Posts Tagged ‘Haines’

Why does the snow sparkle so?

Saturday, January 7th, 2017

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).

_mg_484120170104_150607-reduced

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

Saturday, October 22nd, 2016
20160930_172321-rduced

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? (more…)

Celebrating the end of the snow drought

Tuesday, February 3rd, 2015

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.) (more…)

Alaska weather on a roller coaster

Tuesday, February 11th, 2014

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. (more…)

Two kinds of cold in Alaska

Friday, February 1st, 2013

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. (more…)

Not the last great Alaska snow race

Saturday, March 3rd, 2012

Today is the start of the world famous Iditarod trail sled dog race (“the last great race”), so I thought maybe I should give an report on another (unofficial) great race: the Alaska snow race. It has been a very snowy winter in many parts of Alaska and there is plenty of talk and a little bragging and comparing between towns, so why not make a little fun of it? In no way am I wanting to make light of the real hardships experienced in places like Cordova and Valdez, where schools were closed for more than an isolated “snow day” due to fears of structural failure of school buildings, among other problems. Believe me, I understand the issue of dealing with tons of snow, since I live in one of the major league snow towns (Haines). What I want to do is compare details of a longer list of places facing heavy snow this winter, and look at why. First the standings, as of the leap day checkpoint: units are inches for snow and feet for elevation.

table

(more…)

The highly channeled winds of coastal Alaska

Friday, January 20th, 2012

Alaska is a big place, and the weather system affecting our state right now is even bigger, but I’m going to show you that is it the small scale that counts when it comes to winds of the south and southeast coasts. As I write this, virtually the whole state is under the influence of the strong pressure gradient between a large, deep low in the Northeast Pacific and strong but gradually weakening high pressure in Siberia and the Alaska interior. (The high was up to a crushing 1060 mb a few days ago, compared to the still hefty 1040 mb on this map) Here is the surface map from 3 pm/00z this afternoon from the GFS model (It’s the 12 hr forecast which is about as good as an analysis):

GFS40_Pacific_t85slp_20120120_1200_F012

You probably know that where the isobars are drawn with the closest spacing is where the gradient is the strongest and therefore where the wind is supposed to be the strongest. (more…)

Wind Driven Snow Rollers

Saturday, December 17th, 2011

My tips for witnessing unusual, interesting or simply beautiful weather phenomena have always included spending as much time as possible outdoors and keeping your eyes up, as in looking up at the sky often. A couple days ago I found some unusual weather down at my feet. Snow rollers! My other advice is to always have your camera with you, which I did not, but it was close and I was able to fetch it before the mid afternoon dusk turned to complete darkness. Between the duskiness, the falling snow and the flat light, my photos turned out pretty rough, but by the next morning, after a few hours of rain, the snow rollers were history…you would not have suspected a thing. (Please click on the photos to see larger versions.)

snow rollers, Haines, Alaska, Jim Green

Snow rollers form when the snow possesses a certain layered tackiness that allows the top layer to peel off the underlying layer (or sometimes the ground) and stay together as it gets rolled into a ball or tube. The rolling can be bone by either gravity or the wind. No elves or gremlins are needed. If by gravity, a pretty steep slope is usually needed. If wind, then you can guess that a pretty strong wind is needed. (more…)

Skagway gets slammed

Wednesday, June 2nd, 2010

By the time we get to June, we expect the weather to settle down a bit…even here in Alaska. But weather would be boring if it were not for a few surprises now and then. Skagway was sucker-punched this day with a sharp front featuring wind gusts up to 52 mph (22 m/s) and a quick temperature drop of 15F (8C). Check out the loop made from the FAA’s wx cam at the Skagway airport. You can see the large plume of dust kicked up by the wind:

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1.56 MB animated gif

This gusty south winds impacted more than Skagway. Somewhat gusty wind shifts could be tracked up the panhandle. At Eldred Rock, about 35 miles south of Skagway in the highly channeled northern Lynn Canal, winds switched to south at 37 kts with gusts of 51 kts (43 & 59 mph or 18 & 25 m/s) about an hour before Skagway. Haines got hit with less ferocity, but still enough to get everyone’s attention and kick up a bunch of dust and pollen. Here’s a shot of the pollen being whipped up and blown right up and over the 2000+ ft (600+ m) shoulder of Mt Ripinski in Haines:

_MG_7094-Ripinski-pollen

Skagway, the real windy city

Skagway, if you’ve never been there, sits in a narrow valley extending off Taiya Inlet—the northern end of Lynn Canal (a fjord, not a man made canal). The wind sweeps through the town proper with pretty much the same strength as it does at the closely adjacent airport (where the weather station is). So we can say the airport ASOS (automated wx station) is quite representative of the town, something that cannot be said for many cities. This day, Skagwegians and thousands of visitors off the 4 large cruise ships in port were no doubt enjoying the 77F (25C) warmth and light winds at 1pm. Yes, the north winds had been blowing–up till a couple hours earlier–around 15 mph (7 m/s), which, incidentally,  is why the temperature had risen so quickly.

