SPC 1730Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1125 AM CST Sun Jan 03 2021

Valid 041200Z - 051200Z


Scattered thunderstorm activity is possible along Pacific Northwest
coastal areas, mainly late Monday afternoon, with lightning also
possible along the northern Sierra Nevada.

Much of North America will remain under the influence of branching
westerlies, downstream of a persistent strong zonal jet across the
southern mid-latitude and subtropical Pacific, which may nose as far
east as 140-145 W latitude during this period.  Stronger surface
cyclogenesis associated with this feature will remain focused across
the northeastern Pacific, but an emerging mid-level perturbation and
associated occluding surface front are forecast to progress inland
of the U.S. Pacific coast Monday through Monday night.  The front
appears to be preceded by a plume of moisture emanating from the
subtropical latitudes, and models suggest that moisture influx will
become maximized across the northern California coast into the
northern Sierra Nevada during the day Monday, before becoming
cut-off by the inland advancing cold front.

Downstream, it appears that mid-level troughing may undergo some
further amplification east of the Mississippi valley into the
western Atlantic.  This will include a number of embedded short wave
perturbations, including one advancing east of the New England
coast, where it will provide support for further deepening of an
offshore surface cyclone.  As this occurs, the trailing surface cold
front, and narrow plume of moisture return emanating from the
southern Gulf of Mexico, are expected to shift south of the Florida
Peninsula and Keys, with considerable further mid/low-level drying
across much of the Gulf of Mexico.  This will contribute to the
maintenance of generally dry and/or stable conditions across most
areas east of the Rockies.

...Pacific Coast states...
Models suggest that the development of thermodynamic profiles most
conducive to convection capable of producing lightning will be late
Monday afternoon, around 05/00Z (plus or minus an hour or two),
along the Oregon into Washington coast.  It appears that this will
take place within the post-frontal regime, and coincident with the
inland progression of the mid-level thermal trough axis (with temps
at or below -30C at 500 mb).

Otherwise, models suggest that mid-level cooling may steepen lapse
rates sufficiently to support convection capable of producing
lightning within the moist pre-frontal regime across northern
California coastal areas Monday afternoon.  Convection capable of
producing lightning may also develop into the northern Sierra
Nevada, aided by intensifying pre-frontal lift supported by
low/mid-level warm advection and orography, which may become focused
near or to the west of the Tahoe Valley vicinity by 05/00Z.

..Kerr.. 01/03/2021

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