{"id":2469,"date":"2026-06-15T16:47:13","date_gmt":"2026-06-15T16:47:13","guid":{"rendered":"https:\/\/discussions.weather.arizona.edu\/?p=2469"},"modified":"2026-06-15T16:51:28","modified_gmt":"2026-06-15T16:51:28","slug":"welcome-to-the-2026-north-american-monsoon-season-june-15th-2026","status":"publish","type":"post","link":"https:\/\/discussions.weather.arizona.edu\/?p=2469","title":{"rendered":"Welcome to the 2026 North American Monsoon Season: June 15th, 2026"},"content":{"rendered":"\n

El Ni\u00f1o-Southern Oscillation<\/h2>\n\n\n\n

Since the start of the year, we\u2019ve been in the process of shifting from a weak La Ni\u00f1a pattern during last winter to El Ni\u00f1o, as shown below. Specific information on current conditions, outlooks, and history of the El Ni\u00f1o Southern Oscillation can be found at the Climate Prediction Center (CPC) site here<\/a>. <\/p>\n\n\n

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Sea Surface Temperature Anomalies from CPC for May 10 to June 6.<\/figcaption><\/figure>\n<\/div>\n\n\n

The band of warmer-than-normal water along the equatorial Pacific shows the developing El Ni\u00f1o, where sea surface temperature anomalies (>. 5\u00b0C) continue to expand and strengthen. One indicator of ENSO conditions, the Ni\u00f1o 3.4 index (a three-month average of +0.5\u00b0C or greater), reached the threshold for March-April-May, signaling the start of El Ni\u00f1o. Since then, the threshold has been surpassed many times on a week-to-week basis.  <\/p>\n\n\n\n

The Southern Oscillation, the -SO part of ENSO, is the atmospheric circulation pattern established by anomalously warm\/cool sea surface temperatures. Warm temperatures tend to change the typically easterly trade winds to westerlies. The wind anomalies at 850mb, though, aren\u2019t strong yet. Though there has been talk of a strong El Ni\u00f1o \u201cSuper-El Ni\u00f1o,\u201d that isn\u2019t the current situation yet, even though forecasts are still predicting this El Ni\u00f1o to be a strong one. <\/p>\n\n\n

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850mb wind speed and direction anomalies for May 10 to June 6 (top), 200mb anomalies (bottom) <\/figcaption><\/figure>\n<\/div>\n\n\n

The other question is how El Ni\u00f1o will affect the upcoming monsoon? Research indicates there isn\u2019t a clear relationship between monsoon precipitation and the El Ni\u00f1o Southern Oscillation (ENSO), with positive phase ENSO years allowing for different types of monsoon season (early\/late, dry\/wet). The table below shows the top 10 wettest and driest monsoon-season precipitation totals at the Tucson Airport; among the wettest monsoons, only 1 or 2 occurred during El Ni\u00f1o. <\/p>\n\n\n\n

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Monsoon season total precipitation stats for Tucson Airport: https:\/\/www.weather.gov\/twc\/Monsoon<\/a><\/figcaption><\/figure>\n\n\n\n

That said, winter precipitation is strongly influenced by ENSO, with El Ni\u00f1o tending to be wetter and La Ni\u00f1a drier. The CPC forecast of a wetter-than-normal monsoon season may be due to Eastern Pacific hurricane activity; El Ni\u00f1o does have a positive impact on East-Pac hurricane activity. <\/p>\n\n\n\n

And, as always, the problem of trying to forecast precipitation amounts for the monsoon is the randomness of thunderstorms! So, are the storms we have seen in the past few days the monsoon? Purists would say no, because the westerlies still dominate the general circulation…but how are we to know if that happened in other years? <\/p>\n\n\n\n

Dewpoint temperatures have at times exceeded 54\u00b0F, but the daily averages are still likely to remain below this threshold in Tucson.<\/p>\n\n\n

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2m dewpoint temperature observations from UofA campus for the past week.<\/figcaption><\/figure>\n<\/div>\n\n\n

Past Weather<\/h2>\n\n\n\n

The water vapor satellite imagery below shows broad subtropical mid-level moisture from the tropics to the Midwest. Earlier in the week in Arizona, surface moisture was low, so not much precipitation reached the ground, with the threat from thunderstorms being lightning, isolated heavy rain, and microbursts.  <\/p>\n\n\n\n

