RCNYILWX

If the ECMWF weeklies are on the right track, you can toss that CFS January prog as far as you can throw it. Here's a loop of the weeklies put together by a frequent poster on the New England sub: Because there were very valid fears about a warm outcome this winter and we see already how mild December was, the increasingly likely development of major high latitude blocking in the Arctic and Atlantic can only be a good thing. We take and hope more of the subforum can benefit this month and likely beyond. Can probably also include this in the medium-long range thread. PS: Happy New Year to all! Here's to a snowy next couple months and eventually better things to come in 2021 than what 2020 gave us.

Just a note about RFD, we strongly suspect it's been running warm the past few weeks. Sent from my SM-G965U using Tapatalk

I think it's definitely plausible north except probably right near the lake, even south can't rule it out. Question there is does the latent heat release from the warmer rain drops eventually win out for southern areas. Recalling the 2019 ice storm, the expected warming above freezing didn't happen during the steady precip because winds stayed northeast the whole time and the surface wet bulb zero line struggled to advance northward. That'll be the key to watch tomorrow is the surface wet bulb zero line.

I think that it looks like mostly snow and maybe some sleet up there and I guess that's why no advisory, though since there will be some travel impacts, thought they might have erred on the side of caution. Sent from my SM-G965U using Tapatalk

If the 21z RAP is right, the only areas getting above freezing through the event are basically southeast of I-55 and along the Lake Michigan shore. I noticed that in our AFD, mentioned all areas along and south of I-88 warming to above freezing. I think that's probably too optimistic except along the Lake Michigan shore and a bit inland of there, and obviously if something like the RAP is right, ice accumulations could end up higher than forecast. [mention=14]Hoosier[/mention] made a good point earlier about accretion rates potentially being higher farther north where the warm nose is not as warm. That's something to watch and another reason to be concerned about some locations overperforming ice wise. Another thing we'll have to watch observation wise is how cold the low level cold wedge remains. The December 28 2015 event that's been discussed verified colder at that level than model forecasts, and if something like that happens tomorrow, also could have a zone that stays sleet for a while until flipping back to snow. Finally, was a bit surprised my office and DVN didn't extend the advisories to the northern tier counties staying snow, since it seems they have solid potential to come in at near typical advisory criteria for snow anyway. Will be an interesting event to watch unfold.

This might be worst/best case scenario, but was thinking that even for the areas that get more snow and sleet plus some ice, going to be very dense, high water content stuff, so the impacts would be more than those snow amounts would typically entail, along the lines of your thinking.

Would recommend looking at the 00z HREF page tonight for freezing rain tomorrow night into Friday. They recently added 3 hr and 24 hr FRAM mean ice accumulation to the winter parameters. FRAM (freezing rain accumulation model) is what we use in the NWS for ice accums and it's much more sophisticated than the QPF to ice accums that's available on COD, Pivotal Wx, WeatherBell, etc. Here's a link to a pdf about the FRAM if you're interested in learning more: https://www.google.com/url?sa=t&source=web&rct=j&url=https://vlab.ncep.noaa.gov/documents/10157/137122/FRAM_VLAB_Presentation.pdf/50ff7877-c52d-80f4-1413-b294db7710e9&ved=2ahUKEwjUmoSJ8_btAhV6B50JHVLaDZYQFjAAegQIBBAC&usg=AOvVaw2fMu-m4aPPk_bnXxwA6ivl&cshid=1609372449468 Sent from my SM-G965U using Tapatalk

I had sold on sustained sleet with this, but what you had shows how convection can modify the thermal profiles and keep sleet going and even the mixed large flakes when otherwise you'd probably be freezing rain quicker. Fascinating stuff. Sent from my SM-G965U using Tapatalk

Depending on what rates are like, non-zero chance it could go back over much later/pre-dawn hours, as the guidance is showing some modest cooling aloft ahead of the frontal zone. Sent from my SM-G965U using Tapatalk

KFFL in southwest DVN CWA getting close already with scattered 3600' clouds and broken at 4700'. OTM broken clouds at 4600'. Not seeing any red flags yet that the antecedent dry air is going to be more prohibitive than expected. Sent from my SM-G965U using Tapatalk

