SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0750 AM CDT Mon Jul 01 2024
Valid 011300Z - 021200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
THE NORTHERN/CENTRAL PLAINS...
...SUMMARY...
Severe thunderstorms will be possible today across the northern/
central Plains, especially parts of Nebraska and South Dakota. Areas
of damaging winds and sporadic hail will be possible, along with a
few tornadoes.
...Synopsis...
A strong mid/upper-level anticyclone centered over north TX is
forecast to shift east-southeastward over northern LA and weaken
slightly. This will occur as height falls spread across much of the
Great Plains States ahead of a synoptic-scale trough, initially
located from the northern Rockies across the western Great Basin to
the Sierra Nevada. The trough is expected to progress eastward
through the period, faster on its north end (thus becoming more
positively tilted). By 12Z tomorrow, it should extend from Lake
Winnipeg southwestward across ND, central WY, and UT, to near LAS.
A series of minor shortwaves and vorticity maxima will be embedded
in the foregoing southwest flow aloft, and will traverse the
central/northern Plains today and tonight. That includes small,
convectively generated/enhanced perturbations embedded in a
mid/upper-level monsoonal moisture plume, evident in moisture-
channel imagery from west-central/northwestern MX across AZ, the
Four Corners region, and most of CO/NE. Farther east, a mid/upper
trough -- initially from the lower St. Lawrence River region of
southeastern Canada across Update NY/PA/WV -- will move eastward off
the Mid-Atlantic and New England Coasts between 00-06Z.
The surface map at 11Z showed a cold front -- associated with and
preceding the leading mid/upper trough -- across northeastern/south-
central BC, northern parts of SC/GA/AL/MS, across central AR. The
front is forecast to move offshore from all the Atlantic Coast north
of about SAV by 00Z, then extend from there through a wave over
central GA to near a line from MOB-BTR-GGG, becoming ill-defined
farther northwest. Another cold front was drawn from a triple-point
low over southwestern ND southwestward across central WY and
northern UT. By 00Z, the latter front should reach the central
Dakotas, northwestern NE and northwestern CO. A broad area of low
pressure should slow/stall the front temporarily over northeastern
CO and south-central/southwestern NE tonight, while it advances to
the eastern Dakotas and southeastern UT.
...Central/northern Plains...
Scattered thunderstorms may develop this afternoon over a broad area
of the western Dakotas, and the central High Plains, along/ahead of
the cold front and near a lee trough/weak dryline over parts of
southwestern NE and eastern CO. A few strong-severe thunderstorms
also may form in the post-frontal upslope-flow regime near the
Bighorns and offer severe hail/gusts eastward toward the western
Black Hills.
The most favorable environment for severe will be across parts of
southern/central NE near a prominent moist axis, zone of warm
frontogenesis, and also possibly differential heating (from the
southern rim of morning clouds/precip). In this regime, backed flow
and relatively maximized moisture will maximize both kinematic and
thermodynamic parameters favorable for supercells. A corridor of
60s to low 70s F surface dewpoints -- already apparent from eastern
OK across western KS to western NE -- should shift northeastward
through the day, eroded on the west side by heating/mixing (as per
modifying the 12Z DDC RAOB) but reinforced father east through moist
advection. That moisture, and strong diurnal heating, will support
a narrow plume of MLCAPE around 2000-3000 J/kg. Locally large
hodographs are expected in the backed surface winds, yielding
effective SRH in the 250-450 J/kg range. Supercells with all severe
hazards (including a few tornadoes and large hail) will be possible
in that regime, especially with relatively discrete storms.
Significant (2+ inch diameter) hail cannot be ruled out, but that
threat may be mitigated somewhat by relatively warm temperatures
aloft in the monsoonal moist plume.
Upscale growth of early convection into lines an clusters is
possible, both in the southern NE regime wherever activity becomes
outflow-dominant before encountering the moisture plume, and farther
north as a possible frontal/prefrontal QLCS. The most sustained
potential for upscale evolution appears to be with the central/
southern NE activity shifting tonight into eastern NE, western IA
and the Siouxland region, where inflow-layer moisture and
instability should be greatest. As such, the potential for
cold-pool-aided convective-gust enhancement remains represented by a
significant-wind area inside the broader 15% unconditional wind
line. If confidence increases in a specific MCS corridor, that
probability may need to be raised in a succeeding outlook.
...Southeast...
Widely scattered to scattered, multicellular thunderstorms are
expected this afternoon between the frontal zone over GA/SC/AL on
the north, and on the south, sea-breeze and differential-heating
boundaries. The most intense cells will be capable of water-loaded
downbursts near severe limits. A very moisture-rich boundary layer
will persist across the region, with surface dewpoints commonly in
the low/mid 70s F and PW near 2 inches. Strong surface heating will
offset modest mid/upper-level lapse rates enough to yield MLCAPE in
the 2000-3000 J/kg. Low/middle-level flow and shear should be weak,
though a belt of strong northerly to northeasterly winds in upper
levels (near anvil level) may aid in storm organization. Severe
potential should be isolated and pulse in nature, with short-lived,
localized clustering possible, and should wane after sunset.
..Edwards/Kerr.. 07/01/2024
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