Day 1 Severe Weather Outlook

Valid 101300Z – 111200Z


Severe storms producing large hail and locally damaging wind gusts
are expected from eastern Oregon into western and southern Montana
during the afternoon and evening. A cluster of storms, some severe,
is also expected over eastern North Carolina during the afternoon.
Other isolated activity is likely from the Black Hills into the
central High Plains with marginal hail and wind.

…Northern Rockies this afternoon/evening…
A closed midlevel low near the northern CA coast this morning will
evolve gradually into an open wave while ejecting northeastward
toward ID by tonight, as other subtle speed maxima rotate around the
eastern periphery of the low. Northeast of the ongoing convection
across northern CA, surface heating beneath relatively cool midlevel
temperatures will contribute to MLCAPE of 500-1000 J/kg, within a
corridor of deep-layer southerly shear of 35-50 kt. Scattered
thunderstorm development is likely in the zone of ascent immediately
northeast of the ejecting trough, where a few storms could produce
damaging outflow winds and isolated large hail.

Farther northeast into ID and MT, broken bands of convection are
expected this afternoon as surface heating over the high terrain
coincides with ascent accompanying a lead speed max aloft. Storm
development should extend eastward across southern MT through the
afternoon. Surface heating and boundary-layer dewpoints in the 50s
beneath steep midlevel lapse rates will drive moderate buoyancy
(MLCAPE up to 1500 J/kg). Meanwhile, low-level easterly flow
beneath southwesterly flow aloft will result in long hodographs
favoring supercells. The stronger storms will be capable of
producing large hail and damaging winds, primarily from mid
afternoon into this evening.

…Eastern NC this afternoon…
A quasi-stationary front just inland from the NC coast, in
conjunction with local sea breeze circulations, will help focus
thunderstorm development this afternoon. Rich low-level moisture
(boundary-layer dewpoints in the mid-upper 70s) along the coast and
strong surface heating inland along the boundary will contribute to
MLCAPE in excess of 2000 J/kg. West-northwesterly flow aloft and
any sea breeze augmentation of near-surface, south-southeasterly
flow will result in sufficient vertical shear for organized clusters
and/or some supercell structures, with the potential to produce
damaging winds and isolated large hail.

…Central Plains vicinity this afternoon into tonight…
A messy scenario is unfolding across CO/NE/IA/KS today into tonight
with multiple MCVs, ongoing convection, and cloud debris within the
northeast extent of the southern Rockies monsoonal moisture plume.
Forcing for ascent will likely persist across IA in a zone of
low-level warm advection, and some low-level moistening and
destabilization is expected. However, relatively warm profiles
aloft and modest lapse rates do not appear favorable for large hail,
and it is not clear if storms will be rooted clearly at the surface
where low-level shear/hodograph curvature will be stronger. Farther
west, forcing for ascent will be weak and confined to a diffuse
surface boundary into southeast NE, which could focus isolated
strong thunderstorm development this evening.

A few diurnal storms are expected in the developing upslope flow
regime by this evening across eastern CO and western KS. Farther
east, clouds will likely slow surface heating and a lingering EML
will be warm enough to maintain some convective inhibition through
much of the afternoon. Low-level warm advection will increase
across KS tonight in response to a weak nocturnal low-level jet,
when more widespread convection is expected in one or more clusters.
Lingering steep low-midlevel lapse rates and PW in excess of 2
inches will support some threat for isolated strong/damaging winds
with heavy precipitation loading, and perhaps isolated marginally
severe hail.

..Thompson/Kerr.. 08/10/2019


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