Saturday, February 28, 2015

Update on Snow Chances

In our last blog, we talked about the chances for snow in our area on Monday and/or Tuesday.  Our conclusions were:

  • Any precipitation would fall as snow.
  • The overall weather pattern was not a good one for snow in the Inland Northwest.
  • Not all of the computer guidance agreed on exactly what was going to happen.
Two days later, those conclusions still hold true.  Usually at this point we have a pretty good idea of what's going to happen.  But in this situation, we're still no more confident than we were two days ago.  Here's why.

Here's the GFS forecast for Sunday evening.  The low is way up in northern Canada with a trailing cold front (blue line).

GFS forecast of precipitation (green shading) and sea-level pressure (thin lines) for Sunday evening.

Here's the forecast for Monday afternoon.


GFS forecast of precipitation (green shading) and sea-level pressure (thin lines) for Monday afternoon.


As you can see, the front splits.  Half of it goes into the upper plains while the other half drops down the West coast.  This leaves the Inland Northwest dry, which is pretty common for this kind of storm moving down from the northwest.

Let's look at the Canadian GEM model:

Canadian forecast of precipitation (blue green shading) and sea-level pressure (thin lines) for Monday afternoon


This looks very similar to the GFS model.  The GEM does bring a bit more snow into the Panhandle, but keeps eastern Washington dry.

So why isn't our confidence higher?  Because the ECMWF has a slightly different scenario.  It thinks the cold front will hold together as it passes over our area.  So much so, that it gives about 1-2" of snow to the Panhandle and eastern Washington, east of Moses Lake.

What's more is that each model has been consistent with itself.  Often, we'll see forecasts from the computer models that will change 12 hours later.  In those situations, our confidence is lower.  But in this case, each forecast from each model is very similar to its previous forecast.  So the GEM and GFS insist that the Inland Northwest won't see much from this storm, while the ECMWF continues to insist that we will see 1-2" of snow.  

So, are there any other computer forecast models?  Yes, there are.  Here's the UKMET forecast:

UKMET forecast of precipitation (blue and green shading), sea-level pressure (thin black lines) and 500mb heights (red lines) for Monday afternoon.

You can see that the UKMET has light precipitation over all of Washington.  This is similar to the ECMWF, just lighter on the precipitation.  If this were to verify, eastern Washington might see a dusting of snow.

The SREF model is an ensemble, which means that it's actually a group of 23 similar models.  Here's a display of the SREF forecast snowfall for Spokane:

SREF forecast of snow for Spokane

Of the 23 SREF models, only 6 of them have any snow for Spokane, and only one has nearly an inch of snow.

So given all of this, the odds are slim that eastern Washington will see any snow on Monday.  Not impossible, just not likely.  Thus, the forecast of "a 40% chance of snow showers" for Spokane.  The northern Panhandle has a bit better odds, but still not a slam dunk.

After that, we don't see any significant precipitation for at least another week.








Thursday, February 26, 2015

Is There Snow in our Future?

It's been so long since we've seen snow around here, that most of us have put away the boots and snow shovels for the season.  Is there any chance we'll have to get them back out of storage?  It's not likely, but there is a chance.  Let's take a look.

First, the stage will be set in the next couple of days.  A somewhat weak storm is moving down from the north today (Thursday), but this will largely miss our area to the west.  Some folks are getting some rain and high elevation snow, but mostly it's just clouds.  As this storm moves south of the region on Friday, it will pull down some cold and dry air from Canada.

GFS forecast precipitation (green shading) and surface pressure (thin black lines) for Saturday morning

Saturday  will be a rather raw day, with temperatures in the upper 30s to lower 40s and a brisk north wind.  This new air mass will mean that any precipitation from the next weather system will fall as snow instead of rain.  That next system will arrive Monday and Monday night.  There are three computer models that we look at for the weather 5 days out: the GFS (US model), the GEM (Canadian model) and the ECMWF (European model). 

Here's the GFS forecast for Monday night:
GFS forecast precipitation (green shading) and surface pressure (thin black lines) for Monday night
The GFS shows the majority of the next system sliding down east of the Rockies, which is what most of these storms do.  But you can see that the GFS does indicate some snow making it into the Panhandle and extreme eastern Washington.

Now take a look at the GEM model for this same time:

GEM forecast precipitation (shaded) and surface pressure (solid lines) for Monday evening

Not identical to the GFS, but similar.  The ECMWF (not shown) actually has a bit more precipitation for eastern Washington than the GEM or GFS.  Earlier runs of the ECMWF were showing a more significant storm for the Inland Northwest, but the more recent model forecasts have backed off on that idea.

