Rex Block Breaks Down as Showers, Storms Begin to Re-Enter the Picture

Today will likely see clouds increasing from southwest to northeast during the day as a Rex Block breaks down, which occurs. This occurs when an area of high pressure is located directly north of an area of low pressure. The high blocks the low from making a quick exit. In this case, New England is under the ridge of the high pressure with the low pressure system sitting over the South. This changed up the weather pattern from our previous block, which resulted in plenty of rain.

Below: 500mb height anomaly showing a ridge built over southern Canada and the northeast with a trough over the southeast:

As this pattern breaks down, it will allow the low pressure system over the south to meander northward. Scattered showers on Wednesday will be most likely over southern New England with a majority of the region likely seeing a mainly dry day. Forcing will be weak, so showers will never really fill in at any time, but they will be around throughout the evening and overnight hours. Several hundred units of CAPE will be present, allowing for some instances of thunder.

Below: HRRR showing expected weather this evening:

The Rex Block will fully collapse by Thursday, allowing for a period of large-scale, upper-level troughing to take hold across the northeast. The closed low pressure system over the Great Lakes will likely be deamplifying as it crosses New England, causing it to weaken. This will allow for periods of scattered showers from Wednesday night through Friday.

Moisture will continue to build through the end of the week, but forcing for rain will remain fairly weak as the system weakens. This means washout potential is low and extended periods of dry weather remain likely between the showers and storms in any given location within New England. A warm front will approach southern New England on Thursday, allowing for an increase in humidity.

The wave of low pressure passing New England Thursday and Friday will move east for the weekend. This will be replaced by an upper-low sliding eastward from the Great Lakes into southeast Canada. This will keep the chances for scattered showers and thunderstorms in the picture through the weekend. Shower chances will likely drop for much of the day Friday before going back up later in the day and into the overnight hours, similar to today and tonight.

The weekend will continue the theme of late this week. As the upper-low slides eastward, it will rotate waves of energy through New England, allowing for scattered showers and storms to develop. Emphasis should be placed on the word scattered, as there will continue to be dry periods mixed in between the showers. A widespread soaking rain remains highly unlikely. The chance for strong to severe thunderstorms is also low at this time.

Aside from precipitation chances, temperatures will be hanging around seasonable levels for the most part, with warm conditions over interior western New England. The chilly ocean air will keep things cooler for eastern New England and especially the coastal plain. Humidity will be ticking up through the week, likely reaching the highest levels of this young warm season thus far. This will be coming on an increasingly strong and moist southerly flow ahead of the system to our west. This drops back down on Sunday with the passage of a cold front.

That cold front on Sunday is a sign of things to come for much of next week. Signs are pointing toward a cooler end to May relative to seasonal averages. After this upcoming weekend, there could be a sustained period of cooler weather across the northern United States as troughing continues to dominate. While exact temperatures are hard to say at this point, New England could see plenty of highs in the 50s and 60s through most of next week.