Utah Long Range Weather Forecast for Spring 2019

Following an exceptionally dry 2017-2018 winter season, snowfall has rebounded across the state of Utah this winter.  This was especially true in February, when snowfall was well above average across most of the state.  As it stands now, the snowpack in the Colorado mountains is decidedly above average state-wide (image source: NRCS).

 

 

Across the Salt Lake City Metro Area and Wasatch Front, snowfall has actually been a little below average this winter, at least along the I-15 corridor.  Through the end of February, the Salt Lake City Airport had received 35.4″ of snow for the season, compared to a season-to-date average of 42.4″. 

However, across the eastern benches snowfall has been a little above average.  The climate reporting station near the mouth of Big Cottonwood Canyon had received 84.0″ of snow for the season through the end of February, compared to a season-to-date average of 69.5″.

Now that March has arrived, it’s time to start taking a look at the spring season, which historically is the wettest season in Northern Utah.  Meteorological spring is defined as the period from March through May.

Currently, we are in a weak El Nino phase.  This is something that has been advertised since last fall, but only in recent weeks have ocean temperature anomalies in eastern El Nino Pacific started to take on a true El Nino signature.  Weak El Nino conditions are expected to persist into the spring and possibly linger into the summer as well (image source: NOAA). 

 

For Northern Utah, El Nino does not have a particularly strong signal one way or another during the winter months, but during the spring it tends to exhibit a bias towards wetter than normal conditions.  Southern Utah has a stronger wet signal during El Nino phases, both during the winter and spring months.

An interesting twist to the outlook this year is the cooler than average waters of the North Pacific off the west coast of Canada and the U.S.  This has been indicative of a negative Pacific Decadal Oscillation phase (or -PDO), and has created a favorable environment for colder than average temperatures across the Western U.S. recently along with frequent low pressure troughs pushing into the west coast.  See below (image source: NOAA).

 

 

Given the favorable pattern outlined above for an active pattern across the Western U.S., this raises the odds for a wet spring across all of Utah, and a snowy spring across the higher elevations.

Another factor we look at in the spring forecast is western U.S. snowpack and current drought conditions.  Moisture (or a lack of) at the surface tends to play a feedback role in the atmosphere, especially later in the spring when convective rains/thunderstorms become more common.  Surface moisture is also a sign of recent weather patterns, which can be tough to break without a large scale change in the upper atmospheric flow pattern.

Currently, drought conditions still remain over much of Utah and portions of the Great Basin (image source: NOAA).  However, compared to last summer and fall, the drought situation has substantially improved thanks to a wet and snowy winter.

 

 

The next image shows current snowpack percent of average, in terms of snow water equivalent, across the Western U.S. (image source: NRCS).  This is a great look for the Western U.S. with widespread above average snowpack for all but the far northwest.  Places that previously were experiencing serious drought last year, such as Utah and California, have received well above average snowfall this winter.  This means more moisture available later this spring as low pressure systems track across the West.

 

 

Looking at past years with similar El Nino and PDO regimes that also had above average winter snowpack, we came up with four analog years:  1995, 1993, 1978, and 1969.  We also came up with two other weaker analog years (1953 and 1979) that were factored into our outlook to a lesser degree than the four stronger analog years.

Here are the average precipitation and temperature anomalies for the above mentioned years.

Precipitation:

 

Temperature:

 

While there are always factors that will occur that cannot be predicted in advance, most signals point toward an active spring season across Utah.

As a result, we are anticipating a bias toward above average precipitation and colder than average temperatures across Utah this spring. 

Snowfall across the Salt Lake City area in March and April is tricky, since much of it depends on whether or not cold enough air arrives with individual storms for precipitation to fall as snow rather than rain.  March and April tend to see less snowfall in SLC compared to December through February, with an average of 13″ during the two months combined.  This year, we anticipate several more snow events in SLC with near to perhaps slightly above average snowfall during the March-April period.

By later in the spring, we’re expecting above normal thunderstorm activity to go along with above average precipitation.  Salt Lake City averages 2 thunderstorm days in April, increasing to 6 thunderstorm days in May.  We think SLC will end up with more thunderstorm days than usual in May.

Flooding due to snowmelt, along with increased odds of above average spring precipitation, could become a concern later this spring as well.  Canyon country in Southern Utah in particular is likely to see an elevated flooding risk this spring due to above average higher elevation snowpack and expected wetter than average conditions this spring.

There is always a degree of uncertainty with long range forecasts, but we believe based on past evidence that the odds favor an active spring.

Here are our precipitation and temperature odds for March through May:

Precipitation Odds:

Above Average:  40%
Near Average:  30%
Below Average:  30%

 

Temperature Odds:

Above Average:  20%
Near Average:  30%
Below Average:  50%

 

As for the summer season, it’s a bit too early to say how that will play out, but we will see how things progress this spring and will release a summer outlook down the road.

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