SPC 2000Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0130 PM CST Thu Jan 28 2021

Valid 282000Z - 291200Z


Scattered thunderstorm activity is possible, mainly near the coast
and coastal ranges, from central California this evening into the
vicinity of the Los Angeles Basin by 4 AM PST Saturday morning.

...20Z Outlook Update...
The main surface front is now inland of coastal areas, as far south
as Santa Barbara county, and surface cooling will overspread the
remainder of southern California, into the lower Colorado Valley by
late tonight.  However, latest NAM and Rapid Refresh forecast
soundings indicate that thermodynamic profiles supportive of
convection capable of producing lightning will probably remain
confined to beneath the mid-level cold core (including 500 mb temps
at or below -28 to -30C).  As of 20Z, across and to the south/east
of the San Francisco Bay region, this is still mostly well offshore.

Some convective development has been evident along and west of the
northern coastal ranges, west through north of Ukiah.  With
additional heating this afternoon, some of these cells may deepen
through sufficiently cold layers to produce lightning.  Also, thin
spots in the overcast are contributing to at least very weak
boundary-layer destabilization across parts of the Sacramento
Valley.  With further breaks, and additional insolation, the
development of a couple of thunderstorms may still not be out of the
question late this afternoon.

Otherwise, the primary risk for thunderstorm development appears to
be late this evening and overnight along the coast and coastal
ranges near and south of San Francisco Bay, perhaps as far south as
the Los Angeles Basin by 12Z Friday, as the leading edge of the
colder mid-level air advances southeastward.

..Kerr.. 01/28/2021

.PREV DISCUSSION... /ISSUED 1015 AM CST Thu Jan 28 2021/

No changes have been made to the ongoing forecast. An upper trough
is currently off the CA coast, and will spread inland through the
afternoon and night.  Cold temperatures aloft, steepening lapse
rates, and large scale forcing will result in widespread showers
across much of CA, with a few convective elements occasionally
reaching sufficient depth to produce lightning.  No severe storms
are forecast.

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