Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 061508 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1008 AM EST Sat Mar 6 2021 .SYNOPSIS... Dry weather persists through the middle of next week. Colder than normal through the weekend, but then a significant warm up will lead to well above normal temperatures away from the immediate coast by mid week. A cold front moves through on Friday bringing our next chance of precipitation. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 950 AM Update... Made minor adjustments to cloud cover and temperatures across southern New England today. Have increased highs toward the 75th percentile of guidance, which only brings up temperatures a few degrees. Most notable difference is across the interior where some spots get into the lower 30s. Increased sky cover toward the latest HREF/HRRRE guidance, which brings in some of the cloud cover from the eastern Great Lakes this afternoon. Rest of the forecast is on track. 710 AM UPDATE... Forecast remains largely on track so only made minor changes to bring near-term forecast in line with latest observations. 4 AM Update... Low pressure lingers over Labrador and Eastern Quebec, although there are signs of weakening. Expect continued west-northwest winds into Srn New England with gusts of 15-20 kt, maintaining a feed of colder than normal air and drier than normal air (dew points in the single numbers). Mixing will reach to at least 900-mb, tapping temps that support max sfc temperatures in the upper 20s and 30s. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... The upper low in Canada starts drifting east. High pressure from the Midwest starts building in bringing lighter wind. But the cold dry air will linger tonight and Sunday with dew points in the single numbers. Light wind tonight will allow min temps in the single numbers and teens, perhaps a few 20s along the coast. Mixing on Sunday will bring max sfc temps generally in the 30s, possibly some upper 20s in NW Mass. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Highlights... * Significant warm up for the new work week with the peak of warmth on Wednesday and Thursday with highs in the 60s away from the immediate coast. * Next chance of any meaningful precipitation does not arrive till Friday with a cold front. The new work week looks to feature a transition into a +AO/+NAO/-PNA regime, which is favorable for a more significant and extended period of warmth. Not surprisingly, the CPC has 80 percent probability of above normal temperatures for Southern New England. Along with the lack of snow cover away from the interior and downsloping effect from strong southwesterly flow, blended model guidance will likely be too conservative with the high temperatures for most afternoons. Lending further confidence to anomalous warmth during this period is that both the NAEFS and ENS Situational Ensemble Awareness Table show heights at all levels and 1000mb temperatures rising to 90th percentile for Tuesday and 97.5th to climatology maxima for Wednesday and Thursday. 850mb temperatures spike to between +9 to +11C as 572 Dm heights build into Southern New England on Thursday. These are all above 90th percentile values according to SPC sounding climatology for Chatham, MA. A look at the 850mb and 925mb wind fields really show the low level jet cranking up late Wednesday into Thursday. With the precipitation and the cold front holding off till Friday morning, Thursday could well end up being the warmest day of the week and of the year so far. Also, with such a strong southwesterly flow, onshore flow is not expected to be an issue for Eastern MA coast, including Boston. The south coast, Cape and Islands as well as locales around Narragansett Bay would be cooler due to SSTs still in the mid 30s to low 40s. Given such a strong signal for temperatures to overperform, have used the 90th percentile of guidance for forecast highs for Tuesday and Wednesday while the maximum of guidance for Thursday. Should there be more sun than clouds on Thursday, would not be surprised to see upper 60s or even a few 70 degree readings especially in the CT River valley and Merrimack Valley, which tends to see temperatures overperform due to downsloping. Forecast wise, we have mid to upper 50s on Tuesday, upper 50s to low 60s for Wednesday and low to mid 60 s for Thursday. As with a stout southwest flow, locations away from the immediate coast will be warmest with coastal locations around 10 degrees cooler due to cold SSTs. Low temperatures overnight Tuesday into Wednesday as well as overnight Wednesday into Thursday are also adjusted using the 75th percentile of guidance as warm air advection continues in earnest. It is not out of the question that we could see 60s on Friday as well, especially locations in Eastern MA and RI, especially if the wind shift does not occur till the afternoon hours and the sun can break out following morning precipitation. Then it looks like much cooler but seasonable temperatures for the weekend. As for precipitation chances, a passing shortwave to our north could produce some showers on Tuesday but it does not look to produce any meaningful precipitation. But the dry cold frontal passage would lead to gusty conditions at times alongside with a wind shift to the southwest, which allows the warm air advection to begin in earnest. Then for later in the week, models have slowed down the frontal passage to Friday so Thursday is looking to be dry. There are indications that the wave could be deamplifying as the attendant surface low lifts north from the Great Lakes into Labrador. Therefore, we have kept precipitation probability no higher than chance. && .AVIATION /15Z SATURDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. VFR with dry but diminishing west-northwest winds today through Sunday. Strongest gusts today will be near 20 kt, on Sunday near 15 kt. KBOS TAF...High confidence in TAF. VFR. KBDL TAF...High confidence in TAF. VFR. Outlook /Sunday Night through Wednesday/... Sunday Night through Monday: VFR. Monday Night through Tuesday: VFR. Breezy. Tuesday Night through Wednesday: VFR. && .MARINE... Diminishing west-northwest winds through the weekend as low pressure moves off from Labrador and high pressure approaches from the Midwest. Wind speeds 20 to 25 kt today, mainly on the outer waters this morning, and around 15 kt Sunday. Seas linger around 5 feet on the outer waters today, with 1-3 feet closer to shore. Seas further subside from late today through Sunday with heights generally 1 to 3 feet. Still some areas of light freezing spray expected this morning and again tonight. But with diminishing wind, this will be harder to come by compared with past days. Small Craft Advisories come down on the nearshore waters, but linger on the outer waters today for seas and a few leftover gusts to 25 kt. Expect the last of the small crafts to expire/cancel by early tonight. .Outlook /Sunday Night through Wednesday/... Sunday Night through Monday Night: Winds less than 25 kt. Tuesday through Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 9 PM EST this evening for ANZ254>256. && $$ SYNOPSIS...WTB/BL/Chai NEAR TERM...WTB/BL/Chai SHORT TERM...WTB LONG TERM...Chai AVIATION...WTB/Chai MARINE...WTB/Chai is the U.S. government's official web portal to all federal, state and local government web resources and services.