Blocking highs, like the one setting up this week, are often responsible for our highest impact and longest duration weather events. They block energy from easily leaving our state.
Blocking highs can form in different places. But they’re all associated with warm air. The warm air surges north creating a bulge in our upper-level airflow. Technically - this is a chicken-versus-egg issue. Changes in the shape of the jet stream and the energy flow within them, can produce regions of high pressure - as can the feedback between our oceans and our atmosphere. And, conversely, regions of warm air can bend the jet stream and produce regions of high pressure. Regardless of mechanism, once the high forms, warm air surges north.
This creates a feedback loop. The warm air produces a ridge of high pressure. High pressure produces sinking air which keeps skies clear and dry. This produces even warmer air which strengthens the high.
These large regions of high pressure impact our jet stream. The jet stream is our storm conveyor belt. When it moves west to east in a straight line, storms move quickly. This is our most common weather pattern. While the jet stream always has ridges and dips, they're more often than not relatively small.
But when a large ridge of high pressure develops, it pushes the jet stream into a big wave. We call this a meridional jet stream, which is what’s happening this week, and it does two things. First, it tends to make the jet stream faster, giving us strong wind potential. Second, it tends to gum up the works. Weather systems get stuck in this wavy jet stream pattern.
Again, this works both ways. Energy in the jet stream can produce waves, which then lead to areas of high pressure. But - blocking highs - in particular tend to be associated with temperature anomalies. In this case, parts of the Atlantic Ocean are warmer than average, making it easier for ridges of slow moving high pressure to form.
Blocking highs occur regularly but significant precipitation impacts happen in Colorado when we have an upstream storm system. This week we have a large area of upper-level energy moving in from the Pacific Northwest. The combination of potent upper-level energy and the blocking high lead to the long duration of unsettled weather this week.
To summarize, a blocking high forms when warm air and the jet stream interact, creating a feedback loop. This results in a wavy jet stream and the high getting stuck or moving slowly. If storm energy is over Colorado in this setup, it gets blocked from leaving quickly, resulting in long duration storm impacts.
The notable element of this pattern is that while we’re tracking many types of weather this week, they’re all largely driven by the same large area of energy and weather pattern. While we'll see several lobes of energy and moisture move into and out of the region - they're all associated with the broad trough that's being blocked by a nearly stationary high.
____
Have a question or story idea you would like the First Alert 5 Weather team to consider? Email: weather@koaa.com
Watch KOAA News5 on your time, anytime with our free streaming app available for your Roku, FireTV, AppleTV and Android TV. Just search KOAA News5, download and start watching.
