Wetand News

I have gotten a lot of questions and comments about the connection between a colder-than-normal spring and conditions during the summer. Several folks are convinced that a cold spring means a warm summer, mainly based on what happened last year.   So let's look at the data and find out! Let's start by plotting spring (March-May) temperatures over Washington State using the NOAA Climate Division dataset for the past century (through 2022).  Warmer earlier in the period, then cooling in the 1950s-1970s and then warming back to the earlier levels during the past decades.   I then identified the top ten coolest springs. Next, I determined the top ten coolest springs and plotted their anomaly (different) from normal (the averages for 1991-2020) temperature for the summer (July through September)-- below.    The result?  Summer surface air temperatures were substantially cooler than normal after cool springs. So based on climatology, there is no reason to expect a warmer than normal

This is turning out to be one of the coldest springs in a long time.    As I noted in a >previous blog , March was uber-cold over much of the West Coast. And now April is turning out to be frigid as well! Compare the temperatures at Seattle-Tacoma Airport with normal highs (purple lines) and lows (cyan)  since April 1.  Wow.... not a single day reached the normal high and many days had lows below normal. A similar situation has occurred at Yakima! As I noted before, this cold spring is keeping our snowpack in place with minimal melting.  Thus, the latest snowpack numbers indicate a regional snowpack that is above normal , even though our precipitation has been below normal. The forecast for the next ten days by the European Center ensemble forecast system is for surface air temperatures much cooler than normal (see below). It will be particularly cold east of the Cascades:  I worry about crop damage from frost--so agriculture interests need to be prepared. The NOAA Climate Predict

 The Pacific Northwest is home to some of the best rainshadows in the world:  areas of dry conditions downstream of terrain barriers. And on Sunday we were treated to one of the best examples of such features, in the lee (northeast) of the Olympic Mountains. As many of you know, when air approaches a barrier, it is forced to rise, producing clouds and precipitation (see figure below), and when it sinks on the downstream side, the air descends, warms by compression, and drys out.   This is where the rainshadow is found. On Sunday, strong south/southwesterly flow was approaching the Olympics (see a map of winds around 11 AM Sunday).  Thus, the sinking air was on the northeast side of the Olympics. The visible satellite picture at this time clearly showed a nearly cloud-free area in the rainshadow areas.  This is sometimes called the "Blue Hole." The radar imagery at that time showed it was a rain-free zone: Do you want to be impressed?    Here are the precipitation totals for S

One thing that really stands out this winter has been the lack of heavy rain over western Washington, particularly since the start of the new year.   One hardly needed an umbrella for the past few months. To illustrate, below is a plot of the daily precipitation over the past six months at SeaTac.  A handful of wet days (up to 1-1.5 inches) in December and then the spigot turned off in 2023,  with the wettest days only hitting around 0.5 inches.   I have cycled to work pretty much every day. The central issue is that there has been a lack of warm, wet atmospheric river events moving into the Northwest.  Instead, the moisture plumes have gone into California.   Interestingly,  during this winter San Francisco has received Seattle's normal rainfall and vice-versa (see below). . A big change in all this will occur over this weekend.  A strong atmospheric river of substantial moisture will be directed into the Northwest on Sunday and Monday (see the forecast of atmospheric moisture bel

If one looks at the precipitation for the winter season (the water year starting October 1), as shown below, the north-south contrasts have been profound.   California and the Southwest have been hugely wetter than normal (some places enjoying over 250% of typical winter precipitation), while much of Washington and portions of Oregon have received 70-100% of typical values. During the past month, the differences have been starker, with much of Washington State receiving 50-70% of normal precipitation, while Oregon and California have been very wet (see below). As I will discuss in a future blog, these wet conditions have significant implications for the upcoming wildfire season, since they will promote the bountiful growth of seasonal grasses, which inevitably dry out during summer.   The wet conditions in California have decidedly terminated the short-term drought there.     Although Washington State has been drier than normal, it has been colder than normal.  The result is the preser

 This past March brought record cold to a vast swath of the U.S., including the West Coast and the northern Plains.   Here in Washington State, the frigid conditions even continued into April, with snow showers falling to sea-level and serious snow on some of the hilltops near Seattle (see the snowfall at 1100 ft in Bellevue on Sunday night).  April? April 2. Bellevue, Washington at 1100 ft. Courtesy Dr. Peter Benda Satellites can observe atmospheric temperatures from space.   The lower-atmosphere temperatures for March from such satellite (see below) indicate that the coldest temperature anomalies (differences from normal) on the planet occurred in a swath from the West Coast to the upper plains. Portions of eastern Oregon had had their coldest March in history, as shown by the March temperatures at Burns, Oregon over the past 50 years.   I mean no year was even close to March 2023.  A NOAA temperature analysis that presents the differences from normal of temperatures around 10,000 ft

  Take a deep breath.  If you are in the Pacific Northwest, the air is very clean. Its origin is from far to the Northwest: from the Aleutians and the Bering Strait. Using the NOAA trajectory analysis software called HYSPLIT, I traced the path of the low-level air reaching the Washington coast (at 10, 100, and 500 meters above the surface) back for 96 h (see below).  Straight to the Aleutians.  You can almost smell the sea air. The UW WRF model forecast for 1 PM on Saturday shows sea level pressure (solid lines), near-surface winds (the wind barbs), and low-level temperatures (purple and blue are the coldest).   The low-level winds are from the northwest over and downstream of the Aleutians, consistent with the air trajectories above.  Our air started over the frigid Arctic, but you will notice it warmed up as it approaches us. Why is our air much warmer than over the Aleutians?   Because it passed over increasingly warm water. Here is the latest NOAA sea surface temperature analysis