907
ACUS02 KWNS 161732
SWODY2
SPC AC 161730

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1230 PM CDT Mon Sep 16 2024

Valid 171200Z - 181200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL
HIGH PLAINS INTO NORTHEAST MONTANA...

...SUMMARY...
Isolated to scattered severe gusts and hail are possible Tuesday
across a large swath of the High Plains region, mainly from late
afternoon into the evening. The greater concentrations of severe
storms may occur over the central High Plains into northeast
Montana.

...Synopsis...

A mid/upper cyclone is forecast over the Great Basin Tuesday
morning. This system will pivot northeast across the central Rockies
and into the northern High Plains through the forecast period. This
will bring a belt of strong south/southwesterly deep-layer flow
across CO/WY and adjacent portions of the High Plains. A surface low
will deepen over MT through the period, with a surface trough
extending southward through the central/southern High Plains. A warm
front is forecast to extend west to east from southeast MT into
north-central SD during the morning. With time, this boundary will
lift northward toward the International border during the nighttime
hours. As the system deepens and the low-level baroclinic zone over
the Plains strengthens, 850-700 mb flow is forecast to markedly
increase during the afternoon/evening to 30-50 kt. While deeper
boundary-layer moisture is forecast to remain east of the surface
trough axis and north of the warm front, steep midlevel lapse rates
will support pockets of weak to moderate instability. An arc of
thunderstorm activity, with a mix of line segments and discrete
cells, are expected to develop in the vicinity of the surface
low/warm front south/southeast along the surface trough during the
afternoon and evening hours.

...Eastern MT...

Strong ascent will overspread the region as the upper trough pivots
northeast during the late afternoon/evening. Boundary-layer moisture
will be greatest to the north of the warm front across
north-central/northeast MT, but capping will likely remain in place.
Storm motion will likely result in convection remaining elevated to
the cool side of the warm front. Nevertheless, steep midlevel lapse
rates and favorable vertical shear (elongated/straight hodographs)
will support some risk for large hail. As stronger forcing and
sufficient erosion of capping can overlap during the evening, strong
to severe wind gusts also will be possible.

...Northern/Central High Plains Vicinity...

Convection is expected to develop over the higher terrain of CO/WY
during the afternoon. Given strengthening mid/upper flow and weak
instability, some locally strong gusts could occur with this initial
activity near the core of the upper low over western/central CO. As
convection shifts east/northeast through the afternoon and into the
evening, strong heating is expected to result in a steep low-level
lapse rate environment across the High Plains. While deep
boundary-layer moisture will remain further east across the Plains,
steep midlevel lapse rates and surface dewpoints in the 50s F will
result in a corridor of around 1000-1500 J/kg MLCAPE from far
eastern CO into parts of western NE/SD. Strengthening midlevel flow
atop a deeply mixed boundary-layer will likely support severe gusts
(isolated gusts to 75 mph possible) with linear segments spreading
northeast across the central High Plains during the late
afternoon/evening.

...Southern High Plains Vicinity...

Further south, large-scale ascent will be weaker, with stronger
height falls focused north of the region. Nevertheless, low-level
convergence along the surface trough and modest instability (up to
1000 J/kg MLCAPE) will support initial thunderstorm development over
the higher terrain of south-central CO into north-central NM.
Forecast soundings show supercell wind profiles across the adjacent
High Plains by afternoon. Midlevel lapse rates will be somewhat
modest (around 6.5-7 C/km), but elongated/straight hodographs and
plenty of instability through the 700-300 mb layer suggest isolated
hail is possible. Steep low-level lapse rates also will support
isolated strong to severe gusts.

..Leitman.. 09/16/2024

$$