Sunday, December 20, 2015

Monday storm

A strong storm will pass through Washington and north Idaho on Monday.  This is a storm that is worth paying attention to and is expected to produce a swath of heavy snowfall as well as windy conditions near the Foothills of the Blue Mountains.  A small adjustment to the storm track could result in big forecast changes depending on where you live.  So keep informed of the latest forecast for your area.

Our current forecast favor the band of heavy snow to set up over the Wenatchee area extending east along the Highway 2 corridor into Spokane, Coeur D'Alene and the Central Panhandle Mountains.  Here is a look at our latest forecast for snow amounts Monday into Tuesday.

A slight shift north in the storm track could give places like Omak, Republic, Colville, and Bonners Ferry more snow compared to what the current graphic shows.  Meanwhile a further north track could give less snow to Moses Lake, Ritzville, and Pullman.  People in these areas should keep a close eye on the forecast.  Let's take a look at what the models are showing for this storm so  you can see what we are talking about.

Here is a look at what the 18z GFS model from today is projecting for Monday.   Note the position of the low as the day progresses.  The image is moisture and the bright green areas represent a high amount of relative humidity which often leads to precipitation in form of rain or snow.  Areas on the south side of the low track will be prone to milder air and windy conditions with highly reduced snow amounts (if any for the valleys). Locations on the north side of the low track will be colder with snow.  Thus narrowing down this track will be critical for snow totals with this storm.

Now there one alternate scenario that is possible.  The graphic below represents the two possible storm tracks for this storm.  The scenario above represents scenario one which is the preferred solution.  However another model (ECMWF) tracks the low further north placing the band of heaviest snowfall further north.

So, everyone with the exception of the Lewiston area and lower portions of the Palouse and Blue Mountain Foothills should be prepared for a significant storm producing heavy snow.  For the Pomeroy and Alpowa Summit areas very windy conditions will be the big story, and are expected to develop late Monday afternoon into the early evening as the low tracks north of these areas.  Here is the wind forecast from 4 pm to 7 pm Monday.  The graphic shows sustained winds but we could see gusts even stronger around 45-55 mph in this area.

Please keep updated with latest forecasts with this dynamic weather system.

Friday, December 18, 2015

Snowy weather ahead

After a very wet and mild start to the month of December, the pattern has changed with storms now coming at the region from the west and northwest.  This will bring several opportunities for snow and the chances of a White Christmas are looking good for most of the Inland NW.  Let's dig deeper into where we are now and what lies ahead.

The first colder storm that tracked through Thursday and Friday has blanketed the region with snow.  Here's an analysis of snow on the ground.

This is just the beginning of the snow.  A storm Saturday night and Sunday will bring light to moderate accumulations.  Here is our forecast as of Friday afternoon for Saturday night and Sunday.

It looks like snow will reach the Cascades Saturday night and then the remainder of Eastern Washington and North Idaho on Sunday.

A stronger storm is on tap for Monday.  Here is what one of the forecast models is showing.

Dec 18th/18z GFS model run valid 10 am Monday showing 500mb height and 700-500mb Relative Humidity
Note the large area of green over the region indicating lots of moisture.  Here is our forecast as of Friday afternoon for snow amounts Monday into Monday night.

This one could bring moderate to heavy snow amounts for most of the area.  Exception could be around Moses Lake, and Lewiston areas where milder air coming up from the south may limit accumulations as rain may mix in with the snow.

The snow that falls is expected to hang around a while as a cooler northwest flow sets up for the middle to end of next week.   Models are showing an upper ridge building in the Gulf of Alaska with a cool trough over the region.  This could bring cool weather and snow showers to the region especially in the mountains.  Here is what one of the model forecasts look like for Christmas Eve.

Dec 18th/18z GFS model run valid 10 am Christmas Eve showing 500mb height and 700-500mb Relative Humidity
And the latest CPC outlooks agree with this cooler pattern.  Take a look at the temperature outlook below valid Dec 24th-28th.

So, after a mild and wet start to December, it looks like the month will finish colder and snowy with a White Christmas for most.

Tuesday, December 15, 2015

Could we really have a White Christmas?

