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Tim from Springfield (IL)

July 5-8 Severe Threats

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SPC already has a Day 3 Enhanced for WI, with much of IA, MN, and NW IL under a Slight, on Thursday:

http://www.spc.noaa.gov/products/outlook/day3otlk.html

...Upper Mississippi Valley into the Great Lakes...

   Richer low-level moisture with upper 60s to near 70 F dewpoints
   resulting from both evapotranspiration and advection will reside in
   pre-frontal warm sector. Meanwhile plume of steeper mid-level lapse
   rates will advect into this region, contributing to moderate to
   strong instability as the boundary layer destabilizes during the day
   with MLCAPE approaching 3000 J/kg. Winds aloft will strengthen with
   amplification of the northern stream trough. Southwesterly low-level
   winds veering to west and northwesterly with height will further
   augment vertical shear with 0-6 km magnitudes of 40-50 kt.
   Destabilization and forcing for ascent accompanying the
   southeast-advancing shortwave trough should contribute to
   thunderstorm initiation by early afternoon over the upper MS valley
   region, and this activity will subsequently develop southeastward
   into the evening and overnight. Organized storms including
   supercells and bowing line segments are likely with large hail and
   damaging wind the primary threats.  

 

 

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SPC also not ruling out severe for Friday in the OV:

http://www.spc.noaa.gov/products/exper/day4-8/

Day 4-8 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0414 AM CDT Tue Jul 04 2017

   Valid 071200Z - 121200Z

   ...DISCUSSION...
   Model consensus is that the synoptic upper trough will amplify over
   the eastern U.S. with an upstream ridge persisting in the west at
   least through day 7. Several shortwave troughs embedded within the
   eastern U.S. trough will move through the Ohio Valley and Northeast
   States. The amplifying upper trough will be associated with a cold
   front that will move through the Northeast States and Ohio Valley
   day 4 (Friday) and the Mid Atlantic and Southeast States day 5
   (Saturday) where it will stall. A moist, pre-frontal warm sector
   will support moderate instability, and some threat for severe storms
   will exist Friday from the Ohio Valley into the Northeast U.S.,
   shifting into the Mid Atlantic and Southeast States Saturday. At
   this time too much uncertainty exists regarding timing of cold front
   and effects of any ongoing convection on warm-sector destabilization
   to introduce a categorical risk area.

   ..Dial.. 07/04/2017

 

And SPC isn't ruling out tomorrow's marginal in parts of the sub to go slight:

http://www.spc.noaa.gov/products/outlook/day2otlk.html

 ...Northern Plains through upper Mississippi Valley and Great
   Lakes...

   Richer low-level moisture with mid to upper 60s F dewpoints will
   advect into this region, contributing to potential for moderate
   instability. A weak front or surface trough will advance through MN
   and Wi during the day in association with a weak, low-amplitude
   shortwave trough. Storms may redevelop along this boundary during
   the afternoon, primarily from IA into WI and the Upper Peninsula of
   MI. This region will reside along the southern fringe of modest
   winds aloft, and vertical shear will remain less than 35 KT
   supportive of multicells. A few of the storms may become capable of
   producing strong wind gusts from late afternoon through early
   evening.

   Farther upstream, some potential will exist for a few storms to
   develop within zone of deeper mixing in vicinity of a pre-frontal
   trough across western ND during the afternoon. Other storms may
   develop overnight within pre-frontal warm advection regime and
   spread into northern MN. Storms in these areas will be embedded
   within stronger winds aloft supporting some potential for
   organization. However, considerable uncertainty persists regarding
   storm coverage. Will maintain marginal risk category for now, but
   this region will continue to be monitored for a possible slight risk
   in later updates.

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Was shocked when SPC didn't include a risk area for Thursday on their 4-8 outlook. 

 

This looks like a mixed mode event. Strong supercells with very large hail, some tornadoes (possibly strong) mixed in with bowing segments, especially near the effective/warm front. 

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42 minutes ago, bjc0303 said:

Was shocked when SPC didn't include a risk area for Thursday on their 4-8 outlook. 

 

This looks like a mixed mode event. Strong supercells with very large hail, some tornadoes (possibly strong) mixed in with bowing segments, especially near the effective/warm front. 