Link to a loop of the ECMWF weeklies run last night for the 00z/28 cycle: https://33andrain.s3.amazonaws.com/monthly_2020_12/ecmwf-weeklies-avg-nhemi-z500_anom_7day-1609113600-1609718400-1613088000-20.gif.64969e182ab9478fa5381e7fe5f284d5.gif Not sure if it'll work. Tried to post the .gif but file size is too big. In sum, the ++EPO Pac puke dominated start to January goes over to an Atlantic and Arctic blocking dominated pattern. The latter portions of recent ensemble runs also going to that sort of look. Been a lot of discussion on SSW likelihood into January. Certainly don't want to hype it like it often gets, but long range experts are saying there's good precursors going on near Siberia to favor the occurrence. If so, the tendency for -AO/-NAO that's been there could further deepen and point toward a colder outcome than expected from mid January or thereabouts and probably into Feb. If a major anomalous blocking episode develops, they tend to stick around for quite a while. For most recent met winters that had deep Arctic and Atlantic blocking in the heart of the winter, have to go all the way back to 2009-10 and 2010-11. The 09-10 block lasted all the way through Feb and into March, but the 10-11 block collapsed in early Feb (and probably helped those of us who cashed in on GHD I). After a mild start to January, things "could* turn more interesting if we get cooperation from the Pacific. We'll see how things play out as we get closer to that period. Sent from my SM-G965U using Tapatalk

00Z ECMWF looks more concerning for a longer duration of ice on Friday north of I-80 and away from the lake. Dew points at 12z in the lower to mid 20s and still upper 20s to around 30 at 18z. Because of a weaker surface low and it tracking northeast from STL instead of more due north, winds become progressively more northerly. Also at 12z the surface ridging across the western lakes trended stronger at 1028 mb. I still wonder if 925 mb ends up being colder because of the surface pattern favoring it, but if not, that run definitely ups the ante for icing concerns. Crazy thing is part of the event is still out to and beyond the end of the NAM range, so there's still plenty of time for changes. The 00z EPS has a pretty large west to east spread of individual member sfc low positions, with relative clustering on the more west and more easterly camps. Sent from my SM-G965U using Tapatalk

Based on this, any snow accumulated after 06z south of the 850 mb zero line probably sleet to freezing rain in reality. Sent from my SM-G965U using Tapatalk

Admittedly was much more focused on tomorrow's event today but I'd still be concerned about h9 verifying colder as long as you keep that northeast component from the surface high to the northeast. Going into 12/28/15, we were much more concerned about icing than the sleet because of the magnitude of the 850 mb warming but the low level cold wedge was still enough to produce mostly sleet north of I-80. I saw some of the 925 mb progs being warmer than previous runs, so if that occurs then the sleet concern will be unfounded, though we still have plenty of time for changes with this setup. Sent from my SM-G965U using Tapatalk

This sounding below demonstrates the NAM's dry air issues pretty well. It's over LaSalle or Kendall County valid at 21z. If you go to the Precipitation Type parameter on COD, this area is not being counted as snow by the model. Yet you look at that sounding and that's very clearly a snow sounding, a good WAA snow sounding at that. 850 mb is a pretty good proxy for saturation level at which snow reaching the ground is a decent bet. Since the NAM is 3 hour time steps, not counting these areas of the grid space of having qpf as snow cuts into the qpf and snow totals unrealistically. This is an area where meteorologists and weather enthusiasts can add value to the model forecasts when we know their typical biases. Sent from my SM-G965U using Tapatalk

I think analyzing the NAM is as simple as tossing its BMJ parameterization scheme which does terribly with antecedent dry air. Look at the composite reflectivity vs the precip output and that should be all you need to see. It will take some time to top down saturate, but with robust moisture transport and strong forcing you shouldn't lose 3 hours of precip. The NAMs have it snowing hard aloft at 21z. If anything, skew timing earlier and account for possibly earlier northward surge of warm nose and the forecast is in decent shape. Sent from my SM-G965U using Tapatalk

