Wednesday, October 22, 2014

A Tropical Storm for the Inland Northwest?

In the past we've mentioned how much of the moisture that falls on our heads in the Inland Northwest actually traces it's origins back to the tropics.  The rain that is currently falling on the Northwest US is actually a perfect example of this.  The image below shows a global view of atmospheric moisture. 

Global Precipitable Water - 22 Oct 2014

The red/orange colors show the highest moisture is located in the tropics.  But there are lines of moisture (yellow and light blue colors) that extend away from the tropics in both hemispheres.  These are now being called Atmospheric Rivers.  Storms moving across the globe in the mid-latitudes "tap" into the tropical moisture and bring it poleward.  This is all a part of the global atmospheric circulation.  The current imagery shows that the moisture hitting the West Coast of the U.S. is an east-west "river" of moisture that originated in the central Pacific tropics.

But there's a more subtle feature hidden in these images that may impact our weather early next week.  If you look near the Hawaiian Islands (center of the image), you'll see a swirl of orange.  This is Tropical Storm Ana.  She passed just south of the Big Island late last week and it now west of the Islands.

There's a large storm further to the west (look at the large swirl east of Japan).  The computer forecast models expect this storm to merge with Ana as it moves eastward across the Pacific.  Where will it go?

The GFS model has an interesting forecast.  First, here's the weather in the Pacific on Wednesday afternoon.

GFS forecast of Sea Level Pressure (contours) and Precipitation (shading) Wed 22 Oct 2014

You can clearly see Tropical Storm Ana, as well as the Pacific Storm that we referred to in the previous satellite image.  Also you can see the large area of rain that will impact the Northwest Wednesday and Thursday.

By Saturday (image below), the Pacific storm is starting to pull the remnants of Ana to the north.  Meanwhile, a rather strong storm is forecast to hit the Pacific Northwest for the weekend.  The Washington and Oregon coasts will see strong winds with this storm Friday night.  By Saturday night and Sunday, the strong winds will move into the Inland Northwest, so be ready for that.

GFS forecast of Sea Level Pressure (contours) and Precipitation (shading) Sat 25 Oct 2014

For early next week, the GFS has the remnants of Ana moving into the Pac NW.  

GFS forecast of Sea Level Pressure (contours) and Precipitation (shading) Tue 28 Oct 2014
Let's be clear.  This is just one model forecast, and it's still 7 days away.  And even if it comes to pass, this will not be a Tropical Storm by this point.  It is merely the remnants of Ana.  Even so, it could still be a very wet and windy storm.

Here's another model forecast.  This image show the forecast moisture.  The black arrows represent the movement of the moisture.  It's a nice depiction of the potential from this storm.  The first image is the forecast for Saturday. It shows the moisture from Ana merging with the Pacific storm on the left side of the image.

GFS Integrated Vapor Transport Forecast for Saturday 25 Oct 2014

And by the middle of next week, there's a lot of moisture heading for the West Coast.
GFS Integrated Vapor Transport Forecast for Wed 29 Oct 2014

However, as mentioned, the GFS is just one forecast model.  Here's the ECMWF model forecast for this storm Sunday.  The Pacific storm is entering the Gulf of Alaska, with the remnants of Ana to it's south.

But by next week, the ECMWF has the low much farther north, impacting the west coast of British Columbia.  We could still see some rain from this forecast, but not as much as what the GFS is forecasting.

So as usual, stay tuned to the forecasts.  As this situation evolves, we'll try to update this blog to give you a better idea of what to expect.

Tuesday, September 23, 2014

2014 Open House

Saturday September 20th was a Glorious Weather Day as the National Weather Service in Spokane held our 5th Open House event hosting the general public at our facility in Airway Heights. Around 300 guests visited between 10 am and 4 pm and were treated to a number of displays, presentations, events and fun activities.

The Open House was truly that, allowing the guests to roam freely thru most of facility. Staff were on hand in all areas to meet, greet, conduct demonstrations and answer questions. Informative displays explained many of the issues and subjects the NWS deals with on a daily basis. A tented area allowed for added space for more displays and a presentation mini-theater.

Upon entering the front door guests were greeted by Admin Assistant Rose Tibbitts who asked guests to sign in and then explained the overall set up and general flow of the event.

The conference room was turned into a display area with posters, pictures, a presentation on the 2014 wild summer weather and a weather quiz. Do you know the hottest temperature ever recorded in Washington?

