Great Stretch of Weather Continues Amid Zonal Flow

Great spring conditions continue through the rest of this week. This comes as zonal flow sets up over the United States, which occurs when the jet stream lays generally flat across the country without pronounced ridges or troughs. This typically allows for quiet weather and seasonable to mild temperatures, and that will be the case through the rest of this work week.

Below: Large-scale flow pattern set up across the United States for Wednesday, showing a nearly flat jet stream:

A strong west-to-east motion allows for weather systems to move across the country fairly quickly. This also prevents large-scale, strong storms from crossing the country as the motion of the jet stream moves systems quickly across the country without stalling or gaining too much strength.

A zonal flow is the opposite of what's called meridional flow, which is a stronger north-to-south motion. This is the pattern that is synonymous with larger-scale, more powerful storm systems. This is when the jet stream takes on much more of a wavy pattern, allowing for blocking of systems. This pattern also allows for more extreme temperature contrasts, an important factor for (non-tropical) storms to strengthen.

Below: Current weather alerts as of Wednesday morning, showing little signs of large-scale, high-impact storms:

Along with lower impact weather, zonal flow typically lends itself to generally seasonable to mild temperatures. New England will continue to air on the mild side for the rest of the week as warm, Pacific air is able to spread across the country with no blockages. The biggest limiting factor for temperatures will be along the coast due to sea breezes. A sea breeze kept temperatures at the coast in check yesterday and will continue to do so through the rest of the week.

High pressure to the west of New England today should help keep the sea breeze suppressed until later in the day, allowing for mild conditions at the coast compared to yesterday. This high pressure will shift east of New England on Thursday, allowing for an onshore flow and an earlier start for the sea breeze, keeping the coastal plain cooler once again.

Below: Temperature departure from average Thursday afternoon:

As we've said before in set-ups like this, zonal flow means low-impact weather, not no weather at all. A weak, moisture-starved shortwave will dart through northern New England Thursday afternoon into Friday morning. This will bring about scattered showers, mainly for northern New England beginning in the afternoon and spreading eastward through the evening. A few rumbles of thunder will be possible within the showers.

Below: HRRR showing potential weather Thursday evening:

Right on cue, this very nice weather overall will be coming to an end on Saturday as a trough digs into the Great Lakes and pushes east. While timing remains a bit of a point of contention among guidance, it looks like showers may begin to break out Friday night along the system's warm front with the main shield of precipitation moving through from west to east during the daytime Saturday.

This system will have plenty of moisture to work with as it has a connection to high Gulf moisture. This will allow for a period of moderate rainfall with the potential for heavier downpours embedded within it. The system is trending toward a track near, or just south of, the Canadian border. This southward trend does put New England in the zone of the heavier precipitation. Should the system trend northward into Quebec, it would lead to lighter precipitation totals. That will be the main area to watch in the coming days with this system.

As it stands now, a widespread 0.25-0.75 inches of rain will be possible across the region. The system is progressive, which will be the main limiting factor on the total amount of rainfall. There will also be a chance for some thunderstorms along the cold front, especially if it ends up crossing the region Saturday afternoon or evening. Should the system take a northern trend, the threat for thunderstorms would increase.

Below: Current 5-day precipitation forecast (a vast majority of this should fall during the daytime Saturday for New England):

The progressive nature of the system will do its best to salvage Sunday with drier weather returning. It will likely be cooler and windy behind the cold front, however. Dry weather looks to continue into early next week with another warm-up coming after the weekend. We did mention the possibility of warmer weather making its way to New England at the end of April in our monthly outlook published at the start of this month.