Day 1 Severe Weather Outlook

Valid 061200Z – 071200Z

…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS TODAY ACROSS
PARTS OF THE NORTHERN INTERMOUNTAIN REGION…NORTHERN ROCKIES AND
FRONT RANGE…AND PERHAPS NEAR SOUTHERN MID ATLANTIC COASTAL AREAS
AT THE BEGINNING OF THE PERIOD…

…SUMMARY…
Strong thunderstorms may impact parts of the northern intermountain
region, northern Rockies and Front Range this afternoon and evening,
and pose at least some risk for severe hail and wind.

…Synopsis…
Hurricane Dorian appears in the process of accelerating
northeastward near the North Carolina coast. This is forecast to
continue, across and offshore of the Mid Atlantic coast by midday,
as at least a couple of significant short wave troughs dig within
moderately strong northwest flow across the Canadian Prairies
through the lower Great Lakes and Northeast. Models suggest that
the lead impulse may begin to interact with Dorian by tonight
south/southeast of the southern New England coast, but the strongest
low-level cyclonic wind field is expected to pass to the south and
east of Cape Cod by 12Z Saturday.

Upstream, amplified mid-level troughing over the eastern Pacific is
forecast to remain progressive and approach the Pacific coast during
this period. As it does, a weaker preceding short wave trough
appears likely to progress inland of the northern California and
Oregon coast. Models suggest that it will gradually broaden and
turn eastward, then southeastward across the northern intermountain
region and Rockies. As it does, it likely will suppress a prominent
mid-level high now centered near the Colorado Rockies, and lee
surface troughing will gradually develop across the northern into
central High Plains.

…Northern intermountain region/Rockies/Front Range…
A belt of moderately strong mid-level flow (including 30-40 kt at
500 mb) accompanying the short wave trough will contribute to at
least modest shear across the region today. Coupled with the
development of weak to moderate boundary layer CAPE, in the presence
of steep lower/mid tropospheric lapse rates, the environment may
become at least marginally conducive to widely scattered strong
storms which could pose a risk for severe hail and wind. This could
include isolated supercells.

Strongest destabilization, including CAPE on the order of 1000 J/kg,
is expected to become focused within lee surface troughing,
near/just east of the Front Range late this afternoon, as well as
beneath stronger cooling associated with the mid-level cold core,
across parts of eastern Oregon into central and southern Idaho by
early this afternoon.

…Southern Mid Atlantic coast…
The low-level circulation center of Hurricane Dorian is forecast to
reach the Outer Banks area of North Carolina by 12Z this morning,
with tropical boundary layer instability supportive of any
appreciable lingering risk for tornadoes/waterspouts likely east of
the southeast Virginia/northeast North Carolina coastal waters
around the beginning of the period, if not before.

..Kerr/Squitieri.. 09/06/2019

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