Severe Storm Outlook Narrative (AC)
Issued by NWS
ACUS01 KWNS 201624
SPC AC 201623
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1023 AM CST Fri Jan 20 2017
Valid 201630Z - 211200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS TONIGHT OVER
PARTS OF SOUTHERN MS AND CENTRAL LA...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER MUCH OF THE
LOWER MS VALLEY REGION AND ADJACENT AREAS...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE MIDDLE
TX GULF COAST INTO PARTS OF AL/FL...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ALONG THE
SOUTHERN CA COAST...
Severe storms will develop this evening and spread across the lower
Mississippi Valley tonight through Saturday morning, with a few
tornadoes, large hail, and damaging winds all possible. Strong
thunderstorms with at least some severe-weather potential are also
possible near the southern California coast this afternoon.
...Lower Mississippi Valley...
The latest surface analysis shows a weak warm front extending from
just off the upper TX Gulf Coast into southern LA/MS. This boundary
will likely be the main focus for strong to severe storms later this
afternoon and tonight. Model solutions suggest that activity will
first form along or just north of the boundary near HOU/VCT later
this afternoon and spread east-northeastward during the evening.
Relatively steep mid level lapse rates and sufficient deep layer
shear suggest the potential for rotating storms capable of large
hail and gusty winds. Very large hail is possible in the stronger
cells as they track eastward into LA.
Overnight, a consensus of 12z solutions indicate that the convection
tracking eastward across LA will coalesce into a bowing complex that
tracks across southern MS. Meanwhile the NAM/RAP/HRRR solutions
indicate a strengthening low-level jet and low-level cyclogenesis
occurring. Low level vertical shear profiles will also strengthen
over this area, posing some risk of isolated tornadoes. These
trends suggest an enhanced risk of locally damaging winds, so have
added an ENH area for this scenario.
...Coastal Southern California...
Radar and satellite loops show several bands of showers spreading
eastward and inland into southern CA. This pattern will persist
into the afternoon, when a combination of daytime heating and
cooling mid level temperatures will result in marginal CAPE values
and scattered thunderstorm activity. Strong mid and low level
winds, combined with some orographically induced veering, may result
in a marginal risk of gusty/damaging winds and/or a brief tornado.