<img class="styles__noscript__2rw2y" src="https://s.w-x.co/util/image/w/records-daily-cold-warm-ncei.jpg?v=at&w=485&h=273" srcset="https://s.w-x.co/util/image/w/records-daily-cold-warm-ncei.jpg?v=at&w=485&h=273 400w, https://s.w-x.co/util/image/w/records-daily-cold-warm-ncei.jpg?v=ap&w=980&h=551 800w" > The number of daily record temperatures (warm highs in red, warm lows in orange, cold highs in teal and cold lows in dark blue) set in the U.S. in 2020 through Feb. 9. NOAA reporting stations with at least a 30-year period of record were used. (Data: NOAA/NCEI)

At a Glance Warmer-than-average temperatures have dominated much of the U.S. so far in 2020.

According to NOAA, over 5,500 daily warm records have been tied or broken so far this year.

That is seven times the number of daily cold records.

Through January, winter 2019-20 was the warmest on record in the U.S.

A jet-stream pattern has kept cold from persisting in the U.S., particularly in the East.

Colder air may be plunging into the United States this week, but so far in 2020, over 5,500 daily warm records have been tied or set, trouncing the number of cold records.

For the first 40 days of the year, through Feb. 9, NOAA's Daily Weather Records website showed 2,421 daily record highs, meaning the highest temperature on record for a given location on that particular day, were tied or set in the U.S.

Another 3,148 daily record-warm lows, meaning the warmest low temperature on a given day, were also tied or set so far this year, for a total of 5,569 daily warm records to start the year.

<img class="styles__noscript__2rw2y" src="https://s.w-x.co/util/image/w/daily-warm-recs-1jan-9feb-noaa.gif?v=at&w=485&h=273" srcset="https://s.w-x.co/util/image/w/daily-warm-recs-1jan-9feb-noaa.gif?v=at&w=485&h=273 400w, https://s.w-x.co/util/image/w/daily-warm-recs-1jan-9feb-noaa.gif?v=ap&w=980&h=551 800w" > Sequence of daily record-warm high temperatures tied or set across the Lower 48 from Jan. 1 through Feb. 9, 2020. Jan. 8-14 (844 records) and Jan. 29-Feb. 3 (836 records) were the most active periods. (NOAA/NCEI)

By contrast, there were only 307 daily record lows and 481 daily record-cold highs tied or set during that same 40-day stretch.

The contrast is particularly stark when comparing the animation of daily record-cold lows below with the record-warm highs animation above.

<img class="styles__noscript__2rw2y" src="https://s.w-x.co/util/image/w/daily-cold-recs-1jan-9feb-noaa.gif?v=at&w=485&h=273" srcset="https://s.w-x.co/util/image/w/daily-cold-recs-1jan-9feb-noaa.gif?v=at&w=485&h=273 400w, https://s.w-x.co/util/image/w/daily-cold-recs-1jan-9feb-noaa.gif?v=ap&w=980&h=551 800w" > Similar to the animation above, but for daily record-cold low temperatures tied or set across the Lower 48 from Jan. 1 through Feb. 9, 2020. Feb. 4-9 (185 records) was the most active period.

In all, daily warm records outnumbered cold by a ratio of 7 to 1.

When examining temperatures that set records for the month, rather than just a calendar day, the numbers were even more lopsided.

A total of 209 monthly warm records were tied or set in the U.S. in that same 40-day period through Feb. 9. Only four monthly cold records were set in that time.

January 2020 was the fifth-warmest January in 126 years , according to NOAA.

Among the month's many notables, Boston reached the 70s on back-to-back January days for the first time on record, a high more typical of around Memorial Day than the second weekend of January. That same weekend, Charleston, West Virginia, reached 80 degrees for the second January day on record.

(MORE: Winter 2019-20 Has So Far Been the Warmest on Record in the Lower 48 States )

On Feb. 3, highs in the 80s were recorded as far north as Nebraska, setting monthly records in Imperial, Nebraska (81); Atwood, Kansas (84); and Yuma, Colorado (82).

<img class="styles__noscript__2rw2y" src="https://s.w-x.co/util/image/w/1jan-10feb20-US-Temp-deps-esrl.jpg?v=at&w=485&h=273" srcset="https://s.w-x.co/util/image/w/1jan-10feb20-US-Temp-deps-esrl.jpg?v=at&w=485&h=273 400w, https://s.w-x.co/util/image/w/1jan-10feb20-US-Temp-deps-esrl.jpg?v=ap&w=980&h=551 800w" > Temperature departures from average from Jan. 1 - Feb. 10, 2020, in degrees Celsius. The entire Lower 48 was warmer than average in roughly the first six weeks of 2020. (NOAA/ESRL)

Why So Mild?

As the record-cold animation above shows, there have been some intrusions of cold air, as you'd expect in any winter. And they have set a few daily cold records, particularly in the West.

The key is the cold hasn't lasted long before retreating.

One major reason for this is the polar vortex in the stratosphere roughly 6 miles above the Earth's surface has been very strong this winter over the Arctic latitudes.

In this pattern, the coldest air generally remains contained, draining west to east across Canada rather than plunging deep into the U.S. When it does plunge southward, it has lasted only a few days, as opposed to the weekslong stubborn cold patterns we've seen in past winters.

One pressure measure meteorologists use to diagnose the tendency for cold air to plunge into the U.S., known as the Arctic Oscillation, hit a record high in early February , indicating this tendency for cold air to sweep east, not lock in and plunge southward.

<img class="styles__noscript__2rw2y" src="https://s.w-x.co/util/image/w/Arctic_Oscillation_Positive.jpg?v=at&w=485&h=273" srcset="https://s.w-x.co/util/image/w/Arctic_Oscillation_Positive.jpg?v=at&w=485&h=273 400w, https://s.w-x.co/util/image/w/Arctic_Oscillation_Positive.jpg?v=ap&w=980&h=551 800w" > Positive Phase of the Arctic Oscillation A dominant positive phase of the Arctic Oscillation has kept cold air most persistently fenced in over the higher latitudes this year.

According to Guy Walton, a meteorologist formerly with The Weather Channel, about two daily warm high temperature records for every cold low temperature record have occurred in the U.S. so far this century .

In 2019, the difference between daily warm and cold records was smaller , according to Walton.

However, Walton found there were over three times more daily warm records in 2012, 2016 and 2017 , and at least twice as many warm records in 2010, 2011 and 2015 . Only 2013 and 2014 had more cold records in the U.S. in the 2010s.

"The disparity between record heat and chill is a good proxy method for measuring increasing global warmth," Walton told weather.com.