Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 221959 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 359 PM EDT Fri Mar 22 2024 .SYNOPSIS...
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Active period of weather arrives late tonight through Saturday night with heavy rain, flooding, wintry weather, and marine hazards. Drying out Sunday into early next week but rather windy along the coast, especially Cape and Islands. Below normal temperatures will prevail. The next chance of rain will be Wednesday and Thursday as another frontal system approaches.
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&& .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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Tonight/early tomorrow First half of the night is quiet across the region with some increasing cloud cover and light winds ahead of a robust low- pressure system that will move over the region tomorrow. Active weather begins to settle over southern New England during the early morning hours as a surface warm front associated with a deepening low-pressure system begins to lift over the region. Temperatures on the north side of the warm frontal boundary will be well below freezing. As warmer air aloft overruns the cooler air in place, we`ll begin to see precipitation develop in the form of light snow showers across western MA and CT. As the warm nose edges further north, a melting layer develops between about 850 and 900 hPa. With surface temps remaining at or below freezing, this will support a freezing rain profile for north/northwest Hartford county, western MA, and northern Worcester county. Based on latest suite of ensemble guidance, freezing rain may begin as early as 5am across western MA/CT and continue through 09 to 10 am when surface temps will begin to rise above freezing and allow a changeover to rain. Prior to the changeover, substantial ice accumulations from a few hundredths of an inch to a tenth of an inch or more will be possible. For this reason, a winter weather advisory remains in effect for the aforementioned areas expected to experience freezing rain. Winds increasing out of the southeast to 10 to 15 knots during this period as well.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
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Tomorrow By mid-morning tomorrow, surface temps will have increased to above freezing across southern New England. This will result in any remaining frozen precipitation changing over to rain. From there on out, the rest of tomorrow is a complete wash out. A coastal low develops and moves off the mid-Atlantic coast before tracking over or just southeast of The Cape/Islands. An impressive region of frontogenesis develops across southern New England by early afternoon and will support a period of heavy rainfall that may result in urban, small stream, or poor drainage flooding. Latest HREF run paints a swath of 2 to 4 inches of rain across CT, RI, and southeastern MA with the heaviest rainfall between roughly 2pm and 8pm. While confidence in a significant rainfall event is higher than normal, even subtle changes in the storm track could result in the axis of heaviest rainfall lifting north or south, so there still remains a bit of uncertainty at 24 hours out. Given the relatively wide goal post for the axis of heaviest rainfall, a flood watch is in effect for the southern and eastern forecast areas. Only northern Worcester county, Franklin, and Hampshire counties are excluded. In addition to small stream flooding, some larger area rivers in southern RI are at risk for flooding as well (see Hydro AFD section). Temperatures range from upper 30s to low 40s across the interior/northwest areas tomorrow, with more mild temperatures in the upper 40s to low 50s across southeastern MA and RI. Tomorrow Night Surface cold front associated with the low-pressure system moving over southern New England pushes through the region tomorrow evening. This brings precipitation to and end for most of the region from west to east between about 8pm and 2am. Clearing and strong northwest winds from 15 to 25 mph will follow the cold front. Precip lasts a bit longer over The Cape/Islands tapering off between roughly midnight and 4 am. Temps dive into the low to mid 20s across the interior/northwest areas and upper 20s to low 30s across southeastern MA/RI prior to sunrise on Sunday.
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&& .LONG TERM /SUNDAY THROUGH FRIDAY/...
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Highlights: * Mostly dry Sun into Tue, but blustery with below normal temperatures. Quite windy over the Cape/Islands * Increasing risk of wet weather Wed into next Fri. Temperatures trending back above normal late next week. A broad mid level trough is expected to morph into a mid level cutoff over the North Atlantic early next week. This should trap the surface low pressure beneath it, and keep it lingering offshore of southern New England. Still some uncertainty in just how far offshore this low pressure will wind up being. At present, thinking the latest NationalBlend (NBM) deterministic solution is on the pessimistic side of the envelope. Maintained a faster departure of clouds and rainfall Sunday. High pressure over eastern Canada is expected to nudge into our region for Monday and Tuesday, leading to mainly dry and partly cloudy conditions across most of our region. The exception to that will be across far eastern MA, and especially the Cape and islands. Thinking clouds may linger longer there, along with a few showers Sunday morning. Will possibly need a Wind Advisory at some point Sunday into Sunday night into Monday. It`s marginal still, so not very high confidence. With all the other ongoing headlines, will wait until confidence increases before issuing such a headline. The weak high pressure should maintain dry weather MOnday and Tuesday, but also bring in colder air with a persistent N to NE wind. Eventually though, this high pressure should break down and move farther offshore. That will open the door for a slow-moving front to impact southern New England late next week, most likely some time from late Wednesday into Friday. It should not be a total washout, but looking at the prospect of a prolonged period of unsettled weather. Will need to monitor the impact of any additional rainfall on our creeks, streams and rivers, which should still be recovering from the rainfall this weekend. Temperatures should trend warmer mid week, and likely return to above normal temperatures Thursday into Friday.
