Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 240759 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 359 AM EDT WED AUG 24 2016 .SYNOPSIS...
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High pressure will remain in control with higher temperatures today, but continued low humidity. More humid conditions will return Thursday and Friday, which will lead to a risk for showers and thunderstorms Thursday night and Friday as a weak front passes. Another high pressure will bring dry and less humid weather this weekend.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Still expecting a high pressure to move farther offshore while remaining to our south. This will mean a more dominant southwest flow, leading to slightly higher temperatures later on. Humidity levels will remain low as mixing of dry boundary layer keeps dewpoints down into the 50s for most. The big question will be the formation of an east coast seabreeze. Boundary layer winds should remain less than 10 kt, which is a sign the seabreeze could form. Seeing hints at it is some of the high resolution guidance. Based on the expected pattern, with a high pressure moving farther offshore, thinking a weak east coast seabreeze will form, but it will start later than usual. With synoptic southwest onshore flow, expecting lower temperatures along the immediate south coast.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
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High pressure continues to move farther offshore. South to southwest winds continue to increase ever so slightly through this period. Expecting near to above normal temperatures through Thursday. Latest guidance continues to show the slow approach of a prefrontal trough toward western New England late Thursday. Given weak forcing, and relatively lower humidity, decided to keep the forecast dry through Thursday. There is a possibility for a few isolated showers across western MA, but not enough of a risk to put showers in the forecast at this time. This timing may change.
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&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... */ Highlights... - Shower and thunderstorm chances for Friday - Cooler and drier weather for the Weekend - Another shot of wet weather Monday - Monitoring Invest 99L, low confidence forecast into next week */ Discussion... While eyes are on the tropics, still need to evaluate the broader pattern across the N Hemisphere. Most notably are the distinctive signals within atmospheric teleconnections. With maintenance of a Bering Straight / N Pacific low, ridging prevails across the NE Pacific and Gulf of Alaska yielding a strong negative East Pacific Oscillation. Downstream, troughing emerges over the Inter-Mountain West with any upstream disturbances through the flow, but forecast guidance struggling in handling individual features, thus the spread and waffling of the Pacific N American pattern. Nevertheless still favor ridging further E and thus the Atlantic High remains dominant with its presence across the SE CONUS / NW Atlantic. As such, any potential wet-weather outcomes across the NE CONUS do not look promising with respect to the ongoing drought situation. With ridging and anti-cyclonic flow maintained across the NE CONUS, and low pressure prevailing across the Hudson Bay region of Canada, a SW-NE confluent flow regime anchors across the region once again through which disturbances out of the W deamplify. A re-occurring theme, heat and humidity are captured by S flow ahead of weak areas of low pressure zipping through the Great Lakes Region into the St. Lawrence River Valley. Chances for showers and thunderstorms emerge across the NE CONUS ahead of a trailing cold front. An unsupportive environment of lift and forcing, with the bulk of dynamics to the N and quasi-parallel low to mid level flow to the sweeping cold front, the wet-weather chances are isolated to chance. Can`t bet on likely given this synoptic setup. Only promising aspect to the forecast is the follow-up cooler and drier airmasses behind cold frontal passage with high pressure building S out of Canada. It is perhaps with the influence of Invest 99L that the Atlantic ridge weakens lending lowering heights and an allowance of N-stream energy to dive S. A significant change to the pattern to which can have implications and subsequent interactions of energy associated with Invest 99L into the NE CONUS by late next week into Labor Day Weekend. Purely speculative at this time so far out in the forecast. Two areas of uncertainty, that from the broader pattern W, and from the tropics to the SE, makes for one giant headache in the long-term forecast. Thus an ensemble and probabilistic forecast approach, with a nod to the tropics with respect to storm tracks and accompanying strength forecasts, as well as the HWRF. Looking at two periods of wet weather, one around Friday and the other around Monday, with the likelihood of a warmer, more humid airmass initially, followed by chances of showers and thunderstorms for the midday into evening periods. Best chances look to be across N/W portions of S New England, though the outcomes on Monday could prove better given falling heights, cyclonic flow, and potentially higher instability. A more favorable environment of lift and forcing over Friday`s scenario with less parallel flow to the accompanying cold front. With each cold front passage follows refreshing periods of cooler and drier air. A low confidence forecast as we get into next week, approaching the end of September into Labor Day Weekend. Will need to keep an eye on Invest 99L and the remnants of Fiona. && .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
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Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/...High Confidence. Mainly VFR. Increasing mid and high clouds Thursday. Low risk for patchy IFR/MVFR in fog later tonight at the most fog-prone locations. KBOS Terminal...Moderate confidence in the TAF. Some of the latest guidance develops a late seabreeze. Based on the expected light winds within the lowest 2 kft, thinking a weak seabreeze develops late. It is possible southwest winds dominate, and keep this seabreeze just east of the terminal. KBDL Terminal...High confidence in the TAF. Outlook /Thursday Night through Sunday/... Friday...Moderate Confidence. SHRA/TSRA, mainly across N/W portions of S New England. Possible TEMPO MVFR-IFR impacts with any storms. Looking towards midday into evening. S winds backing out of the NW overnight. Saturday into Sunday...High Confidence. VFR. Light winds. Likely sea-breezes. Winds turning E/SE Sunday, potentially breezy late.
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&& .MARINE...
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Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/...High confidence. Tranquil boating conditions through the period as high pressure remains in control of our weather.. Mainly SW winds 15 kt or less with light seas and good visibility. A few gusts up to 20 kt possible Thursday, especially during the afternoon. Outlook /Thursday Night through Sunday/... Friday...Moderate Confidence. S/SW winds, breezy up to 20 kts. Waves building above 5 feet across the S/SE waters. Winds back late into Saturday morning out of the W/NW. Saturday into Sunday...High Confidence. High pressure, light winds, gradually veering out of the S/SE into Sunday, becoming breezy late. Waves remaining below 5 feet.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Belk/Sipprell NEAR TERM...Belk SHORT TERM...Belk LONG TERM...Sipprell AVIATION...Belk/Sipprell MARINE...Belk/Sipprell

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