-- Discussion containing changed information from previous version are highlighted. --
569
FXUS64 KMRX 300131
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
931 PM EDT Sat Jun 29 2024

...New UPDATE...

.UPDATE...
-- Changed Discussion --
Issued at 925 PM EDT Sat Jun 29 2024

A few showers and thunderstorms were seen late this afternoon and
early evening. During the last hour showers have decreased with
very minimal activity still occurring at this hour. Only isolated
convection expected next several hours as heating ends. Late
tonight between about 06 and 10Z outflow from storms to the north
in the Ohio Valley may trigger more isolated to scattered
convection in southwest Virginia and northern TN before morning.
Short range models show more of an increase in convection after
12Z ahead of a cold front that will be approaching the northern
plateau during the later morning hours. Temperatures are very warm
at mid evening, still in the 80s with heat index values still in
the lower 90s. Lows Sunday will be in the 70s and some record high
minimums may be set. Have updated the weather and pop grids as
well as temperatures and dew points to reflect current trends.
Updated forecast has been sent.
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&&

.SHORT TERM...
(This evening through Sunday)
Issued at 254 PM EDT Sat Jun 29 2024

Key Messages:

1. Isolated to scattered showers and storms through this evening. No
severe weather expected.

2. Scattered to widespread showers and storms expected tomorrow.
A few strong storms are probable. An isolated severe storm is
possible.

Discussion:

Not much change for tonight or tomorrow compared to the last
forecast. We remain in quasi-zonal flow out ahead of an
approaching cold front. This has allowed diurnal showers and
storms to develop across the area this afternoon. This activity
will decrease in coverage as we lose daytime heating but a few
isolated showers and storms will likely linger through the night.
No severe weather is expected, but an isolated strong storm is
possible.

Tomorrow, showers and storms increase in coverage as a cold front
advances toward the area. The highest coverage will be during the
afternoon hours, during peak heating. HREF ensemble probabilities
show a 50 to 60% chance for SBCAPE of 2000 J/kg by tomorrow
afternoon. 0-6km shear remains weak and will generally be 20kts or
less. Because of the weak shear and moderate instability, a few
strong storms are probable. While most storms will remain below
severe limits, an isolated severe thunderstorm is possible. The
main threats will be damaging wind gusts. This thinking still
aligns with SPC`s Day 2 Marginal Risk.

Showers and storms will decrease in coverage by Sunday evening as we
lose heating. The cold front will pass through sometime overnight.

&&

.LONG TERM...
(Sunday night through next Saturday)
Issued at 254 PM EDT Sat Jun 29 2024

Key Messages:

1. Brief cooler temperatures Monday before a warming trend quickly
returns for the remainder of the week.

2. Mostly dry through Wednesday, albeit a few isolated showers or
storm possible Wednesday afternoon, with daily chances for showers
and a few storms late week and into the weekend.

Discussion:

A post-frontal air mass will result in a return of cooler, more
seasonable temperatures Monday afternoon. Conditions will remain dry
as high pressure and associated subsidence take control. The
seasonable temperatures will be short-lived however, as upper
troughing atop the eastern CONUS coastline lifts north and east
Tuesday, leading to upper level height increases locally.

Temperatures slightly above normal are then expected to persist
through the remainder of the extended period. By Wednesday
afternoon, shortwave energy traversing over the Great Lakes region
will flatten aforementioned ridging. Weakening subsidence will bring
a return to isolated diurnal showers and storms favoring high
elevations. Daily chances of showers and storms are expected to
continue into the weekend, though there becomes more uncertainty
with expected coverage towards the end of the period. The
uncertainty is linked to a surface boundary and how far south it
drops before stalling out. Recent GFS runs suggest limited coverage
Thursday and Friday as the boundary stalls well to our north, where
as ECMWF suggest greater coverage of activity. A more potent
shortwave is expected to kick the boundary through by the weekend,
with potential for a brief cooler period behind the front.

&&

.AVIATION...
(00Z TAFS)
Issued at 732 PM EDT Sat Jun 29 2024

VFR forecasted through the period except some MVFR ceilings late
Sunday afternoon at KTRI behind weak cold front. Showers and
storms will develop late tonight and Sunday and move across the
area from west to east briefly reducing visibilities and ceilings
during the day Sunday. Isolated showers and a few storms early
this evening. More may develop in NE TN late tonight or early
Sunday.

&&

.PRELIMINARY POINT TEMPS/POPS...
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Chattanooga Airport, TN             76  94  70  89 /  20  70  20   0
Knoxville McGhee Tyson Airport, TN  75  90  66  85 /  30  70  40   0
Oak Ridge, TN                       74  90  63  84 /  30  80  40   0
Tri Cities Airport, TN              72  86  62  82 /  50  80  50   0
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&&

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

$$

SHORT TERM...TD
LONG TERM....KRS
AVIATION...TD