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.

Why It Has Been So Warm So Far?

It has been so warm lately despite being October and Halloween is around the corner. It is like summer does not want to leave despite the calendar saying otherwise. Why is it so warm right now?

Let’s take a look at the upper atmosphere at the 500 millibar level or 18,000 feet.

20161030_500mbgeopotentialheightanomaly_nh_1021-1028

There is upper level ridging over the Lower 48. It is mainly over the Central US. The ridging prevents any cold air from coming down south. There is troughing off the Pacific Northwest, which has kept things wet for them, including California. There is also ridging over Alaska, which is a negative East Pacific Oscillation (EPO). A negative EPO normally supports cooler weather. However, the ridging over Central US is blocking any cold air. There is also troughing over Eastern Russia, which is a positive West Pacific Oscillation (WPO). WPO is similar to EPO as a negative EPO favors cold air being shunted down south. A positive WPO like positive EPO and North Atlantic Oscillation (NAO) keeps cold air from being shunted southward. There is also ridging centered around Yuzhny Island and Svalbard. It is a large area of ridging. I am surprised no one has created an index for that area. I suspect it is an oscillation like NAO and EPO. Would be interesting to check it out. Where are the cool and warm spots?

20161030_1000mbairtemperatureanomaly_nh_1021-1028

Not surprisingly, the warmest areas are where the ridging is most strongest. It is also very warm over the Arctic. The coldest area is over Central Asia, mainly over Kazazhstan. It is cold over most of Siberia. The Eastern tip of Russia is very warm. Rule of thumb, if there is upper level ridging, it will be warmer and drier, while upper level troughing will be cooler and wetter. The upper level trough has deep cold air, there can also be snow fall. Case in point, let’s look at two snow events in Southeast Texas; February 12, 1960 and December 10, 2008. February 12, 1960 is the biggest snowfall event since February 14-15, 1895. The December 10, 2008 gave Houston an early start in the snowfall department before places that see snow like Chicago and New York. Let’s start with 1960.

19600212_500mbgeopotentialheightanomaly_usa

There is a deep trough over Mexico and is moving eastward towards Texas before the February 12, 1960 snowfall. It is a very large upper level trough.

19600212_500mbairtemperatureanomaly_usa

The trough has deep layer of cold air. That is very favorable for snowfall. Snow happens when there is a deep layer of cold air. One reason why snow can fall at above freezing temperature. Shallow layer of cold air is not conducive for snowfall. More likely there will be sleet or freezing rain. One reason why Southeast Texas does not get snow often is cold air is shallow, not deep. Let’s also look at December 10, 2008 snowfall.

20081210_500mbgeopotentialheightanomaly_usa

The trough in the 2008 snow event is smaller than the 1960 snowfall event.

20081210_500mbairtemperatureanomaly_usa

Like the 1960 event, it also had deep layer of cold air. If one wants to compare February 1960 snowfall, the closest is December 2008 in terms of atmospheric setup. Perhaps we will see snow this winter.