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GOES19 upper-level water vapor images from June 15th at 7 am, College of DuPage<\/figcaption><\/figure>\n\n\n\n

Sierra Vista had a 59 mph microburst Saturday, and a thunderstorm produced a small fire in the Rincon Mountains at Saguaro National Park East.<\/p>\n\n\n\n

GOES19 longwave infrared satellite images from June 14th at 11 a.m. to 7 a.m. this morning, College of DuPage<\/figcaption><\/figure>\n\n\n\n

The storms on Sunday produced a 74 mph wind gust at Fort Bliss, Texas. Winds were gusty in Arizona Sunday evening. <\/p>\n\n\n\n

Analysis<\/h2>\n\n\n\n

More moisture is in southern Arizona, with 60\u00b0F dewpoint temperatures returning in Pima, Pinal, and Santa Cruz counties. Yesterday, storms that formed entrained dry, low-dewpoint air from the lower deserts, preventing them from moving into the valleys. Outflow boundaries pushed through the valley from the south and mixed up the boundary layer yesterday evening…so that problem does not appear to exist today, with overnight and morning showers in the Tucson valley.<\/p>\n\n\n\n

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Surface weather station observations for Arizona and New Mexico at 6:30 am, NWS<\/a><\/figcaption><\/figure>\n\n\n\n

The storm-total precipitation map as of 5 am this morning is shown below. It didn’t rain everywhere, and the heavier precipitation was from training storms through the night. So, some areas received over 2 inches of rain, but the NWS did not issue any flash flood warnings.<\/p>\n\n\n\n

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24-hour accumulated precipitation for AZ\/NM (left) and Pima County (right) from MRMS<\/figcaption><\/figure>\n\n\n\n

This morning’s GOES-19 visible satellite picture (below, right) shows the storms over Arizona. The HRRR-UAWRF 12Z initialization (below, left) has the clouds in the Tucson and Gila Bend area correctly placed, but has some clouds in Phoenix that aren\u2019t in the satellite imagery.<\/p>\n\n\n\n

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At 250mb, the monsoon ridge is south of the Texas Big Bend. A trough extends from southern Wyoming westward to northern California. Another trough extends from the tropical Pacific northward a few hundred miles west of Los Angeles. Wind speed ranges from 40 knots in Arizona to 80 knots in eastern New Mexico. <\/p>\n\n\n

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At 500mb, the monsoon ridge is near Hermosillo with a west-to-east axis across Mexico. Most of Arizona has temperatures below \u201310\u00b0C, with westerly winds around 25 knots. <\/p>\n\n\n

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At 700mb, winds are light with the center of the ridge between Tucson and Phoenix.  <\/p>\n\n\n

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Currently, there are no weather balloon launches happening in Tucson; it’s a real shame that we don’t have any observations here anymore. They are a critical piece in understanding current conditions, particularly through monsoon season, and enable models and us to make better predictions. Launches have resumed for the monsoon season in Phoenix as of yesterday, likely due to funding provided by SRP; thank you! Below, we compare the forecast initialization to the observed sounding at 5 am this morning. Slightly drier in the observations compared to model initialization today, at the surface and total column precipitable water. Warmer upper levels in the observations eliminate the Convective Available Potential Energy (CAPE) that’s incorrect in the model. Mid-level dry air in the observations matches what we saw in the cloud initialization, where the model has misplaced clouds over Phoenix. <\/p>\n\n\n\n

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HRRR-UA WRF 12Z (left) and observed sounding (right) at Phoenix for 5am this morning.<\/figcaption><\/figure>\n\n\n\n

Today<\/h2>\n\n\n\n

The HRRR-UA WRF 12Z forecast soundings this afternoon for Gila Bend (below left) and Tucson (below right). <\/p>\n\n\n\n

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HRRR-UA WRF 12Z forecast sounding at Gila Bend (left) and Tucson (right) at 3:30 pm.<\/figcaption><\/figure>\n\n\n\n

There is more Convective Available Potential Energy (CAPE) in Gila Bend than in Tucson, >1500 [J\/kg] vs 300 [J\/kg], as supported by the radar and precipitation forecasts below, which show the strongest storms west of the storms we have this morning. The morning clouds shown earlier are inhibiting the surface heating needed for thunderstorm development. Outflows could cross onto I-10 between Tucson and Phoenix and I-8, causing blowing dust around 7 pm.<\/p>\n\n\n\n