FYI, what a trowal is.
http://wdtb.noaa.gov/courses/winterawoc/documents/color_PDFs/IC55.pdf"...the cyclone structure known as the trowal, which is a kind of acronym for “trough of warm air aloft.”
The concept of the trowal has been a part of the parlance of operational meteorology for nearly 60 years. Use of the trowal concept is intended to highlight to meteorologists where it is in an extratropical
cyclone that precipitation, perhaps banded, may occur over the cold surface air north and
west of a cyclone center. When present, an occluded front at the surface is not always
the focus of precipitation, low ceilings, and other inclement weather. Also, a trowal-like
feature sometimes appears before the surface cyclone may be analyzed as occluded. In
either instance,
it is often the region of the trowal where significant weather and precipitation
occur.