Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 191519 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 1119 AM EDT Wed Jul 19 2017 .SYNOPSIS... Hot and humid conditions will lead to the chance for thunderstorms at times through the rest of the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Heat and humidity will continue to be the main theme today, with maxima rising well into the 80s and even reaching 90 in some areas. This combined with relatively high dewpoints will boost heat index values toward the mid 90s this afternoon. We should be dry through early afternoon, but during peak heating a few thunderstorms may develop. It`s difficult to rule out a thunderstorm just about anywhere within the CWA, but feel that the most likely location would reside across our northwest CWA across the Whitewater and Miami Valleys. This is in line with the latest NMM/ARW model solutions. At this time, am not expecting any severe weather from storms although certainly can`t rule out locally gusty winds in any thunderstorm. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... 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. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... 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. && .AVIATION /15Z WEDNESDAY THROUGH SUNDAY/... Areas of MVFR and locally IFR fog have developed across the area this morning. This fog should quickly dissipate by mid morning, leaving partly cloudy skies across the region. An area of showers and thunderstorms over eastern Illinois is associated with a mid level short wave that is forecast to push southeast and weaken through early this afternoon, with the pcpn associated with it remaining to our southwest. Otherwise, as we destabilize through this afternoon, a few pop up showers or thunderstorms can not be ruled out but the chance appears low enough to leave a mention out of the TAFs. Any activity should quickly taper off this evening, leaving mainly clear skies for the overnight period. This will likely lead to areas of mainly MVFR fog again later tonight. OUTLOOK...Thunderstorms are possible Friday through Sunday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...JGL NEAR TERM...BPP SHORT TERM...JGL LONG TERM...Haines AVIATION...JGL

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