Pueblo, CO...Fargo, ND...Missoula, MT...Rapid City, SD...Great Falls, MT...
Probabilistic Tornado Graphic
Probability of a tornado within 25 miles of a point. Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk
Area (sq. mi.)
Some Larger Population Centers in Risk Area
Billings, MT...Fargo, ND...Rapid City, SD...Bismarck, ND...Grand Forks, ND...
Probabilistic Damaging Wind Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Amarillo, TX...Pueblo, CO...Fargo, ND...Missoula, MT...Rapid City, SD...
SPC AC 041251
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0751 AM CDT Sat Jul 04 2020
Valid 041300Z - 051200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
SOUTHWESTERN/CENTRAL MONTANA TO NORTHWESTERN MINNESOTA...AND OVER
PARTS OF THE SOUTH-CENTRAL HIGH PLAINS...
Severe thunderstorms are most probable this afternoon and evening
from parts of southwestern/central Montana to northwestern
Minnesota, and over parts of the south-central High Plains.
In mid/upper levels, the amplitude of ridging over the north-central
CONUS will diminish through the period. This will occur as a series
of variably amplified shortwave perturbations cross the northern
Rockies, and international-border region between MT and Lake
Superior. A small, initially closed cyclone was evident in
moisture-channel imagery over southern BC, with shortwave trough
southwestward across coastal WA and offshore OR. This will become a
fully open-wave trough today, reaching central MB, southeastern BC,
and northern/southwestern OR by 00Z. By 12Z, the trough should
deamplify somewhat, assume a less-positive tilt, and be aligned
along the SK/MB border then southwestward over western MT. In
downstream difluent flow aloft, a perturbation now over ND will
eject across northern MN and adjoining ON by 00Z, with its southern
lobe crossing the Boundary Waters region overnight.
Farther south, a broad/elongated perturbation -- with several
embedded vorticity maxima -- was apparent over southeastern UT,
eastern AZ, eastern UT, and western/central CO. This feature should
move slowly eastward across the remainder of CO and much of northern
NM through the period. To the east and southeast, a very broad area
of modest cyclonic flow, with several embedded (and mainly
convectively originated) vorticity maxima, will persist from the
Ozarks to the north-central Gulf and vicinity of the FL/GA line.
At the surface, 11Z analysis showed a quasistationary frontal zone
oriented northeast/southwest across southern MB, to north-central ND
and into an extensive area of convective outflow covering much of
the western Dakotas. A low was drawn over the Black Hills with a
trough southwestward across eastern WY. These boundaries should
remain near their present locations through most of today, except
where modulated by convective processes, given the lack of robust
upper-level influences. A weak cold front should develop over
central/southwestern MT today and move eastward, reaching
northeastern to south-central MT by 00Z.
Multiple episodes or clusters of thunderstorms are expected to
affect the outlook area through the period, offering a threat for
severe gusts and hail. The most probable among the scenarios
involves convection forming this afternoon ahead of the Northwest
shortwave trough, on the higher terrain of south-central/
southwestern MT and vicinity, then moving northeastward across MT
and organizing to severe levels near and behind the trailing surface
frontal zone. Activity may overtake that front and encounter richer
theta-e this evening into tonight.
Surface dew points off the mountains should range from the 40s over
west-central MT to low/mid 60s in eastern MT, with upper 60s and 70s
possible along and ahead of the outflow boundary over the Dakotas.
Activity moving off the higher terrain over the western/central
parts of the outlook area will encounter generally increasing
low-level moisture with eastward extent, as well as a diabatically
destabilized and well-mixed boundary layer over central MT.
Forecast soundings suggest MLCAPE should range from around 500-1000
J/kg in the west to over 2000 J/kg near the eastern MT border.
Vertical shear should strengthen somewhat ahead of the shortwave
trough, with time series of forecast soundings and planar progs
showing a rapid lowering of the level of the 50-kt isotach through
the upper/middle troposphere with time, over western/central MT.
Despite weak near-surface winds in most areas, 40-50 kt effective-
shear magnitudes are possible, suggesting supercell potential.
Outflows may aggregate with the formation of a forward-propagating
band or arc of convection this evening, converting the predominant
threat to wind with time.
Strong-severe thunderstorms also may develop near the outflow
boundary and related surface convergence/differential-heating zone
over eastern ND late this afternoon, with convection potentially
persisting into early evening. Weaker deep shear will exist than
over the northern High Plains; however, low-level shear/vorticity
may be maximized near the boundary to support at least transient/
heavy-precip supercell character within a more-dominant
multicellular regime. Steep low/middle-level lapse rates and rich
moisture will contribute to peak MLCAPE in the 3000-4500 J/kg range.
Mesoscale uncertainties preclude a more-focused unconditional
outlook at this time. However, given the potential CAPE/shear
parameter space available to any storm(s) that form, tornado
production and/or localized very large hail cannot be ruled out.
...Central/southern High Plains...
Isolated to scattered thunderstorms are expected to develop this
afternoon over the eastern ranges and foothills of the Rockies, from
the Laramie Mountains southward into the Sangre de Cristos,
including the Raton Mesa and Palmer Divide. Some of this activity
should persist eastward across the adjoining High Plains with a
threat for severe gusts and large hail. The greatest concentration
of convection and associated severe potential may occur for a few
hours late this afternoon into early evening ahead of the shortwave
trough and associated vorticity maxima, over portions of
southeastern CO, and northeastern NM, shifting into parts of the TX
Panhandle. After an initial hail/wind blend of threats, some of
this activity may aggregate outflows to produce a cold pool that
would forward-propagate eastward for a few hours before weakening.
To reflect this relative concentration, 15% wind/hail areas have
Although deep-layer flow will be modest, strong directional shear
and favorable storm-relative boundary-layer winds are evident in
progs across the corridor from southeastern CO to the northern TX/NM
border area. Strong/sustained diabatic heating is most probable
north of an area of clouds/precip now located over east-central NM,
northward to southeastern CO as well. Forecast soundings suggest
steep low-level lapse rates, well-mixed subcloud layers, and
sufficient moisture to support 1000-1500 J/kg MLCAPE, with large
DCAPE. Evening cooling/stabilization of the foregoing boundary
layer will reduce both convective coverage and severe potential,
with time and eastward extent tonight.
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z