DAYS 1-5 (MAY 21-25)
Today we are going to get an example of how a little mesoscale feature, not forecast that far in advance by guidance, can impact the weather fairly significantly – in this case, delaying sunshine and heat by several hours and as a result impacting the sensible weather for the entire day. Only 2 1/2 days ago a meso-scale batch of showers and thunderstorms originated in the Colorado area and has since made its way steadily eastward, passing across far southern New England (mostly just offshore) late last night. The departure of this feature, which produced showers as far north as the MA/NH border and a few heavier showers and thunderstorms closer to the South Coast (with big t-storms offshore), has left us with a delayed warm frontal passage, only across about 1/2 the region as of sunrise, and lots of cloudiness, dampness, and even areas of fog. As the hotter air mass works its way in from the west and southwest, we will see an erosion and departure of this cloudiness and eventually the light and variable wind, even from the north and northeast in some areas, will become more southwesterly. Some East Coast beaches may never fully realize the southwesterly breeze until sometime tonight though, and that will keep temperatures down there, as well as along the South Coast where a southwesterly wind is already coming off cooler water anyway. So we don’t just blast into the heat today – it will be a slow process, especially the further east or nearer the coast one lives, where the 90 degree temperatures may have only existed in a forecast heard in the last few days. Once we get to tomorrow though, we’re in it. Full southwesterly air flow everywhere, and only where that wind comes off water will there be a modifying influence, so there will be parts of southern New England that stay below 90 again, but this should come as no surprise in late May, when our surrounding waters are cold enough to pain the ankles of those who venture in too quickly. (And speaking of, if you do beach it, beware of that chilly water and limit your immersion. It is dangerous if you try to swim in water that’s too cold.) We’ll be watching the approach of a cold front later Sunday, which will generate some strong to severe thunderstorms west and north of the WHW forecast area, but the timing of that front appears too late to bring the heavy duty stuff into our region, only remnant showers and embedded weakening storms Sunday evening and night. Ironically, the best instability in our atmosphere occurs today, but most of the atmosphere doesn’t cooperate and storms will never be realized. Tomorrow, however, we may see a couple isolated cells pop up ahead of any cold frontal activity – air mass storms in the heat of the day. Though most will not see that. Regardless, the cold front that arrives Sunday night puts an end to our brief early-season heat, and we’re right back to near seasonable air for Monday. We’ll have at least partial but not maybe complete clearing, as the frontal boundary will be a bit sluggish on departure, and a few rain showers may skirt the South Coast region because of that. But for the most part, Monday will be a rain-free day with much lower humidity than we’ll have Sunday. Tuesday’s and Wednesday’s weather will be governed by high pressure, the center of which will be north of our region Tuesday, which will be a fairly cool and breezy day. The center of the high slips a bit south and weakens by Wednesday, which will still have a broad scale onshore flow, but more southeasterly, and less brisk. Just don’t let this weekend’s burst of heat make you think summer is here to stay. It’s still very much springtime here in southeastern New England…
TODAY: Through mid morning – clouds and areas of fog, even patchy drizzle especially near the coast. Midday – decreasing clouds from west to east. Remainder of day – sunny. Increasingly humid – dew point rising into 60s. Highs 75-82 Cape Cod / South Coast, 82-89 just inland from South Coast as well as immediate East Coast, 89-96 inland, hottest over interior valleys. Wind variable under 10 MPH becoming SW 5-15 MPH from west to east.
TONIGHT: Clear except patchy ground fog. Lows 63-70. Humid – dew point lower to middle 60s. Wind SW up to 10 MPH.
SUNDAY: Sunny to partly cloudy. Slight chance of isolated afternoon thunderstorms. Highs 75-82 Cape Cod / South Coast, 83-90 just inland from South Coast and portions of immediate North Shore & South Shore, 91-98 elsewhere with hottest interior valleys. Wind SW 5-15 MPH but some localized weak sea breezes on eastern shores.
SUNDAY NIGHT: Variably cloudy. Chance of showers and thunderstorms. Patchy fog. Lows 65-72. Humid – dew point 60s. Wind SW 5-15 MPH, higher gusts.
MONDAY: Sun/cloud mix. Passing showers possible South Coast / Cape Cod. Highs 75-82. Less humid. Wind W-NW 5-15 MPH.
MONDAY NIGHT: Clearing. Lows 50-57. Wind N 5-15 MPH.
TUESDAY: Mostly sunny. Highs 64-71, coolest coast. Wind NE 10-20 MPH.
TUESDAY NIGHT: Clear. Lows 49-56. Wind E up to 10 MPH.
WEDNESDAY: Mostly sunny. Highs 67-74, coolest coast. Wind NE 5-15 MPH.
DAYS 6-10 (MAY 26-30)
High pressure slips to the south and our air flow turns more southerly May 26 with some more cloudiness, then add in the chance of showers for May 27 as a disturbance and frontal system move through from west to east. Based on current timing, Memorial Day Weekend May 28-30 looks dry with high pressure in control, along with seasonably to slightly warmer than normal temperatures.
DAYS 11-15 (MAY 31 – JUNE 4)
End May / early June looking like weak zonal flow pattern with minor disturbances. Overall regime is seasonable temperatures and drier than average weather.