SPC 0700Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1100 PM CST Sun Feb 21 2021

Valid 231200Z - 241200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Aside from the Columbia Plateau vicinity of the Northwest, the risk
for thunderstorms appears negligible across much of the U.S.,
Tuesday through Tuesday night.

...Discussion...
Models indicate that a blocking mid-level ridge centered over the
southern mid-latitude eastern Pacific will maintain strength through
this period, even as a significant short wave impulse within the
westerlies begins to progress around its northwestern periphery. 
Short wave ridging ahead of the perturbation, and to the
north-northeast of the ridging, appears likely to shift eastward
into the western Canadian provinces and Pacific Northwest.  As it
does, it may begin to impinge on the southwestern periphery of a
deep mid-level low initially centered across the Arctic latitudes,
which may begin to gradually shift east-southeastward toward the
northern Hudson Bay vicinity.

Farther south, inland of the Pacific Northwest coast, mid-level flow
is forecast to split, with the western of a pair of inland migrating
short wave perturbations taking a sharper south-southeastward turn
to the lee of the Cascades.  Larger-scale flow, in general, across
much of the Intermountain West through the Mississippi Valley is
forecast to trend broadly cyclonic, with low amplitude downstream
ridging overspreading the Ohio Valley and Mid Atlantic states, in
the wake of large-scale troughing rapidly progressing east of the
Atlantic Seaboard.

While a cold front associated with the lead troughing may progress
through much of the remainder of the southeastern Gulf of Mexico and
Florida Peninsula, accompanied by low-level cooling and drying, a
moistening return flow may continue to slowly develop across the
southwestern Gulf of Mexico.  Modest low-level moistening (including
mid 50s to lower 60s surface dew points) appears possible as far
northwest as Deep South Texas, and perhaps the Hill Country/Edwards
Plateau vicinity.  However, models indicate that this will be capped
by a deep, warm and dry lower/mid tropospheric layer.

...Northern Intermountain West/Rockies...
In association with the evolving large-scale pattern, models
indicate that a large pocket of cold mid-level air (-35 to -40C at
500 mb) will begin to shift southeastward through much of interior
North America.  By Tuesday, this likely will include much of the
northern intermountain region and northern Rockies, where it may
support weak boundary-layer destabilization and convective
development during the day with daytime heating.  While
thermodynamic profiles may be mostly below freezing, it is possible
that some of this activity could become capable of producing
lightning.  This potential may become maximized across the Columbia
Plateau vicinity Tuesday afternoon, aided by forcing associated with
the impulse digging to the lee of the Cascades.

..Kerr.. 02/22/2021

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