When Does Summer Start in the Inland Northwest

OK, you're looking at the calendar and at the weather outside.  It's June 17, and the temperatures are in the 50s with cloudy/rainy weather.  In most locations, those weather conditions aren't typically found in mid-June.  But in the Inland Northwest, it's not that unusual.

Temperatures at 346pm on 17 June 2014

The culprit is a large area of low pressure that slowly moved across our area.  It's now east of us, but the moisture often wraps around these slow moving lows.  So our rain and clouds are actually coming from Montana.

Infrared Satellite image at 3pm 17 June 2014

This kind of weather leaves folks wondering if summer will ever arrive.  Which leads to the question:  When does summer start?

If you look at your calendar, you'll see that June 21st is the first day of summer.  But in reality, that's just the longest day of the year.  It doesn't mean that meteorological summer has arrived. Try telling folks in Phoenix, Arizona who have been seeing triple-digit temperatures since early May that it's still Spring.  It's kinda silly to think that a season will start on the same day for all locations, Miami to Anchorage.

Meteorological summer is defined as the months of June, July, and August.  This is a little better than the calendar definition.  But again, not very realistic to apply to all locations.

So how do we define summer in the Inland Northwest?  We could come up with any number of measures (e.g. average temperature, hours of sunshine, etc).  But in general, we define summer as being from the 4th of July to Labor Day.  Now of course, in any given year, we can see hot weather in May and June.  But these warm spells typically are only for a few days, and are often followed by a rather cool period.  July and August are more likely to be dominated by warm-to-hot weather, with a few cooler spells occasionally thrown in.

The chart below shows the percent of days that the daytime high temperature is colder than 70F.  As you can see, there's still a fair number of days in late June (20-30%) that don't reach 70F.  But by early July, those cool days become very rare, less than 10% of the time.  Conversely, by the end of August, we're already starting to see an increase in sub-70F days.  In other words, summer in the Inland Northwest is about 2 months long.

Percent of Days at Spokane Airport where Max Temperature < 70F

Our temperatures are going to rebound rather quickly though.  Here's the forecast for the next 7 days.  By Friday we'll be approaching 80F, and mid-80s by Sunday and Monday.  These past few cold days will be a distant memory.

7 day temperature forecast of Spokane, WA

Severe Weather Tomorrow??? It's a Possibility.

We have all heard of the calm before the storm, today could be just another chapter in that book. This afternoon will feature highs in the 70's and 80's under mostly sunny skies. Come tomorrow the chance for showers and thunderstorms will be on the rise as an area of low pressure approaches the Inland Northwest. Temperatures will continue on the warm side of normal, but increased moisture will push ahead of the low pressure center increasing our chances for convective activity or thunderstorms. In this post we will evaluate the chances for thunder around the region and the potential timing through various weather maps and products.

So lets start out with today and move forward from there. Our current pattern has a ridge of high pressure directly over the Inland Northwest keeping conditions calm and pleasant. The ridge also allows for warm southwesterly flow to advect into our area bringing above normal temperatures today. We will take a look at the current set up in the following image.

 11am PDT Infared satellite map with 500mb heights

From the image we can see the area of low pressure to our west and the current ridge over us. The ridge is also diverting much of the cloud cover to our north. As the low slowly moves onshore the ridge will continue to be shifted to the east allowing clouds to move east of the Cascades. Not only will this bring increased cloud cover for tomorrow afternoon, but also increased moisture through the atmospheric column allowing better instability. So lets take a look at the increased moisture moving in. This can be accomplished in a couple of manners, but we will look at Precipitable Water or PWATs in the atmospheric column.

Precipitable Water values from 11am today (left image) and 5pm Thursday (right image)

The images above show the increase in atmospheric moisture from today to tomorrow from the North American Model (NAM). For much of the Inland NW we will see an increase of nearly a quarter of an inch of precipitable water. Another method to address the amount of moisture would be the change in forecast soundings which show temperature and dewpoints up through the atmosphere. Next we will examine the forecast soundings to see the change in moisture from today to tomorrow.

