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Area Forecast Discussion
Issued by NWS Louisville, KY
Issued by NWS Louisville, KY
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272 FXUS63 KLMK 170541 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 141 AM EDT Sat Aug 17 2024 ...Updated Aviation Discussion... .KEY MESSAGES... * Strong to severe storms will be possible Saturday afternoon and evening. The main threats are damaging winds, hail, and heavy rainfall. There is a low, but non-zero tornado risk. * Scattered showers and storms will be possible Sunday afternoon, but severe weather is not expected. Lingering isolated showers will be possible on Monday, mainly east of US 127. * Dry weather is expected for much of next week, with well below normal temperatures. && .UPDATE... Issued at 925 PM EDT Fri Aug 16 2024 Conditions are still warm and very muggy after sunset, with KY Mesonet obs reporting temps in the upper 70s and low 80s, along with dewpoints in the 70s. A few very isolated showers have popped in our area, likely where there may be some diffuse boundaries from earlier, but also some slightly better theta-e advection and lingering MLCAPE. Otherwise, SBCIN is beginning to spread throughout, and should result in mostly dry conditions for the overnight. Perhaps some patchy valley fog will be possible in some areas by tomorrow morning, but otherwise no impacts to the region. Updated forecast products have been published for the evening, and everything remains in good shape. See short term section below for more details into tomorrow. && .SHORT TERM /THROUGH SUNDAY/... Issued at 325 PM EDT Fri Aug 16 2024 Scattered convection lingers in the Lake Cumberland region this afternoon within an axis of deep moisture (PW near 2 inches). Low- level forcing has diminished since this morning`s wave of convection, and most areas will stay dry this evening and overnight. Cannot rule out an isolated shower or storm this afternoon and evening, however. The low-level airmass continues to warm and destabilize, and isolated development could occur along a differential heating zone or perhaps subtle remnant outflow boundaries from early day convection. However, coverage is expected to remain isolated. Tonight will likely be dry with patchy fog development. A closed low will continue to rotate southeast over Michigan through tomorrow, with mid/upper level troughing digging southeastward over the Ohio Valley. This will provide increased forcing for ascent and strengthening low to mid-level westerly flow immediately downstream of the synoptic cold front. This increased forcing arrives coincident with the diurnal instability maximum, which should be more than sufficient given a lack of morning precip. Fcst soundings show a very warm, well mixed BL with fairly steep low-level lapse rates by early afternoon. Most hi-res CAMs suggest isolated convective development over southern IN and central KY by 17Z, with scattered to numerous showers/storms possible 19-00Z. Some strong to severe storms are likely. Sfc-based CAPE will likely peak above 2000 J/kg Saturday afternoon, with effective bulk shear of 30-35+ kts. Low-level SRH of 100-150 m2/s2 looks likely, which could support some updraft rotation. Fcst soundings do show rather high LCLs through much of the afternoon, however. There is a low, but non-zero tornado risk. The main threat is isolated damaging winds given the more favorable low-level thermodynamic environment. Hail will also be possible in the stronger storms, along with heavy rainfall. Some localized water issues are possible, though the storms will be progressive. Any localized storm mergers, or unusual training, could produce very localized flash flooding. Tonight will be humid with lows in the upper 60s to lower 70s. Temps should max out in the upper 80s to lower 90s Saturday afternoon. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Issued at 325 PM EDT Fri Aug 16 2024 Saturday Night - Monday... Tomorrow evening, scattered clusters of strong or severe thunderstorms should be ongoing around sunset, with convective active focused in the vicinity of a cold front which will be dropping from NW to SE through the Ohio and Tennessee valleys. Current short-to-medium range guidance suggests the potential for strong to severe storms will end by around sunset across southern IN as the effective boundary passes through, but should continue until around or just after midnight across central and southern KY. Would expect a trend toward upscale growth of storms into larger linear segments later in the evening, causing damaging winds to be the primary severe threat in addition to general thunderstorm threats of heavy rainfall/flooding and lightning. Sunday morning should bring a break in showers and storms as the frontal boundary pushes into Tennessee. However, by Sunday afternoon, diurnal heating should combine with lingering low-level moisture to allow another round of showers and storms to develop, with the greatest coverage expected along and east of I-65. It should be noted that the "fuel" available for storms on Sunday shouldn`t be nearly as plentiful as on Saturday afternoon, and the instability profiles are less conducive for explosive convection (i.e. "tall, skinny CAPE"). Shear should also be less on Sunday, with W/NW low-level winds and weaker mid-level flow reducing effective shear to between 15-20 kts. As a result, expect something akin to "garden variety" showers and storms Sunday afternoon into the early evening, with convection tapering relatively soon after sunset. Temperatures should be noticeably cooler on Sunday as low-level cold advection moves in behind the cold front. Continued low-level CAA via NW winds should continue into Monday, with highs remaining below normal across the region. Another lower chance for showers or a storm will be possible on Monday ahead of a secondary boundary which should bring much drier air into the region for the middle of next week. Most of the precipitation should remain east of US 127 on Monday, and all areas should be dry by Monday evening. The Rest of Next Week... Behind this last wave of precipitation Monday afternoon, anomalously dry air should move across the region for much of the rest of next week. ECMWF ensemble mean PW remains below the 10th percentile of model climatology from Tuesday through Thursday, with GEFS/CMC ensembles showing a similar picture. In addition to the dry air, temperatures are expected to remain quite modest for mid-August, with a strong area of sfc high pressure funneling cool air from central Canada southward through the mid-week period. Ensembles are also supportive of below normal temperatures, with the ECMWF Extreme Forecast Index having values below -0.8 for MaxT and MinT next Tuesday and Wednesday. In fact, there is high confidence in lows in the 50s and an outside potential for lows in the upper 40s in the coldest locations next Tuesday and Wednesday morning. Temperatures will begin to recover next Thursday and Friday as the sfc high and upper ridge axis starts to shift eastward, with dry weather continuing into the end of next week. && .AVIATION /06Z TAFS THROUGH 12Z SUNDAY/... Issued at 140 AM EDT Sat Aug 17 2024 Expect a clear night with VFR conditions continuing. Heading into the daylight hours, some uncertainty remains. Some model guidance has convection developing over southern Illinois and Missouri over the next few hours. If this forms, the cloud cover it produces could help limit or delay afternoon thunderstorms at some area TAF sites. Currently, believe LEX and RGA are the sites most likely to see thunderstorm activity during the afternoon and evening hours. There is more uncertainty in SDF`s forecast. If the convection develops over the next few hours to our west, it could continue and pass by SDF as an area of broken showers, but if nothing develops farther west, it will increase afternoon instability which increases the risk for afternoon thunderstorms at SDF. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ UPDATE...CJP SHORT TERM...EBW LONG TERM...CSG AVIATION...KDW