SPC AC 010558
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1258 AM CDT Fri Jul 01 2022
Valid 021200Z - 031200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHEAST AND MID-ATLANTIC...
Isolated to scattered severe thunderstorms capable of producing
damaging winds and marginally severe hail should occur Saturday
across parts of the Northeast and Mid-Atlantic. Isolated severe
thunderstorms may also develop across parts of the northern Plains
and interior Pacific Northwest.
...Northeast into the Mid-Atlantic and Mid Mississippi Valley...
An upper trough/low over Ontario and Quebec should move slowly
eastward on Saturday. A belt of enhanced mid-level west-
southwesterly winds should be present over much of the Northeast
into the Mid-Atlantic. At the surface, a cold front is forecast to
progress east-southeastward across these regions through the day.
Thunderstorms are expected to gradually increase in coverage and
intensity Saturday afternoon along/ahead of the front from southern
New England into VA and vicinity. Even though mid-level lapse rates
should remain modest, diurnal heating of a moist low-level airmass
will likely support around 1000-2000 J/kg of MLCAPE by late Saturday
afternoon across these regions.
Sufficiently strong mid-level flow will be present to foster 35-45
kt of deep-layer shear. Accordingly, a mix of multicells and
supercells appears possible. Damaging winds should be the main
threat, especially as cells congeal into small bowing clusters
along/ahead of the front. Marginally severe hail also appears
possible with any supercell that can be sustained.
Farther west into WV/KY and the mid MS Valley, mid-level flow is
expected to be weaker. Still, enough instability and marginal
deep-layer shear should be present along/south of the cold front to
support loosely organized clusters and isolated damaging winds. Some
guidance also suggests that remnant outflow from convection that may
be ongoing Saturday morning across eastern KS into MO may focus
renewed thunderstorm development across parts of the mid MS Valley
and vicinity Saturday afternoon.
Upper ridging should extend across much of the Rockies and adjacent
High Plains on Saturday. Multiple weak mid-level perturbations may
round the crest of this upper ridge and advance east-southeastward
across the northern Plains through the period. Given the
weak/nebulous large-scale forcing aloft, it remains unclear how many
thunderstorms will develop across this region. Regardless, weak to
locally moderate instability present along/east of a surface lee
trough and strong deep-layer shear will support a severe hail/wind
threat with any convection that can develop.
With continued uncertainty in overall convective coverage, have
expanded the Marginal Risk to account for probable high-based
thunderstorm development off the higher terrain into southeastern
MT, northeastern WY, and eventually the Dakotas Saturday afternoon
and evening. Any convection that can persist into ND/SD would
potentially pose a better severe threat as it encounters greater
low-level moisture and related instability.
A closed upper cyclone should remain centered off the coast of the
Pacific Northwest on Saturday. A mid-level perturbation is forecast
to move northeastward across northern CA into the interior Pacific
Northwest through the period. High-based convection should initially
develop over the Cascades in central OR as ascent preceding the
mid-level shortwave trough overspreads this region.
Even though low-level moisture is expected to remain limited, steep
mid-level lapse rates and a deeply mixed boundary layer should aid
convective downdrafts reaching near-severe levels as thunderstorms
spread generally northeastward though the early evening. Isolated,
marginally severe hail may also occur with the strongest cores.
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