The strongest atmospheric river of the season thus far is now imminent and can attain our coast later tomorrow (Monday).
Atmospheric rivers are fascinating creatures. Why does ambiance focus water vapor into fast paced slender currents? And why do such currents present such bountiful precipitation and are so optimum for selling floods and landslides? These questions are amongst those who I and others have researched over the previous a long time and just about perceive.
Below is a graphic displaying the important thing parameter that characterizes ambiance rivers, one thing known as Integrated Water Vapor Transport (IVT),that’s forecast for Monday night time at 10 PM. IVT is basically the magnitude of the water vapor being moved by the atmospheric. Mathematically, water vapor fixed instances wind pace.
In tis determine, the blue areas are places with very excessive values of IVT (over 800 within the models proven)
Bringing a whole lot of water vapor within the space gives a supply of water for clouds and precipitation, notably as air is pressured to rise on our terrain.
A bunch at Scripps Institute of Oceanography in San Diego even have an atmospheric score system, much like Saffir-Simpson Scale for hurricanes (Category 1-5)–see below– and it based mostly on the IVT and period. The occasion we are going to expertise this week will attain at the least a Category three stage!
What makes these occasion notably threatening is that there shall be two main pulses of enormous quantities of water vapor intrusion…. one late Monday/Tuesday and the opposite Wednesday morning, one thing proven by the forecasts of water vapor transports at these instances (see beneath). Each is related to separate low stress facilities and robust winds.
You discover how the values decreases because the moisture plumes transfer inland? Why do you suppose that’s?
The reply is that water vapor is being precipitated out as rain and thus misplaced from the ambiance. The mountains are squeezing out the water vapor like one would do by squeezing a sponge.
But you need to see the precipitation, I’m certain.
For the 72 hours ending at four PM Wednesday, there shall be 5-10 inches on the windward facet of regional terrain, with some locations getting OVER 10 inches close to the CA/Oregon border. Oregon is within the bullseye of this occasion. And such heavy rain shall be falling over areas that had the massive fires final September, which is a matter of concern.
Atmospheric rivers usually are related to heat air, and this one is not any completely different, with freezing ranges rising to 5000-6000 ft on Tuesday. Not good for snowboarding at Snoqualmie these days.
Finally, why are there atmospheric rivers within the first place? For us right here within the Pacific Northwest, they’re related to conditions with greater than regular stress over California and decrease than regular stress over Alaska. The result’s a big stress gradient between the 2 the produces robust southwesterly movement that pulls heat, moist air into our area.
To illustrate, take a look at the forecast map of heights (like stress) at round 5000 ft for Tuesday morning. Temperatures is proven by shading and winds by wind barbs. A low close to Alaska and excessive stress/heights off of CA. An enormous change in stress and thus robust winds (from the southwest), bringing the nice and cozy, juicy air in the direction of us.
This is just not going to be an excessive, damaging occasion, however anticipate some localized flooding, particularly in western Oregon.