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.

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