Thermal trough heats us midweek, but 20 degree drop coming

Weather

PORTLAND, Ore. (KOIN) – Wednesday is our first 80-degree day of May with a little help from our friend, the thermal trough.

When the air warms up in mass and rises, it will create lower pressure near the surface because there is less air. Basically, during days like today, we cut off the onshore flow of the cool Pacific Ocean and we bring in a warmer easterly wind coming off the Cascades. This process will warm up our temperatures here in the Willamette Valley and most of the time, out to the northern coast if we can get that east wind to those folks.

However, this process is ephemeral and will be swiftly out the door by the time we get to our Thursday. Below is a general idea of the current weather pattern near the surface today. Look at the warm air from Nevada up through California and into Oregon today.

This process will take our temperatures to the lower to mid-80s today. We have yet to even hit 70 this month (we hit 69 on May 4). Check out all the heat down towards Sacramento and up into Medford today. We shouldn’t be hitting the 90s around here, but that boost to the 80s is definitely in the forecast.

Observations as of midday show the east wind coming out of the mouth of the Columbia Gorge today and fanning out to areas of the Willamette Valley. Temperatures hit 70 before lunchtime for many locations that are tapping into the heat. However, it’s cooler out towards Hillsboro and Forest Grove where the impact is not necessarily as aggressive. We have just about hit our first 70-degree day by noon and we will hit our first 80-degree day by the late afternoon. This is going to be 10 to 15 degrees above average and it is all because of this specific weather setup that we have today that we mentioned above called a thermal trough.

Check out the scene coming from the KOIN tower and looking out towards the Moda Center to the northeast. You can see that there are some thin clouds around, but you can still see Mt. St. Helens and out into the hills of the Cascades. That filtered sunshine will stick around today because we have a nearby system that is going to take our warm weather today and bottle it back down to the south by tomorrow afternoon.

This is the system that I am referring to! If you look at the moving graphic below, there is a large mass of clouds and movement to our west. If you really focus in on the state of Oregon, you can see those thin clouds moving in across the region. You can really see the coastal clouds of California today too. It looks like the clouds are socked in for the whole coastline of California today. Not the case for Oregon today, but the high thin clouds will be consistently streaming in behind our ridge of high pressure that shifts to the east this afternoon. The system moving through tomorrow is going to be a multiple day process. We can count on a 20 degree drop to our afternoon temperatures Thursday. Those temperatures remain cool through the end of the work week. It’s possible that we have some 50 degree highs Friday and Saturday. The true spring seesaw in action this week.

Now that you can see that system coming in on the satellite, we can take a look at the weather pattern from the visual standpoint of a weather model. That drop in the Gulf of Alaska is a trough, with that area of low pressure embedded into that kink in the jet stream. Right now we are analyzing the direction and path of this system. That will determine how much rain we end up receiving from this system and the overall impact. That shift is going to be the main cause for our drop in temperatures. What is interesting about what is unfolding in the next 24 hours, is we are dealing with two different types of troughs. We are focusing on a thermal induced trough, which is warming our temperatures today. Eventually we give away to the basic wave pattern of a trough that denotes cooler temperatures and dense air. If you’re interested in this, you can learn more through our educational page about pressure here.

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