Tropical Storm Beta formed in the Southwest Gulf of Mexico on September 17th and meandered up near the coast before finally making landfall in Southeast Texas. Being stuck in between a digging trough feature over the southern plains and a high-pressure system to the East kept Beta at a slow pace before moving inland. Once inland, however Beta began to weaken significantly and become more of an open circulation. This process opened the door for nearby stronger flow to pick up and steer the system to the NE which would lead to the transition of Beta into a post-tropical cyclone and eventual remnant low. As upper level winds accelerated the system eastward across the Southeast US, the system began showing frontal-like tendencies and would become more than just a remnant low.
As Beta continued to weaken as it moved inland, its once closed and cutoff circulation became open and elongated. This not only allowed for the ingesting of dry air to the NW into the system, further weakening it, this made Beta vulnerable to be pulled away by strong upper level flow which was evident by a digging trough feature over the southern plains. This would begin
to accelerate Beta to the northeast, bringing it across the rest of the southeast. As the system advanced over the Tennessee Valley it ran into a shortwave trough from the Northeast US. This helped to amplify the other trough feature that Beta was riding eastward as shown in the figure above with the jet streak signature from Arkansas to the Mid-Atlantic coast. This shortwave interacting with the large trough feature over the southern plains would provide the necessary energy to allow Beta to undergo some frontogenesis before passing over the southeast and moving off the coast.
In class we’ve learned how to identify frontal boundaries. The most obvious thing to look out for is temperature change, after all a frontal boundary marks the separation of two different air masses and the most common types of fronts (cold/warm) indicate where the boundary between a cold and warm airmass resides. However, there are other things that can indicate a frontal boundary such as moisture, wind direction/shift, and vorticity. Beta showed evidence of a 
frontal boundary as it made its way across the southeast. The middle figure shows precipitable water (moisture content of air above a fixed point) that shows moist air as the colder colors and dry air as the warmer colors. Beta is positioned over Tennessee and looks to be pulling moist air northward from the Gulf. A distinct boundary running from SW Alabama to NE Georgia separates moist and dry air and indicates where a potential cold front could be while another boundary across KY-VA indicates where a potential warm front could be. The figure on the left shows cyclonic vorticity which can be maximized at the boundaries of fronts. Two areas of maximized vorticity appear around the same areas of where the moist boundary lines hinted at a cold and warm frontal boundary. The slight packing of thickness contours in the figure on the right seem to coincide with the presence of the shortwave trough mentioned earlier. This small tightening of the temperature gradient sets up a weak baroclinic zone that will help to establish a more distinct boundary, particularly at the location of the potential warm front.
Another concept we learned in class is the frontogenesis equation and being able to perform sign analysis on the four terms (shearing, confluence, tilting, diabatic) in order to figure out whether frontogenesis (overall positive) or frontolysis (overall negative) is present. The
middle figure shows plotted frontogenesis (purple contours), temperature (red contours), and warm air advection (red fill pattern). The frontogenesis plotted here is a magnitude, so while it’s not clear which terms are positive and negative, it does at least indicate that these terms are present in some capacity and this plot appears to focus along where a potential warm front might be which could be why there is a local maxima of warm air advection. The first two terms (shearing, confluence) can be deduced from this figure. The wind barbs along with the temperature contours show that both of these terms are positive as you have both terms showing both a decrease in temperature in both the x and y directions (negative) as well as a shift from westerly winds to easterly (negative –> shearing) and southernly to northerly (negative –> confluence) resulting in both terms being positive. For the tilting term, the figure on the left shows omega values which can help determine the change in pressure over time in the y direction. Based on the figure this results in a positive change in omega, but with an increase in potential temperature with decreasing pressure, this results in an overall negative tilting term. The diabatic term is difficult to predict, but based on the figure on the right, the diabatic term is negative due to the slightly positive increase in temperature as you go across the front due to lack of cloud cover and overall small change in thickness. Overall, we have two positive and two negative frontogenesis terms, indicating that whatever frontogenesis that’s occurring is relatively weak. This is not surprising given the fact that typically remnant lows associated with posttropical cyclones produce weak frontal boundaries if they develop into anything at all outside of a weak low.
Tropical Cyclone Beta went from a tropical storm to a meandering low that was picked up by an upper level trough, amplified by a shortwave, and likely produced a weak cold front with an accompanying warm front that, while weak, was able to produce some convective activity across the southeast (see figures below).
