RCNYILWX

Interesting how some offices went with an advisory instead of snow squall warning.  Seems like the snow squall warning is a better fit in this situation (low amounts, short duration) but what do I know.

At this point, with the steady weakening of the band, it doesn't really meet SQW criteria. Not working now so I'm not sure the exact discussions that went on but perhaps they felt it better fit a longer lead time with possible impacts into the commute from period of snow followed by quickly falling temps.

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Euro kinda hops on board too.

Euro ensemble also with a chilly and active look at h5 out out beyond the early to mid week cold shot next week.

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This is probably an obvious statement to make, but we did check a few years ago and there's a strong correlation between precip anomaly and snowfall amounts. CPC has essentially the entire subforum in enhanced probabilities for AN precip in the DJF and JFM outlooks. They also have a lean toward cooler anomalies for a portion of the sub in the JFM outlook. So if the above normal precip works out, that would seem to increase the odds for above normal snowfall when also accounting for the head start, unless it ends up being a blowtorch winter.

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Yeah this is going to be a real nice wind event.  I spent 2hrs mulching leaves this afternoon, which will prob be a waste of time since they most likely would have blown into Indiana anyway lol. DVN with some beefy wording in their latest disco.   

 

Sustained winds Wednesday look to be 30 to 40 mph with gusts over 50mph likely. It is very possible that some wind gusts may approach orexceed 60 mph in spots.

 

 

 

 

I did the wind forecast for the event for LOT today. We went peak gusts in 45-48 kt range. My current expectation for this event is high confidence in widespread 50+ mph gusts and we'll likely have a few ob sites reach warning criteria (58+). Not certain we'll have widespread verification of warning criteria (county based verification) assuming we go with a warning but frequent gusts in 50-55 mph range will be enough to cause tree damage and power outages and probably blow over some semis on north to south or southwest to northeast interstates. There's probably little functional difference to the public between a high end advisory event and a lower end warning event.     

 

 

One aspect I didn't look too closely at today is cloud base height. With strong cold advection and steep lapse rates we'll certainly develop a stratocu field. If there's something that could lead to underperforming it would be cloud bases under 3kft because the highest winds aloft are generally up around 850 mb. BUFKIT soundings are indicating that we will tap into those top of channel (mixed layer) gusts but if cloud base height is lower that could limit things somewhat to solidly advisory criteria and lower likelihood of warning criteria being met.

 

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Takeoffs and landings might be a bit bumpy on Wednesday.  This is @ORD on Wed afternoon.  Nearly dry adiabatic into 65 kt flow at 850 mb.  Likely would be high wind warning criteria if this verified exactly as is but we'll see how it evolves in the next couple days.

Most recent NAM is actually a bit more bullish on winds at the 850 mb level than the GFS, which is usually the other way around. Verbatim peak gusts on 06z Euro for LOT CWA are 50-60 mph. On BUFKIT, using the momentum transfer tool, usually like to see mean mixed layer gusts closer to 50 kt and top of the channel winds solidly over 50 kt to feel confident about widespread warning criteria.

06z GFS would be close for probably southwest CWA but more of a high end advisory look elsewhere in the CWA, while 06z NAM looks more supportive of warning criteria for more of the CWA. From these, high end advisory is a lock and warning criteria certainly possible. We'll see how things trend the next 2 days. Possible that the PM forecast package today goes out with a High Wind Watch or tomorrow morning.

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00z GFS with a hard shift toward the Euro for the weekend system.
And this just in from the GEM

 

And then the Euro completely backed off lol

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It is not easy to get lake enhanced snow into Chicago in early to mid November.  Here's why. Progged low level flow is basically full fetch down the lake over all that mid 40s to nearly 50 degree water.  A lot of November setups will fail because the airmass just isn't cold enough.  One example is 11/24/2004, which had a distinct snow minimum surrounding the lake.  Another case which Alek will remember is 11/21/2015, which kept it raining in downtown Chicago for the majority of the time (while hammering inland toward ORD) until finally switching over toward the end.

In the 2004 case, 850 mb temps were around -5C.  In 2015, they were more in the -6C to -8C range.  This time they are progged to fall to -10C while the low level flow is still directed into the IL shore.  Typically by the time 850 mb temps are that cold at this time of year, the flow has already shifted to favor IN or MI.  

 

 

I know 11/25-26/18 is not as good a comparison because the air mass was also too warm aloft initially but it was another case of full fetch down the lake making it tough to get much accums downtown. All of the snow lakeside fell on the morning of the 26th when low level flow turned northwesterly and cold advection intensified.

