A Fairly Normal Fall

We have had some warm periods and some cool ones.   Some wet periods and some dry ones. 

But looking at the entire fall, everywhere came out in the wash, leaving us with a fairly typical fall.

As we will see there is an important message in all this:  the weather on a particular day is often not "normal" but that is itself "normal", with mean conditions for a particularly date averaged over above-normal and below-normal gyrations of past years.

Consider temperatures during the past 12 weeks at Seattle-Tacoma Airport (below).  The purple and blue lines show the average maximum and minimum temperatures, respectively.   We had some warmer than normal periods, but almost the same number of below-normal ones.   This is what a normal fall looks like temperature-wise.

Did we approach or exceed some daily temperature records?   Yes, as shown below, with purple dots being the daily high and the blue dots the daily low records for Seattle-Tacoma Airport.  Sea Tac achieved a daily high record in early November and tied some low records earlier in the period. 

Keep in mind that it is normal to break some daily records...we do this all the time. 

Why is it normal?  Because there is a certain amount of random variability in the weather/climate systems and sometimes the requirements for unusual events just come together naturally.

What about precipitation?  Similar points.  Below is the cumulative precipitation at Sea-Tac, with observed shown by purple and "normal" by the blue line.  This fall is ending up slightly wetter than

normal, but we got there through very wet and very dry periods.  Typical.

Let's get a better view of our fall from a spatial viewpoint.   First, the difference of average daily temperature from normal for the past 90 days (9/19 through 12/17).  The entire NW is close to normal (light green or yellow, or different from normal by less than 2F).   Portions of the southwest U.S. are warmer than normal (particularly Arizona and New Mexico).

Precipitation?   Slightly wetter than normal over most of Washington and near normal over Oregon.  California is drier than normal (2-5 inches).

Bottom line: a totally unremarkable fall over the Northwest.






from Cliff Mass Weather and Climate Blog http://ift.tt/2BQmsEo