093 FXUS61 KBOX 010235 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1035 PM EDT Wed Mar 31 2021 .SYNOPSIS... Cold front slips through southern New England late tonight and Thursday morning. Low pressure moving up the front brings rain to the region during that time. Colder drier air is then drawn over the region as the low pressure moves off to the Maritimes. Dry but unseasonably chilly conditions continue Friday. Low pressure south of Nova Scotia Monday may retrogress, keeping us quite cool until a warmup later Tuesday into Wednesday. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... 1035 PM Update... Tweaked the forecast to reflect observed trends of timing and location of rainfall chances overnight. Also adjusted temperatures. Still expecting rain to overspread our region overnight. Did try to also refine the area most at risk for an isolated thunderstorm, which is by no means a guarantee. Thinking the risk will be confined to mainly portions of RI and southeast MA late tonight. Previous forecast... Overview...Cold front over Central NY/PA/Appalachians will swing east tonight, crossing Srn New England midnight to 8 AM. Upper trough swings east through the Midwest. Upper jet supports this trough with winds reaching 135 mph. Southern New England and much of the USA Northeast coast moves under the right entrance region of the jet tonight. This is an area of lift and supports cyclogenesis, and its placement over the cold front will lead to a wave of low pressure developing along the Mid-atlantic coast early tonight. This low then moves up the front, passing Southern New England 6 to 8 AM. Convective parameters are marginal or unfavorable. Total-totals will be in the upper 40s and mid-level lapse rates 5.5 to 5.8C/km. Will continue to mention isolated thunder. PW values are forecast near 1.25 inches, which is near max values that have historically occurred. With this moisture and the lift from the upper jet, expect rain and potential for areas of heavy rain. Low level jet of 50-60 kt is forecast to move past during the night. This may support gusts around 30 kt tonight, especially along the coast. Radar shows showers moving into Western portions of our area, while a more substantial area of rain is moving up from Maryland-Virginia. This area of rain extrapolates into CT 7-8 PM and across the remainder of the region by 10-11 PM. Observed dew points in the mid 40s to around 50 mid afternoon. As the air saturates, this provides a target for expected min temps. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... Low pressure moves off up the coast of Maine Thursday. Winds turn from the northwest trailing the low. This will bring in colder air Thursday, especially in the afternoon. Temps aloft at 850 mb support 50s during the morning and 40s in the afternoon, so high temps may be in the morning with steady or slowly falling temps in the afternoon. Rain tapers off by midday, just as the air gets cold enough for snow in Western Mass...so any chance for snow may be a race between the departing moisture and incoming cold air with best chance in the Berkshire East slopes. Closed upper low lingers over the Eastern Great Lakes Thursday night. This will maintain some lift over New England, but data shows drier air also moving in. Will forecast partial clearing with min temps in the 20s to low 30s. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... 430 PM update... Highlights * Generally expecting dry and quiet weather through the extended. * Remaining relatively cool until a warmup Tuesday into Wednesday Friday to Sunday... A deep upper trough is over New England Friday with anomalously cool weather expected. Highs mainly 40 to 45 but may not get out of the upper 30s in the east slopes of the Berkshires. On Saturday into Sunday, an upper low cuts off to our southeast and surface low pressure develops over the ocean to the south of Nova Scotia. Meanwhile, high pressure nudges into our region from the southwest. Saturday will be sunny but clouds will be on the increase Sunday. Expecting both days to remain dry, however. Highs moderating into the 50s but nighttime lows will be in the 20s Friday night/Saturday morning and 30s Saturday night/Sunday morning. Sunday night into Tuesday... This part of the forecast has changed a bit. The GFS remains farther east than the ECMWF with the cutoff low south of Nova Scotia. But all models agree that there will be a retrogression into the Gulf of Maine. There is a slight chance that showers could make it as far west as the northeast part of MA. However, the main impact will be gusty northerly winds keeping it on the cool side...with highs remaining in the 50s both Monday and Tuesday, except for possibly upper 40s on Cape Ann Monday...and lower 60s in the CT River valley Tuesday. Wednesday... There is some discrepancy in models, but overall expecting a ridge of high pressure over southern New England, with quiet weather and temperatures climbing into the 60s. However, clouds will quickly be on the increase late in the day and showers are possible Wednesday night and beyond, as a warm front and low pressure approaches the region from the west. && .AVIATION /03Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Forecast largely on track. Adjusted the timing of lower conditions moving into southern New England. Low level wind shear is mentioned in the southeastern terminals late tonight, as southerly winds increase to 40-50 kt at 2000 ft above the ground. Previous discussion... Tonight... Increasing low level moisture, and a developing coastal low pressure. This will bring lowering ceilings and an area of rain...possibly heavy rain with low vsbys. Expect IFR/LIFR in rain and possibly fog. Gusty south to southeast winds in the coastal plain and along the coast with gusts to 30 kt. As the coastal low pressure passes Srn New England toward morning, these winds will shift from the west and then from the northwest after passage. Thursday... Low pressure moves off up the coast of Maine. IFR conditions will lift as drier air moves in later morning and midday. Expect improvement to VFR from west to east during the afternoon. With the cold advection, expect gusty northwest winds reaching 25 kt. Thursday night... Northwest winds start the evening gusting near 25 kt but diminish under 20 kt overnight. Partial clearing of skies with VFR conditions. KBOS TAF...Moderate confidence in TAF. KBDL TAF...Moderate confidence in TAF. Outlook /Friday through Monday/... Friday: VFR. Breezy. Friday Night through Saturday: VFR. Saturday Night: Mainly VFR, with local MVFR possible. Sunday: Mainly VFR, with local IFR possible. Sunday Night: VFR. Breezy. Monday: Mainly VFR, with local MVFR possible. Breezy. && .MARINE... 1035 PM update... No changes to the forecast at this time. Previous discussion... Tonight... Gusty south to southeast winds along the coast with gusts to 30 kt. As the coastal low pressure passes Srn New England toward morning, these winds will shift from the west and then from the northwest after passage. Winds and expected seas of 5-6 feet will continue to support Small Craft Advisory headlines during the night. Thursday and Thursday night... Gusty northwest winds near 25 kt, diminishing Thu night. Seas 5 to 7 feet through Thursday night, mostly on the outer waters. Small Craft Advisory continues. Outlook /Friday through Monday/... Friday through Friday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Saturday: Winds less than 25 kt. Seas locally approaching 5 ft. Saturday Night through Sunday: Winds less than 25 kt. Sunday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers. Monday: Winds less than 25 kt. Local rough seas. Slight chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 AM EDT Friday for ANZ231>234-251. Small Craft Advisory until 4 PM EDT Thursday for ANZ230-236. Small Craft Advisory until 8 AM EDT Friday for ANZ235-237-250- 254>256. && $$ SYNOPSIS...WTB/GAF NEAR TERM...WTB/Belk/GAF SHORT TERM...WTB LONG TERM...GAF AVIATION...WTB/Belk/GAF MARINE...WTB/Belk/GAF