Unlike storms in December or January, this system will be more spring-like.  What does that mean?  In the heart of winter, our atmosphere is typically very stable.  Snow tends to be more widespread and light.  But in the spring, the surface is warmer while the upper-atmosphere is colder.  This causes a more unstable atmosphere.  The result is precipitation which is more showery but can be heavier.  But it also can be more difficult to accumulate snow on the ground during the afternoon hours.

Temperatures on Tuesday might be rather chilly, with some locations not making it above the freezing mark.  If this happens, it would be the coldest day since January 3rd.

GFS forecast high temperatures for Tuesday March 3rd

Thus, at this point it doesn't look like a widespread heavy snow event.  Rather, some locations in the Panhandle and extreme eastern Washington could see a few inches of snow.  It's too early to have much confidence in this scenario.  In fact, it's more likely that this storm will stay to the east of our area, as they typically do.  

Stay tuned and we'll update this blog in a day or two as the forecast becomes clearer.








Monday, February 23, 2015

Mountain snow at record lows? Any relief in sight?


Many across the Inland Northwest may be wondering if our mountain snow pack is at near record levels and if there is any relief in sight.  We'll answer those questions in this blog.

First, let's look at precipitation in the mountains.  Given the lack of snow pack in the mountains, the assumption might be we haven't had much moisture.  As the image below shows, this is clearly not the case.  All of the Pacific Northwest mountains have received their normal precipitation since the start of what we call the Water Year (October 1st).


So, how does our snow pack look - not good!


Clearly, a good portion of what has fallen in the mountains has been in the form of rain.  This is especially true across the central and southern Washington Cascades, and Oregon.  Much of this rain fell early in the season (October and November) before a snow pack had been established.  There have been more mountain-rain events during the winter as well. 

So, now let's answer the question, is this a record for low snow pack?  Let's break it down by region, starting with Northeast Washington and North Idaho.  Each dot is a SNOTEL site showing where we are at this year compared to normal.  

More simply put...

red = awful snow pack
orange = not good
yellow = a little low on snow
green = doing well




As you can see, the snow pack is not good, and downright awful in spots.  Now, to see if this is a record we need to look at individual sites.  Let's look at Mount Spokane (Quartz Peak) and Lookout Pass.


Blue Line = highest recorded snow pack
Green Line = where we should be
Black Line = this season's trace (2014-2015)
Red Line = lowest recorded snow pack

So looking at the black line (this year's trace), both sites are close to a record low, but not quite there.  It's important to note that SNOTEL data started in the late 1970s and early 1980s.  Thus, the traces for "lowest" and "highest" snow pack ever only go back about 35 years at most.

How about Southeast Washington, it looks very bad.  See for yourself...

Let's look in the Blue Mountains at Touchet...



Also well below normal, just above the record low value.

And finally, the Cascades, how do they look?  The West Slopes are in bad shape.  Mission Ridge area also in bad shape.  Further north however, the mountains surrounding the Methow Valley are doing much better.


Let's see the traces from Stevens and Harts Pass




Stevens Pass isn't looking good, but is above record low value.  Harts Pass in the North Cascades is actually running right where they should be for this time of year.

So, while the snow pack is low this year, most areas are not at record levels.  You may be asking yourself "what's the problem?" since the mountains have received their normal precipitation, just in the form of rain instead of snow.  The mountain snow pack acts like summer precipitation in the western US.  By that we mean, in the West, we don't get a lot of rain in the summer.  But the mountain snow pack acts like rain in the mountains, and keeps our rivers running through the dry summer/fall months.  With a low snow pack, it will likely melt earlier than normal.  This will likely result in low stream flows in the late summer and fall months.  Whether this has an impact (e.g. irrigation, fish, etc) remains to be seen.

The Northwest snow pack typically peaks around April 1st, so we still have about a month to at least ease the bleeding.  Looking ahead, are changes in store?  Yes, but not in a big way.  Here's the GFS precipitation forecast for Thursday night and Friday.

GFS 24-hour Precipitation forecast ending Friday morning

The light green shading represents 0.01" to 0.10" of liquid, which isn't much.  The low pressure system (red L near Portland) is actually moving from north-to-south, meaning that most of the precipitation will stay west of our area.  For the mountains, all of this will fall in the form of snow.  In the lower elevations, the precipitation could be in the form of rain or snow.  But as is typical with spring weather here, snow that falls during the afternoon/evening hours probably won't accumulate.

