December Warmth Sends Temperatures Up to 30 Degrees Above Average
A very mild weather pattern for early-December standards has engulfed a large swath of the Lower 48 states. Temperatures will soar up to 30 degrees above early-December averages through this weekend as the mild air spreads from the western and central states to the East Coast.
For some locations, the low temperatures this week will be as warm or even warmer than the average high for this time of year. In addition, some record highs and record warm low temperatures could be set through the week ahead.
Below are the forecast details.
Cold Air Stays Bottled Up North
As we start meteorological winter, which runs from Dec. 1 through Feb. 29, true arctic air remains locked up in extreme northern Canada, well to the north of the U.S. border and even well north of all the major Canadian cities.
Current Canada/Northern U.S. Temperatures
The white line denotes the approximate freezing line (32 degrees Fahrenheit, 0 degrees Celsius). Note in this December warm spell it extends well into Canada.
Friday, at least 16 Canadian cities set daily record highs, particularly in Manitoba, where the city of Morden, southwest of Winnipeg, soared to 14.2 degrees Celsius (about 57.6 degrees Fahrenheit). An additional fourteen daily record highs were set in Manitoba Saturday-Sunday, including Emerson (7.1 degrees Celcius/44.8 degrees Fahrenheit on Sunday) where records date back to 1877.
Highs reached the freezing mark as far north as Thompson, Manitoba on Friday (roughly 55 degrees north latitude, about 470 miles north of Winnipeg). The average high on December 4, there, is -13.8C (7.1 degrees F). Just a bit farther northeast of there on Saturday, Gillam, Manitoba, reached the freezing mark which also was a new daily record (0.3 degrees Celcius / 32.5 degrees Fahrenheit).
In the U.S., both Marquette, Michigan (50 degrees at the NWS office in nearby Negaunee Township), and International Falls, Minnesota (45 degrees), tied their daily record highs Friday.
On Saturday, International Falls tied its record warmest low temperature for the month of December, only dipping to 36 degrees just before midnight. Then on Sunday a daily record high of 45 degrees was set. So much for the "Nation's Icebox," at least for awhile.
Portland, Oregon set a new record high of 63 degrees on Monday, as well as a record warm low temperature of 46 degrees. South Lake Tahoe, California tied their daily record high on Monday when the mercury rose to 56 degrees. Williston, North Dakota also tied the record high for Dec. 7 with a high of 49 degrees.
While December is early in the winter season, it is quite common for chunks of bitterly cold air to reach the U.S. during the first half of the month.
However, most computer model forecast guidance shows no such thing happening right into the middle of this December for the eastern two-thirds of the U.S. and Canada, as the arctic jet stream remains well to the north in Canada.
Although some colder air should reach the western and central states later this week, the airmass is projected to be fairly modified, meaning that the coldest air still remains locked up in northern Canada. The result may only be a drop to near or slightly below average in terms of temperatures.
Looking Ahead
Forecast Highs Compared to Average
Darker shades of orange and red correspond to areas that are forecast to see temperatures the farthest above average for the day indicated.
There are no signs of any major blasts of cold air reaching the U.S. in the near future.
Through this week, the relative warmth is likely to continue. The most unseasonable warmth is forecast across the central U.S., but that warmth should eventually spread to the East Coast by late in the week and this weekend.
Forecast Highs Compared to Average
High temperatures will be 10 to 30 degrees above average in many locations across the country this week. Some daily record high temperatures may be set as well, particularly this coming weekend.
Low temperatures will be up to 35 degrees warmer than average in some locations at times this week. Some areas will see low temperatures that will be warmer than their average high temperatures.
Forecast Highs Compared to Average
One example is Minneapolis where the average high for mid-to-late this week is in the upper 20s. Low temperatures will only drop into the 30s this week with record warm low temperatures possible (current record is 34 on Thursday, 35 Friday and 37 on Saturday).
