...February 23, 2008 Winter Storm Summary...
A blanket of snow spread across east central Kansas and into central Missouri Saturday night, February 23, 2008. This snow was associated with what is called a progressive short wave trough. Basically, it is a weak trough of low pressure in the upper atmosphere that moves steadily to the east across a region. Although these types of systems may not look that potent, they are capable of producing a broad area of snow cover, rather than a more concentrated area that we see a lot with stronger storm systems. Many times, as in this instance, an inverted surface trough of low pressure forms with such a system, which helps to focus the moisture across the region (see figure 3). The tricky part of this event, was the fact that the temperature at and just above ground level (up through about 5000 feet) was initially above freezing. However, the air was also quite dry at these levels. What can happen, is when the snow from the moist layers above 5000 feet, begins to fall through the dry, warm layer, it melts and evaporates the moisture. The process of evaporation requires heat, which is taken from the air, thus cooling the air, much in the same way as moisture evaporating off of skin, helps to cool the body. This warm layer, eventually was cooled down to below freezing by this process, plus the precipitation falling into the layer helped to moisten it (see figures 1 and 2). So after a short while, big wet snowflakes, which can add up quickly, were making their way to ground level. If the air had been cold and more moist to begin with, some areas could have seen much heavier snowfall from this type of storm system. In fact on February 25th and 26th of 1993 such a system brought around a foot to a foot and a half of snowfall to areas from Kansas City...eastward into central Missouri.
Figures 1 and 2: Soundings from 6 pm and 9 pm in area where snow was developing. Click on pictures to enlarge.
Figure 3: Map below shows upper air pattern (white lines) and surface pressure pattern (dashed blue lines) as of midnight.
Below is a IR satellite animation of the event as it passes from eastern Kansas through central Missouri.
Here is a graphic showing snowfall totals for this event.