With more rain — and even some snow — in the weekend forecast, Boulder County was placed under a flood warning Friday night, with rock slides, standing water, minor flooding and widespread power outages reported.

Local police and sheriff’s dispatchers spent the evening responding to calls of flooded alleyways, overflowing culverts and soaked basement floors affecting residents in all pockets of the county, and particularly those in west Boulder and the foothills.

The flood warning, announced by the National Weather Service, is in effect until 9:15 a.m. Saturday for Boulder County, as well as southeastern Larimer County, southwestern Weld County and central Broomfield County.

A less-serious flood advisory in place until 11 p.m. Sunday.

As the Boulder Office of Emergency Management notes on its Facebook page, the flood warning placed in effect Friday night applies to areal flooding, as opposed to flash flooding.

Areal flooding, the OEM writes, “is in a large area and occurs when the ground is saturated and can no longer hold the rainfall. It’s slow developing and will most heavily impact low-lying areas, shallow or narrow creeks and tributaries, and known problem areas.”

Shortly after 9 p.m. Friday, with rain having pounded much of the county for the previous 12 hours, NWS reported that up to 2 inches of rain had fallen over areas already saturated by a rainy April and beginning of May. Another 1.5 inches were expected to fall by Saturday morning.

Meanwhile, stretches of the Boulder and St. Vrain creeks were reported overflowing, with the St. Vrain experiencing several minor rock slides.

In Lyons, where full recovery from the 2013 flood is still years in the offing, several businesses south of Bohn Park reported flooding.

And, as of 10 p.m. Friday, nearly 400 customers in Boulder, Jamestown and parts of Longmont and Niwot were without power after nearly 5,000 suffered outages initially. Xcel spokesman Mark Stutz said the outage’s cause wasn’t clear.

As the rain fell, meteorologists maintained that, for the second Mother’s Day in a row, Boulder County will likely see some snow, a capping insult on what has been a persistently soggy start to the month.

“I think we’ll see some flakes,” said Nezette Rydell, meteorologist in charge at the National Weather Service in Boulder. “I don’t know how much accumulation we’ll have, if it will be 1 or 2 or 3 inches. But I think flakes are a good bet. We’re going to be right on the rain-snow line.”

And whatever happens in the way of snow Sunday, it will feel more like winter than spring on Sunday night as temperatures fall below freezing with a forecast low of 28 degrees.

“If you’ve got a tomato plant, if you jump the gun, you can probably save it if you cover it up,” Rydell said.

Boulder recorded 1.7 inches of snow last Mother’s Day, which fell in 2014 on May 11. A transient, later identified as Kathryn Fishman, 59, died while sleeping outside at Scott Carpenter Park as that storm descended.

Boulder’s snow record for May 10, the day that moms’ holiday will be observed this year, is 5.2 inches, set in 2003.

As of 7 a.m. Friday, Boulder had seen 1.64 inches of precipitation for May, all of it coming as rain. As of 3 p.m. Friday, Longmont had seen 1.78 inches of rain.

On his weather blog, meteorologist Matt Kelsch said that into Sunday morning, “Snow totals of 1 to 6 inches should be expected from 6,000 to 8,000 feet, with 6 to 12 inches above 8,000, and maybe some local areas of 2 feet in the mountains of Larimer and northern Boulder County. I cannot yet rule out some accumulation in the Denver-Boulder-Fort Collins corridor.”

The Colorado Department of Transportation said Friday that it has crews patrolling roadways vulnerable to flooding, as well as those that were impacted by the September 2013 floods.

Should it be necessary to protect the traveling public, CDOT said it will close roadways or bridges.

Motorists can check on cotrip.org to assess roadway conditions before they travel this weekend.

Low-impact flooding reported across area

As was the case for the historic floods of September 2013, the Front Range’s week-long rainy stretch has been fueled by moisture coming from both the Pacific Ocean and the Gulf of Mexico, although that’s where any similarities end between then and now.

The showers “are not really on steroids now, as they were then,” Rydell said.

But across the region, the rain that has persisted much of the week, dropping up to 3 inches in some Front Range locations, has taken its toll — with up to another 1 to 2 inches of additional rain on tap through the weekend.

In Frederick on Friday morning, a public works crew shut down a stretch of Bella Rosa Parkway just west of Colorado Boulevard after water began topping the street.

Public Works Director Rory Hale said a crew arrived at 9 a.m. and began pumping water at about 10 a.m. to protect a transformer that powers two nearby subdivisions. He expected the pumps to continue running all day.

Frederick police Chief Gary Barbour said water has run over Bella Rosa Parkway twice during recent rains and caused some washing away of the shoulder.

Firestone Police Chief David Montgomery said his department has emergency staff available and ready to activate if necessary like it did during flooding in 2013.

“At the moment, we are monitoring all conditions of the weather and operating under normal conditions,” he said.

Mountain View Fire Rescue reported that Weld County Road Five was closed between Weld County Roads 34 and 36 ½ because of overflowing at Highland Lake.

Several trails and underpasses in Longmont also remained closed because of high waters. City officials reminded residents that flood preparedness information could be accessed at the city website.

Boulder public works spokesman Mike Banuelos said Friday that Boulder Creek Path underpasses were closed by minor flooding at 13th Street and Arapahoe Avenue and also at the 17th Street underpass.

Path users were also urged to use caution between Foothills Parkway and 55th Street due to standing water in some areas.

As for the Boulder Creek itself, its flow at Broadway at midday Friday was measured at 370 cubic feet per second.

“That’s a little bit higher than normal, but it’s actually lower than what the creek usually peaks at during spring runoff,” Banuelos said.

‘The ground is at full saturation’

Meanwhile, Boulder County spokeswoman Barb Halpin said the Boulder Office of Emergency Management has been monitoring the weather and will continue to do so throughout the weekend.

Both Boulder Creek and St. Vrain creek are running at or below the flow levels typical for low-level flooding, but Halpin said that could change and that the public should be alert for updates.

“The spots that we’re concerned about are the ones that are already showing some real minor small rock movement — and I mean very small rocks,” Halpin said. “There has been some rock movement up above Jamestown and some west of Lyons.

“We’re not looking at a widespread flooding situation like 20 months ago,” she added. “But depending on what the storm systems do, if one sits up and parks itself somewhere, that’s our biggest concern because the ground is at full saturation.”

Kevin Stewart, flood warning program manager at the Urban Drainage and Flood Control District — which works with seven metro-area counties, including much of Boulder County — said Friday, “I’m not hearing of any dire concerns” relating to flooding.

“The kind of flooding from storms today is going to be low-impact — streets, low-lying areas, not any major flooding,” Stewart said Friday.

Also, the Boulder City Manager’s Office announced Friday that Barker Dam just east of Nederland is expected soon to fill and spill over its spillway, as it is designed to do each spring before peak seasonal stream flows occur at lower elevations.

“It usually trends a little more to the end of May, but given the wet last few weeks we’ve had, it’s not surprising” that it would occur now, Banuelos said.

The next work week appears to offer a chance to dry out, with temperatures Monday forecast for a high of 55 under partly sunny skies.

Staff writers John Bear and John Fryar contributed to this report

Charlie Brennan: 303-473-1327, brennanc@dailycamera.com or twitter.com/chasbrennan