522
FXUS64 KMRX 050217
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
1017 PM EDT Thu Jul 4 2024

...New UPDATE...

.UPDATE...
Issued at 1015 PM EDT Thu Jul 4 2024

Forecast is on track this evening with a few isolated showers
possible overnight. Chances of rain begin to increase by the
morning hours as a cold front approaches the region. The primary
time period for highest precipitation probabilities will be the
mid- day through the afternoon hours. Most areas are forecast to
see a half-inch or less, but localized spots may see heavy downpours
with up to 2 to 3 inches of rain on Friday.

&&

.SHORT TERM...
(This evening through Friday)
Issued at 312 PM EDT Thu Jul 4 2024

Key Messages:

1. Low chance for a shower or thunderstorm into this evening,
mostly across northern portions of the forecast area.

2. Numerous to widespread showers and thunderstorms expected to
impact the area tomorrow ahead of a cold frontal passage.
Marginally severe storms are possible.

Discussion:

Showers have been very isolated this afternoon across parts of the
forecast area, mainly north of I-40. Lightning hasn`t yet been
observed and we are approaching the hottest part of the day so
only a short window of time remains for anything to develop. If a
storm does occur, there`s a chance it could be strong with heavy
downpours and gusty winds. Heat indices have been hovering in the
low 100s across parts of the area this afternoon. Expect the
advisory to expire at 8 PM EDT as we turn cooler into the evening
hours.

Tomorrow: a bit of moving parts with tomorrow. A trough will pivot
across the northern part of the country into tomorrow with a low
pressure center pretty much stacked below it. A cold front will
extend from this system bringing some relief to the area for the
weekend. With increased cloud cover ahead of this system as well
as a west to east draped boundary bringing precipitation ahead of
the front, temperatures tomorrow will not be as hot as today. A
few degrees lower, which makes a difference with how moist the
atmosphere is. Therefore, heat indices will be below the advisory
criteria. This could potentially change for tonight`s forecast
like it did last night for higher heat indices.

Numerous to widespread much needed rain and some thunderstorms
will increase in probability tomorrow into the afternoon and
evening. Only a marginal threat for severe weather expected as
indicated by the SPC this afternoon. Ingredients-wise, CAPE will
be in the neighborhood of the 1000-2000 range, more than enough
moisture, and although shear not all that strong vertically,
all could support organized cells and clusters of storms. The
very moist airmass which makes sense for such high PWs,
initiation of convection will not have an issue with the
destabilization that will occur with increased day-time heating.
With that being said, the main threats with any strong to possibly
severe storms tomorrow will be damaging winds and heavy rain
makers. We are also in that time of the year when parameters aloft
don`t support the typical spring time severe set-up.

&&

.LONG TERM...
(Friday night through next Thursday)
Issued at 312 PM EDT Thu Jul 4 2024

Key Messages:

1. Not quite as hot, but still slightly above normal through much of
the long term.

2. Mostly dry conditions expected this weekend in the wake of a
front Friday night into Saturday morning.

3. Rain chances increase notably early next week.

Discussion:

In general, the long term will feature a persistent troughing
pattern from the Great Lakes into the Ozarks, while upper ridging
remains situated from Florida up through the mid-Atlantic coast.
This will leave our forecast area beneath weak, but increasingly
south to southwesterly flow. Resulting lack of strong ridging will
mean we`ll see a break from the mid 90s heat of late, but upper 80s
to low 90s will still be on tap, especially in the south. Rain
chances will be mostly confined to thunderstorms in the mountains
through the weekend, but coverage of afternoon convection should
take a notable uptick as we move into the Mon-Wed timeframe.

Going into a bit more detail here, a front will be moving through
the region Friday night into Saturday morning. It`s not a
particularly strong front but models do show decreasing dewpoints on
Saturday along with northwesterly low level winds. Would think this
will favor a lack of convection during the daytime hours on
Saturday, especially by the afternoon hours. Did leave some rain
chances lingering in the mountains through late in the day but I`m
not exceptionally confident in that aspect of the forecast. Low
level convergent flow between the surface high to our north and
southeasterly surface to H85 flow east of the Appalachians will
likely result in some afternoon convection over the mountains again
on Sunday but would not be surprised of this rainfall stays mostly
on the NC side of things and thus expect dry conditions most places
to round out the weekend.

For the Monday through midweek timeframe, the aforementioned upper
trough to our northwest shifts slightly closer as a plains shortwave
moves through the base, and the remnants of Baryl are pulled
northeast out of Texas towards the Ozarks and lower Mississippi
river valley. Expect to see diurnally driven, widespread showers and
thunderstorms across the southern Appalachian region as a result.

&&

.AVIATION...
(00Z TAFS)
Issued at 743 PM EDT Thu Jul 4 2024

VFR conditions are forecast to continue tonight. Showers and
thunderstorms should remain out of the vicinity of local
terminals. Higher chances of showers and thunderstorms will arrive
on Friday with likely rain showers in the vicinity of terminals
and the chance of mid-day to afternoon thunderstorms.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             78  94  75  92 /  20  70  50  20
Knoxville McGhee Tyson Airport, TN  77  92  73  90 /  20  70  70  20
Oak Ridge, TN                       75  91  72  90 /  30  70  60  10
Tri Cities Airport, TN              72  91  72  88 /  10  70  70  30

&&

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

$$

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