A Midlatitude Cyclone for the Ages

I see that Mother Nature has screwed us over again. One look outside the Sci Hall windows and you will understand what I mean. It's April 10, and the forecast is for 8-12 inches. Of snow. And wind. And curses. Today is a day where I lament my choice to attend UW Madison and not UC Santa Barbara. Oh well, at least there are no earthquakes, landslides, overcrowding, traffic jams, smog, tsunamis, droughts, surfer dudes, wildfires, etc. etc.

On the bright side, today's weather is a classic example of a midlatitude cyclone. What is it? A midlatitude cyclone is a transient weather disturbance with a low pressure center. This low pressure center allows wind to blow inward. In the northern hemisphere, the winds spiral inward in a counter-clockwise fashion (due to the rotation of the Earth). Check out a PPT of midlatitude cyclones here. A midlatitude cyclone is much like it's low latitude big brother, the hurricane: both have low pressure centers and counter-clockwise spiraling winds. However, the hurricane tends to be more compact, and has a greater difference in air pressure from the outer reaches of the storm to the center. This is what give the hurricane its strong winds.

Midlatitude cyclones also have cold fronts and warm fronts. In other words, there are areas of the cyclone where cold air is advancing, and another area where warm air is advancing. Since the midlatiude cyclone winds spiral inward in a counter-clockwise fashion, it makes sense that cold air from the north will be pulled in towards the center of the storm on the NW and west side of the cyclone. As the storm continues to spin, the cold air will advance around the spiral towards the east. This advancing cold air is the cold front. Conversely, warm air from the south is pulled toward the center of the storm on the SE and east side of the cyclone. Thus, we usually see the warm front here.

This is the classic example of a midlatitude cyclone. Of course in reality, it may not always be this easy. Today's storm is a pretty good example (see figures). The top left figure is a satellite image from the National Weather Service. This image shows water vapor in the air, and it is easy to see the counter-clockwise spiral pattern of the midlatitude cyclone. The low pressure center is parked over eastern Iowa at this time. The top right image is also from the NWS. Here we see a radar display of precipitation. Again, note the spiral pattern, and how it extends all the way to the Gulf of Mexico. Also note that in the northern part of the storm we see alot of blues (snow) and greens (rain) in the southern parts. The third image is from weather.com, and is simply a close-up of the storm. At this time, the cold front probably extends to the south or south-southeast from the center of the cyclone. The warm front extends roughly eastward.

Midlatitude cyclones are a common occurrence for Madisonites to see. They can occur any time during the year, but are most easily recognized in the winter months, when they are better organized. In the summer, they tend to be more "discombobulated" or disorganized, probably because of increased atmospheric turbulence.