NA December Weather Discussion
Posted 10 December 2011 - 07:25
The models continue to have no idea how to handle this pattern more than about 5 days out. The European model has been calling for incredible warmth for the entire U.S. in its weeklies for a while now and nearly the opposite has verified with two Arctic air outbreaks already so far across my neck of the woods. The weeklies on Thursday continued that pattern with cold the first two weeks and then what looks to be near record warmth for all of the U.S. during Christmas week into New Years... with above freezing temperatures surging up into central Canada. Very unlikely. That model in particular has been horrid so far. The GFS hasn't been much better. The Japanese model is the only one that has had some semblance of accuracy.
In any case, temps will be seasonably mild here through the middle of next week when a significant storm is possible, which will usher in colder air. The models are in some agreement on a storm dropping into the desert southwest and cutting up the plains into the western Great Lakes. This would be the perfect storm track for snow here in Minnesota. A secondary low would form off of the frontal boundary from that system and move up the east coast, perhaps bringing snow there and ushering in colder temps. If so, it would be the first significant snow of the season here... not unlike another analog winter, 2008/09.. which saw cold in early December but no significant snowstorm until mid month. If it misses us and goes east across the southern and eastern Great Lakes like some models suggest, it will seriously shrink the chances for significant cold across much of the northern U.S. since the lack of snow cover here would moderate any truly cold air masses to come down from Canada.
The pattern so far has been quite the opposite of what many forecasters had predicted when they said we'd have a severe, early start to winter with major blocking taking place in northern Canada and Greenland. Instead, it has been nearly the opposite with unusually low heights in northern Canada and Greenland with a strongly positive Arctic and North Atlantic Oscillation mode in place. This has delivered mild weather to Europe and the eastern U.S. with the chill being in more traditional places for the positive NAO mode: Central Asia/near the Caspian and central Russia and northeast Siberia as well as Alaska and NW Canada. The wildcard is the unusually warm waters in Hudson Bay which have prevented it from its normal November freeze up. It is now freezing rapidly, earlier than last year... but it has kept that part of Canada from seeing serious cold despite the strong vortex in place there. In any case, the rapid freeze up of the bay and the Labrador Sea region will only encourage continued low heights in the region and reduce chances for blocking activity.
That said, the models keep hinting at blocking highs building near Franz Josef Land in Russia and near Scandinavia which often move across the icecap into northern Canada and deliver frigid cold to the eastern half of the U.S. The GFS is showing such a connection from central Russia to NW Canada in the 6-10 day period which would break the vortex that has developed from Greenland across the icecap to the Bering Sea... a pattern that keeps the continents mild and wastes all the Arctic cold out over the oceans. This pattern has been one reason why the Atlantic ocean is cooling rapidly and the AMO went negative during November for the first time since 1995. A negative AMO will actually only discourage blocking and encourages a more northerly position of the polar jet across the Atlantic, keeping northern Europe mild and wet.
Posted 12 December 2011 - 00:30
The models are still conflicted on the storm later this week. The short-term NAM model is the only remaining model to show the storm cutting up towards Wisconsin and Lake Superior, which would bring significant snowfall to northern Minnesota. The Navy NOGAPS also shows a wave of precipitation moving out ahead of the storm that could bring a couple inches of snow here, but it, like most of the other models, have trended eastward with the main storm. I'm keeping my fingers crossed!
The only problem is that if we don't get this storm, the chances aren't looking good for the next two weeks. To me, there's nothing more depressing than a brown Christmas!
There are signs that a stratospheric warming event might take place over the next couple weeks. This would set up the conditions needed for blocking to take hold, especially over Canada, which would make conditions ripe for a significant Arctic outbreak across the U.S. But we're talking after New Years for that. In the mean time, the models are all over the place from cold to blowtorch warm... though I remain skeptical of the overwhelming warmth the European model and GFS are seeing further out. I just don't think the models are set up to handle the type of pattern we're in, so they keep fighting to put ridges and troughs in places that contradict each other.
In any case, I'll be crossing my fingers and doing a snow dance for the storm later this week... though I can't help but be glum and pessimistic as I've seen so many storms come knocking only to slip to our south and east.
Posted 15 December 2011 - 03:10
RIght now in Bemidji at 9pm it is 32˚F under cloudy skies with intermittent very light snow and mist with dense fog. Visibilities have been under a quarter mile all evening and driving has been nearly impossible and quite dangerous as the roads are icing over and it's difficult to see your hand in front of your face, much less other cars or an animal that decides it's a good time to cross the road.
Temperatures will begin to drop over night and fall throughout the day tomorrow reaching the lower single digits by Friday morning.
With only a couple chances for light snow before Christmas, it looks like it'll be the 2nd Christmas in my life with no snow (the last was 2006). Temperatures will be seasonably cold the next few days but will moderate and remain above normal over the next week.
Mid-range: There is so much uncertainty in this pattern, but it currently looks like, at least through the 14 day period, that it will remain quite mild across most of the U.S. and western Europe as an unusually strong polar vortex remains entrenched in the northern Hudson Bay region and also in NE Siberia with a strong, zonal flow for most of the mid-latitudes.
