We’ll be in for a quick shot of Arctic air this week but the worst of the cold will build down the Front Range directly to the Panhandles with lessening impacts as you head further east. New Year’s Eve looks seasonably chilly with no weather issues expected. A chilly couple of days will be followed by quick moderation as we move to the end of the work week, back to near average early January levels by the weekend. Otherwise there will be a system to watch for late week or early next weekend. Details on that won’t be resolved until later in the week. Colder weather may follow the week of Jan 5th.
With just 3 days left in December, lets’ first take a look at where we stand. It’s been a warm month (relative to average) over most of the country with the limited exception of parts of Florida and the outer banks of NC.
A lot of the warmth has to do with mild Pacific flow and a lot of cloud cover. The charts below show a plot of the cloud ceilings (level of the cloud layer above the ground). Grey indicates an overcast of some sort..lower or higher. Blue indicates clear skies to 25,000 feet. It’s easy to see there have not been many clear days this month at any of the stations shown here. (Click to make the charts more readable).
While we’ve had a couple mild days, the big thing these clouds have done is keep lows well above average, as shown in the charts below. Average is the blue filled area of the chart which gradually eases downward from left to right. (Click to make the charts more readable). This is the biggest reason December is running so much above average.
Not surprisingly, the warm December and the mild Pacific flow have kept season snow totals on the low side. These totals are 2014-2015 season totals through yesterday at 7 AM. Paducah KY and Kansas City MO have had more snow than Chicago! The heaviest totals east of the Rockies are in the snow belts of the Great Lakes and are more due to November’s cold and lake effect snows. Through today, in fact, Chicago has had NO MEASURABLE SNOW in this month, and if none falls before midnight 12/31, this will be the first time since 1912 that this has occurred and only the second time in Chicago recorded history. (Click to make the charts more readable).
So where do we go from here? The answer is COLDER. This is nowhere near a record setting cold outbreak — and in fact we’ll have been colder in November, but it will be a lot colder than we’ve seen this month. We’ve been watching for this turnabout in the weather since mid month. Take a look at the surface chart for Canada this morning:
That’s our Arctic high, building in Yukon and far NW Canada. The Arctic boundary is still well to our north. Here are the surface temperatures this morning over North America, Asia and the Arctic. (Click to make the charts more readable). Compared to posts 1-2 weeks ago, the 0F line has definitely moved south and covers a good chunk of central Canada across the Arctic and into east Asia. The cold in east Asia is a little less expansive than it was several weeks ago, but it also has resurged into central Russia.
Snow cover has filled in a little to the northwest. (Click to make the charts more readable). Ignore greys and blacks, and focus on the cold-toned colors only as the model tends to over-estimate snow cover.
That’s good news for us, as it means that the lack of snow locally will allow the Arctic air to warm before reaching us as it moves over bare ground, and it will allow it to moderate to less severe levels late in the week. This type of airmass over snow covered ground could easily result in below zero cold. As it stands right now, though, the core of the cold will build down the Front Range of the Rockies and push rapidly south into Texas and more slowly spread east. Lows will drop to 5 to 7 degrees below average for SEMO/SW IL/STL..mid teens.. Tuesday night, that’s with some cloud cover. Lows in KC will drop to 10-12 degrees below average.. around 7-10F in the city, slightly colder, 3-8F in the rural areas. W/NW MO will be deeper into the cold air. Further west, out across KS, lows 0 to +5 can be expected. Bitter cold, lows -10 and colder will hold up over NE/CO/WY where there is deep snow cover on the ground. Temperatures will quickly recover to more seasonable levels in the mid to upper 30s for highs as we close out the work week. The map below shows lows for Wednesday Morning 12/31/2014:
Longer term, cold will return as the pattern in the stratosphere shows. This series of maps shows the polar vortex at stratosphere levels as a tight swirl of purples and greys. It is currently strong and over the pole. Note the warmer air developing near China and Sibera -again at the stratosphere level..so warmer is still many tens of degrees below zero.
This begins to deform the vortex into a weaker lobe over Russia and Hudson’s Bay by New Year’s Day.
Next Sunday, we have a weaker and split vortex over Hudson’s Bay and another over central Russia, The Hudson’s Bay location is a cold signal for the lower 48.
In terms of rain or snow.. the outlook is much less clear. We may have some flurries or very light snow as the cold air and Arctic boundary pass us by and squeeze out what’s left of the moisture in the air, but as you can see in the chart below, the air is already very dry over us and to the north and northwest, the moisture already having been swept out by last week’s cool front.