NAM forecast soundings from 2pm today (left image) and 2pm Thursday (right image)

From the sounding you can see the major differences in the amount of moisture present. The red line would indicate the temperatures and the green indicates the dewpoint which reflects the amount of moisture in the atmosphere. For the left image a dry layer is noted around 500mb (where the green line moves away from the red) whereas for tomorrow (right image) much more moisture is present (green and red lines are closer throughout the image). So from these two examples the change in moisture can easily be noted, but will we have the instability to promote the thunderstorms? We will now at these parameters that promote thunderstorms.

For thunderstorms to occur, many things need to be present including lift (forcing), moisture and instability (atmospheric stability). We will first look at the lift for the area and the one way to do this is to compare from today's conditions to tomorrow. Below is an image looking at the Q vector convergence in the upper atmosphere or Div-Q. Div-Q is a generalized way to assess the lifting potential in a portion of the atmosphere.

Upper level Div Q from 11am today (left image) and 5pm Thursday (right image)

From comparing the images we can see the major differences concerning forcing. Tomorrow the low will move onshore bringing a good amount of forcing ultimately aiding in thunderstorm development. With the right image being for 5pm tomorrow, we will most likely be looking at a case that will unfold more in the late afternoon and evening hours rather than early in the afternoon. Would this be a good or a bad thing with it unfolding in the evening? For now it looks good. We have been hitting our high temperatures in the late afternoon/early evening which would be the best time for the stronger storms, so this would also would aid in thunderstorm development. We have already looked at the moisture profiles for the area and have concluded that higher amounts of moisture will be in place. Finally we will look at one of the convective parameters that are normally consulted to address thunderstorm potentials which is CAPE or the Convective Available Potential Energy. First we will once again look at the NAM model. It has been the most aggressive when it comes to CAPE values, but paints a similar picture to the others as to the areas with the best chances for seeing thunderstorms.

NAM CAPE values for 5pm Thursday

From the NAM we can see a broad area with values surpassing 1000J/kg and localized areas greater than 1500J/kg (blue and green shading). If you remember around a week ago on the afternoon of June 3rd we had thunderstorms for much of the area. These storms were also working with around 1000J/kg of CAPE. With the NAM being on the upper end of model perspective lets take a look at another one. Next we will examine the model often used by the Storm Prediction Center (SPC) in Norman, OK which is the SREF or the Short Range Ensemble Forecast.

SREF CAPE values for 5pm tomorrow

Although not as colorful as the NAM, the SREF is also showing higher values for eastern Washington and into the Idaho Panhandle. It also has peak values in the 1000J/kg to 1250J/kg range. So we do have some consistency among short range models of the potential for higher amounts of CAPE. So with all of this in mind, now comes the million dollar? will we see thunderstorms and if so, how strong will they be? Concerning the chance for thunderstorms, it is a given. We will see thunderstorms tomorrow. The next question is where? As we can see, the best forcing will be in the eastern third of Washington and the Idaho Panhandle so these are the locations with the best chances. We do not want to omit the chance for the east slopes of the Cascades or the Basin, but the threat will not be as great as the other locations. From the SPC, they create a calibrated outlook of the thunderstorm chances for a location so lets take a look at what they think.

SPC calibrated thunderstorm probabilities between 5am-5pm Thursday

So from the SPC, they highlight a 40% chance for much of northeast Washington into the Idaho Panhandle.  These are some of the higher values I have seen from this for our area so it would lead me to think the chance for thunderstorms is essentially a slam dunk.  Finally the big one.....will any of the storms be severe? Here at the office we seem to think the potential is definitely there for strong storms. Comparing to last week, we had similar CAPE values, but tomorrow we actually have better dynamics to support storms. The SPC also does a product for the chances of severe storms and here it is.

SPC severe thunderstorm probabilities for 5pm Thursday

While the chances for severe storms do not look very high, they still highlight the potential for portions of the area. This product usually only has slight chances for us when severe events do occur, so the potential is there. The region will want to keep an eye on the skies tomorrow as active weather looks to be a given.

Memorial Day Weekends in the Inland Northwest...Nice or Not?

 Now that Memorial Day is approaching, our most common question we get at the National Weather Service is "what's the weather going to be like this weekend?" After all, this is the start of the summer camping season for many of the denizens of the Inland Northwest. Before folks hear the answer, they often have the preconception that weather in this part of the country really doesn't become conducive for prolonged outdoor activities until early July. With that notion in mind, we decided to take a climatological glimpse of what Memorial Day weekends in the past truly delivered.

