-- Discussion containing changed information from previous version are highlighted. --
000
FXUS64 KMRX 200529
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
129 AM EDT Sat Apr 20 2024

...New AVIATION...

.UPDATE...
Issued at 953 PM EDT Fri Apr 19 2024

Cold front was moving into the mountains of east Tennessee late
this evening. As projected by various runs of a few different CAM
models, additional showers have popped up in the higher terrain as
a result of the front moving into these areas. Believe we still
have a few hours left of these scattered showers, but expect all
precip to clear to the east of the CWA well before daybreak. No
other changes appear necessary.

&&

.SHORT TERM...
(This evening through Saturday)
Issued at 245 PM EDT Fri Apr 19 2024

Key Messages:

1. Scattered showers and storms will continue into the early evening
hours with some possibly becoming strong to severe, mainly along and
east of I-75. Damaging winds and hail in excess of 1 inch in
diameter are the main concerns.

2. After the storms, cooler conditions will return with overnight
lows in the 50s and highs on Saturday remaining in the 60s for most
areas.

This Evening/Tonight

Currently this afternoon, fairly zonal flow is in place aloft with a
broad jet of over 100 kts north of Tennessee through the Great Lakes
region. A surface cold front is currently moving onto the Cumberland
Plateau. Ahead of the front, scattered convection has developed
across northern and eastern portions of the area with additional
development expected as the front advances eastward. The environment
consists of 500 to 1,000 J/kg of MLCAPE with fairly uni-directional
effective shear of 35 to 45 kts. Luckily, the overall forcing is
limited, in addition to very weak shear in the lower levels, keeping
the threat as damaging winds and hail. Places further north will
continue to be in the higher end of the shear magnitude due to upper-
level flow with places further south expected to see DCAPE values
closer to 800 J/kg or more. Area-wide, there is notable (>600 J/kg)
CAPE in the -10 to -30 region with WBZ heights only around 10,000.
This will allow for some melting of hail before it reaches the
ground with RAP data suggesting 50 dBZ reflectivity values around
25,000 feet AGL sufficient for 1-inch hail. These values are lower
in southwest Virginia. While shear is certainly sufficient for more
organized or even supercell structures, the environment is limited
by the overall forcing. Overnight, the front will move through the
area with lingering showers and storms diminishing west to east
around sunset. Winds will shift to a more northerly direction,
allowing for seasonally cooler conditions compared to last night.

Saturday

By Saturday, the cold front will have pushed off to our south with
high pressure expanding from the northwest. Increasing subsidence
and northerly flow will allow for low-level moisture to exit the
area, promoting mostly sunny and mild conditions. This will also
support efficient mixing and a drop in RH`s to near or below 30
percent across most of the area. Thankfully, a lot of vegetation has
returned, and low-level flow is expected to be fairly light.

&&

.LONG TERM...
(Saturday night through next Friday)
Issued at 245 PM EDT Fri Apr 19 2024

Key Messages:

1. Low chance of rain, mainly across our southern areas, on Saturday
night and Sunday morning associated with a surface low to our south.

2. High pressure arrives early next week with cooler temperatures;
chance of frost across the higher elevations and plateau on Monday
morning.

3. A quick system will bring low chances of precipitation towards
the middle of next week with high pressure returning behind the cold
front.

Discussion:

Generally quiet weather is expected for most of the extended period
with limited impacts. As a surface low pressure system moves across
the Southeast CONUS, widespread cloud cover and rain chances are
expected Saturday night into Sunday. This will mainly impact our
southern areas with clearer sky conditions and drier weather
arriving Sunday evening into the overnight hours.

Cooler temperatures and light winds will result in opportunities for
patchy frost across the higher terrain and plateau areas on Sunday
night into Monday morning and again on Monday night into Tuesday
morning. At this time, limited impacts are anticipated. With the
cold surface high pressure airmass and Eastern CONUS troughing,
temperatures will be 5 to 10 degrees below normal early next week.

Ridging begins to build back in on Tuesday with a low pressure
system moving quickly across the Great Lakes region. This will bring
another cold front across our region on Wednesday. However, with
high pressure and ridging across the Lower Mississippi Valley
limiting moisture advection northward across the Tennessee Valley
and Southern Appalachians, probabilities of precipitation remain low
with only light accumulation expected.

High pressure is forecast to return in the wake of the departing
cold front late next week.

&&

.AVIATION...
-- Changed Discussion --
(06Z TAFS)
Issued at 103 AM EDT Sat Apr 20 2024

MVFR conditions are forecast for all sites through the night as
low level moisture lingers across the area. VFR conditions are set
to return by late tomorrow morning and remain through the end of
the period. Winds will remain northerly at CHA and TYS, and west-
northwest at TRI, generally less than 10kts.
-- End Changed Discussion --

&&

.PRELIMINARY POINT TEMPS/POPS...
-- Changed Discussion --
Chattanooga Airport, TN             69  50  61  44 /   0  50  40   0
Knoxville McGhee Tyson Airport, TN  67  48  58  40 /  10  40  30   0
Oak Ridge, TN                       68  47  61  41 /   0  20  20   0
Tri Cities Airport, TN              65  43  57  37 /   0  20  20   0
-- End Changed Discussion --

&&

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

$$

SHORT TERM...CD
LONG TERM....JB
AVIATION...