Matt Makens

La Nina in the works doesn't help our chances of a wet August, and the state of
the Northern Pacific and Atlantic Oceans make the wet signal even weaker for the
month.

Brian Bledsoe laid the framework for our dry outlook in his La Nina update
earlier this week
[https://www.weather5280.com/blog/2020/08/03/la-nina-update-and-potential-analog-year-as-we-look-ahead-to-fall/]
. Let's dig into a few other correlations.

For August, precipitation correlates most highly with PNA, SOI, and PDO
ocean-atmosphere teleconnections. With that in mind, in looking at the past 40
years worth of data to find a similar comparison to the state of those
teleconnections today, there are 14 'similar' years.

Of those years, here is the frequency of a wetter than average August.

You can see that wet Augusts occur very frequently in Florida but very
infrequently across the Western US and in the Midwest. Zones in Colorado have
had about 1/3 of Augusts end up being wet in our current setup.

The lack of a monsoonal flow regime, as we forecast throughout the summer
[https://www.weather5280.com/blog/2020/07/11/update-monsoon-outlook/], has
significantly hurt our chances of seeing a wet August. The atmospheric setup
simply isn't favorable for much rainfall. 

I can throw in the MJO as another oscillation that we look to for signs of
wetness, but it do only briefly points to phases where we could see some wet
weather but not long enough phases to overcome the dryness.

Historical correlations are one thing, to get modeling to agree to that
climatology is another.

The Euro and the CFS both point toward a drier than average west, some wetness
through the nation's midsection toward the East. They differ in subtle
placements of wetness, including eastern Colorado. 

For our region, I'm inclined to lean toward the Euro placement with greater
confidence since it matches more with those 14 analog years shown above.

Per temperatures, you can assume that a drier than average forecast will mean a
warmer than average forecast. That's our going thought also, for the same
reasons as above: teleconnections and modeling.

As with precipitation above, the CFS (below) is a cooler overall. We'll lean
close to the analogs and Euro given everything we've discussed.

At the end of the month, I'll look back at August with some surprise if I see
that CFS had greater accuracy with a wetter and cooler Eastern Colorado. It
doesn't match the current setup. 

However, perhaps some stalled frontal boundaries could produce lots of water on
the plains with cooler temperatures. In the future, we will discuss the increase
in flooding potential headed toward fall from cold fronts that can stall out in
our region. Could the CFS be picking up on something here? We'll see. 

For now, status quo continues with our stagnant weather pattern.

August outlook includes little moisture