Flash Flood Warning 4, NWS Huntsville, AL

Area Forecast Discussion
National Weather Service Huntsville AL
532 PM CST Thu Feb 16 2023

...New AVIATION...

.NEAR TERM...
(Remainder of today and tonight)
Issued at 242 PM CST Thu Feb 16 2023

There have been no significant changes to forecast reasoning for
the remainder of the afternoon since the earlier morning update,
with the risk for severe thunderstorms expected to increase from
W-to-E over the next 1-3 hours. Although open warm sector
supercells currently tracking from southeastern MS into central AL
may ultimately reduce the risk for development of discrete
cellular convection prior to the arrival of a cold front in our
region, we still anticipate a broken QLCS featuring organized
multicell clusters and embedded supercells (capable of all severe
hazards) to accompany the front as it shifts eastward into the
local area later this afternoon.

Latest model guidance continues to indicate that the
aforementioned cold front will begin to decelerate considerably as
it crosses the I-65 corridor around 00Z, with the boundary not
expected to exit the southeastern portion of our CWFA until
perhaps as late as 4-5Z this evening. Although this may warrant a
local extension of Tornado Watch 39 to include our three northeast
AL counties, widespread convective overturning and loss of
diurnal destabilization should reduce the overall risk for severe
convection in these zones. What will become more of a concern in
this region (as well as the remainder of the CWFA) is flooding. At
this point, the risk for flash flooding appears highest across
northeast AL, where echo training of moderate-heavy convective
cores may occur for several hours this evening until the cold
front finally clears the region. However, as deep-layer ascent
begins to strengthen downstream from a positively-tilted mid-level
trough crossing the Mid-MS Valley, widespread light-moderate
postfrontal rain will occur for several hours in the wake of the
wind shift, with areal flooding possible elsewhere. In spite of
strengthening cold advection in the wake of the front, low stratus
clouds will limit cooling, with lows predicted to be in the m-u
30s.

&&

.SHORT TERM...
(Friday through Saturday night)
Issued at 242 PM CST Thu Feb 16 2023

Strong synoptic scale forcing for ascent will continue throughout
much of the day tomorrow, until the axis of the positively-tilted
mid-level trough (discussed above) begins to cross the region
during the late afternoon/early evening hours. Thus, we expect a
regime featuring low stratus clouds and isolated light showers or
sprinkles, which could be mixed with a few snow flurries at times.
Given the combination of strong cold advection and low clouds,
highs will struggle to reach the u30s-l40s.

Mid-level flow will quickly transition to a zonal orientation
late Friday night, to the north of a flat subtropical ridge
centered across the southeastern Gulf of Mexico. Thus, we expect
skies to clear rapidly and support optimal radiational cooling
conditions early Saturday morning as a surface ridge builds
northeastward into the TN Valley. A hard freeze will occur this
period, with lows in the l-m 20s. Highs will rebound into the l-m
50s on Saturday, as the low-level ridge translates eastward,
inducing light south-southeasterly return flow. Mid/high-level
cloudiness will begin to increase late in the day as a weak
disturbance ejects northeastward from the southern Plains into the
OH Valley by 12Z Sunday, and this will lead to milder temps in
the m-u 30s Sunday morning.

&&

.LONG TERM...
(Sunday through Thursday)
Issued at 242 PM CST Thu Feb 16 2023

Extended range models still indicate that a pronounced northern
stream trough will shift eastward from northern Plains on Sunday
into the New England vicinity on Monday. A weak cold front related
to this trough is expected to drift southward into the region at
some point on Monday, but low-level moisture return should be
inadequate to support any meaningful chance for precipitation. By
late Monday night, we expect to see a partially modified maritime
airmass return northward across the TN Valley in response to
surface cyclogenesis in the lee of the southern Rockies. Isolated
to widely scattered showers and perhaps a few thunderstorms will
be possible at times from Monday night-Wednesday, but coverage and
intensity will be dictated by the precise location of a slow-
moving warm front. It appears as if a stronger mid-level trough
and accompanying surface low may bring a more widespread coverage
of showers and a few storms to the region Wednesday evening, but
due to uncertainty in the timing and track of this system, we have
kept POPs in the chance range. One thing that appears more
certain is that temperatures throughout the extended portion of
the forecast will be influenced by strengthening and amplification
of the subtropical ridge to our southeast, with highs in the l-m
70s Tuesday-Thursday and lows in the u50s-l60s.

&&

.AVIATION...
(00Z TAFS)
Issued at 532 PM CST Thu Feb 16 2023

Heavy rain and embedded storms will continue to move across the
area this evening, and the primary concerns for TAFs will be
reduced vsbys/cigs due to storms and lightning. Gusty winds up to
25kts will be possible, and winds will shift from southerly to
northwesterly as a cold front moves through this evening. Showers
and storms should come to an end by sunrise, but MVFR cigs may
linger through Friday afternoon.

&&

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

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

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