Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 271805 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 205 PM EDT Sat May 27 2017 .SYNOPSIS... With warm and moist air over the Ohio Valley, there will be occasional chances for showers and thunderstorms through the weekend. After a cold front moves through the region Sunday night, drier conditions are expected for Monday. && .NEAR TERM /THROUGH TONIGHT/... A fair amount of sc has developed across the area this morning, especially along and south of a weak boundary that is laid out across our area. These clouds should begin to mix out/lift into more of a cu field as we progress through this afternoon and begin to destabilize. Good instabilities are progged to develop through this afternoon with ML Capes forecast up into the 2000-3000 J/KG range by mid to late afternoon. Forecast soundings continue to show some capping along and north of the boundary, but across our south it does appear that at least some scattered thunderstorms development will be possible. This may be aided somewhat by a very weak wave that is forecast to push east along the boundary through mid to late afternoon. Wind fields are not all that impressive though with both the 0-3 km and 0-6 km shear values somewhat marginal for organized storms. However, given the degree of instability, some strong to severe storms will be possible with any development later this afternoon into early evening with the main threat being large hail and damaging winds. With mid and upper level flow parallel to the boundary, some training storms may also be possible if things do get going. This combined with PWs forecast to push up into the 1.5 to possibly 2.0 inch range, would support a locally heavy rain/flash flood threat. && .SHORT TERM /SUNDAY/... After any storms along the boundary have dissipated or moved SE of the ILN CWA this evening, another break in the action is expected. From here, attention will turn to the severe (potentially very severe) convection occurring well upstream across Missouri and southern Illinois. This activity is not even expected to reach the lower Ohio Valley until late evening, and thus, any impacts on the ILN CWA will be well into the overnight hours. 00Z runs across the suite of models have been fairly consistent in depicting this activity propagating into the instability / greater theta-e air mass, roughly along an ESE trajectory. The ILN CWA will be on the northern fringe of this, still in a favorable area for convection to develop ahead of a mid-level shortwave, but removed from the best thermodynamic environment at a sub-optimal time of day. A severe threat will exist -- mainly a damaging wind threat -- but should not be as significant as areas further south and west. The main focus here will be in the overnight / early Sunday morning hours. Once the morning activity has passed east, another break is expected through the first half of Sunday. Additional storms associated with the cold front will be discussed in the Long Term AFD section below. With less certainty in the pattern, will not allow a completely dry forecast for this time period, as there should still be some isentropic ascent with continued warm advection aloft. The temperature forecast through the first three periods of the forecast is one that is largely dependent on convection and clouds, so perhaps it would be better read as a mid-point of the expectations -- get some clearing and it will be too low, get some convection and it will be too high. There will be a general SW-to-NE gradient in temperatures across the ILN CWA through the period, and depending on the position of the surface boundaries, a tighter gradient may exist than what is currently in the forecast. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... A cold front will move east through the region Sunday night. Scattered showers and thunderstorms are expected along and ahead of the front. A few strong to severe storms will be possible late Sunday afternoon into the evening hours with damaging winds and large hail the primary severe weather threats. Precipitation should exit east of the eastern CWFA after midnight, with clearing expected behind the front. The first half of the week will feature a large closed upper level low which is forecast to rotate slowly east across Ontario. Embedded disturbances rotating around the low, along with weak sfc trof axes, will bring a low chance threat of a few showers from time to time, mainly during the peak heating of the day. Otherwise, partly cloudy conditions with seasonable temperatures in the 70s are expected. As the upper level low finally rotates farther east by the end of the work week, we should finally see a distinct dry period as surface high pressure settles over the Ohio Valley. Again, temperatures will be near seasonal normals. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... We have started to see some spotty shower and thunderstorm development along and south of a stalled out boundary situated west to east across central portions of our area this afternoon. As we continue to destabilize through this afternoon, expect to see the activity become more widespread and will cover the threat with a VCTS at the southern TAF sites. This activity will be diurnally enhanced so expect a downward trend as we head into this evening. Most of the models are keeping the bulk of the main MCS later tonight off to our southwest but the NAM and a few of the higher res models are showing some additional development farther north into our area later tonight into early Sunday. Will therefore allow for some prevailing -shra and a VCTS at all the TAF sites to account for this possibility. There are still a few linger MVFR cigs around at the moment but these should continue to lift into VFR for this afternoon. Expect VFR cigs then into this evening before dropping back into MVFR later tonight into Sunday morning as pcpn moves back in. OUTLOOK...Intermittent chances of thunderstorms along with MVFR ceilings will be possible through Monday morning. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hatzos NEAR TERM...JGL SHORT TERM...Hatzos LONG TERM...Hickman AVIATION...JGL

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