Winter Finally Arrives: Snow resumes Saturday night; 3″ to 7″ metro range; heaviest north

Season’s 1st “signifcant” winter storm for metro Minnesota Saturday night & Sunday

3″ to 7″ likely snowfall range in the metro by Sunday evening

Heaviest totals favoring north & northeast metro

(Models favor 3″ to 5″ at MSP Airport – more like 5″ to 7″ north metro)

6″ to 10″ likely along I-35 north of metro to Duluth by Sunday night

Winter Storm Warning includes most of Minnesota from Morris to the metro into northern Minnesota

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-Twin Cities NWS multimedia briefing here

Much colder air follows the system – near 0F by Monday AM?

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Heaviest snowfall totals north of the metro – wintery travel condtions pretty much statewide

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Image: Twin Cities NWS

Several 1″+ snowfall totals with Friday’s “appetizer” round

MPX: 1 WNW Prior Lake [Scott Co, MN] trained spotter reports SNOW of M1.1 INCH at 10:00 PM CST —

MPX: Lakeville [Dakota Co, MN] trained spotter reports SNOW of M1.2 INCH at 09:30 PM CST —

MPX: Shakopee [Scott Co, MN] trained spotter reports SNOW of M1.3 INCH at 01:00 AM CST —

MPX: 1 W NEW Prague [Scott Co, MN] trained spotter reports SNOW of M1.4 INCH at 12:05 AM CST —

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Image: Caltech

Winter” finally arrives

Friday was the appetizer. The main course is served tonight.

The season’s 1st major winter storm rolls into Minnesota with significant, even heavy snow Saturday night & Sunday. It may not be a “Domebuster” but looks like the first significant snow for the metro since late February.

We’ve been talking about snow this weekend for a week in the weather lab. The models really locked onto growing snowfall totals Thursday, and by Thursday night’s (0z) run it was clear we had a significant winter storm approaching Minnesota.

Here’s a breakdown of our 1st sginifcant snow system of the season.

System: A fairly strong “inverted trof” of low pressure moving in from the Pacific Northwest.

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Image: Twin Cities NWS

Timing: Snow should begin in western Minnesota by 6pm Saturday, and spread east into the metro between 9pm and midnight.

Duration: Snow should last in the metro until about noon Sunday. That would be about 12 hours of snow of varying intensity.

Moisture: Various models are printing out between .33″ (Euro) to .53″ (GFS) to .47″ (NAM)

Snowfall Totals: The models estimate about a 13:1 snow:liquid ratio with this system. That would translate to an overall snowfall range of 3″ to as much as 7″ for the metro. I think most of the metro may end up between 3″ and 6″…with the best chance of 7″ in the north metro.

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Image: Iowa State University

The heaviest snow with this system will be north of the metro. I could see 6″ to 10″ including St. Cloud, Brainerd, and Duluth by Sunday evening.

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NAM snowfall via

What if? If there is a scenario where the models are off, the most likely scenario is that the storm edges a bit further north. With the metro on the southern end of the heavy snow gradient, this could conceivably reduce snowfall totals.

One more shot at a (hopefully) good model run by Saturday noon.

At this point it looks like we’ll see a nice coating of white around here by Sunday PM.

We’re big boys and girls and used to snow in Minnesota winters, but this will be the first big snow for the metro so do expect some slick roads and snow covered travel this weekend. Gusty winds will become a factor by Sunday PM.

Let it snow!

The magic of “snow crystals”

Snowflakes are among the most amazing creations in nature. The creation ice crystals out of “thin air” is one of nature’s miracles.

It’s great to see snow in our landscape again, but if you want a really up close look at snowflakes… is a must see.

I’ve had the distinct pleasure of interviewing North Dakota native and Caltech physics professor Dr. Kenneth Libbrecht a few times. His fascination with snowflakes began as a boy in North Dakota. He turned that into a career studying and growing snow crystals in a lab…and taking amazing photographs of his creations in the lab and natural snowflakes.

All images courtesy of Caltech and

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It turns out different snow crystal types form at different temperature and humidity levels.

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The morphology diagram tells us a great deal about what kinds of snow crystals form under what conditions. For example, we see that thin plates and stars grow around -2 C (28 F), while columns and slender needles appear near -5 C (23 F). Plates and stars again form near -15 C (5 F), and a combination of plates and columns are made around -30 C (-22 F).

Furthermore, we see from the diagram that snow crystals tend to form simpler shapes when the humidity (supersaturation) is low, while more complex shapes at higher humidities. The most extreme shapes — long needles around -5C and large, thin plates around -15C — form when the humidity is especially high.

Why snow crystal shapes change so much with temperature remains something of a scientific mystery. The growth depends on exactly how water vapor molecules are incorporated into the growing ice crystal, and the physics behind this is complex and not well understood. It is the subject of current research in my lab and elsewhere.

It’s great to appreciate the snowflakes we see this weekend, and the microscopic detail and magic we can’t see.