Saturday, October 3, 2015

Is the end of fire season expected soon?

So while we can't argue that the worst of fire season is behind us, it should be noted there are still fires burning across portions of the Inland Northwest. Here's is what satellite information was showing on the last day of September:

MODIS Visible Satellite Imagery from 9/30/15

While these fires are far from the raging infernos we saw earlier this summer, it's still rather impressive for the end of September or beginning of October.  However, as we all know this year is different. First off, look at these precipitation totals since the beginning of April

Idaho Precipitation % of normal 4/2/15-10/1/15

Washington Precipitation % of normal 4/2/15-10/1/15
That is a lot of red and dark red shading over the Inland Northwest which correlates with meager precipitation amounts ranging 25-70% of normal. That's pretty dry. In fact, since the beginning of April through the beginning of October it was the driest period on record for both Spokane and Boundary Dam, WA (extreme NE corner of the state).

So combine the record dry conditions with nearly record warmth for both sites and it is no wonder the fire season has been so long. Here is a look at the temperatures for both sites.

So obviously record warm and dry conditions led to our active fire season, but unlike a typical year, things just aren't winding down as quickly as we are accustomed to. Climatologically, the days of active fires will be limited. We say that because the shorter days are leading to cooler temperatures and higher relative humidity levels  (both items are generally detrimental to good fire growth) while the chances for measurable precipitation are rising quickly. Climatologically the chance of measurable rain ranges from 20-25% over locations where the fires are currently burning. However by the end of the month those chances nearly double. So despite these facts, look at the latest fire danger ratings for the Inland Northwest:

Current Fire danger ratings
That map shows the fire danger is still high (yellow) or even very high (orange) across a sizable portion of the Inland Northwest, with moderate conditions (light green) found everywhere east of the Cascades. So what does that mean? According to the Wildland Fire Assessment System (WFAS) a high fire danger means, "All fine dead fuels ignite readily and fires start easily from most causes. Unattended brush and campfires are likely to escape. Fires spread rapidly and short-distance spotting is common. High-intensity burning may develop on slopes or in concentrations of fine fuels. Fires may become serious and their control difficult unless they are attacked successfully while small.

So is this danger level unusual for the beginning of October? Since 2006 (earliest year of  the graphical archive), the current fire danger has only been matched one time. That was in 2012. All other years saw low to moderate fire danger ratings across the area.

So what was the fire weather like in 2012? This satellite picture tells the story

MODIS Satellite imagery from 10/4/12

Just like this year, there were quite a few fires burning during the beginning of October. In fact, based on the satellite image, they were much bigger and included the Wenatchee Complex (southwest of Wenatchee) and the St. Mary's Misson Rd fire south of Omak. So what happened that year? The dry weather and fires continued to burn through the middle of the month, but several days of rain (not necessarily heavy) and cooler temperatures put an end to that fire season.

So what did the weather pattern look like for the end of that fire season? Well leading up to the end of the fire season, the upper-level pattern exhibited a large ridge parked right off the BC/WA coast with dry northwest flow over the region. Also, note the low-pressure area off the California Coast.

Early October 2012 500 mb pattern. 
So how does the pattern look for most of this week? Although it's far from identical, it does have some similarities, including the low near California, and the ridge over the Pacific Northwest.
500 mb pattern for Monday afternoon (10/5/15)
So what did the weather pattern that led to the end of the fire weather year in 2012 look like? The ridge broke down quite quickly and was replaced swift southwest flow into the Pacific Northwest and a deep low over the Gulf of Alaska. Again this brought cooler temperatures, periods of light rain (moderate in places), as well as significant cloud cover.
Mid-October 2012 500 mb pattern (Oct12-14)
How about this year? Is anything similar expected? Again although not a perfect match, there are some good similarities including a deep Gulf of Alaska low and deep southwest flow pointed into the Pacific Northwest from the eastern Pacific.
500 mb forecast for Oct 10, 2015
So how is our confidence in this solution and will this be the end of the fire season?  There are a few additional tools we can look at. One of the more interesting ones is called the NOMADS ensemble probability tool. This tool queries 21 GFS ensemble members or model runs and calculates the chances of any given parameter. Using this tool we can look at things such as what is our chance of seeing over a tenth of an inch of rain in a day?  When asking that particular question, here is the answer for the Grizzly Complex located over northern Shoshone County, ID.

