Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 211141 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 641 AM EST Tue Nov 21 2017 .SYNOPSIS... Mild day today as winds shift to the southwest. A cold front approaches the region tonight, and will combine with moisture working up the eastern seaboard to bring a period of rain through Wednesday morning, especially SE New England. Dry and colder conditions expected Wednesday night through the end of this week. Milder with a few showers possible Saturday as a cold front approaches, then blustery and colder weather follows Sunday into Monday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... No significant changes to the forecast this morning. Only minor tweaks to bring forecast back in line with observed trends. Expecting gusty winds to develop quickly this morning as low level warm advection gives the mixing process a little kickstart. Previous Discussion... Mid-level ridge axis will push northward towards the Maritimes today as cold front from the west approaches the region. Overall anticipate a dry day as southwest winds take hold of the region. Strong WAA will continue to stream into the region as 925mb temps warm near 7-9 C by the afternoon. Bufkit soundings indicate mixing to near 900 mb thus expect temperatures to warm well into the 50`s with locations across southeast Mass near the upper 50`s. If we mix a bit higher, then cannot rule out a few spots reaching 60F. Clear skies across the area today. Cross sections show some moisture across the Cape and Islands which could bring a mix of clouds and sun. Otherwise the focus is on the winds for today. Increasing LLJ ahead of approaching front will mix down to the surface today. Expect southwest winds gusting to around 25-35 MPH. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Dry weather to start tonight ahead of approaching cold front from the West. High pressure to the east of the region will help increase southerly low level moisture off the ocean. This flow will increase low level moisture and thus some isolated showers after 2 AM across the south coast. Upper level shortwave will help push the front closer to the region during the early morning hours. While moisture appears to be meager with this front, the focus is more on the coastal low which will develop off the coast of the Carolinas. Moisture from this low will stream into the region resulting in PWAT values increasing to 1 inch which is 1-2 STD above normal. Appears that the 2 systems will remain split from each other, however the interactions between the upper and low level jets will help increase lift across the region. In fact, some model guidance suggest strong lift around daybreak which could lead to heavy downpours which will impact the Wed morning commute. Still a spread in where the heavy axis will be located with the EC and RGEM on the western envelope compared to Hi- res guidance and NAM. The GFS continues to the eastern outlier and thus trended away from it. Right now appears the the axis of heavier rainfall will occur across the I-95 corridor and points eastward. However this axis could still shift if the two streams do meet up, of if coastal low trends farther eastward. Regardless, looks like a good slug of rain with QPF amounts around 0.5-1 inch. These amounts could also increase within any thunderstorms. Went ahead and inserted a slight chc of thunder as dewpoints reach into the 50s and models continue to show some surface Cape. Highest confidence will be across the Cape and the Islands. Conditions will quickly improve from west to east during the day on Wednesday. In fact, once the cold front moves through the region, dry air will quickly usher into the region resulting in clearing skies and dry weather. CAA will spill into the area resulting in temperatures to fall during the day. NW winds will also be on the increase as wind gusts increase to 25-30 MPH by the afternoon. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Highlights... * Mainly dry and cool Thanksgiving Day and Friday * Milder with a chance of showers Saturday * Blustery and colder Sunday/Monday 21/00Z guidance suite remains in rather good agreement on the overall pattern through this portion of the forecast. In general, looking at a persistent mid level trough lingering near our region, although the amplitude and axis varies with time as various shortwaves move through the flow. This should mean temperatures trending below normal, especially late this weekend into early next week. Dry weather likely to persist into Friday, despite a cold front getting close to the northern MA border Friday. The most supportive moisture and dynamics for showers are expected to remain over northern New England. Our next chance for precipitation looks to be sometime this weekend. It`s not looking like a great risk, as humidity levels are somewhat lacking. However, there are a couple of fronts to move through, so this potential will need to be watched over the coming days. Colder air arriving Sunday into Monday could generate some ocean-effect showers toward the coast. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday/...High confidence. Today...VFR. Increasing SSW wind gusts 25-35 kt through the day. Tonight into Wednesday...VFR to start. Rain will overspread the region from southwest to the northeast after 2 AM lasting into Wednesday morning. MVFR/IFR cigs within heavier rain showers and fog. Conditions will improve to VFR quickly from west to east during the day on Wed as cold front passes through. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Wednesday Night through Saturday/... Wednesday Night: VFR. Windy with local gusts to 30 kt. Thanksgiving Day through Friday: VFR. Friday Night: VFR. Breezy. Saturday: VFR. Breezy. Slight chance SHRA. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday/...High confidence. Today...Building seas across the region as LLJ increases ahead of approaching cold front. Southwest wind gusts around 35-40 kts will result in gales across the waters. Went ahead and included Mass Bay, Boston Harbor and Narragansett Bay as strong mixing will occur during the afternoon. Tonight into Tomorrow...Southwesterly gales will continue but subside across the near shore waters. SCA will be needed as seas will remain above 5 feet and gusts near 30kts. Approaching cold front will bring widespread rain for the waters and limit vsbys by Wed morning. Front will sweep through Wed afternoon switching winds to the NW with gusts near 30 kts by Wed evening. Outlook /Wednesday Night through Saturday/... Wednesday Night: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Seas up to 5 ft. Thanksgiving Day: Winds less than 25 kt. Local rough seas. Thursday Night through Friday Night: Winds less than 25 kt. Seas up to 5 ft. Saturday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Gale Warning from noon today to midnight EST tonight for ANZ231>235-237-250-251-254>256. Gale Warning from noon today to 6 PM EST this evening for ANZ230-236. && $$ SYNOPSIS...Belk/Dunten NEAR TERM...Belk/Dunten SHORT TERM...Dunten LONG TERM...Belk AVIATION...Belk/Dunten MARINE...Belk/Dunten

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