Mega-monster Storm Brings Unusual Weather Patterns

Computer models indicated that a series of low-pressure systems would move out of the southern Plains during the two days before Christmas, 2009. The first, the weaker storm would trek northeastward into Missouri while a second, much stronger, system came across the Desert Southwest, and into the southern Plains before heading northeastward.

As the system came across the Southwest, it spawned a major dust storm. This dust storm was responsible for a multi-car, fatality-ridden accident on Interstate 10 just north of Phoenix.

Two days later, tapping moisture from the Gulf of Mexico, the storm system, exploded and dropped more than a foot of snow on Oklahoma, several inches as far south as the Dallas-Fort Worth Metroplex and even a dusting further south in Waco. High winds, coupled with the snow, created blizzard conditions and brought vehicular and aircraft traffic across this entire region to a standstill.

Not content with this legacy and the breaking of numerous weather records, the storm continued its rampage on Christmas Day (Fig.1). A total of at least 40 snowfall, rainfall and equivalent liquid precipitation records tumbled across 15 states (link to be added).

Even more impressive than breaking records, the storm performed some unusual meteorological gymnastics. For example, the storm's path, contrary to the typical southwest to northeast path, curled to the left of its expected path, stalled over Iowa and then continued it's loop-d-loop before heading northeastward. (Fig.2) Some hurricanes have exhibited this type of stalling-looping pattern. But middle latitude lows over the mainland U.S. rarely do so. Oceanic storms and storms that move into the nearly semi-permanent Hudson Bay low pressure system do it much more frequently. (Fig.3).

This stalling character allowed warm air to push westward ahead of the storm and cold air to race eastward south of the storm. It also pushed the blizzard conditions further westward across the Northern Plains than were expected initially.

But the temperature advection pattern, linked to the counter-clockwise spiraling of the low-pressure system, was dramatic (Fig.4). Notice the shape of the 30-degree isotherm (line of equal temperature) during early afternoon on Christmas Day. With superimposed winds (winds blow along the wind staff INTO the station circle), it's easy to see how the warmer air moved westward north of the low and the cold air plowed eastward south of the low.

In fact, the shape of this isotherm closely resembles that of the Chinese Yin-Yang pairing. The pattern I chose for this article shows the white (representing warmth) and the dark (representing coldness). The outer circle represents the whole or balance, which is to what the temperature pattern eventually balances out.

Meteograms (multi-variable weather tables) show the same effect (Fig. 5). To the west of the low, temperatures warm dramatically during Christmas Day, while to the south and southeast, temperatures plummeted (meteograms). Hence the usual north-south temperature pattern became flipped with the coldest air to the south of the low. That scenario continued into the day on December 26. Temperatures across Missouri, Iowa, Wisconsin, much of Illinois and southern Minnesota were colder than temperatures to the north and west in an axis extending from International Falls, MN to Sioux Falls, SD.