Matt Makens

Spring 2021 looks to be warmer for most across our region. Drought areas will
continue with drier than average conditions, and the wetter than average
conditions will be nearer the Midwest to the Appalachians and central
Mississippi, and for the Pacific Northwest.

In this post I'll address what has happened in the past couple of months, how
the ocean-atmosphere connections have evolved, the status of the La Niña
forecast, and I will combine all those factors into the Spring forecast.

To begin, where have we been since January 1st in terms of precipitation and
temperatures to build on our analog years.

Precipitation departure from average is shown here, as percentage of normal. 

For the January and February period the following analog years were used, with
varying significance: 1950, 1967, 1976, 2002, 2011, 2014, and 2020. The
composite precipitation anomaly of those years is shown.

It is quite notable to see the analogs respond well to the La Niña correlation.
Precipitation in January and February is negatively correlated to the SOI, which
would indicate the analogs followed along with that correlation.

However, the precipitation anomalies for January and February 2021 did not
totally follow suit. There was greater wetness in portions of the Corn Belt, and
most notably the wet areas of the Midwest shifted toward the southeastern coast. 

A possible explanation for this shift is an ocean-atmosphere change in the
Central Atlantic ocean where a colder phase than forecast could possibly explain
an increase in precipitation along the coastline there. Such a change will also
have an impact on the Spring 2021 outlook. 

However, I believe there to be a more likely situation that played out and
shifted the wetter than average conditions from the Midwest to the coast, and
that reason is the extreme cold event that gripped most of the Central US.
Weekly precipitation for the southeastern US didn't climb markedly until the
country was under a strong cold are event, that cold air with the associated
jetstream, pushed the storm track farther south/east than what would be
considered normal established in the analogs. Such an extreme event is always
possible in seasonal outlooks, but in this regard we can still trust our analog
years.

Let's take a look, including that cold outbreak, at the temperatures since
January 1st and how the analog years pan out.

Temperatures departure from average is shown here.

Temperatures using the same analog years above indicate cold air is
possible/likely to occur across much of the northern and into the central tier
of states. We just discussed the rarity of the cold air event in how far south
it reach and its duration. Such an event won't be reflected in the analogs, but
we know the analog years do consider cold air a factor for central and northern
areas of the county.

With this said, if we could remove the unusual week of cold air gripping the
nation, we would likely see the analogs performing quite well. 

A jetstream associated with that event does remain capable of additional events
that could break the analogs for the Spring 2021 outlook - always possible - but
let's focus on what is forecastable for the moment. 

La Niña and other ocean-atmosphere oscillations are not likely to change phase
as we head into Spring 2021. Let's look at La Niña's forecast (ENSO forecast).
I'll show several US and International sources. 

The idea here is the same, on each chart going beyond February, you'll see a
number of forecasts plotted. Some trend toward 0 or neutral Niño conditions.
Some trend more negatively or strengthening Niña conditions. 

Four of the six forecasts shown trend toward neutral conditions heading into a
summer timeframe. That will certainly have an implication on the Fall 2021
forecast for the country; ENSO's impact on the US is low in Summer. I am not
discounting the two models showing a strengthening of La Niña and this must be
watched closely during Spring and Summer 2021 for implications felt in Fall
2021. 

For now, we can see a consensus that La Niña does remain to influence Spring
2021. 

Other ocean atmosphere connections can be shown here with projections, however,
I see little change to those that would bare any great consequence to the
forecast. With this in mind, I want to keep the same analog years of varied
weights for the Spring 2021 outlook. 

Precipitation average from March through May based on my analog years:

And, of those years, how many were wet years? I answer this question because it
gives weight to the placement of the precipitation as shown above (meaning, was
there an excessively wet year that skewed all analog years to appear wet). 

In this case, the frequency of wetness matches well with the composite average
of analog years shown above. I feel good about the precipitation outlook.

Temperatures average from March through May based on my analog years.

The temperature outlook implies similar cold air events to that of February 2021
will remain possible. Historically speaking, the northern and western areas of
the country are more likely to get that cold air than in the deep south. 

With our historical guidance complete, let's turn to forecast models.

I'll being with precipitation outlooks from various sources. 

Takeaways for the US are that a pronounced dry signal is present across the
Southwestern region to the Gulf Coast region. Pockets of wetness and nearer
normal conditions are present for the Pacific Northwest, parts of the Northern
Plains, and an area of wetness near the Appalachians to the Great Lakes, and in
some instances into the Mid-Mississippi. That sounds just like how my analogs
appear above. 

And temperature outlooks from the same sources.

Takeaways for the US are a pronounced warm signal from the Southwest into the
Central states. The Northwestern US is commonly near to colder than average, and
a hint of colder weather near the Upper Midwest and Great Lakes.

This does not quite look like the analog from above. In reviewing previous
forecasts by those same models, temperature projections did not grab ahold of
the colder than average conditions for much of the US in the January-February
timeframe. Although some tried, the group was far too warm in projections.
Further, my experience with seasonal model projections is that there is a warm
bias much of the time. I'm inclined to believe there's a colder potential in
sections of the west and northern US. 

As I discuss my thoughts along with my colleagues at Weather5280, here's our
outlook for Spring 2021.

Precipitation:

Temperatures:

Spring outlook 2021