SPC 1730Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1125 AM CST Wed Jan 27 2021

Valid 281200Z - 291200Z


Thunderstorms are possible across parts of coastal and interior
central California, mainly Thursday night, but the risk for severe
weather appears negligible.

Models indicate that the amplified regime across the eastern Pacific
will undergo transition during this period, with initially sharp
mid/upper ridging (between 140-160 W longitude) becoming suppressed
by the first in a series of digging short wave impulses.  As this
occurs, fairly deep, elongated downstream troughing is forecast to
gradually progress inland across the Pacific coast.  It appears that
this will include at least one vigorous short wave impulse, which is
forecast to dig into its base, accompanied by a sizable mid-level
cold core with 500 mb temperatures at or below -30C.  A modest
surface cyclone and associated reinforcing low-level cold intrusion
may also develop southward along the California coast, into areas
near and southwest of Monterey by late Thursday night.  

Farther east, broad mid/upper ridging likely will be maintained 
across the Rockies into the Mississippi Valley, with perhaps some
further amplification across the Great Plains.  To the southeast of
a blocking high near/northeast of Hudson Bay, it appears that a deep
mid-level low will be forced southeastward toward the lower Great
Lakes region.  This will prevent eastward development of the
upstream ridging, and contribute to the evolution of large-scale
troughing across the Atlantic Seaboard into the western Atlantic.

Strong cyclogenesis is forecast to proceed over the western
Atlantic, in association with a preceding vigorous short wave
impulse digging off the southern Mid Atlantic coast by the beginning
of the period.  In its wake, a cold front will advance southeast of
the Florida Peninsula, with the leading edge of associated lower/mid
tropospheric drying advancing through the Bahamas, Caribbean and
southwestern Gulf of Mexico.  While a southerly return flow,
emanating from the southwestern Gulf of Mexico, may develop
north-northwestward into the Rio Grande Valley and parts of the
southern Great Plains, this will be elevated above a cool/cold,
stable boundary layer.  Beneath relatively warm and capping layers
aloft, forecast soundings suggest that this is unlikely to yield
destabilization supportive of thunderstorm activity.

An initial frontal precipitation band, spreading south and east of
the Monterey vicinity at 12Z Thursday, may be preceded by strong
southerly flow around the 850 mb level on the order of 40-50+ kt. 
This may contribute to large, clockwise curved low-level hodographs
across coastal areas into southern portions of the San Joaquin
Valley early in the day, before the low-level jet weakens.  However,
forecast soundings within this regime indicate thermodynamic
profiles with little potential for lightning, and lingering stable
layers near the surface which is expected to preclude a severe
weather risk.

In the post-frontal regime, strong mid-level cooling, associated
with the digging mid-level cold core, is expected to contribute to
weak destabilization along and inland of the central California
coast late Thursday through Thursday night.  Latest forecast
soundings suggest that thermodynamic profiles will probably become
supportive of scattered convection, occasionally capable of
producing lightning.

..Kerr.. 01/27/2021

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