Area Forecast Discussion
Issued by NWS Louisville, KY
Issued by NWS Louisville, KY
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936 FXUS63 KLMK 220732 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 332 AM EDT Sun Sep 22 2024 .KEY MESSAGES... * Warm and humid today, with scattered afternoon and evening thunderstorms ahead of a cold front. * Multiple waves of scattered showers and storms are expected tonight through Tuesday night. There is a low chance for strong to severe storms Monday and Tuesday. && .SHORT TERM /THROUGH TONIGHT/... Issued at 331 AM EDT Sun Sep 22 2024 Radar is quiet early this morning in central KY and southern IN, and skies are mostly clear. There is plenty of action upstream across MO and into western IL, where a convective complex is evolving eastward near a sfc cold front. The sfc cold front extends NNE through eastern IA, WI, and Lake Superior to a low over northern Ontario. A warm, moist airmass is in place in the Lower Ohio Valley ahead of the cold front, with sfc dewpoints currently in the mid/upper 60s. The sfc cold front is forecast to approach the region from the northwest today before sinking into the Lower Ohio Valley later this evening. Mid and upper level ridging over the Ohio Valley will deamplify today as the ridge axis slides east. This occurs as upper level shortwave energy races east-northeast across the Midwest and Lower Great Lakes. The upstream convection is forecast to move into the region from the west by midday or early afternoon (late morning in southwestern Indiana). Some early day sfc heating/destabilization will take place, though satellite imagery shows plenty of cloud cover preceding the convection. The eastern two-thirds of the forecast area will have the best chance at realizing SBCAPE > 1000 J/kg. Overall, the complex will be in weakened state by its arrival. Some additional development will be possible along the leading edge of this activity. Scattered thunderstorms are likely this afternoon into the evening hours. Deep-layer shear of only 20-25 kts will limit convective organization and strength. The severe weather risk is low, though cannot rule out locally gusty winds with a few storms. Moisture will increase just ahead of the sfc boundary with slightly stronger southwesterly low-level flow. PW values increase to 1.8+ inches this afternoon, and a pool of moisture sinks south and east over the Ohio Valley tonight along the frontal boundary. A general lull is anticipated behind the first wave of showers/storms this afternoon, but then additional isolated to scattered development will be possible tonight given the position of the cold front and rich moisture in place. Short-duration bursts of heavy rainfall rates could produce brief ponding on roads, increasing the risk for hydroplaning. However, the overall flooding risk is low given the ongoing drought and beneficial nature of any rains at this point. We`ll see a relatively large temperature gradient from NE to SE today. Areas further south and east that see more early day sun will see temps climb into the upper 80s and lower 90s (south-central KY, Bluegrass Region). Southern IN will only see highs in the upper 70s and lower 80s. Tonight, lows will be fairly uniform in the mid/upper 60s. && .LONG TERM /MONDAY THROUGH SATURDAY/... Issued at 331 AM EDT Sun Sep 22 2024 ===== Monday - Wednesday ===== Unsettled weather will be the main story for the first half of next week, though the precip chances are much needed now that most of the region is experiencing moderate (D1) to severe (D2) drought conditions. We`ll start off Monday with a Marginal Risk for some isolated strong to severe storms. An upper shortwave trough will be digging over the central High Plains on Monday, though still largely to our west throughout the day. A meandering quasi-stationary front will be nearly parallel to the Ohio River, keeping our Kentucky counties within the warm sector, and the focus for any thunderstorm development to the south of the river. There`s considerable uncertainty in the Day 2 outlook due to the possibility of widespread cloud cover and perhaps some ongoing precip Monday morning, which would end up limiting our destabilization. With the upper trough axis still well off to our west, overall forcing may end up being weak throughout Monday. We may get our best convection chances from differential heating boundaries within the warm sector Monday afternoon, and expanding outflow boundaries would possibly fire up additional scattered convection into the early evening hours. Gusty winds and small hail would be the primary hazards with any stronger storm, in addition to heavy rain and lightning. By Tuesday, the upper shortwave will shift east across the central US, which will ramp up the large-scale ascent and mid-level flow overhead to roughly 50kts. Uncertainty also exists for Tuesday storm potential, largely due to the lingering cloud cover that could limit peak heating again. However, if (and it`s a big IF) we are able to realize any considerable instability, our chances for severe storms will be much higher, given the stronger forcing, enhanced mid-level flow, and better deep-layer shear. Cloud cover plays a large role in the uncertainty for severity, though being in a humid airmass, and with the forcing expected, can at least expect some shower and storm activity anyway for Tuesday. The question remains on whether we will be unstable enough for strong to severe storms. Due to this, SPC has noted that they will hold off on introducing any severe probs for Tuesday at this time. the upper shortwave will eventually slide east beginning on Tuesday night and into Wednesday. This will help push the meandering boundary east of our region on Wednesday. Slightly lower PoPs are to be expected for Wednesday, but will have to hold onto higher chances in our east as the front takes it`s time moving east. Confidence on temps each day remain somewhat uncertain too, but generally looking at upper 70s and lower 80s each day. Could end up with some drastic differences on high temps, depending on cloud cover, possible outflow boundaries, and of course the showers and storms. ===== Thursday - Sunday ===== Models begin to diverge by Thursday, with differing solutions on the evolution of the upper shortwave, and downstream from there. Confidence remains very low for this time frame, and will take several more days to gain any confidence. With a tropical system coming into the Gulf of Mexico around this time period, interactions between the mid-latitude flow pattern and this system could lead to impactful weather across the region by late this week into next weekend, though confidence in this is very low. Unfortunately, we remain in a "wait and see" position at this time until models begin to converge on a particular solution. && .AVIATION /06Z TAFS THROUGH 12Z MONDAY/... Issued at 210 AM EDT Sun Sep 22 2024 Radar is clear early this morning in central KY and southern IN. A convective complex is evolving eastward across Missouri, and this convection will likely arrive in our region in a weakening state toward the midday and afternoon hours. HNB could see TSRA as early as late morning. SCT TSRA will be possible at this activity pushes east across the area through the afternoon hours. Additional isolated to scattered convection will be possible late this evening into tonight as a cold front pushes into the region. Otherwise, the only aviation impact early this morning is potential fog development. RGA and HNB are most likely to see MVFR or lower visibility due to fog. BWG may also see brief fog vis restrictions. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ SHORT TERM...EBW LONG TERM...CJP AVIATION...EBW