Models Show Strong Hint Of Cold Mid To Late September Across Most Of US!

Written by on August 29, 2013 in United States of America with 0 Comments

It may be hot now over the heart of North America with 100s showing up over parts of Saskatchewan and Manitoba this week and to a lesser extent next week but there are strong indications of a significant hemispheric pattern change coming up in the next few weeks.

September is sure to start off warm to hot from the Plains west into the Great Basin but we should watch closely at disturbance pushing into the Pacific Northwest this weekend as modelling shows this crossing southern Canada this weekend into early next week, intensifying as it crosses the Prairies, then drops into the Northeast bringing wet, windy, cool conditions with a flood risk perhaps.

Below is the latest 500mb charts which show this feature really intensifying and showing that it has the might to really dent but not burst the heat bubble currently over the Plains.

48 hrs (Fri)

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

Between Friday and Sunday the system crosses southern Canada, bringing a heavy rain, flood and even severe weather risk to the Northern Rockies and Plains states.

84 hrs

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

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By Monday, the system begins to wind up, forcing the ridge to it’s south to begin retrograding west towards the Great Basin. This allows the system to drop southeast.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

The 132 hr surface/precip chart shows a decent band of rain and storms covering the East Coast and even southern plains. Behind this is pretty decent blast of cool, refreshing air out of Canada.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

144 hrs

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

Once the front clears with it’s rain and storms, yet another cool Canadian high should drop down bring more sunny, pleasant late summer days with low humidity. At night, beneath clear skies and light winds, don’t be surprised to see frost and lows in the 30s over sheltered nooks of PA, western MD and WV with widespread 40s elsewhere.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

Notice in the 168 hr chart above that while this front clears the coast, so an even stronger and more wound up system is crossing southern Canada. Could this be the next rain/storm bearing front with yet another wave of cool, refreshing Canadian air? Very likely and yes, as we head through September. With each passing front, we will begin to see cooler and cooler air coming down.. All we need is some blocking to draw down some of that arctic stuff that’s building fast up across the pole!!

Signs Of A Cold Spell Brewing Mid To Late September?

The CFSv2 shows plenty more heat over the centre of the continent in the 6-10, backing west, northwest in the 8-14 with a cool look to the East which suggests to me that each system riding the north flank of the Plains/Great Basin ridge are strong enough to recarve troughs out and keep the mean trough focused in the East. This could be an ugly pattern setting up from Marquette to Virginia Beach. In week 3-4, the majority of the nation is back to below normal with the heat all but wiped out.

6 to 14 day

wk1_wk2_20130827_NAsfcT

Week 3-4

wk3_wk4_20130827_NAsfcT

Notice in the 500mb height anomalies for week 3-4 that there’s positive heights showing across the arctic. Could this be the model sniffing out a mid to late Sept cold spell from the Plains east? By that I mean an early hard frost and freeze and downright cold days?

wk3_wk4_20130827_z500

The newest run of the CFS 500mb means for Sept has blocking over the Davis Straits which correlates to negative heights over Southeast Canada and the Northeast US.

cfsnh-3-9-2013

All oscillation signals point to a negative trend into early and mid Sept.

AO

ao_sprd2

NAO

nao_sprd2

PNA

pna_sprd2

All this of course fits in nicely with my longer range ideas.

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