Monday, August 22, 2016

The Portland Hot Box

The questions that everyone should ask is why would anyone live in Portland, Oregon during the summer, when Seattle and Puget Sound is so close?

Portland, located in the northern Willamette Valley, is a hot box, frequently 5-10F warmer than the more temperate Seattle, which is cooled by the Sound, Strait and the Pacific.


Let's review the temperature data, and those in Portland will be excused for skipping the details.

 Here is a plot of the temperatures at Sea Tac (red) and Portland (green) airports. Portland is warmer virtually every day, and sometimes by a considerable amount.  Portland reaches the 90s F quite frequently

How about the average maximum temperature over the past month?   Mid to upper 70s in Seattle, mid to upper 80s in Portland.

Extreme temperatures?   Here is a plot of daily highs--yellow lines-- at Portland and Seattle.  In Portland, many days have daily records above 100F in mid-summer, several as high as 105-107.

In contrast,  Seattle almost never gets to 100F (one day).


OK, it is clear.  Portland is a hellishly warm place during the summer.  But why?   The key is they have poor access to the cool water and thus natural air conditioning of the Pacific.  As shown by the terrain map, Portland is in a topographic "bowl", with moderate terrain on all sides.    Hard for cool air from the Pacific to get to the city.  The Columbia and Willamette rivers are too narrow to do much good.


In contrast, Seattle has direct access to Puget Sound, the Strait is close, and there is a sea level path to the ocean.

Portland Purgatory versus Seattle Cool. Portland also has weird donuts. (see below, so hot down there they put bacon on the donuts)


 The only thing that makes Portland livable is a ready supply of chilled microbrews.  Without them, Portland would be abandoned during the summer.

Saturday, August 20, 2016

One Last Hot Day But Is a Bigger Heat Wave in Our Future?

Yesterday, Seattle-Tacoma Airport got to 95F, breaking the previous daily record, while Willamette Valley locations hit the century mark (see Friday max temps below).  Ironically, eastern Washington cooled substantially from Thursday due to a surge of cooler air from the north (and which was MUCH stronger over Montana).


Temperatures should be similar over the western WA and Oregon interiors today, but a push of marine air is expected tomorrow west of the Cascade crest as a significant trough of low pressure moves through.

The coast should be cooler today, as the offshore flow weakens and the thermal trough moves inland. The visible satellite imagery this morning shows a sign of this....a tongue of stratus hugging the coast.  You will also notice the plumes of smoke from a few fires over the Olympics and Cascades.


Temperatures above Seattle are just as warm this morning as yesterday and the low level northerly winds (which cool) are weaker (as shown by the time-height cross sections from the profiler at Seattle Sand Point below).


The UW WRF high resolution model surface temperature  forecast for  5 PM (below) shows very warm temperates again over the Willamette Valley and southwest Washington (96-100F), with lower 90s extended north to the southern Puget Sound.    Cooler along the coast.



Sunday will bring a major push of marine air and temperatures dropping by 10-20F.  The latest numerical forecasts suggest an even stronger ridge of high pressure building mid to late week, with temperatures climbing again into the 80s and 90s. (see sample below).  The wildfire threat is increasing, as the above normal heat dries the surface fuels.


Friday, August 19, 2016

Breaking the Daily High Temperature Record Today

Temperatures are surging in western Washington today (Friday).  Yesterday was warm enough, with highs reaching the mid-80s over Puget Sound, and over 100F near Portland and the eastern slopes of the Cascades.   Look closely and you will see some 90s over the eastern and southern slopes of the Olympics where downslope flow gave a temperature boost.


Today will be warmer.

