Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 130902 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 502 AM EDT Fri Oct 13 2017 .SYNOPSIS... High pressure will remain in place over the Ohio Valley through the rest of the week, before moving east of the region going into the weekend. A cold front is expected to move through the area on Sunday, bringing rain and gusty winds, and cooler temperatures to start the new week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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As the lines between the two areas of stratocumulus have become more set in place over the past couple hours, the cleared area between the two has seen plenty of time for fog/stratus development, and a dense fog advisory has become necessary. As of this writing there are eight observation sites within the advisory at 1/4SM, and another three at 1/2SM. Previous discussion (313 AM) > Fog potential is the greatest forecast concern for this morning, and really the only concern through the near term of the forecast. A retreating shield of stratocumulus clouds now covers only about the northwestern third of the ILN CWA. As these clouds have eroded, reduced visibilities have been very quick to develop in the clear skies -- signs of a boundary layer that is very favorable for fog development, with antecedent RH values at or near 100 percent, and calm winds. A few observation sites have already reported 1/4SM early this morning, but the challenge comes from another batch of clouds -- some patchy stratocumulus now moving NNW into the eastern sections of the ILN CWA. These clouds may be able to put an end to the dense fog conditions, but it`s unclear how far they`ll make it into the area. The plan for now is to issue an SPS to cover the fog development, but continue to monitor the two areas of clouds to determine if it will become widespread and prolonged enough in any set location to warrant the issuance of an advisory. It would not be surprising to see leftover fog and/or stratocumulus leading to mostly cloudy conditions for at least a few hours after sunrise this morning, but clearing conditions and drier air aloft will help keep conditions more sunny by afternoon. Not much else to describe with the weather today, aside from some disparity in theta-e in the 925mb-850mb layer, supporting some warmer conditions in the southeastern sections of the ILN CWA. Thus, there may be a bit of a max temperature gradient across the forecast area, with upper 70s in the southeast and lower 70s in the north.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Generally quiet conditions are expected through tonight and into Saturday, as surface high pressure is expected to remain just east of the region. There are conflicting signs regarding the possibility of fog developing again tonight into early Saturday morning, but the start of a period of theta-e advection just off the surface is a sign of concern. Nonetheless, there are some sizable model differences in the handling of this flow of moisture, and winds may not be quite as dead calm as they are at the present (one night before). Thus, would prefer to not put fog in the forecast quite yet. Warm advection through the entire boundary layer will become more pronounced on Saturday, and thus temperatures will increase notably from Friday -- reaching the upper 70s to around 80. With how things have gone recently, and the generally dry conditions, this forecast will go slightly above the raw model numbers from the GFS/NAM. Late on Saturday, high and mid level clouds may begin to move into the area, as a result of the frontal zone developing across the Great Lakes. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Period starts with a vigorous cold front approaching from the west. Front will contain high shear but marginal instability typical of autumn. There will a chance of showers by late Saturday night, with showers likely and a slight chance of thunderstorms on Sunday with frontal passage. In addition to widespread wind gusts around 30 knots in the tight pressure gradient surrounding the front, there may be isolated stronger gusts as showers tap a 55 knot 850 mb jet. Front will exit quickly east by Sunday night, allowing showers to end. A large area of surface high pressure under a zonal upper flow is then expected to provide dry weather Monday through Thursday. Temperatures are forecast to exhibit a non-diurnal cooling trend Sunday in strong cold advection behind the front, with early highs around 70 slipping into the 60s Sunday afternoon. Below normal highs around 60 on Monday will be followed by lows down to the mid and upper 30s Monday night in rural locations, possibly allowing patchy frost to form. A warming trend to the low 70s will be noted later in the period as the high sags to the south and a southerly flow develops. && .AVIATION /09Z FRIDAY THROUGH TUESDAY/... As generally-VFR stratocumulus clouds depart the region this morning, patches of additional lower clouds and fog will develop. IFR fog is expected at all TAF sites over the next few hours, and there is a possibility that dense fog and LIFR conditions could build into some of the airports, especially KILN/KCMH/KLCK. Thus, the TAFs are somewhat pessimistic through the mid-morning hours, before conditions will gradually improve. Aside from these overnight concerns, the rest of the forecast is fairly simple, with light southwesterly flow and VFR conditions. There may be a possibility for additional fog or low cloud development going into early Saturday morning. OUTLOOK.. MVFR conditions and gusty winds Sunday in showers/thunderstorms. && .ILN WATCHES/WARNINGS/ADVISORIES...
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OH...Dense Fog Advisory until 10 AM EDT this morning for OHZ046-054- 055-063-064-072-073-078>082-088. KY...Dense Fog Advisory until 10 AM EDT this morning for KYZ093- 096>100. IN...None.
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&& $$ SYNOPSIS...Hatzos NEAR TERM...Hatzos SHORT TERM...Hatzos LONG TERM...Coniglio AVIATION...Hatzos

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