Area Forecast Discussion
Issued by NWS Wilmington, OH

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424 FXUS61 KILN 272351 AFDILN Area Forecast Discussion National Weather Service Wilmington OH 751 PM EDT WED JUL 27 2016 .SYNOPSIS... A stalled frontal boundary near the Ohio River will provide a chance for scattered showers and thunderstorms through this evening. A wave of low pressure traveling along the front will bring an increased likelihood for showers and thunderstorms Thursday into Friday. Unsettled weather will continue into the weekend as several disturbances aloft interact with a persistently moist and unstable airmass. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Afternoon satellite imagery reveals the stationary front positioned just south of the Ohio River where dewpoints are in the low to mid 70s. Isolated to scattered showers and storms are forecast through this evening mainly in the vicinity of the front. Mid level energy currently triggering a thunderstorm complex over the Lower Mississippi Valley will lift northeast and become caught up in a digging trough over the Upper Midwest. This will carry the energy into the Ohio Valley late this evening into early Thursday, with the better forcing triggering a better chance of showers and storms across our southwest between 04-10Z. This scenario is supported by various CAMs, though they remain split on timing. The good news is that any activity tonight, though it will develop in a moist environment with PWATs around 2 inches, should be pretty progressive as it pushes east through the greater Cincy Tri-State area. Aside from some recent heavy rain over Ripley County and just south of Cincinnati, this area has not seen much excessive rainfall lately. Cannot rule out some storms with heavy rain, but am not expecting more than a very localized flash flood threat from the activity late tonight. Went close to guidance for lows tonight in the upper 60s to lower 70s. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... Main concern on Thursday will be a higher potential for some flash flooding across mainly south-central Ohio and northeast Kentucky as a potent shortwave crosses the ILN CWA and interacts with a very moist airmass. This shortwave energy will develop a couple weak surface lows that will lift through eastern KY into south- central OH in a moisture rich environment with PWATs of 2 to 2.2 inches (2-3 sigma above normal for this time of year). Warm cloud depths will be >4km and a modest LLJ will lead to favorable moisture transport across our southeast, though conditions will be most favorable just outside of the ILN CWA. Given bulk shear vectors from the southwest, do expect potential for training cells over southern Ohio and northern KY. Synoptic models are in pretty good agreement with the axis of heaviest precip setting up over our southeast, so have issued a flash flood watch for this area. At this time expect 1.5 to 2 inches of rainfall within the watch area with locally higher amounts possible. Later shifts will have to monitor whether the better forcing and axis of heaviest precip may shift further west, though. While 0-6km wind shear across our south will range from 25-35 knots, forecast soundings show a nearly saturated column through the mid levels with tall skinny CAPE <1000 J/kg. Thus, severe potential should be limited. Precip chances will decrease Thursday night as the best forcing pushes east. Cloud cover and rain will keep temperatures down across our southeast, where highs will likely struggle to reach 80. It will be warmer northwest of I-71 where temperatures will climb into the low to mid 80s. Lows Thursday night will be in the mid to upper 60s. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... The long term will start with a series of upper level disturbances moving across the area along with a front stalled out. This will help to keep the chance of rain in the forecast almost through the entire extended until Tuesday when weak mid-level ridging moves into the region. Looking more into the details, Friday will open up with a shortwave moving across the region and the leftover frontal boundary from earlier in the week still across the area. Upper level lift is sufficient with weak PVA moving across and moisture values remain above average for this time of year with PWATs forecasted to be around 1.70". Instability is also present with ML CAPE values around 500 J/kg. As the shortwave exits Friday PoPs will slowly taper off due to weak subsidence behind the wave. Saturday through Sunday another weak shortwave trough will remain in close proximity to the area with a surface front located across the CWA. This will help to bring the chance of rain right back to the area. Given the weak upper level trough quickly pulling east the cold front stalling across the area seems likely. Given the chance of showers and thunderstorms during the day have kept high temperatures near climo. Monday into Tuesday as the shortwave trough exits weak mid-level ridging will then build overhead as mid-level high pressure builds over the central United States. There still remains timing differences on when the high will build and how far it will build east. For now have just trended PoPs down. && .AVIATION /00Z THURSDAY THROUGH MONDAY/...
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Convection has developed this afternoon/evening across parts of the southern Ohio Valley but has remained south of the terminals. Forcing will remain fairly weak through the evening hours, so kept TAF sites dry through evening period. VFR conditions are expected for the first part of the TAF period. A H500 s/w will begin to approach the region late tonight, allowing for a surge of moisture northward as a weak sfc boundary begins to pivot back into the area. -SHRA with potential for TS across southern TAF sites will work into area from southwest as warm front begins to slowly lift northward. Activity will increase in coverage after 09z, with most widespread coverage expected along and south of the I-71 corridor. BR could result in MVFR VSBYs at KLUK before pcpn moves in, but anticipate that increase in cloud cover/pcpn should keep VFR VSBYs at all other sites. Went ahead and sped up onset of SHRA/TS activity per latest hi resolution models. Before 18z, potential for TS should be limited to southern TAF sites as shield of SHRA moves ENE thru area. As main pcpn shield migrates east of wstrn sites by early aft, instby may begin to increase for western parts of area. Therefore, kept VCTS in for remainder of period despite uncertainty regarding mesoscale environment in wake of morning/early afternoon activity. OUTLOOK...Thunderstorms likely Thursday night through Saturday.
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&& .ILN WATCHES/WARNINGS/ADVISORIES... OH...Flash Flood Watch from 2 AM EDT Thursday through Friday morning for OHZ079-081-082-088. KY...Flash Flood Watch from 2 AM EDT Thursday through Friday morning for KYZ097>100. IN...None. && $$ SYNOPSIS...Kurz NEAR TERM...Kurz/Sites SHORT TERM...Kurz LONG TERM...JDR AVIATION...KC

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