Temperatures aloft have warmed further and easterly flow has developed over the crest and western slopes of the Cascades, as illustrated by a time-height cross section over SeaTac Airport (time on x axis, height on y axis).  As a result, temperatures will surge over the western slopes of the Cascades (into the upper 90s in places)

Seattle-Tacoma Airport reached 87F on Thursday and currently it is running 8F ahead of yesterday, which suggests strongly it will reach into the lower 90sF today.
To give you an idea of how unusual the temperature aloft are right now, below is the climatology of 850 hPa (around 5000 ft) temperatures at the Quillayute radiosonde site.  The red line is the all-time record temperature and the silver dot is today.  Yes...we are right at record levels.
A strange aspect of the temperature records at Seattle this time of the year is that the the record high are relatively low for the second half of August (upper 80s to around 90F) and go up again in September.  The figure below shows this (red dots) as well as the observed highs and lows.    We will easily set a new daily record today.
Why a drop in the record highs and some recovery in a few weeks?  The sun starts to weaken in August, working against record highs.  An important mechanism for the big temperature surges is easterly flow over the Cascades, with downslope flow on the western slopes causing compressional heating as air descends to higher pressure.  This easterly flow is generally forced by large scale weather disturbances, which are weak during mid-summer, but increase in amplitude by early September.  Thus, we can get some very warm days in September when easterly flow is strong.

But we won't break really big records and temperatures near Seattle won't get into the upper 90s F as some folks were suggesting.  Why?  Because the thermal trough, the area of low pressure associated with low-level warm air,  is centered south of us, resulting in a modest north-south pressure difference (higher to the north).  As shown in the temperature, wind and pressure forecast for later today (below), this will cause northerly winds that will move cooler air into Puget Sound.  Still warm, but not crazy warm.  The easterly flow is also bringing in slightly cooler air aloft.  Furthermore, sinking on the western slopes of the Cascades will produce some leeside troughing  (low pressure) along these slopes, which will increase the north-south pressure gradient (again bringing in somewhat cooler air).


Those poor folks in Portland don't enjoy this natural air conditioning and will burn... heading above 100F.  At least they have fine microbrews to cool down with.

Wednesday, August 17, 2016

Glory and the Space Needle

Yesterday morning at the top of the Space Needle dawned sunny with low clouds on the horizon (see image), but around 7 AM low clouds pushed into Seattle, reaching the upper reaches of the Needle (shown below)

6 AM
 7AM
8:30 AM
 

But something beautiful and subtle occurred as the low clouds extended toward the Space Needle:  a glory, characterized by colorful, concentric rings.  Here are a few shots from the SpaceNeedle cam: 




It is not rare to see glories when flying above clouds when the sun is high in the sky.


Glories are optical effects that occur when you have the right configuration of sun and clouds. They result when light is scattered back to the viewer by a field of relatively uniform, small cloud droplets and is always opposite the sun (centered at the anti-solar point), just as the shadow of an object (like the Space Needle or aircraft) would be.   It is possible to realistically simulate the generation of glories using the equations describing electromagnetic waves and their interactions with droplets (Mie Scattering) as shown below (the upper left corner is the simulation):


Keep your eye out for glories next time you are flying.


Monday, August 15, 2016

How to get aircraft turbulence information?

Some folks are a bit nervous about flying, with turbulence being a major concern.  They feel better knowing what will happen or is happening.  So where can you secure such information?

My favorite is from the NOAA/NWS Aviation Weather Center on their ADDS Turbulence website (www.aviationweather.gov/turbulence).  You can see an example below.  This page has turbulence SIGMETa (colored turbulence warming areas) in the upper left, pilot reports of turbulence (PIREPS) in the upper right, and model-driven turbulence forecasts at many levels and times (bottom panel).

The pilot reports are particularly useful and they are color-coded (green for light, orange for moderate, and red for severe).    Below is  a recent example for the Midwest.
 Turbulence symbols look like strange omega symbols--here is a blow up of how they look:


Light turbulence is routine--a modest movement that is not even uncomfortable, sort of like driving on a rough rode.  Moderate turbulence makes it a bit uncomfortable to walk around, but generally doesn't send things airborne (although the seat belt sign is virtually always on in moderate turbulence).  Finally, there is severe, which CAN send you airborne.

The final plot (on the bottom) provides forecasts of non-convective turbulence (from wind shear and mountain waves).  It is useful, but sometimes gets the pattern wrong.

To check out turbulence on an international route, go to this  NOAA site: /www.aviationweather.gov/progchart.   An example over the Pacific (shown below) indicates turbulence with yellow dashed lines and thunderstorms by the scalloped red areas.   The Great Circle route to Japan looks clear, except for some thunderstorms over Japan.



Another source, and one particularly good for international routes, is turbulenceforecast.com.   They have some of the same things as the NOAA site, but they have other products as well.  You can even sign up for warnings.


