Well, for Seattleites who missed out on the snow earlier this week, I guess the mantra of the day might be: "If at first you don't succeed, try, try again."

Indeed, another storm is on its way -- actually, two storms simultaneously this time, because Mother Nature has a wacky sense of humor -- that has the potential to mix with some colder air around and at least bring a chance of snow once again to western Washington.

So much so, that a "WINTER STORM WATCH" that was already in effect for the greater Puget Sound area has been expanded to cover the rest of Western Washington except for the coast.

The "Watch" simply means that conditions are right for snow to form, but it's not a sure thing or imminent. It's sort of like the National Weather Service's way of saying "head's up!" (If we get to a "Winter Storm Warning", that means snow is imminent.)

In addition, a HEAVY SNOW WARNING is in effect for Southwestern Washington from 7 am through 6 pm Thursday, which is looking like they're going to get the brunt of the storm. As much as 3-4 inches are possible during the day, and then another inch in the evening before it changes over to rain.

As usual, the forecast is pretty complex and dependent on a number of factors, and definitely subject to change (Feels like we need to add in "no purchase necessary" and "void where prohibited," doesn't it?). Some forecasting models have it cold enough to snow, others have snow levels over 1,000 feet, at which point, Thursday is just a rainy day. So as you can see, it's another marginal snow situation instead of "Arctic Blast -- '05!"

The other factor in play is how hard the rain/snow will fall and how dry the air is ahead of the system. In this case, when that moisture first falls out of the cloud, a lot of it evaporates into the dry air. But the evaporation process takes energy from the air, effectively cooling it by a few degrees. When temperatures are in the 30s, many times that can make the difference between rain and snow. And it can fluctuate between rain and snow as the precipitation intensity changes. So, yeah, that's a little tricky to forecast :)

Our Best Guess

Anyway, here's our best explanation of what might happen Thursday if the ingredients align:

The first thing to watch is our temperature Wednesday night. As of Wednesday evening, temperatures were all over the place -- from 39 in Tacoma and Seattle to 30 in Olympia and Port Angeles. The colder it gets tonight only helps increase the chances of snow Thursday as it means we'll have farther to warm up in the morning.

Meanwhile, we have two areas of low pressure approaching the area. One is a rather large, wet system that is approaching from the southwest (this is the main moisture source), and a smaller but colder system sinking southeast from the Gulf of Alaska (this is the cool air source).

These two systems are expected to interact with each other off the Washington and Oregon coast and at least bring some of the ingredients together that might make snow.

That colder system is expected to just kinda lollygag off our coast Thursday, while the wetter system is pegged to go into central and northern Oregon but still send some moisture north into Western Washington.

The trick here is whether the Oregon-bound system will draw enough cold air into our area from the cooler system to the north or if that cool air will stay long enough to snow for any real period of time. If so, the precipitation would then move north into our area and fall into the cooler air, falling as snow.

What is fairly certain is that moisture will move into Southwestern Washington sometime Thursday morning, spreading into the Puget Sound area by midday or early afternoon, and the into the North Sound and Northwestern Washington by late afternoon or evening.

That moisture will likely begin as rain in the Southwest Washington and Puget Sound area, but then likely changes over to snow after a short while in Southwestern Washington, and could change over to snow in some spots of the Puget Sound area.

North Sound/Northern Washington areas will be on the northern fringe of the moisture, but since they'll be cooler, what moisture gets there would probably be snow from the get-go by then.

But how long the snow lasts in each region is the trick.

As we mentioned earlier, the Southwest Interior is looking like it'll snow through the day, changing over to rain by mid-to-late evening as a warmer marine flow pushes in behind this system. The changeover for the Puget Sound area would little while later. North Sound/Northern Washington would probably hold onto whatever snow they get until early Thursday night before it switches back to rain.

But if we don't get enough cool air, or enough precipitation intensity, it's all rain or mostly rain with brief snow or mix and looks like any other December day in Seattle.

Either way, the Cascade foothills appear to be the loser in this scenario because we will still be getting some drying east winds from the mountains (why not toss in more monkey wrenches, Mother Nature?)

The winds are expected to be a lot less than Monday/Tuesday as this flow has more of a northerly component, but still enough that you'll be in the drier spots. That doesn't mean no snow if cold enough, just probably less than others. But spots up there that got a little snow Monday night would be on the hook for snow again Thursday.

How Much?

As for any expected snow totals, it's still in a lot of flux, but as of Wednesday afternoon, we're thinking Trace to 3 inches is a good general rule.

Exceptions would be along the Hood Canal/Western Kitsap Peninsula again and southwestern Washington, where as we mentioned earlier, you might see as much as 3-5". From there, it's a sliding scale downward for snow potential as you head north and run out of moisture and precipitation intensity.

For the Seattle-Tacoma area and the rest of the Kitsap Peninsula, we'll go with 0-2" -- a dusting or so near the water and in downtown Seattle and Tacoma to 2" along our higher hilltops.

The general Everett area has a better shot at having the conditions right for snow, plus their elevation advantage, but less moisture to work with, so we'll put them in the 0-2" as well.

North of Everett, we start running out of moisture, so we'll call it 0-1".

Just have to mention again -- note the '0' in there. There's still a decent chance some people won't see any snow. Then again, an intense snow shower could put down a few extra inches in isolated spots.

We'll have a better handle on this Thursday morning when we can see where our temperatures are and how that storm begins to affect southwestern Washington.

Once that jumbled mess of systems pass, we'll just be in showers Thursday night -- likely rain, but perhaps in the form of snow toward morning as the temperatures drop, with better chances in the hilltops and away from water.

But if in fact the snow misses Seattle again, well, there's always "third time's the charm" :)