Monsoon Moisture Next Week

For those who have lived in the desert Southwest, you know that there is a wet season there. And it’s not in the winter.

Here’s the average monthly rainfall for Tucson AZ.  The months of July, August and even early September are the wettest months.  Meanwhile, in the Inland Northwest, these are the driest months.

The cause of the summer rains in the Southwest is known as the Southwest Monsoon.  A monsoon is defined as a seasonal shift in winds that cause a distinct change in the precipitation pattern.  In the Southwest, this change in wind direction is the result of persistent high pressure during the summer near the Four Corners area.  Air rotates around a high pressure center in a clockwise direction.  This acts to draw moisture up from Mexico into Arizona and New Mexico.

Typically this moisture then rotates across southern Utah and into Colorado.  This is the “Frequent” pattern in the image below (courtesy of https://opensnow.com/)



Occasionally this moisture makes it farther north, into Nevada, southeast Oregon, southern Idaho, and then into Montana and Wyoming.  In other words, Washington and the Idaho Panhandle are almost always too far north and west to experience monsoon moisture.  Almost.  If the atmospheric flow pattern sets up just right, we can see some of this moisture, even in western Washington.  And next week’s weather pattern may just deliver this.

I eluded to the potential a couple of blogs ago. Below is a sequence of 24-hour rainfall forecast by the European forecast model.  Each image ends at 5am.

Monday



Tuesday




Wednesday




Thursday 




Friday



You can see that by Monday morning, the rain is confined to California. By Tuesday morning the rain has moved across southeast Oregon into Montana. By Wednesday morning the rain has reached the inland northwest. And it might hang around for a few days.

A few notes:

  • these events often start off rather dry, more lightning than rain.  But as the event continues, chances increase for rain.
  •  these showers and thunderstorms are mainly over the mountains.  But the valleys and basin could also see some rain.
  • Fire starts from lightning strikes are a possibility in this pattern.
  • daytime temperatures are going to be in the 90s next week.  The monsoonal cloudiness will result in some rather warm nights.  Lows in the 60s or even lower 70s.  Not good sleeping weather.

I’ll update this blog when the details and timing become clearer.  


Comments

Post a Comment

Popular posts from this blog

The End is In Sight

Image
We're currently in the middle of a rather unusual heat wave at the end of summer.  And some records could still be reached.  For those who aren't a fan of the heat, there's good news:  an end to the heat wave is in sight. Here's the somewhat odd weather map.  There's a skinny but strong area of high pressure over the Western US that extends up into BC and the Alaskan Panhandle. A weak low off the Washington coast is sending waves of moisture into our area at times.  This caused all of the clouds last night along with a few showers and thunderstorms.   Meanwhile, the eastern US is still experiencing fall-like temperatures.  Low temperatures in the 40s dipped all the way south into North Carolina this morning.  State College, PA has already had 3 nights in the 30s. By Thursday of this week, the weather pattern won't have changed a whole lot.  Another surge of cool air invades the Great Lakes region, while high pressure continues to dominat...
Read more

When Can You Start Cutting?

Image
The answer to this blog’s title isn’t an easy one, and it’s going to depend on what risk you’re willing to take. The overall set up is this. The large low pressure system will wobble around the Northwest and vicinity for the next few days. But even when the low is east of us, we’re not out of the woods. Rainfall over Montana or even BC can wrap around the low into our area, even as late as Tuesday. So if you want a sure-fire dry forecast, you’ll probably have to wait until Wednesday.  But some folks have a lot of hay to cut and can’t wait that long. So here’s some probabilities of rain and amounts to consider.  If you live up north near Colville or Newport, odds are pretty high that you’ll see more rain, especially on Sunday night and Monday.  And it could be as much as a third of an inch. If you’re closer to the Deer Park area, the story is similar, but the amounts and probabilities are a bit lower.  Maybe a quarter inch? And if you’re down by Spokane, well then the...
Read more

Rain Returns - Update

Image
The computers are remaining true to their word.  Our long dry spell will be ending on Wednesday, with the potential for a nice rainfall.  More showery chances of rain then continue through the weekend. First I’ll show you the average of all of the computer forecast rainfall for Wednesday. 0.1” around Spokane, with 0.25” north and east of the metro . Here’s a few of the individual computer forecasts.  The US GFS model gives around a half inch to parts of northeast Washington. . The UK is similar to the blend of models. The European AI forecast is a bit more generous with the rainfall.  And lastly the European model predicts over an inch for parts of Ferry and Stevens counties.  There could be some thunderstorms on Wednesday as well.  So everyone should get a little rain, but some folks could get more. Tuesday: Sunny and very warm.  Highs in the 80s. Wednesday: showers and thunderstorms.  Highs in the mid to upper 60s. Could be gusty in the afternoo...
Read more