Dec 052013
 

A burst of unseasonal, wintry weather is sweeping across southeast Australia due to a strong, upper cold front in association with a shortwave disturbance crossing the region. The front is triggering widespread rain, thunderstorms and mountain snowfalls.

The WeatherTheatre SceneOne, 4-12-2013-12z analysis, vertical views reveal a deep, narrow tropopause fold along the upper front enveloping a peak in the theta surface where cold polar air is situated behind it.  A narrow elliptical, polar jet filament on the planar view is characteristic of the short wavelength of this disturbance.

Surface cyclogensis is occurring in response to the upper front and strong thermal gradient over southeast Australia.  Forecast models indicate a surface low forming near the southern NSW coast rapidly developing and moving southeast across the Tasman Sea in the next 24 hours.

WeatherTheatre SceneOne 4-12-2013-12z Australia Southeasterly View

WeatherTheatre SceneOne 4-12-2013-12z Australia Southeasterly View. A deep, narrow, curved tropopause fold (upper surface) revealing the upper front envelopes the 300K theta (lower) surface, indicating the associated cold air.  Red shadings correlate with the strongest winds (upper surface) and warmest temperatures (lower surface). Conversely, blue shadings correlate with the weakest winds (upper surface) and coldest temperatures (lower surface).

WeatherTheatre SceneOne 4-12-2013-12z Australia Top-down View

WeatherTheatre SceneOne 4-12-2013-12z Australia Top-down View. A narrow shortwave trough associated with the upper cold front moving over southeast Australia is revealed by the sharply curved, positively tilted, elliptical polar jet filament, seen in the red shadings on the tropopause, which merges with the subtropical jet at the apoapsis. Red shadings correlate with the strongest winds (upper surface) and warmest temperatures (lower surface). Conversely, blue shadings correlate with the weakest winds (upper surface) and coldest temperatures (lower surface).

WeatherTheatre SceneOne 4-12-2013-12z Australia Westerly Vertical View

WeatherTheatre SceneOne 4-12-2013-12z Australia Westerly Vertical View. The upper front features prominently on the left of the image where it is revealed by a tropopause fold enveloping a mounded theta surface associated with the cold air. Red shadings correlate with the strongest winds (upper surface) and warmest temperatures (lower surface). Conversely, blue shadings correlate with the weakest winds (upper surface) and coldest temperatures (lower surface).

WeatherTheatre SceneOne 4-12-2013-12z Australia Northerly Vertical View

WeatherTheatre SceneOne 4-12-2013-12z Australia Northerly Vertical View. A cut-away view of the upper front stands out in the foreground, showing the theta mound in the centre surrounded by a folded tropopause in the frontal zone. Red shadings correlate with the strongest winds (upper surface) and warmest temperatures (lower surface). Conversely, blue shadings correlate with the weakest winds (upper surface) and coldest temperatures (lower surface).

Dec 032013
 

A strong, upper cold front is situated south of Australia, in the background of the WeatherTheatre SceneOne, 3-12-2013-0z Analysis, Southerly View.  The front is marked by a deep tropopause fold and associated elevated theta surface behind, indicating a good depth and spread of cold air following.

A tongue of warm air stretches across Southeast Australia preceding the front, reflected in the valley in the 300K Theta surface, where the intersection with the surface corresponds to the 27 degree celcius isotherm.  Forecast models project widespread rain across Southeast Australia ahead of the front and the cold-air behind the front should bring unseasonal snowfalls to the Southeast Australia mountains on Thursday, 5th.

A tropopause lowering over the Tasman Sea, seen on the left side of SceneOne and coming into view in the last few frames of the Southerly to Westerly Orbital View, is associated with a cut-off low which is expected to gradually weaken in the next two days.

WeatherTheatre SceneOne 3-12-2013-0z Southerly to Westerly Orbital View.

WeatherTheatre SceneOne 3-12-2013-0z Southerly to Westerly Orbital View. A strong upper cold front appears south of the continent in the first few frames. A cut-off upper low over the Tasman, which is also driving a cut-off surface low, comes into scene in the last few frames as a lowered tropopause in the top foreground. Red shadings correlate with the strongest winds (upper surface) and warmest temperatures (lower surface). Conversely, blue shadings correlate with the weakest winds (upper surface) and coldest temperatures (lower surface).

WeatherTheatre SceneOne 3-12-2013-0z Southerly View

WeatherTheatre SceneOne 3-12-2013-0z Southerly View. A strong, upper cold front stands out in the background, apparent by the folded tropopause (upper surface), shaded red due to the strong jetstream winds associated with the front. The fold wraps around a large mound in the 300K Theta surface below which provides an indication of the depth and spread of the cold air. Red shadings correlate with the strongest winds (upper surface) and warmest temperatures (lower surface). Conversely, blue shadings correlate with the weakest winds (upper surface) and coldest temperatures (lower surface).