All week long, Thursday temperatures were a major point of contention among guidance. This stemmed from a weak frontal system moving right through the middle of New England. This brought the system's warm sector into southern and central New England while keeping northern New Hampshire and western Maine on the cool and rainy side.
How far north this warm sector pushed would ultimately determine highs for the day. The typical spring sea breeze also conspired to complicate the temperature forecast with coastal areas of southern New England getting held to cooler temperatures. All of this led to afternoon temperatures landing all over the place in New England.
Throughout the spring, especially from mid-April to mid-May, New England's temperatures are riddled with potential pitfalls. These pitfalls mainly come in the form of a sea breeze, stubborn cloud cover and a bombardment of backdoor cold fronts. As we like to say, there are just so many things that can steal warmth from New England during this one month period.
The above features can cause a change in guidance from supporting widespread 70s to suddenly having most of the region stuck in the 50s. This is why we rarely speak of warm-ups this time of year with confidence. Guidance can turn on a dime, and it almost never turns toward warming. Warm-ups this time of year will almost always be very localized, as seen in yesterday's temperatures.
When writing about the potential warm-ups in New England this time of year, there will almost always be a "but" attached to it. Last Monday, for example, saw mild temperatures (for southern New England, anyway), but it was still a far cry from the 85-90+° warmth that built into the Mid-Atlantic. You can see in the image below that a southwest flow around high pressure ended up being cut just short of New England thanks to a backdoor cold front that maintained a cool, northerly flow in New England.
Observed temperatures and wind direction on Monday, April 29th:
Yesterday, the chilly air coming off the ocean led to the immediate coast of New England, particularly the south coast, being held to the 50s most of the day while areas just a bit farther inland surged well into the 60s and eventually the 70s and even low 80s.
Looking ahead, Saturday will remain on the cooler side for many. The typical areas that are less prone to having mild temperatures stolen will continue to be warmer. These areas being the Connecticut River Valley and Champlain Valley. High will range from the low 50s near the coast to near 70° in the warm spots of western New England. Sunday will be a cool and raw day for everyone (almost everyone, temperatures love to be varied across New England this time of year, eastern Maine will be a touch warmer).
So, when's the next warm-up? It's looking to come on Monday and Tuesday of next week (May 6-7). Temperatures are looking to get well into the 60s for pretty much everyone with plenty of 70s. This will come as a system moves through on Sunday and Sunday night, bringing a round of showers. Behind this system, a fresh flow from the west will kick in, bringing a milder air mass with it. A westerly flow will also mean that areas closer to the coast will have a chance to warm as well.
850mb (around 5,000 feet above sea level) temperature anomaly from Sunday afternoon through Wednesday morning. You can see a warmer air mass moving in from the west and a backdoor cold front dropping into eastern Maine later on Monday:
As we mentioned before, there's almost always a "but". The but with this warm-up will stem from the timing of the system. The timing has been trending later with showers now expected to begin more toward Sunday afternoon and evening. Clouds and spot showers may linger from this system into Monday morning.
The mild temperatures will hinge on clouds mixing out for the afternoon. If the clouds are stubborn and hang around, it will be cooler. Also, a backdoor cold front may drop into northern Maine on Monday, making for a cooler Tuesday.