Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 131404 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1004 AM EDT Wed Mar 13 2024 .SYNOPSIS... Dry weather persists today and Thursday with unseasonably mild temperatures, but sea breezes on the immediate coast will keep it much cooler in those locations. 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. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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10 AM Update... After a cold start this morning with lows below freezing, sunny skies and the mid march sun angle have allowed temperatures to rebound nicely into the mid 40s already. Still expecting high temps to top out in the mid to upper 50s this afternoon with a solid chance at 60F for our typical warm sports in Hartford and Bradley, and a low chance in Taunton and Norwood. With ocean temps still in the 40s, A sea breeze will keep coastal communities colder today in the upper 40s. The question is how far inland will the sea breeze reach with very weak synoptic flow. 310 AM Update... * Plenty of sunshine today with some clouds arriving in the afternoon * Highs mainly upper 50s/lower 60s but cooler immediate coast The closed upper level low east of the Canadian Maritimes will continue to move further east and away from the region today. This will result in rising height fields as a mid level warm front approaches. We still expect plenty of sunshine today...but do expect an increase in mid/high level cloudiness by late in the day. Low risk for a few brief sprinkles by evening...but boundary layer is quite dry so do not expect much more than that. 850T warming to between +4C and +6C coupled with a relatively dry airmass in pre-greenup should allow temps to overachieve a bit. Thinking highs inland from the coast will be mainly in the upper 50s to the lower 60s with perhaps even a few middle 60s in the lower CT River Valley. Winds will be rather light too...so quite a comfortable afternoon for mid March standards. Meanwhile...weak pressure gradient will allow for sea breeze development along the immediate coast. This should keep afternoon temps in the upper 40s to the lower 50s in this region.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
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Key Points... * Light/Calm Winds tonight with lows mainly in the 30s * Plenty of sun Thu with highs 60s to near 70...cooler coast Details... Tonight... Some mid/high level cloudiness this evening in association with the mid level warm front. We may even see a few brief sprinkles...but given the dry boundary layer do not expect much more than that. Otherwise...expect at least partial clearing overnight with a ridge of high pressure taking control. Light to calm winds will allow for overnight low temps mainly in the 30s...but a few upper 20s are possible in the normally coldest outlying locations. Thursday... Upper level ridge axis approaches from the west. This will set the stage for a beautiful Thursday across most of the region. Plenty of sunshine expected with 925T climbing to between +9C and +12C inland from the coast. Thinking temps likely overachieve a bit in pre- greenup with highs mainly in the 60s inland from the coast. In fact...a few locations in the Lower CT River Valley may hit 70. Weak gradient though will allow for sea breezes along much of the immediate coast...which will hold highs in the 50s in most of those locales.
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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 /14Z WEDNESDAY THROUGH SUNDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Today...High Confidence. VFR. Light NNW winds shifting to the SE this afternoon with a sea breeze component developing along portions of the immediate coast around roughly 14-16Z. 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 14-16Z. KBOS TAF...High confidence in TAF. ESE sea breeze develops around 15Z. KBDL TAF...High confidence in TAF. 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... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today through Thursday...High Confidence. Any lingering marginal 5 foot small craft seas across our eastern waters will subside by daybreak. Otherwise...a weak pressure gradient will keep winds/seas below small craft advisory thresholds today through Thursday with good vsbys. 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. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Frank/BL NEAR TERM...Frank/KP SHORT TERM...Frank LONG TERM...BL AVIATION...Frank/BL MARINE...Frank/BL

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