Sunrise 6:35 AM   Sunset 8:19 PM Moonrise 1:15 AM   Moonset 10:48 AM

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FXUS64 KMRX 300739 AFDMRX

Area Forecast Discussion National Weather Service Morristown TN 339 AM EDT Tue Apr 30 2024

New SHORT TERM, LONG TERM

SHORT TERM
(Today and tonight)
Issued at 244 AM EDT Tue Apr 30 2024

Key Messages:

1. Showers with a few thunderstorms move through today.

2. Showers end this evening followed by low clouds and fog developing overnight.

Discussion:

Precip approaching the area from the west appears to be driven mainly by QG forcing ahead of a shortwave trough and a jet entrance region, enhanced by a nocturnal LLJ of 30-35 kt. These dynamics will maintain the precip into the western half of the area in the next few hours, but the lack of instability will be a limiting factor as it moves east of I-75. Very few lighning strikes have been observed in Middle TN and northern AL, and IR satellite shows cloud top temperatures have remained steady state.
The forecast for this morning will have categorical PoPs west of I-75 with just a slight chance of thunderstorms. All CAMS show a weakening and dissipating trend to the precip after 12Z as it moves east of Knoxville where there is very little to no CAPE.
However, there may be some additional development this afternoon as the shortwave trough brings some cooler temperatures aloft.
Some CAMS show development in the northern Plateau around 18-20Z that spreads east, and stays mainly north of I-40. The forecast will have a chance of showers and thunderstorms continuing into the evening to account for this possibility. This chance shoudl end after sunset once the trough moves east of the area and dry air aloft builds in.

Tonight, a surface high will quickly build over the area, with a moistu boundary layer remaining in place. This appears to be a goodo setup for some fog or low clouds to form later in the night, and several models are picking up on this. Areas of fog will be mentioned for the entire area late tonight.

LONG TERM
(Wednesday through Monday)
Issued at 244 AM EDT Tue Apr 30 2024

Key Messages:

1. Continued above normal temperatures at least through next week, with the highest temperatures well above normal occurring Thursday.

2. Active weather pattern to bring chances for showers and thunderstorms Friday and continuing through early next week.

Discussion:

At the start of the extended period Wednesday, skies will be clearing after a cold frontal passage earlier Tuesday. Wednesday will begin a considerable warm-up in temperatures from today.
Surface high pressure and ridging aloft will bring the 80 plus temperatures back to the region. Thursday still should be the warmest day of the next several with mid to upper 80s for highs in valley. Skies will start out clear Thursday night but an increase in clouds will move in late at night as another weak system with a cold front crosses the western Great Lakes early Friday and increases moisture over the Tennessee Valley during the day Friday.

A secondary low is expected to form Friday morning over the mid south and lower Mississippi Valley Friday. It is expected to merge with the northern system and then move east into the eastern Tennessee Valley by sunset. A deep upper trough will be to the north of the Tennessee Valley and keep the slow moving system moving through Saturday and then keep the front just to the south Sunday. A good chance of showers and some thunderstorms through Saturday night or early Sunday. Long range models show a possible break in the rain Sunday into early Monday as the ECMWF shows the upper flow becomes more zonal Sunday into Sunday night but the GFS is more active with good chances for more activity Sunday and Monday as shortwaves move through along and near the slow moving frontal system. Kept good rain chances the last 2 days due to the uncertainty. Temperatures after Thursday will stay in the upper 70s to lower 80s.

AVIATION
(06Z TAFS)
Issued at 117 AM EDT Tue Apr 30 2024

Showers will enter East TN from the west over the next several hours. CHA will likely have the greatest impacts, with MVFR vis/cigs as the showers move through between 09-12Z, with a chance of TS and IFR vis with heavier rain. The showers are expected to weaken as they move east, so TYS is less likely to have MVFR conditions and TS, but it is still possible and will be mentioned as a TEMPO there. Chances are still lower at TRI later in the morning/early afternoon so a PROB30 will be used there. After the showers exit this afternoon, low clouds at MVFR levels may linger into the evening at TRI, but TYS and CHA are likely to be VFR.

PRELIMINARY POINT TEMPS/POPS
Chattanooga Airport, TN 75 58 84 59 / 80 0 0 0 Knoxville McGhee Tyson Airport, TN 71 56 81 57 / 80 20 0 0 Oak Ridge, TN 72 55 82 57 / 80 10 0 0 Tri Cities Airport, TN 70 55 78 53 / 60 40 0 0

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

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