278 FXUS63 KLMK 181050 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 650 AM EDT Tue Jun 18 2024 .KEY MESSAGES... * Persistent early season heat wave expected, with highs well into the 90s each day this week, and heat index values approaching 100. * Spotty coverage of afternoon thunderstorms today, then dry Wednesday through Saturday. * Flash drought development possible next week. && .SHORT TERM /THROUGH TONIGHT/... Issued at 321 AM EDT Tue Jun 18 2024 Hot weather continues today, with the main question mark being the extent and coverage of afternoon convection. Upper-level ridge centered along the VA/NC border will expand westward through the day, but deep southerly flow will have the Ring Of Fire pattern as close as western Kentucky. Low-level thickness progs suggest temps this afternoon will fall a couple degrees short of Monday, and dewpoints near 70 will support heat index values in the mid/upper 90s, perhaps touching 100 in the urban areas. While the ridging will reduce cloud cover in areas from Lake Cumberland up through the Bluegrass, there could still be a window for isolated storms around peak heating. Farther north and west, precip chances could run more toward 30 percent, and with a juicy and weakly sheared environment a few pulse storms could produce locally gusty winds. Convection will wind down quickly with the loss of heating, so any POPs after sunset will be restricted to southern Indiana. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Issued at 321 AM EDT Tue Jun 18 2024 Synopsis...Highly anomalous mid-level blocking high, positioned over the Eastern Seaboard at the beginning of the period, will eventually move southward and extend latitudinally over the southern half of the CONUS in response to increased activity of upstream troughing moving over the Upper Midwest/Great Lakes and tropical upper cold low punching across the Gulf of Mexico. Therefore, additional hot and humid days with heat indexes in the mid to upper 90s are anticipated through the weekend with rain chances and potentially some heat relief possible on Sunday accompanying a front. Model Confidence/Evaluation...There is high confidence in the temperature/heat index forecast through Saturday given agreement among models in the evolution of the mid-level blocking high. Besides the uncomfortably hot and humid conditions, there is a non- zero chance of a few record highs late this week supported by EFI maximum temperature and NAEFS/ECWMF ESAT mid-level height values. On the other hand, confidence in Wednesday PoP lowers with respect to the rest of the week based on the still close position of the moisture plume axis advecting from the Gulf of Mexico to the Mississippi Valley. Next window for showers and storms will arrive on Sunday ahead of a weak front approaching from the west. However, uncertainties remain regarding moisture availability after the hot and dry spell plus model differences in spatial coverage. That being said, severe weather probabilities are negligible given warm temperatures aloft and weak deep layer shear. Wednesday - Saturday...Expect temperatures to keep rising, at least a few more degrees, as the center of the anomalous mid-level high transitions over the Lower Ohio Valley during the Thursday-Saturday timeframe. Best chances to tie or break afternoon highs would be Saturday at SDF (98) and LEX (97). As mentioned in the previous discussion, a heat advisory could still be considered due to combination of afternoon heat indexes in the upper 90s and mild overnight lows for an extended period of time. Regarding precipitation potential, mostly dry conditions will persist the rest of this week and the first half of the weekend, but a few isolated showers and a stray thunderstorm cannot be ruled out Wednesday as the high remains to the east and southerly winds favor weak moisture convergence over the forecast area. Sunday - Tuesday...Have continued indicating increasing rain and storm chances ahead of the incoming front; however, spatial coverage and convective intensity is still uncertain based on mesoscale factors difficult to forecast at this time and synoptic differences found in the guidance. Even with the arrival of wetter conditions, forecast indicates highs in the lower 90s at the start of next week. Additional upstream shortwave energy and the potential interaction with tropical moisture from a Gulf surface low (as suggested by some runs of the GFS and ECMWF) could yield additional rain/storm chances the rest of next week. && .AVIATION /12Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 644 AM EDT Tue Jun 18 2024 Prevailing VFR conditions expected through the valid TAF period, with diurnal Cu and cirrus ceilings. Light SSE winds will pick up as mixing deepens, veering to SSW and remaining just shy of 10 kt. There's a narrow window of opportunity for convection just after max heating, and we'll include PROB30 groups at BWG and HNB from 21Z til 00-01Z Wed. Not confident enough to include it in SDF, and probabilities are too low at LEX and RGA. Light S-SE winds again after sunset, with minimal concerns for fog. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ SHORT TERM...RAS LONG TERM...ALL AVIATION...RAS