Area Forecast Discussion
Issued by NWS Louisville, KY
Issued by NWS Louisville, KY
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811 FXUS63 KLMK 171856 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 256 PM EDT Mon Jun 17 2024 .KEY MESSAGES... * Persistent early season heat wave expected, with highs well into the 90s each day. * Heat index values not expected to reach advisory levels, but societal impacts are likely. * Spotty coverage of afternoon thunderstorms today and Tuesday, then dry Wednesday through Saturday, with flash drought development possible. && .SHORT TERM /THROUGH TUESDAY/... Issued at 256 PM EDT Mon Jun 17 2024 A hot, humid afternoon is in progress with temperatures currently in the upper 80s to lower 90s. Heat indices are near 100 in some areas and will top out in the 95-105 range this afternoon. Anomalous mid and upper level ridging will remain anchored over the Mid-Atlantic while strengthening and expanding through Tuesday. This afternoon, an upper level shortwave impulse is noted lifting north over the Mid- MS Valley where convection is ongoing. Showers and some storms are expected to continue lifting NNE through western TN/KY toward far SW IN into this evening, bringing a better chance for rain to our far western counties in west-central KY and SW IN. Otherwise, convection has yet to develop in central KY and southern IN and will remain very sparse through the evening hours. An isolated storm cannot be completely ruled out, but most will stay hot and dry. A few showers may linger past sunset into early tonight, but any convection will weaken with sunset. Increased cloud cover will be present overnight with partly to mostly cloudy skies. Expect a warm night with Tuesday morning lows in the low to mid 70s. Tuesday will feature a bit more cloud cover than today with lingering mid and upper level moisture. This should help suppress sfc heating at least a little bit. It will still be warm with temperatures rising into the lower 90s in most areas. Afternoon heat index values are expected to top out in the 95-100 range. Mainly dry conditions look likely. There is a brief window during peak heating when rain chances max out around 10-20%, but confidence is low on shower development due to increased subsidence aloft. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Issued at 256 PM EDT Mon Jun 17 2024 Tuesday Night - Saturday Night... An anomalous upper ridge continues to center around the mid Atlantic Coast region through late week, and then will try to hold onto a flatter W-E orientation into at least the first part of the weekend. As a result, mostly dry and hot conditions are expected to persist under this regime. Overall, humidity values aren`t expected to be as bad as they could be, as dew points are generally expected to range in the mid/upper 60s most of the time. Those dew points combined with highs in the mid/upper 90s each day Thursday-Saturday (possibly Sunday too), are expected to yield heat indices mostly in the mid to upper 90s each day late week into the first part of the weekend at least. Given that overnight lows will remain quite mild, we could get into a situation where we see a prolonged period of sub Heat Advisory criteria, but enough of a duration where a headline could be needed. Some initial collaborations have gone on today, but will hold off on taking messaging farther given that heat indices really aren`t projected to even get above 100, and that a the duration is in question given a late weekend cool front possibly arriving. For context, LREF probabilities of heat indices 100F or more only peak at around 20% for the Friday/Saturday time frame. As far as precipitation chances go, we should be mainly dry, although some data suggests a few very isolated precipitation chances during peak heating. A look at forecast soundings shows a mostly capped thermodynamic profile, and given the lack of a trigger under upper ridge, prefer to lean toward the majority of the dry data through this stretch. Sunday - Monday... Lower confidence for the late weekend/early week timeframe as some data supports the upper ridge breaking down in response to a northern Plains shortwave tracking into the Great Lakes region. It is possible that these lower H5 heights, and a surface cool front trailing from the parent low pressure hold off until Monday, but will have to wait until those details become clearer. The potential for any long duration heat headlines could ultimately depend on what happens Sunday, so until this becomes clearer a late week headline is too low of a probability. With respect to the cold frontal arrival either Sunday or Monday, this will also bring the first shower and storm chances back to the region since early week. Carrying chance pops in the time frame to account, but it is possible that the hot and mostly dry conditions ahead end up contributing to a slower frontal arrival, which will ultimately result in a hotter/drier Sunday. Past experience has me leaning toward the hotter/drier Sunday, but plenty of time to work that out in coming forecasts. && .AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 144 PM EDT Mon Jun 17 2024 VFR conditions likely. The TAF sites appear likely to remain mainly dry, though isolated thunderstorms are possible from mid-afternoon through the evening hours. HNB appears to have the best chance at seeing at least brief rain late this evening as convection moves NE across western TN/KY into southwestern IN. Confidence in timing and any impacts due to TSRA is low due to the limited coverage. Thunderstorms will weaken with sunset. It does look like we`ll see more enhanced mid-level cloud cover tonight and into Tuesday with light southerly winds. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ SHORT TERM...EBW LONG TERM...BJS AVIATION...EBW