December has arrived! Today marks the beginning of meteorological winter, and the opening weeks of December can be quite variable when it comes to weather. This time last year we’d recovered from a November chill, but we were already watching renewed cold building north of us, and we were also seeing the first indications of what would become a big snow storm for SEMO/SW IL on December 7th. This year, despite today’s chill, we have milder weather on schedule for the medium term and we’ve got no indications of any big snows anytime soon. Atmospheric signals are present which argue for a colder pattern to lock in mid month or later-but that would likely be a dry pattern too.. so any big snows would have to come with the transition. We’ll cover that in a bit.
There was a light winter weather event this morning over SEMO/SW IL as some moisture rode up and over the cold front which took temperatures from the 70s this weekend to the 20s this morning. The radar image (below) taken at 7:35 AM today showed some scattered light sleet and freezing rain showers over SEMO/SW/S IL. Some glazing was apparent and it only takes a little to produce big problems. Winter Weather Advisories and Freezing Rain Advisories expired at noon.
That event was right on cue as meteorological winter began today and we closed the books on November and Autumn. No surprise to anyone November was a cold month. St. Louis and Kansas City were 6.1 degrees below average. Temperatures ranged from 6 to 69 in KC and 14 to 73 in STL.
Taking a look at North America, the blue and green tones show the cold was widespread with only Alaska, Yukon, California, Nevada, Arizona, Utah and parts of SW Oregon warmer than average.
In the northern Hemisphere, North America, central Asia and northern Siberia were cold, while the Far East and Europe enjoyed a mild month.
The sustained cold did not set in until around the 10th, when the first Arctic surge dropped south. That front can easily be seen in this surface map from early afternoon on November 10th.
The coldest morning would be a week later on the 18th when early morning temperatures looked like this:
As in 2013, the pattern flip was assisted by a Super Typhoon re-curving into the Pacific. Here’s an image of Nuri (20W) near peak intensity. Maximum sustained winds were 155 kts (182 mph).
Nuri became a record setting mid latitude storm system which pumped warm air into the Arctic, that pushed cold air south into the U.S. (This image shows ex-Nuri at it’s peak as an “extratropical” storm system.
November was a dry month. Rains were a 1/2-1″ or less in E KS/W & NW MO and 3″ or less in the remainder of MO and S IL. All areas finished below average thanks to the cold weather pattern. Rainfall was 25 to 50% of average n E KS/W MO and 50-75% of average in E MO & S IL. Abnormal dryness, as defined by the U.S. Drought monitor, had not yet returned to the region, but may do so in the next few weeks. These next three maps show the total observed precipitation, the difference from average and the percent of average (click to make the images more readable).
The St. Louis area had 4 days with a trace of snow, 1 day with .7″ of snow and 2 days with 1-2″ of snow. These combined totals brought 3.8″ in the snowfall bucket for November, above the long term average. Kansas City had 5 days with snow, all of .3″ or less and finished with just 1/2″ in the snowfall bucket for November, below the long term average.
Autumn (Sep-Nov) was cool and wet for some and cool and dry for others. KC was 2.1 degrees below average and rainfall was 2.29″ above average. St. Louis was 1.9 degrees below average and had 1.37″ above average rainfall. Much of SEMO/SW IL had only 50-75% of average rain, with the same for areas just south of KC and over into eastern KS.
These next three maps show the total observed precipitation, the difference from average and the percent of average for meteorological Autumn. (click to make the images more readable).
Looking forward, we had been mentioning a relaxing of the cold pattern as we headed into December. Early this week notwithstanding, the pattern by late in the week end the weekend will feature a mostly west to east flow over the U.S. The cold upper low has rotated up into northeast Canada and mild Pacific flow is dominating, even into western Canada, our usual cold air source.
There is also a subtropical jet stream bringing moisture into the Southwest and SoCal. This southern jet loses moisture over the southern Rockies but regains it over the Gulf. That moisture flow will head ENE through the south, southeast and east. This will bring an opportunity for late week rains over mainly southern/eastern areas of the district. Moisture for Topeka/KC unfortunately, looks marginal at best. This type of pattern is called a “split flow” and is typically a dry one for the Central Plains and western Midwest. Take a look at these three longer range model runs for the Midwest out to 10 days (December 11th). Keep in mind these are ONLY model runs and likely will change in the coming days. Nonetheless, at this time there is general agreement that the first week and a half of December will produce only .10″ to .20″ of moisture for KC and Topeka. STL fares better with .30″-.60″ while SEMO/SW IL look to get an inch or better of moisture.
A look at the same model’s snow projections agree on little to no significant snow (note the snow totals over SEMO/SW IL are in part interpreted from the icy mix that fell this morning).
The only real chance for any “wintry” weather will be as the warm air arrives Wednesday night and Thursday morning when we could have a repeat of this morning’s weather conditions over SEMO/SW IL and as far NW as STL, with some light icy mix possible.
In summary, expect a moderation in temperatures this week after a cold 24 hours though Tuesday. There is the chance for a LIGHT icy mix for STL/SEMO/SW IL Wednesday night into Thursday. Temperatures recover back to the 40s Friday and into the 50s next weekend. The next cold shot (after this one) looks to be a week away at the earliest and that one appears similar to today’s. Significant rains look to bypass KC/Topeka and are more likely from STL south and east. No big winter storms apparent on today’s data through at least the next week-10 days. LONG term signals pointing to more prolonged and stronger cold mid month or the back end of the month.