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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0751 AM CDT Sat May 21 2022

Valid 211300Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF THE
SOUTHERN PLAINS INTO THE LOWER OHIO VALLEY...LOWER GREAT LAKES AND
NORTHEAST...

...SUMMARY...
Scattered severe thunderstorms capable of producing both damaging
winds and large hail should develop through evening from parts of
the southern Plains into the lower Ohio Valley, lower Great Lakes
and Northeast.  A tornado or two may occur as well.

...Synopsis...
The large-scale mid/upper-level pattern will continue to be
dominated by a positively tilted trough from northeastern Canada
across the northern Plains to the Great Basin and southern CA. 
Numerous shortwaves will be embedded in the associated cyclonic flow
over the northern Plains and western CONUS, and downstream southwest
flow across the Midwest and Great Lakes.  However, the great
majority of these, and of the fastest flow aloft, will remain behind
the surface front described below.  Exceptions will include MCVs
produced by ongoing convection over the Ozarks to IN.  A weak but
still well-defined southern-stream shortwave trough is apparent in
moisture-channel imagery over central/south-central TX, and should
weaken further as it moves northeastward to parts of east TX and AR
by this evening.

The 11Z surface analysis showed a cold front from southwestern QC
and southeastern Lower MI across western IN, south-central MO,
south-central OK, to between MAF-HOB, northwestward into central NM.
The front should move slowly eastward/southeastward by 00Z to
southern parts of QC/ON, northern IN, southern IL, southern MO,
extreme southeastern OK, and central/southwest TX.  By 12Z tomorrow,
the front should reach parts of OH, western KY/TN, northern LA, deep
south TX, and southern Coahuila.  A wavy warm front -- drawn
initially across portions of eastern NY/PA and northern NJ -- will
shift northeastward over most of New England through today.

...Southern Plains to Northeast...
Widely scattered to scattered thunderstorms are expected to develop
through the period (including ongoing clusters from parts of IN/OH
to northwestern AR).  While severe may occur at almost any time from
the most intense cells, the greatest concentration of potential
should be this afternoon, up and down the over 2000-mile-long swath.
Damaging gusts and large hail should be the most co*mon severe
threats, though a tornado or two may be possible (especially over
parts of western/northern Maine and the Ozarks to lower Ohio
Valley).

A lengthy corridor of 60s F surface dew points already is observed
from southeastern MO northeastward to northern NY, with upper 60s
and low 70s over much of AR and TX ahead of the front.  Areas of
cloud cover will slow diurnal heating over much of the corridor east
of the Mississippi River; nonetheless, preconvective MLCAPE of
1000-2000 J/kg should develop.  Buoyancy will be greater amidst
larger boundary layer theta-e and stronger heating over AR and TX,
with 2000-3000 MLCAPE co*mon.  Except from near the lower Great
Lakes across northern New England, and perhaps parts of northern AR,
substantial mid/upper winds and their contribution to deep shear
will remain well behind the front.  Near the Canadian border, some
supercell potential may persist from southern QC into northern and
northwestern ME this afternoon/early evening before weakening.  [For
severe-weather concerns in adjoining parts of Canada, refer to
Environment Canada public weather alerts for Quebec-south via
weather.gc/ca/warnings.]  Clusters of strong-severe thunderstorms
also may concentrate along outflow boundaries ahead of the front,
left by morning convection from parts of the lower Ohio Valley to
AR.

Elsewhere, isolated, localized damaging gusts or marginal hail may
occur this afternoon from pulse/multicell convection, across a broad
area of the South ahead of the cold front.

..Edwards/Kerr.. 05/21/2022