SPC AC 011718
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1218 PM CDT Fri Jul 01 2022
Valid 021200Z - 031200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE
MID-ATLANTIC TO THE NORTHEAST...AND ACROSS PORTIONS OF THE NORTHERN
Isolated to scattered severe thunderstorms capable of producing
damaging winds and hail are expected Saturday across parts of the
Northeast and Mid-Atlantic, as well as across parts of the northern
Plains. Isolated severe thunderstorms may also develop across parts
of the interior Pacific Northwest.
...Northeast into the Mid-Atlantic and Mid Mississippi Valley...
A belt of stronger mid/upper westerly flow will overspread the
region as an upper trough pivots eastward across the Great Lakes and
New England. At the surface, a cold front is forecast to develop
east/southeast across the Northeast and Mid-Atlantic. The front will
extend westward into the Ohio and Mid-Mississippi Valleys, sagging
southward across these areas through the end of the period.
Ahead of the front, a seasonally moist airmass will be in place,
with mid/upper 60s F dewpoints common. While midlevel lapse rates
will remain modest, heating into the 80s F will support 1000-2000
J/kg MLCAPE. Deep-layer flow will remain mostly unidirectional,
though increasing speeds with height will support 35-45 kt effective
shear magnitudes across the Mid-Atlantic and southern New England.
As a result, organized supercells and bowing clusters are possible.
Steep low-level lapse rates and high PW values, combined with rather
weak low-level shear will favor damaging gust potential. Modest
lapse rates and somewhat warm temperatures aloft will limit the
large hail potential, but any organized/sustained supercell could
produce marginally severe hail.
Deep-layer flow will become weaker with westward extent along the
front into the Ohio and Mid-Mississippi Valleys. However, surface
dewpoints into the low 70s will support MLCAPE values as high as
2000-3000 J/kg amid modest effective shear (20-30 kt). Widely
scattered thunderstorm clusters along/ahead of the cold front could
produce sporadic strong gusts through the early evening.
An upper ridge will be oriented across western WY/MT on Saturday.
Northwesterly mid/upper flow will increase modestly over the region
as several shortwave impulses cresting the ridge migrate
east/southeast into the northern Plains. Southeasterly low-level
flow will maintain modest boundary-layer moisture along/east of the
surface lee trough extending southward from eastern MT toward
WY/SD/NE border vicinity. Strong heating and steep midlevel lapse
rates will support MLCAPE around 1500-2500 J/kg. Flow will generally
be weak from the surface to around 600 mb before increasing to
around 30-50 kt above 500 mb. However, vertically veering profiles
will result in effective shear magnitudes around 35-45 kt,
supporting organized convection.
Weak large-scale ascent and some warming between 850-700 mb may
ultimately limit convective coverage. However, most forecast
guidance is consistent in at least widely scattered supercells
develop, with some propensity toward upscale development during the
evening as a southerly low-level jet increases. Any cells that
develop will have the potential for producing damaging gusts and
large hail. If upscale development occurs, an accompanying increase
in damaging wind potential is expected into parts of SD.
...Oregon/Northern Rockies Vicinity...
The upper ridge axis initially oriented near ID/western MT will
slide eastward as an upper low and associated trough develop
south/east along the Pacific Coast. Increasing southwesterly flow
and large-scale ascent ahead of the coastal trough will overspread
the interior Pacific Northwest/northern Rockies vicinity. Low-level
moisture will remain limited, though sufficient midlevel moisture
and steep midlevel lapse rates will support modest destabilization
(around 500-1000 J/kg MLCAPE). High-based cells capable of strong
outflow winds and marginal hail will be possible as storms quickly
progress northeast during the afternoon/early evening.
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