Looking farther into the future, we get another chance of some light precipitation early next week.  Here's the same GFS forecast for next Monday and Monday night.

GFS forecast of 24 hour precipitation ending Tuesday morning, March 3rd

Again, not a strong storm by any means.  Other models (Canadian, ECMWF) are even less excited about this system.  So there's nothing coming in the next week that will bring much mountain snow.

How about farther into the future?  The 6-10 day outlook isn't encouraging.  Here's the expected temperature pattern:



Just about the entire lower-48 states will be below normal next week.  So that's encouraging.  But here's the precipitation outlook:


The dry weather continues for the western US.  That doesn't mean we won't see any more snow.  The GFS does show some other potential for snow into March.  But suffice to say, the weather pattern doesn't look cold and wet.



Wednesday, February 18, 2015

Rare and Beautiful Clouds Over the Inland Northwest

If you live in Eastern Washington or Northern Idaho and looked up to the skies the morning of February 18, 2015 between 6:30 and 8am, you may have observed a rare and spectacular phenomenon!  This morning, many folks (including us at the NWS Spokane office) couldn't help but be in awe of these amazing clouds.
Photo courtesy of Jon Fox

video

But what are they and why do they form?  

This phenomenon is often referred to as fallstreaks or cloud holes.  Much research has been done on the subject dating back to the late 1950s.  Since this phenomenon is relatively rare, it's easy to conclude that the atmospheric conditions in which it forms are also very specific.  Research has shown that the holes or fallstreaks mostly commonly form in altocumulus or stratocumulus clouds.

After several days of mostly clear skies over the Inland Northwest, moisture was approaching from the west bringing the region a layer of altocomulus stratiformis.  As we do every morning at 3am, we launched a radiosonde that sampled the atmospheric conditions just a few hours prior to the sunrise and cloud punch holes.  This image below shows that sounding.
The area on the sounding circled shows increased moisture where the cloud layer most likely formed a few hours later.  The approximate height of this cloud is at about 400 mb, 7 kilometers, or 23,000 feet.   According to the sounding, the temperature at that layer is approximately -30° Celsius.

On visible satellite imagery, we captured a few images as the sun came up and illuminated the feature from above.
video
So what's the explanation??  I'm going to quote one of many articles and papers that have been written on the subject.  This excerpt comes from an article that appeared in Weather - December 2008, Vol. 63, No.12 by David E. Pedgely.

"These circular (or sometimes cylindrical) holes are formed when aircraft penetrate supercooled liquid cloud layers such as altocumulus.  The passage of the aircraft is believed to produce large numbers of ice crystals, which then grow quickly by the Bergeron-Findeison mechanism in the vapor-rich conditions (water-saturated air is supersaturated relative to ice).  This growth depletes the cloud of water vapor, causing the liquid droplets to evaporate and the formation of a hole in the liquid cloud layer with a visible trail of ice crystals falling out beneath."

"It seems that their most likely explanation is the penetration of shallow, highly supercooled altocumulus clouds by aircraft whose wakes freeze some droplets over a radius of about 100 m.  These ice particles are then spread by wake turbulence over a radius of 1 km or so in about 10 minutes within the cloud, where they grow at the expense of the droplets.  The resulting crystals fall into, and continue to grow in, clear but ice-suspersaturated air, and gravity sorts them into a fallstreak, where a weak downdraft develops through drag and evaporation."

In short, an aircraft traveled directly above or through the cloud layer.  It has been proven that it is not a result of anything the aircraft is emitting, instead it's the sudden and drastic decrease in pressure over the wing or propeller tip that initiates the process of  depleting the cloud and causing the liquid droplets to evaporate.  The result is the appearance of a hole that has been created with trailing ice crystals falling out beneath.

A quick search of aircraft routes this morning show how many flights follow a similar path departing out of Seattle and head east-southeast near the origin of the fallstreaks.  

Many folks also noticed a sun dog (or parhelion) as shown in the picture below to the right of the sun.  This also has to do with atmospheric optics.  The plate-like hexagonal ice crystals falling through the hole refract the light from the sun.  This halo is fairly common with cirrostratus clouds present.


While the cloud hole punch or fallstreak phonemena are rare because of the very specific atmospheric conditions necessary, there are numerous examples available online from around the world.  Many of the meteorologists (including myself) here at the National Weather Service have never seen this in person so we certainly understand the curiosity that this ignited.

The combination of cloud physics and optics can result in stunning scenery.  Here are a few more photos from NWS employees.