Thursday would be the day 3 outlook.

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Just now, snowlover2 said:

Thursday would be the day 3 outlook.

I think he was meaning yesterday's day 4-8 outlook, as Thursday would've been day 4 and there was no area outlined.

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3KM is nasty for parts of MN, IA and west-central WI. Considering trying to get Friday off so my chase range isn't limited by having to be back by 3AM and then working on no sleep.

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This is the HRW-NMMB for Thursday evening. It's one of a few possible solutions that show severe thunderstorms generally in MN/WI, similar to the SPC day-3 enhanced risk, (issued 7/4.) Chance of thunderstorms/severe weather in Ohio may be of interest to a few people on this board, even though it isn't related to the MN/WI risk area.

 

FTFVSKX.jpg

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7 hours ago, IllinoisWedges said:

Am I one of the only ones not seeing an insane event for Thursday? If so, please do explain to me why it looks different than every other typical event so far this year. 

It doesn't look like anything crazy. A cold front drops through from the northwest.

Given rich boundary layer moisture and strong heating supporting upwards of 2000-3000 J/kg MLCAPE, veering winds with height (SW near the surface to NW at 500mb) and more than adequate deep layer shear magnitudes, large hail and damaging winds seem likely with initial discrete/semi-discrete supercells. 

Convective evolution with time is a bit unclear. While upscale growth into a linear system would "enhance" a damaging wind threat, most of the short range guidance seems to favor more of a broken band of storms. If this does happen, one couldn't rule out an isolated tornado threat by early evening. Still, if there is a tornado or two on a northwest flow day with large CAPE and ample shear in July in the upper Midwest, that's nothing unusual at all. 

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So far SPC just has a marginal along the OV (including most of OH, SE 2/3 IN, and S IL) for Friday on their D3 outlook this morning. 

A slight could be forthcoming for Friday perhaps as early as tomorrow's first Day 2 outlook.

http://www.spc.noaa.gov/products/outlook/day3otlk.html

...Ohio Valley area...

   A moist pre-frontal warm sector with dewpoints in the upper 60s to
   around 70F will reside across the OH Valley into a portion of the
   Northeast States. Destabilization of the boundary layer will result
   in moderate instability in the presence of modest mid-level lapse
   rates. At least a modest increase in deep-layer winds is expected
   with 30-40 kt unidirectional westerly between 2-6 km. A significant
   upper speed max is forecast to move southeast into the Great Lakes
   and Ohio Valley region, but this feature will remain post frontal.
   Nevertheless...storms should redevelop within the weakly capped warm
   sector and along the southeast advancing cold front during the
   afternoon. Vertical shear from 25-35 kt will support primarily
   multicells with storms evolving into clusters and line segments. A
   few strong to damaging wind gusts will be possible through early
   evening. Trends will continue to be monitored for a possible slight
   risk in later updates.
 

 

 

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BTW, the latest D1 just came out a half-hour ago--still has a small slight risk for central MN, and now a larger strip of NE ND.  Brief tornadoes can't be ruled out:

http://www.spc.noaa.gov/products/outlook/day1otlk.html

...ND/MN...
   The primary band of westerlies is across Canada today, with the
   southern fringe of stronger flow aloft over portions of ND/MN/WI.
   Full sunshine is occurring in this region, with dewpoints in the mid
   60s to lower 70s yielding afternoon MLCAPE values over 3000 J/kg.
   Forcing for ascent is weak, and water vapor loop suggests only
   subtle upstream features that might aid in convective initiation.
   This suggests that overall coverage of storms will be low.
   Nevertheless, forecast soundings show thermodynamic and shear
   parameters favorable for organized/supercell storms later today.
   Large hail is likely the main threat, as storms may remain isolated
   and maintain discrete mode.  However, damaging winds or a brief
   tornado cannot be ruled out.
 

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4 hours ago, Quincy said:

...a tornado or two on a northwest flow day with large CAPE and ample shear in July in the upper Midwest, that's nothing unusual at all. 

