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 in many, many places from the tropic to the polar regions. But there are not many better places to observe, learn about or sail on the sea breeze than in Alaska. Let’s start with an example:

This METEOGRAM, courtesy of U. of Wyoming shows a textbook example recently at Skagway:

sfgrama.140527_0753.pagy

Skaway meteogram with sea breeze

The graphs run from midnight on May 26th to midnight on the 27th and show temperature, dew point and RH on the top one, wind, and clouds on the middle one and pressure on the lower. Focusing on the wind barbs, you can see the sea breeze pattern: calm or light north wind at night, followed by a shift to a south wind late morning which builds to around 15 knots (17 mph or 8 m/s)and continues into the evening, weakens, then switches back to light north around midnight.  The actual direction in this case is dictated by the orientation of the valley…about 30 degrees clockwise from due north-south. Seward’s sea breeze comes right out of the south, while at Valdez it is a west breeze, and Homer, southwest, all due to channeling by topography.

Another take

In Nome where the coast is not fjorded like the south and southeast coasts, the sea breeze is free to change directions in response to various forces. If other factors are weak, it will start as a southeast breeze, and clock around with the sun, south then southwest, west and sometimes rotate to the north as a land breeze, or due to a larger offshore pattern. When this happens the temperature, held low when the wind was blowing off recently icy Norton Sound, spikes in the evening as the wind off the land hits the city. Nome’s high temperature of the day can be set at 9 or 10 pm in this fashion. Click on this graph for a readable version, and examine the progression at Nome last summer. Note the large temperature swings as well as the clocking wind. (The graphs have been stitched together and sometimes jump in their scales. **also note that the time scale is different than the previous meteogram– it is in UTC or Z time. The graphs do not run midnight to midnight local time as above, so look for 8Z as midnight at 20Z as noon to get the correct perspective for a daytime sea breeze timing**)

NOME-sea-breeze-meteogram-2013-06-12

NOME-sea-breeze-meteogram-2013-06-12

The Sea Breeze vs the large scale wind field

This sea breeze circulation powers a wind that must be added to or subtracted from what the wind is doing in response to the larger scale pressure pattern (larger horizontally and deeper vertically, itself a product of hemispheric-scale temperature differences).  If the large-scale pressure pattern causing the wind to blow onshore, a sea breeze on top of that will look stronger. If the wind is offshore, the sea breeze might be weaker or nonexistent. A weak pattern allows a sea breeze to be the main wind force.

The sea breeze front

Sunshine heats the land and gets the sea breeze going, but consider this: in areas with a regular sea breeze, it happens on most cloudy days in spring and summer too. One reason is because cloudy coastal weather is associated with a general onshore flow, so little daytime warming is needed to trigger the winds. Conversely, clear weather is often due to large-scale offshore flow, which can work against a sea breeze. Usually, however, the heating overcomes the offshore flow and the sea breeze kicks in, many times with a sudden reversal of the offshore wind, an obvious  sea breeze front. Such a front is often marked by a sudden drop in temperature and very gusty winds kicking up blowing dust, debris and sometimes dust devils. Here’s a post I did on a particularly strong one, again in Skagway.

Sea breeze- land breeze

The air continues to circulate in a sea breeze fashion while the temperature difference exists, or until larger pressure forces overpower it. Usually, the effect develops in the morning, maxes out in the afternoon and slowly weakens in the evening (That can be quite late given the long solar days of spring and summer) That’s why in some areas it is called the “day breeze.”  Sometimes the effect reverses and a land breeze blows, but a real land breeze caused by local temperature differences is usually much weaker than the sea breeze.

Kill the sea breeze for record heat

A strong offshore pressure pattern can make a strong wind blow off the land when the sea breeze is not blowing. On rare days the offshore pressure pattern is strong enough to hold off any sea breeze effect all day. Then the warm interior air keeps flowing to the coast, warmed further by compression and unobstructed sunshine. That’s when coastal areas hit their highest temperatures, into the mid 80s to upper 90s F (30s C).

Good and not so good places to find  sea breezes

It is interesting to note that while many coastlines in Alaska are home to a very regular sea breeze, some parts of the coast are not conducive to the effect. In particular, slopes that face south or west are prime for maximal daytime heating and their coasts are good bets. East and north coasts tend to miss the breeze.  This contrast can be seen in the two towns on opposite sides of  Prince William Sound. West-looking Valdez gets a regular and strong sea breeze most days, while east-looking Whittier does not. Besides the aspect, Valdez is located along a channel from ocean to interior, whereas Whittier’s channel does not connect with the warmth of the interior, but jumps a pass and ends up on the water again, Turnagain Arm off cool Cook Inlet.

Do you know of other examples of places which do not get much of a sea breeze. I’d love to hear that or any comments or questions. Use the comment link below.

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 »

The power of the sun

Although the world apparently did not end on Dec 21, 2012 the date triggers strong feelings for most Alaskans every year. Of course it is because it marks the winter solstice…the shortest day of the year…and the promise of longer days ahead. It’s a few weeks past the solstice before most Alaskans notice any change, and even longer for the increasing solar radiation to have any noticeable effect on the weather. So, congratulations, we’re about at that point, and in my psychological bag of tricks for keeping upbeat through the Alaskan winter, it is the point beyond which things have got to just keep getting better. My advice is to get outside as much as possible and ingest some of the increasing daylight. At this point in the cycle (January 12th) here are the daylight stats:

city day length (hr:min) daily change (hr:min)
Barrow 0:00 n/a
Kotzebue 3:45 +0:08
Fairbanks 4:54 +0:06
Nome 5:02 +0:05
Anchorage 6:16 +0:04
Bethel 6:22 +0:04
Juneau 7:00 +0:03
Kodiak 7:08 +0:03
Ketchikan 7:37 +0:03
Adak 8:13 +0:02

Read the rest of this entry »

Why is it so cold in Glennallen?

The question in the title came to me in an email, but for every email I get there are probably hundreds asking the same question in Glennallen. Sure, there are thousands more asking it about where they live, be it Fairbanks or Juneau or Orlando for that matter. But I want to look at what appears to be a unusually cold spot this winter, the capital of the Copper River Valley, population, after throwing in close neighbors Gulkana, Gakona, Copper Center, etc, of a 1,100 or so very tough Alaskans.

Let’s look at the weather depiction map from yesterday Morning, courtesy of the Alaska Aviation Weather Unit. A great example, as Gulkana (that’s where the weather station is located), labeled with its 4 letter code PAGK, was the colder than any station except Northway (PAOR)! It was 40 below (Fahrenheit or Celsius, take your pick), colder than Fairbanks at the time and most of the rest of those off the map to the north. Those around it are way warmer, with only Eureka (PAZK) being in the same ballpark. Talkeetna (PATK) and Anchorage (PANC) are not even below zero! Are not all these places in the Southcentral zone?

Read the rest of this entry »