Tucson’s Monsoon 2016 Forecast

It’s the most wonderful time of the year for meteorologists in the Grand Canyon State.

June 15th marks the official start of the Monsoon, a 108 day span that accounts for over half of Tucson’s annual rainfall. El Niño’s officially over. La Niña’s likely to settle in. What could it mean for the Super Bowl of southern Arizona weather? Here’s my 7th annual take on what to expect during Monsoon.

WHAT THE CPC SAYS

cpc051916

The latest Climate Prediction Center (CPC) outlook for the July-September timeframe calls for equal chances of above, normal or below average rainfall for Arizona. As I touched on last year, the CPC tends to paint with a rather broad brush. There are local effects that can sway seasonal precipitation forecasts one way or the other. Here are a couple of factors I’m focusing on for Monsoon 2016.

WORKING IN OUR FAVOR

Jeff 2016 La Nina Tracker

After a record-setting El Niño, waters off Mexico’s west coast are starting to cool off. Models are in agreement that this trend continues throughout the Summer. The latest forecast for sea surface temperatures in the eastern Pacific show waters roughly 0.5-0.7° cooler than average, indicating a weak La Niña.

How does this benefit southern Arizona? What El Niño is to the Winter, La Niña is to the Monsoon. The working theory is cooler than normal Pacific waters up against hot temperatures on Mexico’s mainland drives a more unstable atmosphere. That increased temperature difference between land and sea could develop more storms in Mexico, allowing subsequent moisture to enter southern Arizona.

Since record keeping began in 1950, a weak Summer La Niña has been present 10 times. Of those 10 La Niña events, Tucson recorded above normal Monsoon rainfall 9 times. In all, Tucson’s average Monsoon rainfall during a weak La Niña computes to 8.36″, which is well above the seasonal normal of 6.08″. Tucson’s two wettest Monsoons on record (13.84″ in 1964, 13.08″ in 1955) occurred during a weak La Niña event. It’s important to note that a weak La Niña does not guarantee above average Monsoon rainfall. It increases the odds that it’ll happen.

epac-forecast

Another potential factor that may sway Monsoon 2016 toward a wetter side is the eastern Pacific hurricane season. Mexico’s meteorological government agency is forecasting near normal activity, which may include 17 named storms. 9 of those storms are expected to become hurricanes.

WORKING AGAINST MONSOON RAINFALL

100 july

The biggest factor that could shut down a stormy Summer is where the Monsoon high sets up shop. Quick refresher: the Monsoon is defined by a seasonal shift in winds aloft, changing from the west to the east or southeast. This flow funnels in moisture from Mexico and the Sierra Madres, fueling our daily rounds of thunderstorm activity. The “sweet spot” for the Monsoon high is the Four Corners area.

20160607_west_trd

Recent research has shown this dome of high pressure likes to settle into areas which were dry during the Winter & Spring. Thanks to El Niño’s meager influence this past Winter, much of Arizona and New Mexico saw the drought come back with a vengeance. As of June 7th, a good chunk of the southwest was under moderate drought. Severe drought was present in much of Santa Cruz and Cochise Counties.

If high pressure sets up in these areas, it could shunt moisture south of the border & leave southern Arizona with below normal Monsoon rainfall. Not a good sign, considering a lingering La Niña into Winter historically leads to less rain & mountain snow.

POTENTIAL TRENDS

Two key trends I’ll be watching closely this Monsoon: first – will the expanding drought lead to a higher frequency of dust storms? I’m leaning toward yes; at the very least, more than last year. Recall that we went into last Summer running a rainfall surplus, hence the lack of haboobs. As of this writing, Tucson sits roughly 0.40″ below average for rainfall for 2016.

cfs_anom_precip_noram_201609_120

The other trend is whether storms will linger well into September, like the last few years. Again, the initial indication is no. Climate models (posted above) lean toward our daily rounds of thunderstorm activity fizzling out after Labor Day. Historically speaking, this is when we expect the Monsoon to start winding down.

MY FINAL CALL

Numbers don’t lie. More often than not, a weak La Niña has historically delivered above average Monsoon rainfall to the Old Pueblo. A huge plus – one that I think outweighs the biggest factor working against a wet Summer: where high pressure sets up. Last year’s Monsoon was pretty decent. I expect more of the same this time around.

Tucson’s average Monsoon rainfall: 6.08″
My Monsoon 2016 rainfall forecast: 6.85″ (+0.77″ above normal)

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7 thoughts on “Tucson’s Monsoon 2016 Forecast

  1. Thanx for the optimistic prediction! Can you guess weather (pun) the monsoons will reach Southern California? We live in Wrightwood and can really use the rain!! Thanx again!!..Mark

    1. Thanks for reading Mark! Sorry for the delay in replying. It’s really hard to pinpoint when Monsoon moisture enters southern California. Hope for high pressure to settle in over Las Vegas or a tropical system off the Baja coast. That could be the ticket to storms in your backyard this Summer.

  2. The article mentions four corners high preasure blocks monsoon moisture. This is opposite of the idea that Colorado Plateau heat helps draw moisture northward? Don’t get me wrong, as seeing how mid July is forcasted to be quite dry in much of New Mexico, if I were to bet in Vegas, I’d bet on a very bad summer “non-soon” drought, sandwiched between a dry 2015/2016 winter, and a predicted dry 2016/2017 winter, I think AZ and NM will see drought conditions surpassing 2010! Maybe where Im confused is even though a hot four corners helps draw the monsoons north, the core of that heat has to move more over Oklahoma to kick-start the northward draw. However there is an abnormal busy highway of storms lows over the northern Rockies for much of the summer, so the heat will stay centered over northwest NM/northeast AZ, record temps, dry winds, wildfires, and all that continuing into fall 2016. I’m really tempted to go to Vegas now!

    1. Thanks for posting Jan. The article does not say the Four Corners high blocks Monsoon moisture from entering southern Arizona. In fact, it’s the exact opposite. We want the high pressure center to set up shop over the Four Corners (AKA Colorado Plateau) to get our daily rounds of storms fired up.

      Regarding the drought: sometimes the Monsoon high can settle over places with elevated drought levels, which could be southeastern Arizona & southwestern New Mexico. That’s a bad spot, as it (in theory bottles) up Monsoon moisture in Mexico. It should be noted that more research needs to be done regarding drought correlating with high placement.

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