The Operations Area was set up so that the normal forecast and observation functions could continue uninterrupted, while guests could interact with a forecaster at an AWIPS workstation. Forecaster Steve Bodnar manned the AWIPS workstation for most of the day explaining how we formulate and issue our forecasts and warnings.

Guests then walked into the Electronics Shop where Electronics Systems Analyst Dwight Williams explained the various system he and the El Techs maintain and repair. Displays on the Doppler Radar, ASOS, NOAA Weather Radio and the Cooperative Observation Program were featured in this area. 

Then it was outside to the tented area for some special displays and events! The Kids Activity Area is always a big hit at our Open House Events. The kids could conduct the Rain Gauge Experiment, see the Cloud-in-a-Bottle, make a Wind Sock, Learn about Lightning Safety and more! Forecasters Robin Fox and Laurie Nisbet lent their tireless energy to this active part of the tour.

Service Hydrologist Katherine Rowden staffed the Hydrology Table again, giving demonstrations with the large Flood Plain Model. Adjusting the flow from the 2011 Open House, the demonstration was done at set times allowing Katherine to stay relatively dry. She also had information on the office Hydrology Program and the recent Burn Area Emergency Response team work she participated in for the Carlton Complex Fire.

Speaking of Fire, Incident Meteorologists Jon Fox and Todd Carter donned their Nomex clothing and staffed the Fire Weather table. They had videos, handouts and a wealth of knowledge on how we become part of the Incident Management Teams that manage wild land fires.

Also in the tented area was a mini-theater were presentations were done. Scheduled at various times during the day subjects included "The NWS, Who We Are and What We Do", "Volunteer Observers" and "The Winter Outlook". Science Officer Ron Miller lent his expertise to the presentation on what we expect for this upcoming El Nino winter. 

A Special Presentation was done just before noon as Meteorologist in Charge John Livingston presented Nancy Taylor of Lacrosse WA with the Thomas Jefferson Award. Mrs. Taylor is a Cooperative Observer, taking a once-a-day observation of temperature, rainfall and snowfall. She received the award for her years of dedicated service. This is the highest award given by the NWS Cooperative Observer Program and one of five given across the nation in 2014.

The Event concluded with the 4 PM Weather Balloon Launch. Always a popular part of the day, Observations Program Leader Mark Turner gave folks an idea of why we still release weather balloons with instruments attached, how far they go, where they end up, and then answering all the other questions that people ask about this program.

Thanks to all who came out to our 2014 Open House and if you missed it, look for announcements for our 2016 Event in about 2 years!


Friday, September 19, 2014

Was this the hottest summer ever?

Some of you may have heard that this was the hottest summer ever in the Inland Northwest.  This strong statement may have been inferred from the statistics put out by the National Weather Service office in Spokane.  So let's take a look and see if this is true.

First, we need to define summer.  The calendar says that summer is from June 21st to September 21st.  But this is astronomical summer, which is defined as the longest day to the autumnal equinox.  This doesn't have anything to do with summer.  Another definition is meteorological summer, which is just the 3 months of June, July and August.  But if you've lived in the Inland Northwest for awhile, you know that June is most definitely not a summer month.  It can have glimpses of summer, but consistent warmth is rare.  So we typically define summer as Independence Day to Labor Day, or more simple, July and August.  Yes, that's right, there's only about 2 true months of summer in our corner of the world.

So now let's look at the numbers. Here's the average temperature for July and August.

Average Temp
73.5°F (1998)
78.5°F (1939)
77.6°F (2004)

Sure looks like 2014 was indeed the hottest summer ever.  But before we pass judgement, lets look at another measure of summer.  We typically track the number of days that reach 90°F or hotter.  Why?  Because one really cool day can offset 3 hot days when you average them together.  Counting 90°F days measures how many days were truly hot, regardless of how cool the other days were.  So here's the numbers:

Number of 90+F Days
39 (1958)
80 (1938)
56 (1970)

These numbers seem to tell a different story.  Yes, there were more 90+°F days than normal, but they are far from the record levels.  In fact, in all 3 cities, the number of 90+°F days in 2014 is actually less than 2013.

So which is right?  Was it a record hot summer, or just a bit hotter than normal?  The answer lies in the definition and calculation of "Average" temperature.  The average temperature is an average of both the max and min temperature.  So lets see the numbers for the max and min separately.

