Lexington, Massachusetts, USA
000 FXUS61 KBOX 181733 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 133 PM EDT Thu Apr 18 2024 .SYNOPSIS... Cloudy, much cooler, with scattered showers at times today with the majority of them across interior southern New England. Dry and seasonable for the daytime hours on Friday. A cold front brings another round of showers Friday Night into early Saturday. Dry for the rest of Saturday with gusty winds. The dry stretch of weather continues as we head into early next week. && .NEAR TERM /THROUGH TONIGHT/... 11 AM Update... Only a few minor updates to the forecast, this was done to POPs as decaying showers are drifting east. Did add in slight chance POPs into eastern Massachusetts. These showers are fighting the drier air to the east, as seen on radar, the returns on radar are becoming weaker as the showers move east. Rest of forecast still on track though as onshore flow will keep our temps suppressed today with little sunshine. See previous discussion for more details. 305 AM Update... * Cloudy & much cooler today with scattered showers...focused inland * High temps only in the upper 40s to the lower 50s The mid level warm front has resulted in showers along with a few downpours early this morning...generally southwest of an ORE-ORH-PVD line. The mid level ridge axis across southern New England was keeping the forcing/deeper moisture for the shower activity mainly across the west and southwest portion of our county warning area. This shortwave will continue to deamplify as it moves eastward into the mid level ridge axis. Therefore...we expect the bulk of the scattered showers to remain across interior southern New England today. Even in those locations...not expecting the entire day to be a washout. A few brief light showers will probably survive all the way to the coast...but regardless the majority of the day will feature dry weather in this region. High pressure across Quebec will generate easterly flow level flow today and this will combined with mainly cloudy skies. The result will be cool high temperatures only reaching into the upper 40s to the lower 50s. && .SHORT TERM /FRIDAY/... Key Points... * A few lingering showers dissipate this evening * Partial sunshine returns Fri with highs in the 50s to near 60 Details... Tonight... A few lingering showers will be exiting the coast this evening as the deamplifying shortwave will be moving east of the region. Otherwise...clouds will probably be slow to dissipate given there is not any real push of drier air behind the shortwave. Overnight low temps will mainly be in the upper 30s to the lower 40s. Friday... Some modest upper level ridging moves over the region on Friday. This should allow for some partial sunshine to return along with milder temps then today. We should see more clouds return by later in the day/early evening out ahead of an approaching cold front. Highs on Friday should recover well into the 50s to near 60 in most locations. Surface high pressure off the coast will still result in onshore flow which will hold highs along the immediate coast to between 50 and 55. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Highlights * Scattered showers Fri Night into early Sat. This is followed by drier, mild and breezy conditions Sat afternoon. * Dry, breezy and cooler on Sun. Still dry and quiet Mon/Tue, but milder. Shower chances return late Tue into Wed. Friday Night through Saturday... Flow turning more cyclonic during this timeframe. Will have a cutoff rotating from Ontario northward through this period. A shortwave embedded within the cutoff will lift from the central/eastern Great Lakes Fri Night into Quebec by early Sat. Another shortwave/trough will dig across the Great Lakes into New England by late Sat. A cold front crosses the region Fri Night through Sat. Could have a secondary cold front swing through Sat afternoon. Main change to the forecast at this point was more focused on temperatures, dew points and relative humidities overachieving in a well mixed boundary layer on Sat. At this point both the GFS and NAM Bufkit soundings showing an extremely well mixed boundary layer. The GFS mixes roughly to 750 hPa, while the NAM up to 650 hPa! Given the W to WNW flow have bumped our temps up to the 75th percentile of guidance as the NBM performs poorly in these situations. The result are fairly widespread 60 degree readings and wouldn't be surprised if we get some low 70s across either the CT or Merrimack Valley. This will also bring down much drier dew points, so went toward the 10th percentile of guidance for dew points and RH values. At this point have min RH values ranging from 30 to 40 percent away from the south coast. Bumped up the wind speeds/gusts toward the NBM90th for now to increase things a bit, but if the NAM is correct then we will need to increase things further in future updates. Given this setup and we are still in pre-greenup there could be elevated fire weather concerns, though this could be mitigated for portions of the region depending on how much precip falls as the front slides through. A bit of a backtrack here time wise, but think the fire weather concerns will be more impactful than the showers Fri Night into early Sat. At this point think that there won't be a whole lot of precip that is realized other than across portions of the south coast, but particularly the Cape/Islands. Ensembles show moderate to high probs (30 to 80 percent) of 24 hr precip AOA 