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. 

And now for the meltdown...

As we said in our last blog, after this round of snow and cold, the weather is going to warm up. But first, let's take a look at how we did.  Here's the forecast we showed on Friday for the weekend snowfall.  On top in yellow are the snow fall reports we've received.

Snowfall forecast (shading) made on Friday of weekend snowfall.  Yellow numbers represent reported snowfall.

Overall, this was a pretty good forecast.  We had a little too much snow forecast for the Wenatchee/Omak area as well as the Cascade valleys.  The Idaho Panhandle and Spokane area as well as northeast Washington panned out pretty much as forecast.

But now we will have the meltdown.  The cold air that invaded the Inland NW on Saturday is already starting to push out of here.  Pullman is up to 42F on Monday morning, and it's warmed to 32F at Spokane.  It's only a matter of time before the warm air wins.  The Columbia Basin will stay below freezing for an extra day or two.  The last areas to warm will be the northern valleys.  Omak and Bonners Ferry may not see temperatures above freezing until the latter half of the week.

Meanwhile, the parade of Pacific storms will continue.  These storms will bring rain, and lots of it.  We're also going to see a warm southwesterly wind.  The snow that is on the ground in the Spokane/CdA area and the Palouse will most assuredly melt.

Let's look at the moisture from these Pacific storms.  Below is the Integrated Moisture Transport analysis on Monday morning.

Integrated Moisture Transport Mon 3 March

The yellow/red shading represents atmospheric moisture.  The arrows indicate the direction and speed that this moisture is moving.   We can see a good connection of moisture from the Hawaiian Islands to the Pacific Northwest.

Here is the Integrated Moisture Transport forecast for Wednesday afternoon.

Integrated Moisture Transport Wed 5 March

We can see a big system that is reaching the Pacific NW coast at this time.  But also look at the lower-left corner of the image.  There's good moisture coming from the tropics well west of Hawaii, that is feeding into the next system in the central Pacific.

That system arrives on the weekend for more rain.  Here's the Integrated Moisture Transport for Saturday afternoon. 

Integrated Moisture Transport Saturday, 9 March

In other words, we have a lot of moisture headed our way.  Here's the meteogram, showing the computer forecast for precipitation for Pullman, WA.

Precipitation forecast for Pullman, WA

The NAM (in red) and GFS (in blue) both show as much as 1.3" of rain for Pullman by Thursday afternoon.  Often times these computer models over-forecast the rain amounts.  But even scaling back a bit would result in an inch of rain.  You can see on the right side of the graph that there's more rain in store for Sunday, probably on the order of an additional half inch.

We also have a good deal of snow on the ground.  Here's a snow depth analysis:

Snow depth analysis on Monday morning, 3 March

The Palouse doesn't have a lot of snow, but Spokane and valleys to the north and east do.  Granted, the snow on the ground is rather dry, and doesn't have a lot of moisture in it.  There's probably about a 1/2" to 3/4" of moisture in the snow.  Snow that melts will contribute to the flooding threat.  And all of the snow from Wilbur to Spokane and down the Pullman is going to melt, probably by Thursday.  

Our soil is still frozen hard.  Here's the latest 8" soil temperatures courtesy of the WSU Ag Weather network.

8" soil temperatures March 3

So we're still facing the same situation we had in mid-February:  Lots of rain and melting snow will be unable to soak into the ground as it usually does.  The result will be localized flooding.   In this event, water will pond in places that it typically doesn't.

Additionally, we could start to see some of the rivers in the southern Panhandle and southeast Washington start to show rises. 

Another round of Winter

It's not unusual to see some winter weather in the first week of March.  And this year will be no different.  So let's take a look at what we can expect.

Phase 1 is the arctic front.  It will be moving into the Inland Northwest today (Friday).  Here's the University of Washington WRF model forecast temperatures for this morning at 7am.

You can see the coldest air is just north of the US/Canada border, as well as in northwest Montana.  Now look at the forecast for this afternoon:

More blue and purple color.  In other words, temperatures in some locations will be falling today instead of rising.  That happens a lot in the winter for folks in the Dakotas or Minnesota.  Here in the Inland NW though, we typically find this is hard to do.  So temperatures may rise a couple of degrees, but not a lot.

The northeast winds will blow all night and through Saturday.  It will be a rather raw day on Saturday.  Below is the WRF forecast for Saturday afternoon.  Temperatures east of the Cascades will be in the teens with a stiff northeast wind.  Not a good day for outdoor activities.

It will be interesting to watch the temperature at Spokane Airport on Saturday.  The coldest March day in Spokane is 13F, which occurred on March 12, 1906.  At this point, our forecast is for 14F.  So it's gonna be close.

OK, so we'll have plenty of cold air.  But we need some moisture.  And that's Phase 2.  There is a moist warm front in the Pacific headed our way.  Here's the satellite image from Friday morning.

IR Satellite image 1015am PST

The batch of clouds over the West Coast will stay south of us, giving California some much-needed rain.  We might see a little light snow from it on Saturday afternoon/evening, just a dusting if anything.  Our storm is in the middle of the image, south of the Aleutian Islands.  We won't see the entire storm.  But the important part is that band of clouds north of the Hawaiian Islands.  This won't be a true "pineapple express", but similar to it.

That moisture will reach our area late Saturday night.  Snow will start in earnest before sunrise Sunday and continue through Sunday night before changing over to rain on Monday.  

How much snow will we get?  Here's a display of the GFS and NAM forecast snowfall.

The GFS forecasts are in the blue/purple colors, and the NAM are in the red/orange colors. The white lines area averages of the various models. Time goes from left to right.  So you can see that one GFS forecast gives us 14", while a NAM forecast would give us only 3".  That's quite a range.  But it's not unusual.  We often see these kinds of differences in the computer models.   

We've discussed in a previous post on this blog the difficulty of forecasting snowfall.  Even if you get the temperature and moisture forecast correct, the snow ratio can still make a big difference.  A light fluffy snow would pile up a lot more than a wet heavy snow.

Here's our current forecast for snowfall Sunday through Monday morning.

As we saw, there's still a lot of variation in how this event could pan out.

After this event, we will warm up and change to rain.  There is the potential for some heavy rain around Wednesday or Thursday.  This coupled with the melting snow and frozen ground could lead to more flooding problems, similar to what we saw in mid-February.