ST. LOUIS — Up to 4 inches of rain is expected to drench the St. Louis area through Saturday, threatening to inundate creeks and rivers, and spark localized flooding.
Mark Britt, a meteorologist with the National Weather Service office in Weldon Spring, said Thursday that the area will be under a flash flood watch from 6 a.m. Friday until noon Saturday.
The heaviest rainfall will be from about Friday afternoon into Saturday morning, Britt said.
“It could be anywhere from 2 to 4 inches across the entire area,” he said.
The average precipitation for the entire month of January is 2.4 inches, Britt said. And St. Louis just wrapped up its fifth-soggiest year ever in 2019.
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“So this will be a lot of precipitation,” he said. “If we get 2 to 4 inches, or 3 inches for this event, it will cause a lot of runoff and easily cause localized flooding in neighborhoods. It could cause creeks to come up and rivers to come up.”
Runoff from the heavy rainfall could bring flash flooding on smaller creeks and streams; river flooding would come later in the weekend and into next week, the weather service office said.
The Meramec River at Valley Park, for instance, is expected to see moderate flooding beginning Sunday, with the river cresting at 22 feet.
Britt warns people not to drive into low-water crossings or around barricades blocking flooded roadways. “Even if you’ve driven down the same road all your life, you don’t know if that street or road has been washed out,” he said.
Friday’s high temperature is expected to be about 65 degrees. Temperatures are expected to drop to about 25 degrees from Saturday night into Sunday. The colder air arriving late Friday will bring a potential for a dusting of snow, probably Saturday evening, Britt added.
For updates, go to the National Weather Service website or Facebook page.
'It's not the heat ...' and other St. Louis weather truisms
Just in case you're not from here

To deal with the weather, we've grown accustomed to certain things. Like that bad joke your uncle tells you, these things about St. Louis weather — they're old hat for natives, but might need some explanation for new residents.
Tornado sirens

The outdoor warning siren is used across the country for various reasons. In St. Louis, the distinctive wail signals when it's time to dash to the basement. Or it's just a test, in which case the odd disembodied voice will let you know.
'Starm mode!'

You know the weather will be severe when the TV stations enter "storm mode." With our Midwestern accent, it's better as "starm mode."
A map in the corner of the screen? Scrolling list of counties under the weather warning — or of schools that have canceled classes? That's "starm mode."
#STLwx

Does that cloud look foreboding? Is there hail falling? Make sure to head to Twitter to share, and use St. Louis' favorite hashtag: #stlwx. The wx is an old-school abbreviation for weather. STL is self-explanatory.
It's not the heat, it's the humidity

Sure, it gets hot in St. Louis. But what really makes us wilt is the humidity. We'll complain about the humid climate here to anyone who will listen — until we go to a drier climate and feel like fish out of water.
Tom Evans of St. Louis embraces the high temperatures on Tuesday, June, 14, 2016, in Tower Grove Park. "The heat doesn't bother me. I have a beverage. I come to the park almost everyday to read," said Evans, who says he reads about two books a week. Photo by Laurie Skrivan, lskrivan@post-dispatch.com
Predictions aren't perfect

The weatherman got it wrong! Any time it rains unexpectedly, or snows more/less than predicted, that's the mantra.
Nicole Brown of Hazelwood tries to save her umbrella from strong winds on Tuesday, April 26, 2016, as rain from an afternoon storm began to fall. Photo by Christian Gooden, cgooden@cgooden@post-dispatch.com
Live shots from Tamm Avenue overpass

The frigid TV reporter's gloved hand holds a microphone, and before he or she even says where the live shot is from, you know: the Tamm Avenue overpass. Overlooking I-64 (we all call it 40), the overpass is the place for the "snow is accumulating and traffic is slow" live shot.
Even newspaper photographers head there to take snow pictures. This one is from a storm in February 2014.
French Toast Map

That Weatherbird is so helpful, he'll even show you how much bread, milk and eggs to get from the grocery store. What do you make with those items? French toast, of course.
What would we do without the Weatherbird?
Also look for TV news highlighting empty bread shelves at the local grocery store. Combine this with shots of people carrying gallons of milk, and you're all set.
Salty

How do you show that crews are preparing for winter weather? Stand in front of a massive pile of salt. Look at it — it's huge and will melt anything it touches.
Snow days

Is there snow in the forecast? There will be a snow day for some local school district — even if there's just a dusting. This gives non-natives the chance to grump: "When I was a kid, we walked to school barefoot in 10 feet of snow and never had a snow day."
Isabel Guariglia (left) is pulled up by her sister Martha Guariglia, after they spin down the hill on a saucer sled at Deer Creek Park in Maplewood on Thursday, Jan. 5, 2017. About an inch of snow fell across the area closing some schools, and causing some problems with the morning commute. The women are from Webster Groves. Photo by David Carson, dcarson@post-dispatch.com
It'll change

"Don't like the weather? Just wait five minutes."
The fog starts to lift from the lake in Lone Elk Park on Tuesday, Nov. 3, 2015. Photo by J.B. Forbes, jforbes@post-dispatch.com
Sandbags

Before it floods, we sandbag.
Sometimes it works, sometimes it doesn't. If you're old enough, you have vivid memories of sandbag assembly lines during the 1993 flood.
Image: David Pierce (right), of Union, along with a group of friends and neighbors, put sandbags around the Pacific home of an elderly woman they had just met, on Wednesday, Dec. 30, 2015. Pierce was off from work and decided to come help. Photo by Huy Mach, hmach@post-dispatch.com
It's going to flood

We live near several rivers, and floods are an annual occurrence. Some areas will flood, despite levees and other sandbag walls. How bad the flood is can be measured by which roads are closed. Highway 141 at Interstate 44? Yea, closes frequently because of floodwater. But when water from the Meramec covered both Interstate 44 and Interstate 55 in December 2015, that's how we knew it was a flood.
On a serious note, if a road is covered with water, do not drive through it. Turn around, don't drown.
Image: A Missouri Department of Transportation worker adjusts cones on a flooded section of south bound Route 141 underneath Interstate-44 after a storm flooded the area on Tuesday, April 7, 2015 near Valley Park. Photo by Huy Mach, hmach@post-dispatch.com