Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 250217 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 1017 PM EDT TUE MAY 24 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 WEDNESDAY MORNING/...
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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 low 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.
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&& .SHORT TERM /6 AM WEDNESDAY 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 /02Z WEDNESDAY THROUGH SUNDAY/... Surface high pressure will continue to move away from the region, allowing for a steadier, albeit light, southerly flow to become established. A very weak midlevel disturbance will approach the area by 12z, allowing for an increase in midlevel clouds overnight (likely inhibiting development of BR at any of the terminals). This disturbance may provide enough lift for spotty shower activity to move through western TAF sites of KCVG, KLUK, KDAY, and KILN in the 12-18z time frame. CAMs continue to differ on extent of coverage of activity, so kept KCMH and KLCK dry for now. During peak diurnal heating after 18z, there may be scattered SHRA/TS development across the area, but confidence doesn`t warrant inclusion in the TAFs as of right now. Southerly winds will remain light (around 10kts or less) through the period for all sites. OUTLOOK...Thunderstorms possible Wednesday afternoon through Sunday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hatzos NEAR TERM...KC SHORT TERM...Hatzos LONG TERM...Novak AVIATION...KC

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