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Jan 28-29th Baroclinic Rider


Chicago Storm
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It's amazing how often we see these east/west oriented fronto snows end up along that route 20 corridor in Iowa, and southern WI to near IL border zone.  What makes it more interesting is how pretty much every time the models show it setting up further south in the mid range.  It's just poor modeling for this particular type of setup apparently.  

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Going to need the RGEM to score the coup. 6z still solid for N IL. Otherwise, everything is wagons north again (6z Nams, 6z HRRR, and 9z RAP, and 6z GFS slightly north). Think everyone had an idea this would go a bit further north in the end, but some of these moves are stupid in the past 24 hours. Still time for more changes I guess...

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1 hour ago, Chicago WX said:

Going to need the RGEM to score the coup. 6z still solid for N IL. Otherwise, everything is wagons north again (6z Nams, 6z HRRR, and 9z RAP, and 6z GFS slightly north). Think everyone had an idea this would go a bit further north in the end, but some of these moves are stupid in the past 24 hours. Still time for more changes I guess...

In the past the Canadian had been better at depicting these waves dropping south out of Canada. I think models are struggling where the baroclinic zone sets up after this first wave rolls through today. They should get a better idea by tonights runs. I think the bands will settle further south, like the rgem/gfs are showing 

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it doesn't look like the 12z rgem is gonna back down on its further south location of the banding, but it does have a more NE orientation once its get over by dtw.  Hopefully the bands can stay on an east to west line trough michigan. It would be a bummer to only get an inch while areas just 30 miles to the NW see 8-10. seen that horror picture too many times.

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Some (rambling) thoughts before I go to sleep:

While the 6"+ snow potential has clearly shifted north, I continue to believe that the NAM and CAMs are too aggressively far north in their depictions of accumulating snow.

For me, the NAM remains a toss with it still spinning up a meaningfully stronger weak surface low reflection and being way farther north with the stationary front. For it to show this, means it's also stronger aloft. The NAM can do better with warm advection setups, but if it's too strong with the system and low level mass response, the magnitude of 850 mb winds and warm advection will also be too strong to an extent, and affect placement of mesoscale banding.

Even though the ECMWF shifted north with the heaviest banding, if you still want snow in northern Illinois, important to note that the ECMWF and its ensembles have 9 km resolution, so it's not like you can toss it for being a too smoothed out global model. The near 0.2" QPF gets down to around I-88, so with higher than 10:1 ratios, still can put you in 3+ range.

Tomorrow evening into the overnight, as cold advection starts to increase, large scale forcing will also increase (modest mid level support and upper jet right entrance region), expecting light to moderate snow north of I-80, with a threat for freezing rain south. Wouldn't be surprised if the backside snow lingers all the way into Sunday morning.

If you're looking for sources of error - check out the non-NAM and RAP/HRRR depiction of 850 mb fgen tomorrow - still over northern IL. It appears the sweet spot for the fgen response may be in 850-700 mb layer, though the models can certainly err in the placement of response to an fgen circulation. Sometimes low level response can be more dominant, or you can get dual banding.

Mesoscale snow band forecasting is essentially forecasting convection, so it's more challenging and uncertain than already tough winter weather forecasting. The GEMs (and 2.5 km HRDPS) continue to be stubbornly steadfast in their more southerly solutions and the GFS has trended north since yesterday, but still gets 1/4"+ liquid equivalent down to the I-80 corridor (slight improvement from 06z).

I certainly wouldn't discount pessimism about getting the higher end amounts down into the heart of the metro, but gut feeling is decent accums (~2-4") get down to a bit south of I-88, and the northern tier is still in play to get into the heavier banding. Just not ready to buy into the CAM idea of little/no snow south of the WI state line. Also not ready to buy into the Canucks scoring a total coup on this, though it sure would be nice





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