Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 201930 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 330 PM EDT Sun Aug 20 2017 .SYNOPSIS... Above normal temperatures will persist across the Ohio Valley through Monday ahead of a cold front. The cold front will bring showers and thunderstorms on Tuesday, then drier and cooler air moves in for the rest of the week. && .NEAR TERM /THROUGH TONIGHT/... Afternoon cumulus have developed across the CWA, and there`s even a couple of showers across Auglaize and Hardin Counties at 19Z. HRRR has been consistent in showing some shower activity across central Ohio this afternoon/early evening. Still believe the relatively dry/warm air aloft would limit coverage of showers and also preclude convection from growing very tall, but per radar trends and consistency with the HRRR among other models have introduced isolated showers for the next few hours across portions of central Ohio. Any showers along with cumulus will dissipate close to sunset. Then looking at infrared imagery it appears there will be some high clouds poised to move across the CWA overnight, especially later at night due to dissipating upstream convection. With clouds, fog should not be widespread nor dense, but still expect patchy fog near river valleys. && .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... Expectation is for any nocturnal upstream convection to have dissipated by the time it would make it into the CWA early Monday, although it`s not out of the question lingering showers make it into the far northwest CWA. Either way, some high clouds will be left behind for Monday morning. More cumulus are expected by afternoon as well, and therefore have started to trend the sky forecast upward a little for Monday, and it`s possible that much of the CWA could wind up more partly cloudy than mostly sunny for Monday. In addition, latest guidance suggests the potential for convective development in the afternoon/early evening mainly across the northwest portion of the CWA. Larger scale forcing is still best well northwest of the CWA, but moisture looks better and models suggest sufficient CAPE to generate a few cells as long as any capping erodes. Maxima will rise into the upper 80s, perhaps even hitting 90 in a few spots. Factoring in dewpoints in the mid 60s will yield heat index values into the mid 90s on Monday. Much of any convective activity on Monday would likely dissipate after the sun sets, but as a cold front approaches will continue with very low pops across the northwest corner of the CWA late at night. && .LONG TERM /TUESDAY THROUGH SUNDAY/... The main focus for the long term period will be the potential for severe weather and flash flooding on Tuesday. Thunderstorms will begin to move into northwestern portions of the forecast area Tuesday morning. In addition cannot rule out some isolated convection along and just southeast of Interstate 71 during the late morning and into the afternoon hours. These storms will have a damaging wind and hail potential. As the line of storms across northwestern portions of the forecast area move towards the southeast it will encounter a better environment with higher, although not substantial, cape values. Expect the main threat with the line to be damaging winds with locations northwest of Dayton having the lowest threat and a higher threat along and just southeast of Interstate 71. With the flow orientation believe that the wind threat south of the Ohio River will be a little less, however isolated damaging winds will still be possible. With the orientation of flow and the potential for the multiple rounds of thunderstorms, flash flooding will also be a concern generally southeast of Interstate 71. The cold front will move through Tuesday night. This will be followed by cooler and drier conditions for several days. With good CAA Wednesday and Thursday increased cloud cover substantially with cu expected to develop during the day on both of these days. Expect less cloud cover on Friday and Saturday as we lose the CAA. Temperatures Wednesday through Saturday will generally be in the 70s across most locations. Another system begins to approach for Sunday so there will be an increase in cloud cover and precipitation chances will begin to move back into the region. Temperatures will also be slightly warmer on Sunday with WAA. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... Cumulus have already developed this afternoon, although with limited vertical extent. HRRR continues to suggest a few showers developing later this afternoon or evening, potentially affecting KCMH/KLCK but believe it`s too dry/warm aloft and therefore kept TAFs dry. Cumulus will dissipate this evening with the setting of the sun. Then expect some cirrus overnight particularly late and into Monday morning due to upstream convection. This may interrupt fog formation somewhat, but at least river valley locations should see patchy fog and thus KLUK and also KLCK have inclusion of visibility reductions. In addition to high clouds, more cumulus build ups are expected Monday late morning/afternoon under southerly flow. OUTLOOK...Thunderstorms are likely Tuesday into Tuesday evening. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...BPP NEAR TERM...BPP SHORT TERM...BPP LONG TERM...Novak AVIATION...BPP

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