Why does the snow sparkle so?

Lately around here we’ve been blessed with decent snow cover. A nice change from the last two winters. Nice fresh show that stays fresh thanks to lack of warm surges. To add to the beautiful scene, the snow has had lots of sparkles of light reflecting off the surface from the bright moon or nearby lights (there’s plenty of time to see this with days still solstice short). Here’s a couple photos (click on them for larger versions).

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Why so sparkly lately?

The answer is not in the snow itself, but what happened to the snow after it fell. It is true that normal snow crystals can and do sparkle, but the really big sparkles we’ve seen take bigger crystals… in this case frost crystals that have formed on the snow over a few days. This sort of frost is called surface hoar, ie., hoarfrost that has formed on the surface of the snow. Check out the daytime photos (of the same snow in the upper photos) that show the detail. One clue is the small amount of frost on the alder twig in the second photo.

20170104_150625-reduced 20170104_150715-reduced Hoarfrost in general tends to form during light wind situations when there are cold surfaces and lots of water vapor to crystallize onto those surfaces. The most rapid frost formation occurs when there is a source of liquid water close by such as a stream or fog. Yes, we did have some fog in Haines over the last few days. Uncommon during cold weather at this time of year…because the calm winds which allowed the fog to form are uncommon during cold weather here. Note for backcountry travelers: New snow over surface hoar can create a weak layer in the snowpack and increase avalanche danger.

Precipitation patterns & perceptions

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Pick-up soccer on the Haines school sports field on 30 Sep 2106. Most years the field or the weather are not in too good of shape at this time of year.

Of all the weather elements, precipitation seems the most chaotic when it comes to spatial and temporal patterns. In reality, I think wind is probably more variable over both time and distance, but I guess we must understand that, since we don’t talk about it nearly as much as peculiar precipitation patterns such as long wet or dry periods, heavy precipitation events, adjacent areas getting very different amounts or types of precipitation, etc. When do these peculiarities rise above perception and prove to be truly unusual? Read the rest of this entry »

Are you SAD yet?

Everybody is different, but the reduced light in the North and the gloomy weather in many parts of Alaska at this time of year affect almost everyone to some degree or another. Seasonal Affective Disorder (SAD) is the fancy name for the winter blues, bad weather blahs, cabin fever, hibernation instinct…fill in the blank with your term. If you are not familiar with the phenomenon, here’s the Mayo Clinic’s briefing.

hours of sunup on Nov 15th

November 15th potential sunlight

Daylight

Northern areas have much shorter days than more southerly parts of Alaska or elsewhere at this point in the winter, but there are mitigating factors helping them: longer twilight morning and evening, fewer clouds and more reliable snow cover to reflect available light and provide contrast. Read the rest of this entry »

Celebrating the end of the snow drought

happy skierWhile some folks back east may have been mightily inconvenienced by recent snows, here in Alaska most people like to see a little snow in the winter. This winter many of us have seen very little. Here in Haines, one of the snowiest sea level towns anywhere, things were looking pretty brown until last week, when we got almost a foot of nice light snow. You could almost hear the relief around town, as folks got back into the swing of snow removal, or dusted off their skis. My family did both, plus made a batch of snow ice cream. (Never made snow ice cream? Strangely, as a meteorologist, Alaskan, skier, etc, I’d not even heard of it for my first 20-some years in Alaska! I was going do a whole post on snow ice cream but discovered it’s not the novelty I thought it was…just Google it.) Read the rest of this entry »

Sea breezes: an Alaskan spring-summer staple

You’ve heard it said…Alaska has sooo much coastline… We do, about 34,000 miles (54,700 km) worth, and we have the perfect weather phenomenon to go with it: the sea breeze. The sea breeze is a local wind blowing from water to land arising from the relative warmth of the land vs. the water. Warmer land leads to rising and/or expanding air and lowers the surface pressure, drawing in the cool  air off the water. It is not unique to Alaska–It is found Read the rest of this entry »

Is April a dire weather month in Alaska?

I try to keep the number of errors in my Alaska Weather Calendar to a minimum. I have a team of freelance editors and proofreaders to help me, otherwise it would be hopeless. My hat is off to them. Nonetheless, errors slip by, Read the rest of this entry »

Alaska weather on a roller coaster

Wind-blown dust in Haines and other places.

forecast-map

Red flag wildfire danger for the Mat Valley.

Strong pressure gradient along coast.

Back into the freezer

The strong “January thaw” that pushed well into the interior and tied the all time January record for Alaska is being pushed toward the back of our memories by seasonal and colder weather. Boy, it feels colder after a long warm spell! Wind chills here in northern Southeast Alaska are bouncing down to 5 to 15F below zero (-20C to -26C) at times. Read the rest of this entry »

Flying through the JAWS of Southeast Alaska Weather

While waiting to board my Alaska Airlines flight from Juneau to Seattle April 9, the all-to-common announcement came over the PA about a likely weather delay. As I happened to have my laptop handy with Internet access available, I quickly checked the Juneau airport weather observations. I did not see any weather issue that would keep the 737 on the ground. The ceiling and visibility were way above minimums. The wind was strong, but pretty well aligned with the runway…not too bad. Here are the observations in METAR format (click here for help in reading them).

PAJN 091353Z 12021G36KT 10SM -RA FEW018 BKN036 OVC050 06/02 A2918 RMK AO2
     PK WND 12036/1349 PRESFR SLP880 P0001 T00560022
PAJN 091453Z 13028G37KT 7SM -RA FEW013 BKN032 OVC045 05/03 A2914 RMK AO2 
     PK WND 13041/1431 SLP867 VIS LWR S-SW P0000 60004 T00500028 58048 

PAJN 091553Z 12022G33KT 3SM -RA FEW013 BKN032 OVC045 05/03 A2912 RMK AO2 
     PK WND 12036/1501 SLP859 P0004 T00500033

What was I missing? Before I could dig deeper, one of the pilots got on the PA and re-educated me, and the whole crowd–mostly seasoned Alaskan flyers with way more weather and aviation savvy than you’d find at a typical airport down south. Read the rest of this entry »

Signs of Spring in Alaska

We’re a few days into Spring, at least according to astronomers. Last Wednesday (3/20) was the Vernal (Spring) equinox–equal night, equal day. While the flowers may be blooming many places in the Lower 48, such traditional signs of spring are a long way off here in the frozen north. But here are a few signs of the season for this equinox time of year in Alaska: Read the rest of this entry »

Two kinds of cold in Alaska

Dry cold, wet cold?   no.

Winter cold and summer cold?  no. Bitterly cold vs extremely cold?  no. Calm vs windy cold? close.

All these would make good blog subjects, but what I’m thinking about today is domestic cold vs imported cold. Seriously.

I have a good recent example. Read the rest of this entry »