Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 260816 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 416 AM EDT Fri May 26 2017 .SYNOPSIS... Low pressure tracks across Rhode Island and eastern Massachusetts this morning then offshore this afternoon. Periods of rain will continue today with rain heavy at times across northern Massachusetts this morning. High pressure builds into the region beginning tonight and ushers in a drier airmass that lingers through much of the holiday weekend. This high will provide mild days and cool nights to the area Sat and Sun. The next chance of rain will arrive Sun night into Mon as a trough of low pressure moves across the region. Scattered showers possible much of next week, mainly diurnal and by no means a washout. Temperatures will warm to near normal values. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Widespread showers will continue to move through the region early this morning as vertically stacked system moves through southern New England. Looking at satellite data, you can see the low pressure circulation just south of Long Island. The systems weak warm sector has pushed across the Islands as temps are near 60F with a southeast wind. The reminder of the region continues to be on the cool side of the low. This as well as due northerly winds/stable air will limit any more thunder development. However, near the occlusion center of the low we could see a rumble of thunder. Over the next few hours, the focus shift towards the western half of the region where the heaviest precipitation will fall. Guidance continues to show a deformation zone/comma head set-up over this region and with several guidance members showing over an inch of precip, may need to watch for nuisance flooding. As the low continues to approach, pressure gradient will tighten resulting in a few gusts to near 20 mph. Today... The upper circulation slowly moves into the Gulf of Maine. This will result in a diminishing trend in the precipitation. However with moist, cyclonic flow aloft remaining overhead, anticipate plenty of clouds and scattered showers for much of the day. Conditions will begin to improve during the later half of the day. Cloudy skies today will limit diurnal heating. Expect high temps to run below average today remaining in the upper 50s to low 60s. The possible exception could be across the southwest portion of the area which stands the best chance to briefly break out of the overcast later in the day. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/... Tonight... Upper level low will continue to move into the North Atlantic tonight. Heights will be rising as northwest flow continues. Passing shortwave on the backside of the low may trigger a few showers overnight but overall trend will be dry. Temperatures will remain steady overnight with lows in the 50s. && .LONG TERM /SATURDAY THROUGH THURSDAY/... */ Highlights... * Mainly dry weather w/mild days and cool nights Saturday and Sunday * Risk of rain returns Sun night into Monday * Temperatures warming to near normal Tue thru Thu along with a risk for scattered showers each day, although by no means a washout Synoptic Overview... Main large scale feature this period will be a building mean ridge over western Canada which induces downstream troughing over the Great Lakes. This will yield an active/amplified northern stream with cyclonic flow into New England much of next week. This will translate to a risk of showers each day (mainly diurnal) but also temperatures warming to near seasonal levels. Daily Details... Saturday... Dry weather prevails in response to NW flow aloft and weak high pressure at the surface advecting across the area. Typically this setup supports at least some sunshine however models are depicting lots of low level moisture remaining trapped beneath the subsidence inversion. Both the NAM and GFS moisture profiles suggest BKN-OVC strato-cu much of Saturday. Thus mostly cloudy appears to be the model consensus. Although the combination of light winds (weak high pressure overhead) and temps warming into the upper 60s - low 70s will yield very pleasant conditions. Sunday... Ensembles and deterministic guidance in very good agreement that deep layer east coast ridge lingers long enough to provide mainly dry weather here. Any showers likely hold off until after sunset. Thus a fairly nice day with temps 70-75, 60s at the coast given cooling seabreezes. Moisture profiles suggest more sunshine eastward across RI and eastern MA. Monday... Still some uncertainty regarding the timing of next system. Model consensus would support risk of showers Sunday night into Monday as northern stream trough advects across the area. Cooler given cloud cover, southeast onshore winds and risk of scattered showers with highs only in the 60s. Tuesday thru Thursday... Long wave trough sets up across the Great Lakes with cyclonic flow into New England. This setup supports isolated or scattered diurnal showers each day but by no means a washout. Somewhat warmer low level flow becoming southwest. This will support highs in the 70s, 60s for the south coast of MA/RI including Cape Cod and the Islands. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/...High confidence. Today...MVFR/IFR cigs and vsbys in rain and fog this morning improving to MVFR by the afternoon. Heaviest rainfall in the morning with -SHRA in the afternoon. Northeasterly winds could gust to 20 knots. Conditions may improve to VFR across western terminals in the late afternoon. Tonight...Any low cigs or vsbys should improve to VFR overnight. Cannot rule out patchy fog in low lying regions. Northwest winds with gusts to near 20 kts. KBOS TAF...High confidence in trends, moderate confidence on timing. KBDL TAF...High confidence in trends, moderate confidence on timing. Outlook /Saturday through Tuesday/...moderate confidence. Saturday and Sunday...Mainly VFR. Light winds Saturday, with seabreezes at the coasts. Light S-SE winds Sunday. Sunday night through Monday...Cigs/vsbys trending to MVFR/IFR in showers. Winds from the southeast, trending from the south Monday. Tuesday...Mainly VFR, with scattered diurnal MVFR showers. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/...High confidence. Today and Tonight... Passing low pressure system will keep seas above 5 feet for most of the period. Northerly winds will switch to the northwest by tonight. A few gusts to near 25kts are possible across the near shores, but confidence is to low to extend the adv. Outlook /Saturday through Tuesday/... Saturday...light and variable winds with seabreezes at the shore. Dry weather and good vsby prevail with high pres overhead. Sunday...light southeast winds expected with high pres just offshore. Dry weather and good vsby during the daylight hours then risk of rain and fog overnight. Monday...another front sweeps across the area with the risk of scattered showers. Modest SE winds develop. Tuesday...winds becoming southwest. Low risk for a few afternoon showers. && .TIDES/COASTAL FLOODING... A surge of 1 foot occurred with the past high tide resulting in minor coastal flooding across the MA east coast. This surge remains across most of the east coast thanks to persistent easterly flow from passing low pressure system. The focus turns to the high tide for tonight. Currently a surge of 0.2 to 0.4 feet is forecast and combined with the peak of astronomical tides (Boston at 12.41 feet), should see at a minimum coastal flooding of low-lying locations notorious for becoming inundated during such tides (i.e., Morrissey Boulevard in Boston). Additional coastal flood statements may be necessary but confidence is to low. Especially as heights are beginning to rise and surface low turns to the northwest. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 6 AM EDT Saturday for ANZ235-237- 250-254>256. Small Craft Advisory until 6 PM EDT this evening for ANZ251. && $$ SYNOPSIS...Nocera/Dunten NEAR TERM...Dunten SHORT TERM...Dunten LONG TERM...Nocera AVIATION...Nocera/Dunten MARINE...Nocera/Dunten TIDES/COASTAL FLOODING...Staff is the U.S. government's official web portal to all federal, state and local government web resources and services.