341
ACUS01 KWNS 211253
SWODY1
SPC AC 211252

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0752 AM CDT Fri Jun 21 2024

Valid 211300Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE NORTHERN
HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY AND OVER THE FOUR
CORNERS REGION...

...SUMMARY...
Scattered strong to severe storms are expected from parts of the
northern High Plains into the upper Mississippi Valley, mainly this
afternoon and evening. Scattered strong/severe thunderstorms are
also possible across the Four Corners vicinity. A few strong storms
may occur from parts of the lower Great Lakes to southern New
England.

...Northern High Plains...
A shortwave trough will shift eastward from the Canadian Rockies
toward Saskatchewan, with southeasterly low-level flow deep into
Montana ahead of this shortwave trough. Relatively strong (40 kt)
mid-level flow will develop across central Montana as the upper
ridge flattens. Scattered robust convection should easily develop
within a flow regime favorable for supercells. Forecast soundings,
especially for central Montana, exhibit favorable deep-layer shear
with strong buoyancy and relatively low cloud bases. Scattered
supercells should evolve by early afternoon then propagate
southeastward along the instability axis toward
eastern/south-central Montana through early evening. Very large hail
and gusty winds are expected along with some tornado risk.

...Middle Missouri Valley/Siouxland to Upper Mississippi Valley...
Scattered thunderstorms persist this morning regionally in vicinity
of the convectively modified frontal zone. A mid-level impulse over
Colorado/southeast Wyoming this morning will reach the Siouxland by
late afternoon and early evening, all while a south-southwesterly
low-level jet markedly intensifies after sunset. Strong diurnal
heating south of the boundary will ease CINH across the warm sector
and scattered storms are expected to develop and intensify. Updrafts
may initially develop along the cool side of the boundary but with
time surface-based storms are expected. Hail, wind, and perhaps a
couple tornadoes can be expected with supercells occurring near the
front.

...Four Corners Region...
A seasonally high PW plume will advance into the Four Corners region
as a low-latitude shortwave trough over southern California/Nevada
ejects over the Great Basin, strengthening mid-level flow across
southern Utah into southwestern Colorado. Sustained multicells and
some supercells should develop along the southern fringe of this
shortwave trough, where strong shear will support organized
longer-lived updrafts. Large hail and strong/gusty winds can be
expected, and some tornado risk may exist as well.

...Lower Great Lakes to southern New England...
Strong boundary-layer heating will once again occur across the lower
Great Lakes region into portions of southern New England, with a
southward-shifting front focusing scattered convection into
early/mid-afternoon. Within a moderately unstable environment,
localized wind damage will be the primary concern with the strongest
storms his afternoon through around sunset.

..Guyer/Mosier.. 06/21/2024

$$