Wednesday, May 25, 2016

May 21, 2016 Thunderstorm Flash Flood

North Spokane got hit by a strong thunderstorm that produced an excessive amount of rain over a short period of 45 minutes requiring a Flash Flood Warning to be put out for the Indian Trail neighborhood. The thunderstorm started to build around 2:30 pm and continued to build over the next half hour before dissipating. There were many reports of rain from as little as .69" in Spokane Valley to 2.24" in North Central Spokane with possible higher amounts that were not recorded. A gust front formed as a result of the quick development of the thunderstorm and we also noted a temperature drop of 10˚ over the Spokane area within an hour.

Storm Totals
Below is an image of the 24 Hour Rainfall Totals. The shaded areas below are estimates generated from the radar–most of the values within the shaded areas were verified by storm spotters in the area. These values may include light rainfall data that may have occurred before and after the initial storm, but it gives a rough estimate of where the majority of the rainfall took place.

Photos from around the Area
There were many photos from the public on social media and those photos have been placed on a map in the link below. There are photos from directly under the storm as well as some of the other storms that were around the area.   

Radar Image
There are 3D radar images of the storm below  that started at 2:34 pm and continue until 3:15 pm. The radar indicated where the strongest rainfall was and also where hail could possibly have fallen. There is some yellow that is visible on the map to help show the shape of the storm. The 3D imagery of the map focuses on the red portion of the radar and less on the yellow and green (the lower dBZ). The red indicates any rain that was over 50 dBZ which is considered heavy rain. We can see how the storm built along with the heavy rain in a vertical motion.    

We can see in this first imagery that the storm was starting to build above the Indian Trail area in North Spokane but showed no indication of possible heavy rainfall. However, there is a hint of yellow on the map that showed that there could possibly be moderate rainfall.
Radar image at 2:34 pm PDT

After 12 minutes passed, we can see that the storm was vertically stacked with heavy rain up to 20kft which is roughly 3.7 miles. The storm over Indian Trail was stronger than the rest of the storms in the area due to the fact that it was towering over the rest and it also was recorded with a stronger dBZ.
Radar image at 2:46 pm PDT

The heavy rain continued even at 2:52 pm, as the storm maintained heights upwards of 20kft showing no relief of the heavy rainfall. The storm that was to the south east of the strongest storm had not gained a lot of strength. 
Radar image at 2:52 pm PDT

At 3:03 we can see that the storm intensity had greatly decreased from what it was at its heaviest and was only reaching heights of 8kft (roughly 1.5 miles). Within a matter of 17 minutes, the storm had lost most of the heavy rain that was contained within it. 
Radar image at 3:03 pm PDT

The last radar image that showed the storm was at 3:15 pm. By this time we can tell that the storm was over and there was no storm building up behind it. There was little red visible on the map indicating the worst of the rain was gone.
 Radar image at 3:15 pm PDT

This last image shows where the location of possible hail would have fallen in the storm. The small pink area shows anything that depicts on the radar over 60 dBZ which indicates extreme rain or moderate hail.
Radar image at 2:46 pm PDT

Storm Motion
Along with the rain, there was also a gust front that was produced from the downburst that occurred. This map shows the direction the wind was moving. We can see a definite line along Highway 291 where there is green along one side and red on the other. The green shows the wind that was moving toward the radar which is labeled KOTX. The red shows the wind that was moving away from the radar. As time moved along, we can see that the gust front on the west side of the storm was moving towards the radar and away from the storm.
Wind Direction at 3:03 pm PDT

Wind Direction at 3:15 pm PDT

Monday, April 18, 2016

April heat, mountain snow melt, and thunderstorms

April is sure off to a warm start by Inland Northwest standards, with some locations off to the warmest start on record.   Will the warm weather continue?  The answer is a definite yes!   The warm weather is going to lead to significant snow melt in the mountains this week which could cause some river flooding, as well as the potential for thunderstorms for the end of the week.  Lots to discuss, so let's get into it.

