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Archives for the SPC Convective Outlook are updated daily (approximately) with a live map at the beginning of each article. Follow the link at the end of the article to check for current updates on the NOAA/NWS Storm Prediction Center website. Also, see Archives for Chicago's hourly weather data on CARDINAL NEWS Magazine.


Thursday, July 11, 2024

SPC Jul 11, 2024 1300 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0755 AM CDT Thu Jul 11 2024

Valid 111300Z - 121200Z


Severe thunderstorm gusts are possible over parts of southern
Arizona from midafternoon into early evening.

In mid/upper levels, the overall pattern will change little through
the period, with mean ridging in the West, and troughing over the
Great Lakes and vicinity. The persistent anticyclone will remain
over the Great Basin, with some deamplification of ridging to its
north leading to more-zonal flow across the northern tier of states
from WA-ND. A weak shortwave trough -- apparent in moisture-channel
imagery over parts of central/eastern MT -- should move slowly
east-southeastward across the northern High Plains today amid
difluent flow. Meanwhile and downstream, a pronounced shortwave
trough now over parts of WI/IL/IA should eject northeastward over
the Upper Great Lakes and weaken, while smaller/upstream
perturbations help to maintain the mean trough. Both the
low/middle-level remains of TC Beryl, and a closely associated
shortwave trough of midlatitude origins, should shear northeastward
across southern QC, the lower St. Lawrence Valley, and northern New
England, weakening considerably.

At the surface, 11Z analysis showed a low near the NH/QC border with
slow-moving, weakening cold front across western New England, the
coastal Mid-Atlantic/Carolinas, southern GA, and FL Panhandle,
becoming quasistationary along the northwestern Gulf Coast. This
front should continue weakening near or just east of its present
position through the period, over the Northeast, and also weaken
over the Gulf Coast and southern Atlantic Coast States. Enough
low-level shear exists over parts of ME today to support a
conditional supercell potential, but strength/coverage/longevity are
in question due to weakness of both instability and lift.
Elsewhere, a lee trough analyzed on that chart over eastern parts of
MT/WY/CO should remain over the central/northern High Plains today,
with some eastward drift possible.

Widely scattered to scattered thunderstorms are expected to develop
this afternoon, over the Mogollon Rim and smaller mountain ranges to
the south. That will occur as strong insolation at those higher
elevations preferentially removes MLCINH, in the presence of
generally greater low-level moisture than previous days. Some
strengthening of flow aloft is expected over this region, around the
southeastern rim of the anticyclone. This will support convective
motion off the Rim (and small mountain ranges to its south), then
atop well-heated/deeply mixed boundary layers of the desert floor.
Isolated strong-severe gusts are possible from the relatively early,
more-discrete activity.

With the lower-elevation boundary layers being very deep (surface to
around 600 mb), but enough moisture maintained through mixing to
keep surface-based buoyancy (MLCAPE in the 500-1000 J/kg range),
expect some aggregation of outflows with additional development atop
those -- especially over southeastern AZ. The net result should be
both translation and developmental propagation of convection
southwestward to and across the international border, with swaths of
strong-severe gusts possible.

...Northern High Plains...
Isolated to widely scattered, high-based thunderstorms are expected
to form near the lee trough, where both relatively maximized
convergence and strong surface heating should contribute to enough
lift for convective initiation. The main concern up and down the
corridor should be damaging to severe gusts, given the deeply mixed
subcloud layer and ample downdraft-acceleration opportunity that
will afford. Isolated severe hail also may occur, amidst enough
deep-layer shear for some organized thunderstorms (effective-shear
magnitudes of 30-40 kt). Lack of greater moisture and buoyancy will
be a limiting factor for coverage and intensity of convection, which
should diminish rapidly after dark.

..Edwards/Bentley.. 07/11/2024

SUNRISE AND SUNSET TIMES IN UTC (if you're not logged in to Google)
CHICAGO UTC-6 during CST (Central Standard Time, e.g., winter)
CHICAGO UTC-5 during CDT (Daylight Savings Time, e.g., summer)