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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0750 AM CDT Sun Jul 17 2022

Valid 171300Z - 181200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF A
SWATH FROM THE OZARKS TO THE CENTRAL APPALACHIANS...

...SUMMARY...
Damaging thunderstorm gusts and isolated large hail are possible
today from the Ozarks to the central Appalachians.

...Synopsis...
In mid/upper levels, a strong anticyclone will remain centered over
the Four Corners region, with mean ridge northward across the
northern High Plains.  On both sides of that ridge, these shortwave
to marginally synoptic-scale troughs will strongly influence
downstream convective potential:
1.  A northwestern trough with embedded, co*pact cyclone now
centered over Vancouver Island.  The 500-mb low should pivot
southeastward then eastward over WA through the period, with related
height falls spreading west-east across MT this afternoon and
tonight.
2.  A messy trough now over the upper Mississippi and lower Missouri
Valleys, containing several vorticity lobes/smaller-scale shortwave
troughs.  The two most prominent embedded perturbations are apparent
in moisture-channel imagery over central/eastern MN and from IA to
northeastern KS.  An MCV precedes the latter over northern MO, as
evident in co*posite radar-reflectivity animations, and should eject
eastward to east-northeastward over the Ohio Valley region through
the period.  Meanwhile, the broader trough should extend from Lower
MI to northeastern AR by 12Z tomorrow, likely preceded over the Ohio
Valley and central Appalachians by more MCVs generated between now
and then.

The 11Z surface analysis showed a wavy, quasistationary front from
the southern New England coast across PA, northern OH/IN, central
IL, and northwestern MO, beco*ing a weak cold front from a low over
the Flint Hills southwestward across the northern TX Panhandle.  As
another low initially over northern IN (near an MCV) ripples east-
northeastward along the boundary, the trailing portion will beco*e a
cold front and move southward over most of IN, IL, MO, KS, northern
AR, and much of OK through the period.

...Ozarks to central Appalachians...
Scattered to locally numerous thunderstorms, in bands and clusters
along/ahead of the front, should affect much of this corridor
through this evening.  Though isolated severe gusts/hail may occur
within the broader area enco*passed by marginal probabilities, the
greatest concentrations of organized convection and severe potential
still appear likely from the Ozarks to the lower Ohio Valley, and
farther northeast in the mid/upper Ohio Valley to central
Appalachians region.  Damaging gusts will be the main threat,

The prefrontal boundary layer will be characterized by rich low-
level moisture, with surface dew points in the upper 60s to low 70s
F.  Though slowed somewhat by abundant cloud cover over much of the
region, diurnal heating of that moist air mass should steepen
low-level lapse rates and, in tandem with the rich moisture, grow
MLCAPE to near 1500 J/kg, locally to around 2000 J/kg.  The MCV over
northern MO will pass northeast of the western outlook area by peak
afternoon buoyancy, but large-scale lift and modest deep shear
related to the broader trough will aid in convective organization
and maintaining an environment for upscale growth.  Meanwhile,
another MCV -- initially over northern IN - will move eastward
across OH today, with its UVV plume and low-level mass response
aiding in lift to support strong-severe convection shifting from
parts of OH/northeastern KY into adjoining PA/WV.  A line or arc of
thunderstorms, with embedded bow/LEWP formations, should be the main
source for damaging to locally severe gusts in that region.

...Northwestern MN/northeastern ND region...
Isolated to scattered thunderstorms are possible over the region
this afternoon and evening, with a conditional potential for severe
gusts and isolated large hail.  The main uncertainty remains
convective coverage, given the substantial MLCINH expected to linger
over the region through the day, and how much lift along a weak
surface front/trough moving into the area from the west will be
needed to overco*e that, in concert with diurnal heating.  The
strongest deep-layer forcing and greatest convective coverage is
expected to remain north of the area, over parts of eastern MB and
adjoining ON.  However, any activity that can be sustained south of
the international border, amidst the stronger capping, will have the
potential for severe.

Forecast soundings, modified for diurnal evapotranspirative moisture
increase (dew points mid 60s to low 70s F) and heating, yield quite
favorable buoyancy, with MLCAPE up to about 3500-4000 J/kg. 
Low-level winds, through weak, will veer with height, and strong
upper-level northwesterly flow will aid in ventilation aloft for any
sustained convection.  Given the large CAPE but weak low-level
forcing, models (including CAMs and ensembles) unsurprisingly
exhibit great spread on convective coverage, from nothing at all on
the U.S. side to a supercell or two, to a dense, upscale-evolving,
forward-propagational cluster on either side of the border.  At this
time, the prudent course appears to be to stay the course, and await
a co*bination of 12Z and later model guidance and mesoscale
diagnostic trends before making further modifications, one way or
the other.

...Southwestern/central MT...
Widely scattered, high-based thunderstorms should develop over
higher terrain of southwestern MT and eastern ID from midafternoon
through early evening.  This is expected during a period when MLCINH
is minimized due to diabatic surface heating, and the eastern
fringes of increasing large-scale ascent preceding the WA upper
trough/cyclone spread over the area.  Convection should move
northeastward over a deeply mixed boundary layer with steep lapse
rates, but weak/marginal moisture.  Forecast soundings suggest
modest mid/upper-level lapse rates, also helping to limit MLCAPE to
under 500 J/kg over most of the area.  Still, downdrafts from fairly
fast-moving convection, directed into a favorable layer for
evaporative cooling, should result in some strong/isolated severe
gusts before this activity weakens through the evening.

..Edwards/Mosier.. 07/17/2022