SPC 1200Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1221 AM CDT Thu Apr 08 2021

Valid 081200Z - 091200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
NORTHERN GULF COAST ACROSS EASTERN TENNESSEE AND KENTUCKY...AND
NORTHWARD INTO SOUTHERN LOWER MICHIGAN...

...SUMMARY...
Isolated severe thunderstorms are possible during the day from the
northern Gulf Coast states into parts of the southern Great Lakes.

...Synopsis...
An upper low will deepen slightly as it moves from northern MO into
southern MN, with a negative-tilt upper trough pivoting north across
the OH Valley by 00Z. Minor height falls will occur across the
Appalachians, with more substantial height falls from the OH Valley
into the upper Great Lakes. Strong westerly flow aloft will persist
from the southern Plains across the Southeast during the day, with
additional height falls into Friday morning as a shortwave trough
drops southeast across the Rockies.

At the surface, low pressure will move from IA into MN, with little
if any deepening. A cold front will extend southeast from the low,
across WI, Lower MI, and southward into central KY, middle TN, and
AL. This front will become stationary across LA, and will return
north as a warm front overnight across TX, LA, MS and AL.

Heating along with a 150-200 nm wide ribbon of 55-60 F dewpoints
will contribute to destabilization ahead of the cold front, with
isolated to scattered daytime storms (a few severe) from GA into
Lower MI.

...Northern Gulf Coast northward across eastern TN/KY and into Lower
MI...
A slow-moving line of storms now over southern LA may persist beyond
12Z Thursday from southeast LA into the western FL Panhandle. This
activity should weaken through midday due to weakening lift as the
upper trough pivots north. Strong wind gusts will be possible with
this activity.

Heating ahead of the cold front will remove capping by around 18Z,
with scattered storms likely from northern GA into TN and KY, as
well as across IN, OH, and Lower MI. The most favorable combination
of shear (effective SRH around 200 m2/s2, decreasing late) and
instability (MLCAPE around 1500 J/kg) is likely from northern GA
into KY, which will support strong to severe storms. Hail and
localized wind damage will be possible, and perhaps a brief/weak
tornado as storm mode will likely be cellular. This threat may
extend as far east as the western Carolinas. 

Other storms from OH into Lower MI may pose at least a marginal wind
threat, but instability will be weaker here. Arcing bands of storms
will be oriented relatively parallel to the deep-layer shear vector,
which will average near 30 kt.

...North TX / Red River Valley overnight...
Southwesterly 850 mb winds will increase late Thursday night across
TX, along with warm/moist advection. Various ensembles indicate only
a low chance of elevated thunderstorms due to capping and moisture
quality. At this time, the conditional threat of thunderstorms
appears too low to introduce hail probabilities. However, cool
temperatures aloft would favor marginal hail if a storm or two
forms.

..Jewell/Wendt.. 04/08/2021

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