A Cool, Damp Period Associated With the Spring-Like Frontal Waves Over the Eastern United States, July 18–25, 1956

The occurrence of well-defined polar fronts in the Gulf Coast States during the month of July, while not necessarily a rarity, has been at least an unusual happening during the past several Julys. Upon reference to the Historical Weather Maps [I] it was noted that there have been Julys when as many as five polar fronts have swung southward over these Gulf States, while, on the other hand, there have been other Julys when the southern limit of the polar fronts has remained north of the 35th parallel. However, in most of the cases observed there was an ephemeral duration of the front in these southern latitudes; certainly few had the longevity of the case of July 18-25, 1956, the subject of the present study. That such prolonged activity should occur during a summertime frontal condition may in part have been due to the fact that temperatures in the airmass to the north of the front were considerably lower than the mean temperatures as shown by Showalter [2] in his study of summer airmass properties. And also that several stations in the southern portion of the country recorded temperatues in the upper air that were equal to or below the minimum values presented in the paper on “Extreme Temperatures in the Upper Air” [3]. Surface temperatures over the Eastern States during