Chilly Next 2-3 Weeks Over Eastern US But Could August End Warm To Hot?

Written by on August 11, 2013 in United States of America with 0 Comments

After a warm-up and return to higher humidity, the chill returns this week to the Eastern United States and more or less all models show a very cool next 2-3 weeks with the trough firmly under the thumb of a strong blocking high to the north, helping keep unusually warm weather up across the arctic circle of Canada. Expect temperatures of 10-25F above normal across a large swath of Canada with the core of warm shifting from the Yukon to Quebec over the next 7 days. Underneath and from St Louis to Washington DC, expect temperatures running 5-15F below normal, especially from mid week through to the following weekend. The chill appears to intensify late this week through the following week with a core centred over the Tennessee Valley.

With this setup comes the continuation of heavy rains which shift from the Central Plains towards the Southeast up into the Mid-Atlantic. The weather over the Great Lakes, Ohio Valley into the Northeast really from Baltimore north looks terrific as next week progresses.

Check out the amount of rain expected from the QPF over the next 7 days. Looking ugly over the Southeast!

p168i

Below is the mean 500mb height anomalies in the 8-14 day from the CPC.

NAEFS_zdns_d264_00

Below is the 8-14 height field which shows the classic western ridge, eastern trough. With the jet stream flowing to the south into the Southeast, expect embedded disturbances to ride along, enhancing rains and thunderstorms across an already saturated region. This next 2 weeks could see an additional 5-10 inches of rain from Missouri, Arkansas across Tennessee, Alabama, Georgia and the Carolinas. This could help push seasonal and perhaps help push some cities well on their way towards ANNUAL rainfall records. Atlanta has seen 21 inches of rain since June 1

NAEFS_hght_d264_00

 

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Below is the 6-10 day CPC surface temperature anomalies and there’s no disputing the chill which deepens in the East over the next 2 weeks as the blocking high currently over northern British Columbia and the Yukon slides east across Canada. As this happens, so the trough and chill underneath intensifies.

6-10 day

610temp_new

Interestingly in the 8-14 day the chill weakens and warmth from the block over Quebec bleeds into New England.

8-14 day

814temp_new

What will be interesting will be whether a potential warm-up kicks in sooner or later.

NAO To Go Strongly Positive! Could Ridge Return To East To End August?

For North America, the NAO signal weakens during summer with far less usage compared to the fall and winter months. However as we barrel through August and the atmosphere over the northern hemisphere turns colder in the north, so that signal starts to show it’s hand once again. The GFS ensemble is projecting the NAO to go back positive as early as next week and strongly so at that. I would not be surprised to see a flip from mean trough over the next 2-3 weeks to a ridge and last blast of summer in the East by week 4 or towards the last week of August and start to September. The CPC 6 through 14 day period may be hinting at that and we could see warmth back over the Northeast as early as week 3 or beyond August 25.

Here’s the GFS NAO ensemble outlook.

nao_sprd2

The CFSv2 500mb heights anomalies show well the chilly setup in the East over the next 3 weeks but it’s week 4 which could see a flip. This model shows a slower warm-up in the East I think compared to the CPC above.

Week one shows the strong block and abnormal warmth over NW Canada and Alaska with constant feed of chilly air into the Midwest and East but week 2 sees that high slide east bringing abnormal warmth to eastern Canada while it cools down some over the Northwest. That movement over Canada of the blocking high, deepens the trough beneath and so the chill is locked in.

wk1_wk2_20130810_z500

By week 3 the blocking high splits with a piece sliding back west while another pushes over to Greenland which would keep the chill in place in the East. However if the trough and cool Canadian high manages to drop far enough south and east, so warming southwesterly winds on it’s backside may pull back north northeast warming the Eastern US. The CFSv2 appears to keep the Eastern US cool but a reversal could arrive Aug 31 and Sept 7.

Week 3-4

wk3_wk4_20130810_z500

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