Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 241833 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 233 PM EDT Mon Oct 24 2016 .SYNOPSIS... A wave of low pressure tracking along the coast will move offshore this morning with rain quickly exiting the region. Otherwise, winds become blustery out of the W/NW beneath a cool, dry airmass which continues through 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 /THROUGH TONIGHT/... No major changes to the forecast for this afternoon. A few clouds have made it over the Berkshires, with evidence of some mechanical turbulence across the CT River Valley. Clouds are dissipating farther to the east, making it harder to see this continuing farther east. Tweaked temperatures and sky cover this morning to reflect observed trends. Colder air arriving has led to decent mixing, and gusty winds. Expecting these winds to diminish some this evening, with the loss of solar heating. Cyclonic flow continues higher up in the atmosphere, which will steer a couple of shortwaves across our region. The main question will be the amount of available moisture. Still thinking there should be some clouds, but not quite enough to result in showers. Lower temperatures tonight. However, there should still be enough wind flow where frost is not likely. So, no frost/freeze headlines tonight. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... Tuesday... Expecting another day of gusty west to northwest winds to develop by mid morning. Some diurnal clouds develop, too. More clouds should be along the coast, and over the ocean, where the humidity is more favorable. High temperatures should be about 10 degrees below normal. Tuesday Night... Anticipating the start of a rather cool, if not cold, period. Northwest winds should be still be blowing, so not thinking frost will be the real concern. Instead, looking more at freezing to subfreezing temperatures across portions of southern New England. Will hoist a freeze watch where there is moderate confidence for a potential freeze, and the growing season has not already ended. Farther inland, we would expected those same conditions, even though no watch will be issued. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Highlights... * Unseasonably chilly but mainly dry 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, low risk for wintry mix early Thu if several conditions are met * Confidence in weekend forecast low Overview and model preferences... Labrador trof will continue to impact the region as ridging builds from the great lakes through early Thu. Clipper system, which looks to be undergoing an occlusion process as it approaches S New England then brings more wet/unsettled wx for Fri, especially as the trof takes on a slight negative tilt. Models are in good agreement through this point, enough such that a general blend of deterministic guidance can be used as a baseline. However, into the weekend there are disagreements at the handling of a secondary trof which may/may not phase with the Hudson`s Bay vortex. GFS appears like the biggest outlier, with a much deeper trof than both its own ensemble mean, ECMWF and some of the ECENS members. Now it is too early to tell how this phasing will occur, but given the fact that the GFS solution seems far different from many of the others, will lean more heavily on the ECENS/GEFS and ECMWF beyond Fri. Details... Wed through Wed night...The coolest portion of the period. H85 temps dive well below 0C, while H92 near -2C. This, combined with continued NW unmodified flow, should yield highs mainly in the 40s and low 50s. However, good radiational cooling ahead of CI deck on Wed night should yield several locations below freezing (and in the 20s). This suggests frost in locations where the growing season continues, so stay tuned if you continue to have growing interests. Otherwise, ocean effect rain showers likely for the Cape/Islands and immediate coastal Plymouth County MA thanks to N flow and delta-T values between H85 and the sea sfc exceed 20C. Thu into Fri... Clipper low pres undergoing slow cold occlusion process will be approaching on Thu as the attendant trof gradually shifts toward a negative tilt. Precip shield out ahead of the occlusion may take until late Thu to initiate across the W as soundings show a fair amount of moisture in the lowest lvls that will need to be overcome. By Fri night, as the initial low pres shifts N toward Canada, secondary (triple-point) low may form and traverse directly over S New England into Fri, enhancing the rainfall process. PWATS are modest, mainly around or even below 1.00 inch, so it will take this secondary low for moderate-heavy rainfall. QPF values around 0.5-1.00 inches are possible should this occur. Otherwise, temps closer to seasonal normals thanks to warmer nights under cloud cover (mainly 40s and low 50s. Highs in the 50s and low 60s. One other minor note here, there is a slight chance for wintry mixed precip at the onset early Thu. This is highly dependent on timing, how efficiently the veering winds are able to scour out the low valleys, and dynamic cooling potential. It would really need all these things to line up right (or wrong depending on your perspective) for this to occur. However, feel it is at least worth noting here given the cool airmass and low dwpts (wetbulb process) in place before the precip shield arrives. Sat and Sun... Removing the GFS with this update, and using thermal wind (mean- jet) arguments, noting steering should be mainly S of New England with any additional vort-maxes and/or mid lvl F-gen. Therefore, will allow for the high pres to the N to dominate the pattern across the region, with the primary focus for additional rainfall well to the S. Will yield NIL pops for now, but maintain that this remains an uncertain forecast as the wave in question has yet to be even sampled. Temps will be very close to seasonal normals, as H92 temps average +4 to +6C. Although overnight mins would be colder with the crest of high pres and radiational cooling. Early next week... Low confidence. Even using the blends for the weekend yields different results as the upper flow pattern suggests zonal flow and fast moving (albeit weak) shortwaves moving through. Therefore, will suggest seasonable conditions with a low risk for occasional shra, but at least at this point, it does not look like a true washout. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday Night/... Through 00Z...High confidence. VFR. Gusty W to NW up to 25 kt continue. 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. Tuesday night...High confidence. VFR. Gusty NW winds up to 25 kt near the immediate coast. Diminishing winds well inland. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Wednesday through Friday/... Wednesday into Thursday morning...High confidence. Mainly VFR. 20-25 kt winds out of the NW near shore early Wed. Thursday into Friday...Moderate confidence. Low risk for some wintry mix when precip starts on Thu. Otherwise expect rain lingering into Fri with IFR/MVFR conditions. Winds veer from NE to SE and finally to S by Fri. Sat...Moderate confidence. Mainly VFR with some improvement. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday Night/...High confidence. Small craft advisories in effect through Tue. This afternoon...Winds turn NW today and stay blustery with gusts to 25 kt. Tonight into Tuesday...Persistent NW winds with gusts 25-30 kt. Seas 5-7 ft over the outer waters. Tuesday night...Gusty northwest winds and seas slowly subside. Small Craft Advisories expected to continue for at least the outer coastal waters. Outlook /Wednesday through Friday/... Wed...High confidence. Last day of continued Small Craft Advisory conditions. Winds out of the N-NW will continue to gust to around 25 kt into the morning hours on Wed. Seas will gradually recede form 5-7ft, dropping below 5 ft by Wed evening. Wed night into Thu...High confidence. Mainly quiet boating weather regarding seas (which should only top out at 3-5 ft), while winds will gradually shift from NE to SE through the day. Some rain overspread the water by evening Thu. Thu night into Fri...Moderate confidence. As areas of rain overspread the waters, winds out of the E-SE will increase, gusting 25-35 kt at times, this suggests a risk for Gales, although at the very least small craft advisories will be needed. Seas build to 8-10 ft potentially, if low pres passes directly over the waters. The winds shift to the S on Fri, but remain elevated. Sat...Low confidence. It`s possible conditions subside through the overnight hours Fri night, such that mainly quiet boating weather is experienced by Saturday. However, there is also a risk for winds and seas to remain at low end SCA thresholds. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT Tuesday for ANZ230>237-250- 251-254>256. && $$ SYNOPSIS...Belk/Doody NEAR TERM...Belk/Doody SHORT TERM...Belk LONG TERM...Doody AVIATION...Belk/Doody MARINE...Belk/Doody is the U.S. government's official web portal to all federal, state and local government web resources and services.