RCNYILWX

Throw in the SWE and the temperature of the snowpack going into a thaw. At mid day today, our snowpack had unusually high SWE (1.6" on 6-7" SD at LOT) and in general the temperature across the heart of it was quite cold due to extended cold stretch. Those factors initially make it more resilient, with a warmer snowpack going in more prone to "ripening" faster. There's going to be steady melt but it appears that temps and dew points up in the metro and points west should stay low enough to prevent a nuking of the snowpack over the next several days. That is unless dew points trend higher absent insolation, as it does appear we should stay cloudy through the period.

Last year's ice storm in far northern Illinois has minimal if any road impacts and tremendous infrastructure impacts. That was our worst ice storm since I've been here, definitely worse impacts than 2/19/19. Honestly tough to say how the road impacts will play out tonight, especially if temps come up close to freezing with the aforementioned lighter winds.

Here's the ice accumulation forecasting reference I was alluding to in my post.

Yep you got it, the main consideration is infrastructure impacts such as power outages. If dangerous travel conditions were the main emphasis, we'd have freezing drizzle events with a glaze to a few hundredths that would be warning worthy.

Re. ISW discussion, while the officially listed criteria is still 0.25"+ of flat ice accretion, that's no longer the sole consideration. We have some research based guidance that places more emphasis on the importance of wind in attaining higher end impacts. Wind results in more evaporative cooling, which translates to higher radial ice accretion that more strongly corresponds to true ice storm type impacts. Winds also bring down trees and powerlines. This case is less straightforward because of the lack of wind tonight. I can't speak to the decision process today yet, but if we don't upgrade, the lack of stronger wind will probably be a contributing factor.

We did get an all in storm total of 16" in Chesterton. It appears the heaviest last night was far enough west of the county line that there's a relative gap just west of where you are. Out of curiosity, if you drive through there, interested if it's around a foot in the Town of Pines/Beverly Shores area. Sent from my SM-G998U using Tapatalk

ORD is up to 16.1" (January normal is 11.3") on the month and 20" (normal to date 16.1") on the season, vs. 0.4" in January and 4.7" on the season as of 1/19/2023. We're in decent position to make a run at normal+ for the season, which is definitely a surprise. We've had consistent snow cover in the suburbs since January 5th. And I doubt we fully melt it out next week unless we get much higher dew points with how glaciated the bottom layer is. Seems possible we keep some snow depth through the end of the month. Either way, the ORD snowfall data and this long of a stretch of snow cover and cold temps in a strong Niño has to be taken as a win, even though things could've gone even better than they did.

The EPS was not as bad as the GEFS in the extended, so considering the volatility in the LR guidance maybe it's not a done deal to be bad at the end of the month. Still would think more like mid February for anything resembling the pattern we've been in though.

My post from several days ago doesn't look like it's going to age well. [mention=525]OHweather[/mention] can probably speak to this better but it appears there's going to be another Pacific jet extension event, paired with the MJO forecast to go into unfavorable phases. So the favorable look that existed end of the month into February certainly isn't there on the ensembles anymore. That said, with the warmer stratosphere and resultant weakened SPV, the retraction of the Pac jet may eventually lead to another favorable window, aided by the MJO if it keeps moving along like it has been lately. Relative to pre-season thinking for this winter, the stretch we've been in has been quite active and unexpected, up there with the winter 2020-21 rally though with the heaviest snows displaced west and northwest. It's not too surprising to get back into another unfavorable window amidst a strong Niño if things play out as they're looking at this point for late January into the start of February.

The 12z HREF LPMM is chef's kiss. Up to 2.08" QPF in northwest LaPorte, 1.25" in northeast Porter. The PMM 24 hour snow on the SPC HREF page is showing a spot of 30-33" associated with the highest LPMM QPF valid 00z tomorrow evening.

For those who have wanted to chase a Lake Ontario or Erie LES event, I think tonight-tomorrow's event for northeast Porter, especially LaPorte, and nearby is worth considering heading out. The high res guidance is in really good agreement in 1.5"+ QPF, so it's not just the HRRR putting out huge amounts of QPF. This could be one of the better southeast Lake Michigan LES events in a while.

I think while the HRRR is typically too aggressive and too far west, the 3km NAMnest can fairly decent for lake effect. The WRF-ARW and NSSL-WRF are worth a look too when they come into range, via Pivotal, Tropical Tidbits, or HREF page. Finally, the 2.5 km HRDPS (Canadian) may be worth a look when it comes into range, via WxBell or Tidbits.

We have tomorrow evening-Thursday evening f-gen banding to contend with and then much of the guidance except for the GFS looks pretty interesting for high ratio fluff Thursday night into Friday morning with lake enhancement potential into NE IL and NW IN.

Re. 'we don't have any blocking', with all due respect the NAO is currently at about -1.5 according to CPC monitoring. It would be more accurate to say the blocking is not configured in a favorable way to keep the warm nose from surging in eventually along the coastal plain. But H5 anomalies and the teleconnection indices tell you all you need to know about whether there is any blocking.

The current -EPO/-NAO/-AO/-PNA regime will transition to a temporary +PNA later this week as the NAO block breaks down. Long lived AK ridging (-EPO) will retrograde to Aleutian ridging, with deep troughing along the west coast up to AK, setting up a +EPO and amplifying the ridging downstream. This entails a mild week next week, though how far AN will depend on getting a system with higher Td into the region and melting the extensive snow and ice cover. It appears possible but too far out to be a lock. The warm-up does look to be relatively short-lived, however, as the EPS, GEFS, and GEPS are in good agreement in the typical El Niño Aleutian troughing being displaced well to the south/southwest, which will set up another round of -EPO, though 2 of the 3 (EPS and GEPS) ensembles indicate that pairing with a +PNA, which would tend to be a drier, clipperish, LES pattern. The GEFS is far enough west with the AK ridging to have an interesting look for more of the sub-forum. It appears we're looking at a +AO/+NAO for that stretch, unlike now. We're talking out at the end of these ensembles though, so wouldn't put too much stock in either outcome yet. Main point is that the warm-up next week does not look to be the end of winter temps, and we'll see on the details, barring changes from the general pattern progression.

