Lexington, Massachusetts, USA
000 FXUS61 KBOX 151403 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1003 AM EDT Mon Apr 15 2024 .SYNOPSIS... High pressure establishes itself over Southern New England through midweek. It will bring abundant sunshine, dry weather, seasonably mild temperatures and northwest breezes through Tuesday. Dry Wednesday through at least mid-day Thursday before more unsettled conditions develop late week. Above normal temperatures return && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 10 AM Update Forecast is more or less on track. Straocu has already begun to develop across portions of southern New England. Temps have jumped off to a quick start as well, with a few locations already above 60 degrees. Had to adjust the near-term temps to reflect warmer than expected start, but otherwise there are no additional changes needed. See previous discussion for further details. 350 AM Update: Key Points: * Areas of fog to dissipate through mid-morning as winds pick up. * Variable amounts of clouds, but dry weather and milder than normal temperatures. Though coastal sea breezes could develop, expect breezy NW winds around 20-25 mph for most. Slow-moving frontal boundary lies along the immediate RI/MA South Coast, with residual showers mainly offshore. Thus most of Southern New England is stuck in a very weak pressure gradient with winds being light to calm. That's also led to an expanding field of radiation fog where winds are calm, particularly in northern CT and western and central MA where some sites are seeing visbys as low as one quarter mile. Current temperatures were in the lower to mid 40s, except upper 40s for the coastal areas. We're expecting dry weather and other than variable amounts of fair weather clouds and northwest breezes, it should a generally pleasant Monday for much of Southern New England today. But until winds pick up, areas currently seeing foggy conditions will continue to see fog around. Expect by mid morning that fog will begin to dissipate, as this is when WNW breezes should start to develop. Coastal sea- breezes on both coasts also look to develop briefly too (E/ESE for immediate coastal eastern MA and S/SW for the RI/MA south coast) in this light sea level pressure pattern; but it should be short lived as stronger NW flow eventually takes hold. While coastal areas and around the higher terrain will see high temperatures in the upper 50s to lower 60s, away from these areas we should see highs reach well into the 60s to lower 70s. Overall pleasant conditions for those heading into Boston today, but there could be a pretty significant difference in temperature along the immediate shore/Boston Harbor area (mid 50s) compared to the western suburbs (mid 60s) if the sea breeze does develop. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... 350 AM Update: Tonight: Cyclonic flow aloft redevelops tonight across Southern New England, with decreasing NW winds and continued dry weather. A few models generate some isolated showers passing near or south of Nantucket as a weak disturbance over the mid-Atlantic passes near our coastal waters, but favoring dry weather with any showers over the waters. Lows in the mid 30s to lower to mid 40s. Tuesday: Tuesday shaping up to be a beautiful day, generally similar to today. Deep dry air aloft favors abundant sunshine and high temperatures in the upper 50s to the mid to upper 60s. That will also favor deep mixing and falling dewpoints during the diurnal heating period, and it is possible that dewpoints could dip into the upper 20s with efficient mixing. Will see northwest winds increase again with gusts around 20-25 mph, with any sea breezes restricted to the immediate coastlines. Because of the combo of deep dry air and the NW breezes, we could see a period of elevated fire weather concerns for Tuesday. See the Fire Weather section for more details. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights: * Unsettled pattern with more dry periods than wet * Very pleasant spring temperatures mid week transition to seasonable by late week and next weekend. Mid level ridging builds into the region starting very early Wednesday, cresting Thursday before moving seaward on Friday as cutoff low centered about the Dakotas weakens and moves northeast into the Great Lakes region. Broader trough and a few shortwaves eject out of Canada late week and early next weekend. Wednesday and Thursday... Surface high pressure located over the southern waters, with strength during the day on Wednesday, will eat away at the advancing rain shield/front associated with aforementioned cutoff low advecting into Ontario. This will lead to a mainly dry period Wednesday into Thursday morning with more substantial cloud cover compared to Tuesday, but as high pressure weakens Thursday, should start to see a few light showers move into the western zones of the CWA sometime around 18Z. Model soundings corroborate the drying trend for mid week showing a very dry column both at the