This. These are also the kind of days where a higher-impact event can sneak up on you in this time of year/region of the country if everything pans out just right (or wrong, depending on your perspective). Here I'm thinking of days like Oakfield, Plainfield, Roanoke, June 23, 2004 (17 tornadoes in WI including two F3s, one of them killer), and August 18, 2005 (record-setting 27 tornadoes in WI including killer F3).

Not saying something like that appears likely tomorrow based on current model progs, but history shows it's one of those days to keep an eye on.

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11 hours ago, CheeselandSkies said:

This. These are also the kind of days where a higher-impact event can sneak up on you in this time of year/region of the country if everything pans out just right (or wrong, depending on your perspective). Here I'm thinking of days like Oakfield, Plainfield, Roanoke, June 23, 2004 (17 tornadoes in WI including two F3s, one of them killer), and August 18, 2005 (record-setting 27 tornadoes in WI including killer F3).

Not saying something like that appears likely tomorrow based on current model progs, but history shows it's one of those days to keep an eye on.

Upon deeper investigation of today's threat, analogs feature quite a bit of severe events from southern MN/IA into WI. Along with about 1/3 of analogs producing one or more tornadoes in the northern IA vicinity, 7/6/14 can be identified as a close analog to the expected environment later today. 

General similarities can be seen in the upper levels, with fairly close matches in the sfc-3km layer, including capping, frontal placement and low level shear. 

That event produced numerous weak tornadoes in Iowa, along with a couple of longer-lived, destructive ones. The 00z 7/7/14 DVN sounding is very similar to forecast soundings across central IA around 00z Friday. 

Convective evolution looks similar to what is expected tomorrow as well. Isolated storm coverage with concerns about longevity of storms, given relatively warm 800-700mb temperatures. Even the SPC day 1 discussions from 7/6/14 sound similar to what's being said this time around. 

Iowa is a fickle state, but today's event could very well be a bit sneaky. Isolated storm coverage, favorable shear (speed, directional and orientation with respect to the cold front). Early day convection doesn't appear to be a big concern and even if there was any, it would probably be minimal and could locally enhance the severe threat, were outflow boundaries to be evident. While capping may delay convective initiation until after 22z, forecast soundings in the immediate prefrontal warm sector show little to no remaining MLCIN by 23-00z.

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HRRR has been all over the place but latest run is not encouraging for central and southern WI (or IA/SE MN) seeing anything of significance. Satellite does show some outflow boundaries in the latter area so will continue to monitor. 12Z 3KM NAM meanwhile was much more bullish on convective coverage and intensity.

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57 minutes ago, CheeselandSkies said:

HRRR has been all over the place but latest run is not encouraging for central and southern WI (or IA/SE MN) seeing anything of significance. Satellite does show some outflow boundaries in the latter area so will continue to monitor. 12Z 3KM NAM meanwhile was much more bullish on convective coverage and intensity.

It's definitely an odd (or at least unclear) setup. All guidance has been highly variable, from NCAR ensembles to HopWRF, HRRR, 3km NAM, etc. The trend has been for already (progged) minimal large scale forcing to be even more nebulous. Forecast soundings don't show a significant cap, yet convective temperatures appear out of reach for most of the warm sector. 

The final evolution may very well include a few cells trying to go up in WI, while more robust activity is delayed until after 01-02z, but as nocturnal cooling takes place, the window for severe could be quite limited. 

An already conditional threat becomes even more unlikely with westward extent across Iowa, despite a seemingly favorable CAPE/shear overlay. Negligible forcing will likely be a large limiting factor.

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Tonight's 0z NAM having all of the Lower Great Lakes in play for a severe weather risk on Friday. Attached sounding is for the Findlay area at 21z on Friday.

mlcape.us_mw.png

nam_2017070700_021_40.99--83.63.png

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Looks like a possible mini bow could be forming and aiming for Wabash and Huntington counties this noon EDT.  But as new SPC meso disc stated we may have to wait till later for increased svr wind potential.

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I would anticipate a new watch being issued west and south of the current watch as outflow moves westward and current svr cells in nw In continue to strengthen.  

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23 minutes ago, Indystorm said:

I would anticipate a new watch being issued west and south of the current watch as outflow moves westward and current svr cells in nw In continue to strengthen.  

Severe cell skirted just to my south with hail.  From what I could tell, no hail where I am.

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