|D4||Thursday Aug 13 2020 - Friday Aug 14 2020
||D7||Sunday Aug 16 2020 - Monday Aug 17 2020
|D5||Friday Aug 14 2020 - Saturday Aug 15 2020
||D8||Monday Aug 17 2020 - Tuesday Aug 18 2020
|D6||Saturday Aug 15 2020 - Sunday Aug 16 2020
||(All days are valid from 12 UTC - 12 UTC)
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
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 highly unlikely during the entire
period (e.g. less than a 30% probability for a regional severe
storm area across the CONUS through the entire Day 4-8 period).
ACUS48 KWNS 100854
SPC AC 100853
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0353 AM CDT Mon Aug 10 2020
Valid 131200Z - 181200Z
...Thursday/Day 4 and Friday/Day 5...
On Thursday, the medium range models including the ECMWF, GFS, UKMET
and Canadian move an upper-level trough across the northwestern U.S.
and maintain southwest mid-level flow in the northern Plains. The
models are in general agreement that a corridor of moderate to
strong instability will develop across eastern North Dakota Thursday
afternoon. The models vary considerably on whether convection will
initiate along the instability axis on Thursday. If storms can
develop, then a severe threat would be possible, mainly from eastern
North Dakota into northwest Minnesota. But the potential is
conditional upon the strength of capping.
On Friday, model spread increases as some solutions move a cold
front southeastward into the Upper Mississippi Valley by Friday
evening while others develop a more persistent axis of moderate to
strong instability further west in the northern Plains. Which
scenario plays out will likely be determined by the timing of an
upper-level trough in the northwestern U.S. Thunderstorm development
could take place along the instability corridor, wherever it ends
up. If the slower solution pans out, then a severe threat would
again be possible in the northern Plains Friday afternoon and
...Saturday/Day 6 to Monday/Day 8...
Model differences from Saturday to Monday are significant. The ECMWF
moves an upper-level trough from the northern Plains into the Great
Lakes from Saturday to Monday while the GFS shows a relatively long
fetch of west-northwesterly flow in the north-central U.S. The
models do have an axis of moderate to strong instability in the
Upper Midwest although there is also variance among the solutions.
Thunderstorms could develop each afternoon and evening along the
northern edge of the stronger instability from the northern Plains
into the Upper Mississippi Valley. A severe threat would be possible
with any convective cluster that can develop and persist across the
northern edge of the warm sector. At this point, uncertainty is
considerable concerning the magnitude and spatial distribution of
any severe threat late in the Day 4 to 8 period.