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Jan 24-26th Potential Something Part 2


Chicago Storm
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Evening update from RC

 

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1055 PM CST Sun Jan 24 2021

.UPDATE...
1015 PM CST

The main tweak to the forecast for Monday-Tuesday winter storm was
a bit of an upward adjustment in ice accumulations for areas near
and south of the Kankakee River. No changes were made to the going
winter headlines. It`s possible that the snow starts a bit later
for portions of northern Illinois, more after sunset than prior to
it, but again didn`t change start time of any of the headlines.

Our burgeoning storm system can be seen getting going on water
vapor imagery this evening. Another feature of note is strong
drying with a jet streak racing from Mexico into southwest Texas.
This dry air will be located at and above 500 mb and could be a
wild card in the snow on Monday evening. The overall flavor of
this storm system has changed due to an earlier intensification
and occlusion process, with ingredients maxing out over the
central Plains and into parts of Iowa. There`s still favorable
moisture and forcing to get into moderate to even heavy snowfall
rates late Monday into Monday evening, but with the synoptic
system gradually weakening, and also some of the moisture probably
shunted southeast by expansive convection south of the OH River,
models have steadily and slowly backed off on QPF.

Turning back to the h5 dry air wild card, it is one because also
being advected northeastward with this air mass aloft is very
steep mid and upper level lapse rates (7.5 to 9C/km above 550 mb).
While some forecast soundings show the DGZ not fully saturated due
to that h5 dry air, the potential for convection (slantwise or
upright) given such impressively steep lapse rates aloft makes it
difficult to predict how it will play out. Could make a case for
lower snow ratios and less efficient accumulation, but if
convection breaks out, that could quickly saturate the entire DGZ
and cause heavier snowfall. All in all, didn`t make any
appreciable changes to the snowfall amounts and going message,
though aside from lake enhancement, possible that some parts of
the area end up on lower side of the range offered in the WSW.

A warm nose aloft (around 850 mb) is still progged to lift into
the southern 1/3 or 1/4 of the CWA, so would expect a changeover
to freezing rain in parts of our far south, probably with a
narrower zone where sleet is probable in between the freezing rain
and snow areas. Another thing to watch is the northward progress
of a 700 mb dryslot, which would scour out ice in the DGZ and
could change areas over to a freezing drizzle for a time late in
the evening into the overnight. Favored for this potential would
be south of I-88. Looking ahead into Tuesday, latest guidance
coming in supports prolonged period of light to moderate snow on
Tuesday under mid level forcing, with lake enhancement into
northeast Illinois. Noting that lake effect parameters do get
more favorable after synoptic snow winds down later Tuesday, with
a signal that there could be accumulating lake effect snow for
portions of northeast Illinois and perhaps extreme northwest
Indiana all the way into Wednesday, which the midnight shift will
assess.

Castro
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GEFS still nice for northern IL, so we have that going for us. I think the best way to look at this event now is one of managing expectations. A few days ago, it looked like it could be something special. Now it trended away from that but it still should be the single largest snow event for many of us in the metro in a while. Also the winds look like they will perform. The lake assist should be nice for parts of Lake and Cook County and LES should continue beyond the synoptic snow Tuesday night into Wednesday. So taking it for what it is, it won't be a bad event.

Sent from my SM-G965U using Tapatalk

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Gonna back off a bit on the synoptic call.  Originally went 6-8" but now I'd go 5-6" imby.  

As far as the lake effect Tuesday night/Wednesday, prelim guess on that is 2-4".  So if both things work out, then it would be 7-10" by the end of Wednesday which would be delightful given how things have been going.

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3 hours ago, weathafella said:

And GFS plunks 30 in BOS by d10.

I missed a lot of big storms since moving to Michigan in 2005, but I did get 24” near Framingham a couple months before I moved in January 2005, and lucked out when visiting my parents the week of the firehose storm in March 2013(?) with 20”. 

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4 hours ago, Hoosier said:

Gonna back off a bit on the synoptic call.  Originally went 6-8" but now I'd go 5-6" imby.  

As far as the lake effect Tuesday night/Wednesday, prelim guess on that is 2-4".  So if both things work out, then it would be 7-10" by the end of Wednesday which would be delightful given how things have been going.

pretty much my call exactly, although 4" of LES here would be high-end for sure

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7 hours ago, RogueWaves said:

At least the drying and dying seem to have taken a pause. The bar is set so low for me personally, this will have to work really really hard to NOT be my biggest event of the season. You guys in SEMI on the other hand..

The bar is a 42hr duration 3.7” event. It’s a pretty low bar here too. I’d take the 6z hrrr and run and get about 4”. 2-4” here still seems like a good call. Honestly wonder if we’ll even get a WWA

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4 minutes ago, mimillman said:

Wherever that band sets up is going to see good 3 day totals along the lakeshore.

I think we'd both be p happy with the 6z GFS

LES is so finicky here and there is never much room for error, you hope the colder guidance is right and you hope the weak wave passing south helps keep flow backed longer than expected

If I had to pick, I'd go Northbrook south to Jefferson Park or so for max combined totals locally, feels like frictional convergence effects are maximized there locally in similarish setups

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Just now, A-L-E-K said:

I think we'd both be p happy with the 6z GFS

LES is so finicky here and there is never much room for error, you hope the colder guidance is right and you hope the weak wave passing south helps keep flow backed longer than expected

If I had to pick, I'd go Northbrook south to Jefferson Park or so for max combined totals locally, feels like frictional convergence effects are maximized there locally in similarish setups

The number of times I've favored Cook county for LE and been disappointed is numerous. We'll see.

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