Hello windy season in the Northwest!
This morning, showers spread northward from Oregon into Washington State (see 6:30 am radar below). Generally only a few sprinkles, but it changed well in any case.
Humidity refers to an amount of water vapor escaping from the southwest — a northwesterly extension of the Southwest Monsoon (also called the North American Monsoon).
This morning’s steam satellite image shows a plume of moisture
as well as infrared satellite imagery.
The Southwest Monsoon occurs every summer from about late June to late August. It occurs when high pressure tends to build up around New Mexico, resulting in moisture being swept up from the Gulf of Mexico. , through Arizona and western New Mexico, then up through Nevada into eastern Oregon (see chart below, showing above-altitude water level at 500 hPa (you can think of this as pressure at high altitude) 18,000 ft.) The white area shows the direction of the flow at that level.
Over the past day, monsoon moisture has been enhanced by a strong center of lows developing in western California (see map below, showing wind and altitude/pressure at 500hPa/18,000 ft). This actually increases the flow of moisture-laden moisture from the south.
Over the past 24 hours (see below), clouds/monsoon showers have brought light rain to eastern Oregon, with some spreading west to the Cascades. Here in Seattle, there’s only one trace.
24-hour rainfall ending at 10 a.m. Tuesday
Over the next 24 hours, more light showers will hit the area as the lows off California head northwest into our region. Here are the total rainfall for the 24 hours ending at 5 p.m. Wednesday. You can see showers swirling around the low seas offshore and more monsoon moisture heading into eastern Oregon.
An interesting research question my team is working on is about the effects of global warming on regional precipitation and, in particular, monsoon humidity. Our early research shows MUCH more summer monsoon rainfall in eastern Oregon as things warm (see below). But we have much more work to do with higher resolution climate simulations to solve this problem.
The difference in summer rainfall between the late 20th and 21st centuries. Green shows more summer rainfall. These high resolution climate simulations assume a large increase in CO2 (RCP scenario 8.5) ….probably too much.
