Area Forecast Discussion
Issued by NWS Louisville, KY
Issued by NWS Louisville, KY
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047 FXUS63 KLMK 281724 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 124 PM EDT Fri Jun 28 2024 ...Updated Aviation Discussion... .KEY MESSAGES... * Hot and muggy with a few showers around today. * Storm chances increase Saturday into early Sunday. Locally heavy rain and gusty winds will be the main threats. Above normal temperatures return by early/mid next week. * Another period of unsettled weather returns to the region by late Wednesday and Thursday. && .UPDATE... Issued at 1116 AM EDT Fri Jun 28 2024 Current forecast remains in good shape this morning. Sat and obs show mostly sunny skies across the CWA. Temps had already climbed into the lower 80s in the I-65 corridor and points west. To the east, temps were in the upper 70s to near 80. Afternoon temps should top out in the upper 80s with a few spots hitting 90-92 (mainly in the urban areas). Heat index readings will be in the upper 90s with a few spots topping 100. Model soundings from the 12Z CAMs continue to show a cap around 700- 650mb this afternoon. Really am not seeing a tremendous amount of forcing to get parcels to break through, but that cap is a bit weaker down across south-central KY and the Lake Cumberland region. Overall, a few showers may pop up in the heat of the afternoon mainly SE of a line from roughly Bowling Green to just south of Lexington. && .SHORT TERM /THROUGH TONIGHT/... Issued at 317 AM EDT Fri Jun 28 2024 Fairly quiet weather expected in the short term as our region sits between upper ridging over the SE CONUS and a stronger belt of westerlies across the northern CONUS. That being said, a couple of sensible weather items worth discussing. Surface high pressure centered over the NE CONUS will continue to slide eastward today. Meanwhile, a surface low will slide through the upper Midwest and into the Great Lakes region. We`ll see light SE surface winds this morning take on a more steady S component through the afternoon as a warm front develops and moves east of our area. As previous discussion mentioned, we`ll see an uptick in theta- e advection with our area in the warm sector, and PWATs will rapidly accelerate up above 2" through the column. As a result of this, expect to see convective development initiate, however forecast soundings continue to show a pretty stout inversion around 650 mb or so. Looks like there could be a good 8-10 thousand feet of vertical depth between where parcels are convectively released and where they encounter the inversion, which will be sufficient for some isolated rainfall. However, the cap looks unlikely to break and this seems to be confirmed by forecast models continuing to only show light qpf blips (showers) rather than more intense pockets of QPF (t-storms). So, will elect to just put shower mention in the forecast with the idea that the inversion/cap will hold. Good thing the cap is there, as the overall sounding is fairly unstable with plenty of positive area up to the EL. Best coverage of pops should be along and east of I-65 through the afternoon and evening, and then across our northern CWA toward dawn on Saturday. Overall, most folks should stay dry. Outside of the precipitation chances, temperatures look to recover back above normal. Given the warm advection component and enough solar insolation through thin upper clouds and few-sct afternoon cu, highs are expected to mostly reach into the 89-93 degree range. Max heat indices could peak around 100 for some. Continued warm advection, some upper sky cover, and high dewpoints all point to a mild and muggy overnight. Lows will mostly stay in the mid to upper 70s. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Issued at 317 AM EDT Fri Jun 28 2024 ===== Saturday - Sunday ===== An upper shortwave will be swinging across the Great Lakes region on Saturday, which will drag an associated sfc low across southern Ontario and into Quebec. A southward extending cold front will stretch as far south into Texas, and will be pushing east-southeast towards the Ohio Valley through the day. Ahead of the arrival of the front, we will have plenty of time for temps to reach the lower 90s. Additionally, a more humid airmass will be in place, with sfc dewpoints likely approaching the mid-70s. This temperature and dewpoint combination will result in afternoon heat indices exceeding 100 degF. The cold front will gradually approach the Ohio River late in the day, which will provide the opportunity for a marginal severe risk in the afternoon. Plenty of sfc heating in a humid airmass will support afternoon destabilization ahead of the front. The 100-member LREF has a 70-80% probability of exceeding 1000 J/kg of SBCAPE Saturday afternoon across the forecast area. A 50-60% prob of exceeding 1500 J/kg exists west of the I-75 corridor. It`s possible some areas could realize upwards up 2000 J/kg of SBCAPE, though the probabilities fall below 40%. Along with the instability expected, a very high PWAT airmass will be present. Model soundings suggest we could have PWATs exceeding 2 inches. LREF mean-ensemble paints 2.05- 2.15" across the region, which would be near the daily max values from SPC sounding climatology from BNA and ILN. Despite these two favorable indicators, wind shear appears to be fairly weak, with model soundings generally agreeing around 20kts of bulk shear. Sounding profiles show tall CAPE profiles, with deep warm cloud layers, which will support precip-loaded storms capable of wet microbursts and heavy rain rates. With rather marginal flow, storm motions will also be fairly slow, leading to an additional concern for localized flooding issues. SPC continues with the Marginal risk in Day 2. PoPs will continue into Saturday night and early Sunday morning as the front sweeps through the region. Drier air aloft will be increasing overnight, though low level capping will help decrease any storm strength as we get later into the night. Still see the potential for some storms, but the loss of heating will be in our favor. PoPs will gradually exit from NW to SE through Sunday morning and afternoon, with the front taking it`s time to clear our southern counties until later in the day. This delay will keep low chance PoPs going across south-central Kentucky through the early afternoon hours. Eventually we`ll be PoP-free by late Sunday afternoon. Temps will also respond to the post-frontal regime, with lower 80s across southern IN, and temps back to near normal for Kentucky counties. The real difference will be felt in those dewpoints. Dewpoints are expected to be in the low-60s north of the Ohio River, mid-60s across central Kentucky, and low-70s along and south of the Cumberland Pkwy due to the front lingering. This will result in a pretty big difference in heat indices from north to south for the forecast area. ===== Monday - Tuesday ===== Dry weather will be around to start July, thanks to upper ridging and sfc high pressure shifting cross the Midwest. Monday`s high temps will be below normal for July 1, with readings only expected to be in the low-80s. Sfc high pressure will continue to shift off to the east for Tuesday, which will place us into a more warm return flow pattern. Highs on Tuesday will exceed 90 degF, though mild dewpoints will keep heat indices below triple digits. ===== Wednesday and Beyond ===== An upper shortwave riding in the flow will flatten out the upper ridge by Tuesday night. Another cold will be approaching the region by Wednesday, leading to PoPs making their way back into the forecast. It appears this front could stall out somewhere within the region by Thursday, which would promote additional shower and storm development as we get into the end of the week. && .AVIATION /18Z TAFS THROUGH 00Z SUNDAY/... Issued at 124 PM EDT Fri Jun 28 2024 VFR conditions are expected to continue through the period. This afternoon look for a diurnal Cu field around FL040 with south to southwest winds of less than 7 knots. A few isolated showers may pop up over in the KLEX/KRGA area, but sparse coverage precludes a mention in the TAF at this time. For tonight, winds will slacken off toward sunset and then become more southeast. A few high clouds will stream in from the northwest, but conditions will remain VFR. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ UPDATE.......MJ SHORT TERM...BJS LONG TERM....CJP AVIATION.....MJ