FXUS61 KBOX 310319 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1019 PM EST Mon Jan 30 2023 .SYNOPSIS... A weak cold front moves across the region tonight, accompanied by scattered showers of rain and snow. Behind the front, mainly dry and seasonably cold Tuesday through Thursday. Dangerously cold airmass arrives late Friday into Saturday, with widespread below zero temperatures expected by Saturday morning. Some ocean- effect snow showers are possible across Cape Cod. Temperatures rebound quickly Sunday. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 1010 PM Update: While conditions still are seasonably mild, upper 30s-low 40s across most of southern and eastern sections in Soutehrn New England, cold frontal trough continues to sag very slowly SE across interior northern MA. Associated light precipitation is definitely of an anafrontal character in weak-UVV regime; while this light precip should fall as light rain, did note some light snow with 1-2 SM visbys in the colder air across the Berkshires and into eastern NY. Agree with prior assessment that while a transition from light rain to wet snow is anticipated as the column cools and the front continues its SE push, mild ground and generally very modest precip rates should preclude significant accums. Did up QPF/snow amounts a bit but nothing more than an inch from Worcester west; that which falls will also be confined to non-asphalt surfaces. May need to consider a special weather statement for patchy slippery spots north and west of I-95 if moisture remains on roads/if drier air is slower to arrive. Otherwise, just accounted for current obs in the forecast as see no compelling rationale to make changes to lows, in the 20s N/W of I-95 to low-mid 30s elsewhere. Previous discussion: Cold front moving into the Berkshires with area of post-frontal snow showers focused across central and eastern NY. As the front pushes E across SNE tonight, expect a few rain/snow showers developing across the interior. Initially, ptype may be rain but as the column cools rain showers will transition to snow showers. Not expecting any snow accums given short duration of snow showers and precip/qpf too light to overcome warm ground. Low temps in the mid to upper 20s northwest of I-95, low to mid 30s elsewhere. Could be some slick spots late tonight into Tuesday morning, NW of I-95 if any residual road moisture lingers. SW winds this evening become NW overnight in the post frontal airmass. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... 4 PM update... Tuesday... Dry, post frontal airmass overspreads the region. Any leftover morning clouds, gives way to partly to mostly sunny conditions from late morning into the afternoon. Seasonably cold with highs in the 30s. Chilly NNW wind 10-15 mph, but not too harsh by late Jan standards. Tuesday night... 1030 mb high advects into SNE. Thus, dry weather with diminishing NNW wind. Very dry airmass, so potential for cold temps, given light winds. However, models differ on cloud cover. Therefore, did a 50/50 blend between NBM and colder MOS guidance to derive mins. This yields lows in the teens for much of the region. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Highlights... * Seasonably cold and dry Wed into Thu * High confidence in dangerously cold airmass late Fri into Sat * Temperatures moderate quickly Sunday Wednesday into Thursday... Broad trough across the Gt Lakes and NE during this period. With low amplitude pattern in place, coastal low expected to remain well south of New Eng with as it tracks eastward from NC coast, so not expecting any precip from this system. Generally cold and dry conditions Wed as high pres builds in from the west. 850 mb temps will be -13 to 15C Wed moderating to -6 to -8C Thu. Below normal temps Wed with highs upper 20s to lower 30s moderating to upper 30s Thu. Cold night Wed night as good radiational cooling conditions develop with lows in the teens. Friday into Saturday... Polar vortex drops SE from Hudson Bay region and moves into the Maritimes Fri night and will deliver pure arctic airmass to SNE. Fortunately, with lack of high latitude downstream blocking it's a quick shot of arctic air, focused in the late Fri through Sat period as heights will already start rising on Sat. Timing of arctic front is somewhat uncertain as ECMWF about 6 hr quicker than GFS/GGEM but this only impacts Thu night/Fri morning temps regarding how quick the arctic air moves in. Even using the somewhat slower timing, temps will be falling through the teens and into single numbers Fri afternoon. It will be rather windy as well Fri into Fri night in strong cold advection pattern with potential for 35-45 mph gusts, peaking Fri afternoon/evening. Wind chills by late Fri will already be down to zero to -20F. While winds diminish somewhat late Fri night it will still be windy through the night into Sat morning. 