Oddly chilly spring: Snow, cold dip far south in May

An upper-level low that has been circulating rain bands over us the past couple of days is the remnant of a jaw-dropping historic weather event in the states west of us.

Spring 2013 has firmly established itself as one that will be remembered for extreme late-season cold and snow in much of the central and eastern United States. May 3 to 5 through the Plains states and Mississippi River Valley perhaps exemplified this to the greatest level.

A few interesting facts:

• Arkansas had never experienced snowflakes in May dating deep into the 1800s. That changed on Friday, when several counties in northwest Arkansas not only had snowfall, but as much as 5 inches of it. The new state record for latest snowfall on record, May 3, lasted one day, as more snow fell early on Saturday, May 4.

• Minnesota, Wisconsin and Iowa do sometimes see snow in May. But each of those states likely received their greatest single snowfalls on record for the month, with 18 inches at Blooming Prairie, Minn., 17.7 inches at Stockholm, Wis ., and 11 inches at Britt, Iowa.

• Rochester, Minn., got 14 inches of snow in last week’s storm. Not only was that a May record, but it was triple the total amount of snow Rochester has gotten in every previous May combined dating to 1886.

• Tulsa, Okla., saw its latest snow on record, the first ever past April 18. For perspective, Tulsa is about 70 miles south of Roanoke’s latitude, and 200 feet lower in elevation than the bank of the Roanoke River.

• In the first five days of May, 53 locations recorded their lowest temperatures ever seen in the month of May. Those locations were clustered mostly in the south-central U.S., including Dallas (38 degrees) and Houston (42) in Texas, Little Rock, Ark. (38), and Jackson, Miss. (36). But they also included Cheyenne, Wyo., (9) and Deadhorse, Alaska ( minus-24).

The short-term cause of the May wintry weirdness was the development of a “cut-off’” low pressure system. Cold air diving south from Canada became trapped in a bubble deep to the south, with upper-level winds rotating around the system with such velocity that it became entirely separated from the jet stream.

The cut-off low has since wobbled eastward to just west of our region. It’s not as cold as it was, but has been spinning moisture through in several waves.

Widening out the view to the entire season, the May cold and snow in the central U.S. was a continuation of the pattern of blocking high pressure that we’ve seen most of spring.

High pressure in the northern latitudes has been pushing cold air farther south, away from the north pole, and forcing the jet stream to remain unusually far south for so late in the season.

We may not be done dealing with unusual cold yet. There are indications that a particularly cold shot of air, possibly enough for frost or freeze issues, may arrive in our region early next week, after a few warmer days to end this week.

It will warm up and stay that way sooner or later — obviously more toward later in this oddly chilly spring season.

Weather Journal runs on Wednesdays.

Weather Journal

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