Friday January 18th… Dear Diary. The main purpose of this ongoing post will be to track United States extreme or record temperatures related to climate change. Any reports I see of ETs will be listed below the main topic of the day. I’ll refer to extreme or record temperatures as ETs (not extraterrestrials)
Severe Arctic Outbreak Likely For The United States
It’s extremely rare that I repost an article by Bob Henson or Dr. Jeff Masters from Weather Underground since I generally like to give different news in association with weather and climate, but today’s main news and topic directly overlaps what this blog is all about, reporting synoptic patterns which may produce either hot or cold extreme temperatures. Today the proverbial writing is on the wall that recent stratospheric warming leading to a split of the polar vortex will lead to a very cold weather pattern over the eastern and central United States, Canada, and portions of Europe.
The forecast 500 millibar pattern by the European model late next week is something for many meteorologists to behold. Warming over the Arctic in association with the North American block is equally impressive:
Today I’m going to get technical via Bob with the nuts and bolts of why this pattern can still occur on a planet beginning to succumb to severe global warming. Most of what Bob writes in his article is met tech speak for what would typically occur many times during the winter. Due to carbon pollution it appears that strong arctic outbreaks are becoming more rare, but no less severe. Too, remember that it can still get cold enough to kill many via frostbite. Cold winter storms add to the misery. Don’t forget that last year we had severe nor’easters combine with sea level rise to produce much misery in the Northeast, for example.
Without further ado here is most of the Category 6 post:
February Deep Freeze On Track: A Late-Winter Outlook That Just Might Pan Out
Bob Henson · January 18, 2019, 10:34 AM EST
|Above: Snow covers a farm field on Thursday, January 17, 2019, near Ottawa, Illinois, about 50 miles southwest of Chicago. Northern Illinois could get 4″ to 8″ of snow from Friday into Saturday as a major winter storm sweeps across the Midwest and toward the Northeast U.S. Image credit: |
Scott Olson/Getty Images.
As far back as November, seasonal forecasters at The Weather Company (TWC) warned that the upcoming U.S. winter would bristle with late-season cold risk across the East, especially in February. It now looks more and more like that bold call may turn out to be just right, for a variety of reasons.
The imminent chilldown comes on the heels of a remarkable month-long stretch of consistent mildness that’s spanned nearly all of the contiguous U.S. At many locations, temperatures were among the warmest on record for the 30-day period straddling New Year’s Day (Dec. 16 – Jan. 15). The mildness—a welcome break for many, but a curse for snow lovers—kept weather-related holiday travel trouble to a minimum while holding Boston to its slowest snow-season start in 83 years of records.
|Figure 1. U.S. temperatures averaged 4°F to 10°F above normal east of the Rockies for the period from December 15, 2018, through January 14, 2019. Image credit: NOAA/NWS/WPC.|
All this is about to change, and the relative mildness we’ve seen so far this winter will make the transition all the more wrenching. First off, a winter storm dubbed Harper will drop major snowfall from the Central Plains on Friday across the Ohio Valley into the interior Northeast, perhaps dumping 1 to 2 feet over the weekend on parts of New England and upstate New York. See weather.com for frequent updates on Harper.
In Harper’s wake, a large pool of cold air will slide into the Midwest and East, perhaps setting at least a few daily record lows. Long-range forecast models are consistently calling for one or more shots of even colder air in the next 1 to 2 weeks. If the latest TWC outlook is correct, wintry jabs will continue pummeling the central and eastern U.S. straight through February and into early March.
|Figure 2. U.S. temperature outlooks issued by The Weather Company for February and March. These outlooks show the strength of warm and cold departures from average that are deemed most likely by Weather Company forecasters. NOAA’s seasonal forecasts, which cover three-month overlapping periods rather than single months, are keyed to the probability of above- or below-normal temperatures rather than their intensity, although the two variables are often closely linked. Image credit: The Weather Company.|
Splits in the stratosphere
The last few days of 2018 did more than bring mildness to the eastern United States: they also produced a heat spike about 15-20 miles above the North Pole that far outpaced anything seen at ground level. It was a vivid example of a sudden stratospheric warming (SSW), a wintertime circulation readjustment typically triggered by lower-altitude weather features such as blocking highs whose effects percolate upward. In turn, the SSW impacts can filter downward weeks later. This two-step process has long been explored by Judah Cohen (Atmospheric and Environmental Research) and others for its influence on Northern Hemisphere winter weather; see Cohen’s weekly analyses.
Every couple of years, on average, a major SSW sends temperatures in the polar stratosphere soaring by 90°F (50°C) or more in only a day or two. Last month’s SSW was a doozy, as shown in Figure 3.
|Figure 3. Temperatures above the North Pole at the 10-mb level (about 18 miles or 30 kilometers high) jumped more than 60°C (108°F) near the end of December 2018. Temperatures in the magenta trace were calculated for recent weeks by NASA’s GEOS FP forecast and analysis system. Image credit: Paul Newman (NASA), Eric Nash (SSAI), and Steven Pawson (NASA), courtesy Judah Cohen (AER).|
SSWs can have a profound impact on the pole-centered circulation known as the stratospheric polar vortex. Often an SSW will disrupt the vortex, morphing it into multiple lobes, pushing it toward lower latitudes, and sometimes even splitting it in two. True to form, the latest SSW broke the polar vortex into two main centers, as discussed this week by Capital Weather Gang, and these “daughter” vortices have been unable to recombineh
The question facing us now is how long it might take before these vortex disruptions work their way downward and influence the weather at ground level. Typically this happens when easterly winds at lower altitudes becomes juxtaposed with stratospheric easterlies produced by the distorted polar vortex, a process that can take up to several weeks.
Once the winds are vertically aligned, it becomes easier for the stratospheric warm air to descend to lower levels, a process nicknamed “dripping paint” for how it appears on plots of atmospheric pressure surfaces over time.
As it descends, the warming can induce a blocking pattern near the poles, which in turn supports the build-up of cold air masses that can push well southward into U.S. latitudes. Sometimes this evolution is expressed as a negative phase of the Atlantic Oscillation (AO) and/or the North Atlantic Oscillation, the latter being an index of the strength of flow across the North Atlantic. The strongest nor’easters tend to occur with a negative NAO, which allows storms to intensify near the East Coast rather than scooting quickly offshore. A negative NAO also favors intrusions of Siberian air westward into northern Europe.
The longest-range day-to-day weather forecast models, including multiple runs of the GFS and European models, increasingly agree that such a scenario may unfold around the last week of January. Other, more general dynamical and statistical models that extend out a month or more, such as the NMME, strongly support the idea of cold blasts extending through February across the Midwest and East. (Keep in mind that in midwinter, even intense cold isn’t always record cold—especially in our warming climate, where it’s become increasingly difficult to set large numbers of record lows.)
That last bit from Bob is very true. It will be interesting to see how many cold”ETs” this pattern going into February produces. Of course, I’ll be reporting on any extreme cold the next few weeks.
Here is some more climate and weather news from Friday:
(As usual, this will be a fluid post in which more information gets added during the day as it crosses my radar, crediting all who have put it on-line. Items will be archived on this site for posterity.)
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The Climate Guy