532
FXUS64 KMRX 170553
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
153 AM EDT Tue Sep 17 2024

...New AVIATION...

.UPDATE...
Issued at 1017 PM EDT Mon Sep 16 2024

A light rain is currently falling over the very northeastern
portions of Tennessee into southernmost portions of Virginia,
primarily east of Interstate 81. Dry air is clearly evident in
both surface observations and radar, with forward progress of the
rain on a bit of a pause for now. Still, expecting the rain shield
to make progress overnight into more of East Tennessee and
southwest Virginia as the atmospheric column begins to saturate.
If the atmosphere moistens slower than expected, this may impact
rainfall accumulations by morning and extent of rain into East
Tennessee.

Forecast seems to be on track for the most part, with only minor
edits made to the various weather groups to match trends seen in
radar, satellite, and surface obs.

&&

.SHORT TERM...
(This evening through Tuesday)
Issued at 257 PM EDT Mon Sep 16 2024

Key Messages:

1. Rain will spread into northern portions of the area tonight and
tomorrow with an approaching tropical low.

2. Rain amounts will be highest in the terrain along the NC border,
with lower amounts in the Valley.

Discussion:

The tropical low near the SC coast will track NW through this
period. Some light rain is currently crossing the mountains, but it
is encountering a low level dry air mass in the TN Valley.
Gradually, the column will moisten in NE TN and SW VA, with
measurable rain likely in the Tri-Cites around 06Z. The precip
shield will spread westward through Tuesday morning, reaching the
Plateau before 12Z. Easterly winds at 850 mb may result in
downslope drying effects in the Valley, so the highest QPF amounts
will be in the higher terrain along the NC border, where 1.5-3
inches of rain are expected. In the adjacent Valley and foothills,
amounts will be in the range of 0.5-1 inch, but possibly lower
depending on how strong the downslope winds are. With the expected
cloud cover and precip, temperatures on Tuesday will be much
cooler, with highs in the upper 60s north to upper 70s south.

&&

.LONG TERM...
(Tuesday night through next Monday)
Issued at 257 PM EDT Mon Sep 16 2024

Key Messages:

1. Precipitation chances continue through Wednesday.

2. Warming trend with low confidence precipitation chances expected
the second half of the week

3. Dry and warm over the weekend.

Discussion:

Wednesday night will see the remnants of Potential Tropical Cyclone
8 spinning directly over the southern Appalachian region near
northeast TN and southwest VA. The late Tuesday through Wednesday
period will be some of the best chances to see widespread rainfall
from this system, but there will likely be a sharp gradient between
north and south of Interstate 40. Precipitation will once again be
moving in from the east/north and a good portion of it will stay to
the east of the mountains where upslope flow produces heavy rain on
the windward side of the mountains. Rain will definitely spill over
into the western side of the Appalachians, but expect the vast
majority of the precipitation to remain north of Interstate 40.
Currently am expecting to see over an inch of rain in northeast
Tennessee and southwest Virginia, decreasing down to practically
nothing around Chattanooga.

Forecast becomes a bit more uncertain for the second half of the
work week, mainly with regards to precipitation chances as the
remnants merge into a low pressure system and the ridge tries to
ride up over it leading to a continuation of the rex block set up.
Deterministic models are in disagreement with how much and how
widespread any showers and possibly thunderstorms would be for the
second half of the week... But a general trend of higher PoPs north
of I-40 is starting to emerge. QPF amounts are expected to be light,
but we could see near an inch of precipitation in the northeast, and
possibly higher amounts along the mountains. Otherwise expect a
warming trend for the week topping out on Saturday as the warmest
day with temperatures about 5 degrees above seasonal normals.
Precipitation chances dry up once we move into the weekend and the

&&

.AVIATION...
(06Z TAFS)
Issued at 144 AM EDT Tue Sep 17 2024

Light rain at times being observed at TRI the past few hours that
will eventually reach TYS later this morning. CHA should remain
VFR for the TAF period with the only impacts from the tropical
system being NEly winds and lowering CIGS throughout the day. TRI
and TYS will mostly categorize as MVFR for much of the day with
light to moderate rain, BR, and low CIGS at times. Tonight will
need close monitoring when we are forecast to clear some, so fog
may be an issue overnight.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             81  63  85  64 /  20  10  20   0
Knoxville McGhee Tyson Airport, TN  75  65  80  64 /  70  20  40  10
Oak Ridge, TN                       75  63  79  63 /  70  10  40   0
Tri Cities Airport, TN              71  62  75  62 /  80  40  50  10

&&

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

$$

SHORT TERM...Wellington
AVIATION...KS