RCNYILWX

Couple of 1" hail reports in western Lower MI; nothing came of this elsewhere.

The pseudo dryline greatly narrowed the risk zone on this side of the lake. Plus the core of 500 mb cold pool lagged enough to limit lapse rates and destabilization east of the dryline.

Only had low-mid 60s temps with near/around 50 Td over northeast IL and far NW IN, which yielded 200-300 j/kg MLCAPE. Needed the 500 mb cold pool to lag less and/or temps around 70 to boost MLCAPE and get it done, as the instability we had wasn't enough to balance out the 40-45 kts of effective bulk shear.

The forecast surface pattern for Tuesday afternoon/evening looks pretty darn near ideal for a significant mid-to-upper MS Valley severe weather outbreak (much as it was on 3/31 last year) and I'm seeing many NAM forecast soundings with large 3CAPE values and strong low-level shear; however there are some caveats.
 - Most of those NAM soundings also have very wonky wind profiles above 700mb, with sharp backing to due southerly at 500mb followed by veering again but weakening at 300mb.
- 18Z GFS wipes out instability across IA/IL with a huge amount of ongoing convection throughout the day. This is likely overdone; but still a legitimate potential fly in the ointment.

Synoptically it's definitely a good setup. I noticed the more meridional flow pattern aloft resulting in the backing you noted. That looks most problematic over Iowa due to the closed off mid-upper low. There will likely be very good sfc-700 mb veering, which may be enough to get it done despite the backing aloft unless/until things get too messy.

Wind profiles are better with south and eastward extent but then the lapse rates are forecast to be pretty weak during the day on Tuesday.

Certainly possible the GFS is overdone with elevated convection near and north of the front, but it does make sense conceptually to have some. I think it's pretty likely the warm front will get hung up a bit farther south in the LOT CWA until the late afternoon and evening.

Haven't looked at latest guidance today because I'm on midnight shifts. Last night I was most concerned locally about Tuesday night when the lapse rates improve and strong forcing arrives while the stout southerly low level flow does work in offsetting nocturnal stabilization.

God that April sucked. And coming just 4 years after 2014 which similarly had a much BA pattern locked in for the first 6-8 weeks or so of "spring," I was really afraid that was the new normal.

When April 2019 started off better, felt optimistic, and then had incessant precip the 2nd half plus of that month including the two big snow events. The genuinely nice Aprils are rare around here, but the truly awful ones like 2014 and 2018 definitely stand out.

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Today locally is what every day was like in April 2018. Glad we don't have a cold pattern locking in.

Re. the SPC outlooks yesterday, took a hindsight look at yesterday's 12z HREF plus the Nadocast Twitter feed.

A good case can be made that SPC should have issued a 10% hatched tor in the general vicinity of the area affected by strong tornadoes, by the 1630z or 20z update.

Plenty of boxes were checked environment wise in the HREF mean fields, plus some of the neighborhood and paintball UH probs.

The 24-hour STP based calibrated tornado probs had a spot of 10% right near one of the strong tornado tracks.

Since they had a slight with 5% tornado probs, it wasn't an egregiously underdone forecast. 8/24/16 is a much better example of that when doing hindsight assessment of the day's SPC mesoanalysis fields.

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Yup...NAM tease. The lack of prior support from the globals was always a red flag, although one can hope.

NAM'med, as they say. If I had the power to get two changes in NCEP modeling done tomorrow, I'd discontinue the NAM and only have 24 hours of publicly available CAM data (and RAP data).

Had quarter sized hail here in southeast/south central Naperville. Lots of smaller hail with several stones around to just under under quarter size.

Euro definitely the most ominous solution of all the models. Lapse rates are good esp for this north and this time of year thanks to that EML. This def bears some similarities to 2-28-17 though for that event we had a well defined wf up this way. I like that sfc winds are south to even slightly backed. Shear isn't crazy but definitely sufficient with that cape profile. Definitely am still worried about cap holding till cf moves in. That dewpoint depression and/or dryline feature could help fire storms ahead of cf if there's enough convergence on it and cap can break. Good thing is storms would likely be discrete. Sfc low is strong but wish it was more compact and not stretched out. Definitely not a perfect setup but definitely one worth chasing. 

Doing a deeper dive at the office now using ECMWF ERA5 reanalysis maps to look at antecedent conditions prior to some notable cool season events. This one definitely has questionable moisture with Gulf currently scoured out.

2017 not a bad comp w.r.t. Td over the GoM within this range of the event, though it had a better sfc pattern for more rapid moisture advection with the primary CO low a good deal stronger and a much stronger surface high (1035 mb) off the east coast.

