Posts Tagged ‘climate’

Heatwaves, Southeast Alaska style

Friday, May 19th, 2017

We’ve had some warm days lately in northern Southeast Alaska, and if perception is worth anything, it always feels warmer just coming off winter. Actually much of Alaska feels this surge of warmth in May (and sometimes in April), but it is a time of the year when southeast can keep up with the interior and southcentral areas in terms of summer-like warmth. (And compare our sunny, 70F (21C) to Colorado, Wyoming, etc., where they just got more than a little snow.) Here’s the daily high-low graph for Skagway, Anchorage, and Fairbanks since April 1.
temperature graphYou can see that Skagway (as well as other parts of the panhandle, particularly the northern parts) is an early bloomer with regard to spring temperature spikes compared to the other regions. However, this is starting to change the interior keeps getting steadily warmer, and coastal warming stalls out some as onshore flow increases.

Onshore vs offshore flow

Onshore vs offshore flow is a crucial driver of the weather/climate in coastal areas. In general, high pressure predominates over the continent in winter producing offshore flow which brings dry, cold, windy weather to the coast (yes, there are commonly interruptions that bring mild, wet weather, especially in early winter). In summer, pressure is usually lower over the continent and onshore flow results, keeping coastal areas cool, with ample clouds, fog etc. Right now we’re in the crossover season…the offshore flow has been still with us at times, but the cold interior air that hits like a ton of bricks in January is gone. The interior has thawed out, and as that moderately warm air descends to the coast, it warms further due to compression, and places like Skagway, Haines, Juneau, Valdez, and Seward might be surprised to find themselves listed as the warmest spots in the state, and sometimes get to gloat over big regions in the lower 48 that are hanging onto winter. Skagway has bagged quite a few daily Alaska hot spot medals this spring. The following meteogram shows an example day from Skagway. When the north winds picked up early in the morning the temperature jumped too. With the addition of the sun during the day it make it to 65F (18C), cooling off some as a light southerly (a weak sea breeze) developed.

Skagway, AK meteogram

Here’s the past 30 days’ winners in Fahrenheit:

19-Apr 54 at Talkeetna
20-Apr 58 at Klawock
21-Apr 58 at Annette
22-Apr 69 at Annette
23-Apr 65 at Skagway
24-Apr 60 at Annette...Northway
25-Apr 60 at Juneau...Klawock
26-Apr 61 at Haines
27-Apr 55 at Koliganek...McGrath...Whittier
28-Apr 57 at Eagle...Northway
29-Apr 62 at Skagway
30-Apr 58 at Eielson AFB
1-May 59 at McGrath
2-May 61 at Eagle...Skagway
3-May 61 at Palmer
4-May 59 at EAGLE
5-May 66 at Skagway
6-May 67 at Nenana
7-May 69 at Eagle
8-May 66 at Eagle
9-May 64 at Koliganek...Fort Yukon
10-May 68 at Skagway
11-May 71 at Skagway
12-May 70 at Kaltag
13-May 65 at Shungnak
14-May 65 at Galena Airport...Kaltag...Tanana
15-May 69 at Bethel...King Salmon...Nenana
16-May 73 at Annette...Nenana
17-May 74 at Fort Yukon
18-May 67 at Fort Yukon

As spring progresses, the crossover runs its course and the interior ends up warmer than the coast most days. Note in the list above that maritime stations such as Annette and Klawock are more represented early in the list, interior stations more so toward the end and coastal “in between” places such as Skagway, Whittier, King Salmon, and Bethel appear scattered among, but would be shown to be strong mostly in the middle if the list ran from, say, March through June. [Anyone know of a tabulated source for this state high/low data? It gets weary calling up each daily bulletin and copying/pasting.]

In spring and summer the large-scale onshore flow manifests itself as a stiff sea breeze in many places due to the local sharpening of temperature differences. More on the sea breeze phenomenon here and here.