The probability of seeing 0.10" of rain or more in 24 hrs over northern Shoshone County. 
So if you key in on the clustering of the blue bars, you can see that there is some consensus that by next weekend (10/10 and 10/11) that the weather pattern will support an increasing chance of rain (it peaks at 25% for the 24 hrs between 5pm Saturday through 5pm Sunday). Notice also that there is a small chance of light rain during the middle of the week.

Stay tuned and we shall see if this will truly be the end of a historically warm and dry fire season across the Inland Northwest.

Thursday, September 10, 2015

What will El Nino bring this winter?

After such a dismal snow year last year, many of you may be asking what kind of winter we will have this year.  Many may have already heard that a strong El Nino is present.  El Nino often brings warmer temperatures, so does this mean another bad year for snow?  In this blog we'll try and answer this question.

First of all, what patterns tend to set up during El Nino Winters?  Here is a graphic from the Climate Prediction Center...

Idealized weather pattern during an El Nino winter.  During El Nino winters, a strong and persistent Jet Stream over the Pacific is oriented over the southern tier of states.  Cold air intrusions from Canada into the northern states are infrequent.

Typically during El Nino winters, the jet streams splits with the cold northern branch over southeast Canada while the wet Pacific Jet Stream sends weather systems to our south across California.  This tends to give us warmer winters, while precipitation tends to be more variable with some years a bit wetter than normal while other years a bit drier.

What is the official forecast from the Climate Prediction Center calling for?  The graphics below issued August 20th shows highly increased odds for a warmer-than-normal winter, with slightly elevated chances for drier-than-normal conditions.

To evaluate the current state of El Nino, we need to look at the equatorial region out in the Central and Eastern Pacific.  Here is map showing the current SST (Sea Surface Temperature) anomalies over the past month through September 5th.

Sea Surface Temperature (SST) anomalies in the Pacific for 9 Aug - 5 Sep 2015.  Red shading indicates warmer-than-normal while blue shading shows lower-than-normal SST's.

The important area to key on is along the equatorial region in the Central and Eastern Pacific (middle part of graphic).  Values warmer than 1.5C are an indicator of Strong El Nino conditions.  Currently there are values greater than 2.0C, which supports a strong El Nino.

So how does this compare to past events?  Let's take a look.

Three-month average sea surface temperatures in the Nino 3.4 region of the equatorial Pacific for 2015 and the past 6 strong El Nino winters.
The purple line on this map is this year's current and projected trace.  While some uncertainty still remains regarding the peak of this event, it should end up as one of, if not the strongest El Nino, most similar to the strength of the 1997-1998 Strong El Nino.

So what has happened in past winters during Strong El Nino episodes?  There have been six cases since 1950.  First let's look at temperature composites for December, January, and February for past strong El Nino years.

As you can see, for the Inland NW, three of the six were much warmer than normal (1957-58, 1982-83 and 1991-1992) and two were near to slightly above normal (1965-66, 1997-98).  The 1972-73 Strong El Nino was actually cooler than normal.

What about precipitation?  Let's take a look...

In this graphic the yellow and orange shaded areas indicate drier than normal while the greens and blues indicate wetter than normal.  There's even more variability than with temperatures.  Two of the strong El Nino winters were wet (1957-58 and 1982-83), two were dry (1965-66 and 1991-92), and two were near normal (1972-73 and 1997-98).

So what do we gather from all of this?  The most important point is that every El Nino year is different.  Some of the differences are related to the timing of when the typical El Nino pattern develops.  During the 1972-73 event it wasn't until mid-February before an El Nino-like pattern kicked in.  Other years El Nino conditions start by January.  The main message here is that El Nino conditions are most favored during the second half of winter.  Thus, parts of November and December are at times more prone to fall and winter storms over the region.

Strong El Nino years also differ in terms of snowfall depending on where you live.  Below are images for snowfall for past episodes with the value on the far right the current 1981-2010 normals.

As you can see, for Spokane, every strong El Nino has brought at or below normal snowfall, with three of the six having less than 20 inches.  Meanwhile for Wenatchee amounts have varied greatly with each year different.  For Republic each strong El Nino year has brought close to normal snowfall, except for a snowy 1965-1966 year.  Bonners Ferry was also very snowy during the 1965-1966 El Nino, with at or below normal snow the other years.

