KBOX issues Area Forecast Discussion (AFD) valid 2019-11-27T11:57:00Z 921 FXUS61 KBOX 271157 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 657 AM EST Wed Nov 27 2019 .SYNOPSIS... An offshore high pressure now offshore will maintain dry weather this morning. A cold front moves across New England later today, bringing a period of showers into tonight. A few showers may linger into Thanksgiving morning across the east. Otherwise, it will be windy and cooler. Another high pressure will bring dry and cold weather Friday into Saturday. The next storm system brings rain and/or snow to the region Sunday into Monday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 7 AM Update... Fog and low clouds have indeed lasted longer than originally expected, mainly over the coastal plain of southeast MA, coastal RI, and Cape Cod. A Special Weather Statement has been issued to address this patchy dense for. This comes as a warm front starts to move north across southern New England. More humid air will follow this front. Expecting fog to dissipate in the hours immediately after daybreak, but not confident on the timing. Current forecast is for it to lift by around 9 am. Previous Discussion... A low pressure will move into the Great Lakes by late today. Timing will be critical, as the complex pattern of fronts will make a big difference for rainfall distribution. With the parent low pressure so far to the west, the push behind these fronts will not be particularly strong. Thinking the warm front associated with this low struggles to make it much farther north than the MA/NH/VT border by the end of today. Thus, the heaviest rainfall should be more towards northern New England. The location of this front should also mean above normal temperatures for much of southern New England, despite the clouds. However, it will not be nearly as warm as it was Tuesday. Still, it will be warm enough where only rain is expected. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Just about all of the deterministic guidance continues to advertise a triple-point low pressure developing and traversing the warm front, and dragging a cold front across southern New England this evening. Rainfall chances will diminish behind this front, but linger into Thursday as colder air moves in aloft. These rainfall chances will linger longest towards eastern MA, and especially the Cape. Precipitation still will be primarily rain. However, some wet snow may mix in at the highest elevations of the Worcester Hills and towards the Berkshires before ending late Wednesday night. It will be noticeably colder Thanksgiving day. The arrival of the colder air will also lead to gusty northwest winds. There is potential for wind gusts to reach advisory level thresholds. Still do not have enough confidence in the details to issue those headlines this morning. The greatest risk for these stronger gusts will be towards the Cape and islands. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Highlights... * Cold and dry Fri and Sat * Storm system Sun into Tuesday brings rain and/or snow * Drier toward mid week Details... Thursday night... As we move into the overnight hours the column stays dry so not expecting any cloudcover to speak of, save for some lingering ocean effect clouds over the outer Cape. The surface low continues to edge eastward, slackening the pressure gradient albeit slowly. Thus, winds will remain gusty much of the night. CAA continues with mixing to near 900mb, tapping into the 30-35 kt 925mb LLJ we could see winds gusting 25 to 35 mph. Temperatures dip into the upper 20s inland and low 30s along the coast. Friday and Saturday... As we transition to a high pressure ridging setup the pressure gradient continues to decrease but remain enough to keep winds gusting 20-30 mph. Saturday winds continue to come down as an inverted ridge of sfc high pressure extending from southern QC moves overhead. Cold and dry air remains in place both Friday and Saturday under building high pressure. Northerly flow brings 850mb temps down to -4 to -6 C and will support surface highs generally in the 30s each day, approaching the 40s along the south coast on Friday. Sunday and Monday... The second half of the weekend into the new workweek becomes unsettled with the potential for an impactful winter storm. Looking at the big picture we see a potent surface low forming in the lee of the Rockies on Saturday. This low and mid level shortwave reflection will in time move across the midwest and into the mid Atlantic by Sunday night into Monday, generating a triple point low in the vicinity of our southern waters around Sunday night. While this has the potential to bring some significant wintry weather to southern New England uncertainty is high given run-to-run and model discrepancies, especially in the track of the low. While EC and GEFS ensembles continue to show a wide range of possibilities including near the 70/40 benchmark, 24 hour trends have been slightly north, or a better chance of rain away from the interior. At the moment a period of overrunning light snow appears likely Sunday given the cold antecedent airmass in place, followed by a transition to rain away from the interior high terrain, and snow again on the tail end as cold air is wrapped around the exiting low on Monday. That being said, at this time range (5-6 days) all possibilities are still on the table. Tuesday... Likely the tail end of precipitation comes to and end sometime Tuesday as the low exits to the east and N/NW winds bring in a cooler airmass. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/...High confidence. 12Z Update... Today and Tonight... Local IFR in fog and low clouds early this morning towards the south coast, as well as in some of the river valleys across CT, RI and southeast MA. This fog is expected to dissipate by 15Z. VFR though most of today. Timing lowering conditions towards the time of the evening push. Expecting mainly MVFR conditions, with areas of IFR towards northern New England and across the higher terrain. Thinking conditions will lower rather quickly, but not certain yet on the timing. Main concern would be for a slower timing, which would permit better conditions this evening. Conditions should improve to mainly VFR again after midnight. Lingering MVFR in any showers. Gusty NW winds develop behind a cold front. Thanksgiving Day...Gusty NW winds continue, and likely increase in strength. Mainly VFR, with areas of MVFR early in lingering showers towards eastern MA. KBOS TAF...High confidence in TAF trends. Moderate confidence in onset timing of rainfall. KBDL TAF...High confidence in TAF trends. Moderate confidence in onset timing of rainfall. Outlook /Thursday Night through Sunday/... Thursday Night: VFR. Windy with gusts up to 35 kt. Friday through Friday Night: VFR. Windy with areas of gusts up to 30 kt. Saturday through Saturday Night: VFR. Breezy. Sunday: MVFR/IFR conditions possible. Breezy. Chance SN, chance RA. && .MARINE... Short Term /through Thursday/...High confidence. 4 AM Update... Tweaked the timing of the Gale Warnings for tonight into Thursday to better reflect current expectations. Previous Discussion... Rather light winds and seas this morning. Increasing southerly winds today will lead to building seas. Rain showers develop this afternoon and continue into tonight. Showers could linger across the eastern coastal waters into Thanksgiving Day. Expecting Small Craft Advisory level winds to develop this evening, with NW gales to develop after midnight and continue into Thursday. Rough seas develop on just about all exposed waters, starting with the south coastal waters this evening. Eastern waters are more impacted by rough seas Thursday. Outlook /Thursday Night through Sunday/... Thursday Night: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 16 ft. Friday: Low risk for gale force winds with gusts up to 30 kt. Rough seas up to 12 ft. Friday Night: Low risk for gale force winds with gusts up to 35 kt. Areas of rough seas. Saturday: Moderate risk for Small Craft Advisory winds with local gusts up to 30 kt. Areas of rough seas. Saturday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain, slight chance of snow. Local visibility 1 to 3 nm. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Gale Warning from 1 AM Thursday to 7 AM EST Friday for ANZ231- 232. Gale Warning from 1 AM Thursday to midnight EST Thursday night for ANZ233-234-251. Gale Warning from 4 AM to 1 PM EST Thursday for ANZ230-236. Gale Warning from 11 PM this evening to 10 PM EST Thursday for ANZ235-237. Gale Warning from 1 AM Thursday to noon EST Friday for ANZ250- 254. Gale Warning from 7 PM this evening to 7 AM EST Friday for ANZ255-256. && $$ SYNOPSIS...Belk/BW NEAR TERM...Belk/BW SHORT TERM...Belk LONG TERM...BW AVIATION...Belk/BW MARINE...Belk/BW