Odds of a White Christmas - Update #1

 As we discussed in our previous blog about White Christmas, the odds are typically low in an El Nino winter, and this one is no exception.  That said, if Christmas arrived tomorrow, a fair number of you in the Inland NW would consider it a successful White Christmas.  I'll show you two maps.  The first is actual observations of snow depth on the ground, taken by observers just like you. It shows for those locations that reported, a few inches of snow are still on the ground across the northern valleys and even in spots of the Spokane/CdA metro area.


The second is a computer attempt to display these observations along with other data.  After taking a drive yesterday, I can tell you that the gray area in the map below is pretty spotty when it comes to snow cover.


So how does the forecast look for getting more snow, or at least holding on to the snow we currently have?  The odds aren't great, but there is a ray of hope.

The next chance of precipitation will arrive around Tuesday.  The atmosphere will be rather warm aloft, but dry.  This means that precipitation could start off as snow Monday night but will probably change to rain on Tuesday.  This is a fairly weak system so we shouldn't get a lot of precipitation out of it.  Probably 0.10" to 0.20".  Temperatures will be warm, but we won't get any wind.  So all that said, it probably won't wash away all of your snow.

After this we get a short break in the weather.  During this time, the atmosphere aloft cools a bit.  Let me show you.

Here's the temperature at an elevation of about 5000' on Tuesday. The only place with temperatures below freezing is the Methow Valley.  Everywhere else is pretty mild.  This is the reason we'll see rain on Tuesday.


Now here is the forecast for next Saturday, two days before Christmas.  See the difference?  The entire Pac NW is below freezing at 5000 ft elevation.  This is good news for snow chances.  Does it guarantee snow?  Unfortunately no, but it is a needed ingredient.


Will there be any storms moving through during these pre-Christmas days?  The odds are low, but not zero.  I'll update this blog in a few days to hopefully give more precise odds.






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