# The Southwest's first atmospheric river of the season

> A plume of subtropical moisture is soaking Arizona, Utah and western New Mexico, with 88 weather alerts in force and dew points in Phoenix at summer-monsoon levels; dry, mild weather returns from Monday.

- Publication: Global Systems Lab, Transmission Data brief No. D-2026-01
- Published: 2026-11-01
- Authors: Global Systems Lab
- URL: https://globalsystemslab.com/transmission/southwest-atmospheric-river-november-2026
- Data as of: 1 November 2026, 19:00 UTC (noon in Arizona)
- Topics: Weather, Southwest, Flooding

**Notice.** This is experimental research by Global Systems Lab, provided as is and without warranty. It is not an official forecast, warning or statistic and must not be used for emergency, safety, planning, engineering, financial, legal or other professional decisions. Third-party data may be preliminary, delayed or revised, and their use does not imply endorsement by any agency. Full terms: https://globalsystemslab.com/disclaimer

## Headline numbers

| Measure | Value | Note |
|---|---|---|
| Active weather alerts | 88 | AZ, NM, NV, UT, CO; 72 for flooding |
| Stations reporting rain | 71 of 201 | 34 of 45 in Arizona |
| Phoenix dew point | 66 °F | air temperature 68 °F |
| Most rain forecast | 1.22 in | Flagstaff, next 72 hours |
| Strongest gust | 55 mph | Wolf Creek Pass, Colorado |

![Figure 1. Dew point at every airport weather station across Arizona, New Mexico, Nevada, Utah and Colorado at about 19:00 UTC on 1 November. Darker green means moister air; a dark ring marks stations reporting rain, showers or thunder at the time.](https://globalsystemslab.com/transmission/southwest-atmospheric-river-november-2026/files/fig-moisture-map.png)

The desert Southwest is having a very un-desert day. A long, narrow plume of subtropical moisture,
the kind of feature meteorologists call an **atmospheric river**, has swung north-east out of the
Pacific near Baja California and is pouring rain across Arizona, southern and central Utah, western
New Mexico and south-western Colorado. The National Weather Service office in Phoenix describes it
as the first atmospheric river of the season and one of the strongest to reach the region in the
past decade, measured by how much water vapour it carries. By midday in Arizona, 88 weather alerts
were in force across the five states, 72 of them for flooding.

This brief reads the event through the lab's [NOAA Weather Map](https://globalsystemslab.com/noaa-weather-map/): the latest
report from each of the region's 201 airport weather stations, the Weather Service's forecasts for
seven cities, and the warnings in force. The station readings were taken at about 19:00 UTC, which is
noon in Arizona and 1 pm in New Mexico, Utah and Colorado.

## Where it is raining now

At report time, 71 of the 201 stations were reporting rain, showers or thunder. The wet area
follows the plume's path from south-west to north-east: 34 of Arizona's 45 stations were reporting
rain, along with 13 of 32 in Utah and 15 of 67 in Colorado, mostly on the Western Slope. Nevada,
which sits west of the plume, was largely dry (4 of 22 stations), as was most of New Mexico at
midday (5 of 35), though the heaviest rain there is expected to arrive this afternoon and tonight.
Thunder was being reported at Nogales on the Mexican border, at Nellis Air Force Base near Las
Vegas and on the plains of eastern New Mexico.

The clearest sign of how unusual the air is comes from the dew point, the temperature at which the
air would become saturated. In Phoenix the dew point was **66 °F**, with the air temperature just
68 °F under light rain. Dew points in the mid-60s are typical of the summer monsoon in July and
August, not of November, when the desert air is normally dry. Tucson stood at 65 °F with a dew point
of 62 °F, also under light rain, and much of central and southern Arizona showed dew points in the low
to mid 60s. By contrast, Las Vegas, on the dry western edge of the plume, had a dew point of 49 °F
and wind gusting to 28 mph.

Further north the same moisture was falling as cooler rain. Salt Lake City reported 50 °F and light
rain, Grand Junction 52 °F and rain, and Flagstaff, at 7,000 feet, 48 °F with rain, mist and gusts to
31 mph. Denver, still ahead of the system, was dry at 63 °F with a dew point of just 44 °F.

## What forecasters expect

The Weather Service's discussions, written by its forecasters each morning, lay out the shape of
the event.

- **Arizona.** The Phoenix office expects widespread showers and isolated storms through today, with
  a Flood Watch for much of central and eastern Arizona through tonight. Some storms east of the
  Colorado River could turn severe, mainly with damaging winds. Phoenix could pick up a further half
  to three-quarters of an inch of rain. Tucson reports that the event had already over-delivered by
  this morning, with a quarter of an inch to an inch of rain at most sites in the previous 24 hours
  and 2 to 3 inches on Mount Lemmon and Mount Graham. A Flood Watch covers all of south-east Arizona
  until 5 am on Monday.
- **Utah.** The Salt Lake City office places parts of southern Utah under a Moderate Risk of excessive
  rainfall, level 3 of 4, with a Flood Watch for much of southern and east-central Utah into this
  evening. A cold front near the Nevada border is turning the higher-elevation rain to snow: up to a
  foot above 9,000 feet, 3 to 6 inches down to about 7,000 feet, and locally 18 to 24 inches in the
  upper Cottonwood canyons and the western Uintas.
- **New Mexico.** The Albuquerque office expects the heavier rain to move into western New Mexico
  today and last into Monday morning. Soils are already saturated, so there is a moderate to high
  chance of river flooding in the north and west. Severe thunderstorms are possible across central
  and eastern New Mexico this afternoon and tonight, with hail, damaging winds and a risk of
  tornadoes, and a few inches of snow are expected on the northern mountains above 9,000 feet.

