Area Forecast Discussion
Issued by NWS Wilmington, OH

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179 FXUS61 KILN 200739 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 339 AM EDT WED JUL 20 2016 .SYNOPSIS...
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High pressure will extend across the Ohio Valley and mid-Atlantic states today, with warm and generally dry conditions expected. As a large ridge builds over the central part of the country, heat and humidity will continue to increase through the weekend, with the warmest conditions expected on Friday and Saturday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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A large ridge of high pressure aloft has become well established over the central plains. At the surface, high pressure currently extends from the mid-Atlantic through the Ohio Valley, and will grow as it shifts gradually southward over the next day or two. Near-surface flow over the ILN forecast area remains quite weak, and this will remain the case through the day today, with only light southeasterly winds expected. The air mass has changed only very slightly from yesterday, allowing for a slightly-adjusted persistence forecast for max temperatures today, with no significant change in surface dewpoints either. The only significant challenge for the forecast today is for any convective potential. First and foremost, the cluster of storms currently over southwestern Indiana has continued to defy model projections by maintaining a slow easterly progression. This cluster split off from an earlier MCS, which had been propagating southeast along the 925mb theta-e gradient. The storms, as they currently exist and propagate, are expected to soon outrun their favorable environment. There is a notable dewpoint gradient from southwest Indiana to southeast Indiana, and less favorable thermal conditions just off the surface will also mean that any elevated instability feeding the storms will become weaker with eastward extent. SPC mesoanalysis indicates about 1000 J/kg of MUCAPE where the storms are currently located, but this diminishes to well under 500 J/kg at the border of the IND/ILN forecast areas. If they were to survive, at their current rate, it would take until 7AM for the storms to move into the ILN CWA. Though a few models suggest a chance for some precipitation in the western half of the forecast area this afternoon -- and a very, very isolated shower/storm or two may well occur -- the vast majority of locations should remain dry. The forecast will do the same as of now.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/...
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The short term forecast discussion will be updated soon. Previous discussion > Surface high pressure across the area on Wednesday will push to the east on Thursday. There is northwest flow aloft, however any disturbances are weak and generally east or west of the area. With no clear preciptiation signal, decided to go with a dry forecast at this time. Wednesday will be the cooler of the two days. As the high shifts to the east southerly flow will increase on Thursday and warmer air will move into the area. Heat index values will approach 100 across southwest portions of the forecast area on Thursday, however have values just under the 100 degree mark (heat advisory criteria).
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&& .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
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With an upper ridge established across the CONUS, a hot and mainly dry period is expected. For Friday, a few afternoon thunderstorms may be triggered in an unstable airmass by a short wave rounding the crest of the upper ridge. Isolated thunderstorms may still occur Saturday under weaker forcing but persistent instability. On Sunday, greater short wave energy entering the northern plains is forecast to develop a surface low that will drag cold front toward the ILN area. A better chance for thunderstorms will exist in increasing moisture and forcing ahead of the front. The chance for convection will continue Monday as the front makes its way across the area. Look for drier conditions Tuesday under weak high pressure behind the front. Temperatures will be hot. Highs in the 90s are forecast Friday through Sunday, with heat indices reaching heat headline criteria over 100. Somewhat cooler readings in the mid and upper 80s are expected Monday and Tuesday due to modest cold advection.
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&& .AVIATION /07Z WEDNESDAY THROUGH SUNDAY/... Surface high pressure centered over the eastern Great Lakes this morning will continue to extended southwest into the mid and upper Ohio Valley through tonight. Some cirrus can be expected from time to time in the northwest flow aloft along with some scattered diurnal cumulus clouds. Winds will be calm or light easterly this morning, light and variable this afternoon, then back to a light east or southeast wind tonight. OUTLOOK...Thunderstorms possible Sunday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...Hatzos NEAR TERM...Hatzos SHORT TERM...Novak LONG TERM...Coniglio AVIATION...Hickman

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