Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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189 FXUS61 KBOX 251332 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 932 AM EDT Wed Sep 25 2024 .SYNOPSIS... Weak high pressure will remain across the region today. An approaching frontal system will bring showers with moderate to heavy downpours starting Wednesday night through Thursday afternoon. High pressure builds back in Friday through Monday and will bring dry and very pleasant early fall weather. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 930 AM Update... * Considerable clouds today with highs in the middle-upper 60s Surface high pressure over the Canadian Maritimes coupled with a lingering upper level ridging will result in mainly dry weather today. Weak warm advection aloft and onshore flow may result in a brief sprinkle/spot shower or two especially across northern MA. Overall...expect mainly dry weather today but the onshore flow will result in considerable cloudiness. The risk for a few showers may increase across the distant interior by early evening...as a bit better forcing approaches from the west. Plenty of clouds and onshore flow will result in highs mainly in the middle to upper 60s. && .SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/... Better moisture and forcing arrive late Wednesday night as a warm front with a 30-knot LLJ. Light rain spread west to east and will become moderate to heavy by Thursday morning as PWATS increase to 1.5-1.75 inches. Forcing continues to increase Thursday as the base of the northern stream trough swings through New York while a 125-knot jet streak moves over SNE. A cold front then moves through SNE late Thursday afternoon to early evening. With low amounts of MUCAPE, around 100-300 J/kg, hi-res guidance is in good agreement, bringing a fine line through. Not expecting severe weather with this fine line with very marginal instability and less than favorable low-level lapse rates around 2-3 C/km. With warm cloud depths around 11kft, the main threat along the fine line will be a brief period of heavy rain. Rainfall rates could exceed 0.5 inches/hr. The fine line will move quickly across the region, limiting the flash flood threat. With the low amounts of instability, a few rumbles of thunder are possible on Thursday afternoon. The fine line moves offshore around late Thursday evening, with drying conditions overnight. When its all said and done, the highest QPF totals look to be in northwestern MA, with HREF LPMM QPF showing up to 2 inches. Further south and east, values begin to drop off, but a widespread 0.5 to 1 inch remains possible even into the Cape and Islands. Temperatures overnight Wednesday drop into the low to mid-50s region- wide, then rebound into upper 60s to low 70s for Thursday. Winds turn south and gust 10-20mph. && .LONG TERM /FRIDAY THROUGH TUESDAY/... Friday - Monday Upper-level closed low moves offshore to the east while another blocking ridge settles in for Friday through the weekend. High temperatures quickly rebound Friday into the low to mid-70s with dry conditions and sunny skies. Temperatures moderate slightly Saturday - Monday but stay in the upper 60s to low 70s. With good radiational cooling conditions, overnight lows will drop into the upper 40s to low 50s. Patchy radiation fog is possible with the longer nights and dewpoints in the mid to upper 50s. Tuesday and beyond There is quite a bit of uncertainty heading into this part of the forecast, as models are generally too quick to break down blocking ridges. Global deterministic guidance is in good agreement with another potent trough dropping out of the Great Lakes sometime mid to late next week. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Today...Moderate confidence. VFR/MVFR today with mid level clouds hanging around 3kft. Winds remain out of the ESE today at 5-10 knots. Tonight...Moderate Confidence Rain and IFR/LIFR CIGS move from west to east overnight. Showers overnight should remain light with the heavier rain holding off until Thursday Thursday...Moderate confidence Moderate to heavy rain with IFR/LIFR Cigs. There could be embedded thunder and a fine line of convection that crosses the region from west to east in the late afternoon. CIGS clear quickly to MVFR/VFR behind the fine line. BOS TAF...Moderate Confidence in TAF. Mainly VFR with FEW-SCT MVFR layer. ESE winds. BDL TAF...Moderate Confidence in TAF. VFR/MVFR again today with ESE winds. Rain and IFR CIGs move in overnight. Outlook /Friday through Sunday/... VFR. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today through Thursday...High Confidence. Small Craft Advisories remain in effect for all outer open water zones along with the northern near coastal waters for seas of 5-7 feet. Winds remain east today at 10-15 knots, then turn SSE overnight into Thursday at 15-20 knots. Rip Current Statement remains in effect for eastern shorelines as large easterly swells continue to pose a high risk for rip currents. Outlook /Friday through Sunday/... Friday: Winds less than 25 kt. Areas of seas approaching 5 ft. Friday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers. Saturday: Winds less than 25 kt. Seas locally approaching 5 ft. Saturday Night through Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...High Risk for Rip Currents until 8 PM EDT this evening for MAZ007- 019-022-024. RI...None. MARINE...Small Craft Advisory until 8 PM EDT Thursday for ANZ250-251- 254>256. && $$ SYNOPSIS...KP NEAR TERM...Frank SHORT TERM...KP LONG TERM...KP AVIATION...KJC/KP MARINE...KP