Area Forecast Discussion
Issued by NWS Wilmington, OH
Issued by NWS Wilmington, OH
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139 FXUS61 KILN 270156 AFDILN AREA FORECAST DISCUSSION National Weather Service Wilmington OH 956 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 THIS MORNING/... Upper low in the lower Ohio Valley will continue to meander around its current location. As Hurricane Helene makes landfall overnight and begins to track northward over land, will begin to observe an influx of anomalously high moisture values in our CWA. While the rainfall won`t be heavy overnight tonight, we will observe a gradual increase in light rain coverage across our counties from south to north. Northeasterly winds will also begin to increase overnight, but only expecting gusts of 20-25 mph before daybreak. The more notable increase in winds will arrive during the late morning and afternoon hours on Friday. && .SHORT TERM /7 AM THIS MORNING THROUGH 6 PM SATURDAY/... 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 NIGHT THROUGH WEDNESDAY/... 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 /02Z FRIDAY THROUGH TUESDAY/... Anticipating more VFR conditions to start the overnight period before categorical reductions become more prominent. Several aviation impacts expected from the remnants of Helene. Light rain will gradually increase in coverage overnight tonight, becoming more steady (and heavier, especially for our southern terminals) throughout the day Friday. Anticipating mainly MVFR reductions from rainfall. CIGs will reduce to MVFR tonight across our KCVG/KLUK terminals first, gradually progressing northward towards our northern terminals by early Friday morning. CIGs expected to be less than 2000 ft AGL majority of Friday, and while IFR CIGs are certainly possible, not confident enough to include in the tafs yet. Winds will certainly be impactful as a gradual increase in winds is expected overnight into Friday. Strongest winds still expected across our southern terminals, particularly KCVG/KLUK. Could see a slight increase in forecast wind speeds (especially sustained winds) if the Helene tracks more northeasterly, so will have to monitor trends and adjust accordingly. For now, also put a mention of LLWS for every terminal given the fact that several models are suggesting potential for 50-60+ kt winds 2000 ft AGL, mainly during the afternoon hours Friday. 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...Clark SHORT TERM...McGinnis LONG TERM...Hickman AVIATION...Clark