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
510 FXUS63 KLMK 070715 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 315 AM EDT Fri Jun 7 2024 .KEY MESSAGES... * Pleasant weather expected today with mostly sunny skies and low humidity. * Showers and a few thunderstorms this weekend. Locally heavy downpours possible late Saturday night into early Sunday morning across western and southern Kentucky. && .SHORT TERM /THROUGH TONIGHT/... Issued at 313 AM EDT Fri Jun 7 2024 Across the region this morning, mostly clear skies are observed on nighttime microphysics satellite imagery as a swath of deep dry air is continuing to work into the Ohio and Tennessee valleys from the north and west. A broad upper level trough axis stretches from central Ontario down into the southern Appalachians, with deep layer NW flow present over the region helping to advect in significantly drier and marginally cooler air. Satellite imagery also shows valley fog developing over eastern KY at this hour; while some isolated valley fog may develop between now and sunrise (especially in the Cumberland River valley), a more persistent light westerly wind and drier air should limit fog overall. Light winds, clear skies, and dry air has allowed for efficient cooling thus far this morning, with lows expected to fall into the 50s in most locations outside of the Louisville heat island. Today should feature excellent weather across central KY and southern IN, as the dry air mass over the region brings us mostly sunny skies and low humidity values. It will still be a bit breezy late this morning and into the afternoon hours as diurnal mixing allows for 20-25 kt NW flow around 850 mb to mix down to the surface. Expect W/NW winds of 10-15 mph with gusts to around 20 mph today, with winds once again slackening off by around sunset tonight. Temperatures should only be slightly below climatological norms with highs expected to reach the upper 70s and lower 80s; however, afternoon dewpoints in the upper 40s and low-to-mid 50s will make things feel quite pleasant. Tonight, the dry air mass overhead will begin to give way as sfc high pressure and ridging aloft over the lower Mississippi Valley flattens, with moisture from the Great Plains beginning to work over the top of the ridge and into the Ohio Valley after midnight. Additionally, an MCS which is expected to develop over Nebraska late this afternoon will promote the development of a convectively- enhanced shortwave which will eject southeastward overnight into early Saturday morning. Significant instability will remain well west of the Mississippi Valley, so any convective complex which develops later today will be much weaker by the time it enters our area. The forecast late tonight will be strongly influenced by the evolution of the upstream MCS, with latest convection-allowing guidance showing the remnants reaching northwestern portions of the CWA as some light-to-moderate rain showers by around sunrise Saturday. Before moisture and clouds increase early Saturday morning, temperatures should be able to cool into the 50s and lower 60s, with temperatures likely remaining fairly steady or even slightly increasing toward dawn Saturday morning. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Issued at 313 AM EDT Fri Jun 7 2024 The Weekend... MCS development is expected tonight over MO/IA/IL ahead of a strong low level jet across Kansas and Missouri. Remnants of that complex will slide ESE into the lower and middle Ohio Valley Saturday morning, bringing mostly showers and a few embedded rumbles of thunder. Given these morning clouds and showers, it may be difficult to destabilize much in the afternoon, resulting in the best rain chances on Saturday occurring in the morning. Saturday night a WSW-ENE oriented cold front will slip in from the northwest and will likely be draped somewhere along Kentucky by dawn Sunday. The LLJ Saturday night is expected to be much weaker than tonight`s, but fairly impressive precipitable water air of 1.75-2" will pool along the front, resulting in widespread rain from Kansas to Kentucky. Deep layer shear vectors oriented from WNW to ESE suggest that showers/storms will move off the boundary, rather than parallel to it, and models & WPC are progging the heaviest rainfall amounts to our west over southern Missouri. Still, with such high PWATs and the QPF pattern stretched out linearly along the surface boundary, locally torrential downpours and minor flooding issues may still arise, primarily after midnight into early Sunday morning across western and southern Kentucky, especially if any training occurs. Instability has increased slightly for the weekend, primarily Saturday evening through Sunday morning, so will continue to advertise the possibility of scattered thunder. Next Week... Three runs ago the operational GFS was dry on Monday-Tuesday...and now has about 2/3" of rain in southern Kentucky Monday afternoon, and more Monday night-Tuesday, as a wave of low pressure rides up the weekend front, which by Monday should be over the Southeast. However, looking at GEFS plumes with regard to QPF, the operational GFS is a significant outlier. Looking at the individual perturbations of the GEFS, about half of the members are still dry. The 07/00Z runs of the CMC and ECMWF are dry with the front being pushed farther southeast by Canadian high pressure invading the Great Lakes, and most members (though not all) of the Euro ENS are dry. Given the operational GFS`s outlier status and the sudden jump from dry to wet, will refrain from buying totally into that solution. However, still shouldn`t discount it completely, so will go ahead and hold on to the 20-30% PoPs suggested by the NBM. Confidence, however, is very low for Monday-Tuesday. Confidence increases a bit for Wednesday-Thursday with a lack of storm systems in the region and dry weather the result. By Thursday temperatures will moderate into the middle and upper 80s, with 90 degrees possible Friday into the weekend as an upper ridge spreads eastward from the Plains into the Great Lakes and Ohio Valley. && .AVIATION /06Z TAFS THROUGH 12Z SATURDAY/... Issued at 1254 AM EDT Fri Jun 7 2024 VFR conditions are expected through the current forecast period. As expected, winds have slackened considerably compared to this afternoon as a nighttime inversion has set in across the region. Light westerly winds will continue through a few hours after sunrise, when stronger winds aloft begin to mix down to the surface with the help of daytime heating. Would expect to be able to mix into 20 kt NW flow about 5 kft AGL by late morning through the afternoon hours, with sfc wind gusts around that magnitude expected. A dry air mass in place should limit cloud cover to a 5-7 kft FEW- SCT cu field during the afternoon hours. Tonight, moisture will start to return from NW to SE across the region after 06Z, with an increase in mid and high clouds expected initially. Winds are expected to go light and variable quickly after sunset tonight. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ SHORT TERM...CSG LONG TERM...13 AVIATION...CSG