Official North America Fall 2013 Forecast

It’s been a cool summer from North Dakota to Florida and for Eastern areas, August has been downright chilly with temperatures averaging 4-8 degrees below normal. This comes on the heels of a cold and very snowy back end to winter and spring season.

The NAO from the end of July turned negative and this along with saturated ground has helped hold the trough over Central and Eastern areas. A major ridge with hot air has continuously pumped heat out of the Desert Southwest up through the Rockies and all the way to Alaska and Northwest Canada where records highs have been common. This wild upper pattern across the continent has lead to the weird and wild upside down setup of record heat in the far North but as heat was forced north, so cold air got pushed south with day after day of record cold maximums and minimums. Record rains have dominated the Southeast with half foot totals in just the past 48 hours over parts of the Florida Panhandle. We saw Charleston, South Carolina flood Thursday then it was Savannah, Georgia’s turn the following day.

The question is, do we see change in this stubborn pattern as we head towards the first month of meteorological autumn? The answer is yes!

The CFSv2 coincides nicely with the return of a positive NAO. In fact we may be seeing the onset to the most positive NAO episode in months and this will promote eastern ridging.

nao_sprd2

Notice the negative since late July which has helped with the eastern trough along with the wet ground and let’s not forget the PNA which has been hovering near neutral but bouncing up and down much of the summer. Those two oscillations alone have kept things warm in the West except for the immediate West Coast where a strong onshore flow has kept things cool down the California coast in recent weeks. Los Angeles endured it’s longest spell below 80 in August on record. However, inland areas of the West sure did stay warm and that warmth spreads north from Mexico all the way to Alaska and the Yukon while constant cool shots dropped into the northern and eastern states.

pna_sprd2

The most recent cool shot drove Canadian air unusually far south. The Gulf Coast! Typically steamy Mobile, AL even got in on the record chill which kept Atlanta below 70 two days in a row with the chilliest August days (66 & 67F) since 1986.

The upcoming week sees the big change.

Here’s the ECMWF for yesterday.

Geopotential3250032hPa32and32Temperature32at3285032hPa_North32America_0

Here’s this upcoming Friday.

Geopotential3250032hPa32and32Temperature32at3285032hPa_North32America_120

Interestingly the CFSv2 isn’t seeing the heat through next week in the East but by week 3-4 it sees major warmth centred over the Plains. The majority of the country looks warm through the first 10-15 days of September.

wk1_wk2_20130817_NAsfcT

Week 3 and 4

wk3_wk4_20130817_NAsfcT

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The NAO looks likely to go back negative into early or mid September and so I suspect the warmth in the East will ease. However, even if the NAO returns to a negative signal, this doesn’t mean the Northeast won’t be warm but more the Southeast stays cool with further rain. Texas will told onto the heat with the drought unlikely to ease through the fall months. This heat could keep riding around the northern edge of the Southeast upper low and keep the Ohio Valley and Northeast warm and humid.

Here’s the CFSv2 temperatures for the month of September.

usT2mMonInd1

Precipitation

usPrecMonInd1

 

While this is all going on. The cold air reservoir over the pole will continue to building and is already building early with the help of a mainly positive NAO/AO during the summer which has kept the arctic sea ice from melting to levels of last summer. In fact there’s more ice coverage up there than what has been observed since before 2009. So, this additional ice cover, stopping warm water from heating the arctic atmosphere should allow the cold to really grow and build early on. With the abnormally warm waters over both North Pacific and Atlantic, one must wonder if a negative AO/NAO event could be triggered late in September and into October?

I strongly believe the CFSv2 in what it has for October. Check this out…

usT2mMonInd2

Precipitation

usPrecMonInd2

 

With the growing of arctic sea ice and cold air I believe the modelling is seeing and has been seeing for quite some time, a negative AO/NAO. Look out because the current bundling of cold over the pole just now with the positive AO/NAO could be laying the ground work for October and an early taste of winter for eastern Canada and the US.

1098479_10151695321651731_295071348_n

What’s very interesting is that in the last 2 weeks we’ve seen a flip in the CFSv2 for the November-December period.

In earlier runs the model showed the cold October but was then followed by a warm/wet November in the East. The model was sniffing out a return to positive with the AO/NAO. Now it’s the opposite.

Here’s the newest run for November.

usT2mMonInd3

Precipitation

usPrecMonInd3

As for December!

usT2mMonInd4

I would be cautious about the timing of this but the general idea the model has does make sense.

Personally I believe the previous run which has a warmer/wetter November on the backside of what could be the coldest October since 2008 or even 2004 which was brutal in the Northern Plains and very chilly across much of the country is more likely. My reasoning behind thinking that is that I believe there are real similarities to 2009 also with the near neutral ENSO, water temperatures globally as well as the arctic sea ice coverage.

Check out the comparisons…

Arctic sea ice.

testimage_2

Sea surface temps.

2013

1098479_10151695321651731_295071348_n

2009

1011481_10151695382906731_1028834075_n

In my forecast and not a model, I believe September will be near normal temperature wise with a potentially warm start from the Plains on east but the second half of the month could turn decidedly colder with a tanking in the AO/NAO on approach to October which could set the stage for a potentially VERY cold October over the Northern Tier with snow and record cold. This chill would spill periodically into the Southeast.

We should see a flip in November with the return of a trough over Greenland and ridging up the eastern side of North America. This could lead many into a false sense of security, making folks think this upcoming winter will end up like where last winter’s start and middle point ended up.. warm!

Then after a warm, wet November similar to 2009 with a cool, snowy West with a strong Pacific jet bringing one storm after another into the West Coast, the feedback of those warm waters up the west coast and the tripole of warm-cold-warm over the North Atlantic should kick in.

Based on current arctic sea ice extent, SST’s globally, NAO/AO trends and the neutral and likely continued ENSO, there could be an increased likelihood of seeing a stratospheric warming event during December like we saw early December 2009 which eventually lead to a blockbuster winter for the Eastern half of North America, Western Europe and Eastern Asia.

Check out the CFSv2 for JANUARY!

usT2mMonInd5

 

Linking Autumn With The Upcoming Winter

You may ask. What’s makes me think this winter could be any different to last year or 2011-12 which was warm for North America. Well as you can see from the below chart, arctic sea ice is far more extensive this summer compared to recent times but remains well below normal. It’s still only mid-August and the minimum has yet to occur but given the chill up across the arctic, there may or may not be much more melting. This year’s extent compared to recent years is leading to an earlier building of the arctic cold pool which means more pronounced arctic cold shots early on and possibly as early as October as stated above. The still above normal waters of the arctic surrounding this more extensive ice pack means the increased chance of high latitufe blocking is real and one must not ignore the warm waters of the North Pacific and Atlantic. This is ripe for blocking high pressure feedback during the winter months. The setup through this summer and into fall shouldn’t be overlooked and could lead to plenty of fun and games further down the road.

Source: Arctic Sea Ice Monitor

Check out the projected SST’s for winter.

CFSv2

glbSSTSeaInd2

Jamstec

ssta_glob_DJF2014_1jul2013

Both see the North Atlantic tripole favourable for a Greenland block and warm waters in the arctic which promotes stratospheric warming events.

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