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
717 FXUS63 KLMK 220012 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 812 PM EDT Sat Sep 21 2024 ...Updated Aviation Discussion... .KEY MESSAGES... * Above normal temperatures continue, with upper 80s and low 90s the remainder of the afternoon. Isolated storm possible west of I-65 in KY this evening. Some patchy fog tonight. * Multiple waves of scattered showers and storms are expected Sunday afternoon through Tuesday night. There is a low, but non- zero chance for strong to severe storms Monday and Tuesday. && .SHORT TERM /THROUGH SUNDAY/... Issued at 333 PM EDT Sat Sep 21 2024 Things are pretty quiet across the CWA at this hour as morning convection has pushed off to the south and east of the area. A healthy cumulus field has developed in a moist and unstable atmosphere (ML CAPE values 1500-2000 J/KG), however there isn`t much in the way of a trigger for the remainder of the PM hours. As a result, expecting a mostly quiet afternoon with hot temps peaking in the upper 80s and low 90s. We will have to watch our SW CWA around sunset as some hi-res guidance suggests that some convection could redevelop. It appears this would occur on outflow/differential heating coming upstream from the MO Bootheel complex. Given that we need an additional trigger this could be it, but only have low confidence of it actually occurring. Will linger a 20 Pop down in that area to account for the potential and continue to monitor. Should anything develop, heavy rain and locally gusty winds would be a concern. PWATs are in the 1.6 to 1.7 range, and DCAPE are quite high as well. Add in weak steering flow, and locally heavy amounts can`t be ruled out. As we move into the overnight, the only real concern is fog potential given the moist low level airmass and otherwise light/calm winds. Data shows a decent amount of upper sky cover, although with some breaks likely. As a result, could see some fog development, especially across our S and SE where the surface front never quite made it. Will keep the upper sky cover as the limiting factor for more widespread/dense concerns, but can`t rule it out at this stage. The upper ridge axis slides east tomorrow as the mid level flow flattens in response to an ejecting shortwave and associated surface low. Expecting the morning to be mostly dry, however we`ll likely be staring down an upstream convective complex poised to enter our NW CWA by late morning midday timeframe. This complex is expected to be in a weakening state, and tough to tell exactly how far east the better coverage of showers and storms will make it before dissipation. Right, the highest pops are along and west of I-65, and along and north of I-64, or in other words our NW CWA quadrant. The best time frame for some showers and storms will be from mid to late morning until mid afternoon. From there, the degree of re- destabilization is in question, along with south and eastward extent of precipitation, if much at all. Overall, highs will be cooler across our north, with low 90s still more likely across southern KY. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... Issued at 333 PM EDT Sat Sep 21 2024 Sunday Night through Tuesday Night... There is high confidence in unsettled weather for the first half of the upcoming week with multiple waves of showers and thunderstorms likely Sunday night through Tuesday night. A disorganized frontal boundary will stretch from central TX northeast to southern ON Sunday evening, separating a cooler and drier air mass to the northwest from a warm and muggy air mass which will be over our region. An upper level shortwave trough over the central High Plains on Sunday will eject eastward Monday into Tuesday, helping to develop a wave along the remnant front and pushing the boundary farther to the east by the middle of the week. While the main area of forcing associated with the approaching mid- and upper trough will still be a little west of the region on Monday, a moderately unstable environment will be present, with some medium-range guidance showing 1000-1500 J/kg SBCAPE Monday afternoon. The amount of instability realized will be dependent on earlier convection and cloud cover, so there is considerable uncertainty in this amount of destabilization. If we are able to get marginally unstable Monday afternoon, modest mid-level flow would result in deep-layer shear that would be supportive for a few strong storms. Gusty winds and small hail would be the primary hazards with any stronger storm, in addition to heavy rain and lightning. By Tuesday, the mid-level trough should be on our doorstep, with stronger mid-level flow present across the area, leading to greater deep-layer shear. However, uncertainty in our ability to destabilize is even greater on Tuesday, as differences in where the sfc front will be located further complicate the forecast. If we are able to realize sufficient instability, the potential for strong or severe storms may even be slightly higher on Tuesday, though we will first have to see how things evolve over the next few days. For what it`s worth, Colorado State machine learning guidance does have a low end severe threat in our region both Monday and Tuesday, while the ECMWF Extreme Forecast Index shows somewhat unusual values of CAPE and CAPE-Shear parameter during the same time period. The exact temperature forecast remains uncertain for the early week time period, though there is fairly good agreement that temperatures will gradually trend downward as the sfc front creeps southeast. Greater amounts of cloud cover and showers and storms will also keep daytime temperatures suppressed, though breaks in precipitation/clouds would allow for quick warming. Wednesday through the rest of next week... By Tuesday night into Wednesday morning, mid-level trough passage should help push the sfc cold front through the region, bringing drier air in from the west and north. However, it is looking increasingly likely that the region will remain close to the boundary into the mid- and late-week time period, with the humid air mass located just south and east of the region. As a result, slight changes in the evolution of the synoptic pattern will lead to drastic changes in expected sensible weather, particularly as it relates to precipitation chances from Wednesday onward. There are still several camps of solutions in medium-to-long range ensemble guidance which have roughly equal representation, so forecast confidence still looks low for the middle and end of the upcoming week. 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 /00Z TAFS THROUGH 06Z MONDAY/... Issued at 812 PM EDT Sat Sep 21 2024 Showers and storms have nearly dissipated over the region. The remainder of the evening and overnight will feature thinning skies and light winds. In the early morning, some light fog development is expected over BWG/RGA/LEX. Tomorrow morning, a line of showers is expected to move into the region and weaken. Have PROB30 groups over HNB in the morning and SDF/BWG in the early afternoon. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ SHORT TERM...BJS LONG TERM...CSG AVIATION...SRM