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.

Wednesday, July 15, 2015

Will this be the hottest summer ever?

As we wrote in our previous blog, June 2015 was the hottest ever for our area.  But not just in the Inland Northwest.  Here's an image showing the extent of the record heat.

All of the areas in dark red had their hottest June on record.  And for precipitation, this was one of the driest:

This past June wasn't just a little warmer than normal, it was crazy hot.  It was actually hotter than most Julys or Augusts.  The 105F at Spokane Airport wasn't just the hottest June day ever, it was the 5th hottest day in Spokane history (click here to see a discussion of the hottest day ever in the Inland Northwest).  It's interesting to note that Europe was also extremely hot.

  • Germany set it's all-time hottest temperature ever this year on July 5th with a temperature of 104.5F.  
  • Paris had it's second hottest day ever on July 1st with a reading of 102.2F.
  • Geneva hit 103.5F, an all-time record for that city.

The two most frequent questions that we're hearing are: 1) will this be the hottest summer ever? 2) what caused the record June heat?

In order to answer question #1, it's always best to look back at history.  While we've never seen a June as hot as this, there have been some historical hot Junes.  So what happened for the rest of the summer in those years?  Below is a table showing the 10 warmest Junes and the average temperature anomaly for those years.

Average Temperature Anomalies for the 10 warmest Junes

This year has been at or warmer than normal for each month.  Some of the past hot Junes seem to have "come out of nowhere", such as 1922 where the winter and spring months leading up to June were colder than normal.  While 1940 was just plain warm, with every month above normal.  Some years are similar to 2015 (1992, 1938) in that they had mild winters/springs with a hot June.  But in those years, the remaining months of July-September were not consistently hot.

Overall, the historical numbers show us that while the July-September period following a hot June are often warm as well, it's far from a slam dunk.

July is almost half-way over and while temperatures have recently cooled, we're still running several degrees above normal. The NOAA Climate Forecast System continues to predict a warmer than normal Aug-Oct period.  So the odds are good that we'll above-normal temperatures for the next few months and possibly longer (see below).

This leads to the second question:  What caused this hot spell?  The answer to this is much more vague, but it's possibly related to El Nino.  The equatorial water of the Pacific (where El Nino is monitored) has been showing a steady warming for the past 9 months.

Equatorial Pacific Sea Surface Temperature amonalies

The Nino 3.4 region (second graph from the top) shows that El Nino conditions were barely met (i.e. greater than 0.5C anomaly) through much of this past winter.  And most climate folks agree that the weather patterns we saw this past winter were not typical of El Nino (remember all the snow and cold in the Northeast?).  In a typical El Nino event, the signal will begin in late summer, reach a peak in mid-winter, and then fade during the spring.  But this year, the warming strengthened during the spring and summer months. 

Typically, the presence of El Nino has little effect on summer weather in North America.  But the weather patterns this year of late spring and early summer resembled those of El Nino.  And the 3-month precipitation anomaly for this year looked El Nino-like, with wet weather in the southern states (remember all the Texas flooding in May) and dry weather in the Pacific NW.

So was El Nino partly to blame for our hot June?  It's impossible to say with any certainty.  Our last warm June (1992) had a moderate-strength El Nino in the preceding winter that was fading out by June.  And the super El Nino in the winter of 1982/83 had a warm June in 1982.

Some of you may be hearing projections of a "strongest El Nino ever" for this upcoming winter.  Is there any truth to these, or are they just media-hype?  Here's the El Nino prediction from the NOAA CFS model:

The solid black line is the Nino 3.4 temperature anomaly back to 2014, showing the gradual warming.  All the thin red and blue lines are forecasts, and the black dashed line is an average of the forecasts.  As you can see, the average forecast peaks at just over 3.0C around November.

Below is a similar forecast from the ECMWF:

This graph doesn't show the average of all the red forecasts, but you can see that it would be somewhere around +3.0C, peaking in November/December as well.

The official definition of a "strong" El Nino is a 3-month average anomaly greater than 1.5C for 5 months.  These forecasts certainly suggest a strong El Nino for this winter.  And to put it into historical context, there are only 2 winters with El Ninos as strong as the one currently forecast:  1982/83 and 1997/98.  Both of these winters had a strong impact on the winter weather in North America.  We'll be writing more about El Nino in the coming months as the details become clearer.

Thursday, July 2, 2015

Record warm June

June was incredibly hot across the Inland NW, leaving us Meteorologists in awe at the numbers.  And it wasn't just Eastern Washington and North Idaho that set records.  The record warmth stretched all across Washington, Oregon, and most of Idaho as the image below shows.

See the table below for a closer look at the actual numbers.  You can see in some cities such as Ephrata and Portland, the previous records were shattered by 3 to 4 degrees.

So how much above normal was it?  Average temperatures were generally 6 to 10 degrees above normal for the month of June.  That is a huge anomaly when considering this is over a 30 day period.
See image below for the graphical depiction.

The heat wave on June 27th and 28th was exceptionally noteworthy with numerous stations setting their warmest June temperature on record.  Here is a map showing some of the observed readings, with some places such as La Crosse, Walla Walla, Lewiston, Chelan, and Omak reaching or exceeding 110 degrees!

Not only was it hot, but June was also dry which has caused elevated fire danger across the region.  See map below showing the % of normal precipitation for June

So what caused this abnormally warm and dry conditions.  An anomalous ridge was in place over the Inland NW causing the record warmth.

This past June was a month to remember.  We'll see what the rest of the summer offers, with the latest long range outlooks from the Climate Prediction Center favoring increased odds of the continued warmth.