000 FXUS61 KBOX 260554 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1254 AM EST Wed Feb 26 2020 .SYNOPSIS... A weak cold front will settle south of New England tonight and Wednesday, with a moist northeast flow bringing patchy light rain and drizzle at times. Low pressure lifts slowly northeast Wednesday night into Thursday, bringing an area of rain across the region with a wintry mix or a period of light snow across the higher terrain of north central and northwest Massachusetts. As this low exits, cold and blustery conditions move in for Thursday night into the weekend, along with some isolated snow showers at times across the high terrain. High pressure builds over the region Monday, then makes way for more rain sometime Tuesday. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 1250 AM update... Areas of rain continue to move across the region but it is becoming more spotty and expect this trend to continue overnight as mid level drying moves up from the south. Low clouds and fog will persist along the south coast. Previous discussion... Approaching shortwave and deep moisture axis has brought an area of light rain to SNE this evening. Rainfall is concentrated along the Mass Pike and moving ENE. As shortwave moves to the north and east overnight, rain will become more spotty as deep moisture lifts to the north. Low level WV imagery which samples 750-500 mb layer shows drier air in mid levels south of the coast which moves north across SNE later tonight. Otherwise, areas of fog locally dense in spots will persist along the south coast along with patchy drizzle overnight as mid levels dry out. With developing low clouds and light NE winds, temps will not fall much from current readings with lows ranging from mid 30s to lower 40s. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/... A potent mid level shortwave will amplify the mid level flow over southern New England, increasing isentropic lift as well. Despite the increased lift, the deepest moisture shifts north in response to this amplification, which in turns leads to a lower risk for a widespread significant rainfall. The favored areas will again be the higher terrain of central and western MA due to the enhanced orographic lift. Still thinking the brunt of our next weather event holds off until sometime Wednesday night. Temperatures should not budge much due to the persistent and increasing northeast flow. Expecting high temperatures only 5-10 degrees higher than the morning low temperatures, which is still above normal. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Big Picture... Our weather through the weekend will be dominated by a Great Lakes trough that becomes a closed low over Eastern Canada and lingers there through Sunday. Another upper trough digs over California during the weekend, which would suggest a building upper ridge over the Eastern USA Monday-Tuesday. Upper contour heights, which track with the deep-layer temperatures, are normally in the 540s this time of year but starting to slowly rise. Forecast heights are above normal Wednesday night, although a low-level east flow suggest a colder layer at the surface. Heights then drop well below normal by Thursday evening and stay below normal through Sunday. Heights return to normal or a little above early next week. Mass fields are similar through the weekend, but treat the developing ridge and trailing weather system differently Monday and Tuesday. Thus good forecast confidence through the weekend, diminishing early next week. Daily Concerns... Wednesday night-Thursday... Upper trough over the Great Lakes brings a south-southwest flow over the Eastern USA. This draws milder and moist air up into Southern New England Wednesday night. Precipitable water values increase at this time to between 1 and 1.25 inches with highest values over Cape Cod and Islands. Increasing low level east winds of 50-60 kt move up over Eastern MA. Some of this may reach the surface, but not all. Forecast will show easters along the coast at 30 kt. Meanwhile a 170-kt jet moves overhead at upper levels. This means a well-above normal supply of moisture combined with sources of strong lift. Expect rain to move in during the night and continue through Thursday morning before tapering off. Primary surface low remains to our west, while a potential secondary low may move over Srn New England Thursday morning. Low level ageostropic flow is forecast from the north at 40-50 kt Wed night, and a cold air damming signal lingers from Maine into NW Mass. This continues to suggest an area of light snow or rain/snow mix over the Northern Worcester Hills and the Berkshire East Slopes. Expect the rain and mix to taper