First off, the warm start to April.  Here is a map showing the temperature anomalies for the first 16 days of April across the Continental US.

The pattern here is clear, much above normal temperatures over the west (about 6 degrees F Northwest), and colder than normal over the east.  The following COOP sites are reporting the warmest start to April on record:  Lind, Quincy, Plain, Stehekin, Mazama, Priest River, and Colville.  

The warm weather is going to continue this week, with temperatures 15 to 25 degrees above normal through Friday. This is partly in response to high pressure centered right over the area for multiple days allowing continued warming of the air mass over the region.   This is what Meteorologists call an omega block.  Take a look at the GFS model forecast for Tuesday, do you see it?

00z/18th GFS model run forecast of the 500mb heights 18z Tuesday (11 AM PDT Tuesday)
The table below shows our current forecasts as of Monday morning for Tuesday and Wednesday for selected cities, as well as the current records for the date.

The pattern by the end of the week begins to shift.  The strong ridge moves east allowing increased moisture to be brought into the region from the south.  The increased moisture combined with the warm temperatures will increase our chances for thunderstorms.  Below is a graphic from the GFS model portraying the expected pattern for Thursday.

00z/18th GFS model run forecast of the 500mb heights 06z Friday (11 PM PDT Thursday)

It's still too early to narrow down which days and where thunderstorms will occur, and to what intensity.  However the pattern looks favorable and chances will be gradually increasing for late in the week.

The warm weather will also cause snow melt in the mountains with this water making it into area rivers.  This may lead to minor flooding on rivers along the East Slopes of the Cascades and north Idaho Panhandle.  

Here is the current situation with the snow pack across the region.

NOHRSC SWE analysis for April 18th, 2016 09z

As you can see, lots of snow pack remains in the Cascades, Rockies, and north Idaho Panhandle.  The warm weather and snow melt means rising rivers.

The Okanogan River at Tonasket is currently forecast to reach flood stage by the end of the week with several other rivers in the Cascades and north Idaho Panhandle likely to reach at least action stage. Those with interest near area rivers should monitor the latest forecasts by clicking on the link below:

So how long will this warm weather last?  Will this be the warmest April on record?  It's still a bit too early to make this call, but the near record warmth for much of this week combined with the warm start to April will sure help the cause.  There is still next week to get through, and here is the latest outlook from CPC (Climate Prediction Center)

The outlook for April 25th - May 1st calls for slightly elevated odds for warmer than normal temperatures.

In summary, expect near record warmth this week resulting in increased snow melt and rising rivers, as well as an increasing chance for thunderstorms by Thursday or Friday, 

Monday, March 21, 2016

UPDATED....Is a significant snow event possible for Spokane,Coeur d'Alene or the Palouse late tonight and tomorrow morning?

So as we talked about yesterday, an unusually tricky weather scenario looks like it will unfold over the Inland Northwest. So what are we fairly certain about? We are fairly confident that a slow moving upper-level low-pressure system will take up residence over the Inland Northwest and produce a band of moderate to locally heavy precipitation. The big questions to answer are where is this band going to set up and will it cool the atmosphere enough that we could see some significant snow. The setup producing the unusual event looks quite similar to what we discussed in our previous blog. We still expect to see strong lifting associated with a slow moving upper level low parked somewhere over eastern Washington. Notice the green shaded area (representing upper-level moisture) remains parked over eastern Washington and the central Idaho Panhandle through much of Tuesday.

500 mb pattern 2am Tue-5pm Tue
The lifting from the low will be accompanied by plenty of moisture and instability which should be perfect for producing a band of precipitation. Just how much precipitation are we talking about? A lot to say the least. The areas in purple represent totals between 0.50-1.00 inches of liquid and the reds and yellows equate to amounts between 1.00-1.50 inches. This is for the 12 hours between 2am through 2 pm Tuesday. Notice the band of heavy precipitation has eeked farther north than what we were looking at in yesterday's forecast and blog.