Sunday, February 8, 2015

Milky Rain

The February 6th "Milky Rain"

**** Updated on 9 February with additional information at the end of post ****

A Possible Explanation

A highly unusual "milky rain" occurred over much of eastern Washington and Northeast Oregon on Friday, February 6th. Periods of light rain during the morning and afternoon left cars spotted and smeared with a white or grey residue. 


Picture from a Facebook Friend of the NWS Pendleton OR 
Picture taken at the NWS Spokane office 

Picture taken at the NWS Spokane office

It is not unusual to experience "muddy rain" in the Inland Northwest. During the summer months, dirty brown water marks are frequently deposited on our cars. However, muddy rains rarely occur in the winter. And why the unusual milky white color?

Most plausible explanation: A large dust storm in Northwest Nevada occurred Thursday night into Friday. The dust caused traffic accidents and poor visibility in the Reno area. Winds gusting in excess of 60 mph were reported across the northwest Nevada desert. Here are some peak wind gusts documented by the NWS office in Reno Thursday night into Friday.

WIND GUSTS
     LOCATION                                 REPORT
        LASSEN...EASTERN PLUMAS AND EASTERN SIERRA COUNTIES
                JANESVILLE                    62.00 MPH              
                SUSANVILLE  2 NE              66.00 MPH
                ANTELOPE LAKE  5 NNW          70.00 MPH
                PITTVILLE  17 S               73.00 MPH
                HONEY LAKE  15 NE             77.00 MPH
                DOYLE  3 N                    79.00 MPH
                SIERRAVILLE  8 SSE            93.00 MPH

        MONO AND EASTERN ALPINE COUNTIES
                MONO LAKE  1 NW               63.00 MPH
                CROWLEY LAKE  5 W             76.00 MPH
                COLEVILLE  3 E                82.00 MPH
                BRIDGEPORT  4 WNW             91.00 MPH

        PERSHING...CHURCHILL...LYON AND MINERAL COUNTIES
                SILVER SPRINGS AIRPORT        62.00 MPH
                SMITH VALLEY                  63.00 MPH
                YERINGTON MUNICIPAL AIR       63.00 MPH
                LOVELOCK DERBY                64.00 MPH
                SWEETWATER SUMMIT             86.00 MPH

        SURPRISE VALLEY AND NORTHERN WASHOE COUNTY
                FOX MOUNTAIN  12 WNW          60.00 MPH
                LAKE CITY  3 ESE              70.00 MPH

        TAHOE BASIN
                SOUTH LAKE TAHOE  3 SSW       64.00 MPH
                RENO  16 SSW                  134 MPH

        WESTERN NEVADA SIERRA FRONT
                RENO  4 SE                    58.00 MPH
                GARDNERVILLE  4 S             59.00 MPH
                MINDEN-TAHOE AIRPORT          64.00 MPH
                COLD SPRINGS VALLEY  2 W      65.00 MPH
                RENO  18 S                    66.00 MPH
                SPOONER SUMMIT  3 E           68.00 MPH
                GARDNERVILLE  5 E             71.00 MPH
                RENO  5 N                     73.00 MPH
                GARDNERVILLE  5 NNW           73.00 MPH
                WASHOE CITY  2 WSW            77.00 MPH
                NEW WASHOE CITY  3 SW         79.00 MPH
                RENO  9 SW                    82.00 MPH
                VIRGINIA CITY  4 NNW          88.00 MPH
                GARDNERVILLE  5 WSW           90.00 MPH
                E GALENA                        109 MPH

Pay particular attention to the reports from Washoe, Humboldt, Pershing, Churchill, and Lyon counties. These generally sparsely populated counties are part of the "desert of Northwest Nevada" and are experiencing a multi-year drought. Numerous reports of blowing dust came from these counties Thursday night into Friday.


Check out some of the pictures from the Reno Gazette-Journal posted in a Saturday story about the storm that pounded the Sierra Mountains with snow and produced strong winds in western Nevada. Note the milky white or grey color of the blowing dust.

 Reno Gazette Journal

Reno Gazette Journal

Reno Gazette Journal

The white colored soil does not appear to be unique to a small area near Reno. Look at this Google Earth Satellite image. Dry lake beds appear bright white in the northwest Nevada desert and throughout the state.


Google Earth Satellite Image

How does dust from as far away as Nevada get to northeast Oregon and eastern Washington? It would take many hours of a prolonged strong south wind to push dust that far. Below are some images from the University of Washington GFS MM5 weather model. These graphics are tough to read. Our apologies. We may be able to update these graphics with some better ones later.

