Area Forecast Discussion
Issued by NWS Louisville, KY
Issued by NWS Louisville, KY
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281 FXUS63 KLMK 251725 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 125 PM EDT Tue Jun 25 2024 ...Updated Aviation Discussion... .KEY MESSAGES... * The Heat Index may rise above 100 degrees today, especially west of the I-65 corridor. Highs throughout the area will be above 90. * Isolated to scattered showers and storms will be possible late this afternoon into the evening. A few storms may be strong to severe with locally damaging wind the main threat. * Better shower and storm chances arrive Wednesday, bringing much needed rain to the region. A few storms may produce locally enhanced gusty winds and hail. * Shower and storm chances will return to the forecast by Saturday evening into Sunday morning. && .SHORT TERM /THROUGH TONIGHT/... Issued at 310 AM EDT Tue Jun 25 2024 Things are quiet across the CWA this morning with mostly clear skies and light SE winds. A N/S oriented warm front is expected to pass through the area later today, and will bring more steady SSW-SW winds by late morning/midday, perhaps gusting up around 15-20 mph at times through the afternoon. The warm advection combined with mostly sunny skies is expected to allow for temps warming to the low and mid 90s across the area. The passing warm front will also bring a notable dew point gradient from W to E across the area, with locations west of I-65 likely seeing some low 70s values combined with some mid 90s readings. As a result, max heat indices are likely to peak around 100 degrees this afternoon along and west of the corridor. Am a bit concerned that areas around Jasper, IN may touch a brief 105F heat index, however given upstream convection, upper cloud cover is a bit in question. Plan to SPS areas along and west of I-65, where a couple hours of heat index in the low 100s is possible. Outside of the heat and humidity, the big question with this forecast is convective chances later this evening into the overnight. Before we get to that, do want to address the current convection ongoing across northern IL/IN. Models did not handle this initiation well, and it is quite a bit farther south than any solution i`ve seen to this point. As a result, confidence is pretty low in convective initiation, timing, and placement as we go through the day. This initial cluster is diving SE toward our area at a pretty good clip currently, however the downstream environment toward central and southern IN looks to be less favorable given weak deep layer shear and a weakening instability gradient south and east of the Wabash River Valley. So, overall don`t expect this cluster to cause any problems for our area later this morning, however also can`t completely let our guard down given models not handling this at all. With initial uncertainty in models pretty strong, that also makes the evolution of the rest of the day quite uncertain. What we do know is that we should become quite unstable this afternoon with 2000 to 2500 J/KG of ML CAPE expected across our NW CWA. This unstable environment should be somewhat capped around 800-850 mb based on forecast soundings, but steep mid level lapse rates above that look to yield large positive area in the presence of a pretty dry overall sounding. The end result yields a sounding that could yield some pretty gusty downdrafts, given dry low levels as well. Not sure we`ll have enough triggering down here alone to lift parcels above/through the inversion, however do expect that anything that gets going upstream and then survives/cold pool surges into our area will have a strong to severe wind gust potential with it. SPC has upgraded portions of our area to a Slight Risk, and given the gusty look to the soundings certainly see the potential. The big question really is just where/when storm initiate upstream. At this point, like our best chances to be between 21 to 03z across the northern half of our CWA. More storm chances/redevelopment is possible overnight into the pre-dawn, but confidence is even lower in how that evolves. Essentially, have increasing pops from N to S from 21Z onward. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Issued at 310 AM EDT Tue Jun 25 2024 Wednesday - Wednesday Night... Troughing will strengthen and swing through the Great Lakes, sending a cold front south through the Ohio Valley on Wednesday. Ahead of this front, ample deep-layer moisture will be present. Dew points are forecasted to be in the upper 60s and low 70s, with PWATs near 2.0 inches. Along and ahead of the front, forcing will bring lift to present moisture and increase the potential for showers and storms. With greatest potential for storms being in the afternoon, daytime heating will likely bring enough instability for at least marginal convection. A 40kt LLJ along and ahead of the cold front will help to increase shear and storm organization. Main threats with strong storms is damaging winds, hail, and heavy rain. Should see a widespread 0.25-0.5 inches of rain with locally higher amounts possible. Showers and storms will move out of the region as the front pushes through Wednesday evening. Thursday - Friday Night... Behind the the `cold` front, much drier and near normal conditions will settle in. High pressure overhead will lead to clear skies and light winds. Thursday should be a pleasant day with temperatures in the mid-upper 80s and dew points in the low-mid 60s. On Friday, high pressure will shift to the east and winds will veer to a southwesterly direction. Moisture will quickly return to the region raising dew points 6-10 degrees through the day. Ridging over the southern US will bring low-mid 90s temperatures in the afternoon. Friday will be warm and muggy with heat indices in the upper 90s. Saturday - Early Next Week... Troughing will build and swing through the Great Lakes, sending another cold front south through the Ohio Valley. The cold front and troughing will bring forcing and lift to present moisture and instability leading to another chance for showers and storms on Saturday afternoon through Saturday night. Behind the `cold` front, high pressure will build into the region bringing near normal and drier conditions. Relief from heat seems to be short lived as most guidance shows strong ridging moving over the eastern US. Would likely see above normal and muggy conditions return at the end of this long term period. && .AVIATION /18Z TAFS THROUGH 00Z THURSDAY/... Issued at 124 PM EDT Tue Jun 25 2024 VFR conditions are expected to mainly prevail through this TAF cycle with some afternoon wind gusts up to 20 kts. The only caveat to this will be for some scattered t-storm activity at the I-64 corridor sites later this evening. Otherwise, look for a quiet forecast this afternoon into early afternoon with only a few afternoon cu and upper clouds at times. Winds will shift to the southerly direction, mainly light winds toward tomorrow morning with a few variable wind shifts. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ SHORT TERM...BJS LONG TERM...SRM AVIATION...MK