Day 1 Convective Outlook AMEND 1
NWS Storm Prediction Center Norman OK
0502 PM CDT Mon Jul 22 2024
Valid 222155Z - 231200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF NORTH DAKOTA AND NORTHWEST MINNESOTA...THE DESERT SOUTHWEST...AND
THE MID-ATLANTIC/EASTERN NORTH CAROLINA...
AMENDED FOR ADDITION OF HAIL/WIND PROBABILITIES IN NORTH DAKOTA AND
NORTHWEST MINNESOTA
...SUMMARY...
Isolated severe thunderstorms remain possible this afternoon and
early evening over portions of North Dakota and northwest Minnesota,
the mid-Atlantic region, as well as western Arizona to the lower
Colorado River Valley.
...North Dakota/Northwest Minnesota...
Isolated strong to severe thunderstorms are ongoing along a weak
boundary/low-level confluence axis across parts of northeast ND and
northwest MN. A few instances of large hail have already occurred.
The presence of moderate to locally strong instability, along with
marginally favorable deep-layer shear with modestly strengthening
northwesterly winds at mid/upper levels, should support a continued
threat for isolated severe hail and strong to damaging winds as this
activity spreads slowly southward across ND and northwest MN late
this afternoon and early evening. 5% severe hail/wind probabilities
have been included with this amendment to account for this
potential. See Mesoscale Discussion 1695 for additional details on
the short-term severe threat across this region.
...Previous Discussions...
...20Z Discussion...
Aside from minor line adjustments to affect recent/local trends, no
appreciable changes appear to be needed, with respect to the ongoing
forecast. Prior reasoning continues to reflect expectations
regarding convective/severe risk through the end of the period.
...1630Z Discussion...
...Mid-Atlantic states...
A narrow ribbon of slightly enhanced southwesterly 500-mb flow will
remain across NC/Delmarva to the southeast of a broad/weak mid-level
trough centered over the Great Lakes southwestward through the
Ozarks. Although large-scale forcing will be modest, a seasonably
moist airmass (14-16 g/kg lowest 100-mb mean mixing ratios per 12
UTC area raobs) will gradually destabilize through the mid
afternoon. Midday visible satellite imagery shows the initial
stages of a building cumulus field across the Carolinas northward
into eastern VA. Widely scattered to scattered thunderstorms are
forecast to develop this afternoon within the moderately unstable
airmass. Some strengthening in south-southwesterly 850-mb flow is
progged by models later this afternoon into the early evening. A
few of the stronger storms may pose a localized risk for damaging
gusts (45-60 mph). If a transient supercell can develop (primarily
21-01z), a brief tornado is possible. This activity will likely
diminish by mid-late evening owing to nocturnal stabilization.
...Western AZ/lower CO River Valley...
Widely scattered thunderstorms are forecast to develop later this
afternoon/evening as surface temperatures soar into the 100s.
Although flow will be weak due to proximity to the mid- to
upper-level ridge, large surface temperature-dewpoint depressions
(around 50 deg F) will favor evaporative cooled downdrafts with the
more robust thunderstorm cores. A few severe gusts (60-70 mph) are
possible before this activity wanes by mid evening.
...Southeast New England...
Model guidance indicates increased shower/thunderstorm potential
late tonight (08-12 UTC) as a strengthening LLJ shifts northeastward
from the Mid-Atlantic coast to near the continental shelf/deep
Atlantic waters off the southeast New England coast. The latest
models generally indicate meager to no surface-based buoyancy
penetrating the coast, thus precluding low-severe probabilities this
outlook update.
..Gleason.. 07/22/2024
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