The next two images are 850 millibar model wind and temperature forecasts. This is roughly 4700 feet above sea level. These images show a constant average wind of roughly 40 knots (46 mph) from 10 PM on Thursday to 7 AM on Friday. This is a period of 15 hours of a constant south wind at 4700 feet above sea level.


10 PM on Thursday:  The small arrows on this graph show show south winds of 30-50 knots over the eastern half of Oregon



7 AM on Thursday:  The small arrows on this graph show show south winds of 30-45 knots over the eastern half of Oregon and up to 50 knots in Washington.



A forecast sounding for John Day (central Oregon) at 4 AM from the University of Washington GFS MM5 shows the wind speed even stronger above 850 millibars...up to 60 knots (69 mph) out of the south/southwest.


How long would it take for dust to travel from northwest Nevada to the Inland Northwest?  Gerlach, Nevada is near some of those dry lake beds in Nevada.
  • Spokane to Gerlach:  Distance - 490 miles
    • 490 miles / 40 miles per hour = 12.25 hours
    • 490 miles / 50 miles per hour =  9.8 hours
  • Pasco to Gerlach: Distance - 380 miles
    • 380 miles / 40 miles per hour =  9.5 hours
    • 380 miles / 50 miles per hour =  7.6 hours
So, if dust were to arrive in the Inland Northwest by mid day Friday, we would expect it to originate in Nevada between midnight and 5 AM. 

What time did the strong winds start in Nevada?  The first wind damage reports started to come into the NWS Reno as early as 925 PM on Thursday night and continued through the night. Here is an excerpt from the Local Storm Report issued by the NWS Reno. High wind reports continued into Friday afternoon.


PRELIMINARY LOCAL STORM REPORT...SUMMARY
 NATIONAL WEATHER SERVICE RENO NV
 1107 AM PST SAT FEB 07 2015

 ..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
 ..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
             ..REMARKS..

 0925 PM     NON-TSTM WND GST 5 N RENO                39.61N 119.82W
 02/05/2015  M73.00 MPH       WASHOE             NV   OFFICIAL NWS OBS

             A 73-MPH WIND GUST WAS RECORDED AT THE NATIONAL WEATHER
             SERVICE FORECAST OFFICE IN NORTH RENO.

 1255 AM     NON-TSTM WND DMG 2 SW SOUTH LAKE TAHOE   38.92N 120.01W
 02/06/2015                   EL DORADO          CA   LAW ENFORCEMENT

             12 INCH DIAMETER TREE BLOWN DOWN.

 1256 AM     NON-TSTM WND GST 3 SSW SOUTH LAKE TAHOE  38.90N 120.00W
 02/06/2015  M64.00 MPH       EL DORADO          CA   ASOS           

 0431 AM     NON-TSTM WND DMG 2 ENE SOUTH LAKE TAHOE  38.95N 119.95W
 02/06/2015                   EL DORADO          CA   LAW ENFORCEMENT

             30 INCH DIAMETER TREE BLOWN OVER.

 0445 AM     NON-TSTM WND DMG 4 SW SOUTH LAKE TAHOE   38.90N 120.04W
 02/06/2015                   EL DORADO          CA   LAW ENFORCEMENT

             6 TREES BLOWN OVER.

 0450 AM     NON-TSTM WND GST 16 SSW RENO             39.32N 119.94W
 02/06/2015  M134 MPH         WASHOE             NV   MESONET        

             A 134-MPH WIND GUST WAS RECORDED AT THE TOP OF SLIDE
             MOUNTAIN SOUTHWEST OF RENO.

 0545 AM     NON-TSTM WND GST 5 WSW GARDNERVILLE      38.91N 119.83W
 02/06/2015  M70.00 MPH       DOUGLAS            NV   TRAINED SPOTTER

             A TRAINED WEATHER SPOTTER REPORTED A WIND GUST OF 70 MPH.


 0550 AM     NON-TSTM WND GST 9 SW RENO               39.45N 119.94W
 02/06/2015  M82.00 MPH       WASHOE             NV   PARK/FOREST SRVC

             AN 82-MPH WIND GUST WAS RECORDED AT THE GALENA RAWS
             SENSOR.

Other explanations for the blowing dust have been "floating around". Excuse the pun. Here are a few of them.

Volcanic activity in Russia. Maybe, but concentrations of ash would probably be only trace amounts given the distance required to get here. You would also expect western Washington and western Oregon to have reports of "milky rain" in this scenario.