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&& .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
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Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High- greater than 60 percent. 18Z update... Through 00Z... High Confidence VFR. Increasing mid-high clouds from 080-120. Steady 5 to 10 know westerly winds weakening and becoming light southwest by 00Z. Tonight...High confidence in trends. Moderate in timing. VFR through about 06Z with light southwesterly winds becoming more south/southeasterly. Conditions begin to deteriorate after 06Z as precip associated with a surface warm front lifting over southern New England begins to support MVFR ceilings and light precip. Frozen precip will be an issue at the western terminals (BDL/BAF/ORH). A brief period of -SN followed by -FZRA will be possible beginning as early as 08Z. Elsewhere, any precip will be limited to -RA, but likely will be closer to or after 12Z before precip reaches the eastern terminals. Tomorrow...High confidence in trends. Moderate in timing. -FZRA pay persist at BDL/BAF/ORH through as late as 14Z, but will changeover to rain thereafter with surface temps rising above freezing after sunrise. MVFR cigs/vsbys deteriorate to IFR by 18Z as rain overspreads the region. Rain picks up in intensity after 18Z and remains steady through 00Z. Southeast winds gradually increase throughout the day ranging from 10 knots across the interior to 15 to 20 knots over the coastal plain. Tomorrow Night... High trends. Moderate in timing. IFR/MVFR cigs improve to VFR returns as precip gradually ends from west to east from 00 to 06Z. Rain lingers a bit longer over The Cape/Island terminals likely tapering off between 06 and 09Z with VFR returning to this area between 09 and 12Z. Winds strengthen after 00Z behind a surface cold front. 15 to 25 knot sustained northwest winds with gusts up to 35 knots. Outlook /Sunday through Wednesday/... Sunday: VFR. Strong winds with local gusts up to 40 kt. Sunday Night through Monday: VFR. Strong winds with gusts up to 45 kt. Monday Night: Mainly VFR, with local MVFR possible. Strong winds with areas of gusts up to 45 kt. Tuesday: Mainly VFR, with areas MVFR possible. Windy with gusts up to 35 kt. Tuesday Night: Mainly VFR, with areas IFR possible. Windy with local gusts up to 30 kt. Chance SHRA. Wednesday: MVFR/IFR conditions possible. Chance SHRA.
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&& .MARINE...
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Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Tonight Quiet marine conditions through about midnight tonight. Thereafter, winds begin to increase out of the southeast ahead of robust low pressure system with sustained winds of 20 knots and gusts up to 25 knots by sunrise. Tomorrow Conditions deteriorate rapidly tomorrow as a strong low-pressure system moves over southern New England. Steady 20 knot southeast winds persist with gusts up to 35 knots possible, especially over the southern Marine Zones. Seas gradually increase from 4 feet early in the day to 6 to 9 feet by tomorrow evening. Near-shore eastern zones stay a bit lower with 4 to 6 foot seas. A gale watch is in effect through Monday morning. Tomorrow Night A cold front moves over the waters tomorrow night. Winds become even stronger out of the north/northwest with 30 knot sustained winds for most of the marine zones. Wind gusts from 30 to 40 knots. Seas increase to 10 to 13 feet over the outer marine zones and 6 to 10 feet for the near-shore zones. Outlook /Sunday through Wednesday/... Sunday: Moderate risk for gale force winds with local gusts up to 45 kt. Rough seas up to 15 ft. Sunday Night through Monday: gale force winds with gusts up to 45 kt. Rough seas up to 15 ft. Slight chance of rain showers. Monday Night: Moderate risk for gale force winds with gusts up to 45 kt. Rough seas up to 15 ft. Tuesday: Low risk for gale force winds with gusts up to 35 kt. Rough seas up to 13 ft. Tuesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 10 ft. Slight chance of rain showers. Wednesday: Winds less than 25 kt. Areas of rough seas. Chance of rain showers.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...Winter Weather Advisory from 2 AM to noon EDT Saturday for CTZ002. Flood Watch from Saturday morning through Sunday morning for CTZ002>004. MA...Winter Weather Advisory from 2 AM to noon EDT Saturday for MAZ002>004-008>011-026. Flood Watch from Saturday morning through Sunday morning for MAZ005>007-009-011>024. RI...Flood Watch from Saturday morning through Sunday morning for RIZ001>008. MARINE...Gale Watch from Saturday afternoon through Monday morning for ANZ230>237-250-251-254>256.
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&& $$ SYNOPSIS...Belk/RM NEAR TERM...RM SHORT TERM...RM LONG TERM...Belk AVIATION...Belk/RM MARINE...Belk/Dooley

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