There is evidence that a stratospheric warming event is in the works, showing up at the 10mb and 30mb levels, which could usher in a major pattern change shortly after Christmas, which would bring much colder and snowier conditions into much of the U.S. and likely Europe as well.
Lately, the ridging in the Gulf of Alaska and east of Hawaii have favored a strong southeast ridge, and so if the pattern does flip and blocking becomes more prevalent over the Arctic, we could see a case where almost all of the lower 48 is inundated with Arctic air, with the coldest against the normals across the central Rockies and in Utah. If this occurs in the heart of winter, it could spell a lot of misery for a lot of people, especially if the pattern remains active.
The models are beginning to pick this up.. so I'll keep my fingers crossed. I am jonesing for some snow!
Posted 15 December 2011 - 06:16
The front has definitely passed. While in the evening it was dead calm with pea-soupy thick fog and mist, the temperature has fallen to 27˚F and the wind is now gusting up to 20mph from the west with a few bands of snow popping up. The ground has already turned white, though I don't expect more than a half inch of snow or so.
Posted 19 December 2011 - 13:49
Posted 27 December 2011 - 11:31
In the mid-range, it looks as though a trough will move into the eastern U.S. and bring cooler weather to the eastern 1/3 of the U.S... but because of the trough in the Gulf of Alaska, the air masses will be a hybrid of Pacific and Arctic air, meaning the plains will see very mild weather with only the eastern seaboard being colder than normal since the proportion of Arctic air will be strongest there.
For the month of December so far, heights in the high latitudes have been unusually low, especially near Greenland and Iceland stretching across the North Sea moving across the pole and over the Far East, and back into China. Temperatures have been chillier than normal in the SW 1/3 of the U.S., bits of NE Canada, Greenland, Iceland, and NW Britain, generally across the Far East, centered on Japan, across northern Africa, the Middle East, and back across China and the Asian Steppes to the Caspian sea. Warmth has dominated from Alaska down the mountain west of Canada into the plains and east of the U.S., across Scandinavia and continental Europe and northern Russia, and in the north central Pacific ocean.
This regime of cold Arctic/Subtropics and warm Mid-latitudes is the exact opposite of what we experienced in 2009/10 and the first part of 2010/11 when the planet was significantly warmer overall with all the warmth in the Arctic and Subtropics with cold sandwiched in between. A study found that while the extreme cold in the eastern U.S. and NW Europe the past couple winters was unusual.. it was not nearly as unusual as the warmth that took up residence in Labrador and Greenland.
The unusually strong jet across the Atlantic and strengthened trade winds thanks to the strong subtropical highs has significantly cooled the surface of the Atlantic ocean and we saw the coldest November for the Atlantic since 1996. The Atlantic Multidecadal Oscillation actually went a tidge below 0 in November. The last stint with a negative AMO was in early 2009. The AMO has generally been positive since 1995 and set record highs in 2010.
As for the longer range... it appears the La Niña has likely reached its deepest point as far as sea surface temperatures are concerned. The atmospheric component of ENSO, the Southern Oscillation, has been strongly positive recently and the 30 day averages are getting into the upper 20s.. similar to last year, but unusual in recent decades. Rainfall has been much enhanced across northern Australia and Darwin has had nearly 17" of rain for the month so far compared to a montly average of 10". The increased trade winds this causes will likely cause more upwelling of cold subsurface water in the central Pacific. The Niño 4 region, the westernmost Niño region, had been lagging behind the more easterly regions.. but in the past few weeks has really cooled down. This La Niña is beginning to act like a mature, 2nd year event where the coldest water occurs further west.
Coinciding with this are the beginnings of a stratospheric warming event that could mean Arctic air finding its way into Europe and the U.S. in the next few weeks. The bulk of the warming looks to be occurring over western Canada and Alaska, which will displace the polar vortex southward over Scandinavia and the north Atlantic. This could mean Arctic air gets into the western/central U.S. first before moving east. This kind of a pattern would mean significant cold for most of the lower 48 states... but it will all depend on the strength of the southeast ridge, which has been strong this year. If it remains strong, the southeast might remain mild while everybody else is in the deep freeze. If the ridge moves into the south central or SW states, however, it might invite frigid air all the way down to Florida.
At this point, the winter could go in any direction. You have numerous La Niña examples of "slow to arrive, slow to leave" winters... which is the typical pattern in La Niña for the upper midwest (mild fall/early winter, cold mid-late winter/spring). Examples include 1949/50, 1954/55, 1964/65, 1974/75, 1988/89, 2007/08. Most of these were "first year" La Niñas following an El Niño year, however. But that doesn't necessarily mean anything.
There are examples of La Niña winters that were generally quite mild, but with a 3-5 week period of intense winter weather. 1962/63, 1967/68, 1984/85, 1998/99.
