Monday, December 17, 2018

Holiday Weather Gifts

I have received several emails recently asking about weather gifts, so let me provide some ideas for those of you wanting to get a special weather gift for family or friends.

Weather Books

You know I had to mention my own book:  The Weather of the Pacific Northwest, which is available online and at many local bookstore. But there are others.

Want a good general 101-level book?  My colleague Greg Hakim, has written a very good one:  Weather:  a Concise Introduction.  And the price is reasonable for a textbook (which are generally priced ridiculously high)

How about a fast-paced read about a major historical weather event (the Galveston Hurricane)?  Try Issac's Storm, written by local writer Erik Larson.

Want a book about a local storm?  How about the biggest Northwest storm of all time--the Columbus Day Storm of 1962.  Local writer John Dodge provides an interesting detailed account in his book,  A Deadly Wind.

Cloud Charts

There is no more satisfying skill than to be able to "read the sky":  being about to identify clouds and know what they tell about current and future weather.  And a great tool to gain that skill is the cloud chart.  My favorite was created by retired UW Weather Scientist Art Rango:  Guide to the Sky.  Available from many outlets (search for it online) and less than 10 dollars.  A bargain.

Or you can get a free weather chart online and print it out.  Here is one available from your friends at the National Weather Service.

Rain Gauges

Nothing connects you better to the weather than to own a rain gauge and measuring the daily total accumulation.  I do this myself.  You can get a cheap wedge-type gauge or an inexpensive cylindrical ones at local garden and home supply stores (e.g., Lowes, Home Depot).  But if you want a top of the line gauge, get an official CoCoRahs Rain Gauge (CoCoRahs is a volunteer rain gauge network), which is available from many sources for $30-40.  What a wonderful gift for a child interested in weather--and you can encourage them to record their observations and maybe even plot them on graph paper. 

Temperature Sensor

Few things are more useful than knowing the outside temperatures, or more educational to follow.   Inexpensive, and relatively accurate, temperature sensors that can be placed outdoors, but followed from the comfort of your house or apartment. $15-25 dollars should do it.  You can get these online, garden stores, or HomeDepot/Lowes.
Home Weather Stations

Let's say you are really serious.   You want to view all major weather parameters (wind, temperature, humidity, pressure, wind speed, wind direction, precipitation) at your location.  And maybe you want to input the weather readings into your home computer, to plot and analyze them.  Good for you.  Great weather stations are available at reasonable prices.  But I warn you, you get what you pay for.

On one hand, you can drop into Costco and get a fully capable  LaCrosse weather station for only
$ 75.00.  But you may not be happy with it--the sensors are of generally low quality.
But if you just got a holiday bonus or have some extra cash, professional quality weather stations are available for $400-1000, such as the Davis Vantage Pro2 series (see below).   Very good equipment.  They even have point barbs on their rain gauge to prevent birds from using the gauge as a toilet.  Now that is primo!

Whatever you buy and whatever you spend as a gift to yourself, a family member, or a friend, a weather gift is a great way to learn about the atmosphere, gain an intuitive connection with the evolving weather spectacular around you, and make you safer and more comfortable in your daily life.

Saturday, December 15, 2018

Heat Wave Hits Port Angeles While Strong Winds Battered the Region

The first good blow went through the region on Friday, bringing localized gusts of 40-50 mph and the loss of power to around 100,000 customers in western Washington.

Branches always fly during the first storm of the winter and even a few trees were lost.  Forecasts were decent.

But the most interesting aspect of the storm was not the general power outages and wind gusts, but the strong downslope winds and AMAZING  and sudden jump of approximately 20F around Port Angeles, on the northern Olympic Peninsula. 
Lots of power outages occurred in Seattle yesterday with the strong winds.

Here is the  observed temperature plot at Port Angeles during the past few days (time in  UTC/GMT and increases to the right).  Yesterday, the temperatures surged by 20F over roughly 2 hours, from around 46F to 65F, stayed there a few hours and then dropped to around 40 F over a few-hour period.   Talk about extreme temperature changes!

Mama MIA!  What was happening there?

The answer:  a strong mountain wave circulation forced by the interaction of increasing southerly (from the south) flow and the Olympic Mountain range.  This resulted in strong downslope flow descending into the Port Angeles area.  The air  warms rapidly as it sinks due to something known as "adiabatic compression" resulting in the brief heat wave.

Let's take a closer look at the conditions at Port Angeles during the crazy heat wave.  The plot below
shows the sustained winds (blue lines), gusts (red lines) and sea level pressure (green lines) over the same period.  There were two events (low centers) that occurred during the period shown, with the second (Friday's) being the stronger one.   Winds surged to around 40-45 kts, just as the temperatures surge.   A separate plot (now shown) indicates that the strong winds were from the south, thus descending down the steep northern slopes of the Olympic mountains. 

And look at pressure (green line)--a period of very low pressure occurred when the temperatures surged....keep this in mind, it will be important.

A plot of the temperature, wind gusts (red numbers), wind barbs, and dew point (blue numbers) show the conditions around 2 PM Friday.  Strong southerly winds reached Port Angeles (gusts to 45 knots) and you can see the localized warm temperatures (click on plot to expand).

The winds were strong enough to down trees and cause extensive power outages on the north side of the Olympic Peninsula.

So why was there strong northerly winds descending down the Olympics into the Port Angeles area?

A large-scale low pressure trough was approaching the Washington coast, increasingly southerly winds reaching the Olympic mountains.  The air pushed against mountains and a mountain wave developed over and downstream of the mountain crest.   As the air rose, it cooled as it expanded, with the cooling causing the air to become more dense, resulting high pressure on the windward (southern) side of the Olympics

Subsequently, as the air sank on the northern side of the Olympics, it was compressed and warmed.  Since warm air is less dense, an area of low pressure (or a pressure trough) developed over the northern slopes of the Olympics.  To illustrate this situation , here is a simulation of the sea level pressure (solid lines) and wind speed (shading) for 10 AM on Friday.  You  can see the high pressure/low pressure couplet and the large pressure difference between them.  That pressure difference accelerated winds to the north and down into Port Angeles.

The flow configuration is called a mountain wave, because of the wave-like up and down of the airflow, something illustrated by a SW-NE vertical cross section across the Olympics at 10 AM Friday.  The air flow is roughly parallel to the solid lines (potential temperature) see the wave-like structure?  The shading show clouds-- plenty of them on the SW side of the mountain, but none in the descending air to the NE.

And as noted above, the descending air rapidly warms, creating the warmth on the north side of the Olympics.    The high temperatures recorded in the region yesterday show the extent of the warmth, with the highest temps around Port Angeles (click to enlarge).

Clearly, the incoming flow was just right for the development of strong northerly flow  and warmth on the north side of Olympics.  But unfortunately, our friends  around Port Angeles will have to  accept  the fact that they won''t always have Los Angeles weather in December.