Hoosier

Re: Chicago, if you look at the GFS surface maps, it has lower pressures extending farther west than other models. This keeps the winds onshore longer and then once winds turn offshore, it is holding on to an exaggerated warm bubble over the city. After winds are offshore, it is hard to figure out why the city would be staying several degrees warmer than even the immediate suburbs when not talking about a radiational cooling situation.

Changeover time seems to be speeding up a bit. Looks like it could be mixing here by mid morning with all snow late morning.

Mentioned this already but you can see some lake enhancement showing up on the simulated reflectivity products on the western shores of LM tomorrow, which makes sense given sufficient delta T. With that of course brings the concern about too much marine influence, but the flow is actually sheared a bit so that as surface winds start turning more N/NNW, the 925 mb flow is still more out of the NNE. There could be a window to get some enhancement without the full blast effects of the marine influence but overall it shouldn't add on a lot to totals.

I will eat my hat and upload the vid for all to see if it is still 37 downtown at 10 pm tomorrow night.

There is no reason to hang on to that kind of warmth for that long after the winds have flipped offshore.

Ninja'd

The thing that doesn't make sense is that the GFS/HRRR have temps in the mid 30s in the heart of Chicago even 6 hours after the winds have shifted offshore. That doesn't make much sense with strengthening CAA.

1.0" at the Midway co-op.

I expect tomorrow to look decidedly more impressive in and around Chicago metro. Besides the snow, which could be falling at a decent clip at times, mixing suggests gusts of around 35 mph or perhaps a tad higher.

Think like 1-1.5" is a reasonable call here tomorrow. I am not sure what the hell the HRRR is doing with diurnally warming temps in and around Chicago metro tomorrow. CAA and precip should keep temps falling.

Been very wet here lately. This system is going to push me over 10" in the past 5 weeks.

ORD and MDW both light snow.

Woke up for a radar check... looks impressive. Mostly rain here but I have a light out back and can see some wet flakes mixed in with this heavier burst.

Temp has dropped 3 degrees since precip started. Need a few more.

Went outside to see what kind of precip was falling. The answer... it is mostly rain but there is a little sleet mixed in.

Window for snow in Chicago is definitely early on Wednesday when onshore flow is lightest and dynamic cooling is maxed. It is basically a done deal imo that the parts of the city like Midway are far enough inland to get some accumulation but question is how much and how close to the lake can it get. Good learning experience either way.

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 909 PM CDT Tue Oct 29 2019 .UPDATE... 909 PM CDT Tricky forecast overnight into early Wednesday morning as low amplitude shortwave trough over the southern Plains this evening races northeast toward the lower Great Lakes by midday Wednesday. Some backing and strengthening of the low/mid level flow in advance of this shortwave aided by the thermally indirect circulation in the right entrance region of the strong upper level jet will result in a strengthening frontogenetic circulation. Forecast thermal profiles look to be precariously close to the rain/snow line, which naturally lends itself to some uncertainties with respect to p-type and any potential snow accumulations. However, cross sections through the f-gen circulation show strong omega co-located with negative saturated EPV, an indication of weak stability/potential instability. This, combined with the strong omega, could result in some heavy banded precip. The heavier precip rates would tend to push thermal profiles more toward all wet snow due to dynamic cooling. In addition, forecast soundings look exceptionally favorable for large aggregate snowflakes, which could result in greatly reduced visibilities (wouldn`t be surprised to see some 1/2SM to 1/4SM) in the heavier snow. Models generally agree that 2m wet bulb temps will remain near or just above freezing, which given warm pavement temps will result in melting and snow-to-liquid ratios. However, even with the warm ground and marginal 2m temps, snow falling at moderate to heavy clip will accumulate, likely even on roadways. Latest guidance that has come in this evening would generally tend to support the going forecast, which has an axis of heaviest accumulating snow from LaSalle County northeast toward the western and southern Chicago suburbs. I do have concerns that the fairly light surface winds could mean less lake warming in Chicago and the immediate metro area and could allow for more snow falling even into the city limits. Going to update grids and forecast to hit snow a bit harder in the city and burbs with a bit more accumulation, but certainly possible that snow could be a bigger problem into the metro area than this. Strongly considered expanding the winter wx advisory northeast into the metro area, but still not confident in the switch over to snow in the city and even less confident in impactful accumulations. Any snow should switch over to light rain and drizzle by late morning we lose ice nuclei in the clouds and column warms solidly above freezing. - Izzi &&

Impressive to see the models trending snowier toward the lake. Obviously have to take amounts there with a grain of salt but perhaps increases confidence for a period of snow there, except maybe right at the shore.

00z NAM a tad deeper again so far.

Does it get snow to the lake tonight or is that all from Thursday?

Yeah but the storm is still going a couple days from now. We'll get a good idea by tomorrow morning if that has any shot at verifying.

Overdone or not, it is nuts to see a map like that only a couple days out from what tends to be the most reliable model.

lol

Based on hourly obs at DVN, it looks like winds were generally around 10 mph or less. So imagine what more wind is going to do. I can see this being an issue even into Chicago proper eventually if an inch or two falls in the def zone on Thursday. And the foliage in the city probably isn't as far along as it is in outlying areas.

10/7/2000 took out a huge limb in front of my house with 1-2" of heavy, wet snow. It was a LES setup and not anything like this with a deepening low passing through. Trees are farther along now of course but point is it doesn't take much.