Area Forecast Discussion
Issued by NWS Wilmington, OH

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430 FXUS61 KILN 090552 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 1252 AM EST Fri Dec 9 2016 .SYNOPSIS... A cold air mass will remain over the region for the next several days. Some flurries are expected tonight into Friday morning, before an area of high pressure moves into the region for Friday afternoon into Saturday. A complex low pressure system will affect the Ohio Valley Saturday night into Monday, bringing a mix of snow and rain. && .NEAR TERM /THROUGH TODAY/... Flurry/light snow shower coverage and intensity has increased over the past several hours as the flow off Lake Michigan has become better aligned for such activity in the local FA. The numerous flurries/light snow showers will continue through the overnight period into early Friday morning. As the flow slowly becomes more westerly late Friday morning, expect that the light snow shower activity will become more confined to the northern or northeastern third of the FA before drier conditions move in everywhere for the second half of the afternoon. Did bump temperatures down several degrees for tonight despite extensive cloud cover. Obs are already showing several locations in the upper teens, particularly across the Miami Valley, and expect that in the CAA regime, temperatures may fall by an additional couple of degrees. High temperatures are still on track for Friday afternoon to reach near 30 degrees across the entire FA. Am concerned that if cloud cover persists a bit longer across the north/northeast, that temperatures may stay in the upper 20s. && .SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/... As the period begins, the coldest H8 air will have settled across the region. Surface high pressure will begin to build in from the west and the H5 flow will become more zonal. H8 temperature advection will be neutral. So sc will probably be slow to erode across the region. This will limit solar insolation and will keep highs around 30 degrees. A chance of flurries will continue to be used for the majority of the forecast area. Though most locations will not receive any accumulation, a quick tenth or two could occur in a snow shower on Friday morning, likely limited to West Central OH counties. The surface high will continue to build east Friday night. The low clouds will begin to erode, but they will be replaced by some mid to high clouds streaming east in the zonal flow. Temperatures will drop back to 15-20 degrees. Saturday will be the calm before the storm. While temperatures will still be below normal, conditions should be dry with a mix of clouds and sun. Highs will range from the upper 20s across the nrn counties while making the lower 30s around the Ohio River. Models are showing differences in the solution for Saturday night. The 12Z NAM has come in dry as it is deeper with its surface low and therefore keeps the better convergence and pcpn across the Great Lakes. The GFS/ECMWF and CanadianNH are showing more of a general sly flow with broad isentropic lift advancing from the nrn plains into the srn Great Lakes and Ohio Valley. There is still uncertainty where the srn edge of the pcpn will be, but there is enuf confidence to up PoPs across the nrn third of the fa to likely. Thicknesses will be cold enuf for the pcpn to fall as all snow. Right now it is looking like the possibility of 1-2" of snowfall north I-70. Will keep mention of accumulating snow for the northern half of the CWA in the HWO. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Zonal upper level flow will be found over the conus with a h5 shortwave pivoting northeast through the Great Lakes region on Monday. Ahead of the s/w, a baroclinic zone will set up in the Ohio Valley and surface low pressure will strengthen through the day. As the baroclinic zone takes form, precipitation is expected to develop over the north and northwestern of the CWA early Sunday and increase coverage through Sunday afternoon. The upper level shortwave quickly exits east on Monday and precipitation ends from west to east with high pressure building in the Midwest. A broad trough will cross the northern Great Lakes region Tuesday night and Wednesday with zonal westerly flow found underneath it. GFS and Canadian models are sharper with the trough and influences a lot more lift in the region on Wednesday while the ECMWF is more muted and shifts the forcing off of the east coast with very little precip in the Ohio Valley. Given the precipitation was already in the forecast, continued the low chances for the middle of next week and dried out the region on Wednesday. Models are in a sharply cool pattern for the end of the valid period on days 5-7 but show a strong variability in the ensembles of 30 degrees or more in both daytime highs and nighttime lows. While the model spreads for any period are large, the average of the runs and the deterministic run are definitely on the colder side of the ensemble members. Kept the cold pattern of the forecast but tried to trend slightly warmer to account for the variability that in inherent in the longer range forecast. Precip on these days will likely see snow on Sunday, mixing with rain along and south of the Ohio River. Temperatures will warm overnight and the rain/snow line will lift to the I-70 corridor by daybreak Monday. Precipitation on Tuesday at this moment in time would start as a mix or plain rain in the southern half of the CWA and then change to snow in the evening before ending overnight. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/...
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MVFR ceilings and snow flurries will persist in a cold cyclonic flow. Improvement to VFR could occur around 13z at CVG and LUK, but observations will need to be closely monitored to determine if that will happen. Otherwise, all sites should see VFR about 01z Saturday with the arrival of high pressure and a drier airmass. Winds will stay out of the west, with speeds around 10 knots becoming light by the end of the forecast. OUTLOOK...MVFR/IFR ceilings and visibilities possible Sunday into Monday.
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&& .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hatzos NEAR TERM...KC/Sites SHORT TERM...Sites LONG TERM...Franks AVIATION...Coniglio is the U.S. government's official web portal to all federal, state and local government web resources and services.