385
FXUS64 KHUN 121627
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
1027 AM CST Wed Feb 12 2025

...New NEAR TERM...

.NEAR TERM...
(Rest of Today and Tonight)
Issued at 1027 AM CST Wed Feb 12 2025

West-southwesterly flow of 60-70 knots in the mid-troposphere
will gradually strengthen over the course of the day, as a
positive- tilt longwave trough shifts slowly eastward across the
Rockies. Embedded within this flow, a subtle vort max (initially
located near the TX Gulf Coast) will eject northeastward along the
rim of a narrow subtropical ridge (centered north of the Greater
Antilles) and weaken considerably as it enters an increasingly
confluent flow regime aloft. At the surface, an area of low
pressure (related to the vort max) will lift northeastward across
the Lower MS Valley and into western portions of the TN Valley by
0Z, with widespread light-moderate rain expected to persist across
our region for much of the morning/early afternoon within a zone
of enhanced warm/moist advection immediately northeast of the low.
Although rainfall rates with this activity will not be
sufficiently high (in the absence of convection) for flash
flooding, the risk for areal and river/creek/tributary flooding
will remain elevated.

Latest model guidance suggests that stratiform precipitation
(currently ongoing across the region) will spread eastward with
time, likely exiting our region between 20-22Z. At this point, our
focus will shift to the potential for strong-severe
thunderstorms, with this risk largely dependent on the northward
progression of a warm/moist sector airmass that may only reach
central portions of MS-AL-GA by 0Z (as the northward progression
of this airmass will be retarded by the ongoing precipitation
regime). Our best guess at this point is that a narrow axis of
dewpoints in the u50s-l60s (representing the contaminated warm
sector) will reach as far north as the TN River (in our CWFA) from
late this afternoon through early Thursday morning, contributing
to 200-400 J/kg CAPE within an increasingly sheared environment
(highlighted by 80-90 knot WSW flow aloft and a 35-45 knot
southwesterly low-level jet). Present indications are that
clusters of moderate-heavy showers and a few thunderstorms will
evolve with time (both ahead of an approaching cold front and
immediately along the front), and we will need to monitor this
activity for locally damaging winds in the 50-60 MPH range and
perhaps a brief tornado or two. As the surface low begins to
accelerate north-northeastward into the eastern Great Lakes, the
cold front will enter northwest AL around 2-3Z and should exit our
southeastern counties by 8-9Z, ending the risk for severe
thunderstorms as strengthening NW winds advect a colder/drier and
more stable airmass into the region.

&&

.SHORT TERM...
(Thursday through Friday night)
Issued at 343 AM CST Wed Feb 12 2025

The short term will present a brief bout of benign weather. High
pressure will quickly usher in behind the cold front prompting
clear and dry conditions across the TN Valley both Thursday and
Friday. The clear conditions Thursday night will create an ideal
environment for radiational cooling allowing temps to drop into
the mid 20s by Friday morning. Fortunately temps will quickly
warm back up to the mid 50s on Friday providing one more day of
sun ahead of another active period of weather in the long term
forecast.

&&

.LONG TERM...
(Saturday through Tuesday)
Issued at 343 AM CST Wed Feb 12 2025

The main focus in the long term will be on Saturday, as a potent
storm system brings another round of heavy rain and the potential for
severe weather to the Tennessee Valley. A strong upper trough will
shift east through the Central Plains on Saturday, taking on a more
neutral to slightly negative tilt as it progresses east. This will
strengthen both upper and lower level wind fields and will aid in
advecting a moisture rich airmass north from the Gulf. Recent trends
over the past 24 hours have brought the sfc low more north, putting
us deeper into the warm sector and farther displacing us from the
axis of heaviest rain, now expected to be closer to the TN/KY state
line. A QLCS is expected along a cold front and will make its way
through the area overnight Saturday.

Digging into the severe threat first, strong upper level divergence
will strengthen synoptic lift Saturday afternoon and evening at a
time where temperatures are forecast to be in the upper 60s with
dewpoints in the upper 50s/lower 60s. Current model soundings seem to
be underdoing temps/dewpoints at the sfc, so there is still a
considerable amount of uncertainty regarding the thermodynamic
environment and whether or not there will be enough support for
discrete convection ahead of the main QLCS overnight. If this were
to occur, a late afternoon/evening round of supercells could precede
the QLCS and pose a higher risk for severe weather. Even if that does
not occur, wind fields are strong enough to support bowing segments
and embedded rotation within the main line/QLCS. Damaging winds will
be the primary concern at this point, with the tornado and hail
threat a bit more contingent in how much thermodynamic support is
available. Will need to monitor how models trend regarding
temps/lapse rates, as this looks to be the main limiting factor as of
now. The main window for severe weather will come between 6pm
Saturday and 6am Sunday.

With the continued trend to the north, the threat for widespread
flooding has gone down some. We do still want to stress that multiple
rounds of heavy rain earlier on the week have helped to saturate the
ground, and it will take less rainfall for runoff to begin than it
did earlier in the week. PWATs still look to be at the top end of
sounding climatology and will support very heavy rain rates within
the QLCS as it moves through Saturday night. High rain chances are
expected through most of the day on Saturday especially in northwest
AL and southern TN. The current forecast totals range from 3 inches
over far NW AL to near 2 inches over NE AL. Will point out that due
to very low confidence and relatively no signal from models, this
does not account for any discrete convection ahead of the main QLCS,
only light to moderate rain earlier in the day as the warm front
surges north. The heaviest rain will fall between 6pm Saturday and
6am Sunday with rain chances tapering off Sunday morning as the front
shifts to our east. We do expect additional rises on area rivers and
streams as well as ponding water in ditches and low lying areas as
the QLCS moves through. Will keep an eye on rainfall trends and will
communicate any increase in flooding risk as necessary.

Dry weather is forecast by Sunday afternoon, and temperatures will
quickly plummet overnight. With lows dropping to the lower 20s, any
water remaining on area roadways will freeze and result in hazardous
travel conditions due to black ice. Cooler temperatures will remain
through the beginning of the week, with another shot of potentially
heavy rain setting up by the mid-week period.

&&

.AVIATION...
(12Z TAFS)
Issued at 526 AM CST Wed Feb 12 2025

This will be another set of pessimistic TAFs. Very low IFR ceiling
will prevail through the TAF period. Unfortunately, despite IFR
ceiling prevailing, it is likely that both ceiling and
visibilities will bounce from IFR to VFR as periods of lighter and
heavier move through both terminals. Bouncing between flight
categories will be most possible during the middle of the day
during a brief lull in widespread heavy rain from 16-20Z.
Prevailing IFR conditions will pick back up before 0Z as a cold
front moves through the area. This will coincide with thunder
being possible as well as wind shear in addition to the low
ceilings and visibilities. Conditions should clear quickly after
12Z Thursday.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...

AL...Flood Watch through late tonight for ALZ008>010-016.

TN...None.

&&

$$

NEAR TERM...70/DD
SHORT TERM...RAD
LONG TERM...25
AVIATION...RAD