184 FXUS61 KBOX 011738 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1238 PM EST Mon Mar 1 2021 .SYNOPSIS... Frontal system exits late this morning into the afternoon, which will allow for clearing. Strong Arctic cold front bringing in isolated to scattered snow showers and possibly squalls tonight. This will also bring unseasonably cold temperatures, strong winds, and dangerously cold wind chills for portions of southern New England. Unseasonable cold and gusty winds continue into Tuesday. Temperatures return to above average levels for midweek, before turning cooler and unsettled late in the week into the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 945 AM UPDATE... New since the last update, we issued a Coastal Flood Statement for eastern Massachusetts which includes the bay side of Cape Cod Bay between 11 AM and 2 PM Monday. We expect shallow ponding of water on vulnerable coastal roadways around the time of high tide - up to one half foot of storm surge. Next, the first batch of rain continues to push off the coast, delivering between 0.25-0.50 inch of precipitation. A quick break in the action is followed by a secondary band which is moving in a line from south central Vermont southwest towards the Hudson Valley. The line of showers will slowly move across southern New England - exciting the eastern coastal areas between 3 PM and 5 PM. We did adjust our POPs slightly to better represent the current conditions/high-res guidance. Otherwise everything remains on track. You can read the previous discussion below. ======================================================== No major changes to the forecast this morning. A weak low pressure over NE MA will move offshore in the next couple of hours. Winds turn SW by mid to late morning ahead of a cold front. This will help boost temperatures above normal, despite the clouds and rain. Brought temperatures back in line with observed trends and updated expectations. Previous Discussion... Highlights: * Rain tapers off late this morning into the afternoon as frontal system moves through. * Wind advisory remains in effect starting late this afternoon into Tuesday. Subtle shortwave trough lifts from the Mid Atlantic and offshore by this afternoon. A more potent trough digs from Ontario this morning into Quebec/northern New England. A weak low associated with the subtle shortwave lifts from the south coast into the Gulf of Maine this morning. A cold front quickly moves through late this morning into the afternoon behind the low. As that next trough digs in from the northwest could see some snow showers developing across western areas late in the day. In wake of the cold front very dry air will advect in with PWATs falling from 0.75"-1.25" in the AM to 0.1"-0.2" during the afternoon. Aloft, winds shift to the WNW/NW bringing strong cold air advection and excellent mixing. Previous forecast looked pretty good with the gusts expected, so haven't made any major changes. Should see 25 to 35 mph gusts during the afternoon. Expecting strong southerly to southwesterly warm air advection ahead of the cold front moving in. Models have progged 925 hPa air of +5 to +10 degree Celsius advecting in. Went with the 75th percentile of guidance for temperatures across the CWA. The result is temperatures ranging from the upper 40s across the interior and the upper 40s to low 50s along the coastal plain. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... Highlights * Wind Advisory continues across southern New England tonight. Wind Chill Advisory issued for the eastern slopes of the Berkshires into Tuesday AM. * Isolated to scattered snow showers/squalls possible especially before midnight. * Drier, but cold on Tuesday with gusty winds diminishing. Tonight... Upper level trough/cutoff digs from Ontario/Quebec during the evening into Northern New England/Nova Scotia by Tuesday morning. A secondary arctic front slides across southern New England ushering very cold air. Strong to potentially damaging winds remain an issue due to strong cold air advection and a deep boundary layer. There are some indications from NAM/GFS BUKFIT soundings that if we mix to the top of the boundary layer there could be some 50+ kt gusts. This is typically quite difficult to achieve, but not out of the realm of possibilities. Upstream obs where the airmass is currently located, over Ontario and the central Great Lakes, show few locations where there are 50+ kt gusts being observed. Based on this have just kept with the Wind Advisory, but there is potential for isolated gusts of 50+ kts. If mixing appears to be stronger in future updates then a High Wind Warning will be needed. Still think there is a risk of isolated to scattered snow shower activity across the region. A good signal still with the snow squall parameter, steep low level lapse rates and FGEN within the 0-2 km layer. The concern remains on moisture side of things as stated by the previous shift. The 0-2 km moisture appears to be limited per the NAM/GFS and RAP guidance per BUFKIT RH with respect to ice. Given the high res guidance, ARW/NMM/NAM shows diminishing activity moving in from north to south have reduced chances a bit. Still don't want to completely rule out the chances, but the airmass may potentially be too dry. Still thinking that the timing of 02/03Z-06Z looks good especially when using the HREF probability of composite reflectivity AOA 20 dBZ as a proxy with values of 30-70 percent. Highest across the interior and NH/VT and MA border. Dangerously cold Wind Chills across portions of southern New England tonight as we receive an arctic blast. Aloft will see temperatures of -15 to -20 degrees Celsius at 925 hPa. Lowered temperatures to the 25th percentile of guidance given there will be cloudiness and strong mechanical mixing. The result is lows in the