The strong El Nino of 1991-92 saw an early season cold snap in late October. During the 1965-66 El Nino, most areas received near to above normal snowfall.  In 1972-73, a prolonged cold snap occurred in December with high temperatures several days in the teens and lows as cold as -11F in Spokane.  This was followed by another cold snap in January that lasted a week.  Take a look at the Spokane graphic below.

Spokane temperatures in the 1972-73 winter.  Blue bars show daily observed temperatures.  Brown shading shows the normal temperature range.  Red shading indicated above-normal temperatures.  Blue shading shows below normal temperatures.

The strong El Nino of 1997-1998 saw a brief cold snap with highs in the lower teens in January.

Meanwhile the El Nino of 1957-1958 saw no such cold snaps.  Here is the Spokane trace for that winter.

Spokane temperatures in the 1957-58 winter.

So while El Nino years tend to be warmer, most have at least brief periods of very cold or snowy conditions.

For this upcoming year are there any indications of what type of El Nino year we will have?  First, persistent high pressure has been evident in the Eastern Pacific Ocean off the Washington, Oregon, and British Columbia coast.  Note the large positive anomalies (yellow, orange, red colors) in the graphic below.

500mb Height anomalies for April 1 - August 31, 2015.  Red shading indicates higher-than-normal pressure while blue shading shows lower-than-normal pressure.

The longer this persists, the more likely we will prone to early season fall and winter storms as high pressure in the Eastern Pacific results in north-northwesterly flow over the area bringing cooler and potentially wet storms into the area.  However with the current strong El Nino the tendency for upper ridging may not last long.

To summarize, despite the current strong El Nino, be prepared for winter like conditions especially for the early part of the winter.  As winter continues on, El Nino like conditions becomes increasingly favored.  Thus after this winter is over, most will look back and probably think of this being a mild winter.

What does this mean for our mountain snow pack?  We'll address this in another blog in the near future.


Monday, August 31, 2015

Does this mean summer is over?

Our hot summer came to a screeching halt on Sunday with a Pacific cold front bringing our first widespread rain in what seems like months.  The forecast for this week is decidedly cool, with daytime highs in the 70s and lower 80s.  And one look at the calendar begs the question:  Did summer just end without any warning?  Kinda felt like autumn on Sunday didn't it?  And we often say that on average, summer in the Inland Northwest is between Independence Day and Labor Day.

It's hard to define when one season ends and another begins.  But of all 4 seasonal transitions, the summer-to-fall transition is typically the most marked.  A marked transition doesn't happen every year.  Some are more noticeable than others.  The most impressive "autumn arrival" was probably 1959.  Here's a plot of the temperatures for that summer and fall in Spokane:

On September 12, the mercury reached 90F in Spokane.  A cold front moved in, dropping the temperature to 83F on the 13th, 65F on the 14th, and only 51F on the 15th.  But what's most impressive is that after that, the temperature never warmed above 67F for the rest of the autumn.  In other words, Spokane said good bye to the 90s, 80s, and 70s all with one cold front.

At this point we're not expecting a dramatic repeat of that event for 2015.  Spokane averages one day in the 90s in September and 7 days in the 80s.  The record is 10 days in the 90s, back in 1938.  And no, Spokane has never hit 100F in September.

Looking at the warmest 8 summers (based on June, July, and August average temperatures), only one (1958) had a normal September.  The other 7 were all much warmer than normal in September.  

Year Jun Jul Aug Sep
1922 +7.6 +3.2 +2.2 +3.1
1938 +4.5 +5.0 -0.9 +8.2
1940 +6.0 +2.8 +1.9 +5.1
1958 +3.3 +3.0 +4.9 -0.9
1967 +1.2 +0.6 +5.7 +5.7
1998 +0.2 +5.3 +3.0 +5.5
2013 -0.6 +3.9 +3.5 +3.4
2014 -0.6 +5.7 +3.5 +3.5
2015 +9.1 +4.2 +4.2 ???

The folks at the Climate Prediction Center are also favoring a warm and dry September.  Here's the outlook they produced today:

It calls for below-normal precipitation with above-normal temperatures for the month of September.

