SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0225 AM CDT Sun Sep 15 2019
Valid 171200Z - 181200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS TUESDAY INTO
TUESDAY EVENING ACROSS PARTS OF THE NORTHERN ROCKIES INTO THE
NORTHERN PLAINS AND PORTIONS OF THE UPPER MIDWEST...
...SUMMARY...
Strong thunderstorms may impact parts of the northern Rockies into
the adjacent northern High Plains, as well as parts of the Upper
Midwest, Tuesday, accompanied by at least some potential for severe
weather.
...Synopsis...
While mid-level ridging within the westerlies remains prominent
along an axis across the Great Lakes into Hudson Bay, large-scale
troughing may continue to evolve across the northwestern U.S. into
the central Canadian/U.S. border area, in association with several
progressive short wave troughs. The most significant of these
perturbations, including an embedded close low, is forecast to dig
into the Pacific Northwest Tuesday through Tuesday night, while a
compact but vigorous downstream impulse accelerates northeastward
out of the northern Great Basin through the Dakotas by 12Z
Wednesday. The lead impulse will be preceded by another
perturbation of lower latitude origins, which is generally forecast
to undergo considerable deformation while progressing northeast of
the Dakotas through portions of northwestern Ontario and the upper
Great Lakes region.
In association with this regime, modestly deep surface troughing, to
the lee of the northern Rockies at the outset of the period, appears
likely to shift eastward across the northern and central Plains,
while an embedded surface cyclone migrates from eastern Montana into
Manitoba. This is expected to be trailed by a cold front, which
probably will begin to overtake the surface troughing across the
northern Plains by late Tuesday night.
Seasonably moist boundary layer air supportive of moderate large
CAPE may initially be focused along the western periphery of
low-level ridging, across eastern portions of the northern Plains.
Little change appears likely through the period, with a 30-50 kt
south-southwesterly 850 mb jet being maintained along an axis from
Kansas into Minnesota.
...Wyoming through the northern High Plains...
Although low-level moisture may be rather limited, lower/mid
tropospheric lapse rates are expected to become steep with fairly
strong daytime heating and boundary layer mixing. Coupled with
mid-level forcing for ascent and cooling associated with the
vigorous short wave trough progressing out of the Great Basin,
destabilization is expected to become sufficient to support
thunderstorm development. This may initiate by midday Tuesday
across the higher terrain of western into central Wyoming, before
perhaps organizing and propagating northeastward and eastward into
the high Plains by the evening. Substantial sub-cloud evaporative
cooling probably will aid downward mixing of higher momentum air,
including 30-70 kt southwesterly flow in the 700-500 mb layer,
resulting in at least scattered strong to severe surface gusts,
before the onset of diurnal cooling across the Plains.
...Northern and central Minnesota...
More uncertainty exists across this area, but the development of
moderately large CAPE in the presence of 30-50 kt
south-southwesterly flow in the 850-700 mb layer offers at least
conditional severe weather potential. Lower/mid tropospheric warm
advection, either early in the day in association with the lead
perturbation, or during the evening in advance of the more vigorous
approaching impulse, may support the initiation of storms. If this
occurs, potential exists for the evolution of an upscale growing
cluster of storms which could pose a risk for severe hail and wind.
..Kerr.. 09/15/2019
Read more
