It has been really dry lately in Texas. The reason it is dry is that we are in La Nina, which pushes the jet stream further north than usual. It causes storm systems to go further north, which means it allows warm air aloft above the surface to develop unchecked. The warm air aloft is from the deserts of Mexico. The warm air aloft is always there, but it is kept in check by storms systems that destroys them. Another reason why Texas is so dry is the upper level is drier than normal. It could be really humid on the ground, but go 5,000 feet (1,524 meters), it is much drier. The dry upper atmosphere is again from the dry and warm air of Mexican deserts. In wet years, the upper part of the atmosphere is wetter than normal. I am going to be comparing two springs from March to May. The wettest spring on record for Upper Texas Coast is 1997 and current spring, which is likely going to be one of the driest spring on record.
Notice anything? Spring 1997 was unusually humid at the surface and at the 5,000 feet (1,524 meters or 850 millibar) level. Spring 2011 humidity level is within average. However, at 5,000 feet, it is dry. The surface can be very humid, but when you go 5,000 feet (1,524 meters), it is much drier. The low relative humidity at the upper levels inhibit storms from forming. The low moisture level is what kills storms from forming over eastern part of Texas.
If you think Texas is in a drought and abnormally warm, we are not alone. Europe is also in midst of a severe drought and abnormal warmth for the same reason Texas is in, La Nina. Texas and Europe’s drought are one of the worst on record.
Spring 2011 Geopotential Height Anomaly In Europe
There is a blocking feature over Europe at the 18,000 feet (5,487 meters). That upper level high pressure is blocking any storm systems that give Europe rain.
The same atmospheric setup in Europe is very similar to in Texas, low moisture, warmer temperature, and upper level block pattern.