Chinook

I must say, I am getting a lot more interested in this storm, as the swath of snow may very well go through Toledo and Fort Wayne. One thing to note, the ECMWF/Canadian have a heavy snow axis of over 12" (10:1 ratio) from southern Nebraska out to eastern Iowa or western Illinois. The GFS has some freezing rain for this area. In fact, the Canadian does have some sleet in this area, (northern Missouri especially). I am wondering if that counts as snow on the Kuchera snow plots. The area of concern in the shortest time frame would be heavy snow/sleet/freezing rain areas for KS/NE/IA/MO, with Topeka, Kansas City, Des Moines, and Davenport being the most interesting areas with larger populations.

It is definitely true that the models have caught on to a pretty big shift to a wet period for the West. I would say that this is overdue, and should put a dent in the drought conditions. Still, though, the GFS is putting out a big 0" for Denver.

Since I moved here in 2006, the average December snowfall for Fort Collins has been above the 30-year climatology for the 1971-2000 period. 8.3" (1970/71-1999/2000) increasing to 11.5" (2006/07-2019/20). March snowfall has gone in the opposite direction: 11.8" way down to 6.6".

I found some data that show conflicting answers as to what is likely to happen with precipitation during a La Nina. Check this out. The top two maps will show red/orange with increased precip with El Nino, blue/green with increased precip with La Nina. The bottom two maps show increased precipitation in blue/green for La Nina (and does not include any information from weak/moderate/strong El Nino years.) Colorado seems to be the only area in the country with different colors on the comarisons of the top two maps- and also the comparisons of the bottom two maps. This must mean something like the inclusion November and March is quite important. November to March-- more inclusive, because we get plenty of snow in November and March-- December to February only-- Specific La Nina winters (December to February Only, 1981-2010 climatology) November to March--- specific La Nina years

I must admit, the situation did not look good at the beginning of the fall. There has been a significant (fiery) drought here, and a La Nina incoming. A moderate-strong La Nina does not correlate to high precipitation for southern and eastern Colorado. In some of the most recent weeks have had snow go south of us, like in New Mexico, Texas, Louisiana, North Carolina, Oklahoma, and Arkansas. This happened even without a deep arctic air mass mostly. That kind of thing can happen from time to time with an El Nino, but the situation in the Pacific is certainly a La Nina. As of today, the near-term storm does not look like it is going to bring more than 1" of snow to my place, but a reasonable amount for central-southwest Colorado and some of New Mexico, and rain for Arizona. The models have bigger storm for the Rockies/Plains in about 1 week------ every model has the snow missing Denver. So I'm not pleased.

This upcoming 500mb low, diving toward the desert, will provide possibly 5-10" for a good part of Colorado's mountains, but apparently not much for east of the Front Range. Models have some varying degrees of snow/rain for northern New Mexico.

Interesting and helpful change to Pivotalweather- GFS can show maps for every 3 hours

Over on the other side of the Midwest, blizzard or near-blizzard conditions have been hitting Omaha to Des Moines. Omaha has had many hours of 1mi visibility or less with gusts above 40 kt, with some damage to trees. KOMA 151352Z 33030G48KT 1/2SM R14R/2600V4000FT SN BLSN VV012 M02/M03 A2954 RMK AO2 PK WND 31050/1310 SLP009 P0002 T10171033 KOMA 151752Z 33027G45KT 1/2SM R14R/2200V4500FT -SN BLSN BKN013 OVC019 M01/M02 A2964 RMK AO2 PK WND 33045/1744 SLP047 P0001 60007 4/002 933003 T10111022 11011 21017 51034 This is just a section of the storm reports from the last 2 days. If I plotted all the Great Plains storm reports, it would be filled with wind reports

For my place, the wind kicked in maybe after 8PM or 9PM, with some max wind gusts of 51mph at KFNL airport, possibly 40-55mph near me, around midnight. Winds gusts are back up to 40mph now.

I just recently said that there wasn't much of a fantasy storm for Colorado-- and that's true. The models have shifted a little bit. Today's models have some agreement in bringing a diving 500mb trough into Arizona, with potential for lighter snows in Colorado and possibly moderate snows in New Mexico.

