Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 090240 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 940 PM EST Mon Mar 8 2021 .SYNOPSIS... Warm front lifts through late tonight bringing increasing cloud cover. High pressure reasserts itself Tuesday, bringing clearing and warmer temperatures, but it will be a bit breezy. The warmer and dry weather persists into late in the week. The greatest risk of light precipitation is on Friday with a cold front, which will return temperatures to more seasonable levels this weekend. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 940 PM Update... Light winds coupled with a dry airmass in place has allowed temperatures this evening to quickly fall back into the middle 20s to the lower 30s. However, temps will pretty much remain steady or rise a bit particularly across the southeast New England coast after midnight. This in response to a warm frontal passage and increasing boundary layer SW flow off the ocean. We also do expect an abundance of mid level cloudiness with this warm front, which was already overspreading the region. A brief sprinkle/flurry can not be ruled out, but would be so short-lived and localized did not feel it was worth mentioning and maintained a dry forecast. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Highlights * Clearing skies on Tuesday. Breezy with above normal temperatures. * Clear skies and light winds Tuesday night into Wednesday morning. The trough previously mentioned digs into Nova Scotia/Gulf of Maine by late Tuesday. Behind this feature will have a ridge building from Ontario into the eastern Great Lakes and Quebec by late Tuesday. The ridge builds over New England and much of the East Coast by late Tuesday night. Low pressure deepens as it moves into Nova Scotia/Gulf of Maine on Tuesday, but high pressure will build into southern New England. The high remains planted over the region Tuesday night. Tuesday... Cloud cover on the decrease as high pressure reasserts itself into southern New England. Will be a bit breezy especially earlier in the day as the pressure gradient tightens due to the deepening low to the northeast and high building in. Have gone with the NAMNest/ARW/GFS guidance for winds and gusts. This shows that we could tap into some 20-25 kt gusts within the mixed layer. Winds shift to the W and eventually the NW, which will promote downsloping. Given this setup have increased high temperatures toward the 80th percentile of guidance and lowered dew points to the 15th percentile of guidance. The result is high temperatures in the low to mid 50s across much of the region. The pressure gradient relaxes late in the afternoon as the high builds in, so the winds and wind gusts will gradually diminish. Tuesday night... Dry and quiet weather expected with winds becoming light and variable as high pressure builds overhead. Have gone with the 15th percentile of guidance for low temperatures in case winds do not completely decouple. May need to lower temperatures further in future updates. For now lows will be in the 20s across the interior and low to mid 30s along the coastal plain. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... 12z suite of guidance really not showing anything different with regard to the long term period. We start with a very warm pattern with temperatures more like mid-May, which will quickly flip to a colder than normal pattern for the weekend. Overall I stuck with a model blend, except for high temperatures Wednesday, Thursday and Friday where I leaned toward (but not fully all the way to) the warmer of the available guidance. Overall pretty good agreement amongst the guidance, so overall forecast confidence is on the high side. For a few notes regarding each day`s forecast, please continue to read on: Wednesday: high pressure will be moving to our east, and this will fully open the door for warmer air to start advecting into the region as winds start turning south/southwest. Still a dry airmass, so plenty of sunshine should result in mixing the boundary layer to about 3000ft. Extrapolating the temperatures of +2 to +4C from 925mb suggests a max temperature potential of 12-14C in lower elevations. As mentioned above, leaned toward warmer guidance and have painted in mid 50s, especially inland. Could be a few spots that hit the upper 50s. Cooler along the south facing coast given the winds. Can`t rule out a sea breeze along the east coast as well during the afternoon. If that happens, expect a quick temperature drop from the 50s into the lower-mid 40s in areas a few miles from the coast. Thursday: southwest flow is firmly established. 850mb temperatures will be in the 6-8C range, with 925mb temperatures of 8 to 10C. Forecast soundings don`t suggest we mix all the way to 850mb (which would have a potential of 23C at the surface). 925mb would suggest the max potential of 20C, but all the models show some mid level clouds, so we might not be able to achieve the potential. But 63-66F looks very likely. A little short of record highs, but those who like spring should be happy. Cooler again on the south facing coast, Cape and Islands. Winds look a little stronger, so lower risk of sea breezes along the east coast. Friday: A bit tricky on the forecast. Models show a trough swinging through, probably sometime morning to mid day. At the surface, this will be depicted as a cold front. However the cold air advection lags 6-12 hours behind the front, so initially it`s a wind shift with clouds and perhaps a few showers. 