Where is that exactly? Mind if I share with my office? Could be posted on social media and/or the top news write-up of the cold wave.

Extreme cold can definitely be be beautiful - looks like I caught the sundog in the photo. TWC app says -10/-33 here, guessing on a local wunderground site. Still -11/-37 at KLOT. The cold definitely overperformed.

With a wet bulb zero height of 950 mb plus the exceptionally steep low level lapse rates, even though the sounding shows 43 degrees, that could still produce snow or graupel. We've had squalls out here in the fall and early spring that temps reach the low 40s in between squalls coming through and quickly back down to the 30s under the squalls. Sent from my SM-G998U using Tapatalk

Forecast vs. Actual The extended rain up into the central metro uglied things up, but storm total forecast worked out pretty well due to the early thump plus the overnight fluffier snow. Happy with where we messaged the 12"+ probs. 13.3" in La Salle seems really high, though I'm off this weekend and can't speak to the process behind going with that report. Sent from my SM-G998U using Tapatalk

Edit: re. [mention=18064]mannynyc[/mention] post of sim ref a few posts above Looks good for a squall there tomorrow. Too warm in NYC and LI to accumulate but surface wet bulbs and wet bulb zero heights are low enough for it to probably be snow if it stays coherent as it comes through, which both the HRRR and NAMnest are hinting at. If this happens, could be some brief fun, with heavy snow and 40-50 mph gusts. These soundings are pretty classic, featuring very deep mixing, very steep low to mid level lapse rates, sufficient moisture, and instability. Could get a quick coating over interior sections.

The morning thump was legit and for me, observational trends were still unclear enough to not drastically change the forecast overnight. Was leery of making a big change based on guidance (especially the HRRR/RAP), that's often unreliable until even closer in. But once observations (such as 3-hour pressure falls) showed that the northwestern-most low would stay dominant much longer and as part of the process the 850 mb and 700 mb low tracks also farther northwest, how things played out makes total sense. This scenario remained on the table even though a lot of the guidance didn't show it, though a few of the recent ECMWF runs did hint at it. These dynamic systems often surprise for better (the morning thump and legit higher end winter storm conditions) or for worse, lately for worse for us on the whole unfortunately. So it goes. Another challenge for us from a public notification and impacts perspective is that while the snow enthusiasts will be mad at us if we bust high, a significant under forecast is worse than an over forecast. Not that I want to cry wolf, but to an extent as a meteorologist with a public safety responsibility, and we're right on the line, it's not the worst to err on the too snowy side. If we fully go with a warmer solution and the colder, higher impact scenario played out this afternoon, and there's major traffic incidents as a result, that ends up being more problematic. As a good example, on Tuesday, we leaned a bit on the too optimistic side down in the heart of the metro. With the changeover back to accumulating snow/parachutes happening faster in the early afternoon, the roads deteriorated pretty quickly and we had to reissue the WWA for areas that we canceled more quickly than expected. Ultimately, it's all part of the learning process and the challenge for us as forecasters in weighing all of these competing factors. I get the disappointment, and I'm personally disappointed that it didn't work out better during the day down this way and into the city and south. Glad the northwest burbs got into the goods though, a part of the forecast that worked out nicely. Trying not to beat myself up too much, because the warning was definitely warranted this morning. Finally, we've had misses that were much worse than this, without even the morning fun. One of the tops CIPS analogs was 12/19-20/2012, the MSN blizzard, and that one had all the rain and drizzle and no front end snow for us, and the deformation area fell apart as it tried to push across the metro.

We actually missed the goods west and northwest lol. Some 2-3" LES like rates early this morning though and a gravity wave/wake low feature produced a 48 kt gust at ORD. So short lived fun and then rain while western IL cleans up, with Moline, IL up near 15". Totals for the heart of the metro today were only in the 4-7" range (around 5" for the Chicago sites), while the far northwest burbs got up around 10". We should get some light accums tonight but definitely a disappointing near miss. There's 0 snow left OTG in downtown Chicago, as they warmed up to the upper 30s and had close to half an inch of rain.

Agree it's not the lake for this one, the lake would've been primarily an issue for the Chicago shore accumulations if the track was more favorable. Riding the line with a marginal air mass and the near term synoptic track being farther north is what did it. Sent from my SM-G998U using Tapatalk

Just woke up and it's unfortunate HRRR did a decent job - obviously something that can happen but knowing when is challenging. Regardless, the northern low being dominant for longer is what messed up things for us here after the morning thump. With a farther north track you have to adjust everything a bit north and west. I thought things would be more of a mix between the globals and some of the mesos because I still bought into a favorable enough track of the system including 850 mb low, which resulted in change to rain/mix relatively far north but not far enough. Certainly can never discount the strength of WAA, but I believe that a with a more favorable SLP evolution, things would've worked out a little better locally by now with phase 2 of the event. Small details make a big difference when the antecedent air mass isn't that cold, which we knew. Hoping the change to snow happens soon enough to get some new accumulation on top of what will become an impenetrable glacier lol. Sent from my SM-G998U using Tapatalk

Based on the hellacious thump we had up there, 3-5" additional would line up pretty well with the forecast grids I did overnight (Gino did the AFD to help free me up to help out with our morning briefing graphics). It's been a week lol. Lots of extra hours for everyone. Not gonna lie, nice to be done for the week. Sent from my SM-G998U using Tapatalk