Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 212352 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 652 PM EST Mon Jan 21 2019 .SYNOPSIS... Arctic airmass and dangerously cold wind chills continue into tonight with moderating temperatures Tuesday. Much milder air moves in Wednesday into Thursday. An approaching frontal system will bring occasional rain Wednesday afternoon into Wednesday night with a period of heavy rain possible on Thursday. Mainly dry and more seasonable temperatures Friday then turning much colder Saturday. Snow showers are possible Sunday as another front approaches. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 650 PM update... Scattered flurries/snow showers associated with deeper moisture plume and mid level warm advection rotating across eastern MA. This moisture will move offshore by midnight with clearing skies developing. Exception will be over the outer Cape where occasional ocean effect snow showers will persist. Temps will be steady or even rise a few degrees tonight as wind continues and CAA stops as core of coldest air aloft exits. However, dangerously cold wind chills continue. Current forecast on track. Previous discussion... *** Wind Chill Headlines Continue *** *** Lows 5 above to 5 below zero *** Mid level vortex that delivered the arctic airmass to the region is now located over eastern New England. Warmer air aloft (TROWAL) is beginning to wrap around the system cyclonically into southern New England. This is resulting in lots of clouds and some flurries/light snow from time to time across the area. Not expecting any accumulation other than a possible dusting or coating. Any accumulating snow tonight will be confined to the outer Cape from Provincetown to Chatham as WNW winds veer to the NNW, providing a longer fetch. This will result more persistent ocean effect snow showers across the outer Cape. Hi res guidance offering up to 0.15 qpf thru tonight. Snow ratios not ideal as it`s too cold with temps below -20C. Thus not looking at dendrites but more snow grains and/or needles. Nevertheless expecting a coating to 2 inches for most locations between Provincetown to Chatham. Low risk of up to 3" in a few locations. Hyannis westward very little if any snow accums given NNW trajectory. Another frigid night ahead along with a very cold start here as sunset approaches. Not as much of a temp drop tonight given core of cold air at 850 mb and 925 mb is centered over the region at the moment. Thus CAA eases tonight and not expecting radiational cooling as gusty NW winds persist. Nonetheless forecasting lows from 5 above to 5 below for the most part along with wind chills from -15 to -25 for much of the area. Therefore wind chill advisories. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... 4 PM update... Tuesday... Frigid again tomorrow morning along with bitterly cold wind chills. However not nearly as cold as today especially during the afternoon as airmass modifies and winds slacken in response to high pressure building in from the west. Highs actually manage to get into the low and mid 20s along with sunshine. Tuesday night... With high pressure overhead and a very dry airmass in place temps will freefall during the evening. Therefore followed the colder MOS temps. Expect temps to level off second half of the night as SSW pgrad increases along with mid/high clouds approaching from the west. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Highlights... * Rain Wed aftn/night possible starting as snow/mixed precip interior * A period of heavy rain Thu, especially SE New Eng * Mainly dry and turning colder Fri into Sat * Snow showers possible next Sunday Wednesday... Increasing warm advection in SW flow combined with deepening moisture plume moving into SNE will bring rain to SNE, mainly during Wed afternoon. The column is marginally cold enough for some snow/sleet at the onset across the interior, but this should be short lived as increasing SW flow rapidly warms the boundary layer. Temps moderate into the upper 30s to mid 40s during the afternoon. Modest low level jet develops across the coastal plain and soundings show enough BL mixing to support gusts to 35 mph SE New Eng. Wednesday night into Thursday... Good heavy rain signal late Wed night/Thu as low level jet advects anomalous PWATs into SNE. PWAT and low level wind anomalies are 3SD above normal. Widespread rain expected Wed night with heaviest rain likely during Thu as axis of low level jet and frontal wave enhances convergence along the boundary. Some elevated instability so also can`t rule out some convection across SE New Eng. Expect widespread rainfall 1 to 2 inches, with risk of localized 3 inch amounts across RI and SE MA which will result in areas of urban and poor drainage flooding. 