More “free insulation” on the way

Update 5pm:

It still looks like there may be two chances for (generally light) snowfall this week. A clipper on Thursday may spread snow into Minnesota, and a there is the potential for a second shot Saturday.

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PH

You may find yourself doing a double take at the calendar today.

Yes, it’s still December. And no, you didn’t wake up from a long winter’s nap and sleep through Christmas. (Sounds tempting, yes?)

Our wintery landscape has the look and feel of mid-January these days. It’s like living in a snow globe in Minnesota…a few seconds after you shook the pretty scene inside the glass bubble. Snow is still drifting down…ever so slowly.

It’s pretty from the inside, but one step outside and it feels like January 15th. That’s what we call a “window forecast” in weather.

Last weekend’s prolific snow producer was like a clipper on steroids just south and west of the metro. Some tremendous snow totals between 9 and 11 inches fell in a band from Litchfield & Hutchinson to Lakeville, Northfield to near Rochester.

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Impressive snow totals.

(Click to enlarge)

PUBLIC INFORMATION STATEMENT

NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN

1130 PM CST SUN DEC 05 2010

…SNOWFALL SUMMARY FOR DECEMBER 3RD AND 4TH SNOW STORM…

THE ACTIVE WINTER CONTINUED INTO EARLY DECEMBER FOR CENTRAL

AND SOUTHERN MINNESOTA AND WESTERN WISCONSIN…AS A PACIFIC

ORIGIN SYSTEM MOVED EAST SOUTHEAST ACROSS THE AREA ON DECEMBER

3RD AND INTO THE MORNING HOURS OF THE 4TH. SNOWFALL TOTALS

FROM THIS SYSTEM WERE THE HIGHEST IN A SWATH FROM NEAR MORRIS

IN WEST CENTRAL MINNESOTA TO THE SOUTHEAST PART OF THE

STATE…INCLUDING THE SOUTHERN…WESTERN…AND CENTRAL TWIN

CITIES METROPOLITAN AREA.

