Severe Storm Outlook Narrative (AC)
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ACUS02 KWNS 201727
SPC AC 201725

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1125 AM CST Mon Feb 20 2017

Valid 211200Z - 221200Z


Organized severe thunderstorms are not forecast across the
contiguous United States on Tuesday or Tuesday night.

An upper-level low will move eastward from the Arklatex into the
lower Mississippi Valley on Tuesday as upper-level trough approaches
the West Coast. Ahead of the West Coast trough, southwest low to
mid-level flow will be in place across California. Strong
large-scale ascent, steep lapse rates and cold air aloft ahead of
the upper-level trough will create conditions supportive of
thunderstorm development from northern California east northeastward
into southern Idaho during the morning and afternoon. Conditions
will be most favorable for thunderstorm development during the
morning across northern California from Eureka southward to San
Francisco along the axis of a 40 to 50 kt low-level jet. RAP
forecast soundings near Eureka at 12Z/Tuesday show 0-6 km shear of
90 to 100 knots with steep low to mid-level lapse rates exceeding
7.0 C/Km suggesting a threat for small hail and strong wind gusts
may exist as cells move inland.  After coordinating with WFO Eureka,
the decision has been made to not introduce low end hail
probabilities for this outlook mainly due to uncertainties
concerning the magnitude of the threat which could remain below
marginal criteria. Elsewhere, isolated thunderstorms may occur
across the central Gulf Coast along a corridor of low-level moisture
to the southeast of the lower Mississippi Valley upper-level low.
The convection in the central Gulf Coast region is not expected to
be associated with a severe threat.

..Broyles.. 02/20/2017

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