964 FXUS61 KBOX 180933 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 433 AM EST Wed Dec 18 2019 .SYNOPSIS... An inverted trough will lift north and east of the region this morning as low pressure exits. Any precipitation will come to an end by mid morning from west to east. A cold front through during the afternoon and into the evening. This will bring scattered snow squalls and will be accompanied by strong wind gusts. Arctic air will push in wake of the front. This coupled with the winds will bring very low wind chill values. Dry and cold conditions continue Thursday and Friday. Dry weather likely lingers through the weekend into early next week and will be accompanied by moderating temperatures. && .NEAR TERM /UNTIL NOON TODAY/... Highlights... Slick AM commute especially where roads are untreated and black ice has formed. Rain and snow ending across the coastal plain and RI. Scattered snow showers begin spreading into western MA by noon. Details... An inverted trough will lift north and east of the region as low pressure exits. This will gradually bring an end to precipitation across eastern MA and RI. Temperatures will be at or below freezing for much of the CWA this morning. Any areas where the pavement is wet and untreated could be slick as black ice may form. A weak mid level ridge will quickly build in this morning and bring partly to mostly sunny skies. This will be short lived as a cold front slides in from the northwest, which will increase cloud cover from northwest to southeast heading into the afternoon. Snow shower chances will increase across the Berkshires. Temperatures will increase into the low to mid 30s by noon with the coldest readings across the CT River Valley. && .SHORT TERM /NOON TODAY THROUGH 6 PM THURSDAY/... Highlights... Scattered snow showers and snow squalls this afternoon into this evening. This activity could impact the evening commute. Arctic air pushes in tonight bringing gusty winds and producing wind chills between 0 degrees and nearly 20 degrees below zero late tonight into early Thursday AM. The coldest readings are expected where a Wind Chill Advisory has been issued across the Berkshires. A Wind Advisory has been issued for Cape Cod and the Islands due to the strong winds. Details... This afternoon and tonight... Cyclonic flow across the eastern Great Lakes and New England with a cutoff situated over the central Great Lakes. This feature will lift into northern New England by this evening. At the surface a cold front will slide through. The combination of daytime heating, low level moisture and the cold front sliding in will result in scattered snow showers. The latest NAM, GFS, ARW and NMM show nearly adiabatic lapse rates within the lowest 2 km along with strong low level convergence and around 50 to 90 J/kg of CAPE. Looks like an environment with potential for snow squalls, but the best opportunity is across northern New England due to the proximity to the upper low. Think that there will be a period from roughly noon until 9 PM where there will be widely scattered snow showers. Looks like the best opportunity for snow squall activity will be across the Berkshires, CT Valley and Worcester Hills. However, cannot rule out this activity spreading further east. Have some concern that this activity lingers and impacts the evening commute. Expect anywhere from a dusting to an inch of accumulation where snow showers pass through. Any snow shower activity will quickly diminish this evening due to the loss of heating. Still expect strong mechanical mixing as Arctic air filters in. Expect westerly winds becoming northwesterly with speeds of 15 to 25 mph and inland and gusts of 20 to 30 mph. Expect stronger mixing across the Cape and Islands where gusts of 40 mph are expected overnight. Strong agreement amongst guidance and per NAM/GFS Bufkit profiles for strong gusts across the Cape and Islands. Decided to issue a Wind Advisory into Thursday morning. The gusty winds inland coupled with the plummeting temperatures will result in very cold wind chills. Values of 0 to 20 degrees below zero can be expected late tonight into early Thursday morning with the coldest readings where the Wind Chill Advisory has been issued. Low temperatures will fall into the single digits and teens above zero across the region. Thursday... Cyclonic flow persists aloft, however the cutoff will lift northeast of the region. A mid level ridge will build in from the west. This will gradually relax the pressure gradient and bring lighter gusts over land. Skies will be partly to mostly sunny, but it will be chilly with the arctic air in place. High temperatures range from the teens across the higher elevations inland to the low to mid 20s across the coastal plain. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Highlights... * Arctic High high pressure brings dry weather Thu - Tuesday * Temps well below normal Friday will moderate through the weekend into next week Details... Thursday night and Friday... A sprawling high pressure moves into place at the surface with cold NW flow aloft keeping the Arctic airmass over the region. The surface pressure gradient ahead of the advancing high remains tight which will keep winds gusty Thursday night helping to limit decoupling and radiative cooling. Friday winds come down through the morning as the center of the high moves east. Dry weather expected with plenty of sun. Sunny skies may be deceiving, however, as temperatures will feel frigid, only topping out in the 20s Friday. This would be 10 to 10F below normal for late December. Saturday through Tuesday... The quiet weather stretch continues through at least Tuesday under continued high pressure. An upper level shortwave over the desert SW becomes closed off and separated from the steering flow Saturday and a dip in the northern stream moves through to our north late Saturday, but at the moment its looking like we may get some added cloud cover and not much else. That larger system stays well to our south Sun/Mon while another disturbance passes well to our north. For now it continues to look like we'll thread the needle between systems and stay dry. By late Saturday winds come out of the SW and W which brings in warmer air and moderating temps back toward normal. Highs by Saturday are back in the 30s; 30s/40s by Sunday into next week. && .AVIATION /10Z 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/... 09Z Update... No changes to the forecast in the latest update. Brought things in line with current conditions and what is expected over the next 3 to 6 hours. Previous discussion... Tonight...Moderate to high confidence. IFR to MVFR conditions gradually improving to VFR from west to east late tonight into early Wednesday...roughly between 08Z and 14Z. Precipitation will gradually wind down, but have held onto things until roughly 12-15Z for eastern TAF sites due to an inverted trough lifting through. Northwest winds around 5 to 10 knots. Wednesday...Any lingering MVFR conditions will become VFR. An Arctic front brings a period of snow showers and possible snow squalls; best chance N/W of PVD. Brief 30-min vsby reduction to IFR-LIFR levels possible in any snow squall. Tried to best time this activity in the latest TAFs with MVFR conditions between roughly 18Z-00Z. Held off on IFR/LIFR limits due to confidence. Winds W 5-10 kts increase to 15-25 kts gusts 30-35 kts late Wednesday behind the Arctic front. Wednesday Night...VFR. Strong winds with local gusts up to 40 kt. KBOS Terminal...Moderate to high confidence in TAF. Moderate confidence after 18Z. KBDL Terminal...High confidence in TAF. Confidence in TAF lowers to moderate after 18Z. Outlook /Thursday Night through Sunday/... Thursday Night: VFR. Windy with local gusts up to 30 kt. Friday: VFR. Breezy. Friday Night through Sunday: VFR. && .MARINE... Short Term /through Thursday/... Seas will continue to run above SCA levels on the outer waters into Wednesday, and will build further as a strong Arctic front moves across the waters late today and tonight. Gale warnings have been issued for all waters with gusts in the 35-40 kt range starting this evening. These conditions will persist into Thursday. With the colder air moving in and cooler ocean temperatures expect freezing spray across the eastern nearshore waters. A Freezing Spray Advisory has been issued tonight into Thursday morning. Outlook /Thursday Night through Sunday/... Thursday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 10 ft. Friday: Winds less than 25 kt. Local rough seas. Friday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Saturday through Sunday: Winds less than 25 kt. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Wind Advisory from 6 PM this evening to 10 AM EST Thursday for MAZ022>024. Wind Chill Advisory from midnight tonight to 10 AM EST Thursday for MAZ002-008-009. RI...Wind Advisory from 6 PM this evening to 7 AM EST Thursday for RIZ008. MARINE...Freezing Spray Advisory from 1 AM to 10 AM EST Thursday for ANZ231-232-251. Gale Warning from 6 PM this evening to noon EST Thursday for ANZ231>235-237-251-255-256. Gale Warning from 6 PM this evening to 7 AM EST Thursday for ANZ230-236. Gale Warning from 6 PM this evening to 10 PM EST Thursday for ANZ250-254. && $$ SYNOPSIS...BL/BW NEAR TERM...KJC/BL SHORT TERM...KJC/BL LONG TERM...BW AVIATION...BL/BW MARINE...KJC/BL/BW