Sunset tonight

I don't completely understand the system. I just plotted the correlation of the AO index to the 850mb temp. As you can see, I included November, since some of our cold shots come in November. I also don't completely understand how a stratospheric warming at over 100,000 feet above sea level can slowly begin to affect the patterns near the surface. The AO index can go quite negative as the stratosphere undergoes large changes. The AO index calculated by the CPC is based off 1000mb height anomalies, essentially the same as SLP anomalies, in the Pacific, North America, the Atlantic, and Europe. The NAO index is calculated based off 500mb heights mostly toward the Atlantic side of things. Either way, the SLP at Greenland and the central-north Atlantic ocean are highly correlated to both the AO and NAO indices. As for us in Colorado the colder air getting into the West is most correlated with a ridge near Anchorage and Juneau, and development of cold air in the Yukon and Alberta. That does not fit into the scheme of the -NAO pattern, as 500mb heights might be quite high for the East Coast into the central-north Atlantic when that happens.

I definitely feel that- I saw lots more precip in when I lived in Ohio and Michigan, but weaker snowstorms. So yeah, this longer drought is disappointing. I'd love some rain. When we get a -NAO pattern affecting North America, the colder air masses can develop in central Canada, but get pushed east, frequently leading to the 500mb heights in the west getting higher. As you can see, the general expectation of a -AO pattern is correlated to the blue colors in the most of the East and even Central (so that would be colder air), but then it seems to change to orange colors for Utah.

I added up my precipitation for 2020, and I got 13.05". That's below normal , but Fort Collins-CSU only got 11.87". That's a moderate difference. Denver had 8.74". It's obvious that some areas got lower than 10". 80mph may be unrealistic for tomorrow, in the city.

My place got about 2.5" on Saturday, with apparently 0.16" liquid equivalent. Every so-called storm has produced 24-hour snow values of 0.6" to 2.6" since November 1st. When are we going to get an actual snow storm? On a related matter, my place got 0.53" liquid equivalent of snow for December, which is somewhere near or perhaps less than the average value for December. The Decembers since I have lived here, Fort Collins has averaged 0.67". I can't even find a "fantasy storm" except for 240 hours on the Euro.

171% vs 58% vs 50%

Some light snow is beginning to fill the radar in northern Colorado. Last night's models showed some values over 2" for this area, which is a little more than previous models.

The NWS digital forecast is now showing 3-5" of snow west of Dallas (out to 00z Monday)-- this may increase as this forecast incorporates more hours. Here is the late night Euro-- this is still a pretty large snow accumulation

Models are coming into better agreement with the storm system moving south from the Rockies into Texas. It is kind of strange to see this. Most of the time, when a model shows snow for Dallas, it doesn't really happen. Over the weekend, temperatures will be close to freezing around and south of I-20 with 850mb temps of possibly -2C to -4C. There are a variety of model solutions on snow totals, so this should be interesting to see how this turns out.

The models now have some agreement on some version of a 500mb low near the Four Corners and snow for northern Colorado on Saturday. ECMWF has the snow farther south around Trinidad CO, moving down toward SE New Mexico. It's possible that this is a storm that could just disappear, as so many have. By the way, my place hasn't been above 50 since Dec. 26th. They keep saying it will be 50, but the snowcover and lack of mixing has kept us cooler than Cheyenne and Denver at times.

In related news, the low pressure in the western Aleutians in the Pacific was analyzed at 921 mb at December 31st, 18z. Since it was so late in the day, in UTC, it was indeed January 1st in some part of the Eastern Hemisphere. I have not seen a 921mb low for extratropical lows. I believe the record is 913mb for the North Atlantic. I am not aware of any extratropical lows of this value in the Southern Hemisphere, but there could have been something. Edit: Raindance, I wonder when (and if) the models will pick up on such a storm system at some 240 hours out. Perhaps we could say model ensembles already have a hint of a upper trough and surface low near the Great Lakes at 280 hours, and that may be the hint of the connection right there.

It looks like we've got an El Nino going here with mild Pacific air an important factor in the Dakotas, and cool conditions in the Southwest and Southeast.

Pretty nice composite picture and tweet by Jim Cantore

It certainly seems like this could be a regional tornado outbreak, with SRH values of over 300-400 m2/s2 and shear values of 60 kt, and CAPE values of 500 J/kg to 1500 J/kg in southern Louisiana. Convection allowing models show a squall line or at least quite a few cells in western Louisiana, and several more isolated cells near the LA/MS border

There is a mix of snow, rain, and freezing rain in Kansas. As always, the colors I get on this map are not completely the same as the type of precipitation reported at airports. Kansas City: light freezing rain.