925mb temperatures still stay warm through much of the day, so assuming we have sun in the afternoon, we should again see another round of mid 60s for high temperatures. If there are more clouds, or the timing of the front changes, the forecast may bust on the high side. Friday Night/Saturday: 850 temperatures will crash from roughly +2C Friday evening to -12C by late Saturday morning. Depending on when that cold air starts coming in on Friday evening will determine if we can set any "maximum low temperature" records for Friday. I suspect we won`t. Saturday should be sunny but back to below normal temperatures. The high for the day may very well be registered between midnight and 3am, with dropping temperatures after that. The nearly mid-March sun is getting fairly strong, so despite the cold advection, we may see daytime temperatures rebound into the upper 30s and lower 40s. Potential for there to also be a period of gusty winds over 30 mph with the peak of the cold air advection and a fairly tight pressure gradient. This far out, that detail is still fuzzy. Sunday: Still stuck in a cold and dry northwest flow pattern. With 925mb temperatures around -6C and plenty of sunshine, our potential high temperatures should be around +4C. Guidance blend already had highs pushing 40 across lower elevations, and that seemed reasonable so kept it in. Higher elevations will remain in the 30s. Monday; Getting a bit more uncertain. Previous model runs were more robust with bringing in moisture as the day went on. Now the trend seems to be to keep things mostly dry. Have maintained some minimal PoPs for Monday at this point, especially for later in the day. If we do see precipitation, temperatures would be marginal and suggest a rain closer to the coast, snow further inland scenario. Way too early to know for sure. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Tonight...High confidence VFR with SW winds at 5-15 kts. Gusts of 15-20 kts possible toward daybreak as a low level jet moves through. Should see the highest speeds over the higher terrain, Cape Cod and the Islands. Isolated snow shower is possible toward the MA and VT/NH border, but vsbys should remain above 5 miles. Tuesday...High confidence VFR with skies becoming clear. Breezy with NW winds gusting to 20-25 kts especially earlier in the day. Gusts diminishing during the afternoon as high pressure builds in. Tuesday night...High confidence VFR with winds becoming light and variable. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Wednesday through Saturday/... Wednesday: VFR. Wednesday Night through Thursday: VFR. Breezy. Thursday Night through Friday: VFR. Breezy. Slight chance SHRA. Friday Night: VFR. Breezy. Saturday: VFR. Breezy. Slight chance SHRA. && .MARINE... Tonight through Tuesday morning...High confidence Have hoisted a Small Craft Advisory for the outer waters, Nantucket Sound and Cape Cod Bay due to strengthening southwesterly winds and gusts as a warm front lifts through. Resultant waves will build to 3-5 feet for the outer waters. Gusts of 20-30 kts are anticipated. Tuesday afternoon through Tuesday night...High confidence High pressure builds in. This will shift winds to the NW and eventually the N by late Tuesday night. Winds will diminish as high pressure relaxes the pressure gradient. Resultant waves will fall to 2-4 feet for the outer waters. .Outlook /Wednesday through Saturday/... Wednesday: Winds less than 25 kt. Wednesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Thursday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Thursday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Friday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Slight chance of rain showers. Friday Night: Winds less than 25 kt. Local rough seas. Saturday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Slight chance of rain showers. && .FIRE WEATHER... Have held off from issuance of a SPS per coordination with surrounding WFOs and Fire Weather partners. With the deepening low northeast of southern New England on Tuesday and high pressure building in will see the pressure gradient tighten. Winds will shift to the WNW/NW aloft and promote downsloping. This downsloping will aid in bringing milder temperatures, but also will dry things out. In the latest forecast have increased highs and lowered dew points, which the net result is lower relative humidities. Will have minimum relative humidities around 30 to 40 percent with gusts around 20-25 mph during the morning decreasing to 15-20 mph during the afternoon. Still something will have to keep an eye on especially for locations where are snow cover free. && .CLIMATE... March 11 record highest maximum temperatures: BOS 67F (1990) PVD 71F (1990) ORH 66F (1977) BDL 75F (1977) March 11 record highest minimum temperatures: BOS 51F (1925) PVD 48F (1925) ORH 43F (1894) BDL 45F (1925) March 12 record highest maximum temperatures: BOS 71F (2012) PVD 72F (2012) ORH 68F (2012) BDL 74F (2012) && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 2 AM to 10 AM EST Tuesday for ANZ231- 232. Small Craft Advisory from 2 AM to 1 PM EST Tuesday for ANZ250- 254>256. && $$ SYNOPSIS...BL/Nash NEAR TERM...Frank SHORT TERM...BL LONG TERM...Nash AVIATION...BL/Nash MARINE...BL/Nash FIRE WEATHER...Staff CLIMATE...Staff

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