Sitka Nature

It’s been quite warm (by Sitka standards) over the past few days. Thursday’s high temperature of 75F broke the former record high for the date of 68F, set in 1990. It was slightly cooler on Friday, and the high temperature of 70F recorded at the airport did not come particularly close to breaking the record of 77F set in 1964, though several other communities (including Port Alexander on South Baranof island) did set records for the day.

The forecast for Friday called for clouds developing in the afternoon with a chance of thundershowers. I watched for cumulus clouds developing as the day went on, and although a few did, they seemed to stall out or dissipate rather quickly. The one shown in the photograph at the top of this post had mostly been blown apart (or so it seemed) within 20 minutes of the time I took the picture.

Graupel is a type of snow that forms when snow flakes fall through parts of the atmosphere that have supercooled water droplets. Instead of maintaining the form of flat snow flakes and/or elongated snow crystals, the supercooled water condenses as a rime on the surface that results in a pellet shape. Superficially, graupel looks a bit like hail, and many people call it that, but hail is a solid ball of ice that forms in repeated freezing/thawing cycles as water/ice is subject to updrafts and downdrafts in thunderstorms. With a little extra attention, it’s not hard to identify graupel from its less solid feel and slightly fuzzy appearance.

In Sitka, graupel is a fairly common form of precipitation from at least late fall through spring. I remember as a kid noticing that it seemed to fall, sometimes quite heavily, and then shortly after, a more traditional snow would begin. At this point, I’m not sure how strong that relationship is, but it did hold this week. We had a fair amount of graupel Saturday, especially in the afternoon and evening, with snow developing later in the evening and falling through much of the night. Perhaps the conditions that prevail as a front moves through are conducive to graupel formation, with snow falling after the passage of the front.

After nearly two months that seemed unseasonably warm and lacking in precipitation, this week has been a return to what I tend to expect of late winter and early spring weather. Monday’s cooler temperatures with heavy clouds and rain, were followed by a short reprieve in partly-cloudy Tuesday, but Wednesday temperatures dropped again, and we saw rain, snow, sleet, and maybe even a bit of hail broken up by brief patches of blue sky an attending sun.

This spring it was hard to miss all the geese in Sitka as they flew honking overhead or fed and rested on lawns and beaches. Based on reported sightings, at least 250 birds visited town, possibly many more. Most are Greater White-fronted Geese, though there were at least one Snow Goose and a handful of Cackling Geese traveling with them. Geese often show up in town in small numbers during their spring migration, but seeing large flocks on the ground is unusual.

The first report of a large flock in town was Friday morning, April 24. A commercial fisherman noted a flock of over 200 geese at the Turnaround and reported it to the Sitka Birds e-mail list. Over the days that followed, there were several more reports from the Turnaround, Totem Park and Starrigavan.

A conversation with Paul Norwood about some observations he made on a recent kayak trip south of town provided a suggestion as to why they showed up like. He mentioned seeing 2000 geese flying north over Biorka Island on Thursday, April 23. He said there was a light Northwest wind at the time, but it strengthened throughout the day, and later there were many smaller flocks flying back from the north in toward land.

Marge Ward and Marlys Tedin said there had been a similar abundance of Greater White-fronted Geese around town in 2002. Thanks to their detailed records, I was able to find the first large flocks were reported on the morning of May first at Swan Lake. A quick check of the weather history revealed there had been a strong Northwest wind blowing most of the previous day.

Given the weather immediately preceding the arrival of geese in 2002 and again this year, a strong Northwest winds provides a plausible explanation for the goose invasion. However, it is not yet clear whether there were other years when the Northwest wind blew during migration and geese did not show up in town. Maybe the cold winter and early spring also played a role. With snow and ice still persisting on even lower elevation lakes, perhaps locations the geese might ordinarily prefer were not available. Or, perhaps the typical migration route for these geese takes them up Chatham Straight or further east along the mainland. It would be interesting to know if large flocks of geese move up the outer coast, flying across the mouth of Sitka Sound most years, only moving into town in years when unfavorable winds push them back.