An Unusually Strong Cold Cold Front Is Moving Through The Northwest

Over the eastern U.S., the passage of a strong cold front, with a rapid decline of surface temperature, is a frequent winter treat.

In contrast, here in the Northwest, low-level cold fronts are generally weak because the cold air, starting over Alaska and vicinity, passes over relatively warm water.  To illustrate, the current water temperatures (in °C) today are shown below.

The water is well above freezing the whole way (note 4°C is 39°F).

Today, an unusually strong Pacific cold front will be moving through, and you will notice its impact, including substantial snow in the mountains and even a few flakes reaching sea level in "favored" locations this week.

The visible satellite image this morning shows the story (below).  Arctic air is moving southeastward from Alaska, and as it warms from below, it becomes unstable, producing huge fields of cumulus convection (the black circle shows an example).  

The location of the cold front is shown by the red arrow, and the position of the clouds/light showers from a Puget Sound Convergence Zone is indicated by the black arrow.

As the cold front moves through today and cold air sweeps in, the temperature of the air aloft will decline rapidly.

Near sea-level, as at Olympia Airport (below), temperatures will plummet from the mid-50s today to highs in the low to mid-40s tomorrow and Tuesday, with lows reaching freezing.

But go a bit higher, where the low-level warming influence of the ocean is less noticeable, and the cooling will be much greater.  For example, at the Fire Training Academy, just east of North Bend, WA, temperatures will barely get about freezing during the day and decline into the mid-20s on Tuesday.

The forecast temperatures over Washington for Tuesday morning (shown below) will be very cold for onshore flow, with higher terrain dropping into the teens and nearly the entire state below freezing (blue and purple colors).  Only near the water will temperatures get to freezing and above.

You want snow in the mountains?  

You're in luck.  By Wednesday morning, the Olympics and the north Cascades will get a few feet, but this is just the appetizer.  

The main course is later in the week.  Here are the snow totals from the European Center model through Saturday morning (below).  As much as TEN FEET in some locations.  Many locations have a yard or more of snow.

Anyway, the influx of cool/moist air this week is very welcome and will go a long way to help the water situation this summer.

Could it be True? Lowland Snow in March?

A few social media sites are predicting as much as a foot of snow in Seattle next week.

Why such excitement?

Some weather prediction systems are predicting something quite unusual for mid-March:  lowland snow.

Not everywhere, but in favored locations.  And not every weather modeling system.

Consider the predicted snow total from the NOAA/NWS model for the 24-h  ending 2 AM on Thursday (below).  Lots of snow in the mountains, with a snow band across Puget Sound, probably from a Convergence Zone.

Plotting the GFS model snowfall prediction for Seattle from its ensemble system of many forecasts shows that several of the predictions included several inches of snow, although there is a lot of disagreement.  Disagreement means uncertainty.

 

Now, let me prove that I lack promise as a YouTube channel host.  

I suspect that such forecasts of bountiful lowland snow are problematic.    

Let me start by noting that the climatology of significant snow in Seattle plummets after the first week of March, as shown below.  Yes, late March snow has occurred, but it has never been significant.

Another issue is the temperature of the air, as shown by the forecast for Tuesday morning below.  The air over us will be cool, but not the primo Arctic air required for serious lowland snow in our region.   And there is onshore flow from off the mild Pacific.   But cold enough for PLENTY of snow in the mountains.    Get your skis out!.

The US GFS model has a long history of overdoing lowland snow in our area....its forecasts are generally too cold.   In contrast, the UW WRF model shows substantial snowfall in the mountains, but essentially nothing in the lowlands (accumulated snowfall through 5 PM Wednesday shown below).

The European Center's predictions are similar:

In short, plenty of snow in the mountains (which should address many concerns about this issue), but virtually nothing in the lowlands, although a few of you might see some melting snowflakes.

Precipitation totals during the next weeks should be impressive, providing water exactly when it is most valuable before the dry season starts in 2-3 months.

Announcement

I will hold a special online Zoom session at 10 AM on Saturday for Patreon supporters.  Will answer questions and talk more about the snow situation.