After all of this mild and wet El Nino weather, is it really possible to still have a White Christmas?  Believe it or not, the answer is actually "yes".  And the odds are actually starting to improve.  Let's show you what we mean.

First, let's start with the current situation.  The warm and wet weather so far this month gave us a respectable mountain snow pack, but left the lower elevations with very little snow.  About the only exception to this is in the Cascade valleys and the Waterville Plateau.  Here's an analysis of snow on the ground:

As you can see, not very Christmas-like for much of the populated areas.  Just for comparison, here's the morning satellite image:

MODIS satellite image for 15 Dec 2015

It's hard to tell the difference between the clouds and the snow.  The white areas that have a herring-bone appearance are clouds.  But you can definitely see snow on the Waterville Plateau.  They're looking good for a White Christmas.

So what about the rest of us?  Is there any hope?  Yes, and not from just one storm.  There's actually a series of weather systems during the next 7-9 days that could bring us snow.  The first is tonight.  Here's the forecast of snowfall:

OK, so it's nothing to write home about.  The system is a rather weak one, coming at us from the north.  This flow pattern favors locations south and east of Spokane.  Here's what it looks like on satellite:

IR Satellite image 15 Dec 2015

The lack of clouds over British Columbia shows how weak tonight's event is.  The bigger storm just off the Pac NW coast will dive into California, missing us.  But the one behind it (on the left side of the image) will arrive on Thursday for a good chance of snow.  Here's the expected snow totals from that storm:

Definitely a more respectable storm, and probably the first significant snow for most residents.  Will it last for a week?  For the Palouse and L-C valley, it might not survive the day.  Here's the Friday afternoon high temperatures:

Temperatures around 40 along with some afternoon wind could melt most if not all the snow for Lewiston, Pullman, and Ritzville.  But don't fear.  There are still more opportunities for snow.  The reason is that the overall weather pattern will be changing.  Gone will be our warm and moist flow from the southwest.  Instead we'll be getting air from the Gulf of Alaska.

As we get farther out in time, the details are typically in doubt.  Rather than show you a bunch more maps, let's look at a computer snowfall forecast for Spokane.

You can see the first "bump" of snowfall (on the left side of the graph) will bring 1-2" of snow (probably closer to 1").  The 2nd bump on Thursday night and Friday shows another 3-5" of snow.  Then there's another system on Sunday, and yet another possibly next Tuesday.  

Now, don't go thinking we're going to have 14-18" of snow on the ground by next Wednesday.  Even if (and that's a big "if") we get all of the snow from these 4 storms that the computer is predicting, it doesn't account for melting and compaction.  However, all that said, there is a good chance that by next Wednesday, most locations will have at least some snow on the ground.  How much remains to be seen.

By the way, if you like White Christmases, be thankful this year that you live in the West.  Our friends in the East will be celebrating the holiday week in their shorts.  The trough of low pressure over the western US means a warm ridge of high pressure in the East.  Here's the forecast for next week's temperatures:

You don't typically see probabilities that high.  Above normal temperatures east of the Mississippi next week are a done deal.  Here's the precipitation outlook:

Wet in the West and the Ohio valley.  While we're getting snow next week, the Southeast and Gulf Coast will be getting thunderstorms.  

Buffalo, NY still is waiting for their first 0.1" of snow of the season, the latest that it's ever taken.

Oh, if you're wondering what the historical probability of a location seeing a White Christmas, NCDC has a story on that at:

Here's their results:

We'll update this blog in a few days to see if we're still looking at a White Christmas.

Friday, December 11, 2015

Wet December - Will it continue?

December has been off to a WET start!  Some may be wondering if this will continue through the month.  We will address some of the impressive numbers so far this month and also take a peak into the future.

So, how wet has it been?  Here is a map showing total precipitation from December 1st through the 10th for selected areas.

Quite the impressive precipitation totals especially in the Cascades.  Some locations on the west slopes of the Cascades have received amounts in excess of 10 inches.  It's also been wet in the Idaho Panhandle with Mullan Pass coming in with 6.70 inches, and 5.38 inches in Prichard.  

So how do some of these totals compare to normal?  Well these amounts only cover ten days, so its no surprise that these totals are well above normal.  Take a look at the values below.

