SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1020 AM CST Sun Nov 20 2022
Valid 201630Z - 211200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Severe thunderstorms are not expected through tonight.
...Synopsis/Discussion...
In mid/upper levels, mean troughing will be maintained over eastern
Canada through the period. However, the strong subsidiary trough --
now apparent in moisture-channel imagery from near James Bay across
parts of the Mid-Atlantic region -- will move eastward through New
England around 00Z and Atlantic Canada thereafter. This process
will shift low-level winds unfavorably for lake-effect bands over
the lower Great Lakes, foster dry advection in the boundary layer,
and lower effective tropopause levels. Those, in turn, will lessen
lightning potential through the afternoon.
A positively tilted, southern-stream shortwave trough was evident
from northwestern OK across the TX Panhandle, central NM,
southeastern AZ, and the northern Gulf of California. The trough
should pivot eastward through the period -- with faster translation
of its middle/southern parts, while retaining positive tilt. By
12Z, the trough should extend across central OK, northwest TX,
extreme southeastern NM, far west TX, and central Sonora. To its
southeast over south TX, a broad plume of elevated low-level warm
advection and moisture advection/transport will persist, supporting
increasing convective potential (including isolated to widely
scattered thunderstorms) overnight into early morning.
At the surface, 15Z analysis showed a quasistationary front across
Great Abaco, Bahamas, southwestward over the Gulf Stream to very
near Elliott Key and Key Largo FL, then across the Straits just
south of the Lower/Middle Keys. Minor oscillations in frontal
position are possible through the period, but it generally should
remain quasistationary. Most associated convection has remained
(and should continue to be) just below ideal icing layers for
lightning, based on modified MFL/EYW RAOBs and radar cross-sections.
Still, isolated lightning has been observed sporadically south of
the Lower Keys, and weak storm-scale rotation has been noted in
cells over the Straits, east of both Key Largo and Miami-Dade
County. This may prompt occasional deepening of updrafts briefly
favorable for lightning. Activity should remain too weak for a
severe threat.
..Edwards/Thornton.. 11/20/2022
Read more