-- Discussion containing changed information from previous version are highlighted. --
833
FXUS64 KMRX 010256
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
1056 PM EDT Tue Apr 30 2024

...New UPDATE...

.UPDATE...
-- Changed Discussion --
Issued at 1045 PM EDT Tue Apr 30 2024

The wait now begins for lowering ceilings and visibility
overnight. The rainfall earlier and conditions changing to a high
pressure dominant regime, leads one to think there`s a good
possibility of fog and patchy dense fog. Currently, there are a
lot of locations at 100% RH and some are already experiencing
lowering visibility such as, Jonesville, Jacksboro, Dayton, and
Cleveland. Have not gone with an advisory or SPS with this update,
as confidence isn`t all there on how widespread 1/4SM will be.
Stay tuned overnight as the next forecast package will be issued
mid-morning.

As far as the forecast, tweaks were done to weather elements that
would ultimately affect the likelihood of fog overnight
(hourlies, wind, clouds, PoP, etc.). Other than that, no major
changes to note as the inherited forecast is on track.

KS
-- End Changed Discussion --

&&

.SHORT TERM...
(This evening through Wednesday)
Issued at 318 PM EDT Tue Apr 30 2024

Key Messages:

1. Scattered showers continuing into the late afternoon hours, then
dry overnight.

2. Dense fog possible tonight into Wednesday morning.

3. Very warm on Wednesday.

Discussion:

Radar imagery and surface obs show a weak, compact surface low over
the northern plateau this afternoon with an associated front
extending south into the southern TN valley. This will continue to
be a focus for additional shower development into the late afternoon
hours, mainly near or north of the I-40 corridor, as it shifts east
with time. Currently have some scattered showers over the northern
plateau associated with this feature, and expect further increase in
coverage eastward through roughly 21z before diurnal trends takeover
and precip dies off. Model soundings do show some instability
present this afternoon, but think any rumbles of thunder will be
very isolated.

For tonight, surface high pressure will build in after midnight.
Soundings show mid level drying accompanying this surface high
building in, allowing for clearing skies and very good radiational
conditions for fog development. Could easily see the need for a
dense fog advisory overnight. But I would say that there`s enough
variability in visibility fields of model guidance that I`m not
confident enough to hoist one up at the time. I feel quite confident
in saying that there will be some dense fog, it is more so a
question of onset and how widespread it will become.

Thursday looks dry, and very warm. Upper ridging will build in
quickly, with H85 temperatures warming into the mid teens and
significant drying of the air mass taking place as PWATs fall from
around 1.3" this afternoon to around 0.7" tomorrow. Expect to see
highs rise into the upper 80s as a result. I`d like to return these
temperatures to sender, but I don`t have that authority.

&&

.LONG TERM...
(Wednesday night through next Tuesday)
Issued at 318 PM EDT Tue Apr 30 2024

Key Messages:

1. Continued normal to above normal temperatures into next week,
with the warmest day currently looking to be Thursday.

2. Unsettled pattern with chances for showers and thunderstorms
expected Friday into early next week.

Discussion:

Via NAEFS Standardized Anomaly tables, upper level heights on a
range of +1 to 2 standard deviations will allow for above normal
temperatures by the latter half of the week. High temperatures
Thursday may fall just a few degrees shy of daily high maximums.
Subsidence associated with ridging aloft will also keep conditions
dry Thursday.

The ridge axis will be guided eastward as upper troughing moves into
the north-central CONUS, with a surface low in the Canadian province
of Ontario. An approaching surface boundary will lead to increasing
PoP chances Friday into the weekend. The distant nature from the
parent low will result in a rather slow moving boundary, thus, PoPs
will linger through the weekend. Mean ensemble guidance suggest a
range of 20-60% chance of CAPE greater than or equal to 500J/kg
during peak heating Friday and Saturday. For this reason, rumbles of
thunder will be possible at times as well. Given high PWAT value of
1.2-1.5 inches, will keep an eye on the potential of isolated
flooding with any training convection and low probability wording
will be utilized in the HWO.

Much more uncertainty comes into play by the end of the weekend and
into the new week as notable differences exist between operational
long-term models. Generally, a secondary area of low pressure is
expected to develop during this time frame, with low confidence on
the location and timing. While not currently expecting it to rain
the whole time, shower/tstorm chances will lingering through the
remainder of the long term period. Temperatures are expected to
remain near to above normal, though day-to-day fluctuations are
expected based on the coverage of rain and clouds.

&&

.AVIATION...
(00Z TAFS)
Issued at 733 PM EDT Tue Apr 30 2024

A small cluster of showers is south and east of TRI so have
included VCTS for the next hour since it did recently show some
lightning. What`s left of precipitation for the area is over NE TN
and SW VA. For the overnight period, still seeing the right
ingredients to come together for fog and low stratus development
over much of the forecast area; calm or no winds and SKC or high
thin clouds. Have not deviated too much from the 18Z TAF package.
Appears TYS and TRI may experience the lowest flight cats, while
CHA may stay within MVFR. Same thinking as previous aviation
discussion too as far as, fog and low stratus do look like a high
probability, but not too confident on what the worst conditions
will be.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             59  85  59  88 /   0   0   0   0
Knoxville McGhee Tyson Airport, TN  57  81  56  87 /  10   0   0   0
Oak Ridge, TN                       57  82  57  87 /  10   0   0   0
Tri Cities Airport, TN              55  79  53  85 /  40   0   0   0

&&

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

$$

SHORT TERM...CD
LONG TERM....KRS
AVIATION...KS