Usually looking up weather over holidays is easy. The 4th of July always falls on the 4th day of July, and Christmas always falls on December 25th. For Memorial Day though, the days varied from year to year, however before 1971 and the passage of the Uniform Monday Holiday Act, Memorial Day always fell on May 30th. Consequently, what constituted the Memorial Day Weekend isn't exactly clear. To make things simple we decided to only look at Memorial Day Weekends from 1971 and beyond. These dates can range from May 23rd through May 31st.

First what is the normal weather like for this period? Lets begin by looking at the mean 500 mb (18k ft MSL) maps. Sure enough, moist southwest flow typically is still pointed at western Washington and the Cascades. Meanwhile there is a ridge that sets up just west of the Continental Divide along the Alberta-British Columbia border extending into central Montana.

500 mb mean map 5/23-5/31

That map alone suggests the region still might be prone to wet weather so what are the climatological temperatures and chances for precipitation for this time of year? We will start by looking at data for Spokane. But knowing that many people like to get away from the metro area and go camping in the woods, we also decided to look at the weather at the Priest River Experimental Station in north Idaho. Here's a map of where that station is located

And here are the averages:

So not bad. An average high around 70°F with rain expected on roughly 1 out of 4 days doesn't sound too terrible. But that's climatology. Now here's reality. Lets start on a positive note and look at the top 10 warmest Memorial Day Weekends. Here is the list for Spokane.

Top 10 warmest Memorial Day weekends for Spokane. 

For those who like warm and dry weather, the holiday weekend in 1983 was hard to beat. Average highs were above 90° and every day was dry. In fact of the top 10 warmest holiday weekends, 7 of them were bereft of precipitation. At Priest River, the results were similar as far as temperatures. 1983 was the year of the warmest and driest conditions. However note that only 60% of those weekends were dry, and one of those weekends (1985) saw rain on every day.

Top 10 warmest Memorial Day weekends at Priest River experimental station. 

Now let's look at the list of least desirable Memorial Day weekends. For Spokane there were 5 extended weekends which saw the average temperature stuck below 50°F or roughly 10°F colder than normal. The worst year (by temperature) was 1975, however the rainfall that year was light (there were trace amounts of rain which fell on 2 of the 3 days). Perhaps 1989 could be considered a worse year for outdoor activities considering an average temperature of 48°F and just over an inch of precipitation.

Top 10 coldest Memorial Day weekends for Spokane. 

For Priest River, the bad weather Memorial Day weekends were  worse than what was experienced in the Spokane area. 1977 was the coldest year, by far with an average temperature just below 45° although that year was dry. Campers in north Idaho certainly woke up to frost on their tents as lows dipped to 30° on two of the three mornings. From a comfort standpoint, the worst weekend might be the one in 1994 with an average temperature about 8° cooler than normal and measurable rainfall on each day.

Now lets look at a few daily extremes:

Hottest High Temperature: Spokane     94° (May 29, 1983)
                                              Priest River 91° (May 24, 2003)

Coldest Low Temperature: Spokane 35°* (May 26, 1991, *last of several occurrences)
                                               Priest River 29° (May 30, 2011)

Wettest Day:   Spokane      0.79" (May 28, 1988)
                         Priest River  0.96" (May 29, 2010)

Wettest Weekend: Spokane 1.20" (May24-26, 1997...it rained all three days)
                                 Priest River 1.58" (May 29-31, 2010...it rained all three days)

Percent of entirely dry Memorial Day weekends: Spokane 19%
                                                                                  Priest River 23%

This last tidbit is a little unexpected since Priest River is typically a wetter location than Spokane. The answer may lie in the fact that the Spokane observation is taken at least once an hour through the day, whereas the Priest River one is taken once a day. Thus if a trace of rain fell at sometime during the day and it wasn't witnessed it might be recorded as a dry day. Nonetheless, the odds of seeing an entirely dry Memorial Day weekend in the Inland Northwest (especially the eastern third of it) is not good.

