Brendan Heberton

It's been a long, hot, and dry summer. It was well analoged and well forecast.
We now near the end of meteorological summer, and head for a winter that will at
least in part be driven by a likely La Niña
[https://www.weather5280.com/blog/2020/08/03/la-nina-update-and-potential-analog-year-as-we-look-ahead-to-fall/]
. 

A look at current sea surface temperature anomalies show still plenty of heat
content globally, but also the colder than average (La Niña) signal across the
equatorial Pacific. As of August 13th, the Climate Prediction Center had the
chance for La Niña development this fall at 60%, and the chance it continues
through winter at 55%. This outlook continues to felt well inline with what
we've been discussing here on 5280 since last winter. 

Most models are in agreement that we'll see a weak La Niña develop this fall.
Current conditions in the NINO3.4 region is at approximate -0.5C which is just
borderline Niña conditions, whereas a month ago we were in Neutral conditions. 

In our last long range update we looked closely at 2013 as a potential analog
for this coming winter. That year continues to be high on the list, as well as
some others. Below is a look at our current set of five analog years and what
they would indicate we could see for precipitation and temperatures from October
through March 2020/2021. 

For temperatures, a warm Southwest and cold for the Northern Plains are the
strongest indications. For Eastern Colorado this analog set has temperatures
near average, with western and south-central Colorado running above average. 

The precipitation look has a pretty Niña feel to it – wetter than average across
the north, and drier than average for the south. Northeast Colorado is near
average, while southern Colorado, Kansas, Oklahoma, and Texas all are solidly
dry. 

Probably not surprisingly, none of the seasonal models can find any colder than
average temperatures in the long range. Here's a look at the CFS seasonal
forecast (Nov-Dec-Jan left, Dec-Jan-Feb right). Warmer than average across the
board. 

Which actually looks a lot like the European seasonal forecast through February: 

So, are the models right or our early analogs? Hard to say. What we do see is
some indication that IF anywhere will trend toward cool in the models it'll be
the northern tier, fitting our analogs, and most seasonal models are in decent
agreement on their SST forecasts, which would indicate some cooler than average
areas across the CONUS this winter, even if the models themselves can't see it.
That said, perhaps it's an indication that our currently analogs are overdone,
at least on the extend of the "near average" as you head further south across
the U.S. 

As for precipitation, the Euro remains pretty darn dry for the next several
months before gradually becoming wetter as the winter progresses. We don't hate
this idea. It also is in decent agreement with a dry south-central U.S., and
wetter across the north if anywhere. It's near average for Colorado for the
heart of the winter and early 2021. 

One interesting consideration when looking at how dry the seasonal modal above
is for Sep-Oct-Nov is that it's mid-range model output is wetter for many of the
same areas and it takes us through October 9th. So, do we dry out considerably
for the latter half of October and November? Perhaps. It's also likely picking
up on Hurricane Laura's precipitation in the near term across Eastern Texas and
Oklahoma. 

For Northern Colorado, one of our analogs being 2013 probably has people's
attention. This model shows that this pattern can drive an uptick in wet weather
for our region early in the fall before drying out – so that's something to
watch in the coming weeks. No one is predicting the flooding we saw in 2013, but
worth mentioning that even if the fall ends up dry by and large, it doesn't rule
out a wetter period as we head into the change of seasons. 

There's a lot to consider here, and what the oceans do in the next month or two
will be very important in where things ultimately end up this winter. Overall we
have continued drought concerns across at least Southern Colorado, New Mexico,
Texas, and Oklahoma, with some hope for a more active storm track further north
– though unclear how much Northeast Colorado will benefit from that pattern as
of now.

It's August, it's hot, it's far too early to look ahead to winter –– but let's do just that