The Atmosphere is Now in Neutral

Midway through May is a good time to check on the status of El Nino/La Nina,  since its status becomes clearer at this time of the year and will have a major impact on the weather of next winter.

NOAA's latest forecast is out....and I will describe it below.

El Nino and La Nina are on the opposite poles of the same phenomenon:  the shift of the waters of the central tropical Pacific from warmer than normal (El Nino), to near normal (Neutral of La Nada), to below normal (La Nina).

A plot of the sea surface temperatures in this critical area (the Niño3.4 area) is shown below (actually the differences from normal).  After experiencing the cool waters this winter (La Nina), we are now in neutral territory.

The correlation of the tropical water temperature with our weather during the summer is weak in any case, but winter is a different story.   

So what do the latest forecasts suggest? As shown below, although there is quite a range in predictions, the general trend is towards continued neutral conditions for the remainder of the year.

What are the implications of neutral conditions for next winter?

Increased chances of a major wind event from an approaching midlatitude low-pressure system.

Increased chance of a strong atmospheric river that produces major flooding.

Bottom line: neutral years are known for their meteorological action.  

More Serious Rain Returns

 It has been cool, and there has been some light rain over western Washington.   Several of you have emailed me, asking when we will get more serious moisture.

Your answer is below.

Let me show you the latest European Center precipitation forecast for our region.  From 11 AM today through 5 AM Friday, there is light rain over the region, with moderate rain over the mountains.

With winds from the west, the eastern slopes of the Cascades will be rain-shadowed.

Then the rain picks up as a trough of low pressure moves through over the weekend, with the totals through Sunday morning exceeding 1 inch over the western slopes of the mountains.  Saturday might not be a good hiking day.

 The totals steadily increase through Tuesday morning.

You will notice that the precipitation will be relatively light over the lowlands of western Washington. Why?

This is because the winds often blow from the west this time of the year, which tends to produce downslope flow and drier conditions downstream (east) of our generally north-south terrain barriers.

This is illustrated by the winds around 5000 ft on Friday morning below.

During the winter, winds are more southerly, allowing more precipitation in the lowlands.

This type of pattern also produces large temperature contrasts across Washington State.

Consider the situation on Saturday at 5 PM.  Temperatures are in the low 50s in western Washington, but around 70°F in the Tri-Cities.  So head across the Cascades if you want some springtime warmth.