Day 4-8 Severe Weather Outlook Issued on May 17, 2020
Updated: Sun May 17 08:53:02 UTC 2020
Day 4 Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
15 %
61,294
407,293
Rapid City, SD...Dickinson, ND...Scottsbluff, NE...Sterling, CO...Williston, ND...
Day 5 Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Day 6 Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Day 7 Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Day 8 Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
D4
Wed, May 20, 2020 - Thu, May 21, 2020
D7
Sat, May 23, 2020 - Sun, May 24, 2020
D5
Thu, May 21, 2020 - Fri, May 22, 2020
D8
Sun, May 24, 2020 - Mon, May 25, 2020
D6
Fri, May 22, 2020 - Sat, May 23, 2020
(All days are valid from 12 UTC - 12 UTC the following day)
Note: A severe weather area depicted in the Day 4-8 period indicates 15%, 30% or higher probability for severe thunderstorms within 25 miles of any point.
PREDICTABILITY TOO LOW is used to indicate severe storms may be possible based on some model scenarios. However, the location or occurrence of severe storms are in doubt due to: 1) large differences in the deterministic model solutions, 2) large spread in the ensemble guidance, and/or 3) minimal run-to-run continuity.
POTENTIAL TOO LOW means the threat for a regional area of organized severe storms appears unlikely (i.e., less than 15%) for the forecast day.
Forecast Discussion
ZCZC SPCSWOD48 ALL
ACUS48 KWNS 170850
SPC AC 170850
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0350 AM CDT Sun May 17 2020
Valid 201200Z - 251200Z
...DISCUSSION...
Initially amplified mid-level flow may begin to break down by the
middle to latter portion of the coming work weak, as large-scale
western U.S. troughing accelerates northeast of the Great Basin, as
a vigorous upstream perturbation digs into the Pacific Northwest.
As the lead troughing pivots north of the central Canadian/U.S.
border and deamplifies, downstream mid-level ridging over the Upper
Midwest and upper Great Lakes region is forecast to weaken, and the
initially broad cut-off low to its south may devolve into a
low-amplitude wave and progress off the Mid Atlantic coast.
Overall, pattern predictability appears relatively low, particularly
into and through next weekend.
By the end of the period, the latest deterministic ECMWF suggests
that the stronger mid-latitude westerlies may tend to shift into
areas near/north of the Canadian/U.S. border. However, it indicates
that this still could be preceded by the emergence of fairly
significant troughing from the northern Great Basin into the
northern Plains, which could be accompanied by some organized severe
weather potential.
At the present time, though, the most prominent and certain severe
weather potential through this period appears on Wednesday. This
probably will be focused in a narrow corridor near deep surface
troughing across the northern high Plains, where moisture may be
sufficient to support modest CAPE, in the presence of steep lapse
rates. And deep-layer shear may become strong enough to contribute
to organized convection capable or producing severe hail and strong
surface gusts.
..Kerr.. 05/17/2020
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