70-80 kt low level jet develops across SE New Eng on Thu. Soundings show a good low level inversion which will limit these gusts from reaching the surface but still potential for gusts reaching advisory criteria across SE New Eng. Friday into Sunday... Deep trough sets up across eastern Canada as piece of polar vortex rotates south from Hudson Bay with dominant northern stream across New Eng. Blustery and seasonably cold Fri, then secondary front delivers modified arctic air for Fri night/Sat with below normal temps. Mainly dry Fri/Sat although some higher elevation flurries possible at times as series of shortwaves rotate through. Higher risk of snow showers Sunday associated with a stronger shortwave and more moisture as onshore flow develops. Monday... Low confidence given lots of spread in upper air pattern. Followed WPC guidance with continued chance of snow/rain showers. && .AVIATION /00Z TUESDAY 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/...High confidence 7 PM update... Tonight... Scattered snow showers and localized MVFR across eastern MA will end after 02z with partial clearing and VFR. Otherwise, MVFR should be confined to the outer Cape in snow showers with snow accumulations ranging from a coating to 2 inches. Elsewhere VFR with gusty WNW winds becoming more NNW with gusts up to 30 kt, highest over the Cape and Islands. Tuesday.... MVFR cigs continue across the outer Cape. Otherwise VFR prevails along with NNW winds 20-30 kt. Tuesday night... Winds finally diminish. VFR with low risk of MVFR and precip exiting eastern NY into western New England. Brief period of a wintry mix possible but likely holding off until Wednesday. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF Outlook /Wednesday through Saturday/... Wednesday: MVFR/IFR conditions possible. Windy with gusts to 30 kt. Chance RA, FZRA. Wednesday Night: Mainly MVFR, with areas IFR possible. Windy with gusts to 35 kt. RA. Thursday: Mainly MVFR, with areas IFR possible. Strong winds with areas gusts to 45 kt. RA, chance FZRA. Thursday Night: Mainly VFR, with local IFR possible. Breezy. Slight chance SHRA, slight chance SHSN. Friday: Mainly VFR, with local IFR possible. Breezy. Slight chance SHSN. Friday Night: VFR. Breezy. Saturday: VFR. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday Night/... 4 PM update... *** Heavy Freezing Spray Warning *** *** Gale Warnings Continue *** Tonight... Frigid airmass continues to overspread the waters via WNW gales that become NNW overnight. Heavy freezing spray warning eastern MA waters, freezing spray advisory elsewhere. Snow showers limit vsby to about 1 mile at times. Tuesday... NNW gales likely in the morning along with moderate to heavy freezing spray. But improving during the afternoon as temps not as cold and wind eases as well. Tuesday night... Light winds as high pres builds over the waters. No headlines expected. Outlook /Wednesday through Saturday/... Wednesday: Low risk for gale force winds with gusts up to 35 kt. Areas of rough seas. Chance of rain. Wednesday Night: Low risk for gale force winds with gusts up to 35 kt. Rough seas up to 11 ft. Rain likely. Thursday: Moderate risk for gale force winds with gusts up to 45 kt. Rough seas up to 15 ft. Rain. Thursday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 14 ft. Chance of rain showers. Friday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 11 ft. Friday Night: Winds less than 25 kt. Rough seas up to 9 ft. Saturday: Winds less than 25 kt. Areas of rough seas. && .CLIMATE... RECORD LOW MAX TEMPERATURES TODAY/MONDAY.... Boston ... 12 ... 1985 Providence ... 7 ... 1985 Hartford (BDL) ... 8 ... 1985 Worcester ... 8 ... 1985 As of 4 pm here are the observed high temps today... Boston...7 Providence...5 BDL...4 Worcester...-2 These numbers will be updated between 430-5pm when our climate summaries are issued. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Wind Chill Advisory until 8 AM EST Tuesday for CTZ002>004. MA...Wind Chill Advisory until 8 AM EST Tuesday for MAZ003>007- 010>021-026. Wind Chill Warning until 5 AM EST Tuesday for MAZ002-008-009. RI...Wind Chill Advisory until 8 AM EST Tuesday for RIZ001>007. MARINE...Heavy Freezing Spray Warning until 6 AM EST Tuesday for ANZ231- 232-250-251-254. Gale Warning until 7 AM EST Tuesday for ANZ230>237-251. Freezing Spray Advisory until 11 AM EST Tuesday for ANZ233>235- 237-255-256. Gale Warning until 2 PM EST Tuesday for ANZ250-254>256. && $$ SYNOPSIS...KJC/Nocera NEAR TERM...KJC/Nocera SHORT TERM...Nocera LONG TERM...KJC AVIATION...KJC/Nocera MARINE...KJC/Nocera CLIMATE...

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