Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN

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FXUS64 KMRX 240229

Area Forecast Discussion
National Weather Service Morristown TN
1029 PM EDT Tue Jul 23 2024

...New UPDATE...

Issued at 1020 PM EDT Tue Jul 23 2024

PoPs for the last few hours have not been verifying, so will
considerably cut them down overnight for the nearest term of the
forecast. The stronger, more heavier activity has stayed well
south and east of the CWA along the front. However, some lighter
to moderate showers are edging our way from the west, so will keep
that in mind with the updated forecast.



(This evening through Wednesday)
Issued at 248 PM EDT Tue Jul 23 2024

Key Messages:

1. Repeated rounds of showers and thunderstorms may present a
flash flooding threat at times in the short term period.


Moist southwesterly flow will continue through the period,
yielding solid chances for shower and thunderstorm development
during mainly the afternoon hours. However, models continue to
indicate nocturnal, elevated instability so overnight convection
will be possible as well. Confidence in coverage is not great at
times, but in general I believe carrying higher PoPs is warranted.

Guidance brings PWATs up from around 1.5" earlier today, to nearly
2" this afternoon through much of the overnight hours. Cloud cover
has led to questionable surface based instability at times, which
has in turn not been beneficial to widespread convection north of
I-40. But the persistent southwesterly low level flow has some
inherent isentropic ascent built into it which, couple with
continued daytime heating, should allow for convection to fill in
somewhat across the north. We`ll lose coverage this evening as we
lose heating, but again models indicate that overnight rain
chances will remain as aforementioned isentropic ascent lifts
parcels to the LFC. Tend to think that the northern areas will be
favored tonight as that`s where the best jet support and peak low
level ascent will be focused.

As far as weather concerns go, while much of the area remains in
drought conditions, several areas have had repeated rounds of
rainfall the last few days. As such, the southwesterly flow will
promote at least some potential for training convection through
the period, and some isolated flash flooding will be a risk. The
southern valley has the highest relative risk due to a few rounds
of convection today and some flooding issues night before last.


(Wednesday night through next Tuesday)
Issued at 248 PM EDT Tue Jul 23 2024

Key Messages:

1. Seasonally cool temperatures to begin the period returning closer
to near normal temperatures for the weekend onward.

2. Unsettled pattern continues through the long term, with greatest
chances for showers and storms generally in the afternoon and
evening hours. Repeated rounds of rainfall could lead to isolated
flooding concerns.


Upper level troughing will continue to influence weather across
eastern portions of the CONUS as a disturbance translating through
mean flow aloft will promote a frontal passage through the local
forecast area Thursday into early Friday. Frontal forcing and
influence from the right entrance region of an upper level jet will
lead to numerous to widespread showers and storms. Model derived
soundings suggest PWAT near 1.8 inches ahead of the front. Combined
with numerous days of precip in advance of this system, flooding
will remain the main threat, especially for those who see repeated
rounds of locally enhanced convection. Locally gusty winds and
frequent lightning may also occur with stronger storms but the
overall threat for severe weather is quite low.

We see a slight downward trend in moisture into the weekend. PWAT
generally falls to around 1.4-1.6", as minor upper level height
increases bring a warming trend closer to seasonally normal
temperatures. Moisture will remain plentiful enough that daily
chances of showers and storms are possible through the weekend,
however, they are expected to follow a diurnal trend with the
greatest PoP chances favoring high elevation locations. Continued
isolated flooding will remain possible owing to poor antecedent

Models agree in a cut-off low developing just off the northeastern
seaboard Monday into early next week, although more disagreement
comes into play regarding a potential shortwave/closed low ejecting
from the southern CONUS depending on what model you choose to look
at. Overall, continued unsettled weather is expected but lower
confidence regarding coverage exists this far out. Given what seems
like endless yet welcomed rain opportunities, flooding potential
will need to be monitored through the extended forecast.


(00Z TAFS)
Issued at 736 PM EDT Tue Jul 23 2024

Difficult and low confidence aviation forecast this TAF package,
especially before 12Z. The strongest of the activity is currently
over the Carolina`s and Georgia. Showery conditions across our
area have diminished over the past couple of hours. Still expect a
chance of some lingering precipitation with a low chance of
thunder, so have left that out of the overnight hours. Low
confidence forecast comes in with CIGS with regard to timing and
height. Would at least expect MVFR CIGS overnight with possible
dips to IFR. The best chance for this occurrence looks to be at
CHA and TRI. VSBY should remain contained to MVFR should any
terminal fall under it tonight.

SWly flow continues into the day Wednesday, with increasing
chances of thunderstorms towards the afternoon hours, so a PROB30
was introduced.


Chattanooga Airport, TN             71  82  72  83 /  60  70  70  90
Knoxville McGhee Tyson Airport, TN  70  81  70  80 /  70  70  80  90
Oak Ridge, TN                       70  80  68  80 /  70  80  70  90
Tri Cities Airport, TN              68  80  67  79 /  70  70  80  80