NH Fall/SH Spring 2023 Discussion Thread

SPC AC 191722



Day 2 Convective Outlook

NWS Storm Prediction Center Norman OK

1122 AM CST Sun Nov 19 2023



Valid 201200Z - 211200Z



...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF

NORTHERN LOUISIANA AND CENTRAL MISSISSIPPI...



...SUMMARY...

Severe thunderstorms are likely Monday afternoon into Monday night

from east Texas into parts of the Lower-Mississippi Valley and

Southeast. Damaging winds and several tornadoes, a few of which may

be strong, will be the primary hazards. However, some large hail is

also possible.



...Synopsis...

A strong mid-level jet streak across Texas will shift east during

the day and into the mid-Mississippi Valley by Monday night. A

surface low will move eastward through the day from near the Red

River, into the Mid-Mississippi Valley, and then occlude northward

into the Lower-Ohio Valley by early Tuesday morning. A warm front

will move north during the day across the Lower-Mississippi Valley

and bring mid-60s dewpoints into the I-20 corridor during the

afternoon. Thunderstorm activity is expected along and primarily

ahead of a cold front which will move from east Texas Monday

afternoon to central/east-central Mississippi by 12Z Tuesday.



...Portions of northern Louisiana and central Mississippi...

Expect relatively early convective initiation across east-central

Texas, near the nose of the mid-level jet, where morning low

temperatures will be in the mid to upper 60s with convective

temperatures in the low 70s amid at least broken cloud cover. While

shear will be strong (50+ knots), expect storm intensification to be

gradual given ~750 MLCAPE and limited inhibition. However, by

mid-afternoon as storms move into Louisiana, expect more robust

storm development as instability increases and forcing for ascent

intensifies as the mid-level trough starts to become more negatively

tilted.



Significant mass response is expected after 21Z which will lead to a

strengthening low-level jet and low-level shear. This timing will

correspond well to peak diurnal heating and supercell intensity. As

hodographs elongate between 21Z and 00Z, the low-level wind profile

will become increasingly favorable with nearly pure streamwise

vorticity in the lowest 750m of most forecast soundings. Most CAM

guidance shows mature supercells in the region at this time which

would support tornado potential, some potentially strong.



Diurnal thunderstorm activity is expected to become more linear

through the evening with an increasing damaging wind threat.

However, as the low-level jet intensifies, increasing isentropic

ascent may be sufficient for additional warm-sector supercell

development across Mississippi during the evening and into the

overnight hours. The less favorable diurnal timing casts some doubt

on the intensity of these supercells, but the wind profile will be

extremely favorable (300+ m2/s2 0-500m SRH). Therefore, any strong

supercells which develop in this region after dark would pose some

strong tornado threat.





...Mid-Mississippi Valley...

The majority of 12Z CAM guidance shows a surface low track across

northwest Mississippi. Therefore, the categorical Slight risk

closely matches this mean surface low track. However, some guidance

has a farther north track, most notably the FV3 near the MO

Bootheel. Therefore since the Marginal risk is conditional on the

surface low track, it now extends to the MO Bootheel, indicating the

most likely northernmost extent of any potential threat for isolated

damaging wind gusts from a low-CAPE convective line along the

surface front.



..Bentley.. 11/19/2023