The Week Ahead - Want Rain? Careful What You Wish For

Update - 9/22/20:

We're bracing for first major storm of the season as it pushes onshore Wednesday morning.  Lot's of wind and rain.  In fact, per Euro and NAM latest main model runs, I'm upgrading our wind gust prospects Wed afternoon and Fri inland, 30-40 mph+ gusts out of the S/SW possible in Snoqualmie Valley vicinity. With all the leaves still on trees, there may be intermittent power outages.  

A second round of atmospheric river should develop over the weekend, keeping things wet.  By weeks end, we're talking potential 5+" of rain for late September!

weather.us

Longer range still hints and pulling a complete 180° next week with unseasonable warm and sunny weather.  Looking forward to that!

Original story - 9/20/20

Now that we've all taken that deep breath of fresh air, more active weather is wasting little time arriving at our doorstep, and just in time for the first week of Autumn.  

Autumn begins Tuesday, September 22nd, when the Sun crosses the celestial equator from north to south.  To my disbelief, the Autumnal Equinox hasn't fallen on September 21st in several millennia, however, in the 21st century, it will happen twice – in 2092 and 2096. I guess my kids will be around for that:)

Regarding our weather week ahead, Monday looks like the best shot to catch some sunshine, with highs in the upper 60's-low 70's.  Tuesday looks partly to mostly cloudy with a chance of a isolated showers.

But now for the more active weather in the extended forecast. The popular Euro and UW's GFS-WRF models are calling for substantial precipitation Wednesday and Thursday in what meteorologists call an "Atmospheric River". We may also have gusty S/SW winds at times with potential Gale warnings up for Washington's major waterways. 

The soggy stream of weather is due to a strong Low that should develop near the Gulf of Alaska, helping to aim the jet stream right at us.  At this point the brunt of the moisture looks to track to the south of us into Oregon.

Now let's look at extended model projections for cumulative rainfall in the Snoqualmie Valley.  ~3-4 inches of rain looks likely Wed-Fri. That's a real soaking!  If later into October we might be talking more about rising rivers. 

weather.us

Shower activity is likely to round out the rest of the week as this pattern abates.

I'm probably not the only one hoping to still get some nice clean sunshine in the coming weeks before we decline into the usual cold and wet seasons.  However we're about at that time of the year when our rainfall totals really start to outpace our more urban neighbors to the West.  After all, annually we average ~68% more rainfall (measured from Snoqualmie Falls) than Seattle.  If there were historical records from suburban points further east (e.g. North Bend) I'm betting precipitation would be even higher as orographic effects (when moist air begins to lift as it moves over a mountain range) wrings out even more precipitation.  It wouldn't surprise me if a highly localized area like Wilderness Rim, with a unique topography like how it's backed up to Rattlesnake Ridge, is pushing 90-100" of rainfall per year.

Have a great week!

Almanac for September 21st (Snoqualmie Valley):

Average High: 68°       Average: Low 45°

Sunrise: 6:53 am         Sunset: 7:05 pm          Daylight: 12 hours, 12 minutes

Moon Phase (current): Waxing Crescent       Full Moon: October 1st