One of the big questions this time of year is why is it so cold? La Nina is supposed to make things warmer. Where's under high pressure, I thought that's supposed to make that warm? Well, with high pressure, you have to think of the time of year and where the air mass is coming from. In the spring and summer, the high pressure usually sets up to the southwest, or southeast. High pressure has clockwise rotation. So, in those setups, it brings in warmer air. In fact, when the flow is from the southeast, we actually get moisture pulled in to west Texas. In comparison, when we get high pressure from the north in the warmer months, we'll actually see cooler air and lower high temperatures.
In Autumn and winter, the pattern becomes more amplified. That means we're seeing more of a wavy flow of the wind in the levels above the surface. That wind flow is what transports air masses. What we're seeing now, which is depicted in the photos below, is a high amplitude pattern. That means we're seeing a ridge of high pressure in the west and a trough of low pressure in the east. The ridge to the west is pulling cold air from the northwest. That air flows down the Plains and into Texas and the southern United States. As the air moves on the east side of the trough of low pressure, it will begin to warm up along the east coast. So, the single digit temperatures in the Plains will become 20s and 30s along the eastern sea board.
The location of the high and low can determine how cold a certain location will get. That is why we're seeing the extreme cold and snow in states like Arkansas, Louisiana, Alabama and Georgia. If the high was set up farther west, they would still be cold, but not as cold. If the high was farther east, they could be even colder. That, too, depends on how strong the high pressure is. In this case, it's pretty strong. It is keeping us dry and cold, with temperatures not getting out of the 30s from Monday night until this afternoon. The pattern will change Friday and Saturday, with a brief warm up. However, another cold front and associated high pressure system will cool things down Sunday-Tuesday. This one will not be as strong, so highs will stay in the upper 50s.