Latest 12 hr precipitation forecast 2am Tue-2 pm Tue

Previous 12 hr precipitation forecast for 2am Tue-2pm Tue

We still highly suspect that whatever verifies from a precipitation standpoint will more closely resemble the top two panes showing a heavy east-west oriented band vs the more poorly defined precipitation blob in the lower two panes.

Since the forecast is nearing in time we can also use one of our favorite tools called the HRRR (a rapidly updating model that runs hourly and can ingest current weather conditions). Let's see what the latest run of it says. The loop below is a simulation of what the radar is expected to look like. Green and yellow shading indicates where the heaviest precipitation is expected.

Radar simulation for Tuesday morning

So this also boosts our confidence that this event is going to occur. Each subsequent run of this model continues to show a similar radar formation (with small variations in location).

Now the largest problem remains is will the temperatures cool down enough to support snow. The models vary in this regard and there is a fine line as to whether or not snow can fall and then whether it will get heavy enough so it can accumulate on roads. The odds of rain changing to snow over the Inland Northwest look fairly good especially over Idaho and southern Spokane County and northern Whitman County. However a tougher question to answer is will the snow be able to accumulate on the area roads? If the snow gets heavy enough the answer is yes, however if not, most of the accumulations will occur on grassy surfaces. So once again lets look at the plume diagrams to see how much snow 27 different model runs produce over Spokane, Coeur d'Alene and Pullman.

Spokane plume diagram shows snow totals ranging from 0.0 - 2.5" with an average around 0.3" 

Coeur d'Alene plume diagram shows snow totals ranging from 0.0 - 5.3" with an average around 0.8" 

Pullman plume diagram shows snow totals ranging from 0.0 - 3.5" with an average around 0.5" 

Generally speaking, these values are on par with what the models were showing last night, however with the band moving further to the north, the snow totals in Pullman are trending lower. Motorists are still urged to check the latest forecast before venturing out in the morning and be prepared for a potentially snowy commute. Here is our latest snow forecast.

Snow forecast for Tuesday (issued 9 pm Monday )

1145pm Monday Update....the band of precipitation was beginning to take form. Our confidence is growing the moderate to locally heavy precipitation band will develop. Still not sure if heavy snow will accumulate.

1147pm radar imagery. Note heavier precipitation developing between  Davenport and Ritzville. 


Is a significant snow event possible for Spokane,Coeur d'Alene or the Palouse Tuesday morning?

Although the weather of late has been quite wet, the overwhelming majority of the precipitation has fallen as rain (or melting snow) in the valleys of eastern Washington and north Idaho including the Spokane/Coeur d'Alene area and the Palouse. That might change however as an unusual weather pattern materialises on Tuesday morning resulting in the possibility of significant snow. So what is the weather pattern which might lead to this unusual snow? To get significant snow in the valleys this time of year you need several things. First, you want to have a fairly strong upper-level trigger. In this case, we will be dealing with a slow moving upper-level disturbance or vorticity maximum.

500 mb pattern 2 am-2 pm Tuesday

The emphasis is on slow. The loop above shows the disturbance quite nicely between 2am-2pm Tuesday. The green area represents where the forecast model is placing the best moisture. Notice the feature also looks like a semi-circle indicating a tight circulation in the upper atmosphere which should lead to increased upward motion.

Another ingredient we like to see to enhance this upward motion is deep instability. This helps enhance the upward vertical motion between the ground and the upper atmosphere. So will the atmosphere be unstable? You bet. The orange and red shading indicates where we expect to see the most instability (however it's unstable everywhere across the region.
Lapse Rates through the mid-atmosphere 2am Tue
So couple the presence of the instability and the upper-level disturbance and here is where one model solution suggests we will see the greatest lift. Areas in purple and light purple are where the models expect to see the greatest ascent and thus the best potential for precipitation.
Upward motion through the mid-atmosphere 2am Tuesday

Finally, you need an atmosphere which is cold enough to support snow. This is the least confident part of the forecast. Model solutions are suggesting that the temperatures before the precipitation arrives early Tuesday will be above freezing, but then they slowly fall as the precipitation intensifies during the morning at least over a very small area (denoted in light or dark blue).

