Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 221740 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1240 PM EST Wed Nov 22 2017 .SYNOPSIS... A cold front approaches the region today, and with moisture working up the eastern seaboard to bring a period of rain this morning, especially SE New England. Quiet weather Thursday and Friday. Another shot of wet weather and breezy conditions this weekend. Drier and milder toward the middle of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 10am update... OBs and MSAS mass/thermal fields suggest cold front has moved into W MA/CT but remains somewhat dammed against the Berkshires/Litchfield hills. As the peak moisture plume across E MA/RI continues a slow shift to the E with attendant coastal low pres offshore, this should allow the front to begin to make a slow transition E. Initially, the added f-gen provided by the front should lead to a net increase in RA across W MA/CT so will actually feature rising POPs over the next few hours. However, thereafter as CAA/dry air begins to entrain through the column, this RA will end mid-day through the afternoon W-E across S New England. Will maintain a low risk for occasional TSRA as KDP/CC before the radar equipment issue showed good ice signatures aloft. Have slowed the E progress of the higher POPs this afternoon as confluence of higher theta-e and phasing of the approaching front looks to generate a weak meso-low pres which will slow the drier air moving in. Still, most locations should see the end of rainfall by sunset. Previous discussion... Split flow across the region early this morning as northern stream cold front approaches from the Great Lakes. Southern stream shortwave/coastal low off the Carolina coast will move northward up the east coast. This system will remain well offshore but its moisture plume will impact the region. Currently, surface cold front is making its way into upstate NY. Radar imagery shows some showers along this front, but overall moisture is pretty meager. Southern New England remains in the warm sector ahead of this approaching front thus temps early this morning have reside above average. In fact, the office is currently a balmy 51 degrees with Nantucket at 56F. Focusing south, latest GOES-16 satellite shows moisture beginning to stream northwards towards New England thanks to Bermuda high pressure. Current radar imagery shows widespread showers across the Carolina coast, with scattered showers developing across Long Island and into southeast Massachusetts. These showers are associated with the upper level jet and mid- level moisture at 700mb. At the surface, theta-e gradient has set-up with a 1000-925mb frontogenesis which has help aided the showers in southern New England. The profile has moisten up as guidance suggested as rainfall is being reported from WST to EWB. Over the next few hours, moisture will continue to stream into the region as surface cold front from the West approaches. This will help pool the moisture into the area and push PWAT values to above 1.0 inch by the mid-morning hours. Showers will begin to overspread the rest of the region after 7AM. The combination of the upper level jet and LLJ will help aid in strong lift for the region. In fact, guidance continues to hint at strong omega during the mid-morning hours especially along and points east of I-95. This combined with the high PWATs will lead to heavy downpours across RI and eastern MA. NCAR ensembles continue to show the potential for 40dbz during the 7Am to noon time-frame. Also cannot rule out a rumble or thunder as guidance continues to hint as SB Cape thanks to higher dewpoints. Continued to trend QPF towards the EC but with the Hi-res guidance mix in as well. Appears that heavy precip axis will be along of just east of the I-95 corridor. This is also supported by the HREF, NCAR ensembles and HRRR. Generally 0.5 to 1 inch QPF will fall across a line east of IJD to BVY. Highest amounts will occur just east of I- 95. Areas west of the Worcester Hills will see rainfall amounts less than 0.25 inches. As the front pushes through southern New England, precip will exit the region by the mid-afternoon. Behind the front, dry but cooler air will quickly usher into the region leading to temps dropping through the afternoon hours and winds beginning to pick up. Overall anticipate a rainy morning leading to heavy downpours slowing the morning commute. Conditions will improve by the afternoon hours leading to a great, but chilly start to the Holiday travel. