Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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675 FXUS61 KBOX 141048 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 648 AM EDT Tue May 14 2024 .SYNOPSIS... Mild and mainly dry today with some uncertainty regarding how warm Wednesday will be. Heading into a cloudier and unsettled weather pattern for late in the week into the weekend, as a series of slow-moving upper level disturbances move through Southern New England. While it is not likely to be raining the entire period, at least hit or miss showers can`t be ruled out at any time. Temperatures for late in the week into the weekend trend trend slightly cooler than normal on high temperatures and milder than normal on the lows. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 648 AM Update: Varying degrees of midlevel cloudiness continue across most of Southern New England; however there is a layer of broken to overcast stratus over the CT Valley in CT/western MA. The 00Z HREF low level sky cover and RAP-based RH profiles are best handling this stratus layer and once mixing gets going by mid morning, expect any stratus to dissipate in entirety. By then, we`ll be trending mostly clear in all areas and warming up thereafter. As we`ve been messaging via social media, today remains the pick of the week with full sun and dry weather with highs reaching well into the 70s to the lower 80s away from the coast, with readings in the mid 60s along the southern coasts where the sea-breeze has the best chance at developing. On the eastern coast, sea breeze should be kept at bay (pun unintended). No changes to prior thinking pertaining to SHRA/TS chances, which remain low and the relative best chance being over the Berkshires. Our area remains under the influence of subsidence aloft from midlevel ridge and expecting any buildups to stay to our south and west. This is also supported upon review of recent convection-permitting guidance. Previous discussion: Today is shaping up to be the warmest and brightest of the next several days as mid level ridging builds in from the west behind a warm front that lifted through overnight/early this morning. Some lingering showers associated with the warm front should come to an end quickly after sunrise yielding clearing skies for many through the afternoon. Anticipating very healthy mixing today, to as high as 750mb off model soundings, and with 925mb temperatures climbing to as warm as 18C and 850mb temps between 9 and 11C, temps wont have any issues climbing well into the 70s and low 80s across interior southern New England. The caveat to the warm temperatures will be along the south coast and areas north of Narragansett Bay, as brisk southerly flow off the cool ocean (SSTs in the low 50s) will keep temps in the 60s. There will be a considerable amount of instability, with SBCAPE approaching 750-1000J/kg across upstate NY, that will fuel afternoon shower and thunderstorm activity, but with SB/MU CAPE struggling to climb to ~200 J/kg in our region, expecting most of the activity will stay to our north on the advancing edge of the mid level ridge, across VT/NH and NY. Hi-Res CAMs reflect this idea, with several SPC HREF members keeping all shower activity out of our area through 00Z! With that said, can`t rule out a stray shower or thunderstorm spilling over the Berkshires into far northwestern MA after 21Z this evening. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Showers remain possible for western MA and CT tonight but weak mid level height rises have dampened the signal overnight for any widespread precip. While dewpoint depressions will be quite small, southerly flow overnight should remain brisk enough, between 5-10kt, to keep widespread fog at bay. Lows will bottom out in the mid to even upper 50s region wide, coolest across the Cape. Wednesday`s forecast proves to be a bit tricky as low pressure emerges off the mid-Atlantic coast. Overnight guidance took a significant step in the "drier and warmer" direction with low pressure remaining suppressed to our south for much of the day. With mid level ridge still in place, and 925mb temperatures still mild between 13-15C, the temperature forecast will be highly dependent on cloud cover and our mixing potential. Should sunshine break out for a good portion of the morning, it`s very possible temps soar into the mid 70s region wide. With that said, anticipating cloud cover will be most robust across the CT River Valley, in part due to an eastward advancing weak boundary, so the warmest temperatures in our region will be across the Merrimack River Valley and across SE MA. Given the rather sudden shift in guidance, heavily weighted the temperatures forecast using NBM, but later forecasters may choose a more aggressive temperatures forecast should a sunnier trend continue. In order to derive warmer temperatures, also trended the PoP and Sky cover forecast in a more favorable (clearer and drier) direction that supports deeper mixing. Shower chances will increase late Wednesday from south to north as the precipitation shield associated with the low is able push across southern RI and the Cape. Again utilized NBM for the QPF forecast. