A storm bearing down on the Great Plains this week may or may not qualify as another “bomb cyclone.” But it will certainly be big.

The unusually powerful storm is expected to dump significant snow and rain on farms and floodplains that are struggling to recover from a historic storm three weeks ago that pummeled the Midwest and left wide areas swallowed by rising rivers.

The coming storm will hit with force on Wednesday: Rain first, and then thunderstorms that will turn into heavy snow and squalls. Some forecasters believe this system could drop even more snow on the region than the one in mid-March did, as it moves slowly through the region. Parts of South Dakota, northeastern Nebraska and southern Minnesota could be whipped with wind gusts of up to 50 miles an hour and may get a foot of snow — or maybe as much as two feet.

But there are reasons to hope that this round of foul weather will not be as devastating as the last. The air has been warmer — temperatures reached the high 70s in Omaha, Neb., on Monday — and the ground has thawed in many areas, so the soil, though still somewhat saturated, will be able to soak up more rain. And the storm’s overall intensity will probably not be as great.

In other words, this storm may in places appear to be a worse and more blinding blizzard, but forecasters hope that its effects will be less severe.

Of course, they caution that there is no way to predict flooding with certainty. And the forecasters point to a paradox this time around: The more snow, the better.

If most of the storm’s total precipitation falls as rain, the chances are greater that rapid runoff will swell rivers and streams dangerously — setting back efforts to repair dozens of levees that were overwhelmed last month.

But if the storm delivers more snow than rain, the runoff could take days longer. The snow would melt gradually as temperatures rise above freezing during the day and then dip back down at night.

“Snowfall will delay the amount of water coming in, and that could be a real benefit,” said David Pearson, a hydrologist with the National Weather Service in Omaha. “The snow just takes the edge off.”

“The amount the ground can soak up is limited, because it is so wet, but that’s a lot better than having it frozen, because frozen ground is like a parking lot,” Mr. Pearson added. “Water just flows right off.”

Over all, he said, the storm does not seem as powerful at this point as the March tempest, “but it still has a lot of moisture and lot of potential to cause a lot of problems,” he said. “It’s still going to pack a punch.”

Forecasters say that for a storm to officially qualify as a bomb cyclone, the atmospheric pressure must drop at least 24 millibars in 24 hours, creating a particularly strong and rapidly intensifying storm. This one might not produce quite that steep a pressure drop, they say.

But temperatures are set to plunge quickly just the same, as a low-pressure system drawing in moisture to the Midwest is displaced by a high-pressure system full of colder air. Omaha, for example, is predicted to see its daytime high temperature fall from almost 80 degrees on Monday to about 40 degrees on Friday.

The bigger flood risk this time may center on the Mississippi River and its swollen tributaries rather than the Missouri River, where levels have been receding, said Jeff Berardelli, a meteorologist.

“It will be a more prolific snow producer and a more blinding blizzard than the bomb cyclone was,” Mr. Berardelli said of the new storm, partly because it may idle over much of the Midwest for a time.

“It’s likely going to slow down and stall,” he said. “Literally, the storm will barely move.”

But like Mr. Pearson, Mr. Berardelli said that a higher proportion of snow than rain may be a good thing.

“If it melts over a longer period of time, that would be better,” he said. “We don’t want it all happening in a day or two.”

Source: Read Full Article