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Winter 2020-21 Medium/Long Range Discussion


Hoosier
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Some initial thoughts on weekend system...

 

When I posted a few days ago, wasn't too optimistic because of the bad antecedent air mass and rain prior to any snow. What happened in the past obviously doesn't determine what happens in a different event in the future. But, the fact that good rain to snow scenarios are rare suggests that lots of things need to work out at this latitude, so to be skeptical in this range.

 

Give a nod to Euro for decent run to run consistency past couple days. But since it's the only model that's been showing this on the operational, want to see some multi-model support before getting more excited. While the EPS members trended better up until 06z run this morning, what I've noticed in the ensembles overall (including 12z GEFS) is that a majority the members with a solid hit favor areas north and northwest of here. The 12z UKMET looks like many of these ensemble members. It's gonna be a big time thread the needle to get a strong enough system to get good totals without it being biased farther northwest in the key synoptic features.

 

Also wanted to note to use caution in getting too excited by the 10:1 and Kuchera maps from the Euro. As modeled on recent runs, temps don't fall solidly below freezing until the end of the event, along with good cold advection aloft (850 mb) not arriving til Sunday morning. These are all reasons to lean lower than 10:1 for ratios. I'd suggest looking at the snow depth output from WxBell or weathermodels.com as a good first guess and then can assess reasons why you'd get ratios to 10:1 or higher in spots.

 

 

 

 

 

 

 

 

 

 

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.LONG TERM...(Thursday through Tuesday)
Issued at 231 PM CST Tue Dec 8 2020

The upper-level pattern for the rest of the week continues to show
ridging. There are a few changes/trends in the latest model runs for
this weekends potential winter storm. Models are now in better
agreement in taking the storm through the Great Lakes with no
appreciable precipitation for the MPX CWA. 12z GFS/ECMWF/CMC develop
a surface low near the Arkansas/Missouri border and track it southern
lower Michigan Saturday night. Ensembles lend more support toward
this solution with only a few outliers developing a phased system
that would track further north and west. So, what has changed since
yesterday? The northern stream of the jet appears more progressive.
This changes the jet dynamics for the potential storm. A more
progressive northern stream limits potential jet phasing resulting in
a weaker low-pressure system that tracks further southeast. Models
also slow the southern trough, keeping it positively tilted as wave
struggles to eject out of the southern CONUS. My suspicion is that
the trend toward a weaker system to the south and east will continue
if previous systems are any indication this year. Guidance may trend
it back toward the north and west as we get closer to the end of
week, but the bulk of the QPF should remain away from the CWA. This
is a highly complex set up in a split-flow pattern that should
deliver a winter storm for someone, just not for us. Looking beyond
the weekend, cooler weather returns behind the system with high
temperatures near freezing. A few weak systems are possible next
week, the first should track to the north with a chance for light
precipitation Tuesday afternoon.

 

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2 minutes ago, RCNYILWX said:

In that setup, your backyard would be screwed until winds flip northwesterly Saturday evening. Lake is still quite mild.

Sent from my SM-G965U using Tapatalk
 

so rainer for Alek....snow for everyone else. Winter is on.

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40 minutes ago, RCNYILWX said:

In that setup, your backyard would be screwed until winds flip northwesterly Saturday evening. Lake is still quite mild.

Sent from my SM-G965U using Tapatalk
 

It's a thread the needle setup in general, but even more for the city (talking about the heart of the city, not well inland/northwest like ORD) because of the residual lake warmth.  Not that it can't happen there, but it's trickier.  If you are talking 850 mb temps of like -2C or even -4C, that probably wouldn't be good enough to get significant accumulations downtown as long as the flow is onshore.  And forget about it if it's warmer than that.

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22 hours ago, Snowstorms said:

Extended MEI data in the link below. MEI stands for Multivariate ENSO Index. Slightly different than ONI but I find it more transparent. 1931-32 was a warm neutral. 1930-31 was a strong El Nino. La Nina didn't happen till 1933-34. 

https://psl.noaa.gov/enso/mei.ext/table.ext.html

Interesting. 1933-34 was apparently a huge winter for Ontario, New York State, and Quebec.

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00z NAM shows the hurdle lakeside in IL/WI.  It is cold enough aloft to snow but that marine influence is a problem.
Also shows marginal temps overall. Surface 0 line is way up in northwest IL valid 12z Saturday. Gonna need heavy rates to consistently overcome the boundary layer issues.

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