Ash from burn scars in the Western U.S.  Another maybe. Burn scars are relatively small compared to the Nevada desert, so the source region would be limited. Burn scars in northern California, central Oregon and western Washington have received an abundance of moisture recently. Northwest Nevada has not. Soggy or snow covered ash will not blow around like dry ash or dust.


Observed 60 Day Rainfall from water.weather.gov


60 Day Percent of Normal Precipitation water.weather.gov




Thursday, February 5, 2015

How unusual will this next episode of warm and wet weather be for the Inland Northwest?

By now you have likely heard that this is going to be a wet and warm remainder of the week across the Inland Northwest. This wet spell of weather is expected to continue into early next week. So why is this? Well, most of it can be attributed to yet another atmospheric river event. While most atmospheric rivers come and go, this event will be a little different, as we will likely be impacted by a trio of rivers. The first arrived yesterday into last night. The next is expected to unleash its torrent of moisture on Friday and the last will likely impact the region on late Sunday. The video below shows the expected sequence of events. The atmospheric rivers are denoted by the blue, purple and red colors



So what does this mean for the area. Well, it will translate to several things. The most obvious is it will result in very wet weather. Here's the estimated rainfall we are forecasting between today and Sunday night.

Rainfall forecast between today-Sunday night
These are some pretty hefty totals. Notice the reds and oranges spread across the Cascade Crest and extreme northeast Washington/north Idaho. These locations could potentially amass a few spots of 3-6" of precipitation, most of which will fall as rain. While these amounts are impressive, the question is just how rare are they? We get atmospheric rivers all the time this time of year. Certainly it can't be that unusual, can it? Well, if put into perspective for the time of year and amount of precipitation it actually turns out to be a very rare event. One of the new tools in our weather toolkit consists of quantifying an event based on climatology. In other words, how common is a weather event for a given time of year? For this event, we will look at the amount of rainfall expected over a 3-day period (between today-Sunday). Below you will see an image from one of our ensemble models showing the approximate amount of precipitation (black contours or isohyets) combined with the rarity of the forecast amount (the color shading). What's interesting, in this case, is northern California is covered with isohyets in excess of 3 inches, while over the Inland Northwest we see a small area of 1.5"-2+"  inches over extreme northeast Washington and north Idaho (the amount is smoothed and will not catch the locally higher amounts we forecast over the mountains). Despite the lighter rain totals over our neck of the woods, it's actually a less common event as shown by the blue and dark green shading. The blue shaded areas are locations where this event places in the 99.9 percentile (or 1 out of 1000 events)  for all rainfall events between December 22 and March 22nd (between 1985-2012). The dark green shaded areas, which cover a good portion of the Inland Northwest represent a 99.5 percentile event (1 out of 500 events). So technically speaking we will experience the most unusually heavy precipitation in the western US this weekend.
Ensemble precipitation forecast (Thu-Sun) combined with the relative rarity of the amount.
The other unusual weather phenomena we are expecting this weekend will be the warmth. If we once again choose to utilize a percentile ranking of the warmth for this event it's rare, but nowhere close to as rare as the rainfall. Here's a look at the forecast temperature and the respective percentile (for the period between January 27-February 17)  for the temperatures at 850 mbs (around 4500' above sea level) on Friday afternoon. The image below is showing temperatures in the lower to middle 40s (4-6°C)  pale yellow which indicates roughly the 90th percentile (1 out of 10 events). So really it's not rare at all. Temperatures at this level will be significantly cooler than what we experienced on the 25th of January when our 4500' temperature surged into the lower to middle 50s.

Climatology rarity of 850 mb temperature for Friday afternoon (2/6/15)
What will make this an unusual event though is the duration of the mild temperatures. Right now for the Spokane area we are forecasting 4 consecutive days of high temperatures right around 50° (see image below). The last time we saw that many 50°F or warmer days between December and early February (2/10) was in 1963! The longest stretch on record is 6 days set in 1917. A 3-day stretch of low-temperatures of 40°F or warmer is also rare for this time of year. Between tonight and Saturday night, we are forecasting lows at or above that mark. Surprisingly, the last time we saw three nights of lows ≥ 40°F was earlier this winter (in early December). Before that, we had only seen 3 or more consecutive nights of 40°F or warmer lows 7 times since 1881.
7-day outlook for the Spokane area Thursday (on left) through Wednesday (right)
Just the latest chapter in what has been an unusually mild and relatively snow-free winter.