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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0755 AM CDT Mon Jul 18 2022

Valid 181300Z - 191200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM
NORTHEASTERN MONTANA TO NORTHERN NORTH DAKOTA...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
NORTHERN PLAINS "ENHANCED" AREA AND EXTENDING EASTWARD TO UPPER
MICHIGAN...AS WELL AS OVER PARTS OF THE NORTHEAST...

...SUMMARY...
The greatest severe-thunderstorm threat will be for destructive,
severe gusts and hail today into this evening, from northeastern
Montana to northern North Dakota.

...Synopsis...
A broad, strong mid/upper-level cyclone will persist over the Four
Corners States, with a loosely organized synoptic trough extending
from Lake Huron to the Mid-South region.  The trough will split
today, with the northern portion breaking away and accelerating
eastward over the Lower Great Lakes to northern NY and PA by 00Z,
reaching eastern ME and Cape Cod by 12Z tomorrow.  The southern part
of the trough will move much more slowly through the period across
KY/TN and northern MS, reaching eastern KY and the AL/MS segment of
the Tennessee Valley by the end of the period.

Farther west, the height pattern around the north rim of the big
anticyclone will be suppressed by a strong shortwave trough and
embedded/co*pact cyclone -- now evident in moisture-channel imagery 
over WA.  The cyclone will move roughly eastward across northern MT
through the period, with trough extending southward and crossing
central/northern ID, MT, and northern WY.  By 12Z, the 500-mb low
should be over northwestern ND, with trough to the SD/WY line.

At the surface, a low ahead of the northern trough branch was
analyzed over eastern Lake Erie, with warm front across central NY
and southern New England. This warm front will move northward
through most of the region today.  A trailing quasistationary front
over southern Lower MI and southern/western WI will move
southeastward through the northern Appalachians as a weak cold
front, preceded by a surface trough east of the higher elevations.

Elsewhere, a low was drawn near GTF with stationary to slow-moving
warm front across northern ND and northwestern MN, into an area of
outflow over northeastern MN/northwestern WI.  A cold front was
drawn from the low across southwestern MT and southern ID.  By 00Z,
more of that cold front will emerge from the northern Rockies, 
arching from a surface low over southwestern SK across eastern to
south-central MT and northwestern WY.  By that time, the warm/
stationary front should extend from southeastern SK or extreme
northeastern MT to northwestern MN, still intermingling across
northern MN with residual/modifying outflow boundaries from earlier
convection.  A surface trough should extend from the northern ND
segment of the warm front across west-central SD to northwestern NE.
The cold front will overtake the trough overnight, with a triple-
point low possible over northeastern ND by 12Z, and cold front
southwestward across central/southwestern NE.

...Northern Plains to Upper Great Lakes...
Scattered thunderstorms are expected to develop near the cold front
this afternoon over central and northern MT, moving eastward to
east-northeastward, perhaps at the southern rim of a convective band
arching back into the low-level cyclone over Canada.  Convection
will encounter a progressively more moist/buoyant boundary layer
near the warm front as it move eastward across northeastern MT and
northern ND, offering the potential for damaging hail (from any
discrete or embedded supercells), as well as severe gusts.

Mass response to the progressive cyclone/trough will increase both
vertical shear and low-level convergence near the cold front, timing
favorably with diurnal heating and relatively minimized MLCINH over
western parts of the outlook area to support convective initiation. 
For the first few hours, convection should pass over a deep, well-
mixed boundary layer and encounter steep low/middle-level lapse
rates, supporting a corridor of 500/1000 J/kg MLCAPE generally north
of I-94, decreasing southward from there into drier near-surface
air.  Meanwhile, veering of low-level winds with height near the
warm front, beneath strengthening midlevel flow, will support long
hodographs with effective-shear magnitudes in the 45-60-kt range
near the international border, also decreasing southward.  A blend
of supercell and outflow-dominant/bowing multicell modes is
possible, hence the enhancement of both hail and wind probabilities.
Upscale evolution into a mainly wind-producing co*plex is more
probable with eastward extent, and much richer low-level
moisture/CAPE should be encountered across northern ND tonight as
the co*plex proceeds quickly eastward.

Farther east near the warm front and remnant outflows, DCVA and warm
advection preceding a subtle shortwave trough now over southeastern
MB are supporting sporadic strong convection over the Boundary
Waters region.  This activity will move further into an air mass
stabilized by outflow from an earlier MCS across northern MN.  In
the meantime, isolated hail/gusts near severe limits may be
possible.  From northern MN across northern WI and Upper MI, airmass
modification through diurnal heating and warm/moist advection may
support development of a few strong-severe thunderstorms this
evening and tonight, also posing a hail/wind threat.

...Northeastern CONUS...
Scattered thunderstorms should form from midday through early
afternoon over western/northern parts of the outlook area and spread
eastward/northeastward, offering scattered damaging winds, with at
least a few 50+ kt/severe gusts possible.  A few tornadoes also may
occur, especially over northern parts of the outlook area in the
eastern NY/western New England region.

A seasonally strong superposition of rich low-level moisture with
increasing large-scale ascent and favorable deep shear (ahead of the
ejecting northern trough segment aloft) will support convective
organization across the region.  Low-level lift should be relatively
maximized along the surface trough and outflow/differential-heating
boundaries.  MLCINH already is weak over the region, with surface
dew points co*monly in the upper 60s to mid 70s F, though only slow
diabatic heating is expected beneath thickening cloud cover related
to the approaching perturbation (and precursory areas of clouds/
precip upshear).  Despite that and modest midlevel lapse rates,
800-1500 J/kg peak/preconvective MLCAPE should develop.  40-50 kt
flow will beco*e co*mon in the 850-500-mb layer through mid/late
afternoon in the mass response to the trough aloft, aiding in
strong/locally severe gust potential via momentum transfer in the
most vigorous downdrafts.  Both quasi-linear convective
configurations and supercells are expected, with supercells more
probable as low-level and effective shear and hodograph sizes
increase northward.

...Mid-South and vicinity...
Widely scattered to scattered thunderstorms are expected to develop
this afternoon along outflow/differential-heating boundaries from
morning convection, with damaging to marginally severe gusts
possible.  

The slow-moving southern branch of the mid/upper trough will shift a
plume of large-scale ascent over the area.  This will be
conterminous with strong surface heating of a boundary layer
containing rich low-level moisture (upper 60s to mid 70s surface dew
points and PW co*monly 1.75-2.25 inches).  The net result
thermodynamically should be MLCAPE around 1500-2500 J/kg, but with
modest low-middle-level winds and weak deep shear indicating
predominantly clustered/multicellular storm modes.  Water-loaded,
dense cores in individual cells, as well as localized cold-pool
aggregations and related outflow, should post a predominantly
afternoon to early evening gust threat.

..Edwards/Mosier.. 07/18/2022