off Thursday morning as the weather system shifts to our north, ending latest in MA to the north of the route 2 corridor. Winds then shift out of the west with gusts of 35 to 45 kt possible. A gusty afternoon and night. Mixing to 850 mb suggests max temps in the 40s and low 50s, but cold advection suggests this will be reached around midday or earlier with falling temperatures in the afternoon. Temps Thursday night will fall to the 20s. Friday through Sunday... Two shortwaves diving into the Northeast upper trough. This will form a cutoff low over Eastern Canada and encourage cold advection over Southern New England. The mixed layer maintains at 850 mb into the weekend. Temperatures at 850 mb change from above freezing Thursday to -14C Friday and -16C Sunday. This suggests max sfc temps in the 30s Friday and 25 to 35 over the weekend. Nighttime temps will fall to the teens and lower 20s. Cold advection over the Great Lakes may bring a few snow showers to the Berkshire East Slopes. Cold advection over the ocean is initially weaker...the combination of that and west winds make ocean effect snows less likely Friday and Saturday. But winds do shift from northwest by Sunday, and air-water temp differences would be around 15C. This may be favorable for ocean snow showers near the Outer Cape on Sunday. Monday-Tuesday... High pressure builds over the region Monday, bringing subsidence and clearing skies/diminished wind. Another weather system approaches from the southwest, but with questions on precip timing. The GFS is fastest, with precip starting Tuesday morning, while the ECMWF and GGEM show precip holding off until Tuesday evening. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through 12z... Variable conditions trending to MVFR/IFR with areas of LIFR fog near the south coast. Spotty light rain will diminish. Today...Moderate confidence. Mainly MVFR cigs with areas of IFR Cape/Islands. Patchy light rain or drizzle at times, mainly interior. Tonight...Moderate confidence. Conditions deteriorating with widespread IFR/LIFR developing. Spotty rain in the evening, then a period of moderate to heavy rain moving across the region 06-12z from SW to NE. Increasing E winds overnight with gusts 25-30 kt developing near the coast and over higher terrain. Thursday...High confidence in trends. Rain exits 12-15z from SW to NE. IFR improving to VFR by midday with bkn cigs around 4k ft in the afternoon. E/Se winds shift to west by midday with 25-35 kt gusts in the afternoon. Gusts to 40 kt possible over the Islands. KBOS Terminal...Moderate confidence. Mainly MVFR lowering to IFR tonight. Period of moderate/heavy rain moves through 09-12z. KBDL Terminal...Moderate confidence. Mainly MVFR with a period of IFR later tonight as a band of moderate/heavy rain moves through around 06-12z. Outlook /Thursday Night through Sunday/... Thursday Night through Friday: VFR. Windy with gusts up to 35 kt. Friday Night: VFR. Windy with local gusts up to 30 kt. Saturday: VFR. Breezy. Saturday Night through Sunday: VFR. && .MARINE... Still expecting marginal Small Craft Advisory conditions to develop across the outer southern coastal waters late tonight into Wednesday as a low pressure approaches from the SW. Greater confidence in Small Craft Advisory conditions across these waters later Wednesday afternoon. Elsewhere, looking at reduced visibility in drizzle/rain and fog tonight into Wednesday morning. Outlook /Thursday Night through Sunday/... Wednesday Night: Low risk for gale force winds with gusts up to 40 kt. Areas of rough seas. Chance of rain showers. Gale Watch in effect. Thursday: Moderate risk for gale force winds with gusts up to 45 kt. Rough seas up to 16 ft. Chance of rain showers. Local visibility 1 to 3 nm. Gale Watch in effect. Thursday Night: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 15 ft. Gale Watch in effect. Friday: Low risk for gale force winds with gusts up to 35 kt. Rough seas up to 14 ft. Friday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Saturday: Winds less than 25 kt. Local rough seas. Saturday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Local visibility 1 to 3 nm. Sunday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of snow showers. Local visibility 1 to 3 nm. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Gale Watch from late tonight through late Thursday night for ANZ231>235-237-250-251-254>256. Small Craft Advisory from 7 PM this evening to 1 AM EST Thursday for ANZ231>235-237-250-251. Small Craft Advisory from 4 AM early this morning to 1 AM EST Thursday for ANZ254>256. && $$ SYNOPSIS...WTB/Belk NEAR TERM...KJC SHORT TERM...Belk LONG TERM...WTB AVIATION...WTB/KJC MARINE...WTB/Belk