Monsoonal moisture over the Southwest will lessen somewhat early this week, but downpours will persist for some, leading to more flash flooding.
Moisture has been streaming northward into the southwestern quadrant of the U.S. over the last few days, leading to widespread drenching thunderstorms each afternoon and evening.
The moisture was streaming around a strong area of high pressure which was centered over the eastern Rockies and High Plains.
This high pressure system will continue to weaken and shift eastward as a large dip in the jet stream develops over the West Coast.
As the jet stream dives southward it will send that monsoonal moisture eastward, effectively drying out parts of the Southwest.
Still, enough moisture will persist through much of the upcoming week to produce more downpours and instances of flash flooding for some.
Heavy rains occurred on Saturday over southern Yavapai County, Ariz. where forest fires had left large burn scars. 2-4 inches of rain over this region in a short time lead to debris flows and mudslides as well as flooding of Turkey Creek and the Agua Fria.
A local bridge was washed out on the Havasu Creek at Supai, Ariz. as well.
More instances of flash flooding will occur through the first half of this week a bit farther east over the Colorado Rockies, eastern Arizona, and much of New Mexico while areas farther west dry out.
Daily bouts of drenching afternoon and evening thunderstorms will be common from Denver and Boulder, Colo. through Albuquerque, N.M. and Nogales, Ariz.
Thunderstorms across this region can produce rainfall rates of 1-2 inches per hour which is more than high enough to get flash flooding to occur. Especially since moisture values have been elevated for quite a while now.
Along with the heavy rainfall, dangerous cloud to ground lightning will threaten to postpone or delay any outdoor activities.
If flash flooding is occurring or imminent, take the proper precautions if you need to to travel. Never drive through a flooded roadway because you never know how deep the water might be.
Always carry an emergency kit in your vehicle in case you become stranded.
Heed all flash flood watches and warnings and keep an eye on the AccuWeather.com Severe Weather Center.
Matthew has become a hurricane in the Caribbean and may approach the U.S. during next week.
It will feel like an extended winter for those living from the northern Plains to the eastern U.S., as cold and snowy conditions last longer than normal.
Persistent downpours will raise the flood risk in part of the mid-Atlantic into Friday night, while rain will spread over the balance of the northeastern United States into the weekend.
Millions of people across the U.S. could be exposed to drinking water contaminated with chemicals from firefighting foam, according to a recent study.
The final day of September will bring a rare lunar event that hasn’t occurred since March of 2014, a Black Moon.
The holiday weekend will start on an unsettled note, but the weather should improve by Day of German Unity celebrations on Monday.
San Diego, CA (1970)
Strong Santa Ana winds create fire disaster in interior parts of county (September 25 to 30); 500,000 acres burned.
Lander, NY (1982)
15.4 inches of of snow (29th-30th). Total of 32.9 inches for month (Sept. record).
Record dry September: Pittsburgh, PA - Only 0.28" this month; driest September on record (old record 0.57 inches in 1893) Greensboro, NC - Driest month ever (only a trace of rain) Columbia, SC - Only 0.07" of rain.