The United States has entered into a general pattern typical for the summer months. The jet stream has flattened out, and will remain mostly flat across the country without any major ridges or troughs. This is a far cry from this time last year, when an extremely persistent omega blocking pattern was set up, with a large ridge ridge in the center of the country and deep troughs digging into the east and west coasts. This brought cloudy, cool and rainy weather to New England.
With a flatter jet stream, or zonal flow, this keeps weather systems moving across the northern tier of the county at a decent clip. The northern jet stream will generally lay over, or near, New England this week. This will keep weather systems (both low and high pressure systems) moving through the region without any remaining in place for an extended period of time. It's worth noting that the graphic below just shows the general setup this week, the pattern will not be locked into that exact position all week.
With this pattern, neither high nor low will dominate New England's weather, but rather change places. For today, Tuesday, and into Wednesday, New England will be under the influence of high pressure. This won't last long as the next trough of low pressure approaches for later on Wednesday.
This system will bring a round of showers and thunderstorms into New England for Wednesday night into Thursday morning. Some pop-up thunderstorms will be possible Wednesday afternoon amid increasing heat and humidity ahead of the cold front. There could also be some scattered showers across Vermont Wednesday morning. The atmosphere will be moisture-rich, so heavier downpours will be possible. A half inch to inch of will be possible with locally higher amounts where the downpours set up.
HRRR showing potential weather overnight Wednesday night to Thursday morning:
After this system moves through, high pressure will return for the remainder of the week. The high pressure system will begin to build in from the west later on Thursday, move overhead Friday and offshore on Saturday. Again, keeping things moving along. Later on Saturday and into Sunday, the next low pressure system arrives with another cold front.
Depending on the timing of this front, there could be a period of more widespread thunderstorms. The timing of the front will be pinned down later in the week. Either way, a period of unsettled weather will be likely sometime this weekend, but washout potential is low at this point.
After this system, high pressure looks to build back in for Monday. Should this general pattern hold, which it very well could and some guidance seems to be keen on, then we could expect another system with scattered showers and thunderstorms headed toward the middle of next week, likely on Wednesday and/or Thursday. Now looking over a week out, things start to get fuzzy, but you can see the general pattern of highs and lows trading off with neither getting hung up around the region for very long.
Weather maps for Tuesday (June 25) through Monday (July 1). You can see the the progressiveness of the pattern across the north with fronts moving through followed by high pressure:
As far as temperatures go, zonal flow, or near zonal flow, is very supportive of temperatures hanging around average for New England, especially when the jet stream sets up near or over the region. With that said, temperatures will generally be up and down with the changeable pressure, but no major cool downs or heat waves are currently in the picture. Temperature swings are generally looking to range from the high end of seasonable to the low end of seasonable.
This can be seen by looking at temperatures this week. Temperatures will be jumping well into the 80s and low 90s for midweek before dropping back to the 70s to low 80s for the end of the week post-cold front. Temperatures may rise again later this weekend before dropping again at the start of the next work week post-cold front.
One other item to look at with this setup is the correlation between the NAO (North Atlantic Oscillation) and PNA (Pacific North American) indices. We bring these up frequently in monthly outlooks. Basically, the NAO index can be looked at for the large-scale setup over the east while the PNA can be looked at for the west. When both of these indices are around the same area, it can be an indicator of a more zonal flow.
NAO and PNA indices and forecasts. You can see both are right around +1 in the near term (where the red lines begin, the black line before the red lines begin show the observed value dating back to March):
