National Weather Service Boston/Norton MA
637am EDT Thu April 25 2024
Synopsis
Expansive high pressure system builds in across the northeastern United States through the end of the work week with sunny days and chilly overnights. Unsettled pattern sets up for Sunday into early next week with shower chances. Temperatures turn milder but there is a good deal of uncertainty as to how warm Sun/Monday are.
Near Term - Through Tonight
Highlights:
* Sunny, but slightly cooler than what is average for late April.
* Another chilly night ahead which has prompt a re-issuance of a Freeze Watch for many of the same locations, in addition to the Cape and Islands.
A quiet and sunny day ahead with surface high pressure moving down from the northwest and transporting a much drier and cooler airmass over southern New England. While the day starts off in the upper 20s and lower 30s, Freeze Warning remains in effect through 8AM, it will warm into the middle 50s for most locations, though coastal towns will be cooler due to an onshore wind, here the temperatures are in the upper 40s. Otherwise, winds are light and from the northwest.
PWATs (Precipitable Waters) are very low, less than 0.2 inch in most cases - this allows for lower dewpoints this afternoon, which are in the single digits north and low teens to the south - minimum RH values are upper teens and middle 20s.
Given the dry atmosphere, temperatures late this afternoon should drop a bit faster - many spots fall below 40 degrees by midnight. As we go into the overnight these light and variable winds become calm which sets up for a night of good radiational cooling. Nighttime low temperatures drop into the 20s and low 30s, while interior sections of northern Massachusetts may drop as low as the upper teens. Did leaned on the colder MOS guidance for these overnight lows. With that said, have opted for a Freeze Watch for for much of southern New England where the Freeze/Frost program is active, this includes eastern Massachusetts, Cape Cod, Martha's Vineyard, and Nantucket. All of Rhode Island, with the exception of Block Island, and northern Connecticut, with the exception of Litchfield County. Our neighboring WFO OKX did include their zones along our boundary in Connecticut for your awareness. Day crew will assess the guidance and make a final decision on whether or not a Freeze Warning or Frost Advisory is needed. Stay tuned!
Lastly, could be area of patchy fog in prone radiator locations as temperatures will fall close to the dewpoint temperature.
Short Term - Friday
Highlights:
* Mostly sunny and slightly warmer than Thursday. Coastal locations likely experience onshore winds which keep temperatures a bit cooler than interior communities.
There are no big changes to Friday, high pressure holds strong across the northeast while mid-level ridge noses into southern New England. The atmosphere remains fairly dry again, supporting another mostly sunny day. There are height increases and subtle WAA (Warm Air Advection - the movement of warm air) at 850mb and think afternoon high temperatures will be 3 to 5 degrees warmer with many locations reaching the upper 50s and low 60s. Given the high pressure with little winds aloft, do think there will be a good chance an onshore wind develops again, with speeds less than 10 mph and keeping those communities by the coast cooler in the low 50s.
Long Term - Friday Night Through Wednesday
Key Points... * Dry weather through Saturday.
* Scattered showers Saturday night become more hit-and-miss Sunday into Monday; more widespread rain chances on Tuesday and maybe a thunderstorm.
* Warming trend through next week but there remains a good deal of uncertainty as to how warm temperatures will be.
Details... Friday night and Saturday will be dry under the influence of high pressure as a mid level ridge builds overhead. Southern New England will remain on the northern periphery of an east coast ridge through at least Monday. A warm front extending from a low pressure lifting from the Great Lakes into Quebec will move through kicking off some scattered showers Saturday night but lack of strong forcing and rising heigheights aloft will keep rainfall amounts from a few hundredths to a few tenths. The chance for hit-and-miss showers continues Sunday and Monday as we remain on the periphery of the ridge and another passing low, but most areas will be dry much of the time. The more significant chance for showers comes around Tuesday as a low passes to our northwest and moist southerly flow kicks in ahead of it with a subsequent cold front. Guidance is so far keeping the best instability to our west in NY but but still plenty of time for changes, so can't rule out some thunderstorms, especially in western MA/CT.
As for temperatures, radiational cooling will contribute to a cold start to the weekend (in the low to mid 30s) before mild southerly flow kicks in and temps moderate each day. A pesky back door cold front may yet ruin party (i.e. keep 70s out of the forecast) at least for eastern SNE on Monday though a tight gradient is likely from west to east. Low confidence temperature forecast at this time. By Tuesday, however, stronger southerly flow kicks in ahead of the cold front and odds of upper 60s/low 70s are good.
Marine
Forecaster Confidence Levels:
Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent.
Today through Friday
High Confidence.
Surface high pressure sets up over the waters with light winds and diminishing seas - Small Craft Advisory continues for the outer waters do to rough seas, but is expected to fall below 5 feet by the end of today. Tonight and Friday features dry and tranquil boating conditions with gusts less than 15 knots and seas are 2 to 3 feet.
Outlook /Friday Night through Monday/... Friday Night through Saturday: Winds less than 25 kt.
Saturday Night through Sunday Night: Winds less than 25 kt. Slight chance of rain showers.
Monday: Winds less than 25 kt.
NOAA Boston MA Office: Watches - Warnings - Advisories
CT...Freeze Warning until 8am EDT this morning for CTZ002>004. Freeze Watch from late tonight through Friday morning for CTZ002>004. MA...Freeze Warning until 8am EDT this morning for MAZ007-014>021. Freeze Watch from late tonight through Friday morning for MAZ007-014>024. RI...Freeze Warning until 8am EDT this morning for RIZ001>007. Freeze Watch from late tonight through Friday morning for RIZ001>007.
Marine
Small Craft Advisory until 8am EDT this morning for ANZ232>235-237. Small Craft Advisory until 2pm EDT this afternoon for ANZ250- 254>256.
