Priscilla and Raymond are expected to bring significant rainfall to the Southwest over the weekend and into early next week.
The Big Picture
These two storms will bring two bursts of moisture to parts of the Southwest through early next week. Each burst will bring a threat of flooding from southern Arizona to the Four Corners.
Rainfall in this area could be devastating, as several months’ worth of rainfall is expected for areas not used to seeing this much rainfall this quickly.
Between the two storms, 2-4 inches of rain is possible in some spots, with localized areas seeing up to 6 inches.
Rainfall Forecast
Timing The Rainfall And Flood Threat
Through Saturday: Firstly, Prescilla’s moisture will enhance a major flood threat for the Southwest.
Moisture from Priscilla is ongoing in the Southwest today, where flood watches are already in effect in cities including Phoenix and Flagstaff, Arizona; Grand Junction, Colorado; and Cedar City, Utah.
Phoenix’s average rainfall for the month of October is about 0.56 inches. They saw about 0.25 inches of rainfall yesterday and could see 1-3 inches of rainfall through Sunday evening, which would be several months of rainfall in a couple of days.
Jacks Canyon, located east-southeast of Flagstaff, Arizona, saw a more than 5-foot rise in water levels late Friday morning due to around one inch of rain.
Current Radar
NOAA’s Weather Prediction Center has a slight risk for excessive rainfall, or a level 2 of 4 for much of the Four Corners Region.
NOAA’s Weather Prediction Center noted that these impacts could be similar to those of the remnants of Hurricane Rosa in 2018, when extensive flash flood impacts were experienced across Central Arizona.
Priscilla’s threat will begin to diminish by late Saturday.
Sunday – Tuesday: The second burst of moisture will arrive from Raymond’s remnants right on the heels of Priscilla.
Raymond will take a track just to the east of Priscilla’s, and it could also bring another round of rainfall to the Southwest early next week.
While the heaviest rainfall is expected to be slightly further east than Priscilla’s rainfall, should any additional rain fall, it will not take much to cause additional flooding.
NOAA suggests the flood threat will remain a 2-out-of-4 risk, but that the threat will remain elevated at this level through early Tuesday in parts of the Southwest.
Rainfall Could Be Helpful
The Southwest is actually in drought and could use the rain, but rainfall of this amount in such a short period of time is not as helpful for relieving drought as people would think because most rainfall can’t be absorbed by the soil.
Phoenix is over an inch below average for this time of year.
Why Pacific Hurricanes Matter In The Southwest
When the region is called the Desert Southwest, it is no surprise that rainfall is scarce.
Phoenix, for example, has a yearly average rainfall of 7.22 inches, with no monthly average even reaching 1 inch.
But states like California and Arizona do experience bursts of moisture from the tropics several times during a year.
They can often bring several inches of rainfall. That may not seem like a lot to someone in the Southeast, but to the Southwest, this is a big deal.
Desert soil isn’t able to hold moisture as well as other regions, so it doesn’t take much rainfall before runoff and flooding begin. Dangerous land and rock slides are often not far behind.
And recent burn scars are even more susceptible to these dangerous debris flows and landslides.
Rob Shackelford is a meteorologist and climate scientist at weather.com. He received his undergraduate and master’s degrees from the University of Georgia studying meteorology and experimenting with alternative hurricane forecasting tools.