Day 4-8 Outlook

Day 4-8 Outlook Image

Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0333 AM CDT Tue Oct 06 2020

Valid 091200Z - 141200Z

Medium-range models continue to indicate substantial amplification
within a belt of westerlies emanating from the mid-latitude Pacific
this coming weekend into early next week.  This still appears likely
to include the evolution of large-scale mid/upper troughing across
and east of the Canadian and U.S Rockies by Sunday.  This likely
will be accompanied by deepening surface troughing and embedded
cyclogenesis across the Canadian Prairies and U.S. Great Plains,
before shifting northeastward and eastward, toward Hudson Bay and
across the Mississippi Valley by late Monday.

This is expected to be preceded by the inland migration of Hurricane
Delta Friday night, which will pose the most substantive initial
potential for severe weather (in the form of tornadoes) during this
period.  However, as is typically the case with features the scale
and nature of tropical cyclones, the extent of this risk, at this
extended range, remains unclear due to a number of uncertainties. 
One in particular concerns relatively dry/potentially cool low-level
air associated with surface high pressure, which appears likely to
encompass much of the East and Gulf Coast states prior to landfall
of Delta.  An elevated influx of moisture and associated rain
falling into this air mass may further reinforce stable
boundary-layer conditions preceding Delta.  And this could mitigate
the risk for tornadoes inland of perhaps a small corridor near
coastal areas, before Delta weakens.

Thereafter, the most appreciable severe weather potential associated
with the extratropical cyclogenesis is probably Sunday into Monday,
before diminishing by Tuesday.  The high latitude nature of the
stronger cyclogenesis (i.e. across the northern Great
Plains/Canadian Prairies into the west of Hudson Bay), and the
likely dependence on substantive moisture return from the Gulf of
Mexico for appreciable destabilization, contribute to uncertainty
which remains sizable concerning the extent of this risk.

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