekend and into next week, with low confidence in the timing and magnitude of any shortwaves moving across the northern tier of states during this time frame. As such, PoPs will be kept in the 20-percent range through the weekend, with temperatures continuing to gradually warm into the middle to upper 80s by Sunday and Monday. && .AVIATION /19Z MONDAY THROUGH SATURDAY/... Axis of thunderstorms developing across Indiana ahead of an approaching warm front. These storms to pivot northeast through the TAF sites this aftn into the early evening. VFR conditions may drop down to IFR in thunderstorms for a brief period. Have covered this threat with tempo groups for thunderstorms, IFR visibilities and MVFR ceilings. After these storms move through, expect a general lull in pcpn activity through the remainder of the evening with VFR conditions. Another enhanced chance for storms will occur late tonight when a low level jet shifts northeast into the Ohio Valley. Instability will be marginal at this time, so have covered this threat with prevailing showers and VCTS. With the approach of a surface cold front expect ceilings to drop to MVFR category late tonight into Tuesday morning. As surface winds shift to the southwest and then west on Tuesday gusts of 20 to 25 kts will be possible. OUTLOOK...Chance of thunderstorms into Tuesday evening. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...AR NEAR TERM...AR SHORT TERM...AR LONG TERM...Hatzos AVIATION...AR

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