Area Forecast Discussion
Issued by NWS Wilmington, OH

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681 FXUS61 KILN 190737 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 337 AM EDT Wed Jul 19 2017 .SYNOPSIS...
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Hot and humid conditions will lead to the chance for thunderstorms at times through the rest of the week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Mostly clear skies are in place across the region this morning and with light surface winds, we should see some areas of fog persist through daybreak, especially in the southern river valleys. Otherwise, mid level ridging will nose into our area from the southwest through this afternoon. Low level thermal fields are fairly similar to what we saw on Tuesday so expect highs today once again in the upper 80s to lower 90s. This will combine with dewpoints of around 70 degrees to produce heat indicies in the middle 90s this afternoon. Forecast soundings off both the NAM and GFS are showing some warming in the lower levels and this may serve as a weak cap through much of the day. That being said, it will still be tough to rule out an isolated pop up shower or thunderstorm anywhere across our area this afternoon. It does look like there may be a slightly better chance across our northwest where some weak energy aloft will work down toward our area this afternoon.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
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Any lingering shower or thunderstorm activity should again taper off this evening, leaving mostly clear skies overnight. An overnight MCS will likely drop down across the upper Mississippi Valley and toward our area through the early morning hours. The models are in general agreement dissipating the pcpn associated with this before it reaches our area. However it will create some uncertainty for the forecast through the remainder of the day as there could be some lingering cloud cover and/or some sort of outflow boundary from it that makes it onto our area. For now though, the models are still suggesting a bit of a bump up in low level thermal fields through the day compared to Wednesday. Because of the uncertainty though, for now will just range highs from near 90 in the northeast to the lower 90s across the southwest. This will again combine with dewpoints in the lower 70s to produce heat indices in the upper 90s to around 100 degrees through the afternoon hours. This will also lead to good instability through the afternoon hours with the possibility of some thunderstorms to our north feeding south into the instability late in the day across our north.
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&& .LONG TERM /Thursday Night through Wednesday/...
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Thursday night mid level ridging will be centered over the central United States with an upper level low over the Hudson Bay. The same cold front which models have so struggled to get the placement with is now forecasted to stall out around the Michigan/ Ohio border before pulling east. Thursday night the boundary is forecast to be just south of the border with convection likely firing along the front. There will be many factors in play here though as left over convection west of region Thursday morning will likely leave a leftover boundary near the region Thursday night. Predicting the exact mesoscale layout this far in advance is very difficult and therefore have just nudged PoPs up at this time. It also should be noted that at 500 mb a potent short wave will rotating around the top of the ridge with SFC to 6 km shear values near 40 kts in central Ohio. Even though the best instability remains south of the shear there is enough overlap to where some of the storms could become strong to severe. Given this, SPC has placed the northern counties of our forecast area in a slight risk for Day 2. During the day Friday mid level ridging begins to flatten a bit as the quasi-stationary low that was over North Carolina begins to retrograde undercutting the ridge. Again, models have continued to struggle here with how this feature ejects. Friday afternoon forecast soundings again completely destabilize with ML CAPE values mostly above 2000 J/kg. Heat indicies Thursday through Saturday will also be a concern as high temperatures will regularly be around 90 to lower 90s with dewpoints in the lower 70s. The main question mark with heat index values will be whether or not convection gets going and holds down high temperatures at all. Have gone ahead and edged down high temperatures ever so slightly Friday afternoon due to the threat of convection. Saturday the mid level ridge that was over the central United States this week will start to collapse as the upper level low continues to pull west/ retrograde. PWATs do come down a little Saturday (around 1.5") but have continued to advertise slightly higher PoPs Saturday compared to Friday given the weakening mid level ridge. During the day Sunday an upper level low will dive southeast towards the Great Lakes with ILN moving into a RRQ. By Monday morning a surface cold front will begin to work southeast and approach the Ohio/ Indiana border. Ahead of the front the RRQ from the upper level jet streak, increased moisture, and ample instability means PoPs will likely need to continue to be nudged upwards as timing of the short wave gets nailed down. The ECMWF remains quicker than the GFS and pushes the front through the area Monday morning while the GFS pushes the front through the area Monday evening. Behind the cold front, surface high pressure will build into the region allowing for slightly below normal temperatures and more pleasant feeling air Tuesday.
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&& .AVIATION /07Z WEDNESDAY THROUGH SUNDAY/... Skies have gone mostly clear across much of the area early this morning but we are beginning to see some patchy VFR SC forming across portions of eastern Indiana. Am a little concerned this may fill in a bit more over the next few hours so will just allow for some scattered SC at the TAF sites through the early morning hours. Otherwise, with light flow across the area, we should see some MVFR to locally IFR fog development once again through daybreak, especially in the southern river valleys. As we destabilize through the day, scattered cu is once again expected. It will also be tough to rule out an isolated shower or thunderstorm but the chance is low enough to leave any mention out of the TAFs. OUTLOOK...Thunderstorms are possible Friday through Sunday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...JGL NEAR TERM...JGL SHORT TERM...JGL LONG TERM...Haines AVIATION...JGL

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