ACUS01 KWNS 131300
SWODY1
SPC AC 131258

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0658 AM CST Wed Nov 13 2024

Valid 131300Z - 141200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE LOWER MISSISSIPPI VALLEY AND COASTAL PACIFIC NORTHWEST...

...SUMMARY...
A few strong to severe thunderstorms may occur today across the
lower Mississippi Valley, posing a risk for isolated severe gusts
and perhaps a tornado or two. Occasional severe winds may also
develop along parts of the coastal Pacific Northwest.

...Lower Mississippi Valley...
Rich low-level moisture will continue to stream northward today
across parts of the lower MS Valley into the Mid-South as an upper
trough over the Plains continues eastward towards the OH Valley.
Primary surface low and better forcing associated with this upper
trough are forecast to remain well north of the inland-advancing
warm sector. Even so, scattered surface-based thunderstorms should
develop by this afternoon as a remnant/weak surface low off the LA
Coast moves slowly inland. Filtered daytime heating of the moist
low-level airmass should result in modest instability developing by
this afternoon, even though mid-level lapse rates will remain poor
(see 12Z JAN/LIX soundings). Low-level southerly flow will not be
overly strong across the lower MS Valley, but gradual veering and
strengthening of winds with height through mid levels should support
sufficient deep-layer shear for modest updraft organization.

A few marginal supercells/clusters may pose an isolated threat for
strong to damaging winds as they spread eastward across LA/MS this
afternoon and evening. Enough low-level shear should also be present
to foster some updraft rotation and the threat for a tornado or two,
with an isolated severe threat potentially continuing into tonight
across parts of southwest AL and vicinity. The warm sector will
become increasingly pinched off with northward extent in MS and
western TN, with convection generally expected to outpace the
low-level moisture return. Given the expected mismatch of stronger
forcing/shear farther north and better instability to the south,
have opted to maintain the Marginal Risk this update, with some
expansion based on latest guidance trends.

...Coastal Pacific Northwest...
Cold mid-level temperatures (around -24 to -26C at 500 mb) and
modestly steepened mid-level lapse rates associated with an
eastward-moving upper trough will help support weak instability
today across parts of the coastal Pacific Northwest (reference 12Z
UIL sounding). Persistent large-scale ascent across this region will
support both low-topped cells and bands of convection moving
eastward through this afternoon and early evening. Given the
forecast strength of the low-level winds, some of this activity may
occasionally produce strong to severe wind gusts, and perhaps small
hail. Tornado potential remains unclear, as low-level flow will have
a tendency to veer more to southwesterly through the day, which
should limit 0-1 km SRH.

..Gleason/Bentley.. 11/13/2024

$$
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