Winter begins at 5:03 PM Central Time today
Today marks the Southern Solstice or the Winter Solstice in the northern Hemisphere. The sun reaches it’s southernmost track on it’s annual journey. For those of us 35-40 degrees north longitude, as we are here in the district, it means a late sunrise in the southeast, a low tracking sun not far above the horizon through mid day and an early sunset in the southwest. Despite winter’s arrival, truly cold weather still appears a little ways out.
Daylight is at it’s minimum today, with just over 9 hours and 25 minutes from sunrise to sunset. The sun is also dimmer/redder than it is during mid summer as the light has more atmosphere to travel through. Recall the hot, harsh, and bright white mid day sun 6 months ago in June.
The good news is that sunsets have already begun to get later, and as of tomorrow, we gain more minutes in the evening than we lose in the morning for a net gain of daylight. By mid January, we begin to gain daylight in the mornings and the pace of the lengthening days will really increase.
Compare our daylight/sunrise/sunset with other cities across the country today (image: Washington Post). Fairbanks Alaska has just under 4 hours of daylight, Seattle and Minneapolis 8 1/2. Southern cities such as LA, Atlanta and Phoenix hover closer to 10hrs, while Miami remains at nearly 10 1/2 hours.
Let’s take a look at temperatures across the northern hemisphere as winter begins:
Bitter cold continues in eastern Asia including Siberia where temperatures average near 60 degrees below zero. Readings in western and central Asia are a bit less cold.
Across the Arctic where there is no daylight today, subzero readings stretch across the pole to Greenland, the Canadian Arctic and north Alaska.
Europe is relatively mild with no areas below zero, save the high terrain of northern Sweden and Norway.
Here in North America, temperatures are also not bad with very limited areas below zero and no area of the lower 48 below zero.
In the Southern Hemisphere this is the first day of Summer, with temperatures hot over Australia. Antarctica, where there is 24 hour daylight, readings are very cold but not as cold as they are now in Siberia.
December, to date has been quite mild over the lower 48, as this chart shows, with chill limited to a few areas in New England, the outer banks of VA/NC and Florida. The warmth has been concentrated over the central Rockies and Great Basin. Across the district, temperatures have been 2 to nearly 5F above average. Carbondale the “least” warmest with 2.1F above, and Topeka the warmest with +4.9F.
Pacific flow has been dominating North America this month. This moist flow has been cloudy for many areas and that brings up an interesting fact. What’s interesting is that, with the clouds, daytime temperatures have been nearly average with a FEW days above, while nighttime lows have really made the difference being above to well above. In fact for the STL region, only two days in December had lows below average. Two days also had lows warmer than the average high. St. Louis has had 0 clear days, 6 partly cloudy days and 14 cloudy days. Kansas City has had 1 clear day, 4 partly cloudy days and 15 cloudy days. Carbondale has had 0 clear days, 7 partly cloudy and 13 cloudy days. Topeka, KS has seen the best weather with 5 clear days, 1 partly cloudy days and 14 cloudy days. Although it has been a warm month, the source of the warmth lies more in mild overnight lows rather than a string of very warm days.
December has also been mild in Europe, western and central Asia and the Middle East. China, south central, eastern Asia and Siberia have suffered in the cold.
We’ve a bit of rain coming this week with amounts rather modest, and highest in the east and south. This warm system rolls into the area beginning tonight in KC and winding up Monday night there, while arriving Monday for SEMO/SWIL/STL and winding up Christmas Eve with perhaps a few snowflakes as the seasonably colder air wraps back into the system as it lifts out. Barring the GFS, no significant accumulations are expected in eastern areas of the district. The longer duration of the weather system in our east is due to a secondary low which forms along the Gulf Coast and tracks north-northeast. This low becomes the main center of the storm system when it lifts into SE Canada by week’s end. It is this secondary low which the GFS (alone) uses to create accumulating snows for SEMO/SW IL/STL. Kansas City/Topeka are far enough removed to miss any effects of this secondary low and instead get a band of light precipitation with the original low’s cool front and that’s it.
If you’re holding out for a White Christmas, you’re best (and only fading) shot is in STL/SEMO/SW IL and with the lower-resolution GFS model. That model has insisted that a small band of heavy snow develops over the eastern district as a secondary low tracks through KY. The GFS has insisted on this for 24 hours now.
All the other higher-resolution models (including the GFSx which replaces the GFS next month), have nothing of the kind showing up. Here are all the charts for the same time period, noon Christmas Eve:
We’ll have to see how this plays out with today’s suite of incoming data. (Note: the just in morning run of the GFS has backed off on this a little, but still has accumulating snows in the same area Christmas Eve and no other model is producing significant wintry weather).
Christmas itself looks dry and mild at this point with highs in the middle 40s (GFS model run not withstanding).
After Christmas it’s back to cooler weather although not really cold. We’ve got three things keeping us from getting truly cold. The first is that the Pacific flow has kept the Arctic chill from becoming established in our cold air source region in the Canadian Prairies. Mild Pacific flow becomes downslope off the Canadian Rockies and warms further. The Arctic flow is circling the pole well north. There are signs that could begin to change later this week.
That leads to our second issue. Because of that Pacific and downslope flow, temperatures there are only a little colder there than they are here. Readings are in the teens and 20s, while chilly, that’s mild by late December Canadian standards. We need the Canadian Prairies to really get subzero cold before we can start to think about any Arctic air headed in our direction.
The third issue: When cold air moves south, it starts to be modified by the ground it travels over, especially if there is no snowfall. The map below shows plenty of snow in Canada, but not so much south of the border. Except for the mountains, and one spot in North Dakota, you’ll have to go all the way to south central Alberta, Saskatchewan or Manitoba to find snowcover deeper than 6″. We really need snowcover to expand further south and east – and deepen – before any Arctic air developing in Canada has a chance of retaining it’s chill as it head south.
This gives plenty of time for the “cold” air to warm as it moves from the Canadian border to the district. The bottom line is that we’ll likely see a return to near to slightly below average temperatures in the weekend which follows Christmas.
When will it get really cold? There are signs of a change in the upper air pattern to our north which would allow substantial cold to begin to build in Canada. There are also forecast to be significant snows to our distant north and northwest this week and this weekend, which would increase the depth and southward extent of the snowpack. The earliest time these factors would come together to impact us would be in the days before the new year. That’s still 10 days away though and a lot could change timing wise between now and then. As we’ve been mentioning – these transitional patterns where large scale and longer term changes take place make it a tough to have confidence in the specifics just yet.