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> July 8-? Plains/MW/OV/GL Severe Weather, Medium-range: 4-8 day forecasts and observations
post Jul 17 2018, 08:59 PM
Post #21

EF-3 (Very Frequent Poster)

Group: Member
Posts: 715
Joined: 20-January 12
From: South Central Minnesota
Member No.: 26,362

Thursday could look scary across the upper midwest if the atmosphere can recover. MPX hinting at tornadoes already

The main concern for this system is the potential for a repeat of
August 16 2017, which had several tornadoes across Minnesota, and
5 to 9 inches of rain across southwest Minnesota. Both systems had
a compact upper level wave with a deepening surface low, but there
are stark differences.

The first is that this wave is driven by a negatively tilted upper
level jet with a zonal/northwest component as compared to the
southwest flow from August 16, 2017. In addition, the surface low
is nearly steady state or barely deepening on Thursday, while back
in August the low was quickly deepening. These differences along
are why the CIPS analogs do not match up these two weather events.

As for the hydro threat, Pwat values will be near 2, but this
system has limited CAPE and there is not a focused area for ascent
such as a stationary front. The best potential for heavy rain is
northwest of the surface low across west central Minnesota in the
trowal region of the storm. With that said, there is considerable
differences in the surface low track so won't get too hung up on
any particular region at this time.

As for the severe/tornadic threat. The low level hodographs show
tremendous veering and have 0 to 1 and 0 to 3 km helicity values
of 200 to 300 m2/s2. The limiting factor for realizing this
potential is the lack of surface-based instability. If the
atmosphere is able to recover and manage a few hundred joules of
SBCAPE, then we could have the potential for mini-supercells and
tornadoes. At this points think surface-based storms will be
difficult to achieve given the widespread nature of the

NAM 3k has a strong low coming across Minnesota with supercells.
Attached Image


Severe Thunderstorm Watches: 5

Tornado Watches: 0

Severe Thunderstorm Warnings: 1

Tornado Warnings: 0

Largest hail: .25''

Strongest Wind Gust: NA

Warmest Temperature: 102F

90F+ days: 14

Highest Heat Index: 108F

Heat advisories: 6

Excessive Heat Warnings: 1
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post Jul 18 2018, 12:31 AM
Post #22

EF-1 (New Member)

Group: Member
Posts: 80
Joined: 1-April 18
From: KCAK
Member No.: 32,065

Interesting analogue of 08/16/17. I'd be all for that pattern repeating as that August and September were pretty active in the Midwest/GL. Finally, something to watch!
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