Blocking patterns have become a staple feature of spring weather in New England. The region started the spring in a Greenland Block. In the middle of spring New England moved into an Omega Block. Now we'll be entering what's called a Rex Block for this holiday weekend (and beyond).
So what exactly is a Rex Block? It's a rather atypical weather pattern that involves an area of high pressure that sets up directly (or nearly directly) north of a closed low pressure system (which is a low that has a clear center of circulation). This set up leads to more mild and dry conditions in the northern area and cooler and unsettled in the southern area.

This set up is all but guaranteed to set up this weekend as an area of high pressure looks to set up shop over the Great Lakes which will help a closed low get cut off and stall offshore of Georgia and the Carolinas. This will keep that southern storm down in the south.
This set up will not only keep New England dry and bright through the weekend, but it will allow a warm up to occur. New England has been cool and below average for much of the month of May, and this will continue through the end of the work week as a cold front drops through New England today (Wednesday). Once this block sets up, New England will be looking at highs well into the 70s and, in some areas, well into the 80s.
This weekend's Rex Block highlighted on the Euro Ensemble model:

The one exception to these warmer temperatures will be the immediate coast and Cape Cod. The typical spring sea breeze will keep these areas cooler than the rest of the region. Just how much cooler the coast will be remains to be seen, as the high pressure will create these sea breezes daily, but just how pronounced they are remain rather uncertain.
For Memorial Weekend, Friday will be coolest day as the region will still be under the influence of the cold front thanks to a continued northerly wind. Saturday is when the Rex Block takes over, leading to mainly seasonable temperatures. Sunday will be the hottest day with temperatures shooting into the 80s with some interior areas getting well into the 80s.
Memorial Day itself will likely be a notch cooler than Sunday, but still above average. The entire weekend will see mainly sunny skies. Next week is looking to stay warm as well. The transition to summer weather is looking to get underway.

Blocking patterns can be very stubborn and slow to break down. This particular block, however, looks like it will be controlled by the area of low pressure. This means that the block could break down quicker. While this pattern will likely be with us through early next week, it does show signs of breaking down by the middle of next week.
The Rex block is unique in that it brings New England nice, sunny weather whereas the other two blocks we've been in this spring puts New England on the cool and unsettled side. Out of these three blocking patterns, the Rex Block is the least common.
Here's a look at the other two blocks. The first one is the Greenland Block, which was the set up in March. The second one is the Omega Block, which was the set up in Late April.
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