850 mb temps are forecast to drop to -30 to -35F which has multi model and ensemble agreement. These 850 mb temps are about as cold as you will ever see in SNE. In fact, these temps are outside the model climatology for this time of year. ECMWF a bit colder than GFS but the uncertainty lies in the timing of the coldest air which may impact Sat temps. Regarding actual low temps, we expect mins -5 to -15F across SNE with potential for a few -20 readings over northern MA high terrain. These will be the coldest air temps since Feb 14, 2016 when BOS and PVD dropped to -9, ORH -16 and BDL -12. However, the bigger concern will be the dangerously cold wind chills which are expected to bottom out at -20 to -40 late Fri night into Sat morning, with potential for wind chills as low as -45 in the Berkshires. While we don't have records of wind chills, discussion within the office suggest these wind chills may be the coldest we've seen here in 15-20 years! Sat high temps will depend on how quickly the core of coldest air moves out. We followed the NBM which has highs single numbers and teens. It could be milder if the core of coldest air is quicker to depart, and colder if it's slower. Either way, still bitter cold Sat afternoon with wind chills remaining below zero through the day. Temps likely rise Sat night. In addition, a period of ocean effect snow showers are possible over portions of Cape Cod Fri night into Sat morning, but NW trajectory should keep steadier snow offshore. Widespread moderate to heavy freezing spray is expected over the waters. Sunday into Monday... Quick moderation is expected with temps Sun reaching mid 30s to lower 40s. The warming trend may be accompanied by some rain/snow showers Sun afternoon/night but this is uncertain given the model spread. Mon looks dry and seasonable. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 00z update.... After 00z: high confidence. VFR cloud bases with a period of MVFR cigs in scattered light rain/snow showers from NW to SE overnight. SW winds this evening shift to the NW overnight. Tuesday: High confidence. Any early MVFR cigs improve to VFR cloud bases late morning into the afternoon. Dry weather with NNW winds 10-15 kt. Tuesday night: High Confidence. VFR cloud bases with diminishing NNW winds. Dry runways. KBOS Terminal...High confidence in TAF. VFR cloud bases this evening, then MVFR in scattered light rain/snow showers 05z-11z. East wind late this afternoon, slowly shifting to SE, S and then SW, NW after 06z. KBDL Terminal...High confidence in TAF. Outlook /Wednesday through Saturday/... Wednesday through Wednesday Night: VFR. Thursday: VFR. Breezy. Thursday Night: VFR. Windy with local gusts up to 30 kt. Friday: VFR. Strong winds with local gusts up to 40 kt. Friday Night: VFR. Strong winds with gusts up to 40 kt. Saturday: VFR. Windy with gusts up to 35 kt. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 4 PM update... Thru Tue night... Tranquil weather by late Jan standards. SW winds this evening, then a cold front sweeps across the waters overnight with a wind shift to the NW. Scattered showers of rain and snow accompany the front. Front moves offshore Tue, with NNW winds 10-15 kt behind the front. Winds diminish Tue night as 1030 mb high advects into New England. Outlook /Wednesday through Saturday/... Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft. Wednesday Night: Winds less than 25 kt. Thursday: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Seas locally approaching 5 ft. Thursday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Seas up to 5 ft. Friday: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 10 ft. Freezing spray. Friday Night: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 10 ft. Freezing spray, chance of snow showers. Saturday: Low risk for gale force winds with gusts up to 40 kt. Areas of rough seas. Freezing spray, slight chance of snow showers. && .CLIMATE... Record Low Temps Sat Feb 4... Boston -2 in 1886 Hartford -8 in 1965 Providence -2 in 1918 Worcester -4 in 1934 Record Low Maximum Temps Sat Feb 4... Boston 11 in 1886 Hartford 12 in 1996 Providence 13 in 1996 Worcester 8 in 1908 && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...KJC/Nocera NEAR TERM...KJC/Nocera/Loconto SHORT TERM...Nocera LONG TERM...KJC AVIATION...KJC/Nocera/Loconto MARINE...KJC/Nocera/Loconto CLIMATE...