752
FXUS64 KMRX 040549
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
149 AM EDT Thu Jul 4 2024

...New AVIATION...

.UPDATE...
Issued at 1020 PM EDT Wed Jul 3 2024

Forecast remains on track this evening. Convection across KY is
expected to remain away from our area as ridging and subsidence
continues to have strong influence over our weather.

&&

.SHORT TERM...
(This evening through Thursday)
Issued at 306 PM EDT Wed Jul 3 2024

Key Messages:

1. Hot and more humid conditions expected for 4th of July.

2. Isolated showers and thunderstorms possible during the
afternoon and evening tomorrow with better chances across the
plateau, VA mtns, and parts of the Appalachians.

Discussion:

Overnight lows tonight will remain on the mild side as high clouds
are forecast according to the NBM and CAMs such as HREF as well.

For tomorrow, expect temperatures and dew point values to be a few
degrees warmer, so heat indices will be a bit higher with low 100s
possible in parts of the middle and southern valley. Though it
will not suffice a Heat Advisory issuance.

Into tomorrow, the SE ridge and surface high pressure over the
same general area will become suppressed a bit leading to heights
lowering some. Chances of thunderstorm activity does return
tomorrow, but is on the low confidence side of things as far as
location and coverage. Not much in the way of lift or deep layer
shear to even initiate and sustain thunderstorms. Diurnal heating
may be the main trigger for any sort of development. However,
moisture will be a non-issue as well as instability, with CAPE
values exceeding 1000 J/kg along northwestern parts of the
forecast area. This aligns with SPC`s thinking of keeping the same
area under a marginal risk for severe storms.

The forecast initially went too heavy on dew points and PoPs. So a
lot was cut down or back. The entire forecast area will at least
have an isolated chance of a shower and/or thunderstorm, but have
limited the increased chance of scattered coverage across the
plateau region into SW VA and parts of the Appalachians. Any
activity will begin across the northwest part of the CWA around
mid morning hours and increase in probability with time into the
afternoon and evening. Any storm that becomes strong to marginally
severe, will only run the risk of lightning, heavy downpours, and
possible gusty winds.

&&

.LONG TERM...
(Thursday night through next Wednesday)
Issued at 306 PM EDT Wed Jul 3 2024

Key Messages:

1. Increasing chances for showers and storms Friday and Friday night
with a frontal passage, then dry weather returns during the weekend.

2. Chance PoPs return to the forecast in the
Monday/Tuesday/Wednesday time frame with an approaching upper
trough.

Discussion:

Friday will feature a low pressure system moving across the Upper MS
Valley to Great Lakes region, with a high pressure ridge off the
Atlantic coastline. Ample low level moisture will spread into the
area with the southerly flow from the Gulf of Mexico. The NAM shows
abundant MLCAPE Friday afternoon, in the range of 2000-3000 J/kg,
which suggests a potential for some strong to marginally severe
thunderstorms, although weak deep layer shear will be a limiting
factor in this potential. Most of this activity will be focused
along a pre-frontal trough that moves through late Friday
afternoon/early Friday evening time frame, with the cold frontal
passage occurring after midnight. A drier air mass will build into
the area on Saturday, with the deterministic models showing the
front well to our east by the afternoon. The NBM holds high chance
to likely PoPs in the area for Saturday, and this will be cut back
to align with a faster frontal passage.

A dry westerly to northwesterly low level flow will provide lower
dewpoints on Sunday. The cold front will be stalled to our south,
with a surface high over the OH Valley and central Appalachians. By
Monday the high will shift to the New England coastline, and a
southerly flow develops that spreads increasing moisture back into
the area and increasing temperatures. A broad trough in the
mid/upper levels will be over the Plains. The NBM PoPs of scattered
showers and thunderstorms appears reasonable for Monday through
Wednesday, and will not be changed.

&&

.AVIATION...
(06Z TAFS)
Issued at 142 AM EDT Thu Jul 4 2024

VFR should be predominant through the TAF period at all sites.
There is a chance for scattered showers during the afternoon and
early evening, though thunder is low probability. Included a
PROB30 at TRI where coverage may be enough to lend confidence to
terminal impact. Winds should remain light, southwesterly during
the day then weakening come nightfall.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             96  77  93  74 /  20  20  80  60
Knoxville McGhee Tyson Airport, TN  95  76  92  73 /  20  20  80  70
Oak Ridge, TN                       94  74  91  70 /  20  20  80  60
Tri Cities Airport, TN              91  71  91  71 /  30  20  70  70

&&

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

$$

SHORT TERM...KS
LONG TERM....DGS
AVIATION...Wellington