SNOW REPORTS LISTED BY AMOUNT

INCHES LOCATION ST COUNTY TIME

—— ———————– — ————– ——-

11.70 2 SSW LAKEVILLE MN DAKOTA 0800 AM

11.60 HUTCHINSON MN MCLEOD 0630 AM

11.00 ZUMBROTA MN GOODHUE 0638 AM

11.00 CREDIT RIVER MN SCOTT 0702 AM

11.00 1 S STANTON MN GOODHUE 0754 AM

10.90 WANAMINGO MN GOODHUE 0743 AM

10.70 1 S HAMPTON MN DAKOTA 0807 AM

10.50 CARVER MN CARVER 0700 AM

10.50 2 NW CHASKA MN CARVER 0807 AM

10.50 2 SW CANNON FALLS MN GOODHUE 0825 AM

10.50 SW BURNSVILLE MN DAKOTA 1015 AM

10.20 1 SE NORTHFIELD MN RICE 0743 AM

10.00 BROWNTON MN MCLEOD 0757 AM

9.90 2 W PRIOR LAKE MN SCOTT 0807 AM

9.50 FARMINGTON MN DAKOTA 0730 AM

9.10 LITCHFIELD MN MEEKER 0622 AM

9.00 LAKEVILLE MN DAKOTA 0724 AM

8.80 HAMBURG MN CARVER 0757 AM

8.60 JORDAN MN SCOTT 0743 AM

8.50 1 SSW LONSDALE MN RICE 0807 AM

8.50 3 ENE MONTGOMERY MN RICE 0807 AM

8.50 HASTINGS MN DAKOTA 0928 AM

8.30 WACONIA MN CARVER 0705 AM

8.10 CHANHASSEN MN CARVER 0600 AM

8.00 MINNEAPOLIS MN HENNEPIN 0600 AM

MEASURED AT LOWER ST. ANTHONY FALLS

8.00 COKATO MN WRIGHT 0740 AM

8.00 MANKATO MN BLUE EARTH 0800 AM

7.80 1 SW RED WING MN GOODHUE 0705 AM

7.50 DONNELLY MN STEVENS 0927 AM

7.50 LAKEVILLE MN DAKOTA 0743 AM

7.50 SHAKOPEE MN SCOTT 1039 AM

7.20 W OWATONNA MN STEELE 0835 AM

7.10 INVER GROVE HEIGHTS MN DAKOTA 0742 AM

7.00 WINTHROP MN SIBLEY 0750 AM

7.00 3 SE LAKE ELMO MN WASHINGTON 0807 AM

6.90 5 N COON RAPIDS MN ANOKA 0807 AM

6.70 4 SW ST PAUL MN RAMSEY 0700 AM

6.70 1 NNW COLD SPRING MN STEARNS 0807 AM

6.60 DASSEL MN MEEKER 0843 AM

6.60 EDINA MN HENNEPIN 1036 AM

6.50 3 SE NEW ULM MN BROWN 0742 AM

6.50 WAVERLY MN WRIGHT 0958 AM

6.40 WSW LITTLE CANADA MN RAMSEY 0807 AM

6.10 MINNEAPOLIS MN HENNEPIN 0600 AM

MEASURED AT MINNEAPOLIS/ST. PAUL INTL AIRPORT

6.10 WOODBURY MN WASHINGTON 0828 AM

6.00 GLENWOOD MN POPE 0907 PM

6.00 REDWOOD FALLS MN REDWOOD 0705 AM

6.00 RED WING MN GOODHUE 0705 AM

6.00 MORGAN MN REDWOOD 0705 AM

5.90 1 SW ST PAUL MN RAMSEY 0828 AM

5.80 SE LAUDERDALE MN RAMSEY 0807 AM

5.80 EDINA MN HENNEPIN 0921 AM

5.80 RAMSEY MN ANOKA 1034 AM

5.60 NEW HOPE MN HENNEPIN 0702 AM

5.50 DURAND WI PEPIN 0600 PM

5.50 ANNANDALE MN WRIGHT 0800 AM

5.30 ANDOVER MN ANOKA 1000 AM

5.00 WELCOME MN MARTIN 1218 PM

5.00 ST CLOUD MN STEARNS 0600 AM

MEASURED AT ST. CLOUD PRISON

5.00 KIMBALL MN STEARNS 0600 AM

5.00 6 W EAST BETHEL MN ANOKA 0608 AM

5.00 STILLWATER MN WASHINGTON 0705 AM

5.00 BALDWIN WI ST. CROIX 0705 AM

5.00 2 SSW CAMBRIDGE MN ISANTI 0740 AM

4.80 ST CLOUD MN STEARNS 0705 AM

MEASURED AT SCSU

4.80 SSW MONTEVIDEO MN CHIPPEWA 0807 AM

4.60 NEW RICHMOND WI ST. CROIX 0622 AM

4.60 FOREST LAKE MN WASHINGTON 0807 AM

4.60 1 SW CHISAGO CITY MN CHISAGO 0807 AM

4.50 ALBANY MN STEARNS 0638 AM

4.50 2 NNW NORTH BRANCH MN CHISAGO 0843 AM

4.30 BOWLES MN MORRISON 0858 AM

4.20 AUGUSTA WI EAU CLAIRE 0800 AM

4.00 LITTLE FALLS MN MORRISON 0633 AM

4.00 MILACA MN MILLE LACS 0752 AM

4.00 BELGRADE MN STEARNS 0818 AM

4.00 RICE LAKE WI BARRON 0953 AM

3.80 ELK MOUND WI DUNN 0743 AM

3.80 EAU CLAIRE WI EAU CLAIRE 1038 AM

3.60 LONG PRAIRIE MN TODD 0632 AM

3.50 LEAF VALLEY MN DOUGLAS 0608 AM

3.50 2 N SAUK CENTRE MN STEARNS 0912 AM

3.30 RICE MN BENTON 0705 AM

3.30 7 S HILLMAN MN MORRISON 0803 AM

3.00 WINNEBAGO MN FARIBAULT 0600 AM

3.00 BLOOMER WI CHIPPEWA 0807 AM

3.00 FAIRMONT MN MARTIN 0807 AM

3.00 2 NW GILMAN MN BENTON 0825 AM

3.00 6 NW RICE LAKE WI BARRON 0840 AM

3.00 7 NNW OGILVIE MN KANABEC 1034 AM

3.00 CLAYTON WI POLK 1037 AM

2.80 RIDGELAND WI DUNN 0158 PM

2.60 JIM FALLS WI CHIPPEWA 0632 AM

2.30 3 N CAMERON WI BARRON 0806 AM

The forecast models did an excellent job with laying out the heavy snow area for the clipper, but an unusual injection of moisture from the Pacific Ocean, combined with cold air in the system to squeeze out every inch of snowfall potential.

