ECMWF, CFSv2 Shrinks Plains High & Backs It West Allowing Trough Into East Next Week

Written by on August 26, 2013 in United States of America with 0 Comments

At the moment, the sprawling upper high centred over the Plains is the dominant feature to the US pattern this week but there are noteworthy features causing headaches surrounding this wheel of heat. We have what was once Tropical Storm Fernand pushing copious amounts of moisture into the mountains of east-central Mexico which will cause flash flooding while the remnants of Ivo in the Pacific pushes tropical moisture up into the Baja, northwest Mexico and the Desert Southwest where we’ve seen flash flooding in Yuma, Las Vegas and other cities.

We’re also seeing big storms associated with an upper disturbance which are producing a lot of lightning, embedded severe storms and heavy rain across Ontario and these clusters will sag south threatening steamy Minneapolis later this afternoon into this evening as well as cities such as Madison across to Detroit. Each system is being directed around the one common denominator and that is the hot dome and it isn’t weakening till at least this weekend.

Source: AccuWeather
Source: AccuWeather

The upper disturbance helping trigger the storms and heavy rains across parts of Minnesota and Wisconsin tonight should push into parts of the Northeast tomorrow.

Source: AccuWeather
Source: AccuWeather

The ECMWF shows the energy dropping through the region tomorrow and could become quite potent with a slight, maybe isolated moderate risk of severe weather over parts of New York, Connecticut and Massachusetts as the energy rims the heat and humidity.

Courtesy/Owned by AccuWeather Pro
Courtesy/Owned by AccuWeather Pro

More Tropical Moisture For Desert Southwest Late Week?

There is concern that while the system in the Pacific weakens, the moisture from another tropical low will spread up the Mexican coast and into the Southwest late week into the weekend.

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Here’s the ECMWF at 108 hrs of Saturday morning.

Courtesy/Owned by AccuWeather Pro
Courtesy/Owned by AccuWeather Pro

Any Sign Of The Ridge Breaking Down?

There is increasing model guidance which suggests a low over Canada intensifies at the same time the ridge centred down over the US takes a slight shift west towards the Great Basin. The combination of the low strengthening and the US ridge backing west, allows the low to drop southeast and with it being stronger, this should have more influence on the US upper pattern, helping dig a trough back into the Eastern US.

The ECMWF shows a trough dropping down over the Great Lakes and East towards the end of the weekend and into early next week.



By Saturday after a trim of the temperatures Thursday across the Northern Plains as a slightly stronger upper disturbance crosses the Northern Plains, the heat comes right back into Minnesota and the Midwest where Minneapolis and Des Moines will once again climb into the upper 90s after a day or so possibly back down in the 80s.


Notice by 168 hours or next Monday the hot dome has backed west and there’s a kink in the isobars over Ontario. The upper system should be forming on top of a fairly decent surface feature and this will help drop heights throughout the Eastern US, eventually breaking down the eastern flank of the ridge and forcing it into the Great Basin.


By next Wednesday the upper low has formed and is sprawling out, driving much cooler, Canadian air southeast as the trough gets carved out. Gone is the major heat over Minnesota, Wisconsin, Iowa, Illinois down to Missouri.


The question remains, is this the end of the major Plains heat or does it come right back after the trough in the east gets kicked out into the Atlantic?

The CFSv2 shows the heat week 1 and 2 with weakening and shrinking in week 2, then a turnaround to cool across the nation week 3 and 4.

Week 1-2


Week 3-4


The GFS NAO ensemble shows a downward trend towards the positive side of neutral which could suggest more of a trough than ridge over the next 10-20 days.

The CFS for September shows a mean trough centred over the Southeast with cooler than normal temperatures. Though not easily to see, here is the 500mb height anomalies and surface temperature anomalies.





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