490
ACUS01 KWNS 151958
SWODY1
SPC AC 151956

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0256 PM CDT Sat Jun 15 2024

Valid 152000Z - 161200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHERN PLAINS...AND THE MID MISSOURI VALLEY...

...SUMMARY...
Scattered severe thunderstorms with damaging winds and large hail
are possible from the late afternoon into the evening across the
Mid-Missouri Valley, and also from eastern Montana to the
western/central Dakotas. A few tornadoes could occur in eastern
Nebraska and western Iowa, with isolated significant severe hail and
wind possible across parts of the northern Plains.

...20Z Update...

...Northern High Plains/Northern Plains...
Overall forecast remains on track. One minor change for this update
was to bring 5% wind probabilities back farther west across central
MT where thunderstorms have recently developed. As mentioned in MCD
#1269, a few locally strong gusts may occur as storms continue to
develop across central Montana. Otherwise, the forecast reasoning
outlined in the previous outlook for this region remains valid.

...Central High Plains...
Another minor expansion was made to include more of far northeast CO
in 5% wind probabilities. As mentioned in MCD #1268, high-based
storm development will continue over the higher terrain, before
spreading eastward with time. High-based storm character could
promote evaporative cooling in the sub-cloud layer, and a few
enhanced gusts capable of producing wind damage will be locally
possible across the area into this evening.

...Elsewhere...
Thunderstorm development is still anticipated later this afternoon
and evening across the Mid MO Valley, where environmental conditions
will support strong to severe storms capable of large hail and
damaging gusts. A tornado or two is also possible across eastern NE
and western IA, where 30 to 35 kt low/mid-level flow is lengthening
hodographs. Isolated severe storms are still possible along the lee
troughing across the southern High Plains. High cloud bases and a
deeply boundary layer will promote the potential for damaging gusts.

..Mosier.. 06/15/2024

.PREV DISCUSSION... /ISSUED 1130 AM CDT Sat Jun 15 2024/

...Northern Plains...
A pronounced upper trough/low will progress eastward across the
northern Rockies/High Plains and western Canada through the period.
A related mid-level jet will begin to overspread the northern High
Plains later this afternoon. This feature will contribute to
strengthening flow aloft and increasing deep-layer shear to support
organized severe thunderstorms. At the surface, a low should
consolidate by early evening over eastern MT and the western
Dakotas, with a cold front forecast to sweep eastward over the
northern Plains this evening and overnight. Near and east of the
surface low, around 1500-2500 J/kg of MLCAPE should develop through
peak heating across parts of the western/central Dakotas, as a
modestly moist low-level airmass continues to advect northward.

Current expectations are for high-based thunderstorms to initially
develop early this afternoon across parts of central MT as
large-scale ascent preceding the upper trough overspreads this
region. A well-mixed boundary layer combined with sufficient
instability should encourage severe downdraft winds with any cluster
that can form/persist with eastward extent. Isolated significant
severe winds up to around 75 mph appear possible. The Slight Risk
has been expanded westward some into more of central MT to account
for this scenario.

A somewhat separate area of convection may develop across the
Bighorns of northern WY, and subsequently spread eastward across
western/central SD through this evening with a threat for mainly
severe/damaging winds. Any sustained supercells that can develop
should pose a threat for large to very large hail given the
favorable thermodynamic and kinematic environment present. This
appears most probable across parts of western ND this evening,
although there is still some uncertainty regarding what the dominant
convective mode will be. A tornado or two may also occur across
western ND and vicinity with any supercell that persists this
evening as 0-1 km SRH gradually increases in tandem with a
strengthening low-level jet.

...Mid Missouri Valley/Central Plains...
Morning visible satellite and radar imagery show multiple MCVs
across the central Plains and Mid MO Valley associated with prior
convection. A shortwave trough will move eastward across these
regions through the day, with modestly enhanced mid-level winds
overspreading parts of NE/IA and vicinity. At the surface, a warm
front will attempt to lift slowly northward over this region as
well, but outflow from ongoing elevated convection in northern MO
may slow its progress to some extent. This outflow boundary may also
severe as an effective warm front and thunderstorm initiation zone
this afternoon. Regardless, a gradually destabilizing airmass is
anticipated across eastern NE through mid/late afternoon as filtered
daytime heating occurs.

Most guidance continues to suggest that around 2000-3000 J/kg of
MLCAPE will develop in a narrow corridor along/near the warm front
by 20-21Z, with steep mid-level lapse rates aiding in this
development. Although deep-layer shear does not appear overly
strong, it should be sufficient for a few supercells to develop
initially. In addition to a threat for large hail with these
supercells, a few tornadoes may also occur given the presence of a
30-35 kt southerly low-level jet and enhanced low-level SRH in the
vicinity of the warm front. Some upscale growth could occur this
evening, with a potentially greater severe/damaging wind threat with
any small cluster that can persist into IA and perhaps southern MN.

...Southern High Plains...
Isolated to scattered thunderstorms are forecast to develop
this afternoon through early evening along/east of a weak surface
trough/dryline across parts of the southern High Plains, including
the OK/TX Panhandles southward to west TX. Weak to moderate
instability and modest deep-layer shear should support some
convective organization. Isolated severe wind gusts will be possible
with a generally hot and well-mixed boundary layer, along with some
potential for hail with the more robust cores.

$$