Weather 101 - a Satellite Perspective of Three U.S. Storms

This morning's weather satellite image (Fig. 1) tells almost all one needs to know about United States weather. This particular image shows data from an infrared (water vapor channel) sensor onboard a Geostationary Operational Environmental Satellite (known as GOES). This sensor detects emitted energy from the Earth, and how atmospheric moisture affects its transmission into space. Much like other greenhouse gases, moisture at mid- and high-altitudes prevents infrared radiation from escaping to space. The heat loss is variable enough to separate regions of mid- and high-altitude cloudiness (blues); regions of high moisture content at mid- and high-altitudes (white); and regions of dry air at mid- and high-altitudes (oranges). The color scales (and there can be many) have been chosen by scientists to enhance contrast between moisture regions.

Today's storms

The persistent and prolific northeast rain and snowstorm continues to spin over New England. It's fairly easy to see the spiraling character (counterclockwise spin) of the weather system. The actual low pressure center was located near Boston, MA early on Saturday morning (February 27, 2010), but the circulation pattern reached as far north as Hudson Bay, as far west as Wisconsin and as far south as North Carolina. Near the Virginia-North Carolina border, strong westerly winds, blowing across the Appalachian ridges have helped to create a mountain-induced wave cloud pattern (the patch of blues). Winds at Greensboro, NC were in the 60 to 80 knot (70 to 90 miles per hour) range through a deep atmospheric layer from about 4 to 8 miles above the Earth's surface. As they blow across the mountain range (even miles above the actual peaks) the winds are forced to rise (however slight). This rising permits condensation (water vapor to liquid water) or deposition (vapor directly to ice crystals) to occur.

This cloud pattern is easier to see in Figure 2. Figure 3 shows three images spanning a 6-hour period. Notice that the cloud pattern does not move very far, but rather seems to develop in place along and to the east of the Appalachian ridge line. This is linked to how the cloud's formation is tied to the mountain range.

The second storm system can be seen along the Gulf Coast. It's upper level center was located just to the northeast of New Orleans, LA. This system lacked the huge spiral character of the New England storm for several reasons. It was still in developing mode (comma shape); it was moving rather than stationary; and it was a weaker system. To the south of the low was a developing line of showers and thunderstorms (the small white dots). To the southwest of the low was the so-called "dry slot," where drier air starts to wrap around the low pressure system.

While not linked directly with this low, a very strong sub-tropical jet stream can be seen arcing across south Florida. The high altitude clouds and moisture associated with this feature typically lie on the Equatorward side of the jet stream, with the jet stream located at the poleward edge of the cloud mass.

Finally, the next storm system in the seemingly endless series was coming ashore in southern California. This system was a bit more complex as it contained several low-pressure areas within it. One was located near Seattle, WA. The other was offshore from San Francisco, CA.

There were two jet streams associated with this storm system. One extened from northwest of Los Angeles, CA northward to the California-Nevada border. A second jet stream extended from near Los Angeles to Los Vegas, NV and then eastward to northwest New Mexico.

The Forecast

The Northeast U.S. low is expected to continue spinning and weakening. The Gulf Coast low will head eastward and intensify slightly (Fig. 4). Then as the Gulf low moves over the Atlantic and heads northeastward, it is expected to reinvigorate the northeast storm, bringing another round of snow and increasing winds to most of New England.

But it is the west coast low that is destined to the big weather story.

First, it was bringing heavy rainfall to California this morning. The rain will mostly be beneficial, filling reservoirs and providing relief to the state's water supplies. But, heavy rain was expected to fall in the areas burned last year north of Los Angeles. Lacking trees and grasses, rain falling on bare ground will likely lead to localized flooding and mudslides. According to NWS statements, rain was falling at rates of up to three-quarters of an inch an hour in some locations.

The system was also bringing heavy snow to the Sierra Nevada Mountains. Snow pack in the California mountains is a key ingredient to managing the state's water supplies especially outside of the winter rainy season.

Then the system moves into the southwest, bringing mountain snows and valley rains. Heavy mountain snowfall is expected as far south as the mountains near Tucson, AZ. And showers are even expected in normally dry El Paso, TX.

Once the system reaches eastern Texas, later on Monday, Gulf of Mexico moisture enters the picture. Further intensification is expected as the low tracks eastward across the northern Gulf of Mexico. Below freezing temperatures will likely be a bit further north across the Gulf Coast states than in past storm events. Still, the demarcation line between a cold rain and snow is anticipated across the Tennessee - Georgia border. Further to the northeast, heavy snow could fall across parts of North Carolina and Virginia by later Tuesday into Wednesday. Other places in the Mid-Atlantic and New England may well see further snowfall come Wednesday and Thursday.

And the March 2010 weather outlook (issued on February 18, 2010) reads more of the same. Wet and cold weather is expected in the Deep South and drier and warmer than usual is on tap for the Pacific Northwest (Fig. 5).