Area Forecast Discussion
Issued by NWS Wilmington, OH
Issued by NWS Wilmington, OH
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066 FXUS61 KILN 261944 AFDILN AREA FORECAST DISCUSSION National Weather Service Wilmington OH 344 PM EDT Thu Sep 26 2024 .SYNOPSIS... As the remnants of Helene track north, rain will spread into the area. In addition, it will become breezy on Friday. Low pressure will then linger in the Ohio Valley through the weekend keeping conditions unsettled. && .NEAR TERM /UNTIL 7 AM FRIDAY MORNING/... As one upper level low slips away to the northeast of the region, the second upper level low has separated from the primary jet stream flow stalling over the lower Ohio Valley region. The upper low will interact with Hurricane Helene as it makes landfall in Florida later this evening, pulling it northward toward the Appalachian Mountains. For the near term period, much of the weather impact will be minor, as light rain continues to stream northward within a belt of anomalous deep layer moisture. The pressure gradient does increase overnight in response to the approaching low pressure (Helene). Winds around 15 to 20 mph are likely to be occurring by the end of the period with wind gusts between 20 to 30 mph. && .SHORT TERM /7 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... Key Messages... 1. As Helene remnants approach the Ohio Valley, confidence is increasing that a low pressure between 980 and 985 mb will slide through Kentucky/Tennessee Friday afternoon. Depending on the exact track of the low pressure, a period of strong winds, potentially resulting in scattered damage and power outages is forecast to occur through the afternoon and early evening. 2. Period of moderate to heavy rain will result in rainfall amounts of 1 to 3 inches, generally focused over southeast Indiana, northern Kentucky, and southwest Ohio. While drought has persisted for many months, continuous rainfall may result in scattered flooding in certain area. Riverland flooding can`t be ruled out, depending on the rainfall amounts. This would be more likely into the long term period as additional rain falls. Details: Wind/wind gusts... In collaboration with surrounding offices, a wind advisory has been issued from 10 am to midnight, for winds of 25 to 35 mph and gusts between 45 and 55 mph. The 12Z suite of guidance increased in wind values, as the remnants of Helene are expected to approach the Ohio Valley Friday morning. The pressure gradient will drive strong northeasterly to easterly winds beginning in the morning, intensifying into the early and late afternoon. As Helene continues to gradually strengthen in the eastern Gulf, there is still some uncertainty as to the overall low pressure value as it enters the Ohio Valley. There is certainly the potential for lower and higher wind values depending on the magnitude of the low pressure and the exact track. However, enough confidence was in place to start with a wind advisory focused over a large portion of southwest Ohio, southeast Indiana, and northern Kentucky. The advisory could be expanded or potentially upgraded to a High Wind Warning if necessary. While the track is important, another one of the primary reasons for the uncertainty is because a saturated low-level atmosphere mixes boundary layer winds less efficiently. This would limit the ability for the higher end winds at 1500-2000 feet mixing to the surface. There may be period of dry air where stronger winds are able to mix more efficiently to the surface. These details are yet to be ironed out. Rainfall...PWAT anomalies 200-250% will be present over the Ohio Valley as the remnants move through Friday. While thunderstorm driven rain bands aren`t expected, sustained moderate rainfall rates within the tropical air mass will put down decent amounts of rain during the 3 to 6 hr period. This may result in localized areas of flooding, primarily in the south and southwest portions of the area where terrain may also play an important role. A flood watch was not issued given the lack of sustained rates over a high confidence area. The ongoing drought was also considered. Riverland flooding could become more of an issue in the long term period. && .LONG TERM /SATURDAY THROUGH THURSDAY/... On Saturday, a vertically stacked low pressure system will be located over western Kentucky. The low will move ever so slowly into central Kentucky by Sunday morning. Dynamics and lift will be maximized across the Tri-State during this period, trailing off as one heads north. Showers are in the forecast, with some locally moderate to heavy rain possible for the Tri-State. The period of heaviest rain will be during the day Saturday. Temperatures will be held down on Saturday due to clouds and pcpn, but remaining warm at night. Highs will range from the upper 60s across the Tri-State to the lower to mid 70s in our northern and eastern periphery of the forecast area. Lows will bottom out in the lower to mid 60s. The period Sunday through Tuesday will feature a slow process of the vertically stacked low weakening and shearing over time as it lifts northeast across the Great Lakes and Ohio Valley. Best chance for showers, perhaps a thunderstorm, will be highest on Sunday, with lingering chances of pcpn into Monday. By Monday night into Tuesday, the system will eject northeast as a digging mid level trough and associated cold front move into southeast Canada and the northern Great Lakes. The cold front is forecast to pass through the region Tuesday into Tuesday night. This front will be followed by surface high pressure on Wednesday which will move east of the area on Thursday. Highs on Sunday will once again be held down by clouds/pcpn, in the lower 70s. Highs warm Monday into Tuesday, especially Tuesday ahead of the cold front (75 to 80), with temperatures then cooling some by Wednesday (upper 60s/lower 70s). A rebound in highs will occur on Thursday with sunshine. Lows will initially start out in the 60s with the coolest night on tap for Thursday morning (mid 40s/lower 50s) && .AVIATION /19Z THURSDAY THROUGH TUESDAY/... Still dealing with lingering MVFR CIGs at some of the sites early this afternoon. Improvement to VFR is expected through the afternoon before MVFR CIGs settle in for the remainder of the TAF after 00Z. The TAF period now includes the onset of stronger winds & wind gusts Friday afternoon. These values will likely need some adjustment with future forecasts. LLWS has also been added in for CVG/LUK. ILN may be needed with higher confidence. Plentiful tropical moisture will provide low-end MVFR CIGs, with MVFR VIS expected in moderate rain. IFR restrictions can`t be ruled out. OUTLOOK....MVFR ceilings likely Friday night and possible again Saturday through Monday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...Wind Advisory from 10 AM Friday to midnight EDT Friday night for OHZ042-051>054-060>063-070>072-077>081. KY...Wind Advisory from 10 AM Friday to midnight EDT Friday night for KYZ089>100. IN...Wind Advisory from 10 AM Friday to midnight EDT Friday night for INZ050-058-059-066-073>075-080. && $$ SYNOPSIS...McGinnis NEAR TERM...McGinnis SHORT TERM...McGinnis LONG TERM...Hickman AVIATION...McGinnis