Will this weekend be one that sees dry and warm weather? Looking at the latest weather maps, the answer is a resounding no. Here is our latest forecast issued at 3pm today (Tuesday 5/20)

For Spokane it looks like at least a 20% chance of precipitation each day with temperatures cooling to right around the seasonal normals.

Spokane Outlook

For north Idaho things look a little cooler and a little wetter.

Sandpoint outlook...Priest River graphs are not available

Based on the temperature and precipitation forecasts this does not look to be a top-10 Memorial Day weekend weather-wise.

Big Warm up after a Cold Weekend

We just finished up a rather chilly weekend for late April.  Snow fell in the northern valleys on Sunday morning, and thunderstorms rumbled through the area on Sunday afternoon, following by a few snow flakes Sunday night.  But if you're looking for warmer weather, your wish is about to be granted.

Here's the forecast high temperatures for Monday:

The cool weather (blue and green colors) are largely confined to the western US, while the southern and eastern states have warmer weather (yellow and orange colors).  But then look at what will happen by Friday:

The map is flipped.  Now warmer weather is found in the western US, while the eastern US will experience a cool-down.  This isn't unusual.  What's happening in one half of the country is often opposite of the other half.


Here is a meteogram of forecast temperatures for the next 7 days at Spokane Airport:

The various colored lines are forecasts from different computer models.  The green line is the official NWS forecast.  As you can see, Monday through Thursday will see a warming trend of about 7 degrees each day.  So, Monday's high should be about 55, Tuesday 62, Wednesday near 70, and Thursday into the mid 70s.  The NAM model (in red) is actually going for a high on Thursday close to 80F.

Now technically Spokane hasn't seen it's first 70F day yet this spring.  On April 8th the airport topped out at 69F, while most other sensors in the metro area reached 70F or better.  While Wednesday will be close, Thursday is a slam dunk as far as having our first 70F day of the spring.  So you're probably asking yourself, is this first 70F day early or late this year?  Well, here's the statistics:

Average:  17 April
Earliest:      9 March 1889
Latest:      21 May 1896

Thus technically, we'll be later than normal for our first 70F day (by 15 days), but nowhere close to the record of 21 May.  And since you maybe wondering what the numbers are for the first 80F day at Spokane, here they are:

Average:  12 May
Earliest:     7 Apr 1977
Latest:      22 Jun 2011

So on the outside chance that we actually reach 80F at Spokane with this warm-up, it would be ahead of schedule by about 10 days.

Severe thunderstorms tomorrow? It's possible.

After a seemingly endless barrage of weather systems, yet another is already beginning to show its stripes. Take a look at the satellite picture below. This is a water vapor image.Notice the green area covering the western portions of Oregon and Washington. That's associated with a plume of sub-tropical moisture which should deliver rain (and high mountain snow) to most of the Inland Northwest between tonight and Thursday morning.  Also notice the dark area over the eastern Pacific and the kink in the blue lines located along 130w. This is associated with a fairly vigorous shortwave trough. This trough will become a crucial player for our weather across the Inland Northwest by tomorrow afternoon.

10pm PDT Water Vapor image and 500 mb heights

So as mentioned before we expect widespread rains (and mountain snow) tonight into early Thursday. This will likely prime the atmosphere full of moisture and could set the stage for some active weather tomorrow afternoon across portions of the Inland Northwest. Lets look at some model data for details. First we will start with a course resolution model, the 90km GFS. Here's a look at what that models is showing as far as the shortwave trough moving through the region. The first image shows the previously displayed 500 mb heights combined with what we term Q-Vector convergence. This is a fancy term that essentially shows upper level lifting. In this case the purple shading shows where the lifting in the upper levels is strongest. The top image shows the trough extending from the central Washington Cascades to the SE corner of Washington around 11 am with the best upper level lifting focused over most of the region. The second image shows the same thing only at 5 pm. Notice by this time the trough is focused along a line from Sandpoint to Missoula, however the strongest lifting by that time has shifted into eastern Montana and SE British Columbia. That's all well and good but what does that translate to weatherwise?

