Weather is all about the future and trying to predict the future is hard enough to do, but when “Mother Nature” throws a wrench into the equation, well, it becomes doubly hard to do. I bring this up because that’s what all meteorologists in the northeast are having to deal with this week. Most of the year, the weather is either quiet, or semi-predictable, but it’s weeks like this when two a meteorologist forecasting nightmares rear their ugly head…With the famous omega block and its counterpart the closed/cutoff low, that forecasting becomes more of a challenge.
So what is an omega block and a closed/cutoff low? Well, for all those who were in fraternities or sororities, you have heard the word omega and have seen the symbol. By definition, the omega is the twenty-fourth, and last, letter of the Greek alphabet and the symbol looks like a backward horseshoe, as you can see from this photo. As for a closed/cutoff low, the meteorological term refers to a storm system that becomes completely displaced, basically cut off from the basic westerly current, and moves independently of that current. Cutoff lows may remain nearly stationary for days, or on occasion may move westward opposite to the prevailing flow aloft (I.E., retrogression). These storm systems are closed cyclonically circulating eddies, cut off from the jet stream, in the lower atmosphere, which is between 4 to 12 miles high in the atmosphere, where almost all weather occurs.
This week’s forecast has to deal with both of these two systems, which make predicting, cloud coverage, precipitation, and certainly temperatures hard to gauge. The reason why is for the simple fact that depending upon where both of these systems end up positionally fixed will determine what cities and towns will have what type of weather. So let me break down the setup for you by starting off with the look of the jet stream. I point out the look of the jet stream because of how it has the omega block “Look” to it. A big trough out west, a major ridge in the central U.S., and then another trough along the east coast. With this type of setup and with our area situated on the eastern side of the ridge, precipitation and cloud coverage basically split our region in half. As I fly into our area, you notice that the clouds start out over the mountains and then spread east to the coast from morning to afternoon. Same for the showers depicted in the green color. Depending upon what time of day the clouds and showers cross a particular city or town, will depend upon who gets hot and who stays drastically cooler. In this example, inland areas could easily get some 10 degrees hotter, than say D.C., which has to deal with overcast skies and possibly a shower or two, keeping the area cooler than the mountains and the reverse of what naturally happens.
Cutoff lows also give meteorologists fits, because they slowly wander and therefore impact places over a longer period of time and are not as predictable as other weather systems maybe. In general, any stagnant weather pattern often turns into a dangerous situation, and the same can be said about a cutoff low. The powerful winds of the jet stream are responsible for pushing weather patterns around the world. Typically they move from west to east in a steady fashion, but every so often a storm will get pinched off from the jet stream, as you see by this graphic, and become stalled.
So how long does the pattern last? A cutoff low can linger over one spot for a few days or even a week or more until something comes along to push it away. What is deceiving is that while the systems are considered stationary, they do tend to wobble around, which means the exact same weather won’t occur every single day at every single location. Compare it to a boat that is anchored in a lake. The anchor is thrown overboard and keeps the boat generally in the same spot; however, the boat is still going to drift around a bit. The earth’s atmosphere is essentially water, so the cutoff low does the same thing in the atmosphere.
So why is a cutoff low problematic? Anytime a system remains stagnant you can anticipate some problems. Typically, when a cutoff low develops near our area we receive moisture off the Gulf of Mexico and Atlantic which makes the air quite tropical. During the warm season, this leads to daily rain or storm chances and the potential for repeated downpours and flooding threats. Flash flooding is responsible for the greatest number of weather-related fatalities in the united states.
As you can see, the cutoff low can be very problematic when it comes to forecasting temperatures and sky cover. Earlier graphics showed what one long-range forecast model has in store for us this weekend, with cooler than normal temps with a retrograding cutoff low in the Atlantic ocean. We’ll see if that comes together or is completely off base, but if it comes to fruition, then my temperatures forecast for this weekend is out the window, and you as viewers are frustrated! Hey, I get it, but that’s the case when dealing with something that has happened yet!