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Tuesday, May 3, 2016

It's so dry, fall weather records may be set

Monday, November 28, 2011

(Graph Phillip Schumacher, NWS) Nearly 2 inches of rain in October kept Le Mars from having the driest fall on record. Sioux City is forecast to set a record for the driest fall since the 1800s. The dry conditions this fall are due to La Niņa, which is forecast to continue.
Without rain or snow in the next few days, the lack of precipitation will set records for dry conditions in parts of northwest Iowa.

Since Aug. 1, Le Mars has received 4.88 inches of rain, according to Phillip Schumacher, National Weather Service (NWS), Sioux Falls, science and operations officer.

That's the 14th driest year in NWS records.

(ISU Extension) Lack of late summer and fall moisture have failed to recharge the soil "water bank" at 15 sites in northwest and west central Iowa, according to Iowa State University (ISU) Extension field agronomist Joel DeJong, of Le Mars.
"If you look at just Sept. 1 and on, Le Mars has had 2.62 inches of rain, which would be the 12th driest on record," Schumacher said.

August precipitation in Le Mars was 2.26 inches followed by 0.86 inches in September, 1.70 inches in October and 0.06 inches in November, based on NWS records.

The record for dry fall weather between Sept. 1 and the end of November was set in 1952.

October precipitation of 1.70 inches in Le Mars separates the city from its neighbor to the south by more than an inch, according to NWS records.

Without moisture by Wednesday, Sioux City's .59 of an inch between August and November will set a record for the driest fall since the 1800s, Schumacher said.

"Sioux City had .31 of an inch of rain in September, in October .23 of an inch and in November .05 of an inch," he said.

Sioux Falls, S.D., and Marshall, Minn., are also expected to set records for dry conditions this fall.

"It's been pretty dry east of Interstate 29," Schumacher said.

Drier than normal conditions are also confirmed by Joel DeJong, Iowa State University (ISU) Extension field agronomist who analyzed results of soil moisture samples at 15 sites in northwest and west central Iowa this fall.

The range was from 0.0 inches to 6.8 inches of moisture available for plant growth in the top 5 feet of soil as of Nov. 1, DeJong reported.

The long-term averages from 1954-1972 range between 4.3 inches and 5.9 inches of moisture.

In his Extension Crop update for November, DeJong indicated lack of late summer and fall moisture have failed to recharge the soil "water bank," which can hold about 11 inches of water in the soil.

Good spring precipitation is needed to bring water levels in soil back up to where timely summer rains are not as critical, he stated.

The dry weather is due to a weather pattern, La Niņa, Schumacher explained.

Usually that means it's relatively cool and wet near the Canadian border and relatively warm and dry over the southern U.S., Schumacher said.

Because Le Mars and other parts of northern Iowa are in a geographic transition area between the Canadian border and southern U.S., Schumacher said the outlook now is a little cooler and wetter than normal.

"But since we're right on that edge for winter, if things just shift a little bit farther north, it could be a relatively dry, mild winter for northwest Iowa," he added.

Heading into spring, information from the Climate Prediction Center indicates a little bit better chance for dry, warmer weather in March, April and May, he said.

"If the cool, wet weather from Canada shifts a little farther south, moisture from the Gulf of Mexico could bring northwest Iowa wetter weather, Schumacher said. "Until that happens, we're going to stay in this relatively dry pattern."

Lack of moisture in the air is also the main reason for fewer fall mornings with slick bridges and frost-covered windshields, the NWS science and operations officer said.

"Generally on our colder nights this fall, it's been relatively dry and so you're getting very little frost formation because the dew points are essentially so low, there's no moisture coming out of the air to form frost on the grass, roof and other surfaces," Schumacher said.

Temperatures were below freezing from Nov. 7-17, but since there hasn't been much precipitation, there wasn't a lot of moisture in the air for frost, he added.

Even if the month of December is dry those who are hoping for a white Christmas shouldn't be concerned.

Based on historical weather records, a little more than 50 percent of the time, there's at least an inch of snow on the ground on Dec. 25, according to the NWS official.

"What you really hope for is that it snows somewhere after Dec. 10 or so," Schumacher said. "It's pretty hard to get rid of that snow if you get a couple of inches, because it's usually too cold -- so that's what people want to hope for."

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