We typically look at a model called the GFS for forecasts of the weather for the next 7-14 days.  But when we want to look farther into the future, we look at the CFS (Climate Forecast System).  So let's see what it says for September.  First, we'll look at the CFS that was run back on August 10th.

The yellow and orange colors indicate areas where the model thinks temperatures will be above normal in September.  Large area of abnormal warmth over Alaska and Canada, spreading into most of the western US.

Now let's see the CFS from August 20th:

Notice the change.  The model still expects warmth in the West, just not nearly as strong or widespread.

Now here's the latest run of the model, which was fed the data from August 20-30:

We're back to a large area of abnormal warmth over Alaska and Canada, but only a minor area in the northern Rockies.  

The folks at CPC look at this (and a lot of other data) and concluded a warm September for the West.  So don't put away your summer clothes just yet.

Thursday, August 27, 2015

Strong Cold Front on Saturday

You've probably already heard about the change in the weather for this weekend.  Yet another strong summer front will be moving through the Pacific NW.  And yes, it will bring the potential for rain to the area.  Unfortunately, it doesn't look like much for our side of the Cascades.  Let's take a look at 4 models forecast of 24 hour rainfall for Saturday and Saturday night.  First, here's the GFS

GFS forecast of 24 hour precipitation ending 5am Sunday 30 Aug

The GFS shows the majority of the rain falling over western WA and into BC.  This would bring rain to the Cascade fires, but not as much to the rest of the fires in the Inland Northwest.  Here's the NAM forecast:

NAM forecast of 24 hour precipitation ending 5am Sunday 30 Aug
The NAM paints a similar picture.  But you'll notice more rain that is forecast east of the Cascades near Omak.  This would obviously be great new for the Okanogan Complex and North Star fire.  It's also a bit wetter in the Idaho Panhandle, which would be equally good news.  Now let's look at the Canadian forecast:
GEM forecast of 24 hour precipitation ending 5am Sunday 30 Aug

The Canadian GEM model has been consistently the driest for the Inland NW. This would bring less than 0.10" of rain to the fires.  And one last model to look at:
Forecast of 24 hour precipitation ending 5am Sunday 30 Aug

Similar to the other models.  Heavy rain in western Washington and the Cascades, much less in eastern Washington.

But the bigger story will be the wind.  This storm will be similar to the system we had 2 weeks ago on August 14th.  Here's the current wind forecast:

These are sustained winds, and will be 30-40 mph in much of the Basin, Palouse, and Spokane area.  And here's the forecast wind gust:

Wind gusts of 45 to 55 mph.  This is a strong front.  The winds might actually subside a bit in the afternoon after the front moves through the area.

These kind of winds will cause more blowing dust, similar to August 14th.  Here's what the satellite looked like on that day:

MODIS satellite image showing wild fire smoke and blowing dust on 14 August
The blowing dust in the light brown streaks in the middle of the image.  This event closed down Interstate 90 and Highway 395.  Here's some images from the metroforensics blog:

The wind may also cause problems with the numerous wild fires in our area.  Here's a map showing the active fires that are currently burning.  

Wildfires in the Inland NW 27 August

The cold front will move through the region in the morning with very strong winds.  These winds could cause wild fires to spread quickly.  Eventually the atmosphere will become moister as the temperature falls and moisture arrives.  This could help the fire situation.  The window between the frontal passage and the moisture arrival will hopefully be short, keeping fire danger to a minimum.  But if there are several hours in that window, some of the fires could make significant runs to the north and east.

Monday, August 10, 2015

Potential for Severe Weather this week

As we talked about in our previous blog, the weather pattern is setting up for a potential severe weather event on Thursday, August 13th.  Before we get there, there is a potential for thunderstorms today through Wednesday.  Here's the current weather pattern:

GFS 500mb heights, winds, and Humidity (green shading) valid 11am PDT Monday 10 Aug

The low off the Washington coast will slowly creep south along the coast over the next couple of days.  Remember, winds go counter-clockwise around low pressure in the Northern Hemisphere.  That means to the east of the low, the wind blows from south to north.  This "southerly" wind will bring moisture up from the sub-tropics.  We've already seen our dew points rise over the past couple of days.  

