-- Discussion containing changed information from previous version are highlighted. --
121
FXUS64 KMRX 211509
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
1109 AM EDT Fri Jun 21 2024

...New UPDATE...

.UPDATE...
-- Changed Discussion --
Issued at 1100 AM EDT Fri Jun 21 2024

Another day of mostly sunny to partly cloudy skies with warm to
hot temperatures across the eastern TN Valley and Southern
Appalachians. At late morning temperatures were in the upper 70s
to lower 80s. The dominant upper ridge was now centered over the
Ohio and Tennessee Valleys. Some weakening or eroding of the ridge
will begin this afternoon but not soon enough to break the cap and
have enough cloud development for any showers to form. A brief
shower may form over southwest Virginia or extreme northeast TN
mountains and possibly southwest North Carolina late in the afternoon
on the edge of the ridge but did not add to the forecast. Current
forecast looks good with highs in the lower to mid 90s and partly
cloudy to mostly sunny skies. No update to current forecast
planned.
-- End Changed Discussion --

&&

.SHORT TERM...
(Today and tonight)
Issued at 305 AM EDT Fri Jun 21 2024

Key Messages:

1. More afternoon clouds around today, but dry conditions should
prevail.

2. Temperatures (highs and lows) will continue to run 4-7 degrees
above normal.

Discussion:

Ridging aloft will remain centered over middle/eastern Tennessee
today, however it will begin to weaken after midday with the most
notable height falls in our CWA being over VA, more towards the
periphery of the upper ridge. Forecast soundings across the region
suggest the atmosphere should remain capped today so I did limit
PoPs to 14 percent to keep mention of showers out of the forecast.
Models do show a saturated layer along with some weak instability
present below the capping inversion this afternoon, so I suspect
there will be a fair amount of shallow CU around by the mid/late
afternoon hours. Some models do develop some showers over the higher
terrain this afternoon, but the 00z runs of those models initialized
very poorly, showing ongoing convection over the higher terrain
earlier tonight. I can`t rule out a shower in our far northern
counties where height falls will be greatest, but will disregard the
showery solutions and instead opt for a dry forecast.

Otherwise, continued warmth is the primary talking point. We`ll
continue to see afternoon temperatures running in the range of 4-7
degree above normal. Not record breaking, but certainly warm. Same
goes for overnight lows.

&&

.LONG TERM...
(Saturday through Thursday)
Issued at 305 AM EDT Fri Jun 21 2024

Key Messages:

1. The heat continues.

2. Chances of showers and storms increase around Sunday evening and
into Monday and again Wednesday/Thursday.

Discussion: At the beginning of this period on Saturday morning,
the upper ridge is already starting to flatten out, while at the
surface the very warm airmass continues across the region.  By
Sunday afternoon the upper ridge will have retrograded well to the
west, to Texas and farther west, leaving us in a more active upper
northwest flow and chances for showers and storms.

By Monday a very weak cold front moves through but only supported by
a surface high pressure center of about 1011 mb, a few miles up the
road, but leaving Tuesday drier.  Drier dewpoints will be in place
on Tuesday as well, but the drier air will warm up more efficiently,
so Max Temps on Tuesday may be a little higher.

Then the next better chances of showers and storms comes in for
Wednesday and/or Thursday, ahead of another weak cold front.

Through all this active pattern at the surface only a little above
the surface at 850 mb, the temperature hardly budges, keeping about
19-21 degrees C during this whole time.  So any expectations of
refreshingly significant airmass change will have to wait.  As a
matter fact, a little beyond this forecast period, into the next
weekend models/ensembles show the upper ridge building back into the
area--the heat goes on.

For heat specifics for this forecast period, we lower the dewpoints
slightly as the models are continuing with a moist bias with them,
but we are still getting Heat Index values Saturday through
Wednesday in the mid to upper 90s from Knoxville southward. Thursday
is showing a little relief, if the cold front can make it through.

For thunderstorm threats, neither higher chances of storms (in the
Sunday night into Monday event nor the Wednesday/Thursday event)
offer much in the way of organized storms.  There may be some
briefly stronger storms, but little beyond that.

&&

.AVIATION...
(12Z TAFS)
Issued at 728 AM EDT Fri Jun 21 2024

VFR conditions will prevail through the period, along with light
winds. Expect to see more prominent afternoon CU field today, but
SHRA/TSRA are not expected to develop so will keep all terminals
dry. Do see some patchy fog across the region this morning on
satellite imagery, and that likely occurs again tonight. However
it shouldn`t affect any terminals.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             94  73  95  74 /   0   0   0   0
Knoxville McGhee Tyson Airport, TN  92  72  93  73 /  10  10  10   0
Oak Ridge, TN                       93  72  93  72 /  10   0  10   0
Tri Cities Airport, TN              91  67  91  70 /  10  10  10   0

&&

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

$$

SHORT TERM...TD
LONG TERM....GM
AVIATION...CD