It Is February And It Is Hot

February has been hot like summer. Yes, it is winter, but it feels like summer in Texas. Just look at the temperature anomaly map below.

surfaceairtemperatureanomaly_nh_20170206-20170212

Most of the cold air is over Alaska, Kazakhstan, and Central Russia. Now, why is it warm? We can look at the upper level at around 18,000 feet or 5,000 meters.

500mbgeopotentialheightanomaly_nh_20170206-20170212

There is ridging over most of America, Northern Europe, and Eastern Russia. There is troughing over Northwestern Canada, Japan, and Korea. The troughing keeps things cooler in that part of the world. Has it ever been this hot before in February? Yes, it has been and even reached 90°F in Southeast Texas. There were 100°F in South Texas. It occurred in 1986 and 1996.

Temperature Anomaly Map In 1986
surfaceairtemperatureanomaly_nh_19860218-19860220

Temperature Anomaly Map In 1996
surfaceairtemperatureanomaly_nh_19960221-19960223

Let’s look at the upper levels.

500 Millibar Geopotential Height In 1986
500mbgeopotentialheightanomaly_nh_19860218-19860220

500 Millibar Geopotential Height In 1996
500mbgeopotentialheightanomaly_nh_19960221-19960223

The pattern in 1986 and 1996 look similar. There is ridging over Lower 48 America, mostly over the southern half. There is ridging over Northeast Canada in 1986 and 1996, but not in 2017. There is troughing over Northwest Canada, Japan, and Korea. However in 1986 and 2017, there is ridging over Eastern Russia and Alaska, unlike in 1996 and 2017. There is also troughing over Northern Europe and Siberia in 1986. There is ridging over Northern Europe and Siberia in 1996 and 2017. Here is a composite of 1986, 1996, and 2017 upper air pattern at 18,000 feet or 5,000 meters.

500mbgeopotentialheightanomaly_nh_composite_february_heat_1986_1996_2017

There is ridging over most of America and troughing over Northwestern Canada, Japan, and Korea. There is ridging over Northern Europe, Northeast Canada, and Eastern Russia. Ridging over Eastern Russia is a negative West Pacific Oscillation (WPO), while over Alaska is East Pacific Oscillation (EPO). WPO and EPO are similar to North Atlantic Oscillation (NAO). Negative NAO has ridging over Northeast Canada and Greenland. Troughing over Northwest Canada favors negative Pacific North American Teleconnection (PNA) pattern. A negative PNA produces warmer winters. A negative WPO, EPO, and NAO favors cooler winters.

Another thing is 1986 and 1996 occurred in La Nina. The La Nina were weak that time. La Nina usually favors warmer winters because it is usually drier due to less rain. The most recent heat wave occurred in Neutral, not La Nina. A lot of things come to play from ocean to atmosphere to produce an abnormally warm February.

All the data is from NOAA-Daily Mean Composites.