841
FXUS64 KMRX 161758 AAC
AFDMRX

Area Forecast Discussion...UPDATED
National Weather Service Morristown TN
158 PM EDT Fri Aug 16 2024

...New AVIATION...

.UPDATE...
Issued at 949 AM EDT Fri Aug 16 2024

Main purpose for the morning update was to try and bring PoPs in
line with current and expected radar trends. Currently have a
ragged looking line of convection moving east through middle
Tennessee. It should be approaching the plateau areas in the next
couple of hours, then pushing into the valley areas during the
early afternoon hours. PoPs from both the latest CAM guidance as
well as the most recent hourly NBM breakdowns show increasing
convective coverage during the afternoon hours. This isn`t out of
line with what the previous shift had. Main adjustments for the
morning update were to cut down PoPs outside of the plateau as
our CWA is currently rain free and that trend likely continues for
a few more hours before the incoming line/boundary plus diurnal
trends assist in increasing convective coverage. Otherwise, bumped
up afternoon highs in the south as they were a tad warmer than
hourly forecast grids suggested, and they`re largely cloud free
down there.

&&

.SHORT TERM...
(Today and tonight)
Issued at 237 AM EDT Fri Aug 16 2024

1. A line of strong storms will move through the region this
afternoon, with some severe storms and localized flooding
possible. Damaging winds will be the primary threat with any
severe storms.

2. Heat indices around 100 degrees in the Southern Tennessee
Valley likely before storms move into the region.

3. Uncertainty is higher than normal for rain potential this
evening and overnight. Some showers will be possible.

Discussion:

An unsettled pattern will be in place this period with a
vertically stacked low moving into the Upper Midwest and Great
Lakes today and tonight. There is increasing confidence that a MCS
will move through the region this afternoon. CAMs are in pretty
good agreement on timing (afternoon into early evening). SPC has
the region outlooked in a marginal risk for severe which seems
appropriate since the better forcing and shear is to the north.
Although, CAPE will be decent around 1000 to 1500 J/Kg this
afternoon. Effective shear is fairly low around 20 knots. Damaging
winds will be the primary threat with the MCS this afternoon.

The line of thunderstorms will move through fairly quickly but
high rain rates are likely with precipitable water values near 2
inches. Some flooding issues will be possible but widespread
flooding is not expected since the area has been dry.

Heat indices around 100 degrees will be likely in the Southern
Tennessee Valley this afternoon before storms move into the
region due to increasing southerly flow and sunshine expected
through early afternoon in the southernmost counties.

This evening and overnight is more uncertain when it comes to rain
chances. NBM seems too high on POPs since CAMs have little to no
shower activity after sunset. Minor shortwaves moving through the
pattern could spark some showers and storms overnight but
confidence is low. Frontal passage will not occur during this
forecast period.

&&

.LONG TERM...
(Saturday through Thursday)
Issued at 237 AM EDT Fri Aug 16 2024

Key Messages:

1. Shower and thunderstorm chances continue through the weekend and
into Monday.

2. High pressure begins to build in next week, with northwest flow
expected leading to generally cool and dry weather.

Discussion:

Saturday night will see another chance for enhanced shower and
thunderstorm activity as a boundary dives out of the north/northwest
on the base of the slow moving low pressure system spinning through
the Great Lakes region towards the northeast US. This system will
bring additional heavy thunderstorms which could cause isolated
flooding of poor drainage, and urban areas as the PWAT values will
remain elevated. Outside of flooding, the main threat with these
storms still looks to be straight-line winds right as the
storms/line of storms moves through.

Shower and thunderstorm chances will continue into Sunday as the
wrap around moisture is able to continue to flow into our region.
PWAT values and QPF amounts should both be lower for the second half
of the weekend with less moisture in the atmosphere, hopefully
limiting the flooding threat. Chances for showers and thunderstorms
increase as you move further north (closer to to the low) with the
best chances to see the most widespread storms being north of
Interstate 40, and especially north of the Tennessee/Virginia state
line. As the low continues to take it`s time moving off to the
northeast we`ll eventually dry out on Monday as much drier and
cooler air from the northwest filters in as a ridge continues to
build in strength over the central/southwest US. This sustained flow
of cooler and drier air will keep temperatures generally in the 70`s
to 80`s and dew points in the 50`s. So most of the upcoming work
week should be fairly pleasant weather-wise, especially for the
month of August.

&&

.AVIATION...
(18Z TAFS)
Issued at 142 PM EDT Fri Aug 16 2024

Still expect numerous SHRA/TSRA to develop across east TN through
this evening. Previous timing was a little too quick so I bumped
it back to the 20z-21z timeframe. Should see a definitive break
in convective activity this evening and overnight. One caveat
could be KTRI where some ISOLD SHRA may redevelop before daybreak
as upper support draws near, but not confident enough to include
that right now. Lastly, several guidance sources show fog or low
clouds developing tonight north of the I-40 corridor. Think this
largely depends on mid/high clouds clearing out and whether
terminals see rain. Given at least some uncertainty there, will
leave that out of TAFs for now as well.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             94  73  94  71 /  60  50  60  60
Knoxville McGhee Tyson Airport, TN  91  71  90  70 /  70  50  40  70
Oak Ridge, TN                       89  71  89  69 /  70  50  40  70
Tri Cities Airport, TN              84  68  86  67 /  60  70  20  60

&&

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

$$

SHORT TERM...CD
AVIATION...CD