Some other notable cool season events, November 17th, March 15, 2016, March 27, 1991 to name a few, had much better source region moisture present.

What Tuesday does have is exceptionally steep mid-level lapse rates as you mentioned with cold -15 to -20 C h5 temps. Seeing how February 8th performed with relatively questionable moisture quality, the cold mid-level temps/steep mid-level LRs could help compensate for the potentially middling moisture quality. We're concerned here that if the sun breaks out at all on Tuesday, Td could mix out substantially especially with northward extent.

Perhaps a narrow zone near the warm frontal zone is best bet where you can pool the moisture with a longer residence time and pump up the 3CAPE to the 50+ threshold. Still thinking southern LOT CWA and points south with this in mind.

00z Euro if anything upped the ante a bit, assuming we can trust its dew points. Liking the south third of LOT and points south where the near or over 50 J/kg 0-3 km CAPE is progged.

Also of note, the Bunkers right moving vectors are less crazy than you'd think they'd be for a cold season setup, so anything prior to sunset should be chaseable without having to speed as much.

Had SN/borderline +SN in Naperville earlier this evening with large flakes. This is more reminiscent of a late March or early April event than late February.

Edit: Measured an average of 1.2" on flat surfaces here at around 8:30pm. With a heavier band overhead now, may take one more measurement.

Quite the opposite here. We had a total of 5 days over 50, which in itself is historic for February for our area.
It wiped all the negative anomalies from the first 14 days here too. If February 2018 finished on Feb 14, it would've finished 2 degrees below average. Quite the flip. 

I guess a better way to put it is that it was a noteworthy turnaround, but relative to the all out torch the year before, plus the fact the month still finished at normal, made it stand out less. Certainly not unusual to have widely varying conditions throughout the month of February in a typical winter.

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Where does the mid-late February 2018 warm up stand? 

Unremarkable locally with 3 days in the 60s and 4 days in the 50s, but enough to wipe out the negative anomalies from the cold and snowy first half of the month. The warmth was more extreme east of here.

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The GFS and its ensembles actually have some pretty big changes around and after day 10 compared to the 0Z run. 

Definitely doesn't look as warm going by dprog/DT

Was it late '16 or '17 that had the late Feb really warm spell.  I thought it was '16

Late February 2017. It was the 3rd warmest February on record for Chicago. 1998, a super Niño, is second warmest.

Just surprised at how things turned so strongly away from more sustained blocking and many other LR forecasters much more well versed than me were banking on that. So the pattern did change, but only short-lived and it was completely luck driven to get in on the swaths of snow with the few clippers after the initial southern stream system got suppressed south.

It shows again that strong Niños are a losing battle. Plus I think the past few winters the eastern US has been prone to these ridge amplifications apparently related to the anomalous ocean and air mass warmth in the western Pacific (maybe some CC linkage there). The warmth to end the month and start March does certainly look higher end and may have some threat for severe wx but guessing we don't get into a March 2012-lite situation.

While the weekly guidance has certainly been unreliable, the recent stratospheric warming would tend to support the return of more blocky regime they've been showing toward or during mid March, right when most won't want it of course.

As far as Chicago getting any measurable snow on the board for February, it seems unlikely but the only potential window would be a well timed wave while the cold air is around next weekend.

It's ridiculous, and it's what's reported as how much snow NYC has. Maybe some private company should start doing measurements at the Park if the regular observer keeps screwing up, or choose an airport to have official NYC obs, probably LGA. More often than not it's snowier IMBY than the city but I supposedly have more than double that (which is BS).

From what I've been told by a former coworker at OKX, the CPK conservancy folks do a better job than the security guards that used to do it. But they're still not trained observers like FAA contract observers and probably still lower quality than good long-running COOP sites and diligent CoCoRaHS observers.

If I were to guess, they too often or mostly adhere only to the 6-hour board clearing and don't take intermediate measurements when the situation (melting and/or sublimation of fallen snow) requires it.

the highest liquid equivalent i could find in nj was .46" in east brunswick. lol

There's a 0.5" in Hopewell TWP and 0.48" in Franklin TWP.

The 0z SPC HREF snowfall max did a nice job with the 8-10” snowfall forecast around Staten Island . But the actual falloff in snowfall to the north was more extreme. This may be the first chance we have had to use this model for a mesoscale snow event. It has done very well in recent years with the numerous flash flood events around the area.

 

The nice thing about that page is it uses the WPC forecast ratios so if those are decent, the mean, PMM, and max products will do a better job in hinting at the potential.

Going by the CoCoRaHS precip amounts, liquid equivalent was generally in the 0.35 to 0.5" range in the heart of the band, so the ratios really went nuts at 20-30:1+.