What we’ll be watching for this week is the development of a cut-off low in the Southwest U.S. This happens when a wave of lower pressure at the jet stream level becomes separated from the jet and basically sits and spins over one area. The Southwest U.S. can be a favorite area for these lows to form. The chart below shows the mid level air flow New Year’s Eve with the low spinning over California. Where this low eventually tracks-and when- will become the next potential weather maker for the area. The low doesn’t even exist yet- it’s an area of spin now in British Columbia and diving southeast. At this early stage, it is nearly useless to speculate on any winter weather impacts for our district, much less on what type, and we’ll explain.
The eventual track of this feature and the important mid level low, which helps determine where rain/mix/snow might fall, are really uncertain right now. Take a look at the charts below showing the OPERATIONAL versions of the models going out that far. The track runs anywhere from NM to WI on the north to NM to W KY on the south. Measureable snow is scattered all over the place.
As expected, the most recent runs offered an equally varied solution. Again from CO to MI on the north side and from NM to KY on the south side. The Canadian GEM model didn’t even have a closed low. Snowfall areas are scattered from north TX to Wisconsin.
These are only the OPERATIONAL models; each model has its own “ensemble group” or many different versions which start in the same place and are “tweaked” to run on different equations. Add all of those in and you wind up with what looks like a plate of spaghetti. The green line in the chart below show the possible locations of the mid to upper trough later this week in the GFS model alone. Each separate line is a different solution and would produce different weather.
All of this means confidence in what type of winter weather will occur this next weekend, is virtually non-existent. This will be yet another one of those weeks where you’ll see great differences in the longer range of any 7-day forecasts between channels/stations, and from day to day. About all that can be said with any certainty is there is an increased chance for some type of precipitation late this week and early next weekend and at this point, it’s just something to keep in the back of your mind. We’ll have updates as we move through the work week.
How about the rest of Winter 2014-2015? We’re a third of the way done for Meteorological winter on Wednesday (Dec-Jan-Feb), and so far we’re 4.4F above average for the season to date in KC and 5.4F above average for the season to date in STL (we’ll take the edge off of these numbers a little this week). In November, we stated that the overall pattern favored colder than average conditions for the three month period. At this point we still expect below average temperatures for the season when we average the warm December with anticipated colder temperatures in Jan and Feb. The ocean sea-surface temperature plays perhaps the most vital role in our weather patterns. The chart below shows the sea surface temperature anomalies (difference from average) across the globe. We’re mainly concerned with the subtropical north. We’ve 5 key areas (outside of El-Nino) that are of interest. Warm water in the Gulf of Alaska/PACNW (5), off the southern California coast and Pacific Southwest (4), in the western Atlantic (3), cool water in the north central Pacific (1) and in the northeast Atlantic (2).
It should be noted that these differences from average don’t mean the waters are steaming warm or ice cold, here is the current sea surface temperature across the globe.
The warmer than average areas are still cold and the colder areas are not frigid by any means. Water temperatures warm enough to support deep tropical convection and tropical cyclone formation (26C/78F-yellow) are mostly well south of 20 degrees north and “bathwater warm” ocean water is mostly along and south of the equator (30C/86F).
Each of these sea surface temperature difference (areas labeled 1-5) correlate with certain weather patterns. Taking into account these areas alone, they correlate historically with these types of local Jan/Feb temperatures (as researched by WeatherBell Analytics):
Area 5: Near average temperatures
Area 4: Well below average temperatures
Area 3: Slightly below average KC to slightly above average S IL
Area 2: Well below average temperatures
Area 1: Well below average temperatures
When these areas are weighed with each other in the historical record and other atmospheric/oceanic indexes are applied, the result looks like this:
We’ll see if Jan/Feb average out in this neighborhood and if the winter forecast verifies as below average. Mathematically, we’d need at least one of these two months to be as much below average as December was warm and the other month to be colder than average — or we’d need both months to be some combination over 2 degrees below average.
If we take a look at precipitation for those same years as shown above, a slight dry signal emerges for Jan/Feb; anywhere from 0.25″ to 0.75″ below average for the two month period. In a colder than average regime, below average precipitation does not mean below average snow — as was the case in KC last winter.
That’s it for today. More on our cool-down and any late week system later on this week.