surface and above 700mb with some slight saturation at the top of the mixed layer; the column not expected to saturate and produce precip in our western zones until after the lunch hour Thursday and very late in the evening for the eastern half of the CWA. Even with light showers around, QPF looks rather limited with this wave with a significant majority of guidance forecasting less than a quarter of an inch of rain; there are a few outliers, namely the operational GFS, that are more amplified, producing up to a half inch of rain. There is a bit of uncertainty regarding temperatures during the period, though Wednesday looks milder that Thursday. Mixing will be healthy on Wednesday, to about 800mb, with northwest 925mb flow. Expecting another day of highs in the 60s before winds shift to onshore for Thursday. Onshore flow, SSTs in the 40s, and more robust cloud deck will yield much cooler temps Thursday, with some guidance, like the GFS and MAV, forecasting highs in the upper 40s to low 50s. Friday into the Weekend... With broad trough centering over New England, expecting near to slightly below normal temperatures and another round of unsettled weather for the weekend. While still several days away, global guidance shows a few shortwaves moving through, the first Friday into Saturday and another late in the weekend, that like bring on and off showers to the region. There remains plenty of time between now and late week for forecast details to be sussed out, so stuck with the NBM for this period. && .AVIATION /14Z MONDAY THROUGH FRIDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High- greater than 60 percent. 12z TAF Update: Today: High confidence. Mainly VFR, with any sub-VFR fog that developed overnight to trend VFR shortly after 12z as W/WNW winds start to increase. Will see SCT-BKN VFR decks today (bases 045-070, on the higher end of that range in aftn). With a light pressure gradient to start, winds are a little tricky/nuanced. Light W winds begin the morning before the increase in WNW speeds/gusts; that could put a period of brief sea- breezes at south-coastal sites (SWlys) and at BOS (SElys 4-7 kt between 14-16z indicated with TEMPO). Anticipate after 16z that winds become WNW and increase to around 10-15 kt with gusts 20-25 kt all areas, strongest over the terrain. Tonight: High confidence. VFR. Outside chance at a shower affecting ACK late tonight/midnight. WNW winds continue but slacken to around 5-8 kt. Tuesday: High confidence. VFR mainly SKC. NW winds increase to 8-12 kt with gusts to 20 kt starting mid-morning and continuing til sundown. KBOS TAF...High confidence in TAF. VFR with SCT 050 bases. Could see a possible sea-breeze develop around 14-16z but would be brief as prevailing WNW gradient wins out after 16z, with WNWlys 10-14 kt with gusts in the low-20s kt range. KBDL TAF...High confidence in TAF. Mainly VFR. There could be a brief period of IFR BR/BCFG near the airport early this morning but will dissipate shortly after sunrise as W/WNW winds increase to around 10 kt. Outlook /Tuesday Night through Friday/... Tuesday Night: VFR. Wednesday: VFR. Slight chance SHRA. Wednesday Night through Thursday: VFR. Breezy. Chance SHRA. Thursday Night: VFR. Breezy. Slight chance SHRA. Friday: VFR. Slight chance SHRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 355 AM Update: SCAs remain in effect mainly for residual seas still around 4-6 ft. However decreasing trends to seas are expected. Mainly S to SSW winds around 10-15 kt are expected today and tonight, though could turn easterly along the immediate shore/harbors today. For Tuesday, expect northwest winds around 10-15 mph in gusts. Seas 4-6 ft initially decrease today and becoming 2-4 ft tonight into Tuesday. Outlook /Tuesday Night through Friday/... Tuesday Night through Wednesday: Winds less than 25 kt. Wednesday Night: Winds less than 25 kt. Slight chance of rain showers. Thursday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers. Thursday Night through Friday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. && .FIRE WEATHER... 350 AM Update: We could have a period of elevated fire weather concerns for Tuesday. Abundant sunshine bringing high temperatures in the 60s combined with a well mixed atmosphere bringing dewpoints into the upper 20s to lower 30s support relative humidities around 25 to 30 percent, especially for interior CT, MA and RI. NW winds will also become a little breezy with gust speeds around 20 to 25 mph. The one potential deterrent is how saturated soils are. That said, we will consult with our state forestry partners regarding the need for any fire weather statements or products. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 PM EDT this afternoon for ANZ232>235-237-250. Small Craft Advisory until 8 PM EDT this evening for ANZ254>256. && $$ SYNOPSIS...Loconto/KS NEAR TERM...Loconto/RM SHORT TERM...Loconto LONG TERM...KS AVIATION...Loconto/KS MARINE...Loconto/KS FIRE WEATHER...Loconto
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