Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 131806 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 206 PM EDT Wed Mar 13 2024 .SYNOPSIS...
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Continued dry and clear weather through tomorrow with a outside chance for an isolated shower late tonight. Tomorrow will feature mild temperatures away from the coasts where sea breezes will keep temperatures cooler. A more unsettled weather pattern develops Friday into the weekend, with rainy conditions for Fri and again on Sunday. Temperatures trend above normal through this weekend, with a cooling trend toward more seasonable temperatures by early next week.
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&& .NEAR TERM /TONIGHT/...
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Mainly dry conditions overnight outside of a low chance for an isolated shower/sprinkle associated with a weak mid level shortwave and cold front. Very narrow moisture axis around 850mb with dry air both above and at the surface will make it very difficult for any rain to reach the ground, thus capped POPs at 20%. With a mid level cloud deck around, radiational cooling conditions wont be perfect, but temps overnight will drop into the mid 30s with below freezing possible if skies stay clear. Winds tonight will be southerly less then 5mph.
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&& .SHORT TERM /TOMORROW/...
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Weak mid level ridge builds back in with continued high pressure at the surface. Skies remain mostly sunny again tomorrow setting the stage for another warm day. With 925mb temps jumping from roughly +7C to +11C range, high temps away from the coasts will likely reach the low to mid 60s, with a good chance at 70F for the CT river valley. Near the coasts, seas breezes will develop again, and with ocean temps in the low 40s, high temps will struggle to top the low 50s. Winds tomorrow turn light NW for the interior less then 10mph.
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&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Highlights * Unsettled Thu Night through Fri with rain showers. A few rumbles of thunder cannot be ruled out along with embedded downpours. * Dry on Sat with a mix of sun and clouds. * Another frontal system swings through Sun bringing more showers. Remains unsettled early next week, but shower activity may be more spotty with more seasonable temps. Thursday Night through Friday... Stuck in quasi-zonal southwesterly flow during this timeframe. A shortwave ridge over our region Thu Night will flatten out with a shortwave trough lifting into New England from the central Great Lakes into early Fri. Another trough digs into the Great Lakes/New England late on Fri. A frontal boundary will be situated over our region late Thu through Fri. An area of low pressure will ride along this front pushing it through and bringing us rain showers. Somewhat of an impressive shift in guidance from 24 hours ago with this late week system. Latest suite trending further north with a much more progressive system sliding through. Confidence still not as high as would like it to be given this big shift over the last 12- 24 hrs, so have generally stuck with the NBM for now. However, did dial back to slight chance/chance for now given there are still a lot of differences in the timing, intensity and track of the low riding along the front. Does appear that there is potential for heavy rainfall, especially with a frontal boundary parked over our area. The NAEFS/EPS situational awareness tables still indicating PWATs of 2-2.5 STD above model climatology, but still may generally be located more to our SW. This is also indicated by the latest suite of deterministic guidance and have decent agreement of a PWAT surge of roughly 0.75-1 inch. On top of this surge we have decent warm cloud layer depths of 2-2.5 km and perhaps up to 100 J/kg of MUCAPE. Given the environment there could be some heavy downpours, especially with a perhaps a SSW/SW 20-40 kt 925 hPa LLJ impinging on the region. Though will note this is much different a solution, and further north, than advertised than 24 hours ago. This shift can also be seen in the QPF with now low to mod (10-40%) probs of 24 QPF AOA 0.5 inches with the EPS/GEFS and GEPS guidance. The best shot for our CWA appears to be along/north of the Route 2 corridor. Highest risk is across northern New England with mod to high probs. At this point now essentially have nil probs of 1+ inches of rainfall. Stay tuned as would like a bit more run to run and model to model consistency before locking in on how things evolve. Still have signals that the stronger LLJ slides through and could bring gusty winds. The NBM at this point appears reasonable, but will be something else to keep an eye on as we get closer to Fri. Nudged our temps down slightly on Fri from the NBM as it appears the front may slide through as a backdoor cold front. For now am advertising highs in the mid/upper 40s across northern and eastern MA and the 50s elsewhere. Saturday... Stuck in cyclonic flow, but will have a shortwave ridge initially over the central/eastern Great Lakes early on Sat. The ridge builds into New England late on Sat, but flattens out a bit as it digs into the Great Lakes region late in the day. High pressure nudges into our region during this period. Dry and quiet weather anticipated. However, given the trough digging into Great Lakes will have a fair amount of cloudiness, especially during the second half of the day. High temps range from the 40s to the mid 50s. Sunday into Tuesday... Cyclonic flow persists through this period with a couple of troughs sliding through. Really not certain on exactly how things will evolve as guidance is a bit all over the place. Best shot for showers comes on Sun as a frontal system pushes through. At this point deterministic guidance painting Mon/Tue as dry, but given the cyclonic flow think there could be some spotty shower activity. Temperatures trending near to above normal. && .AVIATION /17Z WEDNESDAY THROUGH SUNDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Rest of Today...High Confidence. VFR. Light and variable winds switching from northerly to southerly. Sea breezes kick back out between 21-23z this afternoon Tonight...High Confidence. VFR with light and variable winds. Thursday...High Confidence. Light NW winds across the interior with sea breezes developing along the coast around 13-15Z. KBOS TAF...High confidence in TAF. Sea breeze kicks out between 21-23z and winds could turn SSW briefly before turning light SSE overnight. Sea breeze develops again tomorrow morning by 14z, but winds will already be SE. KBDL TAF...High confidence in TAF. VFR with light and variable winds. Outlook /Thursday Night through Sunday/... Thursday Night: VFR. Chance SHRA. Friday: Mainly VFR, with local IFR possible. Chance SHRA, isolated TSRA. Friday Night: Mainly VFR, with local IFR possible. Chance SHRA. Saturday: Mainly VFR, with local MVFR possible. Slight chance SHRA. Saturday Night: VFR. Breezy. Slight chance SHRA. Sunday: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA. && .MARINE...
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Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Tonight through Thursday...High Confidence. a weak pressure gradient will keep winds/seas below small craft advisory thresholds today through Thursday with good vsbys. Low chance for an isolated shower over the waters tonight. Outlook /Thursday Night through Sunday/... Thursday Night: Winds less than 25 kt. Chance of rain showers. Friday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers, isolated thunderstorms. Friday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. Saturday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Sunday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...RM/KP NEAR TERM...KP SHORT TERM...KP LONG TERM...BL AVIATION...RM/KP MARINE...RM/KP

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