You want some advice on lessening your exposure to turbulence?  Fly early in the day, because thunderstorms are generally less frequent then.   Don't sit in the back of the plane, which tends to be bumpier.  Avoid switching planes in Denver (a notoriously bumpy place to land any time of the year).  And fly as big an aircraft as possible.   But most important of all is to lock your seatbelt at all times.   Not all turbulence is forewarned. And having your head go through the ceiling is unpleasant.

Announcements:

New Weather Smartphone App, uWx

At the UW, we have developed a wonderful FREE weather app for Android smartphones that also collects pressure for use in weather forecasting. If you want to try it, please go to the Google PlayStore and download it.

Talk in Port Angeles on Wed. August 17th 

I will be talking in Port Angeles about the Future of the Pacific Northwest Under Global Warming at 6:30 PM on August 17th. More information here.

Saturday, August 13, 2016

Was the JetBlue Turbulence Incident Avoidable?

On Thursday night, JetBlue flight 429 hit severe turbulence over South Dakota, sending 24 passengers and crew to the hospital.  This turbulence, associated with a line of thunderstorms, resulted in the abrupt termination of the Boston to Sacramento flight, with an emergency landing in Rapid City, South Dakota.
This blog will analyze the meteorology of this event and examine whether it was possible to foresee and avoid this terrifying incident. (Answer:  it was).  Strangely enough, I was only a few miles from the incident, traveling on an Alaska Airlines flight between Baltimore and Seattle.

The Details

The actual flight path of JetBlue 429 is shown below with information from the FlightAware website. Weather radar information, but from a later time, is also shown.


A key problem for the JetBlue captain was to avoid the turbulence associated with convection (thunderstorm) over much of his/her route.

To analyze the situation we need to know the exact time and location of the incident.  FlightAware provides minute by minute information and I have selected (below) the period of interest before the aircraft was diverted (at 0716 PM Mountain Time or 0116 UTC UTC).  Looking the previous few minutes, you will notice they were flying at 33,400 ft and then dropped suddenly by 100 feet at 0714 PM.  I suspect that is the time of the incident.


Then they returned to their previous altitude.   The location at that time is provided and I plotted it on the map below.  The position is in south/central South Dakota.


Now we are ready to investigate the meteorology of the incident.  Let's start by looking at the radar imagery, based on the National Weather Service radars in the region (image from the NCAR RAP website).  Here is the radar reflectivity at 0115 UTC, with an oval showing the aircraft location.  Red indicates high reflectivity, which is associated with heavy rainfall, strong vertical velocity, and lots of turbulence.  You want to avoid reds if you are in an aircraft.

Clearly, you can see the problem:  the plane flew into a very active portion of the thunderstorm complex.   Notice the arching shape of the red colors:  this is indicative of a very vigorous system.   In short, the aircraft entered a line of very strong convection,  a region that all aircraft should avoid. Strong midwest thunderstorms frequently grow to 40,000 to 50,000 feet and turbulence can exist above them due to upward propagating waves.

Here is a blow up so you can see the situation more clearly.


So how did this line of thunderstorms develop in the previous hour?   Did the pilot have time to avoid them?  To answer this question, let's look at a series of radar images prior to the incident and I will indicate the location of the plane on the imagery.

At 0100 UTC, 13 minutes before the emergency, the aircraft was well upstream of the convective line, with plenty of time to move around it (see below).

Ten minutes before that (0050 UTC), the convective line was apparent, with over 20 minutes to find a path around it.

During the prior hour, the convective line was strengthening and moving to the NE, something that is evident by looking at a series of radar  images (found here).

Normally, pilots fly around major convective lines like this.  There was plenty of time to get around it, and an excellent flight path to the south of the line existed.  So why did the pilot fail to avoid this dangerous feature?

One possibility was that the pilot did not have access to the real-time radar imagery shown above.   Pilots can view their aircraft weather radar, but as described later, such radars have limitations.  The radar I showed you above is available in a number of forms on the internet and a wide variety of web sites.   As a passenger, you can view the radar imagery in real-time at your seat using a laptop/pad and onboard internet services (like Gogo).   In fact, that evening I was following the weather on my Alaska Airlines plane, a few hundred miles away (although Gogo was really poor on my aircraft).   Unfortunately, many airlines do not provide such real-time radar data (from the National Weather Service radar) to their pilots, and I assume this is true of JetBlue.   No pilot would knowingly fly into such a severe line of convection.