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Highlights: * Unsettled late week into the weekend, although below-average confidence in temps and rain chances in this period. * Won`t be raining the whole time, with Fri offering some potential for drier weather, but generally cloudy with periods of at least possible showers. * Seasonable to slightly cooler than normal highs, with milder nighttime lows. Details: Global ensembles point to a generally unsettled and slow-evolving pattern through a large portion of this forecast period. Southern New England`s weather looks to be governed by a weakening/filling upper low detached from the westerlies through late in the week, then right on its heels is another shortwave disturbance that is poised to approach and cross our area around the weekend. Unfortunately that`s really all that can be said as there is quite a bit of uncertainty as far as the location and progression of these two trough features; thus, below-average forecast confidence in temps, PoP and rain amts in light of this uncertainty in mass field details. Took a pretty broad-stroked brush as far the forecast goes in this period; while most days have some mentionable PoP, it there will likely be periods of dry weather in between and it is not likely we`re looking at significant rain amts. With a cloudier-than- not forecast period and a few days of onshore breezes leading to shallower mixing depths, highs were seasonable or slightly cooler than normal and lows were milder than normal. Wednesday Night through Friday: Upper low initially over the OH Valley early Wed night progresses slowly offshore of the NJ coast and deamplifying as it does so; this puts SNE on the northern end of the upper-level circulation. These signals are not typically conducive to significant precip, with the better chances for steadier light rains on Thurs and mainly south of the Mass Pike. I do think the 00z GFS depiction regarding the eastward progression is still too progressive and leaned somewhat toward the slower ECMWF/GEM evolution. With E/SE onshore flow, highs in the upper 50s to low 60s near the coasts with highs well into the 60s; however 850 mb temps are quite warm (around +8 to +10C) and would favor highs several degrees warmer if we can fully mix, but I just don`t see that happening. With weakening shortwave ridge axis poking NE into SNE around Fri, that could be a relatively drier day with lower (around 15-20%) PoP indicated for Fri. Highs Fri could reach into the lower to mid 70s in the CT Valley and western MA, with cooler 60s readings the further east one goes. The Weekend into Monday: This latter period perhaps is the most uncertain with guidance struggling with poor congruence both across modeling systems but also from run-to-run. Interaction, if any, between the slowly- exiting late-weekday upper low and an approaching trough from the OH/TN Valleys probably is contributing to that run-to-run disparity. Opted to keep the forecast with a mention of PoP along with a considerable degree of cloud cover, but that will need to be better defined once models show better agreement in timing and placement of key features. While there are some solutions which indicate a dry weekend and favor better rain chances on Monday, it`s probably too hasty to lock in that drier outcome just yet. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 12Z TAF Update: Tonight...High confidence. VFR. Scattered showers are possible across northern MA, with at times briefly lower VFR CIGs 3-5k ft. Winds are south to southwest 5 to 10 knots. Today: High confidence. VFR. There could be a spotty SHRA/TS around or west of the Berkshires but unlikely anywhere else in Southern New England. Steady southwest winds with gusts developing in the afternoon 20 to 25 knots. Tonight...High confidence. VFR with lowering cigs to around 4000-5000ft in western MA/CT by daybreak where isolated showers are possible. Winds remain persistent from the S/SW overnight. Wednesday... Moderate Confidence Tricky forecast Wednesday with low pressure to our south, but drier trend has developed. Generally VFR with pockets of MVFR. Isolated shower chances persist for western MA/CT but a mix of sun and clouds for eastern terminals. Showers associated with low pressure will remain south until early evening but may impact Cape/Islands/srn RI terminals by 00Z. S/SW winds shift to the SE. KBOS TAF...High confidence in TAF. VFR. Breezy southwest winds with gusts 20 to 25 knots mitigate sea-breeze potential today. KBDL TAF...High confidence in TAF. Early IFR ceilings should prevail until about 13z before trending VFR. Increasing wind speeds Tuesday with gusts 20 to 25 knots possible. Isolated shower chances late this evening. Outlook /Wednesday Night through Saturday/... Wednesday Night: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA. Thursday: Mainly VFR, with local MVFR possible. Breezy. Chance RA. Thursday Night through Friday: VFR. Breezy. Slight chance RA. Friday Night: Mainly VFR, with local MVFR possible. Breezy. Slight chance RA. Saturday: Mainly VFR, with local IFR possible. Breezy. Chance RA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Update: 3 AM Through Wednesday.... S/SW winds persist through Tuesday night before shifting to the SE Wednesday afternoon. Gusts to 25kt possible this afternoon for our far NE waters, though the short fused and small zonal coverage nature of the conditions has prompted us to hold off on a Small Craft Advisory between 15-03Z this evening. Generally dry on today with isolated shower chances for the eastern waters this morning. Shower chances increase for the southern waters late Wednesday as low pressure creeps north from the mid- Atlantic coast. Outlook /Wednesday Night Wednesday Night: Winds less than 25 kt. Local rough seas. Chance of rain showers. Thursday: Winds less than 25 kt. Areas of rough seas. Chance of rain. Thursday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Chance of rain. Friday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Slight chance of rain. Friday Night through Saturday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Loconto/KS NEAR TERM...Loconto/KS SHORT TERM...KS LONG TERM...Loconto AVIATION...Loconto/KS MARINE...Loconto/KS