Average Max Temp
87.2°F (tied 5th)
93.6°F (13th)
90.6°F (13th)
88.5°F (1998)
96.1°F (1939)
92.5°F (1971)

Average Min Temp
60.8°F (1st)
63.4°F (1st)
64.3°F (tied 2nd)
59.6°F (2013)
62.7°F (1990)
64.4°F (2004)

There's a lot of numbers here.  The thing to notice is that for the Max Temperatures, this summer wasn't the hottest.  It was hot, well above normal, but not the hottest ever.  But when you look at the Min Temperatures, you find out that this was the warmest summer ever for Spokane and Lewiston, and the 2nd warmest for Wenatchee.  What gives?  Why were the Min Temperatures so warm this summer?

Turns out, it's not just this summer.  Let's look at the warmest Min Temperatures for Spokane in July and August.

Min Temp

Again, a lot of numbers to digest.  Notice anything unusual?  Of the 15 warmest Min Temperatures for July and August, 12 of them have occurred since 1998.  Are the summer nights really getting warmer?

One way to check this is to look at other nearby sites that are more remote.  There is a long historical record of weather observations from the Priest River Experimental Forest.  As the name implies, these are taken in a forest, far from any urban influence.    Rather than bore you with even more numbers, I'll just tell you that of the top 15 warmest Min Temps July/August at Priest River, only 2 of them are since 1998.  Some are from the 1970s, some from the 1940s.  The warmest is from 1905.  In other words, they are more random, as you would expect.

So why are Spokane summer nights so warm?  The answer is the location of the temperature sensor.  

The official NWS ASOS sensor is located in the middle of Spokane Airport.  It was placed there in 1995.  Notice all the concrete around there?  The sensor is surrounded by it.  That pavement absorbs the sun's warmth during the day, and then releases it at night.  The official sensor has been at the airport since 1947, but the airport continues to grow.  The previous location for the thermometer was north of the current parking lots, away from much of the effects of the runways.

Additionally, the late night wind at the Spokane Airport is often from the northeast during the summer.  Where is that air coming from?

That's right, the city of Spokane lies to the northeast of the airport.  So all of the urban warmth is warming the air that moves over the airport during the night.

Professor Cliff Mass has a similar analysis of the SeaTac temperatures in his blog:

So what was the cause of our hot summer, and how extensive was it?  First, let's look at the state-based ranking of temperatures for July and August.  Here's July:

The number represents the historical ranking.  Since there are 120 years in this database, the 116 for Washington as well as Idaho means that this was the 5th warmest July in the last 120 years.  Again, this uses the Average Temperature.  Parts of the central US had their coldest July ever.

As we've pointed out, August cooled down a bit.  But even so, for Washington, it was still the 7th warmest statewide.  Take a look at the other parts of the West.  Utah had it's 8th warmest July ever, but it's 15th coldest August.

For June through August, the largest anomaly was along the West Coast, although it was still above normal over much of the western US.

So what was the cause of this anomalous warmth?  Meteorologists actually pay more attention to the layers of the atmosphere well above the surface.  And the anomaly chart at 20,000 feet does a nice job of showing the cause of our heat:
500mb Height anomaly for July 1 - August 15, 2014

The "warm" colors are areas where the pressure was stronger than normal.  As you can see for the US, the largest anomaly existed over the Northwest, while a low pressure anomaly prevailed over the northeast US (they didn't have a warm summer). We usually have high pressure over the West during the summer, but this year, it was extra-strong.

The weather pattern actually shifted in mid-August.  Our weather responded by being more normal for the latter half of August.  Here's that same anomaly chart for August 16th through the 31st:
500mb Height anomaly Aug 16-31, 2014

Notice how the entire pattern has shifted.  The strong positive anomaly is now over the Gulf of Alaska, with a negative anomaly over much of the West.

So what will happen this winter?  We'll address that in an upcoming blog.

Tuesday, August 19, 2014

Pattern Shift - How Long will it Last?

The weather pattern across the Inland Northwest so far this summer has been hot and dry.  This has dried out fuels across the region.  Any moisture that has crept up into the region has at times sparked off thunderstorms.  Lightning from these storms have ignited numerous fires across the region.  We have also seen multiple severe weather episodes with damaging winds and large hail reported across the region from July into early August.  The weather pattern has sounded like a broken record with these spells of hot and dry weather conditions intermixed with rounds of thunderstorms sweeping across the region.  This pattern can be attributed to a persistent area of high pressure building up into the region out of the Four Corners area in the Desert Southwest.  This ridge has supplied the heat and potential energy, while weather impulses off of the eastern Pacific have supplied the forcing and moisture to spark off thunderstorms.  This large scale pattern is going to change over the coming week.  The question is: how long will our pattern shift hold over the area? And, can we expect more summer like weather to return before the fall season tightens its grip over the region.

