Sea breezes: an Alaskan spring-summer staple

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Skagway, AK meteogram

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 is causing the wind to blow onshore, a sea breeze on top of that will look stronger. If the large-scale pattern 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.

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