Area Forecast Discussion
Issued by NWS Wilmington, OH

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579 FXUS61 KILN 181344 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 944 AM EDT Tue Jul 18 2017 .SYNOPSIS... An upper level ridge of high pressure will build into the mid Ohio Valley through the end of the work week, leading to a gradual warming trend. There will also be an increasing chance of thunderstorms as we head toward the end of the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Although most locations will start out with clear skies this morning, expect cu to develop as the day progresses. Most model solutions are allowing for some isolated precipitation activity across the region today with a weak boundary in place. Limited precipitation chances to slight chance or isolated at this time due to lack of significant forcing. Temperatures will climb today into the middle 80s across northern and western portions of the region to around 90 across the southeastern portions of the area. Temperatures will be cooler across northern and western portions of the area as these location are expected to have cloud cover and isolated precipitation earlier in the day.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Once again, would expect any isolated shower/thunderstorm activity to dissipate heading into this evening as we lose the daytime heating. Lows tonight will be in the upper 60s to lower 70s. Heights will nudge up a bit more through the day on Wednesday which should allow for highs a degree or two warmer, into the upper 80s to possibly lower 90s. This will combine with dewpoints in the upper 60s to push heat indices into the mid to possibly upper 90s through the afternoon hours. Meanwhile, the GFS and ECMWF have some weak short wave energy pushing east southeast across the southern Great Lakes on Wednesday while the NAM brings the energy more southeast toward our area. Will trend toward the more northern solutions but will allow for a slight chance of pcpn across our northwest through the afternoon to account for some of the uncertainty. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Upper level ridging will be centered over the central United States Wednesday night with an upper level low located over North Carolina. Simultaneously a long wave trough axis will located over eastern Canada. Models have struggled over the last couple of days of how the long wave trough, upper level low, and mid level ridge will interact. On Thursday models have been in fairly good agreement with the mid level ridge remaining over the central United States with the upper level low remaining quasi-stationary. The ILN forecast area remains on the edge of the mid level ridge with only the CVG GFS forecast sounding showing any hint of mid level ridging. Overall though forecast soundings do destabilize Thursday afternoon. ML CAPE values on the GFS average around 1500 J/kg with the greatest instability across the northwestern zones. A weak upper level disturbance is also expected to track across Michigan Thursday afternoon. Given this have the chance of precipitation increasing Thursday afternoon with the highest chance of rain to the north. Due to the forecast areas close proximity to the ridge, 850 mb temperatures also climb to just above 20 degrees C. This combined with dewpoints in the lower 70s will push heat indicies into the mid to upper 90s (approaching 100 across the southwest). Friday afternoon mid level ridging begins to slowly break down as the upper level low that was over North Carolina retrogrades west underneath the ridge. Some weak upper level disturbances will likely continue to rotate around the ridge, but the main contributor to the higher chance of precipitation will be the collapse of the mid level ridge. GFS forecast soundings completely destabilize Friday afternoon with PWATs around 1.70" (at the 90th percentile for this time of year). Have gone ahead and nudged PoPs up Friday afternoon and kept towards a more diurnal component for Thursday evening into Friday afternoon. The other concern for Friday will be the heat. Highs will likely be around 90 degrees across the southwest and with dewpoints in the lower 70s heat indicies will be near 100 (mid to upper 90s for rest of the CWA). Due to the above have kept the mention of high heat index values in the HWO for Wednesday through Saturday). Friday night into Saturday models have changed their tune with the upper level low that was supposed to stay nearly stationary over the Hudson Bay now more progressive with a surface cold front well further north and east of the region. Due to this the track of the heavier precipitation maximum (or potential MCS) with the embedded short wave is now further north. Still though, with the mid level heights falls, anomalously high PWATs, and instability rain will remain in the forecast. Sunday a short wave will dive southeast towards Michigan dragging a surface cold front with it. Models quickly diverge here on solutions. The GFS has the short wave heading east with the retrograding upper level low finally being caught back up in the main group velocity of the east coast long wave trough. This means the front stalls across the area Monday with a surface low tracking across the baroclinic zone Tuesday morning. The front then slowly sags south Tuesday into Wednesday. The ECMWF is similar except the upper level low disperses over southeast Texas. This allows the cold front to clear the forecast area early Tuesday morning. For now have leaned towards the GFS solution. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/... Areas of MVFR fog have developed this morning with some patchy IFR and lower vsbys in the river valleys, especially in the lower Scioto Valley. This fog should dissipate within the first hour or so of the TAF period with sct cu then developing through late morning and into this afternoon. As we destabilize through the day, it will be tough to rule out an isolated pop up shower or thunderstorm. However, the chance appears low enough to leave a mention out of the TAFs. Any pcpn should quickly dissipate this evening, leaving mainly clear skies through the overnight. OUTLOOK...Thunderstorms are possible Friday and Saturday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...JGL NEAR TERM...Novak SHORT TERM...JGL LONG TERM...Haines AVIATION...JGL

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