Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 190136 AFDILN AREA FORECAST DISCUSSION National Weather Service Wilmington OH 936 PM EDT Sun Aug 18 2019 .SYNOPSIS... A disturbance will move across the region tonight bringing a round of thunderstorms. Additional storms will be possible from time to time from Monday through Wednesday until a cold front moves through the region. Cooler and less humid conditions will work into the area Thursday and Friday. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... Convective line is pushing east across western portions of our fa. This is associated with a mid level short wave that will progress east through the early morning hours. For the most part, the convective line has been weakening as it has moved into our area with the strongest activity now to our north in an area of slightly better forcing/shear. The airmass across our east is still unstable though so it may take a few hours for the convective line across our area to completely wind down. Have nudged up pops across about the northern two thirds of our fa through the rest of this evening to account for this. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Guidance suggests that a weak boundary will be in the area which will be a focus for slightly enhanced moisture. With heating this will be a zone of higher instability. With weak disturbances moving across the area, there will be a chance of additional storms Monday afternoon. Cannot rule out the possibility of isolated activity continuing into Monday night. With no change in airmass, expect highs and low to be near persistence. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Quasi-zonal/west-northwest midlevel flow will remain entrenched across the lower Great Lakes region through the first part of the workweek, with a quasi-stationary/oscillating front stretching across the heart of the Ohio Valley for Tuesday into Wednesday. The front will gain a bit of southward momentum Monday night as heights fall aloft and surface high pressure builds east through the heart of the Great Lakes region by Monday night. However, the front will become somewhat washed out across the area by early Tuesday, with southwesterly surface flow resuming area-wide by Tuesday afternoon. And with the remnant synoptic-scale boundary (and potentially several convection-induced mesoscale boundaries) lingering about the area on Tuesday, will maintain a chance PoP across most of the ILN FA -- especially during the diurnally-favorable time frame of afternoon/early evening. Although the deep-layer flow fields appear to be rather weak in nature -- generally 20kts or less through the bottom 30kft of the column -- the moderate to high instability could be enough to initiate some slow-moving convective re-initiation during the afternoon/early evening -- especially in the presence of the aforementioned boundary(ies). Although the best chance for this isolated to scattered development appears to be centered across the middle of the ILN FA, identification of the subtle boundaries which will provide the ultimate focus for such activity is very difficult at these time ranges -- lending itself to lower confidence on exactly what areas may be favored for afternoon thunderstorms on Tuesday. The hottest day of the extended period will likely be Tuesday ahead/south of the aforementioned E-W oriented front across the northern/central Ohio Valley -- with heat index values in the upper 90s possible mainly south of the I-70 corridor. This being said, confidence on these values being met is rather low given the aforementioned uncertainties in cloud/convective coverage during peak heating hours. By Wednesday, mid/upper level troughing across the Great Lakes region will become more pronounced as a stronger/better push of cooler/drier air arrives late Wednesday night into Thursday with the passage of a cold front. The arrival and subsequent progression of the cold front through the region later Wednesday will likely bring with it the best chance for widespread showers and storms Wednesday afternoon/evening than will be the case at any other point during the entire long term period. While the specifics of the this system and the corresponding impacts on the sensible weather locally are still a bit uncertain, feel confident in maintaining high chance PoPs Wednesday into Wednesday night. And although cooler and drier air will be filtering in Wednesday night -- especially near/north of the I-70 corridor, the front/s progression south may be slowed somewhat as it nears the Ohio River as more S/W energy ejects east from the mid-Missouri Valley into the western Tennessee Valley. This may act to stall /or at the very least slow/ the front/s progression southward Thursday morning through Thursday evening before it finally begins to definitively push south of the ILN FA Thursday night. The slowed progression early Thursday may may allow for continued PoPs mainly along/south of the Ohio River before drier conditions return area-wide by Thursday night. Much cooler and less humid air will build into the region for Friday and Saturday as high pressure returns to the area. Confidence remains fairly high in seasonable temperatures and dry conditions for the final part of the week. && .AVIATION /02Z MONDAY THROUGH FRIDAY/... Thunderstorms have continued to develop across Indiana early this evening and have begun to organize into more of a line across central Indiana. Hi res models are showing this continuing to push east into our area through mid to late evening with some possible development along the southern edge. They are also indicating an overall weakening trend as the storms move into our area. We are still fairly unstable across our area though so there is some uncertainty as to just how fast they will begin to weaken. KDAY appears to have the best chance for seeing thunderstorms through the evening hours and will try to time those in with a tempo tsra. With less certainty at the remaining TAF sites, will cover with just a VCTS for a few hour period. These storms are at least partially associated with a mid level short wave that will move east across the region tonight. As we get on the back side of this and continue to lose the diurnal heating, expect pcpn to taper off through the overnight hours. Some mainly valley fog will be possible later tonight, especially in the southern valleys. Otherwise, expect VFR conditions through the remainder of the TAF period. OUTLOOK...Thunderstorms possible Tuesday and Wednesday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS... NEAR TERM...JGL SHORT TERM... LONG TERM...KC AVIATION...JGL

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