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The “enhanced clipper” had staying power, spreading heavy snow from the northern Rockies into the Ohio Valley.

Free insulation!

If you grumbled a little while pushing the relatively light but deep powder off your driveway, you may be relieved to know there are some benefits of all that snow on your roof. It turns out snow is a great insulator!

Here’s the deal. A light fluffy snow like last weekend’s leaves tiny air pockets between the snow crystals as it piles up. The trapped air makes an excellent insulator.

10″ of fresh powdery snow on your roof is roughly equivalent to a 6″ layer of fiberglass insulation! That’s about an R-18 value added to your roof, roughly the same as in many walls of your home. Maybe we should start forecasting snow storms in “R-Value” instead of inches? “We’re looking at an R-18 snow event this weekend….”

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An “R-18 snow” on the weather lab roof?

As long as ice dams are not an issue, it may pay to leave this “champagne powder” on your roof a while.

Heavy too:

All that snow can add a ton (literally!) of extra weight to your roof too. Most homes are designed to handle plenty of winter snow, usually about 30-40 pounds per square foot.

A dry powdery snow (20:1 snow:water ratio) weighs about 3 pounds per cubic foot. On a 20′x40′ roof (800 sq ft) that’s about 2,400 pounds of extra weight on your roof. At the other extreme, an extremely wet (and rare) snow (3:1) can weigh as much as 20 pounds per cubic foot. That’s as much as 16,000 pounds on a 20′x40′ rooftop!

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Chilly week ahead:

It looks like polar air is locked in through Wednesday in Minnesota. If we lose the stubborn clouds (which could happen overnight tonight) we may see temperatures plunge to zero of just below in much of Minnesota early Tuesday morning. If we dip below zero in the metro, it will be the coldest night (and our first sub-zero night) in nearly 11 months…since we hit -5 last January 29th.

Temperatures will briefly moderate to near 30 by Thursday, as a clipper slides by to the north. That system could bring a light snow to southern Minnesota, and maybe a shot of 2″-4″ up north. A clipper ahead of a reinforcing shot of cold air Saturday may bring another shot of snow.

There are signs of a potential thaw along about December 14-16th, but overall December looks like a cold end to a mild year in Minnesota and much of the USA.

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No escape to sunny Florida:

Be glad you didn’t book that warm weather getaway to sunny Florida this week. A hard freeze with low temps in the 20s in on tap. No doubt this will make news headlines on networks and cable news outlets as citrus growers douse trees in ice to try and ward off damage form the freeze.

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Stay warm, and enjoy the pretty snow scene outside your window!

PH

  • Leone Graf

    Your calculations for the weight of snow are great. What people usually forget in the calculations of snow load is that in the northern parts of the state the snow can remain on roofs for months on end. I have personally removed over 4 feet of snow from a ranch house with an L shaped footprint and a hip roof. The snow was packed so dense that I could stand on it and sink in less than an inch. It was extremely heavy. All the construction tables in the world do not account for that condition and weight on roofs!

  • http://jdueck.net Joel D

    It’s nice to know that snow can insulate, but for most homes snow does almost nothing to keep your house warmer. In most homes, the attic and underside of the roof are ventilated to keep them closer to the outdoor air temperature (in order to prevent ice dams caused by the snow on the roof melting and re-freezing). It’s the insulation directly above your ceiling that keeps your house warm, once you move above that and into the ventilated attic, there’s nothing to keep warm anymore, so the snow is basically insulating nothing. The exception would be homes where sprayed foam is applied directly to the underside of the roof, which means the attic is being heated like any other area of the house — this is a new practice, though, and comparatively rare.

    Bottom line, I would suggest sticking with inches for snowfall forecasts ;-)

  • Paul Huttner

    Excellent info Joel…thanks.

    I’m clearly not “hip” (pun intended) on the ins and outs of roof design.

    As I look at my neighbors roofs (mix of newer and older homes) I see some are designed as you suggested…but some have no vents under the soffits or anywhere else I can see, and the roof vents are buried under snow. How does that work?

    Also I should point out that snow has the same insulating effect on the ground…much to the delight of many little critters that survive the winter under the snowpack.

    PH

  • Chris

    We just built a SIP house with a roof of solid foam (R-60 equivelent) Since there is no venting in our roof area we are enjoying the added insulation. It is also great for our septic and our Geothermal loops up here in the great north woods