Clearpost.online It's your post, so post it!

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0738 AM CDT Wed Apr 20 2022

Valid 201300Z - 211200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
CENTRAL/EASTERN OKLAHOMA INTO THE WESTERN OZARKS REGION...

...SUMMARY...
The greatest severe-weather threat for today and this evening
appears to be over portions of central/eastern Oklahoma into the
western Ozarks region, where up to a few supercells with hail,
isolated severe gusts and a tornado are possible.

...Synopsis...
A progressive and nearly zonal upper-air pattern will persist
through the period over most of the CONUS, perturbed mainly by
modest troughing extending southward from cyclones over SK and
eastern QC.  The SK cyclone/trough will move eastward to
northwestern ON and parts of the upper Great Lakes through the
period.  To its south, a shortwave trough -- initially over eastern
CO and northeastern NM -- will move eastward to western MO and
northwestern AR by 00Z.  This feature should pivot east-
southeastward to the Tennessee Valley by 12Z.

Farther west, heights will fall as flow backs to southwesterly west
of the Rockies overnight, in advance of a major synoptic cyclone/
trough located over the northeast Pacific.  A leading shortwave
perturbation -- evident in moisture-channel imagery about 200-250 nm
west of the OR coastline -- will move east-northeastward to
northeastward and ashore today, followed by several smaller
perturbations and shots of DCVA/cooling aloft.

At the surface, 11Z analysis showed a low over western KS between
CBK-DDC, with a cold front across southeastern CO, and a warm front
southeastward over south-central OK to east TX.  The warm front
should shift east-northeastward and gradually beco*e more diffuse
through tonight, as the cold front advances southeastward across
northern/western OK and central/eastern KS.  By 0Z, an elongated
area of low pressure is expected along the cold front from IA to
northeastern OK, with the boundary extending across southwestern OK,
then beco*ing a quasistationary to warm front over the TX Panhandle
to a low in southeastern CO.  By 12Z, the boundary should return to
central/northern OK as a warm front, as the CO low repositions
southeastward to the TX Panhandle.

A dryline was drawn from the KS low across the TX Panhandle, extreme
southeastern NM, and the Big Bend region of TX.  The dryline should
sharpen today as strong heating/mixing occurs to its west, with
continued moist advection to its east.  By 00Z, the dryline should
extend from a frontal intersection over northeastern OK,
south-southwestward over south-central OK and west-central TX.  The
dryline should retreat to the Permian Basin in TX and western OK
overnight.

...OK/KS to mid Mississippi Valley...
Isolated to widely scattered thunderstorms are possible this
afternoon into early evening.  Any sustained convection will be in
an environment supporting supercell development, with large/damaging
hail possible, along with isolated severe gusts.  A tornado also
cannot be ruled out, given a persistent/discrete supercell.  This is
because a substantial increase in moist-sector hodograph size and
effective SRH is forecast to occur during a brief time window
around/after 00Z before near-surface static stability beco*es too
large to sustain surface-based inflow.  As surface dew points
increase into the low/mid 60s F and heating occurs behind the
shortwave trough, peak/preconvective MLCAPE in the 2000-2500 J/kg
range is expected, in at least a narrow corridor ahead of the front
and dryline from southern to northeastern OK and perhaps extreme
southeastern KS.  Veering of mid/upper flow behind the shortwave
trough will act to enhance deep shear somewhat, with effective-shear
magnitudes in the 50-60-kt range forecast.

The main uncertainty -- and it is not a trivial one -- is whether,
and in what numbers, any sustained thunderstorms can form near the
front and dryline this afternoon.  Considerable variability remains
in synoptic and convection-allowing guidance regarding convective
timing, density and initiation location this afternoon/evening over
the "slight" area.  Based on planar surface progs and forecast
soundings from the various models, this is related in large part to
two factors:
1.  Weak but consistent large-scale subsidence behind the early
shortwave trough, and
2.  Differences in heating/mixing on both sides of the dryline,
which will influence amount of low-level lift, and on mesoscale
positioning of the dryline itself.  Convective-scale forcing is most
likely to be maximized near the dryline/cold-front intersection,
whose most probable position at the time of consensus weakest
moist-sector MLCINH (around 22-23Z) should be between OKC-TUL. 
Additional convection may develop along the front to the north/
northeast into southeastern KS as well.  Elevated thunderstorms are
also expected this evening into tonight over the Ozarks toward parts
of the mid Mississippi Valley, with marginal hail being the main
concern.

...OR west of Cascades...
Isolated to widely scattered thunderstorms are expected to move
ashore, and perhaps develop near the coast and move inland as well. 
The most intense cells may beco*e marginally severe.  Behind an
initial frontal band that precedes the leading shortwave trough,
large-scale lift/cooling in midlevels will steepen low/middle-level
lapse rates, both acco*panying the marine layer and over nearby land
areas.  Despite the cool surface temperatures over water, this
should yield surface-based convective inflow parcels with minimal
MLCINH, and MLCAPE in the 100-400 J/kg range (highest inland where
any pockets of sustained diabatic heating can develop).  Nearly
unidirectional deep-layer flow is expected, but because of the
strong mid/upper flow, effective-shear magnitudes in the 35-45-kt
range are possible, supporting potential storm-scale organization.

..Edwards/Dean.. 04/20/2022