8am Tuesday Temperatures

So we have the ingredients in place for a heavy precipitation event (albeit fairly localized). Now the question is where will this band of precipitation set up and will it become heavy enough that it can produce accumulating snows in the valleys. That is a tough question to answer since there has been considerable model variability. What we can gather is more often than not the model solutions have depicted a northwest-southeast or west-east oriented band of precipitation similar to the two panes in top portion of the image below. Some of these amounts are quite impressive. The areas in purple show precipitation amounts above 0.75 inches and the red areas are showing more than an inch. So is it possible that most of not all this will fall as snow? It is certainly a possibility. 

12hr precipitation amounts forecast between 2am-2pm Tuesday
So just how much snow are we talking about?  Well here is a plume diagram showing 27 different model possibilities or solutions for the Pullman/Moscow area. While some of the models are hinting at a little more than a trace of snow, the most impressive solution is showing nearly 8 inches! The average snow amount from all the variations is just over 1" of snow.  For the Spokane area, the forecast is nowhere close to as snowy as for Pullman. The maximum snow forecast is around 2.25" but the average is around a quarter inch. That's a lot of variation, to say the least. 

Plume Diagram for snow for Pullman (Click image for larger view)

Plume diagram for snow for Spokane (Click image for larger view)

So what do we expect to happen? We are fairly confident we will see a band of moderate to locally heavy precipitation develop on Tuesday morning. Again the question is where will this occur and will the atmosphere be cold enough to support heavy snow? The other variable is will the ground be cold enough allow accumulations to occur on the roads? If the snow gets heavy enough (quite possible) we suspect the answer will be yes. Motorists are urged to prepare for the possibility of winter driving conditions for the Tuesday morning commute. Chances are the afternoon commute will be much easier as any threat of accumulating snow diminishes. Hopefully, as the event nears our confidence will grow as to where we expect to see the greatest risk of significant snows. 

Friday, January 29, 2016

A look back at the floods of February 1996

Twenty years ago portions of the Inland Northwest experienced the worst flooding in decades. For those of you that lived through it, this will spur some interesting memories, and for those that weren't here 20 years ago, this will probably be an eye opener!

Setting the Stage

Surprisingly, the winter of 1995-1996 prior to the event was not terribly eventful. Mountain snowpack in the region was only on the order of  50% - 90% of average for that time of winter (See NRCS snowpack graphic below from 2/1/1996). There was a decent amount of snow in the valleys and mid elevations, and that ended up contributing a large volume of run off in short amount of time.

The first half of the winter had been rather mild.  Mount Spokane Ski Resort didn't open until early January. But the pattern changed in late January and the region quickly saw the snow pile up. The graph below shows the snowfall accumulation for the winter at Moscow, ID.  As you can see, by January 18 the town of Moscow had only had 6" of snow for the entire winter.  Over the next 10 days, 42" of snow would fall over that location.

Then came a brutal arctic air mass.  Temperatures plummeted into the sub-zero range with record-setting nighttime temperatures colder than -20F.  This arctic air mass was replaced with an atmospheric river (a.k.a. Pineapple Express) that took aim at the region bringing warm temperatures, winds and copious amounts of rain over several days. Within a matter of a few days, the area went from a deep freeze to near-record high temperatures for February. 

This trifecta of weather conditions created one of our biggest rain-on-snow flood events. This trifecta is the 1) warm temperatures. 2) winds and 3) significant rains. Underneath the snow the ground was for the most part frozen, meaning that almost all the rain and snow melt contributed to the run off as opposed to at least some percolating into the ground. And add to that the somewhat unpredictable nature of ice jams that had formed on creeks and rivers in the preceding cold snap and it was a perfect recipe for major flooding. 

