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Area Forecast Discussion
Issued by NWS Louisville, KY
Issued by NWS Louisville, KY
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472 FXUS63 KLMK 291422 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 1022 AM EDT Sat Jun 29 2024 .KEY MESSAGES... * Very warm and muggy this afternoon with heat index readings peaking around 100 to 105. * Scattered storms today and tonight, especially this afternoon and evening. Locally heavy rain and gusty winds will be the main threats. * Another period of unsettled weather returns to the region by late Wednesday and Thursday. && .UPDATE... Issued at 1022 AM EDT Sat Jun 29 2024 Morning observations reveal partly cloudy skies across much of Kentucky with mostly cloudy skies across southern Indiana. Temperatures had warmed into the lower 80s across southern Indiana and much of north-central/east-central Kentucky with mid 80s across the southwest and far southern sections. Rather oppressive dewpoints were noted with readings in the low-mid 70s making it feel like the lower 90s already. Current forecast remains in good shape this morning. Main concern continues to be what effect the high level clouds spreading in from the west/northwest will do to afternoon forecast temperatures and our convective chances. Current thinking is that we`ll have at least scattered-broken high cloud cover over the region today and that will impact some degree of insolation. Overall highs in the upper 80s to the lower 90s still look attainable. Dewpoints in the lower-mid 70s will be seen early in the afternoon which will push heat index readings into the 100-105 range, before some PBL mixing takes place and reduces the near surface moisture. As for convection, the latest CAMs continue to show rather isolated- scattered coverage for the afternoon. Model soundings show rather marginal shear profiles of 25-30kts with high wet-bulb zero heights. Degree of instability will be determined by how warm temps get, but it appears that we`ll have decent instability develop with MLCAPE values jumping into the 2500-3500 J/kg range during the afternoon. PWAT values will remain in the 2.1-2.2 inch range and storm motions still look to be in the 15-25 mph range. The 3km NAM solutions still show a bit of capping up around 850 mb this afternoon. The lack of convection in the CAMs may be do to the lack of strong synoptic scale forcing being absent from the region. However, it still appears that at least scattered storms should fire during the afternoon mainly in an axis from roughly Bowling Green northeast toward Lexington. Based on soundings/environment, thunderstorms with torrential rainfall, gusty winds, and intense CG lightning would be the main weather hazards. Some localized flooding could occur, especially where storms train over the same locations. After loading up the latest temperature/dewpoint data, still am not seeing the need for a Heat Advisory across our region. Will continue to monitor obs through lunchtime and decide to keep the SPS ongoing or upgrade our far SW to a short-fused Heat Advisory. && .SHORT TERM /THROUGH TONIGHT/... Issued at 315 AM EDT Sat Jun 29 2024 Impressive MCC over Missouri overnight is pushing generally eastward. At the time of this writing cloud tops are starting to warm slightly, but an MCV has developed in regional radar imagery. Given the MCV`s current track and speed as it moves through a favorable environment of high moisture and weak shear, it would potentially graze the southwest corner of the LMK CWA (Logan County) around mid-late morning CDT, though its forward motion may slow some as it drifts south of stronger westerlies over the upper Mississippi Valley and Great Lakes. This along with a shortwave trough riding along the periphery of a large upper ridge over the southern half of the United States, a cold front approaching from the northwest, and diurnal destabilization, supports the idea of scattered showers and storms today, especially this afternoon and evening. Synoptic scale deep layer shear will be on the order of 25-30kt today with weak mid-level lapse rates. Degree of destabilization will be partially dependent on how much cloudiness/insolation we receive today, and it does appear like widespread high clouds will limit destabilization. Wet bulb zero heights will be very high and the column quite wet, so severe hail making it to the ground is unlikely. With weak low level shear, that leaves gusty winds as the main severe threat. Sub-cloud air on sounding progs is not particularly dry and surface dew points will be in the middle 70s, so the best shot at surface gusts will be with the heaviest downpours as they impact the ground. SPC`s MRGL risk looks appropriate. Indeed, heavy downpours will be a possibility given efficient rain producers in an atmosphere of 2.1-2.2" precipitable water values. Forward motion of the storms should be on the order of 15-25 mph, so some locally significant amounts of rain will be possible in any