Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 241942 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 342 PM EDT TUE MAY 24 2016 .SYNOPSIS...
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High pressure will move east of the region tonight. Clouds and moisture will begin to move into the area tomorrow morning, and chances for showers and storms will increase going through the rest of the week, as occasional shortwave troughs move through the mean southwesterly flow. Temperatures will continue to gradually warm, and are expected to remain above normal through the next week.
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&& .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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Surface high pressure is now centered off the southeast coast, with broad surface low pressure over the high plains. With this kind of distance between pressure systems, the gradient in the low levels is very weak, and winds today have been light (under 10 knots) and somewhat variable in direction. Mean ridging is setting up over the eastern third of the country, and temperatures have risen above normal through the entire forecast area today. The overnight period will begin with mostly clear and relatively calm conditions, with the area still well ahead of the shortwave moving through the middle Mississippi Valley tonight. With clouds eventually moving in toward Wednesday morning, temperatures tonight may drop somewhat quickly after sunset, but should steady out after around 4 AM. Min temps in the upper 50s are expected, which is a 4-8 degree rise from last night, but not as warm as suggested by the GFS/MAV.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
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The general pattern for the next few days can be characterized by broad ridging over the southeastern states, with general WSW flow at the mid-levels from the desert southwest into the great lakes states. At the surface, the pressure gradient will gradually become tighter, but not markedly so -- surface winds will likely remain in the 10-15 knot range (at most) on Wednesday and Thursday afternoons. Overall, with weak flow through the depth of the atmosphere over the Ohio Valley, there remain no clear signals for sustained or organized forcing. This makes the convective forecast very reliant on weak mid-level shortwave troughs, which will occasionally pass across the ridge, moving through the region from WSW to ENE. PoPs have been kept in the 20-40 percent range through the entire period, with the understanding that near-term and first-period forecast updates will eventually need to raise these chances on a short-term basis. The first shortwave -- with a fair amount of timing agreement -- is expected to move into the region on Wednesday morning. Instability will only be beginning to increase, as this shortwave will also be accompanied by some 925mb-850mb theta-e advection, paving the way for an increase in boundary layer moisture through the next several days. Initial activity is unlikely to contain thunder on Wednesday morning, but building instability (MLCAPE ranging from 1500 J/kg in central Indiana to 500 J/kg in central Ohio) will eventually support convective development. With the weak forcing and slight capping, only marginal storm coverage is expected, with little to no organization. Instability will become more pronounced on Thursday, as surface dewpoints increase into the mid 60s, and temperatures continue to increase only below 700mb (leading to steeper lapse rates in the mid-levels). However, NAM/GFS soundings indicate a likely cap at around 875mb, which will make storm development difficult without the help of some forcing. As has been mentioned, there is next to zero certainty in timing of any shortwaves at this point in the forecast, so any storm development is expected to remain isolated. Wind flow is also expected to be at a near-minimum on Thursday, which all adds up to too low of confidence to include any threat for strong storms in the HWO -- when it remains a possibility that the day could remain mostly dry for the ILN CWA. With that said, the high amounts of instability being forecast (SBCAPE greater than 2500 J/kg) deserve a mention in this discussion, alongside the acknowledgment that said instability may go mostly unrealized. Temperatures will continue a very gradual rise from Tuesday to Wednesday to Thursday, as low-level warm advection allows for increasing potential for warmth -- though additional moisture will also lead to diurnal cloud development. The warmest temperatures will continue to be forecast in the southeastern CWA, where cloud influence is likely to be lower. It should be noted that these temperature forecasts (lower 80s on Wednesday / lower-to-mid 80s on Thursday) could be too high if areas of convection are able to occur.
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&& .LONG TERM /FRIDAY THROUGH MONDAY/...
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Above normal temperatures with mainly afternoon thunderstorm chances will be characteristic of the long term period. With signal for warmer pattern with the ECMWF went with a target of opportunity to increase temperatures over the superblend. The superblend seemed especially low for Memorial Day. Increased temperatures over the blender however was somewhat conservative in case any afternoon convection limits temperatures. At this point limited any thunderstorm chances on Monday to a slight chance with limited instability.
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&& .AVIATION /19Z TUESDAY THROUGH SUNDAY/... Surface high pressure will continue to move east of the region through the TAF period. Meanwhile...a mid level disturbance to our west will move east into the area on Wednesday. Moisture will increase ahead of this feature in the form of mid level clouds at first tonight. Forcing is weak with this system. However...there could be enough lift for some spotty shower activity moving into the western terminals around 12Z. On Wednesday...the combination of the mid level feature and diurnal heating will result in some scattered shower/perhaps thunderstorms...with coverage expected to be low enough at this time to just carry a vcsh. OUTLOOK...Thunderstorms possible Wednesday afternoon through Sunday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hatzos NEAR TERM...Hatzos SHORT TERM...Hatzos LONG TERM...Novak AVIATION...Hickman

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