Trick or treat? - Weather outlook

Are you wondering about the Halloween forecast?  Will you or your kids get wet trick or treating?  How about temperatures?  Wind? Let's get to it!

First, we are watching a low pressure system south of the Aleutian Islands which is drawing up significant moisture northward from near Hawaii.

Infrared Satellite image from 11 AM PDT Monday, October 29th, 2018.

So will this moisture make it up our way?  Well its hard to tell from a still satellite image, so let's take a look at some model data.  First of all, let's see if this moisture plume is showing up in the models.

18z GFS initialization of 500 mb heights and 700-500 mb Relative Humidity valid 18z (11 AM PDT) Monday, October 29th, 2018

Good news!  The GFS model as well as the other models are picking up on this moisture.

Now, let's see where this model takes it.  Here is it's projection for Halloween.

18z GFS forecast of 500 mb heights and 700-500 mb Relative Humidity valid 18z (11 AM PDT) Wednesday, October 31st

Much of this moisture tops the flat ridge (noted by the H west of California) and moves across Washington, Oregon, and Idaho on Halloween.  But the entire day doesn't look like a washout at this time.  Let's take a closer look at when the best rain chances are.

We will take a look at a new set of model data called the National Blend of Models (NBM). This utilizes many numerical weather prediction model data and post-processed model guidance.  If you want to know more about NBM, click on this link for more details.

So let's start with 5 am - 11 am Halloween

It looks wet Halloween morning for most of Eastern Washington and north Idaho as well as near the Cascades.  It is worth noting that the best rain chances for Omak, Wenatchee, and Moses Lake may arrive prior to 5 am (not shown here).

What about Halloween afternoon?  Let's see.

The best rain chances are near the Cascades, far SE Washington, and the Idaho Panhandle.

Now, for the time you really want, Halloween evening (Trick or Treat time)

This would suggest low rain chances and more likely a dry trick or treat for most of Central and NE Washington.  Pullman, Lewiston, St. Maries, and Kellogg area under a higher threat of rain.

What about temperature?  Here is the 6 PM temperature forecast from the NBM

It will be a little on the cool side with values mostly in the mid 40s to lower 50s.  These are very close to normal values for this time of year.

What about wind?

Winds do not look particularly strong, ranging from 5 to 10 mph for most areas.  The Palouse and areas near the foothills of the Blue Mountains in SE Washington could see slightly strong winds of 10 to 15 mph.  The mountains will be breezy.

Now we will continue to fine tune the forecast, please keep informed of the latest forecasts on our home page found here.