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FXUS63 KJKL 052121 AFDJKL

AREA FORECAST DISCUSSION National Weather Service Jackson KY 521 PM EDT Sun May 5 2024

KEY MESSAGES

- Shower and thunderstorm potential lasts through the next 7 days.

- Severe thunderstorms are possible Tuesday afternoon through Wednesday night. Large hail and damaging winds are the primary threats, with heavy rainfall producing localized flooding also possible.

- Above normal temperatures are forecast through Thursday. A cold front should pass late in the week and bring readings down to near or below normal.

SHORT TERM
(This evening through Monday night)
Issued at 333 PM EDT SUN MAY 5 2024

A weak stationary front bisecting the forecast area from northeast to southwest continues to be the focus for shower and thunderstorm development this afternoon. Some of this activity has at least briefly anchored to terrain features or the frontal boundary itself and produced locally heavy rainfall via training, which has necessitated the issuance of flood hazards.

This front will move little through the short term and will serve as a focus mechanism for shower and thunderstorm development. While today's activity is occurring with little to no forcing for ascent aloft, a stronger shortwave disturbance will approach the area tonight and then cross the area Monday afternoon and evening, bringing widespread showers and thunderstorms.

Transitory shortwave ridging builds over the area by late Monday night and will likely limit shower and thunderstorm activity somewhat before the next system approaches Tuesday.

Highs Monday will likely be limited by cloud cover and fairly widespread precipitation, with highs in the mid 70s to lower 80s.
Lows tonight and Monday night will be dependent on cloud cover, with fog formation likely where there is at least partial clearing by dawn. Lows will range from the mid 50s in the coolest sheltered valleys to lower 60s.

LONG TERM
(Tuesday through Sunday)
Issued at 521 PM EDT SUN MAY 5 2024

Very active extended, with precip chances expected every day. The first couple days of the period (Tuesday and Wednesday) will be the most impactful, as two different strong frontal systems move through.

The period will start off Tuesday morning with a shortwave exiting the state to the east, brief ridging in place, and a very strong upper level system across the Northern Plains creating deep troughing across much of the central and western Conus. As we got throughout the day Tuesday, the small ridge will quickly shift east as the state begins to fall under the influence of the upper level trough and increasing SW flow. This increased SW flow will easily increase moisture and instability across the region, but will also raise temperatures across the state, with highs in eastern KY expected to top out in the upper 70s and low 80s. In fact, a warm front will actually develop and be analyzed moving north of the state by 15Z Tuesday. This warm front will be connected to an occluding low pressure system over the Northern Plains, co-located with the upper level system. As the day progresses Tuesday, WPC has a secondary low forming at the triple point of the 3 boundaries (occluded, warm, and cold), and the occlusion beginning to die off.
This new low will quickly make its way into the Great Lakes region by Tuesday evening/night, with the associated cold front elongating itself along the Ohio River. The front will drop south into the state Tuesday night, likely passing through the JKL CWA during the late night/early morning hours Wednesday. However, this won't be the end of this system...

This cold front will be connected to another low pressure system to our west, which will quickly gain strength Tuesday into Wednesday as it shifts ENE. While the front is impacting the CWA Wednesday, the low pressure system will move into the Mid-Mississippi Valley by the afternoon, lifting the cold front back north as a warm front. By 0Z Thursday, the GFS has the low analyzed across Indiana, with a cold front attached and moving eastward into western Kentucky. This front will continue to traverse KY, passing through the JKL CWA between the early morning and early afternoon hours Thursday according to the latest NBM.

After this system exits to the east of the state, we may have a super brief break in the action. While the surface low will be out of the region, an upper level shortwave/trough will be passing through during the day Friday. This may be enough to bring another round of chances of showers and thunderstorms to the region again. As this exits, models are actually in good agreement that we may see some dry weather during the day Saturday. That being said, the NBM is going gung-ho on bringing pops back in from the west, but so far models are trending away from this occurring. It looks like the surrounding offices didn't go as high on pops as the NBM, so expect to see those chances decreasing with the coming forecasts so long as the modeled pattern holds.

Now..for sensible weather. Obviously with several frontal boundaries moving through the region, and strong SW flow in place, we are setting ourselves up for potential showers and thunderstorms. The first main round will be during the afternoon Tuesday, as the warm front lifts north of the CWA and we find ourselves in a warm, moist, and unstable sector ahead of the cold front. It will slowly dissipate again overnight. SPC has placed much of this warm sector and along the cold front in a slight risk area from 12Z Tuesday through 12Z Wednesday.

From SPC: Deep-layer shear is forecast to be strong enough to support organized convection, including some supercells. However, with mid-level flow generally aligned with the forecast position of the surface boundary, tendency may be for clusters/bowing line segments to prevail. Regardless, scattered strong to severe thunderstorms should spread east-northeastward across the OH Valley Tuesday afternoon and evening, posing a threat for mainly damaging winds and severe hail.

Wednesday morning will start off with lower-end pops, but will quickly ramp up during the afternoon as the cold front makes its way into the state and then begins to lift back north as a warm front in the afternoon. These pops will likely be highest in the southern portion of the state, where the best heat and instability are located ahead of the front. Then by the overnight, the NBM has a line of storms developing along and ahead of the next cold front, passing from NW to SE through the CWA during the late night and into the day Thursday. Again, can't rule out some strong winds and potential hail, though it's passing during the late night/morning will hopefully dampen some of the worst severe potential. Being on Day 5, there is still quite a bit of evolution this system can take, and still some model disagreement, but do keep an eye out as severe potential can't be ruled out.

Friday's passing shortwave brings yet another influx of likely showers and thunderstorms to eastern Kentucky, mainly during the afternoon and early evening with best heating/mixing/instability.
Then for Saturday, as mentioned above, the NBM went with likely pops for the CWA, however based on the latest models, wouldn't be surprised if this will continue to trend drier.

As for temperatures, almost every night, except for the very end of the forecast, is expected to see cloud cover given the continued precip chances. As such, did not do any ridge/valley temp differences for these nights. The warmest days will be Tuesday through Thursday, ahead of the final passing cold front, at which point a change in airmass will take place as winds become more northerly aloft and advect in cooler temperatures. Temperatures for Friday and into the weekend will struggle to reach 70 degrees in some cases.

AVIATION
(For the 18Z TAFS through 18Z Monday afternoon)
ISSUED AT 202 PM EDT SUN MAY 5 2024

VFR conditions are expected into this evening outside of brief MVFR/IFR conditions in isolated to scattered showers and thunderstorms. There are model discrepancies late tonight into Monday which makes forecasting a bit difficult, depending on the arrival of the next disturbance. Some models depict showers and then thunderstorms moving in late in the overnight through Monday morning, while other models depict partial clearing overnight which would allow widespread fog formation during the few hours straddling dawn, before the next round of showers and thunderstorms move into the area after 12z-15z Monday. For now, decided to split the difference, with future forecasts likely being able to hedge more one way or the other with increasing clarity on which scenario becomes more likely. At any rate, expect widespread MVFR and possibly IFR/LIFR cigs and/or visibility after 06z through 13-14z Monday before beginning to gradually improve through the end of the TAF period.

JKL WATCHES/WARNINGS/ADVISORIES
NONE.

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