Omega Block; Cutoff Low to Influence New England's Weather This Week

The cold front that stalled over New England will generally remain in place over the region for the next several days. This will occur as a cutoff area of low pressure slowly meanders around the Tennessee Valley/Great Lakes region. A cutoff low occurs when a closed low pressure system completely cuts off from the main flow of the jet stream.

This allows the storm to basically make its own rules; stalling out, moving westward and making loops over the region. This can go on for days, even up to a week at a time before moving away. This is a common occurrence in the spring time as the jet stream slows down and generally migrates northward. This allows weather systems to slow down as they cross the region. Slower moving systems are much more susceptible to getting cutoff.

Below: 500mb flow pattern Monday afternoon, showing a pretty clear Omega Block situation:

This cutoff low over the east will be one of two set up across the United States this week. These two lows will set up an Omega Blocking pattern. This will be a strong and classic Omega Block, which involves a large ridge of high pressure flanked by the two cutoff low pressure systems on either side of it. This can shape the jet stream to appear as the Greek letter Omega. Dry and mild weather is often observed under the ridge with unsettled and cooler weather in the troughs.

In this specific case, cutoff lows will be positioned over the southwest and eastern United States with a ridge over the northern plains. The cutoff low over the east won't be centered over New England, but the trough will influence the weather for the region. This cutoff will slowly drift east and likely make its closest pass to New England around midweek. This will keep the weather unsettled and on the cooler side for the most part this week.

Temperatures will likely get a bump on Wednesday as the low pressure very slowly drifts eastward. As it does so, the southerly flow around it will strengthen, bringing some milder air into the picture for a day. Cooler air will likely stream back in toward the end of the week as a cold front crosses the region and the low pressure system pulls away, leaving a cold pool of air.

On the precipitation side, this setup will produce near constant cloud cover with occasional rain showers. This pattern is the very essence of the term"unsettled". The best way to put it is that multiple rounds of showers will continuously cycle through New England through at least midweek. It's near impossible to say exactly when these showers will move through, but they'll be around through the week. The wettest day may end up being Tuesday for many in New England.

Below: RGEM showing hourly weather from noon tomorrow through Wednesday morning:

When all is said and done by next weekend, a widespread 1-3 inches of rain will likely have fallen across much of southern and central New England. Lesser rainfall is expected across the northern tier of the region. This will be beneficial rain, especially as it will be falling over the course of several days. Thus will keep the flooding threat low and generally keep the rain low-impact.

Below: Current 7-day precipitation forecast:

Heading into late next week and into the second full week of the month, the Omega Block will steadily break down. This will likely be replaced with expansive ridging over the western and northern United States. A trough may undercut the ridge over east, which makes for a more uncertain forecast heading toward next weekend. Whether it ends up drier and warmer by Saturday or remains cooler and unsettled will depend on whether ridging remains in place or if the trough reloads over the northeast.

Below: Height anomaly late next week showing the expansive ridging building over the west with a potential trough undercutting it across the south and northeast:

Whether you hate this pattern and just want the consistent warmth of summer or love this pattern as it keeps cooler weather around that much longer, there's little denying that this is exactly what is supposed to happen in the middle of spring. Blocking patterns, cutoff lows and very slow-moving fronts are expected in this part of the world this time of year. Spring 2025 will be no exception.