An upper cold front has passed across Tasmania overnight, rapidly moving over the Tasman Sea towards New Zealand today. A broad tropopause ‘curtain’ fold, dramatically illustrating the front, hangs over the Tasman Sea in the 28-11-2013-18z, WeatherTheatre SceneOne Australia snapshots. The heaped up Theta surface below shows the extent of the associated cold air.
A vigorous, early-winter season cold front has lead to the rapid development of a deep surface low over the northeast USA, bringing widespread snowfalls. The front features prominently on 27-11-2013-18z, WeatherTheatre snapshots. The Top-down Perspective of the tropopause shows a large amplitude, positively tilted, shortwave disturbance on the right side. A distinctive and dramatic double-fold tropopause ‘curtain’ is apparent on the Northerly Perspective, as the subtropical jet begins to merge with the polar jet at the jetstreak entrance region. Meanwhile, deep-blue shadings in the background are a very much elevated 300K Theta surface associated with very cold air.
A strong upper front is nearing Tasmania and features prominently in the 27-11-2013-18z, WeatherTheatre Analysis, snapshot. The front is made apparent by a deeply folded tropopause (upper surface), seen in the background of the Southeasterly Perspective below. As a result, rapid cyclogensis is occurring with a surface low quickly deepening. Most forecast models show the low situated east of Tasmania by Thursday night.
A small upper trough over Western Australia, marked by a tropopause vorticity-tube extending down from the surrounding tropopause surface above, can be seen in the right of the snapshot.
Thin filaments of cyclonic-vorticity, visible in the foreground, are due to a Ex-Tropical Cyclone Alessia which is located over the Gulf Country.
The WeatherTheatre, 27-11-2013-0z, North American Analysis shows a strong upper front crossing the Northeastern USA, which is driving rapid cyclogenesis and the formation of a deep surface low. The Northwesterly Perspective shows the eastern side of a deep tropopause fold (upper surface), oriented from the southwest to the northeast. Comparison between the Northeasterly and Northwesterly Perspectives reveals the elongated nature of the front which runs across the eastern USA from the southwest to the northeast. The raised Theta surface below indicates the spread of the associated cold air.
The WeatherTheatre, 26-11-2013-12z, Australia, Analysis snapshots feature a strong upper front over the Tasman Sea, where the sub-tropical and polar jetstreams are merging. Darker shadings on the top-down perspective show the steepness of the tropopause in this region, which is prominent in the upper left of the south-easterly perspective snapshot. A tiered, folding, tropopause surface indicates the merging jetstreams in the frontal region. The polar jet is associated with the lower tier and the subtropical jet the higher tier.
A weakening upper trough, which has been supporting a surface low over Western Australia, appears near the centre of the top-down perspective as a tunnel in the tropopause surface. Another upper trough can be seen to its west and will effect Western Australia over the next 24 hours.
A strong upper front in the polar jet, situated well south of the continent, appears in the right background of the south-easterly perspective snapshot. This is one to watch over the next 24-48 hours as it should cause the formation of a deep surface low east of Tasmania on Thursday evening.
A small disturbance in the sub-tropical jetstream over Western Australia features prominently in this morning’s WeatherTheatre Analysis, at 25-11-2013-18z. It can be seen in the adjacent WeatherTheatre snapshot as a tropopause front with a trailing vorticity tube to the mid-troposphere. The disturbance is assisting a surface low over the Gascoyne/Pilbara region.
A mid-latitude upper front in its mature phase is apparent in a tropopause fold seen south of Western Australia in the background of the south-westerly perspective snapshot. The easterly perspective snapshot shows it on the far right side.
In the background of the easterly perspective snapshot, a persistent upper disturbance and associated tropopause folding situated over the Tasman Sea is visible. This is better seen in the south-easterly snapshot which shows a tiered appearance to the folding, due to the polar jetstream merging with the subtropical jetstream over the eastern Tasman.
The top-down perspective below provides a good indication of the geographic layout and extent of the features described. The two disturbances in the west are visible on the left with darker shadings indicating the steepness of the tropopause surface in the frontal regions.
WeatherTheatre is a 3D weather visualisation on the web, created by Meteorologist and Programmer, Paul Graham, in October 2013.