11am PDT Thursday 500 mb heights and Q-vector convergence

5pm PDT Thursday 500 mb heights and Q-vector convergence

Lets take a look at one more 90km GFS image before moving on. This time we will look at CAPE values. CAPE or Convective Available Potential Energy is simply the amount of potential energy that can be released should we be able to lift an air parcel. You can read more about it here if you desire. Suffice it to say, the higher the CAPE values there more energy or explosiveness there is in the atmosphere. So what is explosiveness tomorrow afternoon? Its actually fairly impressive at least for this region and this time of year. Notice the axis of the highest CAPE values extend from the NE corner of Washington southeast toward the Clearwater Mountains southeast of Lewiston. Keep in mind this area of instability coincides with the passage of the shortwave trough and upper level lifting...a good thing for producing thunderstorms.

CAPE forecast for 5pm Thursday

The parameters shown above are what we meteorologist have looked at for many years, however we are now also getting more refined and specific data from finer resolution models and simulated radar data. So what is this newer model data showing? Its actually quite interesting. Here a look at simulated radar for 5 pm Thursday that was run 42 hours previously (at 11 pm Tue). Notice over NE Washington and the SE corner of Washington there are a pair of bright orange and yellow cells. This model was suggesting that there could be thunderstorms over this area. We see this a lot from the finer resolution models but often can't put a lot of faith in them unless there is some consistency.

Simulated 42hr Composite reflectivity (radar) from 11pm Tue Model run

 So has there been consistency? Lets see the next model run. This one was run 6 hours later and sure enough there are the two yellow and orange areas over NE Washington and a slightly larger one over SE Washington.

Simulated 36hr Composite reflectivity (radar) from 5am Wed  Model run

So that gives us some confidence. Now how about the latest model run? If you look at the image below you can see that the information isn't  quite as convincing as the previous two but it still showed two yellow and orange areas in the same general vicinity. Interesting. So is this enough information to convince us that we will see severe thunderstorms tomorrow afternoon. Probably not, but it does at least hint at a possibility of it. Our confidence is much higher that we will see some thunderstorms...a few of which will produce hail and possible some gusty winds. If the latest models were showing what we see depicted from northern Louisiana toward northern Illinois our confidence would be much higher!

Simulated 24hr Composite reflectivity (radar) from 5pm Wed  Model run

Will the Weather let us see the Lunar Eclipse?

In case you hadn't heard, there's a lunar eclipse coming up.  It will occur on Monday night.  You can read more about it at:

http://eclipse.gsfc.nasa.gov/OH/OH2014.html#LE2014Apr15T

Here's a great figure from http://www.MrEclipse.com  that shows the lunar eclipse times for those of us in the Pacific Time Zone:

So as you can see, the moon will start to disappear around 11pm PDT.  Complete eclipse will take place between 12:07am and 1:25am, or 0707 to 0825 UTC.  The moon will be high in the sky for this eclipse. 

The question then becomes, will we be able to see it, or will clouds get in the way?  The answer isn't a slam dunk either way.  Here's one graphic that we look at when making forecasts for a single point.  It shows the forecast relative humidity in the atmosphere for the next 3 days at Spokane.  The horizontal axis is time (increasing time goes from right to left), and the vertical axis is height.  We call it a time-height chart.

NAM Time-Height of RH at Spokane, WA

The time window of the eclipse is shown with the red lines.  Higher RH (green shading) means clouds, while brown shading indicates dry cloud-free air.  As you can see, we'll have some clouds on Saturday and Saturday night.  But then Sunday will be very dry with abundant sunshine.  For Monday, a few high clouds will move over.  By the time of the eclipse, more clouds are moving into the region.  In other words, it's gonna be close.

Let's look at another kind of forecast from the University of Washington WRF model.  In these graphics, they attempt to take the computer forecast and make it look like what a satellite picture would look like.  Areas of white are clouds, dark colors are the ground.  Here's the forecast valid at 8pm Monday evening:

WRF cloud cover forecast for 8pm 14 April 2014

Note the well defined band of clouds extending from southern BC, across eastern Washington and Oregon.  But then there's a break in the clouds over central Washington, with more clouds over western Washington.  Now let's look at the forecast for 11pm, which  is when the eclipse starts:

WRF cloud cover forecast for 11pm 14 April 2014

We can see that the features in the previous forecast have all translated eastward.  Now the Idaho Panhandle has the clouds, eastern Washington is in the clear slot, with more clouds coming over the Cascades.  And the forecast for 2am, at the end of the eclipse, looks like this:

WRF Cloud Cover forecast for 2am 15 April 2014

Most of eastern Washington has clouds, while the Idaho Panhandle is now in the clear slot.

