Later sunsets, longer daylight and freezing lakes

A strange thing happened this week.

As Minnesota hid under a sea of gray clouds for eight straight days, the sun started setting later this week. Ever so slightly. Almost imperceptibly. Stealthily.

The calendar tells the tale. As of Friday sunset in Minneapolis clicked ahead to 4:33 p.m. from 4:32 p.m.

The later sunsets in the evening start happening the week before Monday's December solstice thanks a quirk in earth's elliptical orbit and tilted axis. Overall daylight begins increasing after the winter solstice Monday.

Earthsky has a good explainer on the miracle of increasing evening daylight before the winter solstice.

The winter solstice is the shortest day. It offers the shortest period of daylight. But the earliest sunsets aren’t on the solstice itself. Instead, they come a couple of weeks before the winter solstice. If you reside in the temperate regions of the Northern Hemisphere, your earliest sunsets are in early to mid-December.

Southern Hemisphere? Click here.

Why isn’t the earliest sunset on the year’s shortest day? You have to think about it in terms of solar noon or midday, the time midway between sunrise and sunset, when the sun reaches its highest point for the day.

A clock ticks off exactly 24 hours from one noon to the next. But the actual days – as measured by the spin of the Earth – are rarely exactly 24 hours long.

So the exact time of solar noon, as measured by Earth’s spin, shifts in a seasonal way. If you measured Earth’s spin from one solar noon to the next, you’d find that – around the time of the December solstice – the time period between consecutive solar noons is actually half a minute longer than 24 hours.

So – two weeks before the solstice, for example – the sun reaches its noontime position at 11:52 a.m. local standard time. Two weeks later – on the winter solstice – the sun reaches its noontime position at 11:59 a.m. That’s 7 minutes later.

The later clock time for solar noon also means a later clock time for sunrise and sunset. The result: earlier sunsets before the winter solstice and increasingly later sunrises for a few weeks after the winter solstice.

The exact date of earliest sunset varies with latitude. But the sequence is always the same. For the Northern Hemisphere, earliest sunset in early December, winter solstice, latest sunrise in early January.

Instant winter

You could feel the bite as the season's coldest air mass invaded. Temperatures bottom out around zero up north and in the single digits in the Twin Cities this weekend. The trade off? Long overdue crisp, bright sunshine.

For the first time this season, temperatures plunge into the single digits near the metro and hover below zero up north.

Freezing lakes this weekend

As winds die and the air goes calm early Saturday, some metro lakes like Harriet, Calhoun and Nokomis may finally be sporting a fresh sheet of (thin) ice as the sun pokes up. Many metro lakes are pushing the envelope date for latest ice in on record.

Lake Minnetonka is a much bigger body of water, but I expect we'll also see an increase in ice coverage on the bigger lakes this weekend.

Snow free Landscape

In the metro, most areas are still snow free. That's pretty rare for mid to late December.

More on the relative rarity of snow free landscape this time of year from the Minnesota Climate Working Group.

How unusual is all this bare ground in the Twin Cities?

Exceptionally warm conditions this December have kept much of Minnesota free of snow cover. Both of the snowfalls to date that were greater than one inch at Minneapolis-St. Paul International Airport (MSP) have melted, leaving grounds bare. 

Just how unusual is to have no snowpack this far into December?

As the accompanying image suggests, about 60-65% of MSP winters since 1900 have at least one inch of snow cover by December 17th, and approximately 50% have two inches or more by this time of year. Relatively deep snow in mid-December is still somewhat unusual, with six inches or more occuring less than 25% of of the time.

Although bare ground is not unheard of in mid-December, as we move deeper into winter, the historical probabilities of it go way down. MSP reaches its average peak snow depth in early February, when we see at least one inch of snow cover nearly 90% of the time.

Warmer Sunday

The recovery begins Sunday as milder southerly breezes return on the back side of departing high pressure. Sunday's warm front-cold front combo brings a few rain and snow showers.

Christmas week forecast: Model opinions vary

The Euro and NOAA's GFS are at odds over temperatures and snowfall chances next week. The GFS is colder with chances for a light coating of snow late next week. The Euro is milder and drier. Here's the side by side comparison:

In the longer range, both models hint at a stronger storm just after Christmas. It could be rain and or snow once again. The GFS hints at colder weather by New Year's.

NOAA's Climate Prediction center still favors a mild temperature bias overall into mid-January.

Stay tuned.

Minnesota weather observers honored

The good thing about being a weather-obsessed state? A wealth of dedicated weather observers feeding important data into the NWS.

Here's news on a much deserved award from the Twin Cities NWS:

National Weather Service Cooperative Weather Observers, Richard and Marlys Hjort, were honored with the U.S. Department of Commerce Thomas Jefferson Award at a ceremony at their home in Chisago City, Minnesota.  Only five Cooperative Weather Observers from across the country are selected for this prestegious award each year, out of a network of 12,000 observers.  

The award is for "unusual and outstanding accomplishment in the field of meteorological observations in the tradition of Thomas Jefferson, pioneer weather observer and third President of the United States." The award is signed by the Secretary of the U.S. Department of Commerce, the Director of the National Oceanic and Atmospheric Administration, and the Director of the National Weather Service.  

Richard and Marlys Hjort are only the third Minnesotans in history to be chosen for this award. Governor Mark Dayton, U.S. Senator Amy Klobuchar, and State Climatologist Greg Spoden congratulated the Hjorts with letters of appreciation for their volunteer service to the state.     

The National Weather Service office in the Twin Cities nominated Richard and Marlys for the Thomas Jefferson Award because of their exceptional dedication to taking daily weather measurements for the National Weather Service during the past 30 years, as well as for the state of Minnesota for the past 45 years.  

They are also recognized for going above and beyond the call of duty to participate in several additional projects that monitor the environment and native species in Minnesota.  These projects include an acid rain study with the Minnesota Pollution Control Agency and the National Audubon Society, monitoring flora and fauna for the USA National Phenology Network, and participating in a project to test a variety of plants to support the monarch butterfly population.  

Richard and Marlys are also award winning members of the North American Bluebird Society, Audubon Chapter of Minneapolis, and Minnesota Bluebird Recovery Program.  They have authored articles for the Minnesota conservation journal The Loon and Minnesota Conservation Volunteer. They also write a weekly "field notes" column for the Chisago County Press newspaper.  In addition, the Minnesota Department of National Resources recognized the Hjorts on a state poster for their innovative design for purple martin houses.  

Richard and Marlys Hjort truly share Thomas Jefferson's passion for public service and love of the natural world.  We are honored to have Richard and Marlys as a part of the National Weather Service family, and we are grateful to have this opportunity to thank them for their exceptional service to our state and nation.  

Weather Holiday gifts

Still looking for that last minute holiday gift for the weather-obsessed? Some of my favorites. (MPR or I have no financial ties to these providers, just some of my recommendations.)

• Weather gear from La Crosse Technology

• Weather gifts from Wind & Weather

• Minnesota Weatherguide calendars