Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 290533 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 133 AM EDT Thu Sep 29 2022 .SYNOPSIS... Mainly dry and trending cooler tonight into Friday, as large high pressure builds into New England. Still uncertain how far north the rain from Ian gets this weekend, but the best chance of showers is near the south coast Saturday night into Sunday. The remnants of Ian are expected to move off the Mid Atlantic coast early next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 955 PM update... Mid level trough axis moves into SNE overnight. Sct-bkn mid level clouds across SNE this evening, with northern extent of cirrus from upper jet skirting the south coast. 850-700 mb moisture diminishes overnight which should lead to a clearing trend and modest radiational cooling overnight, although high clouds will persist near the south coast. Lows will be in the 40s, except low 50s in the urban areas and along the coast. This is due to 1030+ mb over the Great Lakes advecting eastward, precluding winds from decoupling, with winds becoming NNE. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/... 330 PM update... Thursday... Mid/upper trough and cold pool overhead at 12z, but these features ejecting to the northeast, resulting in warming temps aloft and mid level flow shifting from cyclonic in the morning to anticyclonic in the afternoon. This should yield less clouds/more sun Thursday. Although cirrus shield may impact the south coast from strong upper level jet streak along the coast and offshore. Still, a very pleasant fall day tomorrow, with temps just a few degs cooler than today, with highs Thu in the mid to upper 60s. A few degs cooler than normal for late Sep. Although pleasant given fairly light NNE winds, except up to 15-20 mph across Cape Cod and the Islands. Thursday night... 1030+ mb high advects across New England, and accompanied by a cool/dry fall airmass. Likely the coolest night of the week, with lows in the upper 30s to mid 40s for most locations. Given ideal radiational cooling, mid 30s possible across western MA. Hence, areas of frost possible. Leaned toward the colder MOS guidance to derive min temps given the synoptic setup. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Highlights * Dry and quiet weather expected on Friday across southern New England. * High uncertainty in the forecast this weekend into early next week with a tight north/south precipitation gradient. Confidence higher in gusty winds and elevated seas especially late in the weekend into early next week. Friday... Shortwave ridge axis over New England on Friday flattens out and moves offshore, while a subtle shortwave digs into northern New England. Ian will lift into the Southeastern US. High pressure remains overhead of New England Friday and Friday night. Expecting dry and quiet weather through this period with high pressure in control. Will see increasing high clouds from distant Ian lifting into our region through the day Friday, but especially Friday night. Main impact this brings to the forecast is some uncertainty on exact temps on Friday and how strong the radiational cooling is Friday night. Expecting N/NE flow with 850 hPa temps of 7- 10 degrees Celsius at 850 hPa on Friday and S/SE flow Friday night. NBM looked reasonable for highs on Friday with readings in the 60s. Did lower the temps to the 20th percentile of guidance. Thinking that the thin high clouds won`t inhibit radiational cooling much given the light winds. Lows generally in the 40s. Saturday and Sunday... Will be caught between cyclonic flow over Quebec/Ontario and the remnants of Ian over the Southeastern US. Should have some ridging across the Mid Atlantic/eastern Great Lakes during this timeframe as well. Lots of uncertainty with how far north across the SE US the remnants of Ian get. A pseudo warm front lifts toward southern New England during this timeframe and could bring some spotty showers. Lots of uncertainty through this timeframe with how far north moisture will surge into our region. Given the uncertainty have generally leaned on the NBM guidance. Cluster analysis shows that all guidance except for 15 members indicate at least some precipitation over southern New England Saturday. The dry solution keeps a weaker and more compact upper level energy associated with Ian over northern FL, whereas all other clusters feature a broader and further north solution, around 85 members. Still indicative of a tight precip gradient from north to south with the best shot for showers along/south of the MA Turnpike on Saturday. As for Sunday, a similar situation. All clusters feature at least some precipitation over portions of southern New England. Still need to hone in on the exact track of the upper energy associated with Ian. A further southerly solution keeps much of the region out of showers, whereas further north/east brings us a higher risk for showers. At this point appears any activity would be relatively light given the 20-80 percent probabilities of 24 hr QPF AOA 0.1 inches per EPS guidance. The GEPS is more of a compromise than the very dry GEFS guidance. All leading to the idea there is a lot of uncertainty at this point in time. For now have chances of precipitation along/south of the MA Turnpike through the weekend and slight chances further north. High temps in the 60s through the weekend, but will be in the low/mid 60s on Sunday due to northeasterly flow. Confidence higher in increasing wind speeds/gusts especially for Sunday as the pressure gradient tightens over our region. The NBM at this point looked reasonable, but may need to be increased in future updates with a 30-40 kt 925 hPa northeasterly jet pushing in. Monday and Tuesday... A lot of uncertainty on what happens with the upper energy associated with Ian early next week. Still think that the NBM slight chance to chances of precip is reasonable given the uncertainty. Still most confident in gusty winds due to a tightened pressure gradient along the south coast. Temperatures will be below normal with highs ranging from the 50s to the mid 60s. Should see seas remaining elevated. This in combination with an extended period of gusty NE winds will lead to rough seas and potential for some minor coastal erosion issues for the afternoon high tides; fortunately astronomical tides will be on their way down, but something to keep an eye on. && .AVIATION /06Z THURSDAY THROUGH MONDAY/...
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Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today...High confidence. VFR. Sct CU developing. N/NNE wind 10-15 kt with gusts to 20 kt Cape/Islands. Tonight and Friday...High confidence. VFR with high clouds. N/NE wind 5-10 kt. Sea breezes may develop along eastern MA coast Fri. KBOS Terminal...High Confidence. KBDL Terminal...High Confidence. Outlook /Friday Night through Monday/... Friday through Friday Night: VFR. Saturday: VFR. Slight chance SHRA. Saturday Night: VFR. Breezy. Slight chance SHRA. Sunday: VFR. Windy with gusts up to 30 kt. Slight chance SHRA. Sunday Night: VFR. Windy with areas of gusts up to 30 kt. Slight chance SHRA. Monday: VFR. Windy with local gusts up to 30 kt. Slight chance SHRA.
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&& .MARINE...
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Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 330 PM update... VFR cloud bases thru the period. Dry weather prevails, just a low risk for an isolated brief light rain shower until 00z or so across western MA. WNW winds 10-15 kt late day Wed, becomes north tonight, then NNE Thu before becoming light and variable Thu night. Outlook /Friday Night through Monday/... Friday through Friday Night: Winds less than 25 kt. Saturday: Winds less than 25 kt. Chance of rain showers. Saturday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Sunday: Strong winds with gusts up to 30 kt. Rough seas up to 9 ft. Chance of rain showers. Sunday Night: Strong winds with gusts up to 30 kt. Rough seas up to 10 ft. Slight chance of rain showers. Monday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 10 ft. Slight chance of rain showers.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Nocera/BL NEAR TERM...KJC/Nocera SHORT TERM...Nocera LONG TERM...BL AVIATION...KJC/BL MARINE...Nocera/BL

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