Day 4-8 Outlook

Day 4-8 Outlook Image

Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0315 AM CST Mon Feb 22 2021

Valid 251200Z - 021200Z

Blocking may linger within the large-scale pattern across the
southern mid-latitude and subtropical eastern Pacific late this week
into the beginning of next week.  However, the latest medium-range
guidance indicates that prominent/amplified mid-level ridging,
forecast to evolve across the eastern Pacific during the middle to
latter portion of this week, will become increasingly suppressed by
a series of significant short wave perturbations emerging from the
upstream westerlies.

Mid-level flow inland of the Pacific coast appears likely to become
increasingly split, with a number of embedded progressive short wave
perturbations.  The northern branch is currently forecast to
maintain a relatively low amplitude with a west-northwesterly
component, to the southwest of an elongated deep vortex centered
just north of Hudson Bay.  Within the southern branch, it appears
that relatively amplified mean troughing will develop across the
Pacific Coast into the Great Plains.

At the same time, subtropical ridging may become increasingly
prominent across much of the Gulf of Mexico into the Southeast.

This regime may become increasingly conducive to significant surface
cyclogenesis to the lee of the southern Rockies by next
Sunday/Monday, as boundary-layer moistening continues over the Gulf
of Mexico (particularly the southwestern Gulf).  Associated
large-scale forcing for ascent and destabilization could support
increasing severe thunderstorm potential across parts of the
southern Great Plains into the middle/lower Mississippi Valley. 
However, much will hinge on the shorter wavelength developments,
which are still fairly uncertain at this extended range.  One
particular concern is the timing of the northern branch short waves,
and their associated southward surges of colder air to the lee of
the Rockies, relative to the emerging southern branch short waves,
which could displace and/or mitigate the risk for severe storms.

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