RSS Mesoscale Discussions from Storm Prediction Center

SPC Jun 21, 2024 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook
Day 1 Outlook Image
Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0752 AM CDT Fri Jun 21 2024

Valid 211300Z - 221200Z


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

...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

...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

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SPC Jun 21, 2024 Day 4-8 Severe Weather Outlook

Day 4-8 Outlook
Day 4-8 Outlook Image
Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0346 AM CDT Fri Jun 21 2024

Valid 241200Z - 291200Z

...D4/Monday: Northern Plains into the upper MS Valley/Great
A mid/upper-level shortwave trough and deepening surface low are
forecast to move across parts of SK/MB on Monday. A surface trough
will extend southward from the low into the northern Great Plains,
with secondary surface low development possible across the Dakotas.
A warm front will move northeastward somewhere from the eastern
Dakotas into the upper MS Valley. Strong buoyancy is forecast to
develop near and to the south/west of the warm front, with favorable
deep-layer shear providing a conditionally favorable environment for
severe thunderstorms. 

While some severe potential appears likely to evolve somewhere from
the northern Plains into the upper MS Valley and/or upper Great
Lakes, guidance varies regarding the position of the warm front, and
also the southern extent of height falls and large-scale ascent
attendant to the SK/MB shortwave trough. Much of the warm sector
will likely remain capped, but severe storm development will be
possible in closer proximity to the warm front and secondary surface
low, which could potentially grow upscale and move southeastward
along the instability gradient. Severe probabilities will likely be
needed once confidence increases regarding the placement of the
primary surface features. 

...D5/Tuesday: Upper Midwest into the central/southern Plains...
The shortwave trough that moves across parts of SK/MB on Monday is
generally forecast to move east-southeastward on Tuesday across
parts of ON and the upper Great Lakes. Model spread regarding the
timing and track of this shortwave continues to increase at this
time range, and the potential for MCS development on D4/Monday
further reduces predictability regarding the severe threat on
Tuesday. However, some severe-thunderstorm potential may evolve
along a southeastward moving cold front from the Great Lakes/upper
Midwest into parts of the central/southern Great Plains. 

...D6/Wednesday - D8/Friday...
Some threat for strong to severe thunderstorms could continue to
accompany a southeastward-moving cold front on D6/Wednesday from the
southern Plains into the Ohio Valley and Northeast, though
predictability remains low regarding the details at this time range.

By D7/Thursday into D8/Friday, extended-range guidance generally
suggests the potential for a mid/upper-level shortwave trough to
move across the northern Rockies toward the northern High Plains.
However, model spread remains rather high regarding the evolution of
moisture return and any increasing severe potential in association
with this system.

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