So what has caused this abnormally wet period.  The answer is a very strong and active jet stream that stretched across the entire Pacific Ocean which brought numerous storms into the area.  

NCEP reanalysis of 300mb zonal mean wind Dec 1st through Dec 8th, 2015

So what does the future hold in store?  More active weather is in store with the parade of storms persisting.  Let's begin with Saturday...

     18z/11th GFS forecast of 500mb height and 700-500mb Relative Humidity
4 PM Saturday

The bright screen shading on the map is indicative of high moisture content in the atmosphere.  A deep low pressure system is located near Vancouver Island.  This storm is expected to bring snow to the Cascades and northern valleys and mountains.  Locations from Interstate 90 south from Ellensburg to Lookout Pass are expected to see mostly rain in the valleys with snow in the mountains.

So how about Sunday?  

18z/11th GFS forecast of 500mb height and 700-500mb RH 10 AM Sunday
You can see the wet weather continues with the best focus of moisture (with valley rain and mountain snow) over Oregon, Southeast Washington, and Idaho. This day could bring significant snow to the Blue Mountains, Camas Prairie, and Lookout Pass areas.

After this the pattern turns cooler and drier with a potential weak system Tuesday night bringing light snow to the Idaho Panhandle.  But after that models show potential another wet storm on or around Thursday.  

18z/11th GFS forecast of 500mb height and 700-500mb RH 4 PM Thursday
It's too far out to have much confidence in the specifics for this storm, but more rain and snow looks like a good bet.  Beyond this forecast confidence drops, but long range outlooks from the Climate Prediction Center for Dec 19th through Christmas day are favoring elevated chances of wetter and cooler than normal conditions.  

Overall it looks like December is going to finish out much wetter than normal.

Tuesday, December 8, 2015

Another Wind Storm? Not a repeat of 17 November.

Yes, there is another wind storm heading for the Inland Northwest.  But it will NOT be as strong as the 17 November wind storm.  While this event is similar to the storm last month, there are differences.  Let's see in what way.  First, take a look at our blog that we put out before that wind storm.  It's at:

You'll see that we talked about 2 main weather patterns for strong winds.  The November 17 storm was a pattern #2.  Tomorrow's storm will be more of a hybrid between pattern #1 and #2, which is much more common.  In other words, tomorrow's wind storm will be more like what we are used to getting.

For the November wind storm, the surface low that passed by over southern BC was 985mb when it was to our north, and then 977mb in the lee of the Rockies over Alberta.  Below are the surface pressure forecasts for tomorrow's storm.

GFS forecast of Sea Level Pressure for 830am 9 Dec 2015

GFS forecast of Sea Level Pressure for 200 pm 9 Dec 2015
This time around, the low will be about 991 mb over southern BC, and 985 mb in Alberta.  That's about 6-8mb weaker than the 17 November storm.  Also note that the track is slightly south of the storm last month.  This would suggest that the stronger winds will also be shifted farther south than last month.  That's good news for the northern counties (i.e. Bonner, Boundary, Pend Oreille, Stevens), but may be bad news for the southern counties like Whitman, Latah, Nez Perce, Asotin, Garfield, and Lewis.

Also, the jet stream is displaced farther south, over Oregon instead of Washington.  All of this points to a weaker system than November, but still a respectable event that could cause some damage.

Here's the forecast of peak winds:

Comparing this forecast to the previous month, you'll notice that wind speeds are overall weaker by about 10 mph.  The exception to this is in the southeast (Pullman, Lewiston, Winchester), where the forecast is about 10 mph stronger.  So the focus for potential damage will be in those areas.

There is one fly-in-the-ointment to all of this, that wasn't a factor in November.  There is the potential for thunderstorms on Wednesday.  (Yes, this is mid-December.)  We have a VERY moist air mass in place, and the cold front on Wednesday is strong.  This combination could lead to a few thunderstorms.  They won't be "severe".  But, a thunderstorm can bring down stronger winds from the upper levels of the atmosphere.  So any thunderstorms that do form will have to be watched closely.

After the wind on Wednesday, the weather pattern will change to cooler with a better chance for snow in the lower elevations.