Warm vs Hot

Now for those of you in Hawaii or the lower 48 chuckling over the upper 60s to low 70s (18-23C) we call warm, lets consider what might happen if a strong offshore flow sets up, not in the winter when those on the coast endure -20F (-30C) wind chills, or the spring boosting us to 70F or so, but in the middle of summer when the interior has heated to 80 or 85 F (~28C). That’s a rare combination, but that’s when coastal towns push into the upper 80s and even upper 90s (30-37C). Let’s look at the few stations in any part of Alaska that have been 95F (35) or above:

map of Alaska record highs 95F+Click on the map for a larger version, or see the list below for details. (Note: on the map I’ve left off a couple locations that were virtually on top of each other, and several labels where several adjacent stations had the same temperature.)

deg F station    date (YYYYMMDD)
100 FORT YUKON 19150627
99 TENAKEE SPRINGS 19760801
98 HAINES 19760731
98 RICHARDSON 19690616
98 MATANUSKA VALLEY 16 19660806
97 EAGLE 19500618
96 CLEAR 4 N 19690616
96 FAIRBANKS WSO AIRPORT 19690615
96 GLENNALLEN KCAM 20090709
96 MC KINLEY VIEW 19690614
96 SUSITNA MEADOWS 19710625
96 TOK 19690615
96 WEST FORK 19690615
96 WILLOW WEST 20090707
95 LADD AFB 19550725
95 NORTH POLE 19690615
95 SEWARD 19660812
95 SNOWSHOE LAKE 19910621
95 COLLEGE UNIV EXP STN 19690615

I’ve highlighted non-interior stations in green. My data only run through 2010, so if any readers know of any updated records to this list, please share them. The records at Tenakee Springs and Snowshoe Lake seemed a bit implausible to me, so I looked at the scans of the original paper forms…nothing obviously fishy…they are official records. Would you have guessed that coastal or near coastal towns are 3 of the hottest 5 in Alaska? Grab an ice-cold lemonade and let me know your thoughts on the topic via the comments link below.

Summer 2012 forecast for Alaska

Friday, June 1st, 2012

After a particularly nasty winter, Alaskans usually hope for a nice summer to erase the memories. Actually, a lot of Alaskan’s do that after every winter.  Well, we are just finishing up (or still waiting for the end of, depending on what part of Alaska you live in)  a very tough winter in most parts of Alaska, so hope runs high for the summer. Will it soothe or disappoint the weather weary?

The truthful answer? I don’t know. Seasonal forecasts for the warm season have little skill in Alaska. Worse than winter forecasts, which are far from reliable.

There are two points pertinent to this issue:

  1. Temperatures vary much less in summer than in winter. While that might make it easier by reducing the potential forecast error,  in reality the forecast needs to show skill within the context of that variability. This is the technical explanation. From a human standpoint these smaller temperature variations seem to be relatively more important in summer, perhaps because there is more outside activity. There is about as much grumbling about a 3 degree colder than normal summer month as there is about a 6 degree colder than normal winter month.
  2. Correlations of summer weather in Alaska with climate systems such as the El Nino/La Nina are either too weak or as yet too poorly understood to be a very useful predictor of a particular summer. Frankly most people have been trying to figure the links with winter weather, probably because winter weather is seen as more important (dangerous, costly, etc.) and I suppose that is right to an extent.

So I’m not putting much confidence in my prediction, and asking you not to as well. This is more of a theory to be played out over the next 3 months than something to make decisions on. (more…)

Double dip La Niña and what it means for winter 2011-2012 in Alaska

Saturday, November 5th, 2011

This year’s winter forecast is going to look a lot like last year’s. That’s because last winter was a La Nina winter and this winter almost certainly will be one, (or already is depending on your point of view). And how did my forecast for last winter turn out? Here’s that story. A twist to this winter is the speculation by some that there might be some significance to a 2nd consecutive, or double-dip, La Nina.

But first, what is a La Nina, how does it affect our weather, and can it really allow one to make a five month or longer forecast? Very briefly, a La Nina is one phase of a oscillating weather pattern in the equatorial Pacific involving air pressure patterns, winds and sea water temperatures. That a weather pattern roughly 4,000 miles (6,000 km) away can affect Alaska’s weather shows the large, interconnected nature of Pacific weather and climate systems and how important ocean temperatures are to them. The tropical part of this system has been studied for decades and is termed the El Nino/Southern Oscillation, or ENSO for short. La Nina is the cool phase of this tropical system, El Nino the warm phase. It oscillates between the two famous kids on a more or less yearly basis, typically with a lull during the northern hemisphere summer and an intensification in fall and through the winter. Many years the phenomenon is weak or noncommittal…a neutral phase. Here’s a intuitive graph from the NOAA’s Earth Systems Research Lab:

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For more information on the the ENSO see the links at the end of the post. (more…)