SPC AC 210049
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0749 PM CDT Fri Sep 20 2019
Valid 210100Z - 211200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHERN PLAINS AND CENTRAL HIGH PLAINS...
Scattered severe storms capable of producing wind damage, isolated
large hail and a couple tornadoes are possible this evening across
parts of the northern Plains, with more isolated severe storms
possible in parts of the southern High Plains.
...Northern Plains/Central High Plains...
The latest water-vapor imagery shows an upper-level low over the
northern Rockies with southwest mid-level flow over the northern
Plains. A couple perturbations in the flow appear to be moving
across the northern Plains. The first is located in central North
Dakota where numerous thunderstorms are ongoing. The second is
located in western Nebraska where scattered thunderstorms are
ongoing. At the surface, a cold front is located from far
northeastern Wyoming northeastward into central North Dakota. To the
east of the front, a moderately to strongly unstable airmass is
present. This is coincident with moderate deep-layer shear which
will support a severe threat this evening. The mass of convection
over east-central North Dakota is expected to organize into a nearly
continuous line and move slowly east-northeastward. This line will
likely be accompanied with wind damage and isolated large hail. More
discrete cells should continue to develop to the east of this line
across eastern North Dakota and northwestern Minnesota. The stronger
cells within this cluster may obtain supercell characteristics and
have isolated large hail, wind damage and a tornado or two...see MCD
Further southwest across northwest Nebraska and central South
Dakota, a low-level jet will strengthen this evening. In response,
thunderstorm coverage should gradually increase as storms develop
across southern and central South Dakota over the next few hours.
The strengthening low-level jet will create long hodographs
favorable for rotating storms. A few that become supercells will
have potential to produce large hail and an isolated tornado threat.
As storm coverage becomes more numerous late this evening, wind
damage and hail should become the predominant severe threat.
The latest water-vapor imagery shows southwest mid-level flow over
the southern Plains with a minor shortwave trough located over
southern Oklahoma. Scattered thunderstorms are ongoing near the
shortwave trough. Near the trough, the airmass is moderately
unstable with 0-6 km shear in the 30 to 35 kt range. This should be
enough for a marginal severe threat for another hour or two as a
bowing line segment moves eastward across northwest Texas and far
southern Oklahoma. Isolated damaging wind gusts and hail will be
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