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Area Forecast Discussion
Issued by NWS Louisville, KY
Issued by NWS Louisville, KY
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308 FXUS63 KLMK 040612 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 212 AM EDT Thu Jul 4 2024 ...Updated Aviation Discussion... .KEY MESSAGES... * Heat index values this afternoon will range from near 100 in the Bluegrass region to 105 or higher west of Interstate 65. * Scattered thunderstorms this evening will be capable of strong gusty winds and torrential downpours. Overnight the severe threat will diminish but heavy downpours remain possible, which could result in localized flash flooding. * Unsettled weather will continue through Friday with daily chances of showers/storms. Isolated damaging wind gusts, torrential rainfall, and lightning will be the primary hazards. && .MESOSCALE... Issued at 805 PM EDT Wed Jul 3 2024 Convection has continued to grow in coverage along the effective boundary draped across southern IN at this hour. Slow ESE progression has occurred against synoptic winds, mainly from convectively reinforced outflow/cold pooling. Have seen some gusty winds with the strongest storms, however the main show has been with torrential rainfall. Dubois county saw observed 4-5" per hour rates back around the 5-6 PM hour with the intense thunderstorm that developed in the previous update, with some locally higher amounts certainly possible to have occurred. Numerous reports of flooding occurred in that area. Since then, rates have not been as impressive, however still getting a good training component given upstream growth roughly paralleling the effective boundary orientation. Given that efficient rainfall rates are still occurring, some continued Flood Advisories, and isolated Flash Flood Warnings can`t be ruled out into the evening. Overall, storm strength has been limited by weak lapse rates, and it really took an intense boundary interaction earlier this evening over our NW CWA to get a more intense storm. Think this trend will continue with mostly weaker storms (mainly heavy rainfall) outside of any mechanisms to force convection stronger. Will also note a more N-S oriented line of storms moving into western KY, however hi-res models suggest that will weaken as it enters our CWA later tonight. The thinking is that it would move into our worked over environment behind the effective boundary and diminish. That is the going forecast, and will continue to only advertise small chances for a shower or storm overnight once this main line of storms pushes through. Previous Update... The Severe warned storm in Dubois county rapidly intensified on a boundary intersection between the effective frontal boundary draped WSW to ENE across southern IN, and a differential heating boundary created by the upper cirrus shield. SPC mesoanalysis showed good surface moisture convergence (10 g/kg) ahead of the explosive development, combined with visible satellite imagery confirming congested cumulus in the area. Overall deep layer shear around 30 knots, boundary interaction enhancing low level SRH, and the strong updraft helped the storm exhibit some brief supercellular characteristics. The good news is that LCLs are currently around 1250m, which is pretty high and not as favorable for tornadic activity, and the the overall environment (outside of localized enhancement from boundary interaction) isn`t favorable for tornadoes anyway. The storm has since shown signs of pretty strong outflow, so continue to think that damaging winds and torrential rains will be the main threats. Keeping a close eye on the boundaries, and their effect on storm mode, but not overly concerned outside of the microburst/localized flooding threat at the moment. It is interesting to note that the western side of the differential heating boundary mentioned above is also a clear marker between the higher DCAPE airmass (better mixing), and the slightly less favorable airmass under the cirrus shield. && .SHORT TERM /THROUGH THIS AFTERNOON/... Issued at 328 PM EDT Wed Jul 3 2024 Low-confidence forecast in a very warm, muggy, and boundary-rich environment. Plenty of low-level instability, but very weak mid- level lapse rates will limit convection to that which can find forcing. We do have a cold front draped across central Illinois, with lingering outflow boundaries from earlier activity in southern Illinois and central Indiana. Hi-res models light up these features starting around 22-23Z, with the best chances over southern Indiana. Will also be closely watching the differential heating along the southern edge of the cirrus shield, which is draped close to the Cumberland Parkway in south-central Kentucky. Given the steep low-level lapse rates and PWAT values over 2 inches, we could still see a few strong to marginally severe pulse storms, with locally gusty winds and torrential downpours. Best coverage is likely to be in southern Indiana and north-central Kentucky. If storms organize over southern Illinois, that could yield another wave of storms late tonight into Thursday morning. Main threat will be heavy rainfall, given PWATs still over 2 inches and tall/skinny CAPE profiles, and localized flash flooding is possible anywhere that heavy rain can regenerate. WPC has a Slight Risk for excessive rainfall just on either side of the Ohio River. Depending on how long precip continues into Thursday morning, it will likely limit afternoon temperatures and storm intensity. Look for mainly hit-and-miss convection on Thursday afternoon, as the environment is still very moist and lingering boundaries could focus storm development. && .LONG TERM /TONIGHT THROUGH WEDNESDAY/... Issued at 328 PM EDT Wed Jul 3 2024 Thursday Night - Friday Night... Low pressure will move through the Midwest bringing a cold front through the Ohio Valley by Saturday morning. With deep troughing associated with the system, CVA, and a weak, but well-positioned upper-level jet dynamics, showers and storms will be move through along and ahead of this front on Friday. Strong storms and storm coverage is dependent on preceding convective activity today and Thursday. If the environment recovers from preceding convection, present shear and ample moisture will allow for a marginal risk of severe storms due to potential for gusty to damaging winds and heavy downpours. Flash flooding will be possible as the atmosphere is near max climatology for PWATs in the 2.1-2.3 inch range and dew points in the mid 70s. As the cold front moves through Friday night, drier and cooler weather will build into the region. Additionally, Thursday Night (Independence Day) should be mostly dry. A nocturnal inversion will quickly settle into the region around sunset. Firework smoke from 4th of July celebrations will be easily trapped under the inversion and skies will become smokey through Thursday night. Weekend... Drier and near normal conditions will stick around through the weekend. High in the mid-upper 80s, dew points in the low-mid 60s, and a light breeze will bring pleasant summer conditions. High pressure over the region will keep mostly sunny skies with scattered diurnal Cu formation in the afternoon. Early Next Week... Deep troughing will build over the central CONUS and high pressure will move off to the east. Southwesterly flow and moisture will return to the region. Shower and storm chances increased Tuesday as a the trough swings through the upper Midwest. Temperatures will remain near normal with dew points in the low 70s. && .AVIATION /06Z TAFS THROUGH 12Z FRIDAY/... Issued at 212 AM EDT Thu Jul 4 2024 Convection has diminished in both coverage and intensity early this morning, though cannot rule out another storm near BWG over the next hour or so. In general, VFR weather appears likely to prevail outside of thunderstorm activity during this forecast period. Expect very light southerly winds through the remainder of the overnight hours. For Thursday, the thunderstorm forecast is complex with lingering uncertainty. A convective complex is forecast to move ENE across MO, IL, and southern/central IN. TSRA chances increase along the I-64 corridor from mid to late morning into early afternoon. Additional scattered convection will be possible to the south of the main complex as outflow helps generate new updrafts. So during the daytime, BWG and RGA should stay dry the longest with higher TSRA chances from early to mid-afternoon into the evening. An anomalously moist airmass will support extremely heavy rainfall in any storms. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ MESOSCALE...BJS SHORT TERM...RAS LONG TERM...SRM AVIATION...EBW