Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 250557 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 1257 AM EST Sun Feb 25 2018 .SYNOPSIS... Abundant moisture will continue to bring areas of heavy rain to the area through tonight. A cold front approaching from the west late tonight will also bring a chance of strong thunderstorms. Dry conditions will arrive behind the front on Sunday and continue into Monday. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... Widespread showers and embedded thunderstorms were ongoing this evening north of a warm front to our south. With PWATs rising above 1.30 inches, heavy rain is also occurring in the more robust showers and storms, resulting in flooding and flash flooding. Widespread showers and embedded storms will continue into the overnight hours until a cold front sweeps the precipitation to the east. Am still waiting to see how far north the warm front will come into our region and whether some strong to severe storms develop given high shear, a strong LLJ aloft, but weak CAPE. Will continue to monitor through the night. Otherwise, flooding and flash flooding will be of great concern given saturated soils and very heavy rainfall for this time of the year which will almost certainly go straight into runoff. Temperatures will rise this evening/early morning, then fall behind cold frontal passage. Previous discussion---> Moist southwesterly flow with a tropical connection evident on water vapor imagery. This mornings mid level shortwave and associated low level jet have pivoted to the east...leaving the region in a temporary lull in pcpn activity. Focus shifts to energetic mid level s/w which ejects northeast from the plains into the Great Lakes and takes on a negative tilt overnight. E-W oriented front over KY to push back north this evening with non-diurnal temperature rises. Model solutions continue to show very strong dynamics with 75-80 kt swrly low level jet developing into the Ohio Valley this evening. This will allow pw/s to increase and approach 1.4 inches...which would be a record for this time of year. There has been good spread in how this event plays out, with a pre-frontal wave of pcpn and then the strong cold front which passes thru late tonight/early Sunday. More evidence pointing to a pre-frontal cluster of showers and perhaps embedded storms late this evening. Regional radar mosaic showing this development over western KY. Expect this pcpn to move northeast up the Ohio Valley through the evening. The main impact from this pcpn will be heavy rain and the potential for flash flooding. CAM solutions have been trending this way and therefore more confidence in this part of the event. Additional rain of 1 to 2 inches likely with local amounts in excess of 3 inches possible. Although the storms will be progressive, with an increase in pw/s...flash flooding will be possible tonight with this embedded convection. The potential for severe weather is conditional and therefore more uncertainty exists. Marginal instby expected to develop into the tri-state region and get pinched off overnight. With strong wind flow...damaging winds will be possible with this convection. Due to the favorable shear in the lower levels, isolated tornadoes will be possible. The best time for severe weather looks to be between 2 am and 7 am. Also, with the pressure gradient increasing behind the front, wind gusts up to 40 mph will be possible late tonight outside of storms. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/... Strong surface cold front to sweep east of the area early Sunday bringing an end to the severe weather and flooding threat, although river flooding will continue. With the strong pressure gradient continued wind gusts up to 40 mph will be possible early. Surface high will build in from the southwest on Sunday. Per previous forecast thinking, expect early highs on Sunday in the east. In the west temperatures will fall in morning, before recovering a little in the afternoon. High clouds will overspread the area Sunday night as mid level energy passes to our southeast. Temperatures will be cooler with Sunday nights lows from the lower 30s northwest to the upper 30s southeast. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... On Monday morning, a large area of surface high pressure will extend from Texas to western Pennsylvania, enveloping the Ohio Valley in a pleasingly dry air mass. The center of this strong high is expected to drift eastward into the mid-Atlantic states through Tuesday, with dry conditions continuing through Tuesday night. The switch to southerly flow on the back side of the high will allow for some increase in clouds on Tuesday, but also an increase in temperatures. The main concern through the extended forecast period is the complex weather system moving into the region between Wednesday morning and some indeterminate time later in the week -- the latter statement a reflection on the inconsistency in the way the developing mid-level low is being handled by the models. Initially, an expansive area of precipitation is expected to develop early Wednesday morning through the day across the Tennessee Valley and southern Ohio Valley regions, largely forced by low-level warm advection and upper-level divergence and jet support. This first round of precipitation will affect the ILN CWA but will be more of an issue further to the south, with a fairly consistent signal for the heavier rainfall to miss the forecast area. Rapidly strengthening forcing ahead of the sharpening mid-level trough (which eventually will close off into a low) will spread greater rainfall chances across the forecast area on Wednesday night into Thursday, with the potential for wrap-around precipitation in the cold advection behind the low. The main differences in the models regarding this system are in the speed of the development of the mid-level low and its eventual progression to the east. While the 06Z/12Z GFS runs were fairly consistent, the 00Z/12Z ECMWF runs swung wildly from a flat and progressive solution to one that is more wound up and even slower than the GFS. Nonetheless, even the GFS ensemble members show a wide spread in the position of the low. Overall, given these issues, PoPs were changed very little from the previous forecast -- with some slight extension outward in time to allow for some light rain/snow to continue into Friday morning. Though there is likely attention on this system with regards to rainfall potential, given the very wet conditions over the Ohio Valley, it currently looks a little too soon and too uncertain to say if this expected rainfall will lead to additional flooding problems. On the warm side of the mid-week system, temperatures will remain fairly warm -- with highs in the upper 50s to lower 60s. Once a cold front moves through (currently expected in the Thursday night time frame) cooler conditions will move in for Friday and into the weekend. Even still, conditions at the end of the extended period will be fairly close to normal. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/...
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Showers without any thunderstorm activity will persist for the next hour at KILN and KCMH/KLCK with VFR conditions expected to expand west to east. A brief patchy shower may occur for the hour or two ahead of the actual cold frontal passage that should reach the western TAF sites along the I-75 corridor around 9-11z with strong westerly winds gusting to 30kt. Any low cigs will last an hour behind the fropa and then scour out in favor of VFR conditions and a slightly less gusty west winds by 15z. Timing in the eastern TAF sites is about an hour behind this. West winds will lose any gusts in the late day, and any lingering cigs will dissipate by late morning. OUTLOOK...MVFR conditions possible Wednesday and Thursday in showers.
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&& .ILN WATCHES/WARNINGS/ADVISORIES...
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OH...Flood Watch until 10 AM EST this morning for OHZ026-034-035- 042>046-051>056-060>065-070>074-077>082-088. KY...Flood Watch until 10 AM EST this morning for KYZ089>100. IN...Flood Watch until 10 AM EST this morning for INZ050-058-059- 066-073>075-080.
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&& $$ SYNOPSIS...AR NEAR TERM...Hickman/AR SHORT TERM...AR LONG TERM...Hickman AVIATION...Franks

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