Before we dive into some of the details of what can be expected over the next seven to ten days, let's have a little review of the summer season thus far.  The figure below is a daily mean composite of the 500 MB height pattern from July 1st through August 17th.
This is a fairly typical summer pattern that is observed over the western U.S.  High pressure tends to build in over the Four Corners area in the Southwest (indicated by the warmer colors).  This acts to trap in the heat bubbling up from the equatorial region.  This heat will tend to push up into the Inland Northwest as this area of high pressure strengthens and builds northward.  We have also seen a persistent area of low pressure over Alaska and into the Gulf of Alaska (indicated by the cooler colors).  This is a rather amplified large scale weather pattern from the eastern Pacific into the contiguous U.S. and has been a entrenched for much of the summer thus far.  Although this pattern is nothing unusual, the strength of this pattern has been a bit anomalous (as reflected in the graphic below).
This plot shows similar information as in the first, but represents the mean 500 MB height anomalies.  The warmer colors indicate positive height anomalies and the cooler colors represent negative height anomalies for the same period examined before (July 1st - August 17th).  What is apparent from this graphic is the large negative height anomaly located over the Gulf of Alaska and the large positive height anomaly over the Northwest into southwestern Canada.  Heights have also been anomalously low over the eastern U.S., but less in magnitude compared to the area of low pressure over the Gulf of Alaska so far this summer.

So, how has this pattern affected our local weather in July through the first half of August?  Well temperatures have been hot.  Temperatures at the Spokane International Airport have reached 90 degrees in 26 of the 48 days during this period and the average high temperature was 89 degrees.  In comparison, the average number of 90 degree days Spokane will see at the airport is 14 and the average high temperature is 84.2 over this same period dating back to 1881.  That means we have seen almost double the number of 90 degree days than what is typically observed.  July and August are typically dry across the Northwest, but the current water year (beginning and ending on October 1st) has been below normal across the Inland Northwest; through August 17th, Wenatchee is 3.06 inches below its normal value of 7.58 inches, Spokane is 3.83 inches below its normal value of 15.63 inches and Lewiston is 2.80 inches below its normal value of 11.32 inches just to name a few locations.  This deficit has directly contributed to the current drought status in Washington state (see figure below).
This is the current drought status through August 14th.  The yellow area indicates abnormally dry conditions, light orange indicates moderate drought and dark orange indicates severe drought.  Notice that the central portion of the state has been particularly dry through the water year so far.  This area, not surprisingly, is where vegetation has been driest and where wildfires this season have been the most intense.  It is unlikely that the drought situation will improve much until we transition into our wetter seasons from fall into winter.

Now that we have summarized a little bit of what has happened through the summer so far this year, it is time to look at what the rest of the summer has in store for us...well we will at least look at the next ten days.  It appears as though the ridge over the Four Corners area is going to be suppressed and actually slide eastward a bit.  This is going to allow a long wave trough to dig across the Rocky Mountains with a ridge of high pressure building into the Gulf of Alaska.  This is in direct contrast with what we have seen throughout this summer.  The next series of images is a model forecast off of the GFS, which was ran at 4:00 PM PDT on Monday.  Displayed is the 500 MB heights starting with Tuesday afternoon and continuing out at 48 hour increments through Thursday afternoon August 28th.

Notice that the western U.S. is under a trough of lower pressure through at least early next week.  High pressure over the Four Corners area becomes suppressed and moves more over the southeast portion of the U.S.  Meanwhile, high pressure builds and strengthens over the eastern Pacific.  The image below is a rough sketch of the mean 500 MB pattern that can be expected the rest of this week and how temperatures will compare to normal.

The Northwest will be sandwiched between the ridge of higher pressure to the west and the trough of lower pressure over the Rockies.  This will place the region in a northwest flow pattern (or the flow of the atmosphere will be from northwest to southeast).  Since the trough and coolest air will be displaced further east, we are not expecting temperatures much below normal, but we should at least see a relief of above average temperatures for the rest of this week.  Here is what the Climate Prediction Center is predicting over the next 8-14 days for temperatures:

This graphic indicates that the trough of lower pressure that digs in over the Rookies will shift slightly to the east next week.  This is also reflected in the model forecast off of the GFS (refer back to the last image in the series of GFS forecasts shown earlier).  If this idea does come to fruition, then we could be in line for temperatures warming back above average by the middle of next week.  However, this would be in response to the ridge of high pressure nudging eastward off of the Pacific and not from the Four Corners area.