A Mighty Long Rope

Tracking a cold front with satellite imagery is easiest when there's a rope cloud. Formed by the sudden uplift of moist air to the Lifting Condensation Level (LCL) by the hydraulic head of a surface density current, rope clouds are linear features that rarely produce significant precipitation. In some cases they may also be associated with thunderstorm outflow boundaries or mesoscale fronts. Usually their position will correspond very well with the location of the surface discontinuity, although this can vary some in cases like "tipped over" fronts where cool water surface temperatures inhibit the surface front. In some cases kinks or intersections of multiple rope clouds can help to localize uplift sufficiently to initiate thunderstorms. Generally the low cloud top height and narrow scale of rope clouds make them much easier to see with visible imagery than with infrared. An example over Florida was studied by Seitter and Muench in 1985.

Today there is an unusually long rope cloud feature, spreading in a pretty much continuous line from Ontario to Texas. The position of the cold front can be identified also in New Mexico, by the presence of upslope stratus. Comparison with the RUC analysis of equivalent potential temperature confirms the strong density discontinuity. The decreased gradient across the front in West Texas is related to the presence of a short dryline feature in northeast Mexico. A weak outflow boundary from the prefrontal convection extends across from San Antonio to southern Mississippi.