Area Forecast Discussion
Issued by NWS Wilmington, OH

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290 FXUS61 KILN 210815 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 415 AM EDT Fri Jul 21 2017 .SYNOPSIS...
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Multiple disturbances are expected to bring several rounds of showers and thunderstorms to the region through the weekend and into Monday. High pressure and dry conditions are then expected for Tuesday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Weak boundary remains just north of the forecast area this morning. There is an axis of better instability from Illinois eastward into portions of west central Indiana and into central Ohio. There is a complex of storms moving into Indiana and also in advance of this feature isolated showers and thunderstorms in the axis of the better instability. Expect the complex to gradually weaken as it moves into the region, however with favorable airmass in place expect at least some thunderstorm activity from the complex currently along the Illinois and Indiana border. With moist airmass in place any thunderstorm that develops or moves into the region will have the potential for heavy rainfall. There is also the potential for some fog across mainly far northeastern portions of the forecast area early this morning with some more breaks in the clouds and moist airmass in place. After this feature moves through this morning expect a lull in some of the precipitation activity as the atmosphere recovers. With some breaks in the clouds then expected temperatures are expected to quickly rebound into the upper 80s to low 90s. With dewpoints in the 70s, heat index values this afternoon and early evening hours will be in middle to upper 90s across a large portion of the region. Near and south of the Ohio River heat index values are expected to reach the 100 degree mark. Although there is some question in regards to convective activity and impact on temperatures, confidence was high enough that decided to continue the heat advisory across southern portions of the region. The system moving through during the morning hours will likely lay out a boundary for thunderstorm development that is expected to occur during the afternoon hours and into the evening hours. Best chance of thunderstorm activity is expected to be across southwestern portions of the region.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
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Boundary is forecast to shift northward tonight and therefore the focus of shower and thunderstorm activity will also be further north. For tonight and into Saturday went with higher precipitation chances across the north. Cannot rule out isolated strong to severe storms with damaging winds and heavy rain the primary threats Saturday afternoon and early evening. Heat index values on Saturday will be similar to Friday and will be highly dependent on convective activity. Will continue to mention heat in the HWO and monitor for the potential for additional heat advisory headlines for Saturday, primarily again across the south.
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&& .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
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Good chance that convection will be ongoing at the start of the period as a surface low moves across the Great Lakes. Storms will likely translate across the region through the night with some activity possibly lingering into Sunday. Strong to severe storms may occur with the greatest potential on Saturday evening when instability will be the highest. A cold front will move through the region on Monday with at least a low chance of some additional storms in the far southern counties. High pressure will build in Tuesday and Wednesday bringing less humid conditions. The high will move off to the east by Thursday but its influence will remain albeit with higher dew points.
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&& .AVIATION /08Z FRIDAY THROUGH TUESDAY/... A weak boundary can be seen in the observations north of the TAF sites. A few showers have developed south of this boundary in an area of better instability. These showers trail back to a complex of storm in Illinois. There is some question as to the development of additional shower and thunderstorm activity overnight in a weakly forced environment, however given current indications there appears that some isolated to scattered shower and thunderstorm development will be possible for the remainder of the overnight hours. Expect a weakening trend of a complex over Illinois as it moves into the region late in the overnight hours and into the early daytime hours. There is some question on how quickly this feature will weaken and this will lay the framework for later today and convective activity. Given favorable airmass ahead of this system believe that there will be at least some convective activity that moves into the TAF sites late into the overnight and into the early daytime hours on Friday. This may delay and push thunderstorms later in the day a little further south, but given instability expect coverage to increase later in the day across the southern TAF sites. As boundary moves across region Friday evening into Friday night there will be the potential then for thunderstorm activity to shift northward. In addition to the thunderstorm activity, with moist airmass in place some isolated MVFR vsbys have developed even with cloud cover. There is potential for some MVFR vsbys at KCMH and KLCK overnight even if some cloud cover is in place. OUTLOOK...Thunderstorms will be possible at times from Friday through Monday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...Heat Advisory from noon today to 7 PM EDT this evening for OHZ077>082-088. KY...Heat Advisory from noon today to 7 PM EDT this evening for KYZ089>100. IN...Heat Advisory from noon today to 7 PM EDT this evening for INZ073>075-080. && $$ SYNOPSIS...Novak NEAR TERM...Novak SHORT TERM...Novak LONG TERM... AVIATION...Novak

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