The table below shows the dramatic change.  On the morning of February 2nd, the temperature was -26F at Moscow with 19" of snow on the ground.  Six days later, temperatures were in the 50s and all of the snow had melted.  In addition, 3.54" of rain fell between the 5th and 9th.

Up in the mountains, the scenario was even worse.  Here's the weather observations from Wallace, ID.  The 22" snow pack on the 1st of the month had completely melted away by the 9th as 5.55" of rain fell over the period of a week.

How the Rivers Responded

Many creeks and rivers across the Pacific Northwest saw major and near-record flooding. Debris flows and landslides exacerbated the problems throughout the region. In our area, the hardest hit spots were in Eastern Washington and the Central/Southern Idaho Panhandle.

Down along the Clearwater River, Highway 12 lost a 75 foot long bridge section between Lewiston and Orofino. Homes were lost in the Big Canyon Creek drainage near Peck. The video below from KHQ has some dramatic footage of the Highway 12 washout and a home being actually floating down Big Canyon Creek.

St. Maries, ID had four levees breach, partly due to the damage from river ice. This led to the inundation of over 100 homes and several businesses. The picture below show the town of St Maries on the right. The river coming in from the upper left is the St. Maries River and in the lower portion of the picture, the muddy brown areas are the parts of the community that were protected by the levees from the St Joe River before they breached. If you look closely, you can see several roof tops poking through the murky flood waters. 
Confluence of St Maries & St Joe Rivers at St Maries, ID

The North Fork of the Palouse River filled the concrete river channel in Colfax WA, but did not flood the town, giving the 1960's era flood mitigation project its biggest test to date. Just upstream of the project hundreds of community members frantically worked to reinforce the levee protecting the neighborhoods on the north end of town to keep it from breaching.
Palouse River at Colfax, WA

Here is a sampling of some of the other impacts during the event.
  • Several communities were cut off when roads and highways were damaged, forcing evacuations where possible
  • Several residents in the Coeur d'Alene River basin were cut off and had to be airlifted to safety and other rescues were undertaken in boats and ATVs 
  • Numerous roads were closed and/or damaged due to flooding or landslides including Highways 95, 3, and 12 in ID, and Highway 129 in SE Washington. 
  • The dam on Winchester Lake was over-topped and there was a fear the dam would fail and send a flood wave down Lapwai Creek. The dam held, but Lapwai Creek still over-topped the levee in Culdesac ID and forced an evacuation of part of the town 
  • The community of Cataldo ID worked to build a sandbag levee to prevent the river flowing back under the 1-90 overpass but eventually the river got too high, broke through the emergency levee and inundated Cataldo ID with several feet of water. 
  • The Palouse River at Potlatch ID gage set a record and caused extensive flooding in the town of Palouse WA
  • Paradise Creek in Moscow ID flooded campus housing and forced closure of the University
  • The National Guard was mobilized in both WA & ID to assist during the floods
  • Cedars Floating Restaurant on Lake Coeur d'Alene ID was kept from floating away thanks to the efforts of tugboats. 
  • The flooding caused at least $30,000,000 of damage (in 1996 dollars) to infrastructure and homes in Eastern WA and Northern ID

1996 Flood in historical context

You might be wondering how often we see floods of this size in our area. It is certainly one of the largest floods on record for many of our waterways. However, only a handful of stream gages that were affected in this flood have records that go back farther than 40 years or so. As big as this flood event was, even setting records at some gages, the USGS estimated that the only stream gage that reached its 1% chance annual flood (a.k.a. the "100 year flood") was the the Palouse River at Potlatch. The table below is a quick and dirty analysis of where the 1996 flood peak ranks in a selection of stream gage records.

