Day 4-8 Severe Weather Outlook Issued on Jul 18, 2020
Updated: Sat Jul 18 08:58:03 UTC 2020
Day 4 Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
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
Tue, Jul 21, 2020 - Wed, Jul 22, 2020
D7
Fri, Jul 24, 2020 - Sat, Jul 25, 2020
D5
Wed, Jul 22, 2020 - Thu, Jul 23, 2020
D8
Sat, Jul 25, 2020 - Sun, Jul 26, 2020
D6
Thu, Jul 23, 2020 - Fri, Jul 24, 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 180856
SPC AC 180856
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0356 AM CDT Sat Jul 18 2020
Valid 211200Z - 261200Z
...DISCUSSION...
A convectively augmented shortwave trough may advance eastward
across parts of the mid MS Valley, OH Valley, Mid-Atlantic, and
Northeast from Day 4/Tuesday into Day 5/Wednesday. A moist and
unstable airmass should reside along/south of a weak boundary across
these regions. Modestly enhanced mid-level flow associated with the
shortwave trough overspreading a moderately to strongly unstable
airmass may encourage some storm organization. The overall severe
threat with this system appears marginal given rather weak
deep-layer shear forecast. Other convection may form across parts of
the northern/central Plains on Day 4/Tuesday and Day 5/Wednesday as
greater low-level moisture gradually spreads northward. However,
mid-level heights should generally be rising across the Plains in
this time frame as an upper ridge amplifies over the central CONUS
and Canada. This casts considerable doubt on overall storm coverage
and placement.
By late next week through the end of the period, medium-range
guidance suggests that one or more small-scale perturbations may
rotate around the upper ridge. An increase in severe potential may
be realized from Day 6/Thursday through Day 8/Saturday from portions
of the northern Plains into the Upper Midwest, Great Lakes, and
perhaps the Northeast, if this occurs in tandem with sufficient
low-level moisture return. However, the timing and evolution of
these low-amplitude features remain far too divergent in guidance to
accurately pinpoint areas of 15% or greater severe probabilities at
this time.
..Gleason.. 07/18/2020
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