Here Come The Troughs, More Southwest Tropical Moisture, Atlantic Shear

Written by on August 30, 2013 in United States of America with 0 Comments

In yesterday’s post I showed you the troughy look to next week and how the Plains high will eventually break. Through the first half of next week, we see the second of three systems drop out of Canada.

This one will be stronger than the one just gone by but if you notice in the below 500mb charts off the ECMWF, the system that pushes onto the Pacific NW/BC coast next week, which granted will take time to get inland due to the +PNA, will likely be the breaker of the ridge and by next weekend, it should be much cooler across the country with a flatter look. You can clearly see that in the ECMWF over the next 7-10 days.

72 hr

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

Notice the ridge by Sunday simply backs west into the Great Basin, allowing the system to drop out of Canada.

132 hr

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

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Even by mid next week, while there’s a decent trough extending from the Great Lakes into the Mid-Atlantic, there’s still a 592dc high centred over Colorado, so the ridge doesn’t want to go easily.

162 hr

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

By Thursday the Pacific storm is moving into British Columbia as the eastern system pushes out into the Atlantic. Expect wet, windy conditions in the Maritimes and New England along with warming and a rise in humidity.

210 hr

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

By next Saturday, notice it’s that Pacific storm, once it gets inland, allowed due to the fact the eastern system moved out into the Atlantic and it’s this that flattens the upper pattern.

240 hr

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

By next Sunday, the model has NO real high anymore and that Pacific system is likely to produce a deeper trough into the East and it’s this which may or may not present a frost threat to parts of the interior East.

As for the Southwest which has been hit hard of late by tropical moisture. We have got a weakening TS Juliette which will draw moisture north and even the remnants of Fernand which struck east coast Mexico at the start of the week, killing 13 people, will get it’s moisture wrapped around the Four Corners high and drawn up into the Desert Southwest so over the next 48 hours, more showers and storms will keep the flash flood threat going. Look out for continued dangerous weather if you live anywhere near a flood prone area.

Source: AccuWeather

Source: AccuWeather

Finally, as for the tropics. Well the MJO is entering more favourable phases as you can see from the below GFS ensemble.


Here’s a current look at the water vapour across the tropical Atlantic. Notice the LACK of organisation.


The trouble is that there’s too much shear over the basin.

Source: AccuWeather

Will show you more Friday and what the models are hinting at around mid-Sept.

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