Damaging Wind in Tennessee, December 28, 2024

Area Forecast Discussion
National Weather Service Huntsville AL
1128 PM CST Sat Dec 28 2024

...New AVIATION...

.NEAR TERM...
(Tonight)
Issued at 925 PM CST Sat Dec 28 2024

Regional radar data this evening indicates light-moderate rain
spreading eastward across the forecast area, within a
strengthening low-level warm/moist advection regime to the east of
a negatively-tilted shortwave trough and deepening surface
cyclone. Immediately to our southwest, a rapidly organizing QLCS
continues to surge northeastward along a sharpening prefrontal
surface trough, with initial impacts in the southwestern counties
of the CWFA anticipated around 4Z. Although weak cellular
convection has managed to evolve immediately in advance of the
approaching squall line, it is becoming increasingly apparent that
the QLCS will represent our highest risk for severe thunderstorms
as it shifts eastward through the region overnight.

Damaging winds up to 60-70 MPH will be the greatest threat, but
given the magnitude of the low-level jet (55-65 knots), sufficient
0-3km shear exists to warrant concern for development of low-
level mesocyclones and tornadoes (particularly with surges and
breaks in the QLCS). Tornado Watch 722 remains in effect for all
of northwest and a portion of north-central AL (to the west of
I-65) through 4 AM CST to address this threat. Latest near term
guidance from the CAMs still suggests that a slightly more stable
airmass will progressively reduce the risk for tornadoes as the
convective system tracks across the eastern portion of the
forecast area, but locally damaging winds will remain possible in
this region until the line exits around 10Z.

Regarding hydrological impacts from this event, there have been
no significant changes since the update earlier this afternoon,
with storm total QPF amounts of 1-2" (on average) expected to
result in minor rises on rivers and streams. Locally higher
rainfall amounts (driven by convective precipitation) may yield
higher totals in portions of the forecast area, with a low risk
for flooding/flash flooding (especially in urban locations).

&&

.SHORT TERM...
(Sunday through Tuesday)
Issued at 115 PM CST Sat Dec 28 2024

The severe weather threat will thus end early Sunday morning,
although wrap-around -RA/DZ and mild cold air advection will
occur Sunday morning into the afternoon, especially in northern
parts of the area.

Another shortwave and associated sfc low embedded withing the
polar westerlies will track quickly eastward to the north of our
area on Tuesday. Lift/moisture ahead of this system may be
sufficient to generate -RA/SHRA, but just low chance POPs (20-40%)
have been maintained for most of the area.

&&

.LONG TERM...
(Monday night through Friday)
Issued at 323 AM CST Sat Dec 28 2024

A shortwave trough will move through the region on Tuesday, resulting
in a low/medium chance (20-40%) for showers before daybreak. Low
chances (20-30%) for showers will linger across northeast AL and
southern middle TN during the day as a cold front pushes to our
southeast. Any rainfall from this system would be very light and
result in total amounts under 0.1". Southerly flow ahead of the
incoming cold front will keep one more day of above normal
temperatures, with highs in the mid to upper 50s Tuesday afternoon.
Behind this system will be a shift to northwest flow as high pressure
sinks south from the central Plains. Temperatures will be noticeably
cooler from Wednesday through the remainder of the extended period
with highs in the 40s and lows largely in the 20s. With high pressure
remaining dominant through the end of the work week, dry weather is
forecast through Friday night with even colder air arriving over the
weekend.

&&

.AVIATION...
(06Z TAFS)
Issued at 1128 PM CST Sat Dec 28 2024

QLCS line of tsra is approaching the I-65 corridor and will be
affecting the KHSV terminal over the next couple of hrs. IFR vis
with VRB winds gusting near 40kt are possible in/near any of these
tsra. This line has cleared KMSL with just some lingering shra
impacting NW AL. The line of tsra should begin to move east of the
area by the early morning hrs, with cigs near 1K ft and some -shra
also gradually exiting to the east. MVFR cigs closer to 2500ft
look to develop during the late morning period, before cigs begin
to diminish/sct this afternoon. South winds near 15-17kt with
higher gusts will turn to the SW and gradually weaken during the
early morning hrs, before turning west near 10kt this afternoon.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...None.
TN...None.
&&

NEAR TERM...70
SHORT TERM....KDW
LONG TERM....25
AVIATION...09