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Dec 29-Jan 2 potential storm event


Brian D
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Significant differences between the NAM and RGEM at 84 hrs/12z Fri.  The RGEM is quite a bit colder at the surface and would be fairly ominous from an ice perspective.  

There is a lot of warm air flooding north though.  It comes down to how quickly the sfc/near sfc cold layer erodes as that warm layer aloft gets warmer/deeper.  Interesting to note on the NAM there is a fairly wide area where it is 32-33 degrees at the end of the run, so obviously any small changes could have important ramifications.

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Significant differences between the NAM and RGEM at 84 hrs/12z Fri.  The RGEM is quite a bit colder at the surface and would be fairly ominous from an ice perspective.  
There is a lot of warm air flooding north though.  It comes down to how quickly the sfc/near sfc cold layer erodes as that warm layer aloft gets warmer/deeper.  Interesting to note on the NAM there is a fairly wide area where it is 32-33 degrees at the end of the run, so obviously any small changes could have important ramifications.
Admittedly was much more focused on tomorrow's event today but I'd still be concerned about h9 verifying colder as long as you keep that northeast component from the surface high to the northeast. Going into 12/28/15, we were much more concerned about icing than the sleet because of the magnitude of the 850 mb warming but the low level cold wedge was still enough to produce mostly sleet north of I-80. I saw some of the 925 mb progs being warmer than previous runs, so if that occurs then the sleet concern will be unfounded, though we still have plenty of time for changes with this setup.

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Might not get here until next week if it keeps slowing down.  Not too surprising I guess given the type of system.

trend-ecmwf_full-2020122900-f084.prateptype_cat_ecmwf.conus.gif.9da6e097e89ba0b0fa11dba4e23568f1.gif

00Z ECMWF looks more concerning for a longer duration of ice on Friday north of I-80 and away from the lake. Dew points at 12z in the lower to mid 20s and still upper 20s to around 30 at 18z. Because of a weaker surface low and it tracking northeast from STL instead of more due north, winds become progressively more northerly.

 

Also at 12z the surface ridging across the western lakes trended stronger at 1028 mb. I still wonder if 925 mb ends up being colder because of the surface pattern favoring it, but if not, that run definitely ups the ante for icing concerns. Crazy thing is part of the event is still out to and beyond the end of the NAM range, so there's still plenty of time for changes. The 00z EPS has a pretty large west to east spread of individual member sfc low positions, with relative clustering on the more west and more easterly camps.

 

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4 minutes ago, purduewx80 said:

12Z soundings from DVN and ILX do show the incredibly dry air from ~650 to 900 mb. Dewpoints below -50C in that layer are among the lowest ever observed in both locations.

1481486479_ScreenShot2020-12-29at8_21_46AM.png.e9ce1789a15c14be2767e2231db7b0d2.png1333002135_ScreenShot2020-12-29at8_22_06AM.png.5d1996c966da835e7fae4c6fe28ee921.png

 

What does this insinuate?  taking longer to saturate atmosphere, lower than expected QPF?  colder than depicted? 

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27 minutes ago, kevlon62 said:

And the 5-10" highmark in extreme NW on the UP line approaching the state line. Should be a dandy to unfold in real time.

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Glad we have at least 3 McHenry posters all in different areas. Will be interesting to see how this turns out, expect Woodstock to do better than Cary and I. 

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