Sunrise 6:25 AM   Sunset 8:38 PM Moonrise 3:11 PM   Moonset 2:52 AM

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FXUS64 KMRX 180705 AFDMRX

Area Forecast Discussion National Weather Service Morristown TN 305 AM EDT Sat May 18 2024

New SHORT TERM, LONG TERM

SHORT TERM
(Today and tonight)
Issued at 303 AM EDT Sat May 18 2024

Key Messages:

1. Scattered to numerous showers and thunderstorms can be expected today, a few may become strong to severe.

2. Showers and thunderstorms will diminish tonight.

Discussion:

We start the period with considerable moisture lingering over the area and a weak upper level trough to our west. This upper trough will move east across the region during the period and will be exiting to our east by late tonight. The better forcing with the upper jet is forecast to stay to our south and east, but a period of weak upper divergence is indicated this afternoon over our area.
Expect scattered to numerous showers and thunderstorms across the area today, with the best coverage in the afternoon. Model data generally suggests better instability developing than yesterday with SBCAPES in the 750-1250 J/kg range likely across much of the area this afternoon, but also generally shows relatively weak flow and limited shear. The threat of strong to severe storms does not look high. However, a few storms may become strong to severe with damaging winds, large hail and locally heavy rain the primary threats. High temperatures today will be near to slightly below seasonal normals.

The showers and thunderstorms will diminish tonight from west to east as the trough axis shifts east. Low temperatures will generally be a bit above normal.



LONG TERM
(Sunday through Friday)
Issued at 303 AM EDT Sat May 18 2024

Key Messages:

1. A lingering shower is possible on Sunday, most likely along the mountains.

2. Drier and warmer on Monday and Tuesday.

3. Daily chances of showers and thunderstorms to resume Wednesday onwards, with a warm and humid airmass in place.

Discussion:

Our weak trough is finally moving on, and Sunday as a result should be mainly dry for much of the area. CAMs and global models, both legacy and experimental, depict the best chances for a shower or two to be along the spine of the mountains bordering with North Carolina. This makes sense with the trough pulling away to the east, and a surge of median aka drier PWATs entering in from the north pushing any lingering moisture coupled with afternoon heating isolated towards the mountains. After that, we get a break from the storms as the upper ridge moves in and provides for rebounding temperatures and much drier weather to start the workweek. An isolated shower or thunderstorm is possible Monday and Tuesday afternoon, but no washouts expected.

Beyond Tuesday the forecast enters into a low confidence stretch. It seems likely based off of all available guidance that a broad upper trough will be over south-central Canada, with a low moving northwards over Lake Superior pivoting around the broader upper level flow Wednesday morning. At the surface a cold front extending from this low will push towards the Ohio River, but guidance is showing persistence from yesterday on this front not making it to the southern Appalachians. With the front washing out, flow aloft switches to a more zonal pattern, but persistent southerly flow brings increasing moisture and humidity into Tennessee. As a result, the warm weather will likely continue into late week. Starting Wednesday onwards we will have a daily low to medium (20 to 50 percent) chance for scattered showers and thunderstorms being fueled in part by the southern moisture return, but as of now no organized or significant signals for much beyond that.

AVIATION
(06Z TAFS)
Issued at 109 AM EDT Sat May 18 2024

Low clouds and possibly some fog will bring conditions down to at least MVFR at times early in the period, with lower conditions possible. Cigs will lift back to VFR by late morning/early afternoon, but there will be some showers and thunderstorms around especially during the afternoon which will likely lower conditions again to MVFR or lower with any heavier precipitation. Coverage of showers/storms is expected to begin to diminish late in the period.

PRELIMINARY POINT TEMPS/POPS
Chattanooga Airport, TN 80 63 85 63 / 80 40 20 0 Knoxville McGhee Tyson Airport, TN 77 61 81 61 / 80 50 30 0 Oak Ridge, TN 78 61 83 61 / 80 50 20 0 Tri Cities Airport, TN 76 60 78 56 / 70 60 40 0

MRX WATCHES/WARNINGS/ADVISORIES
NC...NONE.
TN...NONE.
VA...NONE.

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