SPC 1300Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0641 AM CST Fri Jan 22 2021

Valid 221300Z - 231200Z


No severe weather is expected across the U.S. today and tonight.

In mid/upper levels, a high-amplitude mean ridge will persist from
the AK/Yukon border region south-southwestward to a high north-
northeast of HI.  To its east, a split-flow pattern is evident in
moisture-channel imagery, around a compact cyclone centered near
Cape Mendocino.  The main/leading vorticity max will move down the
coast toward MRY through 00Z, then pivot eastward across the LAS
area late overnight, while weakening.  Meanwhile, a trailing
vorticity lobe and shortwave trough -- initially apparent offshore
from Vancouver Island -- will dig south-southeastward parallel to
and just off the West Coast, reaching Pacific waters west of VBG by
12Z tomorrow.

Cooling aloft and related steepening of lapse rates, atop marginal
low-level theta-e, may support a few weak thunderstorms ahead of the
compact cyclone today over portions of central/northern CA. 
Strongly difluent mid/upper flow, low-level warm advection, marginal
moisture, and increasing deep ascent will support convective
development this evening and tonight, over and near southern NV,
with MUCAPE generally in the 100-300 J/kg range.  A residual, deep
mixed layer from diurnal processes still should exist starting just
above the surface, and locally strong gusts cannot be ruled out. 

Farther east, generally zonal flow aloft should cover most of the
downstream areas in the central/eastern CONUS.  A weakening,
positively tilted shortwave trough is located over the southern
Plains, and will continue to deamplify as it moves eastward across
the Deep South overnight.  While a rogue lightning strike still may
occur in the associated precip plume near the central Gulf Coast,
weak forcing and lack of greater instability should preclude 10% or
greater unconditional thunderstorm coverage.

..Edwards/Gleason.. 01/22/2021

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