Tuesday, June 18, 2019

A Wetter than Normal Period Ahead

As suggested by extended forecasts a week ago, we are now going into a wetter than normal period over the Northwest.  The latest European Center high-resolution forecast of cumulative precipitation over the next week shows .3-1 inch over the lowlands of western Washington and much more over the northern Cascades and southern B.C.

The European Center forecast highs and lows, as well as precipitation, for Seattle over the next two weeks indicates no heat waves, with temperatures in the mid to upper 60s on many of the days.

Of course, as I have stressed in many blogs, one always wants to look at an ensemble of many forecasts, each a little different, to gauge the uncertainty in the forecasts.  Thus, below you find the cumulative precipitation forecasts for Seattle from the 51 member European Center ensemble for the next 10 days.  ALL of them are going for precipitation, with the average of the ensembles producing more rain than the high-resolution simulation shown above.    I would get an umbrella handy.

The reason for these wet periods is a breakdown in the ridge of high pressure and the predicted arrival of upper level troughs into our region.  For example, at 2 AM Thursday, an impressive trough will be moving into Washington State (see below).

2 AM Monday?  Another trough.

What about the rest of the summer?   Extended forecast skill is never great, but consider that the latest European Center 46-day forecast through early August, predicts wetter than normal conditions over our region and much of the U.S. (see below).  Importantly, also for British Columbia and Alberta.

 And the latest international model ensemble forecast of the precipitation anomaly (difference from normal) for July through September indicates normal to above normal precipitation.

 Rain and cooler temperature this time of the year is of substantial value in reducing the risk of wildfires and smoke, since our fire season ends in three months (mid-September).  Right now there are no major fires over the region and number/acreage of fires for the Northwest and the nation have been below normal.  Good news.

Don't get me wrong--there will be fires--but the situation during the next few weeks is favorable for pushing the wildfire season out in time.  And it will also reduce water usage and help fill our streams.