Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 220200 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 1000 PM EDT Fri Oct 21 2016 .SYNOPSIS... A drier and cooler airmass will filter into the region tonight into Saturday. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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Precip has moved east of the area. Now the forecast concern for tonight will be the potential for any frost to form. We are only running in the upper 40s and low level CAA is forecast to continue into the overnight hours. However, there are a couple of factors (namely clouds and wind) resulting in some uncertainty for just how far temps will drop and whether or not we will actually get frost formation. Clouds appear to be holding together for now, but more clearing may still occur later tonight. The low level flow will back a little through the night and this should allow for some of the lake effect clouds coming off of Lake Michigan to work their way eastward into at least western parts of our area later tonight. With this in mind, will generally keep at least partly cloudy skies going through the night across our area. Meanwhile, surface high pressure over the mid Mississippi Valley will begin to build eastward into the Tennessee Valley overnight. This will allow for a gradual decreasing pressure gradient through the night, but expect it to still stay strong enough to keep at least a little wind going overnight. Given the continued CAA, think temps will fall into the mid to upper 30s across much of our area. However, given the uncertainty of the clouds and the wind possibly staying up, think the best way to handle this situation is to hold off on a frost advisory. Since there is a chance some areas could clear off for awhile and decoupling could possibly occur in some low lying areas, will still go ahead and include patchy frost wording in the grids/forecast for later tonight into Saturday morning. Will also issue an SPS to highlight the possible frost threat and uncertainty.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/... The upper level trough will pivot up across the northeastern United States through the weekend with the flow across our region becoming less amplified. Surface high pressure will build eastward across the Tennessee Valley through the day on Saturday. This will keep us dry but cool on Saturday with highs only in the low to mid 50s. Some short wave energy will drop down across the eastern Great Lakes Sunday into Sunday night. However, the best forcing will remain off to our northeast and the airmass is fairly dry so will maintain a dry forecast through the end of the short term period. Temperatures will modify some on Sunday with expected highs in the mid to upper 60s. && .LONG TERM /MONDAY THROUGH FRIDAY/... The long term will open up Monday with a shortwave diving southeast around a rotating upper level low over Quebec. As the shortwave dives southeast this will help to build the upper level trough axis back west allowing more cold air to spill into the Northeast United States. More recent model runs have tried to trend the shortwave further west and seem to have agreed on the shortwave moving southeast over Michigan. Overall the upper level trough axis will setup east of the area allowing the heart of the cold air to spill east of the Ohio Valley. The associated cold front will push through the region Monday afternoon pushing temperatures back down to near or slightly below normal values. As has been the case the last couple of days the frontal passage appears dry. PWATs ahead of the front only go up to about 0.75" and the area remains on the convergent side of the trough axis. Almost all of the positive vorticity advection is also east of the area. Tuesday morning surface high pressure will move in from the north allowing winds to go mostly calm . Some high clouds may be moving in from the west, but chances seem to be growing that frost may be possible. During the day Tuesday a shortwave will move over the midwest and head east. At the same, the upper level trough axis over New England will pull east. In response to the shortwave, a surface low will form near the Nebraska/ Iowa border. During the day Wednesday the shortwave will strengthen and start to wrap up. Both the GFS and ECMWF are in pretty good agreement with this and have the shortwave wrapping up into a low over Wisconsin Wednesday evening. Across southwest Ohio low level flow will continue to increase ahead of the low with strong upper level divergence. Divergence will come from the RRQ of the upper level jet streak along with upper level diffluence from the splitting of 250 mb winds. Instability at this time looks limited but shear profiles are impressive (SFC-1km ~35kts via GFS forecast soundings). Any change in the placement of the low will easily change the values and orientation of the bulk shear vectors though. Future model runs will help to continue to refine this. Thursday afternoon into Friday the shortwave will push east but the ECMWF and GFS differ on how the shortwave ejects. The ECMWF picks up the shortwave in the main flow moving a cold front through the area. The GFS on the other hand washes the shortwave out and slowly pushes it southeast. The CMC has the shortwave diving into southeast Texas and appears to be the outlier. For now have kept the forecast trended towards ECMWF. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... Upper trough axis is now east of TAF sites. Low level moisture persists in the northwesterly flow ahead of surface high pressure. This will keep ceilings in the MVFR range at ILN CMH and LCK for a few more hours before ceilings lift above 3000 ft later tonight. Ceilings at western sites DAY CVG and LUK have already reached VFR. As the upper trough continues east and the center of the surface shifts to the southeast, VFR will persist, and skies will become mainly clear at all sites by the end of the forecast. Winds of 10 knots or so will keep BR from forming. OUTLOOK...No significant weather expected. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...JGL NEAR TERM...Coniglio/JGL SHORT TERM...JGL LONG TERM...Haines AVIATION...Coniglio is the U.S. government's official web portal to all federal, state and local government web resources and services.