Monday, February 2, 2015

Say Goodbye to your Snow

If you've got snow on the ground where you live, and you're tired of seeing it, you may not have to deal with it much longer depending on your location.  There's going to be a big change in the weather pattern this week.  And the result will be a big meltdown for much of the Inland Northwest.  Here is this morning's snow pack analysis:

There's at least some snow on the ground in many locations.  By this time next week, this map will look very different.  All of the snow at the lower elevations east of Moses Lake will be gone.  The only valleys that will keep their snow will be in the Cascades (e.g. Methow Valley).  Why the big change?  Let's show you what we have coming our way.

Here's the Integrated Vapor Transport forecast for Thursday.  What's that you ask?  It's a forecast that tries to summarize all of the moisture in the atmosphere and combine it with the wind (black arrows).  You might have heard the term "atmospheric river".  It's often over-used, but in this case, it describes what you're seeing below.

Integrated Vapor Transport forecast for Thursday, 5 Feb 2015

This atmospheric river will deliver large amounts of moisture to the West Coast by Wednesday.  What's more, it will continue on and off through at least Sunday or Monday.  In addition to the moisture, the atmospheric river will bring warmth.  The black wind arrows point from south-to-north along the West Coast.  The air you'll be breathing this weekend will come from the sub-tropics (Hawaii is in the lower left corner of the above graphic).  Here's the temperature forecast for this week for Spokane:

The temperature in Spokane will warm into the lower-50s for Friday through Monday. There's a good chance that at least one of those days will be even warmer, say mid-50s.

But there will also be rain with this event.  Lots of rain for some areas.  Here's the GFS forecast of precipitation for the next 7 days at Spokane:

The last 2 forecasts from the GFS have nearly 2.5" of precipitation for Spokane, all in the form of rain.  Typically this model over-forecasts precipitation a low elevations like Spokane, so we don't expect to see this much rain, but it will still be very wet.  That said, here's the same data over the entire Pacific Northwest from the Canadian GEM model:

Precipitation forecast from the Canadian model for Monday 2 Feb through Monday 9 Feb 2015
The forecast from the GEM agrees closely with the GFS.  They show more than 4" of rain for the Panhandle mountains, locally up to 6", with up to a foot of rain for the north Washington Cascades and Olympics. There will be periods of light precipitation for the next couple of days.  The heavy rain will arrive on Thursday and continue through Sunday.  It won't rain every hour of all four days, but there will be several periods of heavy rain.  Notice that we've been using the word "rain" and not "snow".  Even for the mountains, much of this precipitation will fall as rain.  Here's the Weather Story from NWS Spokane showing the rising snow levels:

 So we have warmth, and we have rain.  That will definitely melt some snow.  But the real "snow-eater" will be the wind.  Nothing beats a warm, moist wind when it comes to melting snow.   And it will be windy.  As an example, here's the sustained (not peak gust) computer wind forecast from the GFS MOS for Saturday:

So as we said, the low elevation snow pack should all melt by next Monday, except for the Cascade valleys and parts of the Waterville Plateau (these areas are protected from much of the rain and wind).  The mountain snow pack below 4000' will also take a big hit.  This could lead to some flooding issues in the Idaho Panhandle over the weekend and early next week. 

We'll probably update this blog later in the week as the details of this upcoming event become clearer.  Suffice to say for now that that a big change in the weather is expected.

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