Sell on anything but brief (1-2 hours) sleet with this. Models always hang onto the low level cold wedge too long in strong warm advection setups. I think this a solid thump of snow, mix or brief change to sleet then freezing rain. Sent from my SM-G965U using Tapatalk

I'll take a stab at this. It would be cool to get a take from an actual modeler on the frustration we all share in the apparent degradation of short-medium range forecasts, especially in the winter. My perception since I've worked at NWS Chicago in 2010 is that the operational model forecasts haven't improved much if at all for our region. Meanwhile, I know that the modelling is so much more advanced now than it was then. I think there are a few feasible culprits to lack of good model consensus at fairly short lead times and changes in the forecast in short lead times. 1) Fast flow patterns have seemed to the rule in recent winters. Have seen it speculated on other forums/subforums that the fast flow may be linked to CC. Whatever the case may be, it makes logical sense that faster flow is tougher for even our advanced NWP of today to accurately handle key features that can often start as lower amplitude earlier in the forecast process. As we know, any errors at initialization get amplified the later into the forecast. 2) Lack of more recon sounding data over the all important Pacific basin. I don't know the full story behind data inputs that are no longer there, but it seems clear that satellite (despite the recent advances satellite data) and sparse aircraft soundings out over the open Pacific are insufficient to bridge the gap until RAOB sampling. 3) Doubled edged sword to ever higher resolution: Can very small scale features picked up by higher resolution modelling systems cause errors to increase quicker than more smoothed out data of the past? Further discussion on this can probably be sent to banter, but I'm curious if anyone else has any other ideas on this.

The GEMs especially but also the UKMET have been consistently farther south with wave 1, and we've seen a several run south bump from the other guidance since. Question is do we see the southward adjustments continue once the first wave is fully sampled? In making a hypothetical forecast blend at this point, I think I'd give a nod to the consistency of the GEMs and UKMET and weight them more than the Euro, GFS, NAM. Will be interesting to see trends with the 12z guidance when the wave is fully sampled. Sent from my SM-G965U using Tapatalk

All about how quickly the southern wave gets sheared out. Even on a stronger/NW solution like the UKMET, the wave opens up but is able to lift much farther north with incoming northern stream energy much slower. GEM is much stronger and faster and therefore farther southeast earlier with the northern stream energy, which shreds wave 2 in the confluence. So many pieces coming into play for wave 2 that won't be sampled fully until mid week and it's already a faster flow pattern that gives the models fits, so expect the operational runs to have large variance and large spread in the ensembles until more than satellite data from the key features can get inputted into the model initialization.

Also coming off the very dry surface high, the dew points start quite low and southeast surface wind through 06z or 09z is pulling from dew points still in the upper teens to lower 20s over central Indiana. Sent from my SM-G965U using Tapatalk

For those keeping score of the 00z cycle, the RGEM came in way south with wave 1. Sent from my SM-G965U using Tapatalk

I buy downtown Chicago having issues with a strong east or northeast wind during wave 2. Lake is still mild enough to cause problems immediately along the lake and a bit inland in a marginal air mass. Sent from my SM-G965U using Tapatalk

If you recall the Feb 2019 icing, that's something we got burned by. Much of the guidance kept insisting on warming the boundary layer to above freezing even though surface winds were progged to remain northeast/east-northeast at the surface. Putting down snow cover and not melting it going into the event is a wild card that could point toward sfc temps verifying colder if we get a scenario like shown on the 12z Euro.

Looking at the 12z EPS, wave 1 had a pretty big adjustment south similar to the operational. There's substantial west to east spread on the sfc low placement for wave 2, with the mean actually bumping east of the 06z. Another component we'll have to watch is the possibility of wave 2 getting sheared out in confluent flow to the northeast, which could tug the sfc low track more northeast with time depending on when that occurs. The EPS mean favors this sort of setup, so there's a decent amount of member support for the wave closing off, occluding and then shearing northeast. So many complexities to the setup. Edit: Included wave 2 in 2nd sentence of 1st paragraph