Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 211039 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 539 AM EST Tue Nov 21 2017 .SYNOPSIS... As high pressure moves off the east coast, a cold front will move into the Ohio Valley today, bringing some scattered showers to the area. Cold air will move in behind the front as high pressure builds into the region for Wednesday and Thursday. Temperatures will warm slightly for Friday, before another cold front approaches the region early in the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Surface high pressure is moving off the east coast, as an area of surface low pressure north of Lake Superior gradually moves ENE into northern Quebec. A cold front extends southwest from this low, and is forecast to cross the Great Lakes and Ohio Valley through this afternoon and evening. This front remains, at least as forecast, not the strongest weather feature ever to move through the region. Nonetheless, confidence is increasing in the chances for precipitation -- particularly across the northern half of the forecast area. This is not so much tied to the surface front as to upper jet support and forcing from the mid-level shortwave, as the precipitation is actually expected to occur behind the surface wind shift. Various WRF runs suggest it will be a relatively narrow band of light rain, weaker with southward extend, to the point that there was not quite enough confidence to include PoPs all the way to the southern ILN border. As temperatures cool behind the cold front, it will be close as to whether or not this will occur quickly enough to allow for any snow to mix in, but this forecast will lean on the side of precipitation cutting off before this occurs. Gusty winds will also be an issue today, with gusts in the 20-30 knot range expected, primarily in the northern half of the forecast area. It is interesting that the strongest 925mb/850mb winds are already moving through the region right now, which means that there will be slightly less to mix up into during diurnal timing later this morning and afternoon. With frontal timing primarily expected to be an evening issue, temperatures through the period should be roughly diurnal. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... After the passage of the cold front late Tuesday, a relatively simple weather scenario is expected for Wednesday, as surface high pressure begins to nudge into the area from the middle Mississippi Valley region. Deep-layer NW flow will keep a cold advection pattern in place, resulting in conditions that will be notably cooler (highs in the upper 30s to lower 40s) and somewhat drier (dewpoints in the mid 20s) than on Tuesday. One concern is in how quickly the post-frontal stratocumulus clouds will clear out behind the front, and expectations are that these clouds will likely not dissipate immediately -- persisting, at least in part, through Wednesday morning. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Surface high pressure will settle across the Ohio Valley Wednesday night. It will initially start out mostly clear, but a weakening disturbance in the northwest flow aloft will spread some mid and high level clouds into the region overnight. Temperatures should bottom out in the lower to mid 20s. Thanksgiving Day will be dry as high pressure continues to influence the region. Under a mix of clouds and sunshine, it will be chilly with highs in the lower to mid 40s. For Thursday night into Friday, a mid level trough will dig southeast from the western provinces of Canada into south central Canada/northern Plains. As this occurs, a cold front will push southeast. WAA ahead of the front will boost temperatures into the upper 40s and lower 50s on Friday. For Friday night into Saturday, mid level trough will dig east into the Great Lakes and the Ohio Valley. Aforementioned cold front will move east through our region Friday night into Saturday morning. Moisture is limited, and some models, such as the ECMWF, move the front through dry. Thus, will keep PoPs in the slight chance/low chance range north of the Ohio River. Skies are expected to be partly cloudy behind the front on Saturday. Given a warm start, sunshine, and relatively weak CAA, we should see highs similar to Fridays readings (upper 40s to the lower 50s). For Saturday night into Sunday, secondary energy will dig into the western side of the mid level trough, strengthening it over eastern Canada, the eastern Great Lakes, and New England. This will push a secondary cold front through the region. It appears that CAA stratocumulus will develop and remain over the area, with cloud coverage greatest north and east downwind of the Great Lakes. At this time, lake effect snow showers appear poised down wind of the eastern Great Lakes, so we will keep a dry forecast going. There is an outside chance of a few flurries in our northeast zones if the cloud layer ends up intersecting the favored dendritic growth zone. It will be a cold day with highs ranging from 35 to 40. Finally, for Sunday night into Monday, mid level trough will progress east, allowing high pressure to build into the region. After a cold start in the lower to mid 20s Monday morning, highs will still only warm into the 35 to 40 degree range. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/...
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VFR conditions are generally expected through the TAF period. LLWS will be the main concern through the early morning hours, with strong southwesterly winds just off the surface. Surface southwesterly winds will increase during the day, with gusts into the 20-25 knot range (possibly slightly higher at Dayton and Columbus). A cold front will move through the area during the evening, switching winds to the WNW. Winds may be slightly gusty again (20 knots or so) immediately behind the front. There is a chance of some passing showers, mainly at the northern TAF sites, and this will be covered with a VCSH. There is also a slight chance of some MVFR ceilings around this time frame, and this will be handled in a TEMPO group. Though some clouds (low-end VFR or possibly MVFR) could persist into the morning, VFR conditions are expected again Wednesday, with NNW flow at 10 knots or less. OUTLOOK...No significant weather expected.
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&& .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hatzos NEAR TERM...Hatzos SHORT TERM...Hatzos LONG TERM...Hickman AVIATION...Hatzos

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