Wednesday, March 1, 2017

Winter 2016-2017 Recap: The Winter that Mostly Wasn't

We put the wraps on climatological winter (December-February) yesterday, although winter weather is not out of the question in many parts of the country over the next two to four weeks. Climatological winter was capped off by very springlike weather, including a severe weather outbreak in the central U.S.

We can take a quick look at what winter has been like across the country using the latest map of the Accumulated Winter Season Severity Index. Most of the country has experienced a mild winter, with the only notable exception the northwestern U.S. and far northern New England. Omaha, NE and Des Moines, IA are on track for record mild winters. Note that the AWSSI continues to be accumulated until the last day with a maximum temperature of 32°F, the last day with measurable snow, or the last day with measurable snow on the ground. The factors that are keeping other locations from having record mild winters are snow early in the season and several periods of cold weather in December and January.

The Accumulated Winter Severity Index as of March 1, 2017.
The maps of the average temperature departure from normal for December through January depict very much the same pattern. Average temperatures for the period were above normal from the Plains to the east coast. Colder than normal temperatures occurred in the northwestern quarter of the country.

The map of maximum temperature departures mimics the mean temperature map, but the map of minimum temperature departures shows a larger area of warmer than normal temperatures, particularly in the southwestern U.S.

On a monthly basis it's clear that February was a huge contributor to the warmer than normal winter. Final numbers aren't all in yet, but many locations in the central and eastern U.S. will find that this February will be the warmest on record.

Click on map to see larger version

The precipitation map does not contain too many surprises. Precipitation in most of the western U.S. was much above normal. It was a much drier than normal winter in a bulls-eye in the central U.S. extending from northern Arkansas through Missouri and Illinois. It was also dry in the mid-Atlantic and Florida.

Snowfall during climatological winter was well above normal from the northern Plains to the Sierras, and near to above normal in much of New England. Snow season (July 1- June 30) is not yet over and many locations could yet see some substantial snowfall in the spring. There definitely has been a snow drought in much of the central U.S. Chicago did not have any snow cover in January or February for the first time in the 146 years.

CoCoRaHS observations were included in both the precipitation and snowfall maps.

Ice cover on the Great Lakes is only 10 percent of what it usually is on this date. The average coverage on March 1 is about 43 percent, and as of today it was 4.5 percent.

Ice cover on the Great Lakes as of 2/28/2017

The warm weather in February, especially the last ten days of the month, is particularly problematic for vegetation this spring. The warm weather coaxed trees and bushes to bud and plants to emerge from the soil much earlier than normal. The U.S. National Phenology Network data shows that "spring" is almost three weeks ahead of schedule as far north as the Ohio Valley. The risk of freezing weather is pretty much a sure thing for the next several weeks, and the possibility of damage to emerged vegetation is rather high.

Finally, the severe weather season got off to an early start in the Midwest yesterday with an outbreak of severe weather across the Midwest. Several strong tornadoes caused significant damage and several fatalities in Illinois, Missouri, and Indiana. The severe threat moved east today with severe weather from new York south through Alabama.

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