So what does all this mean?  All indications are that there will be some high wispy clouds on Monday evening around sunset.  There could be a break in these clouds at about the time of the eclipse, depending on where you live in the Inland Northwest.  Thicker clouds are expected to move into the region later in the night.

All of this said, it's a bit far into the future to trust the computer forecasts for this detail.  It won't take much for the weather system responsible for these clouds to wind up being 3 hours faster or slower than depicted here.  At this point, it's a safe bet that it won't be a completely clear sky, but the clouds might be sparse enough and thin enough to still get a good viewing of the eclipse.  And if it turns out that the clouds are too thick, well, we only have to wait until October 8th for the next lunar eclipse.

Unusually wet February and March

Greetings folks, sorry it's been a while since we last posted to this blog, but we have been focused on implementing a new computer system for our office used to compose our complete suite of products and weather grids. Now that we have gotten our feet wet, it's time to discuss the unusually wet February and March the Inland Northwest endured.

So the weather pattern that took a dramatic shift in February unexpectedly continued into March. What was the cause? Recall that a highly anomalous ridge was fixed over the extreme eastern Pacific through the first half of the winter. Here's what it looked like on a 500 mb chart (approximately 17-18k ft). Notice the strong buckling in the flow just off the west coast. This is rather unusual and resulted in almost a record breaking dry spell for the first half of a winter.

500 mb mean map for 10/1/13-1/15/14

Well as the calendars changed to February, the unrelenting ridge gave way and opened the doors to countless storms which surged through the Pacific Northwest for the following 2-month period.
The mean 500 mb charts for February and March exhibited this ridge flattening.

500 mb mean map for 2/1/14-3/29/14

Notice although the ridge is still present (albeit flatter), its actually a much more favorable setup for precipitation since the amplitude of the ridge allows sub-tropical moisture to be wrapped into passing weather systems. Here's is what the anomaly of the atmospheric moisture (called precipitable water) looked liked for the period. Notice the well defined connection of moisture extending from southwest of the Hawaiian Islands northwest to the coast from northwest California to southern Washington (red, orange and green shading).

Precipitable Water Anomaly 2/1/14-3/29/14

So how wet was the two month period? Very was the answer. The map below shows the departure from normal of precipitation for February and March. Every location saw wetter than normal conditions, with the Cascades and Idaho Panhandle mountains leading the pack with well over 10" more than the normal amount of precipitation.

Rainfall departure from normal February & March 2014

From a percentage standpoint vs. normal it was also an impressively wet period. Note the dark blues and purples over the Cascades and north Idaho mountains, indicating where precipitation amounts were 2 to 4 times the normal for that period.

Rainfall % of normal February & March 2014

The unusually wet period has also brought the snow water equivalent (amount of water in the mountain snow pack) to normal or just above normal over the entire region. Note that although conditions were moist over Washington, Idaho, and western Montana, things were still quite dry across Oregon and California (not shown).

Not only did a considerable amount of precipitation fall, but it also did so on an unusually high number of days. Here's a look at the numbers compared to the normals.

Days of measurable rainfall for various locations across the Inland Northwest Feb-Mar 2014

Over locations where the temperature was cold enough, most of this equated to snow. In Holden Village, WA the snowfall for the two-month period was 180.7". That shattered the old record of 166.7" (set in 1999). Not quite as impressive was the 14.0" which fell in Lewiston, ID. This was the most since Feb-Mar in 1985.

So will this unusually wet weather continue? Showers are still fairly common this time of year. In Spokane we typically see some precipitation about 50% of the time during the first half of April. That number drops to around 40% of the days by the end of the month.  In Wenatchee and Moses Lake, the percentage of wet April days is a mere 25%!

The 8-14 day outlook for precipitation shows near normal conditions for most of eastern Washington and north Idaho.

8-14 day precipitation outlook.