Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 201757 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 157 PM EDT Wed Sep 20 2017 .SYNOPSIS... A weak upper level disturbance will move through the area, offering a few lingering showers and thunderstorms today. Drier conditions are expected for the end of the week into the weekend as upper level ridging builds into the Ohio Valley. Warm temperatures will continue into the upcoming weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... With the KILN sounding measuring a precipitable water amount of 1.53 inches -- roughly 90th percentile for mid-September -- the area remains in a moist and somewhat stagnant section of the weather pattern. Fog and copious mid clouds (600mb) have existed around the area so far today. Though this has held temperatures back slightly from the previous forecast, once the sun is out the current high temperatures in the forecast will still likely be reached. Precipitation chances are tough to pin down, with just a weak shortwave moving through the area this afternoon, and no obvious signs of near-surface convergence. With a few showers already on the radar PoPs had to be increased slightly through the next few hours, but a 20 (or 30 at most) percent chances will likely be enough cover the afternoon. Previous discussion > Quick update to allow the dense fog advisory to expire, but to continue an SPS mention of fog for the next hour or two, as the areal extent of the dense fog has has diminished to an extent. A few sites (especially in a Hamilton/Warren/Clinton county cluster) remain at 1/4SM but satellite imagery suggests most of the thicker low-level moisture is confined to river valley locations. Previous discussion > Visibilites seemed to be crashing south of the mid level cloud desk, so issued a Dense Fog Advisory until 9 AM. Mositure seemed shallow enough to only issue it until 9 AM, as the fog will hopefully begin to burn off quickly. EARLY MORNING DISCUSSION>>> Weak mid level low over Central Ohio to continue to weaken and open up as ridging builds into the west. This feature combined with marginal instability may lead to a few showers and perhaps a thunderstorm. Have limited pops to very low chance/slight chance over ILn/s eastern counties. An precipitation that develops will diminish by mid to late afternoon as the mid level ridge builds into the west. Latest satl imagery shows that clearing has taken place over ILN/s southern counties. With a fair amount of lingering low level moisture, and light winds, areas of fog have developed mainly in river valleys. Will issue an SPS for reduced visibility due to the fog. Expect the fog to improve quickly this morning with partly cloudy conditions developing. Warm temperatures to continue with highs from near 80 northeast to the mid 80s southwest. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Mid level ridge to build into the Great Lakes through the end of the week. Expect clouds to diminish this evening with patchy fog developing overnight. Lows to range from the lower to middle 60s. With ridge in place expect general subsidence Thursday. Forecast soundings show an inversion and with a lack of significant forcing have opted for a dry forecast. Warm temperatures look to be around 10 degrees above normal with highs in the mid and upper 80s. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Robust ridge building at the surface and aloft will dictate weather conditions through the period. Latest models indicate 1020 mb surface high pressure over New England in conjunction with a 5900 meter 500mb high extending from the Gulf Coast to Southern Canada. The surface high is shown to retrograde under the upper high to the Great Lakes and Ohio Valley by Sunday, with the system then exhibiting modest height and pressure falls by Tuesday. This weather regime will be absent of forcing and deep moisture, with downward motion the rule in the anticyclonic circulation around the high. Dry weather is expected through the period. Mostly sunny/mostly clear skies will be observed, and temperatures will be well above normal under anomalously high geopotential heights. High temperatures reaching the middle and upper 80s Friday through Monday may slip only a couple degrees to the lower 80s Tuesday. These temperatures, being close to normal for July, will be 10 to 15 degrees above normal for late September. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... The only real concern for this TAF period is the potential for more fog overnight and early Thursday morning. First, while there is a slight chance of a shower at KCMH/KLCK this afternoon, it appears too low to include in the TAFs. Amendments will be used if showers develop and move near the airports. Overnight, fog is expected to develop again. Tempo IFR conditions are expected for most of the TAF sites, with likely LIFR fog at KLUK. The bigger question is at KCMH/KLCK, where IFR is in the forecast, but there is the potential for a period of dense fog as well. There is a chance that some brief MVFR ceilings may form on Thursday morning, but otherwise, VFR conditions are expected going into the day. Winds will be generally light and variable through the entire TAF period. OUTLOOK...No significant weather is expected at this time. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...AR NEAR TERM...Hatzos/Sites SHORT TERM...AR LONG TERM...Coniglio AVIATION...Hatzos

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