Bait and switch

The switch to a cooler south wind in the afternoon is actually fairly common here, but the surprise was the magnitude of the contrast. Check out the progression from the hourly reports:

Site M/A Day Time Sky Conditions           VIS Weather Temp DP Wind(kt)  Alt  RH  Chill Peak
PAGY  AA 02 0853  CLR                       10          70  39 03014G24  920  32%  70
PAGY  AA 02 0953  CLR                       10          73  38 04011     917  28%  74
PAGY  AA 02 1053  CLR                       10          76  37 05011     915  24%  78
PAGY  AA 02 1153  CLR                       10          76  37 03007     913  24%  78
PAGY  AA 02 1253  CLR                       10          77  39 00003     910  25%  77
PAGY  AA 02 1353  FEW100                    10          62  46 22013     909  56%  60
PAGY  AA 02 1453  FEW110                    10          63  44 22014     908  50%  61
PAGY  AA 02 1553  BKN110                     5 H        64  44 20032G44  912  48%  61  45
PAGY  AA 02 1653  BKN100                    10          63  45 19029G35  916  52%  59
PAGY  AA 02 1753  OVC090                    10          59  47 20017G26  924  64%  55
PAGY  AA 02 1853  FEW055 OVC070              6 R-       56  49 21020G25  928  77%  51
PAGY  AA 02 1953  SCT055 OVC065             10 R-       55  49 19013G19  932  80%  51
PAGY  AA 02 2053  BKN055 OVC070             10 R-       55  50 16007     935  83%  53

The report times are in local time (ADT), so this covers 9am to 9pm inclusive. The switch to a south wind and the drop in temperature happened between 1 and 2pm. But, again, locals would recognize that as the sea breeze kicking in. But a couple hours later the wind doubled, with a peak gust of triple the former speed…enough to wreck havoc with loose items or un-braced lightweight people. The “H” under the weather column at 1553 stand for haze but was really local dust, silt etc being lofted by the wind. The peak wind notes on the 1553 ob occurred at 1540 (2340 UTC) a detail I got from the undecoded ob:

METAR PAGY 022353Z AUTO 20032G44KT 5SM HZ BKN110 18/07 A2912 RMK AO2
    PK WND 19045/2340 WSHFT 2336 SLP860 T01780067 10250 20167 53006
    TSNO=

What caused this blast?

As you can see on the surface chart below (valid at 4 pm, close to the time of the Skagway blast), there is a front cutting across SE AK (click on it for larger version). The front is moving north, and on the previous map (6 hrs earlier), it was drawn at Dixon Entrance (not yet in AK). Sure, fronts cause wind shifts and temperature changes, but looking at this chart and thinking June it is not obvious what was going on in upper Lynn Canal. Three things seem to not jive with the ground truth at Skagway. (That’s the fun of weather.) 1: The front is drawn as a occluded front, meaning the warmest air has been pushed aloft, and such fronts often have a subdued effect on the surface. 2: The front is drawn with a broken line, which indicates the analyst decided it was beginning to dissipate. 3. The front is drawn as barely past Sitka, about 100 miles (160 km) south of Skagway.

sfcmap03-00

One solution

Here’s some factors I think bridge the seeming discrepancy. I think the front intensified and accelerated as is moved up SE AK, due to low air densities in northern SE. The analyst who drew in the fronts can hardly catch every detail when he or she has much more than just Alaska to worry about (the chart you and I see on the internet is drawn at the NWS HQ back east—our local offices draw their own or at least add their own detail.) It could be argued that this was a mesoscale effect and did not need to be drawn on the synoptic scale chart. That may be partly true, but looking at the buoys off the coast, one could track this front both with more speed and power than the map suggests. Here’s a graph of wind and pressure for the Cape Edgecumbe Buoy off Sitka:

plot_wind_pres-46084.php

Remember, fronts are boundaries between air masses of differing densities (to keep it simple). Higher density air is going to tend to displace lower density air, push it back or up or both. This is pretty intuitive. Lower density air is air which is warmer, more humid, or under lower pressure, or some mix of the three. What happens when an air mass is moving and displacing less dense air ahead of it, and the air ahead of it is getting less and less dense? Just like an army who has broken through the heavily guarded battle front and finds little resistance behind it, it will accelerate. The warming of the land in the northern Panhandle and onshore into Canada created a region of low density air (for you pilot types the density altitude prior to the front was around 2200 ft (>600 m)).

I’d love to hear your thoughts (or direct experiences) on this situation, or at least what you thought of the write-up.