Monday, March 3, 2014

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.