Sunrise 6:27 AM   Sunset 8:51 PM Moonrise 3:19 PM   Moonset 3:00 AM

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FXUS63 KLMK 181443 AFDLMK

Area Forecast Discussion National Weather Service Louisville KY 1043 AM EDT Sat May 18 2024

KEY MESSAGES

* Showers and a few thunderstorms tapering off by this evening.

* Dry weather arrives Sunday with unseasonably warm temperatures Monday and Tuesday.

* Showers and thunderstorms return Tuesday night into Wednesday.
Confidence remains low in the potential for severe weather.

UPDATE
Issued at 1043 AM EDT Sat May 18 2024

Vis has improved dramatically across most of the area, though some fog still lingers in the typical locations. Dense Fog Advisory was allowed to expire at 14Z. Forecast for the rest of the day is pretty much on track, with overall decreasing trend in cloud cover.
Still looks like a decent chance for afternoon showers/storms mainly in south-central Kentucky, as it remains a moist air mass with cyclonic mid/upper-level flow. Will have to watch for any more focused convection if differential heating creates an effective boundary farther north in central Kentucky.

SHORT TERM /THROUGH TONIGHT/
Issued at 424 AM EDT Sat May 18 2024

Early morning satellite imagery showed mostly clear skies across southern Indiana and much of central Kentucky. The only cloudiness we had was down in our far southeast across the Lake Cumberland region where a few showers continued. Otherwise, dense fog has developed across the region. The fog is not all that widespread with the greatest concentration across the Bluegrass region of central Kentucky back to the southwest along and just south of the Parkways. Some patchy dense fog has developed as far north as southern IN. With skies remaining clear and winds continuing to slack off, guidance suggests that fog will become more widespread as we head towards sunrise. Given the dense nature of the fog, a Dense Fog Advisory was issued earlier and will continue until 10 AM EDT.

For today, we'll see the fog this morning mix out by mid-late morning with partly cloudy skies becoming commonplace. Overall flow pattern across the region will remain quite stagnant as upper level troughing will remain in place across the region. It will be a muggy day across the area. As temperatures warm, model soundings show a relatively uncapped airmass in place. Recent model trends continue the idea of suppressing rain chances further south. Based on latest NAMnest and HRRR runs, the best chances of precipitation today look to be south of the KY Parkways. Area proximity soundings show poor lapse rates and very weak shear which suggests that convection will be relatively unorganized. Nonetheless, scattered showers and a few storms will be possible with locally heavy rainfall and lightning being the main hazards. Highs on the day will be in the upper 70s to the lower 80s.

For tonight, upper ridging will build into the region from the west resulting in drier conditions and mostly clear skies. We'll run the risk of seeing some more fog again given the clear skies, light winds, and wet ground. Overnight lows will be in the lower 60s.

LONG TERM /SUNDAY THROUGH FRIDAY/
Issued at 424 AM EDT Sat May 18 2024

Synopsis...The medium range period will be characterized by amplification of the large scale flow that will initially favor dry and increasingly hot conditions through early next week with active weather starting on Wednesday. After a weak, southern-stream shortwave trough moves away from the region Saturday into Sunday, mid-level ridge will stretch from Texas into the Northeast US in response to strengthening dome of high pressure over Mexico and upstream energy phasing. The resultant mid-level cyclonic circulation will be conformed by upper low over southern Canada and a series of shortwave troughs ejecting across the Midwest by the middle of next week. Of particular interest is the leading shortwave trough and attendant surface low as they will push a cold front towards the Ohio Valley on Wednesday, raising the chances of strong to potentially severe storms.

Model Evaluation/Confidence...Overall, deterministic global models (ECMWF/CMC/GFS) are in good agreement on how the synoptic features will evolve through Tuesday. As expected, forecast confidence starts to diminish on Wednesday and thereafter given the fairly complex wave interaction between the Canadian upper low and parade of shortwave troughs. Nonetheless, most recent runs have an overall better consensus on the position of the occluding surface low and timing of the frontal passage on Wednesday. Correspondingly, CSU and NCAR severe weather guidance continue highlighting low probabilities of severe storms for Wednesday. Another wave of heavy rainfall might be in place late next week (probably Friday) but confidence in specifics at this time is rather low to mention any significant weather.

Sunday - Tuesday...Dry and increasing hot weather is anticipated during this period. First of all, rain chances for Sunday have greatly decreased compared to yesterday forecast. The influence of the building mid-level ridge and surface high pressure over the region will keep rising motions confined below a 700-mb capping inversion while pronounced dry layer settles in on the mid levels.
As the surface high pressure moves to the Mid Atlantic and the next storm system approaches from the Midwest, low-level winds will turn to the south on Monday and southwest on Tuesday enhancing the warm and humid air influx. Highs both days should be in the mid to high 80s with urban areas probably reaching the 90 degree mark. Although a cu field will develop each afternoon, rain chances will be negligible given the dry and stable environment. Only exception would be Tuesday afternoon and evening when a few light showers might move in ahead of the cold front. Last but not least, hydro guidance has changed radically as HEFS now reflects less than 10% of minor river flooding for Rochester and Woodbury. This reduction was primarily driven by recent rainfall trends and forecast accumulations of less than an inch in the aforementioned river basins.

Wednesday...Convection-allowing and parameterized models depict two distinct waves of rainfall on Wednesday. The first wave, probably subsevere, should arrive Wednesday morning as overnight convection weakens and outruns the best frontal forcing roughly stalled along the Wabash Valley as the shortwave and attendant surface low moves farther away to the north. The second and strongest wave should begin along and ahead the effective frontal boundary in the afternoon hours and translate across the forecast area in the evening. In this case, timing of convection will be key as earlier storm activity will tap into daytime instability to produce better chances of organized, strong convection. Overall, forecast space parameters agree with CSU and NCAR algorithms having a greater severe threat along and north of the OH river.

Thursday - Friday...Daily rain chances will continue the second half of the week with potential for heavy rainfall on Friday as another system tracks over or close to forecast area. Localized areal and river flooding cannot be ruled out.

AVIATION /06Z TAFS THROUGH 12Z SUNDAY/
Issued at 424 AM EDT Sat May 18 2024

Main concern for the overnight is the clear skies and wet ground from recent rainfall. Visibilities have started to tank over in the east with a mix of low cloudiness and fog developing. Looking at the latest guidance, it appears that we'll see fog develop at the terminals overnight and have subsequently lowered cig/vsbys down in to IFR and below for the overnight, especially in the 18/08-12Z time frame. After sunrise, cigs/vsbys will quickly rise through the IFR and MVFR range before becoming VFR by late morning.

LMK WATCHES/WARNINGS/ADVISORIES
KY...None.
IN...None.

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