Map Porn: Gulf Moisture Sucked 2,500 Miles North Into Canada
A butterfly flapping its wings in Brazil may not cause a tornado in Texas, but winds blowing from the south can send moisture from the Gulf of Mexico thousands of miles away into remote sections of northern Canada. The maps that show this atmospheric flow are an awesome testament to the power of the weather.
All of the maps in this post were produced by last night's run of the North American Model (NAM). The two dominant weather features over North America today include a low pressure system in eastern Alberta and a high pressure system centered near Lake Michigan.
The central U.S. and Canada are sandwiched in between the counter-clockwise flow around the low and the clockwise winds around the high, creating a stiff wind from the south that allows a conveyor belt of moisture to stream directly from the Gulf into the far reaches of northern Alberta.
The map at the top of this post shows the model's predicted surface dewpoints from around noon today. While temperatures certainly get much cooler as you head farther north into Canada, the maps clearly show that most (if not all) of it originates over 2,500 miles away in the Gulf of Mexico.
This is the mixing ratio for the same time as the dewpoint map at the top of this page. According to Tim Vasquez's Weather Forecasting Handbook, the mixing ratio "represents the mass of water vapor to the mass of dry air in a given volume." In other words, the mixing ratio tells you exactly how much moisture is in the air. The wind vectors (arrows) show that the moisture from the Gulf is being pumped up into Alberta.
The conveyor of moisture is also illustrated by the above precipitable water chart, which shows how much rain would fall if all of the moisture in the atmosphere condensed and precipitated. While the amounts over Alberta steadily decrease with increase latitude, it demonstrates the extent of the Gulf moisture.
This warm, unstable air over the central United States will actually trigger a severe weather outbreak today, with enough instability and wind shear present to produce both supercells and lines of severe thunderstorms over areas from western Texas to central Nebraska. There is an enhanced risk for hail larger than golfballs in the supercells, but the tornado threat should be limited.
Maps like these show the interconnected nature of...well, nature. While local features can have a great effect on the weather, most weather systems span entire continents, and the humidity you feel in Texas could soon wind up thousands of miles away.
