Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 221732 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 132 PM EDT Tue Aug 22 2017 .SYNOPSIS... A cold front pushing through the Ohio Valley will bring organized showers and thunderstorms today, then drier and cooler air moves in for the rest of the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Made a few PoP timing and coverage adjustments in the near term into the early short term period per latest radar trends and CAM solutions. Did adjust temps down a degree or two in the northwest with extensive cloud cover and incoming pcpn shield advancing eastward from Indiana. Although convective coverage has shown a recent downward trend upstream of our FA, expect that there will be enough coverage to warrant categorical PoPs through the morning hours for western/northwestern parts of the FA. Initial cluster(s) of SHRA/TS is/are not expected to pose much of a svr threat as destabilization won/t likely be robust enough through morning to allow for deep convection. Nevertheless, as we progress into early/mid part of the afternoon, southern and eastern parts of the area should destabilize enough that afternoon/early evening activity may pose an isolated damaging wind risk (especially along and east of the I-71 corridor). Even with this, activity should exit the FA around or shortly after 00z, bringing an end to any and all svr risks for late evening into tonight. PREVIOUS DISCUSSION... Varying scenarios playing out via the CAMs, with HiRes NMM/HRRR slowly diminishing the early morning convection over Indiana as it pushes toward forecast area. What precipitation that does work into western forecast area expected bring enough clouds to inhibit destabilization in the western forecast area for the afternoon, so have generally kept severe potential wording further east where enough heating combined with 40kts+ of 0-6km bulk shear will be present as the prefrontal trough pushes through the eastern forecast area in the 18-22z timeframe. Main severe threat will be damaging winds. Greatest confidence in thunderstorm coverage south/east of I-71, along with greater confidence in at least a few severe storms this area. NW of I71, expecting most scattered coverage and less likely to be severe, though a narrow line of storms indicated by numerous CAMs associated with the frontal passage itself. In addition to severe threat essentially east of I-71 corridor, as the progression of the trough slows slightly especially along and south of the Ohio river, concern is an East-West oriented line segment which could pose a more favorable pattern for training storms and a localized flood threat. While ample deep moisture available over nearly all of area in the form of PWs at 1.75-2" and warm cloud depths of 3.5-4k, central Ohio storms likely to be more N-S oriented line segments, which will produce heavy rain but storms should be fairly progressive.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Cold front to push through the region in the 00-03z timeframe Wednesday, with some lingering showers in the far southeast as the surface boundary will be less progressive in nature. Below normal temperatures through this period with the strong cold frontal passage and then surface high pressure building in under an upper level trough where NW flow will dominate the region through Wed. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... Beautiful weather is in store for most of the long term as below normal temperatures, dry conditions, and lower dewpoints take hold across the region. Overall, the long term will be characterized by below normal height anomalies as well as below normal 850 mb temperatures. This will be in large part due to a longwave trough axis that looks to remain in close proximity to the region through the weekend. Wednesday evening will open up with an upper level low pushing east across Quebec. At the same time a potent shortwave will drop south out of Saskatchewan/ Manitoba. This shortwave will drop down towards Michigan Thursday afternoon acting to reinforce the longwave trough axis west. As this happens low level CAA will continue with an expansive cu field likely forming in the afternoon. 850 mb temperatures Thursday fall to around 8 degrees C (GFS slightly cooler than the ECMWF) with 1000/ 850 mb thicknesses around 1375 m. 500 mb heights on the NAEFS are around 1 to 2 standardized anomalies below normal for this time of year with 850 mb temperatures following suite. Even with it being August still thinking high temperatures will struggle a bit Thursday given the likely cu development. Have gone ahead and lowered high temperatures Thursday into the mid 70s with thicknesses alone supporting highs in the lower 70s (esp northern zones). Thursday night into Friday morning the trough axis will begin to modulate and nudge east allowing the best ageostrophic convergence to push closer to the area. Friday afternoon thicknesses and 850 mb temperatures remain similar to Thursday, with the only difference being less cu probably (thanks to PWATs falling to around 0.60"). Saturday morning looks to be the coolest as surface high pressure and ageostrophic convergence settles overhead. Winds will also likely decouple. GFS forecast soundings are hinting at some cirrus moving in but we will likely see some upper 40s in rural zones Saturday morning. Saturday afternoon the trough axis will slowly pull east allowing low level thicknesses and temperatures to ever so slowly recover. By Sunday surface high pressure will be off to the east with temperatures approaching the 80 degree mark. The area also looks to remain dry through Sunday as PWATs hover around 0.50" (or near record low values for this time of year). By Monday models begin to diverge as an upper level disturbance is forecast to dive south into the plains with an upper level jet at 250 mb amplifying. As this occurs the ILN forecast area will fall into a LFQ which means rain chances will likely be on the increase. There still remains uncertainty though on how everything will play out so have just trended towards chance PoPs at this time. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/...
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Convective activity starting to come together for the afternoon hours with main time frame to impact terminals within the first hour or so of the valid TAF period before activity slides east of the local terminal corridor. Did include TEMPO VSBY and CIG restrictions, especially for eastern terminals of KCMH and KLCK where activity will be slowest to clear. Nevertheless, main convective lines will be east of terminals by 21z or so, with just some lingering -SHRA for an hour or two past that. By this evening, VFR conditions are expected area- wide with a veering of winds from WSW to NW past 03z. Light winds will prevail overnight but should stay up enough to prevent widespread BR. This being said, did add a TEMPO MVFR VSBY restriction at KLUK around sunrise Wednesday, despite unfavorable wind direction. Past 12z Wednesday, some diurnally driven VFR Cu will likely develop as CAA scheme becomes established in the area. Cannot completely rule out an isolated -SHRA for northern terminals towards very end of period, but isolated nature of coverage and lack of confidence precluded inclusion for right now. OUTLOOK...No significant weather.
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&& .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...JDR/Sites NEAR TERM...KC SHORT TERM...JDR/Sites LONG TERM...Haines AVIATION...KC

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