JFK had 6.1" on 0.32" liquid (nearly 20:1) and the NYS Mesonet on SI had 0.35".

[mention=58]SnowGoose69[/mention]  [mention=9996]brooklynwx99[/mention] [mention=568]wdrag[/mention] [mention=63]forkyfork[/mention] [mention=65]SBUWX23[/mention] or any other met, or someone with knowledge, who would like to chime in.
It appears that these types of bands are impossible to predict, even right up to game time. That's also what I've always seen said  
That withstanding, is there anything that can point to where a band like this may set up - geographically prior to now casting? Or are we just not technologically advanced enough to see and predict where these will set up?

Amounts like what occurred are essentially impossible to predict but the existence of the strong banding signatures are handled better by today's modeling. This was strong mid-level f-gen, good jet dynamics, and the combined robust lift being well aligned with a very deep and saturated DGZ.

You could find guidance that showed on planar view and cross sections the strong f-gen circulation, good RH, and slantwise instability, the issue is the exact location and the ratios under banding of that nature. I think the HRRR did an excellent job with the depiction of the band on simulated reflectivity.

When you see something like that, you just kind of have to throw out the verbatim snow outputs and assume a very narrow corridor of much higher ratios that could result in totals like what occurred even with QPF probably not being terribly far off, and even that would lbe too low and the gradient sharper than you could possibly forecast. The OKX AFD yesterday was excellent in hinting at what took place. Worth a read.

IDK but don't we always say the best banding sets up north and west of where the h7 fronto?  I feel so blessed to be the jackpot of that map.......best band since Feb 2013......though didn't last as long.......

Yup, that's a typical occurrence, I was just more surprised at the lack of even hints at that enhanced banding, if not in magnitude or exact location. This was definitely a storm for old school meteorology vs. guidance consensus type forecasting.

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Any speculation as to why the near term guidance almost uniformly did so poorly in at least hinting in the QPF output the response to the strong h7 f-gen? From only cursory glances within past few days, it looked like all the QPF was focused along the lower level fgen axis and then subsidence north of it.

In reality, you had the subsidence north of the h7 "death band", so still a sharp cutoff but shifted farther north. It's certainly not uncommon for the models to struggle with the location and magnitude of response to fgen circulations in the QPF fields, but usually you do see hints at least.

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I agree. It will be interesting to see how this storm ultimately unfolds. The 24-hour map on the HREF should be impressive, but could be overdone to some extent.

Yup, concern there is the 00z HREF has the juiced 12z members included in the mean on the SPC page. With the new DESI interface, I think you can subtract out the -12 hour members if you think they're going to be less representative than usual.

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I think straight to warning for some locations just north of the city and a rare near term watch for the city and at least the northern LI zones might be a prudent course of action since there's another model cycle to look at and make a decision on where to go warning and where to go advisory for the highest population zones. Might be better than going straight to advisory and having to upgrade to a warning in places.

I think everyone needs to remember also that this is a strong el nino winter. Those are literally THE worst possible outcome for winter lovers in this region. Also, what comes up must come down, and I don't think people realize how spoiled we were as a region for many years just a short time ago. You want to see a bunch of wimpy winters? Take a time machine back to the 1930s-50s. 
 
I wanted to look at something I've never really calculated. the average annual peak snow depth per decade at Detroit. It's crazy how relatively steady things have remained for a while when you add up the good and not so good winters of a decade. 
1890s- 10
1900s- 12
1910s- 10
1920s- 8
1930s- 7
1940s- 6 
1950s- 7
1960s- 7
1970s- 9
1980s- 9
1990s- 9
2000s- 9
2010s- 11
2020s- 9

You nailed it, I think with that stretch alone we got a higher end stretch of wintet than expected. Obviously for those who didn't benefit it's been a exceptionally lean winter.

For whatever amount of background climate warming you want to add to potential seasonal outcomes, betting on a objectively good winter for winter enthusiasts in a strong El Niño is a losing bet. 09-10 as a moderate to strong El Niño was essentially a unicorn for the areas that had BN temps and AN snow, including here in the Chicago area.

02-03 was a moderate Niño that gave eastern portions of the sub-forum a solid winter, though it was cool and dry out here.

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clippers at long range have always been one of the models worst features. Thats why Im interested to see if the pros think its a clipper-producing pattern or just model theatrics on some runs.

It looks like a pattern conducive to clippers but they're never sure things in any given areas. As an example, December 2017 had a good clipper pattern by recent standards but it mostly benefitted Wisconsin and Michigan. I noted the challenge forecasting clippers accurately at longer lead times in the long term AFD the past few days.

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