Stream Gauges
1996 Flood Peak
Rank in Record1
Years of Records1
St Joe River at St Maries
42.00 ft
Coeur d’Alene River at Prichard
10.24 ft / 17,000 cfs
Coeur d’Alene River at Cataldo
51.62 ft / 70,000 cfs
Paradise Creek at Moscow
11.26 ft / 970 cfs
Palouse River at Potlatch
22.15 ft / 14,000 cfs
Lapwai Creek at Lapwai
9.70 ft / 5,010 cfs
Asotin Creek at Asotin
6.50 ft / 3,030 cfs
Spokane River at Spokane
28.04 ft / 36,500 cfs
Palouse River at Hooper
17.95 ft / 28,000 cfs

1Records may contain some gaps

About the Weather

Weather conditions prior to the cold and snow of late January 1996 were unremarkable. January 1996 started out slow as far as winter conditions were concerned, but the second half of the month saw quite a bit of snow and then cold. On average, nearly a foot of snow fell across the lower elevations during the last two weeks of the month. Then bitter cold air settled into the valleys which dropped maximum temperatures into the single digits.

So the scene was set to cause problems if the right weather came along:
  • Fresh and deep lowland snow pack even as far south as the Lewiston/Clarkston area.
  • Bitter cold valley temperatures to aid in freezing rivers and streams.
  • Frozen ground

Atmospheric River of Feb 4th-8th, 1996

The Atmospheric River is a cold season phenomenon that typically occurs between October and March for the Pacific Northwest. A strong jet stream extends well into the lower latitudes of the northern Pacific Ocean, transporting enormous amounts of moisture into the mid-latitudes. The sample loop below from February 2015 is similar to what happened during the flood event of February 1996. Not all Atmospheric Rivers and their effects on the Pacific Northwest are the same, but all tend to bring in much warmer and wetter weather. If enough cold air is in place then potentially heavy snow followed by rain could be expected in the winter months.

Color Enhanced Water Vapor Satellite - Feb 05-09, 2015

The colorized water vapor image above shows an active Pacific Jet Stream picking up moisture from
the Tropics and moving it swiftly east and north. This is similar to water waves crashing on the beach, except in this case, the atmosphere is the "water".

The upper level weather pattern for the February 1996 Atmospheric River (a.k.a. Pineapple Express) event had a high pressure ridge over the western U.S. and a strengthening Arctic low pressure system over southwest Alaska. This created a strong southwesterly jet stream which stretched past the dateline (180 degrees longitude) in the Pacific Ocean and as far south as Hawaii, which is where the term "Pineapple Express" comes from.

High pressure over the western U.S. was giving way to increased storm activity from the deep low pressure system over Alaska. This low pressure storm system was responsible for maintaining the moist jet stream and sending turbulent and wet waves into the Pacific Northwest.

Here's a loop of how the weather pattern evolved Feb 5-8, 1996. There are several waves or kinks in the flow that moved into the Pacific Northwest.  What's important to note is the overall jet stream position remained stationary for several days allowing for a continuous barrage of moisture and warm air into the region.

Upper level atmospheric wave chart Loop Feb 4-9, 1996

Warm temperatures and wind were the other factors in this event. As mentioned before, it was very cold before the event, which allowed rivers to freeze on the surface and recent snow to stay put.  The cold temperatures also froze the ground, which would cause the coming rains to run-off into rivers rather than soak into the soil.

Red circled area approximately where worst flooding noted.

Cold temperatures on Feb 2, 1996 in purple and blue above show below zero readings locked into the Central Basin of Washington and Oregon extending east into the flooded areas.

By Feb 5, 1996, the cold air (note warmer yellow areas below) in southeast Washington and the Idaho Panhandle was 'washing' away with surface temperature readings in the 40s and 50s which certainly aided in rapid snow melt.  These warm temperatures would continue into February 8th.

 Red circled area approximately where worst flooding noted.

Warm air was also coincident with increased southwest winds which moved over the region overnight on Feb 6th. These winds persisted through the rain event.  Winds of 15 to 25 mph over the Washington and Idaho Palouse extended northward into the Spokane and Coeur d'Alene area as time went on. The wind rapidly melted snow even during the nighttime hours as temperatures remained well above freezing.

