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Area Forecast Discussion
Issued by NWS Louisville, KY
Issued by NWS Louisville, KY
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749 FXUS63 KLMK 160517 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 117 AM EDT Tue Jul 16 2024 .KEY MESSAGES... * Very warm and muggy conditions overnight provide little relief. * Triple-digit heat index values Tuesday. * Showers and storms return mid week as a cold front pushes through the region. * Cooler temps in the 80s for Thursday into Saturday. && .UPDATE... Issued at 903 PM EDT Mon Jul 15 2024 An exceedingly warm and very muggy night is in store for the Ohio Valley, as earlier storms over southeast Indiana are dissipating before they reach the river. Strong to severe convection over eastern Iowa and northern Illinois will continue organizing into a MCS and eventually dive southward. At this time, would not expect it to reach our southern Indiana counties, where we barely have a 20% chance for precip to cover that possibility. If anything we`re more likely to see some outflow as far south as Jasper, Salem, and Madison, but by that point it should be outrunning any convection. Oppressive heat and humidity will continue on Tuesday, with different portions of the area teetering on Heat Advisory thresholds in their own way. In the Bluegrass region, where rainfall deficits are near 4 inches since the beginning of June, it will be driven mainly by temperatures in the upper 90s, not that dewpoints near 70 are any picnic. Over in southern Indiana where rain has been more abundant, it will be driven by the humidity with dewpoints in the upper 70s to make highs in the lower 90s feel like triple digits. Much of the area will see heat index values very close to 105 degrees on Tuesday afternoon. Even where we don`t make it, this will be the third consecutive day of triple digit heat indices with very limited overnight relief. Therefore we will expand the Heat Advisory into the remainder of central Kentucky. There is some bust potential, mainly focused in southern Indiana, if debris cloudiness from overnight convection to our north is thicker or more persistent. && .SHORT TERM /THROUGH WEDNESDAY/... Issued at 325 PM EDT Mon Jul 15 2024 Scattered cu field across the region this afternoon is a result of efficient daytime heating. Temps have warmed into the low to mid 90s, with heat index values ranging between 98-104 degrees. Dry weather continues this afternoon, and should see the cu field diminish as daytime heating is lost around sunset. For tonight, dry weather will continue, but will be keeping eyes on another MCS racing through Chicagoland and then diving southeastward. A mid-level shortwave passing over the Great Lakes will be pivoting around the parent upper low over Canada, which will be the driving force for a cold front pushing the convection into the Ohio Valley. Ahead of the front, low-level jetting will ramp up moisture transport well to our north, and WAA even this far south. Temps overnight will not provide much relief from the daytime heat, especially in the urban areas. Lows will range in the 70s, but SDF could remain closer to 80 overnight. The convection will be weakening as it approaches our forecast area, largely in part due to the nocturnal inversion still in place and keeping our low levels stable. Some elevated instability will remain as indicated by model soundings, so some thunder mention in the forecast will remain. Hi- res models continue to struggle with the evolution of this MCS, so confidence on how far south the precip will go remains in question. Will draw in a 20% PoP to cover the possibility mainly north of the Ohio River for the morning hours. Any morning precip will likely lead to more humid dewpoints for the afternoon. However, any lingering cloud cover from the morning could slow down temps slightly. Still believe tomorrow will be a hot day, with temps in the 90s, and dewpoints in the 70s. It appears that temps might be a few degrees lower than today, but the dewpoints will be higher. With it being the third day in a row for triple digit heat indices, and the warm morning lows, the heat advisory will continue for tomorrow. There`s a chance some afternoon convective development may spark ahead of the front, which could linger into the end of the period. Weak/Marginal deep layer shear will limit any sort of severe threat, but gusty winds in downburst along with heavy rainfall are likely in the strongest storms. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Issued at 325 PM EDT Mon Jul 15 2024 Showers and thunderstorms will be in progress at the start of the long term as a cold front sweeps through the region. 560dm 5H low will move E through the Great Lakes while at the surface an elongated cold front stretching from Quebec into the Central Plains slowly drops through the OH Valley. Moisture pooling just ahead of and along the frontal boundary will provide enough fuel for efficient rainers, with PWATs increasing to above 2 inches which is reaching daily max values according to SPC sounding climatology. Storm vectors closely parallel the boundary as well, leading to training storm potential and flooding concerns. Highest QPF is forecast to occur from 17/00Z thru 17/18Z with lingering rainfall continuing into Thursday morning. ECMWF Extreme Forecast Index (EFI) does highlight an area of higher than normal rainfall amounts among ensemble members roughly along the OH River, which is coincident with our highest QPF amounts. Areas north of the parkways can expect to see an inch to around 2.25", while those south of the parkways can expect less than an inch. With that said, WPC has included portions of north central KY and southern Indiana within a Day 2 (16/12Z - 17/12Z) Slight Risk for Excessive Rainfall and a Day 3 (17/12Z - 18/12Z) Marginal Risk. Environmental parameters regarding severe weather are meager for Wednesday, likely due to the bulk of the activity passing during a diurnal minima. CAPE values will range from 500-1500 J/kg by Wednesday afternoon with most of the impressive shear remaining far to our north closer to the stronger jet stream dynamics. DCAPE values do increase during the day Wednesday, which lends to the potential for stronger gusts associated with convection. As such, SPC has included our region within a Day 2 (16/12Z - 17/12Z) Marginal Risk, which is mainly wind driven. Expect reprieve from the heat in the post-frontal airmass as daily max temperatures drop into the 80s from Thursday through the weekend, slightly increasing each day. Worthy of greater rejoicing is the concurrent drop in dew points. The aforementioned cold front is expected to stall over the northern Gulf States before meandering northward into the TN Valley, bringing a return of shower and tstorm chances back to the southern half of our CWA Saturday and Sunday. Worth of mention is a shortwave that drops out of central Canada Friday, which models show undergoing lee cyclogenesis before becoming detached from upper jet support. This cut-off low will lead to below normal temperatures across much of the central U.S. as highlighted in CPC`s 6-10 Day Temperature Outlook. && .AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 114 AM EDT Tue Jul 16 2024 Very low confidence forecast ahead. A large line of weakening showers/storms is currently pushing southeastward from central IL/IN. This line, if it holds its current trajectory, could impact northern portions of the forecast area shortly after 07- 08z. Models have struggled to capture the extent and area of this line, so their resulting solutions several hours from now will likely be incorrect. Though the line has shown a weakening trend over the last couple of hours, an outflow boundary ahead of the precipitation could spark a few showers to develop in northern portions of the forecast area, so have included VCSH mentions at SDF/LEX. The rest of the forecast period will be highly dependent on how the morning activity plays out. Have generally run with dry conditions after 14/15z as we`ll likely see subsidence aloft in the wake of the first wave for a while, but can`t rule out some scattered storms developing by late afternoon hours (coverage doesn`t seem to justify SHRA/TSRA mention in TAF at this time). The better chances for showers/storms will come tonight as a frontal boundary sinks into the region. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...Heat Advisory until 9 PM EDT /8 PM CDT/ this evening for KYZ023>043-045>049-053>057-061>067-070>078-081-082. IN...Heat Advisory until 9 PM EDT /8 PM CDT/ this evening for INZ076>079-083-084-089>092. && $$ UPDATE...RAS SHORT TERM...CJP LONG TERM...CRG AVIATION...DM