Weather Blog

Trying to pin down where the snow might strike

Trying to pin down where the snow might strike
Background bowling image courtesy Wikicommons contributor "Fir0002/Flagstaffotos" (GNU Free Documentation License 1.2)

It's fast becoming the talk of the town, right along side whether the Seahawks' Marshawn Lynch could have run for a 200-yard touchdown Saturday if the field was long enough: Is it going to snow next week, and if so, how much?

Forecasting models have shifted around from dire predictions of 8-14" of snow in Seattle proper, to just a quick snow-to-flooding-heavy-rain event, to everything in between -- and we've still got a good 3-4 days of future model runs to see shift even more.

To help illustrate the challenges we face in using different forecasting models to predict such a snow storm, I thought I'd use an analogy people might be a little more familiar with...


What's going on is that we're all going to be cold on Tuesday, and a big storm is coming off the Pacific on Wednesday. It depends on where that storm goes as to how our snow scenario will work out.

The areas on the immediate north side of the storm are likely going to get hammered with snow. The areas to the south of the storm will likely be snow-to-rain or just straight rain.

(Why? Because air is drawn to the center of a low pressure system. If the storm is to our south, that means the storm will draw in a very cold north wind out of Canada, where arctic air will be hanging out. If the storm is to our north, it means it will draw in a much warmer south-southwest wind off the 50 degree Pacific Ocean.)

So, picture a professional bowler -- we'll name her, oh, "Lani Na" -- is about to bowl three frames.

Here is the set-up: The bowling ball she's using has a big "L" on it (symbolizing our low pressure storms). The left half of the ball is painted white for snow, and the right half of the ball is painted green for rain.

The pins are the Pacific Coastline. Vancouver, B.C. is standing where the 2 pin is, Seattle is at the head "1" pin and Portland is at the 3 pin. Let's assume Lani is right handed.

Now, knowing that Lani is a professional bowler, we can be reasonably sure she's going to put the ball somewhere near the pocket -- somewhere around the '1' pin.

If the ball strikes the Portland 3-pin head on, areas just to the left (north) of Portland will get snow -- like Seattle and SW Washington -- while south of Portland will get the rain.

If the ball drifts further left and hits the head pin straight on, Seattle-area will likely be split (hah! Unintended bowling pun on two levels) with snow to the north and rain in and to the south.

If the ball goes even further north, like the 2 pin of Vancouver, then Seattle will get the rainy side. (And likewise, too far south, like the 6 pin, and Seattle might not get any moisture at all).

Right now, we are at the point where Lani has just done her approach and the first ball has just left her hand, heading down the alley.

As the ball still has a long way to travel, it's difficult for us to know just yet exactly where the ball is going to strike. Extrapolating out, we're pretty sure it'll be somewhere between the 2 and 3 pins but one inch difference in drift of the ball now will be magnified as the ball travels and will affect where it strikes the pins.

So far, the models have been somewhat consistent in a strike between Seattle and Portland, but this far out, each model run makes minor adjustments that are affecting their predicted snow totals for various Northwest locations. (The analogy would be how other conditions can affect the storm's path, like oily spots on the lanes, for instance.)

But as the ball gets closer to the pins -- as the days get closer to the storm's strike -- we'll be better and better able to calculate and extrapolate where the storms is going since the ball will be closer.

Thus, we'll have to wait until the event draws closer to get a better consensus on landfall and potential snow amounts for each area, if any. But a majority of model solutions at this point indicate the ball will strike somewhere where some or all of the greater Puget Sound/Western Washington will see some snow.

And as I said, Lani is bowling three frames. There are two additional storms that could also make for a warm rain or additional snowfall, depending on where they strike.

So take this as a rare opportunity to get five days' advance planning for what could be a region-wide event. Don't bank on the off chance we might be spared!

You'll also have Monday and Tuesday as reasonably fair weather to get preparations completed and for sure, we'll be keeping tabs on the storms and updating forecasts frequently. (Twitter @ScottSKOMO & Facebook at