Before the advance of the WSR-88D, little documentation existed
about severe splitting storms across the west. Distribution of
the WSR-88D since the mid 1990's across most of the western U.S.
and advanced education of operational forecasters have resulted
in improved identification of splitting storms and the
environmental conditions that surround them. In this particular
case, the left moving storm exhibits severe characteristics early
in its life, displaying a strong mesoanticyclone.
The left-moving storm started out as the dominate storm. A report
of dime size hail was received early in its life. It also
displayed a strong mesoanticyclone, with conventional WSR-88D
tornadic thresholds exceeded. The right-moving storm was much
weaker earlier in its life. As the storms progressed, both storms
became mirror images of each other with the right moving storm
eventually becoming the dominate storm producing one inch hail.
The parent thunderstorm evolved over higher terrain, with the
splitting storms moving over mainly rural areas of the Upper
Yellowstone Valley of south-central Montana.
This poster session will examine the synoptic and mesoscale
conditions that led to the splitting storm environment with an
emphasis on the left-moving storm as seen by the WSR-88D.
Documentation of this case will also help operational
forecasters identify mesoanticylones as the WSR-88D mesocyclone
algorithm is not capable of recognizing anticyclonic motion. Very
few cases of splitting storms have been documented across Western
Region and associated higher terrain.