0.1 inches across the Cape/Islands and even some low probs (10 to 20 percent) of AOA 0.5 inches. It is in this area where there is the best shot for a wetting rain (totals AOA 0.25 inches), whereas totals elsewhere generally will total less than 0.1 inches. This makes sense given the best PWAT moisture plume of up to 1 inch impinges on the Cape/Islands. This PWAT plume advects offshore late Sat AM/early afternoon. There is potential for the secondary cold front to bring the interior some spotty showers, but moisture appears quite limited as we dry out in the low/mid levels (1000-500 hPa layer) in wake of the first front. Given this have dialed back our chances during the afternoon given the limited moisture. Sunday... Cyclonic flow still in place through this timeframe with a deamplifying shortwave lifting through. A mid level ridge will build from the Mississippi River Valley into the Great Lakes region. High pressure nudges into our region from the Mid Mississippi River Valley. Dry and quiet weather anticipated through this timeframe. Could be another day where there may be elevated fire weather concerns. Appears that will have a similar set up to Sunday with a very well mixed boundary layer per GFS BUFKIT soundings. At this point think we could mix up to 750 hPa with once again W to WNW flow. Will be a bit cooler as 850 hPa temps fall to 0 to -3 degrees Celsius. Despite this did increase our temps to the 75th percentile of guidance given the well mixed boundary layer and W to WNW flow. Highs top out in the upper 50s to the low to perhaps mid 60s. Have also lowered dew points and relative humidities to the 10th percentile of guidance. At this point have min RH values of 25 to 45 percent with the driest readings across the interior. Could be another day of elevated fire weather concerns. Monday through Wednesday... Cyclonic flow remains persistent through this timeframe. A mid level ridge builds from the Great Lakes/OH Valley region early on Mon into the Mid Atlantic/offshore by late Mon. Aloft a trough/shortwave slides well to our S Mon Night into Tue. A trough digs from the Great Lakes region early on Tue into the eastern Great Lakes/New England by late Tue or Wed. High pressure nudges in from the Mississippi River and TN Valley on Mon and Tue. Could see a system slide in late on Tue or Wed, but still uncertain on the timing and intensity at this point. Dry and quiet weather on Mon and Tue with mild temps and lighter winds given the pressure gradient relaxes a bit. High temps getting into the low to mid 60s. Could have some showers spreading in late on Tue into Wed or just Wed, but there are significant differences at this point amongst guidance. Due to this have just stuck with the NBM. Temps near to perhaps cooler than seasonable levels by Wed. && .AVIATION /18Z THURSDAY THROUGH MONDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High- greater than 60 percent. Today...High confidence. VFR, pockets of MVFR along and west of the CT River. A few light rain showers this afternoon, temporarily reducing visibilities between 3SM and 5SM. East/northeast winds 5 to 15 knots, and gusting up to 25 knots for the south coast, Cape, and islands. Tonight and Friday...High confidence. VFR, pesky mid-level clouds around 050-070 ft. Low chance for an isolated rain shower across eastern MA and RI between 03z and 09z, otherwise dry. Northeast winds are 5 to 15 knots. Friday...High confidence. VFR and dry. Southeast wind 10 to 15 knots. KBOS TAF...High confidence in TAF. Low prob of a spot shower late this afternoon, generally after 21Z. Per collab with ZBW have added a TEMPO group for this risk. KBDL TAF...High confidence in TAF. Marginal MVFR ceilings this morning with rain showers as we head into the afternoon. Should see ceilings lift to VFR roughly 18-21Z and remain for the rest of the TAF. Outlook /Friday Night through Monday/... Friday Night: Mainly VFR, with local IFR possible. Breezy. Chance SHRA. Saturday: VFR. Breezy. Slight chance SHRA. Saturday Night through Sunday Night: VFR. Breezy. Monday: VFR. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today...High Confidence. A wave of low pressure dropping southeast across the mid Atlantic coast will combined with high pressure across eastern Quebec. This will be enough to generate ENE wind gusts of 25 knots across many of our southern waters...where we have hoisted small craft headlines. Tonight and Friday...High Confidence. The pressure gradient weakens as the wave of low pressure continues to move further southeast and away from the region. Seas will also diminish...but expect some 5 foot seas to linger across our southern outer-waters so will continue small craft headlines in those locations. By Friday...winds and seas should have dropped below small craft thresholds across all waters...but still expect easterly wind gusts to around 20 knots. Outlook /Friday Night through Monday/... Friday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Saturday: Winds less than 25 kt. Chance of rain showers. Saturday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Sunday through Monday: Winds less than 25 kt. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 5 PM EDT this afternoon for ANZ232>235-237. Small Craft Advisory until 5 AM EDT Friday for ANZ255-256. && $$ SYNOPSIS...Frank/BL NEAR TERM...Frank/BL/Dooley SHORT TERM...Frank LONG TERM...BL AVIATION...BL/Dooley MARINE...Frank/BL
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