Chinook

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.

My place got a little over 2", probably like 2.2".

Here is the 00z Euro snow totals chart up to the point -before- the 500mb low regenerates a snowy surface low in the southern Plains. Overall, the GFS, Euro, and Canadian have come into better agreement on QPF in Colorado, where snow should be in my area from 12z Monday- 06z Tuesday. Note: See MO/AR/OK/KS thread for discussion of possible large southern plains ice and snow storm.

The storm is getting closer. This is the Euro depiction that shows that northern Colorado would get 1-3" with sort of a warm advection sector to the storm. The higher elevations of Colorado will get 3-6" or better with upslope, and maybe over 6" as the upslope continues for perhaps some hours (beyond what's shown on this chart). As for the Midwest, Nebraska/Iowa and the Upper Midwest will have the potential for snow over 6"-12". Kansas and possibly northern Missouri could have some sleet or freezing rain. It seems several models have shown low snowfall for eastern Colorado, and this is kind of disappointing, considering the 500mb is so close to the right spot.

My place dropped from 60 degrees to 29 degrees. Look at South Dakota-- they were in the mid 60's, then blizzard, apparently 49.7 degrees colder.

It looks like we really may have something to track over the next 6 days. There could me more snow in Kansas than at my place.

change over to snow in Minneapolis

14 years ago (December 20-21, 2006) view from apartment building

For those interested, this radar web page provides a little better functionality to the new NWS web page. The boxes labeled "3" to "15" on the left hand side are zoom levels (you can zoom out by clicking a different zoom level) https://mrms.nssl.noaa.gov/qvs/product_viewer/

wind warnings and blizzard warnings. NWS point forecast for me shows 52mph wind gusts before midnight.

Today, my area has a few lenticular clouds and mostly clear skies. I am hoping to see Saturn and Jupiter next to each other in about 1-2 hours. Yesterday, my area had about 39 degrees in mid-afternoon when other areas were warmer, with adiabatic mixing. Today, my area is up to the upper 50's. edit: I got lucky. Sometimes the lenticular cloud at sunset is tough to find. I also saw Jupiter and Saturn in the binoculars a few minutes ago.

Some of the ensemble means do indeed have a trough in Utah/Colorado-- about what you want to see, I suppose, if you were going to put your hope in any storm in Colorado at 240 hours in the future. edit: to a degree, this month has showed signs of looking like an El Nino upper level pattern, with positive PNA and cooler temperatures in the Southern Plains and Southeast, and even, nearly a true Miller-A storm for the East Coast.