Cold frontal passages across the Texas High Plains: characteristic behavior and possible causes

Forecasters on the Texas High Plains have noted that cold fronts often appear to slow down during the daytime hours and accelerate at night. The extent to which cold fronts systematically behave in this manner is the focus of this investigation.

Similar studies conducted for the Eastern Plains of Colorado conclude that cold fronts are most likely to experience diurnal variation in movement during the warmest months of the year when upper-level dynamical forces are least influential. Hence, the atmosphere's response to daytime surface heating is deemed most responsible for affecting cold frontal strength and speed of propagation. One such response to surface heating is the growth of the convective mixed layer which acts to erode the leading edge of the colder air mass, causing the front to appear to slow, stall or even retrogress. Another response comes from the unequal heating of the earth's surface over sloping terrain. This process creates a shift in the surface geostrophic wind from a northerly component at night to a southerly component during the day. The northerly flow aids in nighttime frontal progression while the daytime southerly component opposes frontal movement. Certain cold fronts may also behave as density currents, propagating under their own weight. The hydrostatic pressure behind these fronts is in constant battle with dynamic pressures out ahead of it. Propagation of the cold front may be slowed or stopped if the opposing pressure equals or exceeds the hydrostatic pressure behind it.

The investigation looks at Texas High Plains cold frontal passages by means of case studies and climatology. Cold fronts whose movements were altered to some extent during the daytime comprised the three case studies. These spring and summertime cold fronts all had very weak upper-level dynamics associated with them and all were influenced to some extent by the boundary layer processes mentioned above. A climatology of all Texas High Plains cold frontal passages was then compiled for the years 1970 through 1990 in order to determine with what regularity cold fronts passed through Amarillo, Lubbock and Midland. Diurnal tendencies were evident to some extent in all seasons, but were most pronounced during the warmer months of the year.