Area Forecast Discussion
Issued by NWS Louisville, KY
Issued by NWS Louisville, KY
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606 FXUS63 KLMK 212359 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 759 PM EDT Tue May 21 2024 ...Updated Aviation Discussion... .KEY MESSAGES... * Unsettled weather returns Wednesday, with on and off chances for showers and storms through the weekend. * Isolated severe storms possible Wednesday afternoon into Wednesday night. * Stormy pattern with a risk for localized flooding Thursday through Tuesday with strong storms possible Sunday. && .SHORT TERM /THROUGH WEDNESDAY NIGHT/... Issued at 257 PM EDT Tue May 21 2024 An upper level shortwave trough and deepening sfc low are lifting northeast across the central Plains this afternoon, with downstream ridging across much of the eastern US. Southerly low-level flow is beginning to increase in the Ohio Valley downstream of the low pressure system, but the primary low-level jet/moisture transport axis will remain off to our north and west through this evening. Strong heating of a fairly moist airmass (sfc dewpoints are currently mid/upper 60s) has led to MLCAPE creeping past 1500 J/kg. Despite a lack of notable mesoscale forcing, we are eclipsing convective temperatures in northern KY where scattered showers and a few storms are drifting northeast toward Covington. While it`s close, still do not think we`ll see a whole lot this afternoon in central KY and southern IN. A few showers/storms cannot be ruled out, but cu development is tempered by a lack of mechanical forcing and warm air in the mid-levels (as seen on recent SDF ACARS soundings). Rest of the day looks quite warm and somewhat humid with max temps in the 85-90 F range. The first half of tonight looks warm and dry. A band of showers and storms is forecast to sink southeast through Illinois and Missouri, weakening as pushes further east of the Mississippi. These storms will outrun the instability axis, and deep-layer will be weak also. Expect weakening showers and isolated embedded storms to push southeast across portions of southern IN and central KY between 3-10 AM EDT before diminishing altogether. A lull with mostly dry conditions then looks likely from mid-morning Wednesday through early afternoon. Some partial clearing should allow for decent sfc heating and destabilization of a moist boundary layer. HREF mean SBCAPE increases to 1500-2000+ J/kg by mid- afternoon as a weak sfc cold front begins to stall from IN southwest through southern IL. The upper level shortwave trough makes its closest approach over the Midwest Wednesday afternoon and evening, helping to steepen 3-6 km lapse rates to near 7 C/km. A slightly more subtle convectively enhanced mid-level disturbance will likely lift ENE from the Ozarks across TN, which should help boost convective coverage first across south-central KY late Wednesday afternoon and through the evening hours. Overall, isolated to widely scattered storms look possible beginning late Wednesday afternoon. The better chance of seeing storms will be Wednesday evening and overnight. Shower/storm coverage will increase during the evening both as the Ozarks mid-level wave approaches from the WSW and the weak sfc boundary to the north sinks just a bit further south into southern IN. An isolated severe storm does look possible, mainly between 3-11 PM EDT. In addition to sufficient buoyancy, some mid-level dry air and steep low-level lapse rates will contribute to elevated DCAPE. This should result in isolated strong downdrafts capable of localized damaging winds. Locally heavy rainfall, lightning, and small hail are also likely. Large or damaging hail seems unlikely due to marginal deep-layer shear on the order of 30 kt. This will keep thunderstorm updrafts only loosely organized. Brief pulses will likely produce some small hail, though. Limited coverage through early to mid-afternoon will help keep the flooding risk low during the daytime. Increased coverage of showers and storms Wednesday night will boost the potential for cell training over similar areas, and thus increase the risk for localized flooding. Highs Wednesday will likely be in the low to mid 80s in most areas. Lows Wednesday night will be in the 60s. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Issued at 257 PM EDT Tue May 21 2024 Thursday through Tuesday... A cold front will likely stall over the Ohio Valley, and coupled with multiple shortwave troughs of low pressures and continued southwesterly jetstream flow, will lead to increased chances for showers and storms through Tuesday. Temperatures will warm each day from near normal to above normal. Dew points will also remain in the mid-upper 60s, which will lead to warm and muggy conditions through Tuesday. Strong to severe storms are possible, however, this will likely be determined on a day-by-day basis to assess mesoscale evolution and recovery for convective initiation. Moisture is present through the weekend and instability recovery looks possible each day, however, shear remains weak-marginal. The best day (while it`s early) looks to be Sunday. Model forecast soundings show instability and good shear that could lead to strong to severe thunderstorms as a low pressure system moves up the Ohio Valley. Given multiple days of rain and possible training of cells, flooding and flash flooding is possible. Current QPF for this timeframe is 2 to 4 inches, with locally higher amounts possible in the strongest thunderstorms . && .AVIATION /00Z TAFS THROUGH 06Z THURSDAY/... Issued at 758 PM EDT Tue May 21 2024 Tonight, a broken line of showers and thunderstorms is expected to approach the region from the west ahead of a surface cold front. Any precipitation with this line is not expected to enter the area until after 06Z, with HNB being the first site to see increased chances for rain and/or storms. Model guidance continues to show the line of storms weakening as it moves into the region, and confidence is decreasing that showers and storms will remain strong enough to cause significant impacts to operations. As a result, have trended later with MVFR CIGs at HNB and have removed TS mention during the morning hours for now, although this may need to be added if storms hold together. Additionally, a 35-40 kt jet around 2 kft AGL is expected to move across the area after midnight tonight, with marginal LLWS possible between 05-11Z. With the front still west of the area tomorrow morning, winds will pick up again out of the SW, with gusts of around 20 kt possible after 13-14Z. Precipitation chances will subside during the late morning and early afternoon hours, with latest model guidance showing another wave of showers and thunderstorms developing around 20-21Z tomorrow. Will use PROB30 to handle these storms for now, with additional refinements to timing and impacts likely needed in subsequent forecasts. Outside of storms, MVFR ceilings will be possible at HNB and SDF late tomorrow morning as a narrow strip of low-level moisture along the front moves overhead. Ceilings should gradually improve during the afternoon with the help of daytime heating. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ SHORT TERM...EBW LONG TERM...MCK AVIATION...CSG