(WGHP) – It’s officially May, but it doesn’t quite feel like it temperature-wise with the Triad seeing high temperatures in the 60s again this week.
One of the reasons for the cooler temperatures has to do with what’s occurring in the mid-levels of the troposphere, the atmospheric level where the weather occurs. The National Weather Service shares that the majority of the weather we see is driven by winds occurring 15,000 to 18,000 feet above the ground.
This week, a “blocking pattern,” known as the Omega block, is occurring in the mid-levels of the atmosphere and is controlling the weather we’re seeing across the United States.
What is the Omega block?
An Omega block is a combination of two cutoff lows and one blocking high that’s “sandwiched” between the two areas of low pressure, according to the National Weather Service.
A blocking high is any high-pressure system that holds nearly in place or moves slowly compared to the west-to-east flow of air “upstream” from it, according to the American Meteorological Society. The system essentially “blocks” migratory cyclones from being able to move across it.
A cutoff low, according to the National Weather Service, is an upper-level low-pressure system that has become cut off from the normal westerly normal flow of air and moves independently of that current. Cutoff lows may hold nearly in place for days or, on occasion, move in the opposite direction of the normal flow of air, what we would call “retrogression.”
Tuesday’s upper-level pattern is a near-textbook definition of an Omega block. You can see in the graphic below a low-pressure system over the West Coast and a second low-pressure system of the Northeastern U.S. Between them, there is a high-pressure system covering much of the Great Plains.
The upper-level wind pattern resembles the Greek letter omega, Ω, which is where the Omega block gets its name.
What type of weather takes place with an Omega block?
The National Weather Service says that, in an Omega block pattern, the lows typically bring cooler temperatures and precipitation while the high-pressure system brings warm and clear conditions.
The blocking high pressure over the central United States is bringing warmth and sunshine to several states including Texas, Oklahoma, Colorado, Wyoming and Montana.
While temperatures are above-normal in those areas, some locations have recorded record-high temperatures. In May, Montana typically sees high temperatures in the 60s. However, Missoula, Montana, set a record high temperature on Monday with a high of 90 degrees, breaking the previous record set in 1901 by eight degrees. This is Missoula’s first 90-degree day of 2023 and their second earliest 90-degree day on record.
Keep in mind, the Triad has not yet recorded a 90-degree day and our warmest day this year occurred on March 24 and April 5, 6, and April 20 with a high of 84 degrees.
That means Montana’s warmest day of 2023 is 6 degrees warmer than the Triad’s warmest day.
Because of where the strong upper-level winds are positioned and because the pressure systems are close, windy conditions have hit several areas across the United States. The National Weather Service has issued a wind advisory in Nevada, Illinois, Missouri, Kentucky, Alabama, Georgia, South Carolina and North Carolina.
The strong winds led to a dust storm in Illinois on Monday which caused a massive pile-up on Interstate 55 on Monday.
Fire weather conditions from the strong winds and dry conditions has led the National Weather Service to issue Red Flag Warnings in Georgia, Iowa, Minnesota and portions of eastern South Dakota.
According to the Climate Prediction Center, wetter-than-normal conditions are forecast in California, where one of the low-pressure systems is located, and the wet weather is also expected in portions of the Northeast with the second low-pressure system.
How is the Omega block impacting weather in the Triad?
With the Omega block in place across the United States, the Triad will be sitting below a low-pressure system for the first part of this week.
The blocking pattern is the main reason why the weather forecast won’t change much during the first few days of the week. It’s also why we saw sunny skies on Monday morning but increasing cloud cover and spotty showers by the afternoon.
Since the blocking pattern means our weather won’t change much day to day in the Triad, we can expect similar weather to Monday on Tuesday and Wednesday.
Tuesday morning we saw mostly sunny skies, but we’ll likely see increasing cloud cover and a low chance for spotty showers by the afternoon and evening. The same is expected on Wednesday.
With the Omega pattern in place, below-normal temperatures are forecast in the Triad through the end of the week.
Afternoon temperatures will be between 5 and 15 degrees cooler than normal for May, when we normally see high temperatures in the mid-70s.
The position of the jet stream, the upper-level winds, is also part of why we’re seeing an Omega block in place. The Omega block has positioned the jet stream in a location that is bringing gusty winds to several areas in the eastern half of the United States, including the Piedmont Triad.
You may have noticed strong winds Sunday night and one of the reasons for that had to do with a cold front that moved through but also the building Omega block. Wind gusts reached between 25 and 50 mph in the Piedmont Triad from Sunday night into Monday.
On Tuesday, a wind advisory is in place for portions of the Piedmont Triad until 8 p.m. due to the sustained winds between 20 and 30 mph and the possibility of wind gusts reaching up to 45 mph.
Winds remain gusty Tuesday and Wednesday afternoon.
The European model is forecasting gusts to 35 mph Tuesday afternoon and gusts to nearly 40 mph by Wednesday afternoon.
Weather models are hinting that the Omega block will remain in place through the majority of this week.
However, by Thursday and Friday, the Omega block is expected to begin shifting which will allow winds to relax and temperatures to warm slightly heading into the weekend.