Low temperatures in Kansas City will likely bottom out in the 40s at times Thursday-Saturday, and the average high for this time of year is in the lower 40s.
Buffalo, New York, will see low temperatures in the middle to upper 40s Thursday-Sunday. This is several degrees above their average high this time of year which is in the upper 30s.
Thursday through Saturday morning, temperatures are not expected to drop below the freezing mark for most areas east of the Mississippi River, with the exception of parts of Maine and possibly the Upper Peninsula of Michigan.
Numerous daily record warm low temperatures will likely fall by the wayside in the eastern two-thirds of the country.
Daily record high temperatures may be most numerous from the Ohio Valley into the Southeast on Saturday, and then from the Northeast into the Southeast on Sunday.
Among the cities potentially threatening daily records on Saturday are Pittsburgh and Detroit where highs may surge into the 60s. Philadelphia (60s) and Atlanta (low 70s) could threaten daily record highs on Sunday.
Forecast Lows Late Week
Temperatures will be even more out of whack in Canada, where much of the country, except the typically cold Northwest Territories, Yukon Territory, British Columbia and Nunavut will feel temperatures well above normal through the second week of December. At times parts of central Canada could be up to 40 degrees (24 Celsius degrees) warmer than average, especially in terms of nighttime lows.
Some computer models do show some changes by this weekend. A series of frontal systems should sweep from the West into the Plains, perhaps bringing some cooler air at least to the West and parts of the central states. However, even if such a pattern develops, indications are that at least the eastern half of the country stays warmer than average out ahead of it.
Everything seems to be going to plan according to December temperature outlooks that peg much warmer than average conditions across the northern tier. At least for the first two weeks of December, conditions are closely following what is generally expected during a strong El Niño.
Long-range computer models show no significant shift in the pattern for the second half of December either, although there are some signs that parts of the West and southern Plains may cool off slightly later in the month.
What Effects Will This Warmth Have?
As a result of the jet stream staying north of the U.S. frequently throughout November, parts of the Northeast and Mid-Atlantic have remained rather mild and snowless recently. Philadelphia saw its second warmest November on record in 2015, and made it through the autumn to the start of December without a freeze for the first time since 1939.
For Buffalo, New York, it was the seventh warmest November on record. Buffalo has also yet to see accumulating snowfall this season, marking the longest the city has gone in a snow season without receiving its first measurable snow.
(MORE: Still No Snow in Buffalo)
The lack of snowfall and nights below 32 degrees means a tough start for ski resorts in parts of New England and the Appalachians. Over the Great Lakes, on the heels of record late-season ice into spring 2015, lake ice formation may be significantly delayed.
Interestingly enough, a delay in freezing of the lakes could support a later lake-effect snow season, as colder air moving over warmer lake water can lead to the development of heavy snow bands into early winter. This, however, depends on the ability of substantial moisture to coincide with sufficient cold air, something that has struggled to happen so far this season.
It is not just the northeastern quarter of the country that has escaped the bulk of winter’s fury to date.
Florida, in particular, has been on quite a stretch for above normal temperatures. In November, Naples and Fort Lauderdalerecorded their warmest November on record. For Miami and West Palm Beach, it was their second warmest November on record.
Fargo, North Dakota has reached 40 degrees or higher on 257 days so far in 2015. Dating back to 1942, the record is 261 days in 2012, but December 2015 could push them over the edge in just the next week alone.
What About Last Winter?
December 2014 was also a warmer than average month for much of the country. Despite that happening, winter took a fast turnaround in parts of the Northeast.
The pattern changed very quickly in the winter of 2014-15 with record-setting snows hitting parts of New England in January in February.
There are some differences between this winter and last winter, particularly with the strong El Nino currently in place.
Regardless, weather patterns are bound to change at some point, so check back regularly with weather.com for the latest information.
http://www.weather.com/forecast/national/news/warm-united-states-december-2015
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