By Feb 9th, a cold front was finally able to move into the region and shut off the rain and temperatures began to come down to more seasonal levels.

All the weather factors came together to force this historic, rain on snow flood event:
  • Very cold air and snow before the event.
  • 4 days of persistent, moderate to heavy precipitation.
  • Unusually warm temperatures.
  • Periods of southwest winds 15 to 25 mph.
Other contributing factors included:
  • Frozen ground
  • Ice jams on frozen streams and creeks

Fun Fact

The Spokane Weather Forecast Office was transitioning operations in the months prior to this event. The administrative & operational staff moved from the Spokane Airport into our new building between July and September of 1995, and the new crew of forecasters arrived in November and December of that year, just 2 months before the near-record flood event. The weather radar was installed in December 1995 and was still going through it's calibration during the flood.

And here's a requisite picture of the Spokane Falls from February 1996, the 13th most spectacular display there since 1891, according to the USGS river gauge.

Wednesday, January 13, 2016

Active winter weather - how long will it last?

So far the winter of 2015-2016 has been an active one, which started during the fall with the historic November 17th wind storm.  Then a wet December which turned snowy towards the second half of the month, and now another wet period is in the forecast.  Some may be wondering why this is all happening given the strong El Nino year.  We will dig deeper into this, take a look ahead through the remainder of the winter season, and provide a brief drought update.

As mentioned in a September blog, here, every El Nino year is different, and this winter has been no exception.  We currently have one of the strongest El Nino episodes on record.  Here is a look at the SST anomalies over the past month along the equator.

Note on the map the large area of warm Sea Surface Temperature (SST) anomalies of 2-3 degrees C over the Central and Eastern Pacific Ocean along the Equator.  The current strength is threatening the 1997-1998 event which was the strongest El Nino since 1950 based on the SST anomalies.  Strong El Nino episodes tend to bring a wide range of winter precipitation to the Inland NW with milder conditions.  So what did December bring? You probably already know, but it was wet!  Take a look at the percent of normal precipitation map below.

Washington, Oregon, Idaho, and western Montana saw about double the amount of normal precipitation, while southern California was dry.

This changed during the first 11 days of January.

Drier conditions for our region, while southern California got some much needed rain.

So what is causing all of this?  As always, several factors come into play.  El Nino is not the only player and other atmospheric variables come into play.  This year the Arctic Oscillation (AO) has been active. Take a look at the chart below.

The AO turned strongly positive in late December and has since gone strongly negative over the past week as indicated by the solid black line.  So what does this all mean?  Let's begin with the positive phase.

During the positive phase, lower than normal pressure occurs over the arctic regions which tends to lead to an enhanced jet stream across the Pacific Ocean.  This likely factored in to our very wet December.

So, now that we are in the negative phase, what does this mean?

The opposite occurs with higher than normal pressure over the arctic regions.  Colder air often gets displaced south over the central and eastern US and this is true for this episode with very cold temperatures over the upper Midwest and northeast.  This may have contributed to our drier spell in the beginning of January.

So what lies ahead?  Several more storms are on the way.

Satellite shows a series of low pressure systems out across the Pacific which will move into the west coast bringing a mix of rain and snow to the lower elevations with snow in the mountains.  The brunt of the Thursday night into Friday system may miss our region to the south.  Models show additional storms to reach the west coast next week.  What about the long range outlooks from the Climate Prediction Center going out further.  Here is their latest 8-14 day outlooks for Jan 20-28th.

The outlooks call for increased odds of wetter and warmer than normal conditions.  What about after that?  Typically an El Nino like pattern is most prevalent during the later half of the winter into the spring.  Thus, drier and warmer than normal conditions will become increasingly favored, here is the latest seasonal outlook for February, March, and April from the Climate Prediction Center.

The wet weather has been welcome and has brought a significant improvement or end to the drought over Washington and north Idaho.
 This is welcome news to our region since we could see drier than normal conditions develop in February, March, and April.