SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0755 AM CDT Thu Jul 07 2022
Valid 071300Z - 081200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS MAINLY ACROSS
PARTS OF MONTANA...AND FROM THE LOWER MISSOURI VALLEY INTO THE
CAROLINAS...
...SUMMARY...
Scattered thunderstorms, some severe, will be possible today mainly
across parts of Montana, and from the lower Missouri Valley into the
Carolinas. Damaging winds are possible over all areas, with large
hail also expected over Montana.
...Synopsis...
The large-scale pattern in mid/upper levels will continue to feature
troughing off the West Coast, mean ridging across the south-central
CONUS and Rockies, and west-northwest to northwest flow across much
of the Upper Midwest, Great Lakes and Appalachians. The Rockies
ridging is expected to amplify through the period, leading to a net
westward displacement of the main/anchoring 500-mb high across the
southern Plains and toward NM. An embedded shortwave trough -- now
evident in moisture-channel imagery over eastern portions of CO/WY
and central NM -- should pivot eastward over the central Plains,
closely following a smaller, MCV-reinforced shortwave trough now
over north-central/west-central KS. Downstream, a series of mostly
low-amplitude/mesoscale perturbations will cross the Ohio Valley and
Southeast.
At the surface 11Z analysis showed a wavy/quasistationary front from
a low over the Delmarva Peninsula, across west-central VA, WV,
southern IN, and northern MO, with a diffuse segment northwestward
to a low over central SD. A cold front was drawn from a low over
west-central KS across the TX Panhandle and northeastern NM. The
main foci for convection this period should be boundaries south of
the front over the eastern outlook area, and north of the front
across the northern Rockies/northern High Plains regions.
...MT and vicinity...
Isolated to scattered thunderstorms are expected to develop this
afternoon -- mainly over higher terrain of southern/western MT --
and move northeastward while offering the potential for sporadic
severe gusts and large hail. Any supercells that survive into the
more-suitable moisture profiles of central/northern MT will be
capable of significant hail, and depending on storm-scale processes
and boundary interactions, a marginal/conditional tornado threat.
Large-scale support will be more nebulous today compared to previous
days, with net height rises forecast across the region. Convection
will be focused largely by heating of elevated terrain,
preferentially weakening MLCINH sooner compared to lower elevations
in the northern/eastern areas, and secondarily along boundaries left
from prior activity. A drier and more deeply mixed boundary layer
is expected with southwestward extent (and increasing elevation)
across MT, away from a low-level moist/theta-e axis extending from
central SD to north-central/northeastern MT. This should contribute
to MLCAPE ranging from around 2000-2500 J/kg near that axis to 1000
J/kg over southern/western MT near the main, orographically aided
convective initiation zones. Forecast soundings also suggest strong
veering of winds with height, though modest low-level wind speeds
will keep hodographs and SRH marginal in magnitude. Some of the
diurnal activity may aggregate upscale into an evening cluster
across eastern MT into the western Dakotas, nearer to the moist
axis, with severe gusts being the main concern until convection
encounters progressively more-stable boundary layer and stronger
MLCINH tonight in the Dakotas.
...KY/TN to Carolinas...
Again today, a large swath of the area from the Ohio Valley to
Southeast will have thunderstorm potential, with the greatest
concentration likely in and near the "slight"/15%-wind outlook area.
Multicell clusters and pulse storms will be common and locally
numerous, offering the threat of damaging gusts, with a few
severe/50+ kt gusts possible.
Development should be focused mainly along higher terrain, a surface
trough east of the mountains, and especially any number of outflow
boundaries south of the synoptic front -- both from prior convection
and generated throughout today's event. Strong surface heating in a
richly moist air mass (dewpoints commonly in the upper 60s to mid
70s F), along with a deep troposphere, will offset modest midlevel
lapse rates enough to yield MLCAPE in the 1500-2500 J/kg (locally
higher) over much of the outlook area. Deep-tropospheric flow and
vertical shear each will be weak, but oriented such that
southeastward-propagating clusters will be favored. Potential
should wane after dark as the boundary layer stabilizes from a
combination of outflows and nocturnal/diabatic cooling.
...Central Plains to mid Mississippi Valley...
Scattered thunderstorms are possible today over parts of IL as an
eastward extension of ongoing activity in northeastern MO, as well
as near a diurnally heated/modified version of the trailing outflow
boundary across parts of northern MO to eastern KS. Damaging gusts
and isolated large hail will be the main concerns, and at least a
marginal tornado threat may develop with any supercell that can take
advantage of favorable low-level vorticity/SRH along the boundary.
In addition to the northern KS MCV, others are evident in
west-central to central NE and over northeastern KS/southeastern NE.
Mesoscale enhancements to both large-scale lift aloft, and vertical
shear, are possible east and south of these features as they move
eastward today, while the outflow boundary moves/diffuses somewhat
northward. Relatively undisturbed, richly moist boundary-layer air
over the mid Mississippi Valley, central/southern MO and eastern KS
will be available as inflow to convection developing today, and over
IL for convection moving in from MO. By midafternoon, 2500-3500
J/kg MLCAPE and negligible CINH are expected. Weak mid/upper flow
over most areas suggests modes could become clustered and messy, but
favorable low-level shear may persist along or north of the outflow
boundary for support of at least transient supercellular
characteristics. Overall coverage/intensity should diminish from
late evening into tonight.
..Edwards/Goss.. 07/07/2022
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