The Weather Service's gridded forecasts give a sense of how much more rain is coming over the next
three days: about 1.2 inches at Flagstaff, 0.9 inches at Salt Lake City, 0.7 inches at Phoenix,
0.4 inches at Tucson and Albuquerque, a tenth of an inch at Denver, and none at Las Vegas.

![Left, forecast rainfall over the next 72 hours for seven Southwest cities. Right, active Weather Service alerts across the five states, with flood-related alerts in orange.](https://globalsystemslab.com/transmission/southwest-atmospheric-river-november-2026/files/fig-rain-alerts.png "Source: NWS gridded forecasts and active alerts, 1 Nov 2026 ~19:00 UTC")

## The warnings in force

Of the 88 active alerts touching the region at midday, 38 were Flood Warnings and 16 Flash Flood
Warnings, among them warnings for Arizona's Maricopa, Pinal, Gila, Yavapai, Coconino, Pima, Santa
Cruz, Cochise and Graham counties. Fourteen Flood Watches and four Flood Advisories cover wider areas,
including San Juan and Catron counties in New Mexico and Mohave County in Arizona. Away from the
rain, the same storm system is bringing wind and snow: three High Wind Warnings for the mountains of
south-central and south-eastern New Mexico, five Wind Advisories, three Winter Storm Warnings for the San Juan Mountains
of Colorado and Nevada's Ruby Mountains, four Winter Weather Advisories for Colorado's high country,
and an avalanche advisory for the West Elk, Sawatch and San Juan ranges. The strongest gust in the
station network at report time was 55 mph at Wolf Creek Pass, Colorado, with gusts of 41 to 44 mph at
Raton and Melrose in New Mexico, Springfield in Colorado and the Grand Canyon airport.

Flash flooding in the desert is dangerous because it is sudden. Dry washes and dips in roads can
fill with fast-moving water within minutes, often from rain that fell miles away. The Weather
Service's standing advice applies: do not drive into flooded roads, and stay out of normally dry
washes until the water has gone.

## The week ahead

The rain should be short-lived. Forecasters in Phoenix and Tucson expect the moisture to clear by
daybreak on Monday, followed by a dry week with temperatures slowly warming, though staying slightly
below normal for early November. Phoenix's forecast highs climb from 71 °F today to 77 °F by Saturday,
and Tucson's to 78 °F by midweek. Las Vegas stays dry and mild, rising from 69 °F to 74 °F.

Behind the storm, the higher country turns cold. Albuquerque drops from 69 °F today to a high of
60 °F on Monday and a low of 32 °F on Monday night, the first freezing night in the forecast.
Flagstaff's nights stay near 30 °F all week. Utah and Colorado are less settled: Salt Lake City has
another round of light rain likely from Tuesday night into Wednesday, and Denver, which misses most
of today's rain, has its best chance on Monday and again on Wednesday.

![Forecast daytime highs for seven Southwest cities over the coming week. The desert cities warm steadily after the storm; the high country stays cool.](https://globalsystemslab.com/transmission/southwest-atmospheric-river-november-2026/files/fig-week.png "Source: NWS point forecasts issued 1 Nov 2026")

## Reading the data

Station reports are point measurements at airports, and conditions can differ sharply over a few
miles, especially in mountains and during thunderstorms. A station counted as "reporting rain" had
rain, showers, drizzle or thunder in its latest report, not necessarily heavy rain. The forecasts and
rainfall totals are those the Weather Service issued around midday on 1 November and will change as
the event unfolds; the alert count is a snapshot, and alerts are issued and expire throughout the
day. For the latest picture, open the [NOAA Weather Map](https://globalsystemslab.com/noaa-weather-map/), choose a state or the
whole country, and switch the map to dew point to watch the moisture move east.

## Sources

- Airport weather station reports (METAR), NOAA Aviation Weather Center: https://aviationweather.gov/data/api/
- National Weather Service forecasts and active alerts (api.weather.gov): https://www.weather.gov/documentation/services-web-api
- NWS area forecast discussions: Phoenix, Tucson, Albuquerque and Salt Lake City offices, 1 November 2026: https://forecast.weather.gov/product.php?site=PSR&issuedby=PSR&product=AFD

## Data

- Station readings at 19:00 UTC, 201 stations (CSV): https://globalsystemslab.com/transmission/southwest-atmospheric-river-november-2026/files/southwest-stations-2026-11-01.csv
- City forecasts, rainfall totals and alert counts (JSON): https://globalsystemslab.com/transmission/southwest-atmospheric-river-november-2026/files/forecast.json

## How to cite

Global Systems Lab (2026). The Southwest's first atmospheric river of the season. Global Systems Lab Transmission D-2026-01. https://globalsystemslab.com/transmission/southwest-atmospheric-river-november-2026