Dew point at Spokane August 9 and 10

Note that the dew point has climbed from the mid 30s two days ago to around 50.  That trend will continue for the next few days. So we will have moisture.  The hot temperatures will provide the instability. That combination will produce thunderstorms.    Here's a forecast of radar reflectivity from the HRRR model valid later this afternoon:

The HRRR expects thunderstorms from northeast Oregon and central Idaho to move into the Inland Northwest.  Some of these could produce gusty winds and blowing dust.

While these storms could be strong, they are lacking one of the ingredients for a "big" event:  lift.  The low offshore is too far away to contribute much lift.  And as it continues to drift south, it will be even farther away from us.  So the storms for the next three days will have to rely on moisture and instability alone.

But on Thursday, that all changes.  The low will begin to "eject" to the northeast.  This is a common pattern.  The tough part of the forecast is the exact track and timing of the low.  Here's the current forecast from the GFS model:

Yes, it looks nearly identical to today.  The difference is that at this point the low moving to the northeast.  This is a classic pattern for severe weather in the Inland Northwest, and it's similar to some of the bigger events we had in 2014.  That's not to say we're going to see a repeat of a 2014 event.  But the potential is there for strong and widespread storms.  Here's the NAM and GFS model forecasts of precipitation for the 5pm-11pm time frame Thursday evening.

NAM (upper) and GFS (lower) forecast of 500mb heights (thin lines) and precipitation (green shading) for 5-11pm PDT Thursday evening.

First, you can see a difference in the predicted location of the low.  The NAM has it over southwest Washington, while the GFS is slower with the low offshore still.  But both models show convective precipitation over much of eastern Washington and the Idaho Panhandle.    But the ECMWF (not shown) is even farther south with the position of the low, and so it has even less convection. 

Here's the forecast CAPE (atmospheric instability) from the NAM and GFS:
NAM Forecast CAPE Thursday 2pm

GFS Forecast CAPE Thursday 5pm

Both models show plenty of instability, around 1500 J/kg, which is plenty for strong thunderstorms here.  As you can see, the best instability looks like it will be over the northern and eastern mountains.  Details like this could easily change over the next couple of days so stay tuned as we get a better idea of how this event will pan out.  If the ECMWF is right, it could be a non-event, as the low would cross over us at night.  

Saturday, August 8, 2015

Roller Coaster Weather

You've probably heard the old adage "If you don't like the weather, just wait a little while and it will change."  While that saying is undoubtedly over-used, this week it will be true.  The cause of this roller-coaster weather will be a large low pressure system that's currently off the BC coast.  Here's the 500mb pressure map Saturday morning:

You can see the low just west of British Columbia.  During the first half of this week, the low will very slowly move down the coast, reaching Northern California by Wednesday:

This will do a couple of things.  First, it allows the very hot ridge of high pressure that's currently over Texas to amplify over the center of the U.S.  The Inland Northwest will be on the western edge of this ridge, but still close enough to feel its effects.  Our temperatures are going to jump up in a major way, and quickly.  After are mild weekend, temperatures will warm about 8 degrees on Monday, and then another 5 on Tuesday and Wednesday.  The result is a very hot middle of the week.  Here's the current forecast:

The other thing this pattern will bring is thunderstorms.  The area between the off-shore low and the mid-US high will see persistent flow from the south.  This brings moisture with it, which will bring the potential for thunderstorms.  Initially, these will be rather isolated and won't have much rain with them.  Any lightning from them will have the potential to start new wildfires.  

By Thursday, the low will stop moving south and begin to "eject" back into the jet stream to our north.  As it does so, it will track directly over the Pacific NW.  Here's the forecast for Thursday afternoon:

This scenario is nearly a "classic" pattern for strong thunderstorms in our area.  The ingredients we look for are: 

  • Instability: The 3-day hot spell will do a good job of destabilizing the atmosphere.
  • Moisture: The southerly flow will bring up moisture from the south.
  • Lift: The strong low will supply the lift as it moves over our area.
The exact details are still too far out to get into.  So as we get closer to the potential event, we'll likely update this blog.  Suffice to say, if everything comes together just right, we could be looking at a significant thunderstorm event on Thursday afternoon/evening.

In its wake, the low will bring much cooler temperatures.  Here's the forecast high temperatures for Friday:

So, enjoy the roller-coaster ride this week.