stronger storms that develop. WPC has a MRGL risk of excessive rainfall across the region today, which is appropriate given the expected widely scattered coverage. Temperatures today are tricky, given the possibility of widespread clouds, even if only high clouds. Kept the idea of previous shifts and ModelCertainty of going slightly below NBM for MaxT. Dew points in the mid 70s will make for a very humid and uncomfortable day with heat index readings peaking in the 100-105 degree range this afternoon. After chatting with PAH, will hold off on an advisory for now, and will keep an eye on the behavior of the widespread upstream clouds advancing toward the area from the Midwest. Those clouds, and the possibility of scattered showers & storms, cast doubt on whether advisory level heat/impact will be achieved. If those clouds show signs of dissipating and/or precipitation chances decrease, may need to upgrade to advisory, especially west of I-65 and south of the Ohio River. Tonight the front will move into the Ohio Valley with scattered showers and thunderstorms. It will be another warm and muggy night with lows in the lower and middle 70s. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Issued at 315 AM EDT Sat Jun 29 2024 ===== Sunday - Sunday Night ===== The cold front will be bisecting the forecast area at the beginning of the long term forecast period on Sunday morning, but will be progressing to the southeast. Our counties south and east of the Kentucky Parkways will still be in a pre-frontal airmass, supportive of some shower activity through the morning and early afternoon. Eventually the front will pass through the entire forecast area, leaving behind a drier airmass in a post-frontal regime. Drier wx will be expanding southeastward through the region by Sunday afternoon. Cloud cover will also depart with the front, resulting in mostly sunny skycover for most by the afternoon. The cooler NW flow filtering in behind the front will help keep temps near normal as we close out June, with afternoon highs in the mid- and upper-80s. By Sunday night, an upper level ridge will be building across the US, with a sfc high pressure centered over the Great Lakes. This will help keep mostly clear skycover. CAA pattern from northerly flow will allow temps to cool some 10 degrees below normals, with readings possibly in the 50s outside of urban areas. ===== Monday - Tuesday ===== Broad sfc high pressure centered to our north will continue to dominate our forecast for the first two days of July. Dry weather is expected both days. Fairly strong CAA will keep temperatures below normal for Monday. Afternoon highs will only reach the low 80s, which would be nearly 8-10 degrees below normals too. With dewpoints in the 50s, Monday should be a very nice day. On Tuesday, the sfc high will shift over to the New England region, which will drastically change our air advection regime. With the high to our northeast by then, the Ohio Valley will switch over to a WAA pattern in the return flow zone. This will result in temps returning to the 90s, and slightly above climo normals. ===== Wednesday - Friday ===== An upper shortwave will flatten out the ridge by Tuesday night and into Wednesday, resulting in a change in the pattern for the mid- and late-week and Fourth of July holiday. Beginning on Wednesday, we will start off dry, but PoPs will be increasing through the late morning and afternoon hours as a cold front approaches the Ohio Valley. Ahead of the front, plenty of theta-e advection will ramp up our moisture content again, likely pushing dewpoints into the mid- 70s. Accompanied with temps reaching the mid-90s, we`ll likely have heat indices over 100 degF. Wednesday certainly does not appear to be a wash out, but a few scattered showers and storms in the afternoon appear possible. Greater chances for showers and storms will be on Thursday (July 4) as the front gets hung up across Indiana and we get reinforcing support from another mid-level wave and vort max. Currently do not expect the front to meander south of the Ohio River, but moisture convergence along the front will enhance our chances for showers and storms throughout the entire day. PoPs will also linger into Friday as moisture transport remains high. Daily highs in the low 90s will accompany muggy dewpoints, resulting in heat indices near 100 for both Thursday and Friday as well. && .AVIATION /12Z TAFS THROUGH 18Z SUNDAY/... Issued at 633 AM EDT Sat Jun 29 2024 Will stick with prevailing VFR conditions for this TAF period. Spotty SHRA/TSRA are possible just about any time, but the best chances will come with diurnal destabilization this afternoon and evening ahead of an approaching cold front, upper level wave, and possible mid-level disturbance from overnight convection over Missouri. Even then, coverage should be scattered and will keep rain chances at PROB30 at this time. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ UPDATE.......MJ SHORT TERM...13 LONG TERM....CJP AVIATION.....13