Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 250613 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 213 AM EDT WED MAY 25 2016 .SYNOPSIS... 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. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... A broad low pressure in the high plains and an area of high pressure across the Carolinas will continue to provide a weak surface gradient across the Ohio Valley. This will result in light southerly winds through the overnight period. A weak mid level disturbance will approach the area by daybreak Wednesday, allowing for clouds to begin to filter in. Expect that temperatures will drop most rapidly during the first half of the night, then plateau somewhat as clouds begin to move in. Temperatures will bottom out in the mid 50s across the east where mostly clear skies are expected for the majority of the overnight period. Lows near 60 are expected across the Tri-State area. && .SHORT TERM /6 AM THIS MORNING THROUGH THURSDAY NIGHT/... 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. && .LONG TERM /FRIDAY THROUGH TUESDAY/... 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. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
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Surface high pressure sits off to our southeast while a mid-level disturbance currently over lower Ohio Valley will head our direction later this morning. The 25.00Z ILN sounding confirms a very dry airmass near the surface, but southerly flow will continue to draw increasing moisture into the region through the day today. Mid level clouds will increase from the southwest towards daybreak. Given the current dry airmass and expected increase in cloud cover, opted not to include any BR at KLUK, but cannot entirely rule out a brief period of minor, shallow BR there before daybreak. Aforementioned weak mid-level disturbance may provide enough lift for spotty showers to affect western terminals after 11Z this morning, as latest hi-res models continue to show. This activity would weaken as it progresses northeastward toward the Columbus terminals this afternoon. With only weak forcing, do not expect more than scattered coverage, so have only gone with VCSH. Also cannot rule out an isolated thunderstorm this afternoon in response to daytime heating, but have left out of TAFs due to low confidence in timing and location. Winds through the TAF period will be generally out of the south, increasing a bit this afternoon. OUTLOOK...Thunderstorms possible Thursday through Sunday.
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&& .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hatzos NEAR TERM...KC SHORT TERM...Hatzos LONG TERM...Novak AVIATION...Kurz

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