 

For Monday I'm not sold yet it's going to be a big deal lakeside for IL. In addition to the low level flow being a full fetch down the still mild lake (could see northerly Island being locked at 33 to even 34 while flow is onshore), the Euro and the NAM are a bit slower with the CAA so 850 mb temps 12z Monday are only about -8 to -9, yielding delta T with Chicago shore water temp of about 15-16 C. Equilibrium levels less than 6kft prior to 12z only get up to just shy of 7kft by 15z, which is pretty marginal. Gonna need the low level convergence to hold back longer over the southwest part of the lake like the 12z Canadian to allow the cold air to deepen and improve parameters as well as cool the boundary layer sufficiently.

 

The 18z GFS is quicker with the CAA but it also is much quicker with flow turning to NNW and favoring Indiana. Even for inland of the lake in IL, the NAM and ECMWF being marginal with thermodynamics during most favored timing of convergent boundary layer flow casts some doubt on how much lake enhancement there will be.

 

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Could see there being a narrow band of 2-4/3-5 for the late Tuesday night-Wednesday morning round.

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Might have a bit of a meh outcome around here with heaviest band of rain west and strongest winds south.  Updated LOT afd mentioned the possibility of a period of 50+ mph winds in the southern cwa but no wind advisory yet.

We were very open to issuing a wind advisory for southern CWA but ILX, IND and IWX still preferred to hold off. Given the run to run consistency of the HRRR for a corridor of 40-50+kt gusts tonight, I was surprised the neighbors didn't want to issue an advisory. Could very well have high wind warning type impacts if the HRRR comes to fruition. 18z RAP has a large area of 50+ kt winds at 925 mb spreading across central IL and IN. Forecast soundings suggest that there will be sufficient mixing to tap into the high winds aloft, with cold advection and very strong pressure rises immediately following the surface low.

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The models that entrain the tropical system better have a deeper surface low once it gets into our region.  Probably not a coincidence.

Can easily see the tropical connection on the pwat plume on the 12z Euro. Intense 850 mb LLJ in the warm conveyor. Impressive rain event locally modeled by the 12z Euro. Would imagine with the magnitude of the WAA and near record high pwats that embedded thunderstorms could occur due to slantwise instability in the comma head.

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Yeah, 68 on new ob.  Literally just needed another 15 minutes or so.  Unreal.

Very reminiscent of January 30th failing to set a new monthly record low max for January by 15-20 minutes.

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Hey beavis, looks like this could be close.  I forgot it actually has to make it until 1 am central since we are still on daylight savings time.  Outflow is currently just south of MKE and moving south but not necessarily racing.  It better not come through between 12 and 1 haha.  

Based off what just happened at PWK on 5 min obs, appears more likely than not that ORD will fail to set the record. PWK went from ~81 at 12:05 am to ~70 at 12:10 am.

 

Edit: ORD officially failed to set the new monthly record.

 

 

 

Could the filtered sun due to the smoke dampen convective perimeters as compared to what the CAMs are predicting?

Doesn't seem like the smoke should dampen insolation and thus instability too much. Even with pretty thick smoke yesterday we got to low-locally mid 80s highs without a problem.

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IMO using the baseline of the issued Enhanced Risk, placement should either be shifted north into northern IL or expanded from current area to include northwest 2/3 of LOT CWA. Based off path of well defined shortwave tracking across the area around mid afternoon, strongest mid-level winds and deep layer wind shear will be across northern IL and southern WI. There will be more than enough instability area wide and very steep lapse rates, considering that we already had pretty stout elevated hailers this morning over northern IL and southern WI.

Looks like a solid early summer severe day, with large to isold sig hail with initial discrete/semi discrete storms likely trending to more of a damaging wind risk if things as expected congeal/grow upscale. Doesn't look like much of a tornado threat with weak low level winds, little/no directional shear, and soundings showing well mixed low levels. Would likely need outflow boundary interaction for any brief tor threat, or possibly in proximity to the weak surface low moving over southern WI.

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That's true. Aside from the potential for one of these cutoffs to locally produce, we could just as easily see a pattern flip (models can and have been wrong in the long-range) or a random event pop up. Even the worst spring seasons have their share of events. Climo says it's very difficult to get through the last 10 days of April without some notable uptick in severe activity, if that's one piece of optimism I can throw out there.

This isn't a bad thing either for when (if?) a significant pattern change occurs. The slow ULL movement caused by the omega block will produce a very favorable heavy rain setup in the Plains, with a midlevel moisture feed from the EPAC and low level trajectories from the Gulf.