Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 080756 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 256 AM EST Thu Dec 8 2016 .SYNOPSIS...
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Cold air will continue to get colder over the next day or two, and temperatures will remain well below normal. Some flurries are expected on Friday morning, before an area of high pressure moves into the region late Friday into Saturday. On Sunday and Monday, a complex low pressure system will through the Ohio Valley, bringing a mix of rain and snow to the region.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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A large and lumbering area of stacked low pressure is currently located just south of James Bay, crossing slowly eastward through Canada. This feature is dominating the longwave pattern across much of North America, and is keeping the Ohio Valley in a regime of deep-layer westerly/northwesterly cold advection flow. As is unsurprising, the very weak 700mb disturbance moving through the region right now is producing radar echoes but no precipitation -- the dry air below the mid-level clouds is evaporating the hydrometeors as they fall. A dry forecast will be maintained today, but with some question about cloud cover. There is a considerable amount of upstream stratocumulus, which will likely affect the northern half of the ILN CWA through the day, before expanding across the whole area tonight. Further to the south, drier 925mb/850mb conditions are expected, so sky cover will be more of a question of any persisting mid-level clouds. With some sun sneaking through in the southern / southeastern sections of the forecast area, temperatures might be able to rise to near or just above freezing. The forecast is much less optimistic further north, where cold advection and persistent cloud cover will combine to allow very little rise in temperatures. The far northwestern ILN CWA -- currently in the upper 20s -- may not reach values that high again through the rest of the day. With a boundary layer that will be well-mixed, though shallow, some wind gusts in the 15-20 knot range may occur at any point throughout the day -- even into the evening.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
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The short term forecast discussion will be updated shortly. Previous discussion > On Thursday the H5 low will be in ern Canada, with a sfc trof/arctic front working down through the lakes. As the sunrises, there should still be some mid and high clouds, but they should pull e by mid day. During the afternoon, the better H8 CAA will begin to work south of the Great Lakes and a deck of sc will gradually overrun the area. Temperatures will struggle to warm with the increasing cloud cover and caa. Highs will range from the mid 20s in West Central Ohio to the lower and mid 30s in the se counties. As Thursday night progresses, H8 temperatures will drop to -12C and the flow will align off Lake Michigan to bring flurries to the region. Some snow showers will be possible in West Central Ohio closer where the better fetch off of Lake Michigan may set up. The pattern will linger into the first part of Friday, but then the flow begin to back off of Lake Michigan and it should bring a gradual end to the lake effect snow activity. At this time, I am not thinking snow accumulations will be more than a dusting if any. The clouds and pcpn should help the temperatures from dropping too low. Kept lows Thursday night around 20 degrees. Highs on Friday will work only into the upper 20s to lower 30s.
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&& .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... High pressure centered over the Tennessee Valley on Saturday will provide a dry forecast over the CWA, with enough breaks in the clouds for some sunshine during the midday and afternoon. Despite some sunshine, it will remain cold with high temperatures likely remaining below freezing through much of the CWA except perhaps south of the Ohio River into northern Kentucky where high temperatures may hit/slightly exceed the freezing mark. High pressure shifts to the east into the middle Atlantic states Saturday night. Result will be a south/southeast flow in the low levels and some warm advection which will allow for clouds to roll back in Saturday evening and for precipitation to develop well ahead of low pressure over the central Plains. This low is forecast to move northeast into/through the Great Lakes, eventually allowing a cold front to pass through Sunday night or Monday morning. Until then, confidence has increased in a period of precipitation Saturday night into Sunday and therefore have likely pops across the CWA. Precipitation type will likely be snow at the onset, but with some warmer air moving in from the south on Sunday, expect snow to mix with/change to rain particularly south of Interstate 70. GFS is colder than the ECMWF, and therefore used a blended approach for p-type transition Sunday. Eventually, any lingering precipitation would change back to snow Sunday night/Monday morning as colder air moves back in behind the cold front. High pressure briefly builds in for Tuesday, but a fast-moving, weak system may bring a chance of light precipitation by Wednesday, although timing this far out is in question. Below normal temperatures are expected for the long term forecast period. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... The center of a large scale upper level trough was located south of James Bay Canada this morning. This feature will rotate east/northeast through the day. For this morning, considerable mid clouds will exit the region around 12Z. Thereafter, CAA in conjunction with stratocumulus clouds will advect/develop through the day as they move southeast. It appears that the northern terminals will see some MVFR ceilings by 18Z while the southern terminals remain VFR. An increasing pressure gradient along with some diurnal mixing will bring wind gusts into the 20-25 knot range. For tonight, low level flow will shift to a northwest direction, allowing cold air to move across the Great Lakes. This will allow stratocumulus to thicken and lower overnight. There could be some scattered flurries, with a few snow showers possible near the northern terminals. Ceilings will all drop into the MVFR category, with some models suggesting ceilings dropping below 2000 feet in some spots. Winds will remain a little gusty overnight, but perhaps not as high as today with some night time cooling/decoupling. OUTLOOK...MVFR ceilings expected on Friday, which may linger into Friday night. MVFR/IFR ceilings and visibilities possible Sunday into Monday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hatzos NEAR TERM...Hatzos SHORT TERM...Sites LONG TERM...BPP AVIATION...Hickman

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