Rare Freezing Rain Event in the Little Colorado River Valley on 25 January 2006

摘要

Freezing precipitation events are very rare across northern Arizona. There are several reasons for this. First, there is normally not a source of cold air readily available. Second, the sun angle never gets too low due to the low latitude of Arizona and the relatively higher sun angle. Therefore, the boundary layer will inevitably warm quickly during the morning and early afternoon hours. Finally, strong pre-frontal winds often scour out the boundary layer over this topographically diverse terrain, thus not allowing for the temperature stratification conducive to freezing rain. That being said, one freezing rain event did occur during the morning hours of 25 January 2006. The impact of this storm was quite substantial; the freezing rain left a glaze of ice on various major roadways across the Little Colorado River Valley (hereafter LCRV). Portions of Interstate 40 near Holbrook, along with State Highways 61 and 77 were closed temporarily due to the ice. There were numerous vehicular accidents during the morning hours as people drove to work or began their travels, with several fatalities and injuries reported due to the weather. This technical attachment will summarize the two known processes through which freezing precipitation can occur in section 3. In section 4, the synoptic environment from the morning of 25 January in the LCRV will be presented. Finally, using the available data, a description of why freezing rain occurred in the LCRV will be given in section 5.