What about weather radars on aircraft?  They are helpful, but provide only a localized view of the precipitation situation and possess relatively small antennas that do not give high-resolution information.  This is certainly true of the radar on the Airbus 320 (shown below), which was the aircraft involved in this flight (see below).


I assume that the aircraft radar did show the strong line ahead of the aircraft during the final few minutes before the incident, yet the pilot decided to punch through.  A mistake.

My Flight

As noted earlier, I was on Alaska 761 that left at nearly the same time from Baltimore and followed a route roughly 200 miles to the north of JetBlue 429 over South Dakota (see below).  Our pilot skirted north of that convective feature, with light to occasionally moderate turbulence (seat belt sign was on for most of it).

The Bottom Line

For some reason, JetBlue 429 headed directly into a strong convective line.   It should not have done so.   Radar imagery clearly showed the threat and there was plenty of time to avoid it.   Pilots should have access to the same detailed radar imagery that folks in coach with laptops (like myself) can readily access.   They should also receive the training necessary to understand the impacts of various types of convection.   My own conversations with pilots suggest that many do not have sufficient meteorological knowledge and this should be addressed.  With proper use of weather radar and good pilot training, incidents like the JetBlue 429 one should be avoidable.

Destroyed toilet in JetBlue 429.  
You don't see this happening in Boeing aircraft


Addendum

One of the comments left this very relevant link (https://blog.foreflight.com/2015/08/14/oh-hail-cockpit-weather-delta-1889/)

The writer describes a very similar situation where a commercial jet (another A320!) plows right into developing convection that nearly took down the plane.
There is no excuse for the current lack of state-of-technology real-time weather information in the cockpit.  The public should demand it, as should pilots that are putting their lives on the line everyday.

Announcements:

New Weather Smartphone App, uWx

At the UW, we have developed a wonderful FREE weather app for Android smartphones that also collects pressure for use in weather forecasting. If you want to try it, please go to the Google PlayStore and download it.

Talk in Port Angeles on Wed. August 17th

I will be talking in Port Angeles about the Future of the Pacific Northwest Under Global Warming at 6:30 PM on August 17th. More information here.

Thursday, August 11, 2016

California Water Temperatures in the Northwest

Why travel to southern California when you can enjoy equally warm water temperatures?

Where should you head?   British Columbia's Strait of Georgia.


Let's start with a broad view of current eastern Pacific sea surface temperatures (SST).  Cool temperatures (blue) in the Gulf of Alaska and along the West Coast north of Santa Barbara.  Why?   Because summertime northerly winds result in upwelling of cool water below the surface.  You have to go south to Los Angeles before water temperatures rise into the the 60sF (green, 20C is 68F)
Zooming in closer, one sees the coastal upwelling and the warmer offshore.  But if you look even closer (in the NE corner) was will notice some warmer water (yellows and even oranges) in the Strait of Georgia, between Vancouver Island and the BC mainland.

Let's move ever closer.  Cold in the Strait of Juan de Fuca, but into the mid-60sF  within the central Strait of Georgia.   Warmer than Los Angeles!


So why is the Strait of Georgia so warm?  The topographic map  of the region (below) and the depth of waters of the Strait of Georgia  (also shown) give some hints.   The inner Strait of Georgia is isolated from the ocean and has weak tidal currents.  Furthermore, there are substantial areas where the water is shallow.



The result of reducing tidal action less movement of cool Pacific water into the Strait and less mixing of surface water, which can warm during the long summer days.   Such warming results in lighter water at the surface, which further reduces vertical mixing.   Thus, the water can warm into the upper 60s and occasionally into the lower 70s.  It is said that the warmest water north of Baja California is in Pendrell Sound, BC. (see map for location)



 Quite suitable for swimming without a wet suit!


Talk in Port Angeles on Wed. August 17th 

I will be talking in Port Angeles about the Future of the Pacific Northwest Under Global Warming at 6:30 PM on August 17th.  More information here.