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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS64 KMRX 190111
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
911 PM EDT Thu Apr 18 2024

...New UPDATE...

.UPDATE...
-- Changed Discussion --
Issued at 906 PM EDT Thu Apr 18 2024

Will slow the forecast arrival of showers and storms tonight
based on latest radar and hi-res CAM trends. Otherwise the
forecast for tonight generally still looks to be on track, so the
only other changes will be minor tweaks to temps and dew points.
-- End Changed Discussion --

&&

.SHORT TERM...
(This evening through Friday)
Issued at 246 PM EDT Thu Apr 18 2024

1. Showers and thunderstorms expected overnight, stronger storms
more likely, but not a certainty, west of Knoxville.

2. A second chance for scattered strong thunderstorms exists Friday
afternoon across the Tennessee valley. Gusty winds and large hail
possible with the afternoon thunderstorms.

Discussion:

Cold front begins the period across Missouri and will march
eastwards with time until making it to Tennessee by the end of the
short term Friday evening. A couple rounds of showers and
thunderstorms will exist in the warm sector ahead of the front.

First round of showers and thunderstorms is expected overnight
tonight. This means that the remainder of the evening today is
expected to remain dry, so that`s good news. Guidance indicates
showers and storms tonight will generally ride the midlevel heights
axis as the ridge continues to move off to our east by Friday
morning. Given the time of the day being the most unfavorable for
thunderstorm intensity and the ability of storms to mix winds down
to the surface, not feeling aggressive with the idea of strong
storms overnight. Additionally, the more recent CAM runs have backed
off on storm cell intensity and organization for overnight. HRRR has
trended towards an even more scattered, unorganized, depiction for
overnight into morning storms. Still, a few rumbles of thunder are
possible given elevated CAPE as the remnants of the convection from
Western Kentucky and Middle Tennessee move into East Tennessee.

Convection should exit or dissipate by mid-morning, yielding a few
hour pause until the second round during the afternoon. An
approaching 500 mb speed max moves from west to east across
Tennessee heading into peak daytime heating, increasing flow aloft
from 30 knots to 50 knots. Some of the guidance (notably the HRRR
and high res NAM) depict a quick and robust recovery into Friday
afternoon, along with a favorable convective initiation in the
Tennessee valley to take advantage of their modeled environments.
Hodograph shapes are fairly linear, and given the increasing flow
providing plenty of effective shear, a risk for damaging winds and
severe hail is possible. One big uncertainty is cloud cover is
expected to be present in the morning through the afternoon storms,
so not certain how that hinders the convective environment. Still,
the environment will need to be watched for strong thunderstorms.

&&

.LONG TERM...
(Friday night through next Thursday)
Issued at 246 PM EDT Thu Apr 18 2024

Key Messages:

1. Outside of rain chances on Sunday, drier and cooler conditions
are expected into early next week, especially on Monday.

2. Rain chances and more seasonal temperatures will return by
Wednesday and Thursday.

Friday Night through Monday

At the start of the period, subtle troughing will be in place across
the eastern U.S. with a strong upper jet to our north. A cold front
will be moving through the area ahead of high pressure expanding
from the northwest. During this time, lingering showers and storms
from the short term period will be exiting the area west to east
with a shift to northwesterly flow. This will advect cooler and
drier conditions into the area heading into the day on Saturday.
Subsidence and efficient mixing will certainly allow for a drop in
RH`s into the 30s, but luckily low-level winds will be fairly light,
not to mention the return of vegetation in most places. Heading
towards Sunday morning, focus will turn towards a developing Gulf
low, following the recent CAA. During the daytime, a shortwave will
approach from the west with increasing upper divergence as the jet
becomes centered over the northeast. The result will be increasing
PoPs, especially further south where better moisture exists. By
Monday morning, high pressure will be expanding from the west again,
which will produce additional subsidence. Depending on how much
cloud cover and MSLP gradient-induced winds linger, patchy frost
will be at least possible in the morning hours. Notable height falls
and recent CAA will keep temperatures fairly cool.

Tuesday through Thursday

High pressure will keep the area dry and mild on Tuesday. Heading
towards Wednesday, another shortwave will pass to the north with a
surface front also drifting southeastward from the central Plains.
This will lead to an increase in rain chances Wednesday and
Thursday. The overall pattern currently indicates a setup supportive
of showers with only limited thunder coverage due to fairly cool low-
levels. Moisture will also be fairly limited for the time of year,
given PWATs of only around 1 inch.

&&

.AVIATION...
(00Z TAFS)
Issued at 710 PM EDT Thu Apr 18 2024

Some showers and thunderstorms will be around at times especially
later tonight into Friday. Will carry tempo or prob30 thunder
groups for the times when probability looks highest, but timing
confidence is still not high. There is also a high chance (around
70 percent) that conditions will become MVFR at least for a
period Friday morning, so will include that as well all sites.

&&

.PRELIMINARY POINT TEMPS/POPS...
-- Changed Discussion --
Chattanooga Airport, TN             65  80  57  73 /  80  40  10  20
Knoxville McGhee Tyson Airport, TN  63  75  54  68 /  80  80  20  10
Oak Ridge, TN                       62  77  53  69 /  90  80  10  10
Tri Cities Airport, TN              56  73  51  66 /  50  80  20  10
-- End Changed Discussion --

&&

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

$$

SHORT TERM...
LONG TERM....BW
AVIATION...