Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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993 FXUS61 KBOX 182000 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 400 PM EDT Wed Sep 18 2024 .SYNOPSIS... Rain chances increase from south to north tonight into tomorrow, with the best chances across the Cape and Islands decreasing significantly to the north and west. Gusty northeast winds will keep temperatures near or below normal for much of the region tomorrow into the weekend. && .NEAR TERM /THROUGH THURSDAY/... An area of low pressure makes its way north and eventually stalls somewhere south of Cape Cod and the Islands. Guidance remains in disagreement on how far south the low stalls, making the QPF forecast somewhat uncertain for being 12 to 24 hours out. The HREF ensemble has a large spread between the 25th and 75 percentiles due to the unknowns on how far south the low stalls. The 25th percentile QPF from the HREF through 8 am Friday shows 1.75 inches for the Cape and Islands and 0.5 inches for the I-95 corridor from Boston to Providence. The 75th percentile shows 3-3.5 inches for the Cape and Islands, with 1.0-1.5 inches from Boston to Providence. Further west, rain amounts drop off very quickly due to dry air on the NW side of the low. There may not even be measurable QPF north and west of Worcester. Overall, any rain that falls will be beneficial and likely not cause flooding impacts, given the antecedent dry conditions. Regardless of the rain, tonight and tomorrow will feature overcast skies with a blustery northeast wind. Temperatures tonight stay warmer in the upper 50s to low 60s with an abundance of cloud cover and increasing winds. With the onshore flow tomorrow, high temps in eastern MA and RI will struggle to top 70F, while in western MA and CT, temps will reach the mid-70s. && .SHORT TERM /THURSDAY NIGHT/... Uncertainty continues to remain high into Friday night as guidance struggles with where the low stalls south of the region. Rain should continue through Friday night with the best chances over the Cape and Islands, but how far inland rain continues remains a big question mark. Low clouds and gusty NE winds will keep far from ideal radiational cooling conditions from occurring and hedged toward slightly warmer overnight lows in the low to mid-60s. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Not much change in the latest guidance suite compared to the past couple of days. Broad agreement continued, but there also remained significant uncertainty in the details. Trended the forecast with this update towards the consensus solution, without making large changes just yet. Overall, expecting a mid level trough to be nearby late this week into early this weekend. At the surface, southern New England should be between two features; a large high pressure to the north, and a low pressure approaching from the south. Ensembles showed most of the uncertainty was more east-west in nature rather than north- south. Thus, still have the greatest confidence in this low pressure center passing near or just SE of the 40N/70W benchmark Thursday night into Friday. This timing is highly uncertain, and could change with later forecasts, even at this relatively closer time range. Another aspect which will need to be monitored closely with this low pressure is coastal flooding. Astronomical tides are rather high later this week. A slow-moving low pressure with persistent winds with at least some onshore component for the south coast of New England may result in pockets of coastal flooding issues late this week. High pressure should then build into our region from the N this weekend into early next week, leading to more dry weather. Temperatures anticipated to trend below normal by this weekend, and continue into early next week. && .AVIATION /20Z WEDNESDAY THROUGH MONDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Rest of Today...Moderate Confidence VFR north of the MA pike, while south of the MA pike has some lingering MVFR with IFR cigs closer to the Cape and Islands. Although guidance does show improvements this afternoon, with higher dewpoints streaming in, am a bit skeptical if the Cape and Islands will be able to go and maintain VFR. Tonight...Moderate Confidence Winds turn NE this evening, which will bring CIGS down to IFR/LIFR east of the I-95 corridor, while to the west, CIGS should remain VFR with pockets of MVFR possible. LIFR cigs are most likely for the Cape and Islands, but could work into BOS and PVD. Light rain begins to work its way from south to north overnight, mainly just affecting the Cape and Islands northward to BOS. ORH and BDL should stay mainly dry. Tomorrow...High Confidence IFR continues as winds increase from the NE at 10-15 knots inland, and 15-30 knots near the waters. Rain becomes moderate to heavy for the Cape and Islands. The extent that rain reaches inland remains uncertain, but should remain light outside of the Cape. Western terminals may see no rain with MVFR/VFR conditions tomorrow afternoon. Tomorrow Night... Low confidence Guidance tries to show some improvements in CIGS, but am rather skeptical given the continued on shore NE winds. The low stalls south of the Cape and Islands, but rain could still continue for eastern terminals, esspically the Cape and Islands. KBOS TAF...Moderate Confidence VFR this afternoon with east winds. Winds turn NE overnight, bringing in IFR CIGS by 00-02z. CIGS could go LIFR late overnight, but confidence is low at this time. light rain is possible early Thursday morning, possibly lasting into Friday morning KBDL TAF...High confidence in TAF. VFR today with light winds. Mainly VFR overnight and tomorrow, but pockets of MVFR possible. Expecting the rain to stay east of the CT river valley Outlook /Friday through Monday/... Friday: MVFR/IFR conditions possible. Windy with local gusts up to 30 kt. Chance SHRA. Friday Night: Mainly VFR, with areas IFR possible. Breezy. Chance SHRA. Saturday: Mainly VFR, with local IFR possible. Windy with local gusts up to 30 kt. Chance SHRA. Saturday Night: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA. Sunday: Mainly VFR, with local MVFR possible. Windy with local gusts up to 30 kt. Slight chance SHRA. Sunday Night through Monday: VFR. Breezy. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Marine Today through Tomorrow night Worsening marine conditions starting tonight, with northeast winds increasing to 20-30 knots by tomorrow morning and seas increasing to 5-8 feet by tomorrow afternoon. Moderate to heavy rain moves from south to north tonight and lasts through Thursday night. Seas continue to rise into Thursday night and Friday to 7-10 feet. Rip Currents/High Surf With gusty NE winds, increasing surf and long- period swells, we decided to issue a Rip Current Statement for tomorrow. Much of the south and east-facing beaches will have a high risk of rip currents. The rip current statement will likely be extended or upgraded to a high surf advisory on Friday as seas rise up to 10 feet in outer waters. Outlook /Friday through Monday/... Friday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 10 ft. Rain showers likely. Friday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 10 ft. Chance of rain showers. Saturday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 10 ft. Chance of rain showers. Saturday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 11 ft. Chance of rain showers. Sunday: Strong winds with gusts up to 30 kt. Rough seas up to 11 ft. Slight chance of rain showers. Sunday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 11 ft. Monday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 11 ft. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...High Risk for Rip Currents from Thursday morning through Thursday evening for MAZ007-019-020-022>024. RI...High Risk for Rip Currents from Thursday morning through Thursday evening for RIZ006>008. MARINE...Small Craft Advisory from 1 PM Thursday to 8 AM EDT Friday for ANZ231-251. Small Craft Advisory from 5 AM Thursday to 8 AM EDT Friday for ANZ232>235-237. Small Craft Advisory from 8 AM Thursday to 8 AM EDT Friday for ANZ250. Small Craft Advisory until 8 AM EDT Friday for ANZ254>256. && $$ SYNOPSIS...BW/KP NEAR TERM...KP SHORT TERM...KP LONG TERM...BW AVIATION...BW/KP MARINE...BW/KP