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Tonight into Thanksgiving Day... Cold front will be offshore by this evening as strong CAA usher into the region. Good mixing with this cold air aloft resulting in gusty NW winds near 20-25 MPH during the overnight hours. Surface high pressure approaching from the west may be enough to allow for the winds to slacken off resulting in radiational cooling before daybreak. Highest confidence is across the interior. Thus will keep temps cooler than MAV/MET guidance. Chilly start to the Thanksgiving Holiday as high pressure from the west builds into the region. Weak shortwave aloft will increase cloud cover during the afternoon. Moisture associated with this wave looks meager enough to keep the forecast dry. Westerly winds at the surface as temperatures in the upper 30s to low 40s across the region. Overall, a chilly but dry Turkey day as temperatures will remain 5 to 10 degrees below normal. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... */ Highlights... - Quiet weather through Friday - Showers possible at times this weekend, could be breezy Sunday - Turning mild Tuesday into Wednesday, could also be breezy */ Overview... 22/00Z guidance suite is rather good overall agreement into Sunday. More detail differences become more prevalent early next week. Continue to favor a consensus approach to smooth over the less predictable details, particularly with timing and amplitude of various shortwaves moving through the larger synoptic pattern. In general, expecting a mid level longwave trough to linger near our region Friday into Saturday. As previously note, this is more of a split flow during this time. Majority of the guidance merges this flow into a deeper mid level trough Sunday into Monday. This mid level trough expected to finally move over the Maritimes toward the middle of next week. Only concern for precipitation during this time will be this weekend. Besides a series of front Saturday, will need to monitor the progress of an offshore low pressure. At this time, thinking this coastal low remains far enough east to not have a major impact other than increasing the pressure gradient, especially Sunday. && .AVIATION /17Z 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 Night/...High confidence. Through 00Z this evening.. Mixed IFR to VFR conditions continue with most VFR W of the Worcester Hills and mixed MVFR/IFR east through about 21Z. After this point, rapid improvement to VFR all sites from W-E through the remainder of the evening as winds shift to 320. Gusts to around 25-30 kt possible also with this wind shift. Tonight into tomorrow night... Mainly VFR after this evening. NW winds continue to gust around 25 kt through the overnight hours but then drop off during the early morning. These winds shift to mainly W tomorrow and tomorrow night. KBOS Terminal... Mixed VFR/MVFR conditions with last batch of rain through about 21Z along with E-NE flow. Once winds shift to 320 conditions improve rapidly thereafter. With the wind shift, gust 25-30 kt are possible at times, which linger into the overnight. KBDL Terminal... Mainly VFR, winds will shift to NW no later than 20Z with gusts to around 25 kt at times lingering into the evening. Outlook /Friday through Sunday/... Saturday: VFR. Breezy. Slight chance SHRA. Saturday Night: VFR. Slight chance SHRA. Sunday: VFR. Breezy.
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&& .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/... Today...High confidence. Passing cold front during the day and passing coastal low well east of the waters will lead to widespread rainfall today which could limit VSBYS. Seas will remain near 5 feet for the outer waters but SCA have been let go elsewhere. Tonight into Tomorrow...High confidence. Strong CAA across the relatively warm waters will result in gusts NW winds between 25-30 kts. Seas will also build in response. SCA have been reissued to account for this trend. Low confidence on gales for the eastern ocean waters. Conditions will improve on Thanksgiving, but seas will remain choppy into the afternoon. Outlook /Thursday Night through Sunday/... Thanksgiving Day: Winds less than 25 kt. Local rough seas. Thursday Night: Winds less than 25 kt. Seas up to 5 ft. Friday through Friday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Saturday through Saturday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Sunday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Seas up to 5 ft. Slight chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 4 PM this afternoon to 4 AM EST Thursday for ANZ230>234-251. Small Craft Advisory from 4 PM this afternoon to 1 AM EST Thursday for ANZ236. Small Craft Advisory from 4 PM this afternoon to 2 PM EST Thursday for ANZ235-237. Small Craft Advisory from 4 PM this afternoon to 8 PM EST Thursday for ANZ250. Small Craft Advisory until 8 PM EST Thursday for ANZ254>256. && $$ SYNOPSIS...Belk/Dunten NEAR TERM...Doody/Dunten SHORT TERM...Dunten LONG TERM...Belk AVIATION...Belk/Doody MARINE...Belk/Dunten

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