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Area Forecast Discussion
Issued by NWS Louisville, KY
Issued by NWS Louisville, KY
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700 FXUS63 KLMK 160551 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 151 AM EDT Fri Aug 16 2024 ...Updated Aviation Discussion... .KEY MESSAGES... * Scattered thunderstorms are expected tonight through Friday morning. Some locally heavy rainfall is possible, but the risk for severe weather is low. * Unsettled weather is likely Saturday and Sunday with scattered showers and thunderstorm being possible each afternoon/evening. * Dry weather is expected for much of next week, with well below normal temperatures for late August. && .UPDATE... Issued at 856 PM EDT Thu Aug 15 2024 Quiet and dry weather continue across the region this evening but more active weather is anticipated late tonight into early tomorrow morning. The first `round` could come in the next few hours as storms in southern IL attempt to track southeastward, though its possible they may weaken with eastward extent as they encounter increasing MLCIN and a building nocturnal inversion. The more likely round of storms will come after midnight, toward dawn tomorrow as convection (that has yet to develop) develops ahead of a weak impulse and grows upstream. PoPs have been updated to account for the latest trends; otherwise, forecast remains on track. && .SHORT TERM /THROUGH SATURDAY/... Issued at 301 PM EDT Thu Aug 15 2024 Conditions remain dry under partly sunny skies this afternoon. A vertically stacked low pressure system will rotate ESE over the Upper Midwest through tomorrow, with multiple smaller-scale shortwave disturbances wrapping eastward across portions of the Midwest and Great Lakes. Deep-layer flow will be fairly weak tonight. Friday, the northern CWA will be on the southern periphery of moderate (40+ kt) mid-level westerly flow as the parent trough translates eastward. This afternoon, a large moisture gradient remains in place from west to east across the Ohio Valley. Deeper moisture lingers just off to our west, with 2+ inch PW values noted in western KY and IL. Therefore, the atmosphere locally remains fairly stable. Convective initiation appears likely upstream across portions of eastern MO and southern IL later this afternoon and evening. Shower and thunderstorm chances then increase across central KY and southern IN late this evening and overnight as upstream activity evolves eastward. Notable moisture advection takes place tonight with the development of a 25-30 kt southwesterly LLJ. Activity should be somewhat scattered/spotty early in the night, with rainfall chances peaking during the early to mid-morning hours of Friday. Both instability and deep-layer shear will be marginal at best, and the severe weather risk is rather low. Cannot rule out a stronger storm or perhaps a stronger cluster of storms this evening in the western CWA. The main hazard would be locally gusty winds. However, any weak instability overnight will be elevated in nature. The only concerns overnight would be lightning and locally heavy rainfall. Locally heavy rainfall may be a concern through Friday morning, and spotty 1-2+ inch amounts look possible. Significant flooding is not expected, so the main impacts would be ponding of water on highways and perhaps localized standing water in low-lying areas. Low temperatures Friday morning will be in the upper 60s to lower 70s. Friday will start off cloudy and fairly wet. However, conditions will gradually dry out during the afternoon and evening as the front moves through the region and drier air filters in from the west. Some late day sun looks probable in most areas, with the exception of perhaps the far southeastern CWA. Highs will be in the mid/upper 80s. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Issued at 301 PM EDT Thu Aug 15 2024 Friday Night through Sunday Night.... Trailing surface cold front is forecast to be in the vicinity of the Midwest Friday evening. Scattered thunderstorms will be possible across the region, though it looks like the most concentrated area of storms would be over central OH ahead of the approaching mid- level trough axis, and then across southern TN on the remnant outflow from the earlier day activity. Some additional convective development is possible late Friday night and into early Saturday morning as the cold front approaches our region. The frontal boundary looks to cross the Ohio River in the 17/10-12Z time frame and then into southern KY during the afternoon. Lows Friday night will be in the upper 60s to the lower 70s. The upper trough axis will remain in place across the region on Saturday with additional convective redevelopment likely Saturday afternoon and evening. Convergence along the frontal boundary continues to be rather modest. However, diurnal heating and marginal shear will be in place to produce some amount of organized convection, likely in clusters or small linear segments. Heavy rainfall, gusty winds, and lightning would be the main threats with this activity. Overall, the scenario advertised here supports at least a marginal risk of severe given uncertainties on instability, cloud cover and convective evolution. Highs on Saturday carry a bit of uncertainty given potential cloud cover and ongoing convection. Highs in the mid-upper 80s seem reasonable here, though a few spots that get a bit more sunshine could touch 90. Some scattered convection will likely persist into the evening hours before gradually winding down due to the loss of heating and increased CINH during the evening. Overnight lows will drop into the mid-upper 60s. A closed upper low will remain in the vicinity of the Great Lakes on Sunday and will slowly move into southern Ontario through the day. Associated upper level trough axis will pivot slowly eastward into eastern KY during the afternoon. Diurnal heating and expected destabilization will result in additional convection firing during the afternoon with the greatest coverage in areas east of I-65. Temperatures will likely be held down by convection and ongoing/existing cloud cover with highs in the low-mid 80s. The upper trough axis will continue to migrate eastward Sunday night with drier conditions pushing in from the west. Sunday night lows will be in the lower-mid 60s. Monday through Thursday... Moving into next week, the upper level flow across the CONUS will become quite amplified again with a trough axis along the NW Pacific coast and a large trough axis along the east coast. In between these features, another ridge axis is forecast to develop across the high Plains. This ridge does not appear to grow that much to the east during the week, and the Ohio Valley looks to remain in a deep northerly to north-northwesterly flow through the period. Overall, much of the synoptic guidance has little in the way of perturbations coming around the ridge in the Monday-Wednesday period. However, we may start to see that change by late Wednesday/Thursday. For now, plan on going with a dry forecast for the period. Given the sharp northerly flow and the core of the ridge remaining west of the region, temperatures will average well below late August normals through the period. In fact, much of next week will feel more like September. Daytime highs Monday and Tuesday will range from the upper 70s to the lower 80s, warming into the low-mid 80s by Wednesday/Thursday. Overnight lows will generally be in the mid- upper 50s. However, there is a rather strong signal that good radiational cooling setups may occur, especially in the Tue night- Wednesday night period. Here, our typical radiational cooling spots and valley locations could easily see temps drop into the upper 40s/lower 50s. && .AVIATION /06Z TAFS THROUGH 12Z SATURDAY/... Issued at 150 AM EDT Fri Aug 16 2024 The forecast is beginning to get more interesting. VFR conditions will continue outside of any convection, but convection is beginning to filter into the region. So far we have been lucky with most of the activity missing area TAF sites, but as we near daybreak, showers and thunderstorms are expected to become more widespread. Impacts at TAF sites will become more likely, but ceilings are expected to remain VFR. Some reductions in visibility could occur during periods of heavy rainfall, but these periods aren`t expected to last long. Winds during the afternoon and evening hours are expected to gust to around 20 knots in most places. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ UPDATE...DM SHORT TERM...EBW LONG TERM...MJ AVIATION...KDW