Area Forecast Discussion
Issued by NWS Louisville, KY
Issued by NWS Louisville, KY
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
331 FXUS63 KLMK 070157 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 957 PM EDT Mon May 6 2024 .KEY MESSAGES... * Shower and thunderstorm activity have started to decrease this evening. Still, isolated coverage remains possible across south-central Kentucky. * Potential for multiple rounds of strong to severe storms Tuesday through Thursday. All severe hazards will be possible Tuesday through Wednesday night. There is some potential that a significant severe weather event could develop Wednesday afternoon and night. * Localized flooding potential will exist where repeated rounds of heavy rainfall occur, especially Wednesday night into early Thursday. * Breezy Thursday with gusts of 30 to 40 mph possible. * Cooler temperatures return by Friday and persist into the weekend. && .UPDATE... Issued at 956 PM EDT Mon May 6 2024 Current infrared and water vapor satellite loops show decreasing cloud coverage over the forecast area as dry air filters in from the west. This is occurring in the wake of previous mid-level shortwave trough and associated warm-season MCV which will be shortly replaced by a shortwave ridge. Additionally, radar imagery depicts spotty, shallow showers over the Bluegrass and weakening isolated storms weakening over TN. Overall, such activity will continue dissipating and/or moving away before midnight with patchy fog/low stratus developing thereafter based on model guidance and the expectation of weak winds, mostly clear skies, and enhanced soil/BL moisture. Best coverage for the latter will be in the Bluegrass and Cumberland area with lower probabilities farther west. Rest of the forecast looks on track. && .SHORT TERM /THROUGH TUESDAY NIGHT/... Issued at 327 PM EDT Mon May 6 2024 Now through this Evening... The shortwave trough and CVA are moving through the region supplying ample lift to support convection. Showers and storms are developing and growing in coverage currently and will continue until just after sunset when instability dissipates. Around 1500 J/kg SBCAPE, ample moisture advection into the region, and weak wind shear is supporting some strong storms. Slow cloud level winds and storm motions may lead to precip loading downpours, and as a result, gusty winds and some hail. A limiting factor for these storms are weak mid- level lapse rates. Overnight through Tuesday Morning... Convection will dissipate with fleeting diurnal conditions. The shortwave trough will move off to the east of the region and weak ridging will replace it, promoting drier conditions and thinner skies. Southerly winds will allow for weak WAA into the region. Low temperatures are expected to be similar to the previous night in the low-mid 60s. Recent precipitation, light winds, and thinner skies may lead to some thin patchy fog that will only last for a few hours in the early morning before winds begin to pick back up. A strong, stacked low pressure system over the northern Plains will extend an occluded front to the triple point over northern Iowa. A cold front will extend from this point into the mid-Mississippi Valley and a warm front lifting north through the Ohio Valley. A strong line of storms will surge ahead of the cold front. Guidance trends have depicted the line of storms outpacing the cold front and the greatest instability and dynamics, therefore, likely weakening as it approaches the region. Strong moisture advection will steepen lapse rates and provide modest instability for the remaining dynamics to benefit from. With the weakening line, damaging winds and quick spin-up tornadoes are the main threats. Most likely area and timing are counties along the Ohio River and north around 12- 16Z. Tuesday Afternoon through Tuesday Night... Continued moisture advection into the region and an axis of instability over the Mississippi River will allow for convective initiation along this instability gradient. Single cells may develop into supercells with an elevated supercell composite parameter and well curved hodograph. All severe weather threats are possible for Tuesday afternoon and into the overnight hours. Localized flooding threat is also possible for storms tracking over the same area, mostly due to the previous days rain. With a mature, stronger supercell, significant hail and a strong tornado are possible. In the late evening hours, the cold front will draw closer to the Ohio Valley. Stronger forcing along the front may allow for upscale growth into a squall line. As this line moves through the region, instability will diminish and the cold front will weaken and slow, resulting in a weakening QLCS as it moves through the region. This line will likely exit the region before sunrise on Wednesday morning. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Issued at 327 PM EDT Mon May 6 2024 ==== Significant Severe Weather Outbreak Possible Wednesday afternoon-Wednesday Night ==== ==== Local Flooding Possible Wednesday Night ==== Confidence continues to increase for a significant regional severe weather event Wednesday afternoon into Wednesday night, with the Ohio Valley in the bullseye. A surface low will proceed from MO/IA mid day Wednesday to northern IN/OH by sunrise Thursday, with a cold front dropping southwestward to Texas. A strengthening low level jet from the western Gulf Coast to the upper Ohio Valley will be in place ahead of the main 5H trough over the Midwest and south of a couple of 120kt jet streaks crossing the Great Lakes. The atmosphere is expected to destabilize in the afternoon as temperatures rise slightly above convective temperatures into the low and mid 80s with dew points in the mid 60s. ECMWF EFI is showing climatologically very unusual CAPE/Shear values (for early May!) and LREF shows a 50-80% joint probability of CAPE > 1000 J/kg and deep bulk shear > 40 kt. Scattered storms are expected to develop Wednesday afternoon as the atmosphere destabilizes with only weak capping currently showing up on sounding progs. Old outflow from Tuesday evening storms and differential heating boundaries may serve as focusing mechanisms. Tornado threat: Increasing low-level curvature on hodographs showing the potential for plenty of streamwise vorticity ingestion by storms, and eSTP values are suggesting potential for tornadoes >=EF2 Wednesday afternoon. HREF showing a greater than 90% chance of LCL heights below 1km. Hail threat: Forecast soundings are showing wide CAPE in the -10 to -30C hail growth zone with wet bulb zero heights of 7-10k`. Strong deep layer shear of 60-70kt will be possible with steep mid level lapse rates. Strong storm top venting will assist in supporting robust updrafts. Wind threat: In addition to the above, low level lapse rates will be steep and strong precipitation loading in torrential downpours will aid downdrafts. Heavy rain: Model data are showing near record precipitable water values of 1.5-1.9" and deep warm cloud depths getting pushed northward between ridging over Florida and the cold front approaching from the west. The best chance for flooding issues will likely be Wednesday night, after several rounds of showers and storms Monday-Wednesday and as the final round of intense convection moves through ahead of the front. WPC has the entire region in a Slight Risk on the Day 3 ERO. Storms that erupt to the west Wednesday afternoon and evening closer to the cold front may gel into a line as they approach the MIssissippi River and move through southern Indiana and central Kentucky overnight. Though these storms may become slightly elevated and may start a weakening trend as they get east of I-65 after midnight, all severe modes still appear possible. Confidence is greater in this overnight line of storms than in the supercellular afternoon activity. Nighttime storms and flooding are particularly dangerous, so this should be taken seriously. **Like any forecast, there are sources for potential bust. Any convection that might get going Wednesday morning could decrease instability for afternoon redevelopment, as would cloudiness being more widespread, or stronger capping in our position well within the warm sector. While a significant severe weather event is still a possibility, this isn`t a done deal. Stay tuned to the latest forecast information between now and Wednesday afternoon to keep abreast of changes.** Thursday - Monday: Occasional shortwaves will bring scattered shower/storm chances, especially Thursday and Saturday, as disturbances dive down from Canada around a gyre above northern Ontario and Hudson Bay. At this time no severe weather is expected during this period, however. The big story on Thursday will be windy conditions behind the departing spring storm system, with gusts possibly reaching advisory criteria. Friday will be breezy and cool with afternoon highs only in the 60s. Temperatures will then moderate as we head through the weekend to Monday. && .AVIATION /00Z TAFS THROUGH 06Z THURSDAY/... Issued at 756 PM EDT Mon May 6 2024 Impacts/Confidence: - Medium to high confidence in MVFR/IFR ceilings tonight - High confidence in breezy southerly winds tomorrow - Medium to high confidence in MVFR ceilings Tuesday morning - Low to medium confidence in showers/storms Tuesday morning Discussion...Current radar and satellite show decreasing cloud cover and shower activity as most of the weather moves to the east. For tonight, expect dry and mostly clear conditions to combine with enough low-level moisture from recent heavy rainfall so that patchy fog/low stratus can form after midnight. As a result, models continue indicating MVFR/IFR ceilings with MVFR visibilities. Ceilings will eventually improve close to sunrise as decaying line storms approaches from the west and surface winds increase from the south. Chances of morning showers, and even storms, are greatest for the eastern half of the TAF area. VFR conditions will return during the afternoon hours before another wave of storms move through late Tuesday afternoon into the evening. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ UPDATE...ALL SHORT TERM...SRM LONG TERM...13 AVIATION...ALL