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2021 Short/Medium Range Severe Thread


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The final issue for the short term and the one that is likely to
have the greatest impact on just exactly how Thursday plays out
focuses on the expectation of a mesoscale convective complex to
organize across the upper Midwest Wednesday evening in tandem with a
strong upper level wave. Trajectories support a southeast moving
cluster that will likely produce severe weather Wednesday night
aided by an impressive near 50kt 850mb jet. The general movement on
the system would bring it into N/NE Indiana during the predawn hours
Thursday with at least some potential that the tail end of the
cluster works south into part of the northern forecast area.
Considering the possibility that this system will mature enough to
develop a cold pool...am almost anticipating that the convection
will develop further back on its southwest flank into parts of
central Indiana near daybreak Thursday.

The questions that remain are...how far S/SW into the forecast area
the storms can make it Thursday morning and what intensity will they
have when they arrive? The nocturnal jet will weaken by 12Z Thursday
and largely remain to the north of central Indiana. That would
suggest that if the convective complex becomes cold pool
dominant...at some point the storms will outrun their low level fuel
source...weaken and eventually diminish. At this point...that will
likely take place somewhere across the northern half of the forecast
area Thursday morning. Still a lot of details to work out...but
there is some merit that this could serve as the initial salvo in a
1-2 convective punch for the region by leaving a leftover boundary
for new storms to fire on later on Thursday. It also presents some
uncertainty with how much convective cloud debris departs Thursday
morning and how that might impact available instability for new
storms later in the day. 
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Next one, or two may be on the "radar," so to speak:

  During the Fri/D5 to Sat/D5 time frame, a weakening shortwave trough
   is forecast to move from the northern High Plains to the upper MS
   Valley, with low pressure developing over SD and moving into MN.
   Storms appear most likely Friday evening in a zone of warm advection
   from the Dakotas into MN, with marginal instability forecast. Storms
   are expected to persist through Sat/D5 into MN and WI as moisture
   and instability continue to increase. While there is potential for a
   few severe storms in this regime, the weakening wave decreases

   Behind this lead wave, a stronger shortwave trough is forecast to
   affect the northern Plains and upper MS Valley during the Sun/D7 to
   Mon/D8 period. Although predictability is low, this type of pattern
   may result in severe storms, as persistent southerly low-level winds
   bring a return of upper 60s and lower 70s F dewpoints to the region.
   Strong instability may develop, and the Dakotas, MN and WI remain an
   area of interest. If model trends persist, severe risk areas may be
   added in later outlooks.

   ..Jewell.. 08/02/2021


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Still hinting at it...

For the Sun/D6 to Tue/D8 period, there is little run-to-run
   consistency regarding a stronger upper trough that will affect the
   northern Rockies and northern Plains. Models show two distinct upper
   lows across southwestern Canada, with eventual trough amplifications
   across the northern CONUS. If these stronger troughs move over the
   northern Plains and upper MS Valley, they will likely favor severe
   weather, as a large reservoir of 70s F dewpoints and 3000+ J/kg
   MUCAPE will develop in advance. At this time, predictability is low
   to denote areal outlines, but the area of interest where severe
   weather may develop is currently eastern SD and NE, IA, southern MN
   and WI.

   ..Jewell.. 08/03/2021

Personally I haven't yet looked at any model output for this time frame.

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MKX's afternoon AFD...

Sunday through Sunday night: It appears the most active storms may
occur in this period. There is a rather potent wave that will be
riding through the area with an abundance of moist/unstable air in
place. Ahead of the low level trough a SSW 850 millibar jet is
proggd to strengthen during the afternoon/evening with srn WI in the
favorable left front cyclonic shear side. So given the combo of
dynamics and instability certainly some strong or severe storm
potential. In addition we could see heat indices reach the low to
mid 90s.

Monday through Wednesday:

The ECMWF and GEM favor a building ridge after the Sunday/Sunday
night shortwave. Meanwhile the GFS is busier with a flatter and
more active flow. Seeing indications that the heat will thus likely
build back with 925 temps likely back into the mid 20s celsius.
Another front and potentially decent dynamics may arrive towards
midweek setting the stage for a renewed bout of convection, possibly

So they seem to agree with SPC's thinking over the last few days of the possibility for two rounds in the Sun-Tue period. July/August picking up the slack for May/June, at least for some parts of the sub.

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The slasher (Thompson) from SPC upped tor probs to 5% over the tri-state area of IA/MN/WI for today.  Guess things are looking better for naders in that area.

EDIT:  I always used to joke that Thompson (who's prob my favorite SPC forecaster) is the "slasher" as he used to always come in and "trim the fat" away on outlooked areas that were usually overdone, and sometimes over categorized lol.  Seeing him actually upgrade probs was usually a very good sign.

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38 minutes ago, CheeselandSkies said:

Severe warned cell moving into Sauk County looks to have a bit of broad rotation with it. Might head up to do a little spotting (didn't really consider today a "chase" day) if it holds together.

Nope. A couple of those earlier storms to the northwest have shown some transient/low-end supercell characteristics on radar, but have quickly collapsed.

Looks like some slight clearing over far SW WI. We'll see if it's enough.

EDIT: Latest HRRR puts a beefy sup through southern Marquette/northern Columbia Counties around 00Z (7 PM CDT). Based on observed trends I think it's too far north and east with that, if anything like that forms at all.

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