Area Forecast Discussion
Issued by NWS Boston, MA

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285 FXUS61 KBOX 240559 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 159 AM EDT Mon Oct 24 2016 .SYNOPSIS... A brief burst of moderate to heavy rain expected between 2 and 8 am Monday morning south of the Mass Pike and especially near the coast. Otherwise, winds become blustery out of the W/NW beneath a cool, dry airmass which continues though midweek. A period of rain is likely Thursday into Friday as low pressure crosses the region. Seasonable temperatures are expected for next weekend. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 2 AM update... Hi-res guidance and NAM/GFS/RGEM in decent agreement and are targeting CT/RI and SE MA for a brief burst of rain through 6-8 am. As a result we tightened the PoP gradient to the north with little or no rain expected north of the Pike. Low risk of an isold t-storm near the south coast. Rain should exit CT around 6 am and Cape/islands 8-9 am. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TUESDAY/... Monday into Monday night... Cooler, dry and breezy weather. Strong cyclonic flow aloft pushing an impressive H5 polar airmass S with temperatures of -30C. H5-7 mid- level lapse rates becoming unstable. This within a atmospheric column relatively dry. But can not rule out some isolated shower activity especially off the Great Lakes. Attendant mid-level forcing with a vortmax rounding the cyclonic flow. But with downsloping along the 280-290K isentropic surfaces within the low levels, feel any shower activity is mainly confined N/W of our region and any impacts, if any, will be across the high terrain. Scattered cloud decks during the day with deep layer mixing up to H85 where temperatures around 0 to -2C with cold air advection ongoing. Will see the mix down of faster momentum and drier air so expect very low dewpoints in the 20s with NW wind gusts of 20 to 30 mph. Highs around the mid to upper 50s with abundant sunshine but feeling cooler given the breezy winds. Winds taper slightly during the overnight hours. Lows around the mid 30s with cold air advection still dominating. Given the winds, will not go with any frost in the forecast. More concerned about freezing temperatures. But given how marginal overnight lows will be, at or above freezing, in the areas of Southern New England that the growing season is still considered, will pass on headlines at this time and mention in the hazardous weather outlook. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights... * Unseasonably chilly but mainly dry Tue/Wed other than a few ocean effect rain showers across Plymouth County/Cape/Islands * Lows should drop well down into the 20s Wed night/Thu am * Period of rain likely sometime Thu into Fri Details... Tuesday and Wednesday... Strong 1035+ MB High pressure north of Lake Michigan builds eastward into Quebec. At the same time, low pressure over the Canadian Maritimes will slowly shift east. The result will be a north to northwest flow of unseasonably chilly but mainly dry weather into the region Tue/Wed. 850T are expected to drop to between -6C and -8C. In addition, the delivery of this airmass will be from more of a north northwest direction allowing for less modification / downslope than the one this weekend. Therefore, expect highs Tue/Wed to be generally in the 40s but it will feel colder on Tue with gusty winds. Low temps Tue night and Wed night will be below freezing in most locations, other than downtown Boston and portions of southeast New England coast where ocean effect clouds are expected. Wed night should be the coldest night when many locales drop well down into the 20s as winds diminish. While mainly dry weather is expected, the setup is favorable for a few ocean effect rain showers from Plymouth county and onto the Cape/Islands Tue night/Wed. Surface winds will turn more northerly as strong Canadian High pressure builds into eastern Canada. Given ocean water temps still near 60F, the 850mb/sea surface differential should exceed 20C. Although 850 mb temps will be around -5C, the boundary layer will be way too warm to support anything more than a few ocean effect rain showers. Thursday and Friday... Upper trough quickly lifts east of the region as low pressure from the midwest lifts northeast towards the Great Lakes. This will increase the forcing for ascent and allow for a period of rain sometime Thursday into Friday. Specific timing remains uncertain this far out, but latest guidance suggests highest risk will be late Thu into early Fri. The antecedent airmass ahead of this system is quite cold/dry for late October standards. Therefore, it is not out of the question for a very brief period of snow and/or sleet at the onset across the high terrain along the east slopes of the Berks and perhaps even the northern Worcester Hills on Thu. Even if this were to occur for a short time, it would have little impact with a quick change to rain. Lastly, there are some signs that a secondary low will try to develop near the south coast. If this occurs, there might be some enhancement to the rain across portions of our region but it is just too early to say. Saturday and Sunday... Low confidence in this time range. A cold front may bring a few brief showers, but guidance suggests that much of the time may end up dry with temperatures not too far from normal readings. && .AVIATION /06Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/... Through 12z...Area of rain will overspread CT/RI and SE MA through 09z and will exit from west to east 10-12z. Expect a period of MVFR conditions in the rain, otherwise VFR. Today...High confidence. Low risk of MVFR in leftover rain early Cape/islands, otherwise VFR. Clearing this morning, then bkn cu developing in the afternoon in the interior. Increasing W/NW winds with gusts 20 to 25 kts, up to 30 kts across the high terrain. Tonight and Tuesday...High confidence. Sct-bkn VFR cigs. Occasional NW gusts 20-25 kt, although diminishing wind tonight except over higher terrain and along the immediate coast. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Brief MVFR conditions possible between 7z and 10z in rain. Outlook /Tuesday Night through Friday/... Tuesday...High confidence in VFR conditions. Northwest winds may gust to around 30 knots. Tuesday night and Wednesday...High confidence in mainly VFR conditions. A period of MVFR CIGS are possible in ocean effect clouds and a few rain showers across Plymouth county and onto the Cape/Islands. Thursday and Friday...Moderate confidence. A period of MVFR-IFR conditions expected in rain along with some lower clouds and fog patches. Timing uncertain but greatest risk right now appears to be late Thu into early Fri. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/...High confidence. 10 pm update... Have converted remaining gales to SCA for outer waters. Tonight... W gales persist into the evening hours, concluding shortly before midnight as winds turn out of the S ahead of an area of rain and possible visibility restrictions, maybe even a clap of thunder over the S waters, from shortly after midnight into early monday morning. Gales will be converted to small crafts as winds diminish. Waves slowly subside as well. Monday into Monday night... Behind the disturbed weather clearing out Monday morning, W/NW winds increase to near gale force over the waters out through Tuesday morning. Waves remaining 5 to 7 feet. Outlook /Tuesday Night through Friday/... Tuesday...High confidence. Northwest winds should gust to 30 knots over most waters in the strong cold advection pattern given the relatively mild ocean. There is even a low risk for brief winds up to Gale Force. Seas build to between 5 and 6 feet across our outer- waters. Wednesday...Moderate to high confidence. Pressure gradient weakens some, but still expect northerly wind gusts up to 25 knots given good mixing over the relatively mild ocean. Thursday and Friday...Low to moderate confidence. Winds turn to the southeast Thu ahead of an advancing low pressure system and probably more southerly by Thu night. Behind the low pressure system, should see more of a westerly component to the winds develop on Friday. Probably will see a period of small craft wind gusts and seas late Thu into Fri, but still a lot of uncertainty this far out especially with timing. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ231>235-237-250-251-254>256. Small Craft Advisory until 2 AM EDT early this morning for ANZ230. && $$ SYNOPSIS...Frank/Sipprell NEAR TERM...KJC/Frank SHORT TERM...Sipprell LONG TERM...Frank AVIATION...KJC/Frank MARINE...KJC/Frank/Sipprell is the U.S. government's official web portal to all federal, state and local government web resources and services.