Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 271827 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 227 PM EDT Thu Apr 27 2017 .SYNOPSIS...
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A cold front will move east of the area this afternoon. High pressure will briefly build in behind the front tonight. A frontal boundary will develop into the region late Friday and linger near the area into Saturday night.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Cold front bisecting the forecast area will move out of our counties by 6 pm. A bit of instability is developing ahead of the boundary, so some thunder may occur. But for the most part expecting scattered showers. High pressure will build in from the southwest overnight. This will allow skies to clear in the evening. However, expect mid to high clouds to start spreading back in before daybreak. Appears that there may be some valley fog across the southeast where clouds will be later to develop. MOS blend looked reasonable for lows.
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&& .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
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High pressure will move off to the east Friday morning. An east-west front will begin to develop into the southwest counties in the afternoon. This front will become sharper and lift into the northern part of the forecast area Friday night. Some showers may develop in western counties before the end of the day. But activity will increase overnight as mid level short wave moves through southwest flow which will induce a low level jet, enhancing lift. Models are spreading elevated instability across the region which could be sufficient for some severe storms with large hail. In addition, there is a risk of heavy rainfall. However, there is quite a bit of uncertainty on details. Given model differences, forecast has leaned quite a bit on the SREF. Forecast temperatures are on the warmer side of guidance.
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&& .LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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As frontogenesis continues to occur into Saturday, the surface boundary appears likely to set up directly over the ILN CWA. This will result in a significant gradient in both temperatures and weather, with continued chances for showers and thunderstorms gradually shifting north, but a very warm and likely capped air mass further south. Additional precipitation thus looks like more of a concern in the northern half of the ILN CWA on Saturday, then perhaps only with disorganized activity in the northwestern CWA by Saturday night and into Sunday. Temperatures are expected to range by as much as 20 degrees across the ILN CWA on Saturday, with mid 80s in the southeast and mid 60s in the northwest. The very sharp temperature gradient currently forecast here results in lower- than-normal confidence in the exact numbers, however. There remains strong agreement in the general pattern for Sunday into Sunday night, with deepening low pressure at the surface and aloft ejecting from the plains into the Great Lakes, driving a strong cold front through the Ohio Valley. GEFS clustering of the mid-level low has improved, suggesting that timing confidence is becoming a little more certain, but the 00Z ECMWF came in significantly slower than its previous run, functionally negating the preceding statement. One other item of note is that the 00Z models suggest a slight change to the pattern, which appears a little more occluded than depicted before. It looks mostly certain that the ILN CWA will end up completely in the warm sector within a regime of deep and strengthening southerly flow on Sunday, before precipitation becomes more likely on Sunday evening from west to east. With a slight bit of increased confidence in later timing and drier conditions in the warm sector, the temperature forecast has been increased slightly, allowing for mid to possibly upper 80s in the far southeast. The gradient will not be as strong as Saturday, so the northwest ILN CWA should still get at least into the mid 70s, unless pre-frontal precipitation has greater coverage than expected. The front on Sunday night will be strong and moving fast, ushering in a pretty significant change in air mass. Thus, low-level forcing is not expected to be an issue, and convective development along the front should be solid. That will combine with a fairly strong magnitude of shear to allow for some level of severe threat to exist. Waning instability, unfavorable timing, and mostly-meridional flow (questionable directional shear favorability) will serve as limiting factors to the severe threat. As this is still several days away, for an event with several question marks, it is probably too early to make a specific forecast for hazards. With that said, some threat for heavy rain and severe weather could occur. Behind this front, there will be a notable change in air mass -- and strong cold advection that will lead to strong wind gusts, into the 35-40 MPH range. There will also be a significant drop in temperatures -- a difference of around 20 degrees from Sunday. This forecast will continue to undercut the general model blend, coming closer to raw GFS/ECMWF numbers for Monday. No signs of significant weather on Tuesday, with a slight bit of warming in pseudo-zonal flow. By Wednesday, another developing frontal zone will combine with an approaching wave to allow for increases in precipitation chances through the middle of the week.
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&& .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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Cold front will move through the Columbus terminals in the next few hours. Showers and possibly some thunder may occur immediately along the front. Winds shift to west southwest behind the front and will be gusty until around 00Z. Generally VFR ceilings will occur through the afternoon. These clouds will diminish in the evening. High pressure will build in overnight allowing for winds to weaken further and then back to the south southeast before 12Z. This direction will persist through the end of the TAF period. Appears that valley fog will develop which will bring some visibility restrictions to KLUK overnight. Otherwise, VFR will prevail. OUTLOOK...MVFR ceilings and visibilities with a chance of thunderstorms are possible Friday night into Saturday and then again Sunday night and Monday. Wind gusts to 35 kt possible Sunday into Monday.
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&& .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS... NEAR TERM... SHORT TERM... LONG TERM...Hatzos AVIATION...

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