Then, of course, there is always the chance that the winter could simply remain mild. The most extreme case of this is 1999/2000. 1998/99 could almost qualify except for a truly nasty period from mid-December to late January. 2005/06 could also qualify, but mostly due to record warmth from mid-December to early February and then a warm spring. Otherwise you have to go back to the 1930s to find a winter that was consistently mild with La Niña conditions present: 1933/34. And that winter was basically a one-off event of extreme cold in the Northeast with extreme mildness everywhere else.
Right now, my bets are on a "slow to arrive/slow to depart" type of winter a la 1949/50, 1954/55, or 1974/75. So far, this winter has been closest nation-wide to 1974/75 with general mildness in the northern part of the country, with chill in the southern part of the country.. especially out west. That all came to an amazing turnaround in mid-January with one of the worst blizzards in Minnesota history. Heavy snows and then unusual cold lasted into early May.
If you look at the "slow to arrive/slow to leave" winters, which make up about 1/3 of all winter seasons, the La Niña ones tend to have the most lasting cold after new year. The neutral winters tend to see cold into early spring, then a "spring-shot" to normal conditions. El Niño winters often see mild weather into mid January, then frigid cold for 6 weeks or so before near normal to warm conditions arrive for early-mid Spring. The cool weather often returns for late spring/early summer... especially if it has been a strong El Niño event.
So my bet is that winter will get progressively worse for the nation as a whole over the coming 6 weeks with the coldest weather compared to normal for the nation as a whole taking place in the late March-mid April time period. Of course I could be completely wrong, as I was on the early winter forecast... but history is always a good teacher when it comes to weather... and the history leads in that general direction.
Posted 27 December 2011 - 16:00
A bit mre detailed then I was thinking, though a 74-75 pattern does make a lot of sense. It really depends on the strength of the PDO, with the warming moving from TWP north of our cousins the Aussies up thrugh the S. China Sea would suggest a surge of atmospheric moisture moving across the N. Pacific.
This would have a tendency to feed a mild temperature across the US for the next few weeks. It really depends on what happens in the Arctic, if the vortex swings East with the NAO/Azores high slipping South the result would normally suggest a slow in/slow out pattern delaying the warm up to nearly June. With the cooler then normal SSTs in the Atlantic the chance for a vicious Winter Fishing season of the Grand Banks is probable.
This would normally suggest a higher chance for a series of Nor' Easters; however, with the Bermuda High staying South and West this is unlikely. The pattern setting up is the normal El Nino, Tennesse and Ohio valley induation with strong Winter storms daisy chaining up the Western side of the Appies and the chance for another, "Perfect Storm". Again, I would be watching the Northern Jet if a trough forms on the West coast of Europe, a cooler Eastern US Seaboard Winter, with a vicious mid-west Winter, and a mild; but, wet SW Winter. If on the other hand the Bermuda High moves NE to backfill the Azores High moving South, look for a Early El Nino development and a mild US Winter or a "Year without a Winter"...
Posted 02 January 2012 - 07:37
Avg Temp: 20˚F /-6.7˚C Dept: +8˚F/+4.4˚C
Avg High: 28.1˚F/-2.2˚C Dept: +7.1˚F/+3.9˚C
Avg Low: 12˚F/-11.1˚C Dept: +8.9˚F/+4.9˚C
Highest temp: 45˚F (7.2˚C) on the 26th
Lowest temp: -8˚F (-22.2˚C) on the 5th and 6th
Precipitation: 0.32" (-0.47")
Rainfall: 0 (avg)
Snowfall: 6" (-5")
Days with trace precip or greater: 17
December 2011 was much warmer and drier than normal, continuing a trend that began in late November. The first 10 days of the month were actually colder than normal overall, but the overwhelming warmth the last 2/3 of the month left us with our warmest December since 2006. In fact, the month was similar to 2006 as that year also saw cooler conditions early in the month only to be ameliorated and then overwhelmed by warmth later on. Still, Dec. 2011 was 3˚F cooler than Dec. 2006.
The month was considerably drier than normal and stands in contrast to the much snowier than normal Decembers experienced in each of the past 4 Decembers. Most snowfalls were very light and quickly sublimated away in the mild afternoons. The only significant snowfall of the month occurred on the 30th and 31st, when about 4" fell.
For North America as a whole, the eastern half and northern half of the U.S. were each much warmer than normal with much cooler than normal conditions across the southwest. Over Canada, much of the nation was warmer than normal with the exception of parts of Labrador and Newfoundland and the far northern Canadian archipelago. Particularly warm conditions prevailed from the Yukon into northern BC and Alberta and across the Prairies stretching into the northern plains/upper midwest into the northeast of the U.S.
Precipitation wise, Alaska and central Canada saw heavy precipitation along with areas of the desert Southwest, parts of Texas, and areas of the eastern U.S. west of the Appalachians. The western U.S. outside of the deserts was particularly dry with many ski resorts starved of snow. So while you're skiing in 50˚F weather on a 2 foot base at Mammoth in California, head to Eaglecrest in Juneau, Alaska where they're boasting a 12 foot consolidated base with several feet of snow in the forecast!