single digits above zero across the interior and teens along the coastal plain. The combination of these temperatures and the strong winds will result in Wind Chills bottoming out in the single digits below zero to -20. Have a bit more confidence in Wind Chills of -15 to -20 along the eastern slopes of the Berkshires in the latest update, so have hoisted a Wind Chill Advisory. May be a bit more spotty coverage wise over the northern Worcester hills, but here is where an additional advisory may be needed in future updates. Tuesday... Ridge axis over the TN Valley/Southeastern US builds toward the Carolinas/Mid Atlantic. High pressure builds from the Ohio Valley into the Mid Atlantic in response and nudges into southern New England. Strong wind gusts continue, but gradually diminishing as the day progresses. High pressure will relax the pressure gradient as it nudges in, but will see cold air advection through the morning promoting excellent boundary layer mixing. By the afternoon winds become more WNW/W at 925 hPa and will start advecting in warmer air. Despite this will only see a warm up from -20 degrees Celsius aloft during the AM to -10 degrees Celsius at 925 hPa. High temperatures generally in the 20s across southern New England. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights... * Temperatures rebound back into the 40s on Wed. * Mainly dry, but turning unsettled and cooler than normal late this week into this weekend. Rather good overall synoptic agreement continues into Friday. There are minor detail differences, which become more significant towards next weekend. This is mainly due to the handling of a mid level trough off the West Coast, and the resulting downstream effects. Still prefer a consensus approach to smooth over the less predicable smaller scale features. Expecting temperatures to rebound rather quickly Wednesday, with above normal warmth. Just like the cold snap Tuesday, this warmth is not around for long. latest indications are for near to slightly below normal temperatures by late this week into this weekend. Trends suggest even colder weather is possible. it will all depend upon how the mid level flow evolves, and how direct a path to the northern latitudes can be developed. Despite the passage of a low pressure to our north Wednesday, as well as a cold front Thursday, we cannot seem to match up sufficient moisture and lift to generate precipitation. Kept this portion of the forecast dry, although there will be periods of clouds. it still appears a storm moving offshore from the SE U.S. coast next weekend will pass too far offshore to impact our region. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. This Afternoon...High confidence. IFR to LIFR conditions improving to VFR by late afternoon as precipitation tapers off from west to east. Winds shifting from the S/SE to the W/NW as a cold front moves through. Gusts of 30-40 kts developing during the late afternoon. Tonight...High confidence. VFR with strong WNW to NW gusts of 35-45 kts. There may be a few isolated 50 kt gusts as well as GFS/NAM BUFKIT soundings indicate. Could see brief MVFR/IFR snow showers/squalls passing through, we do expect coverage to be widely scattered at best. Tuesday...High confidence. VFR with gusty WNW to NW winds to start. Expecting gusts of 30-45 kts to start. Winds and gusts diminishing during the afternoon. Should see gusts falling to 15-30 kts. KBOS TAF...High confidence in trends. Expect a period of IFR/LIFR into the AM push, improving to VFR in the afternoon. KBDL TAF...High confidence in trends. Expect a period of IFR/LIFR into the AM push, improving to VFR in the afternoon. Outlook /Tuesday Night through Friday/... Tuesday Night: VFR. Windy with areas of gusts up to 30 kt. Wednesday: VFR. Breezy. Wednesday Night: VFR. Thursday through Friday: VFR. Breezy. && .MARINE... Have upgraded the eastern outer waters to Storm Warnings with strong northwest winds expected. Other areas over the outer waters have an outside chance of a few storm force gusts, but confidence not as high in a prolonged period of storm force wind gusts. If confidence increases and is expected to be more widespread then the Storm Warning may need to be expanded. Gale Warnings remain in effect for the rest of the waters into Tuesday. On top of this have widespread moderate freezing spray still expected with an arctic airmass moving in. The Freezing Spray Advisory previously issued into for tonight into Tuesday morning still looks good. Outlook /Tuesday Night through Friday/... Tuesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Wednesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Wednesday Night through Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Thursday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Friday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. && .TIDES/COASTAL FLOODING... Tides are astronomically high today, with Boston peaking at 12.3 FT MLLW which is just below flood stage early this afternoon - this yields a 1.3 FT surge. Winds will become off shore late today/early evening which will prevent any further issues over the next two days even with astronomical high tides. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Wind Advisory from 4 PM this afternoon to 10 AM EST Tuesday for CTZ002>004. MA...Wind Advisory from 4 PM this afternoon to 10 AM EST Tuesday for MAZ002>006-008>021-026. Wind Chill Advisory from midnight tonight to 10 AM EST Tuesday for MAZ002-008-009. Wind Advisory from 4 PM this afternoon to 1 PM EST Tuesday for MAZ007-022>024. RI...Wind Advisory from 4 PM this afternoon to 10 AM EST Tuesday for RIZ001>008. MARINE...Freezing Spray Advisory from midnight tonight to 1 PM EST Tuesday for ANZ231>237-250-251-254>256. Gale Warning from 4 PM this afternoon to 7 PM EST Tuesday for ANZ230>232-251-255-256. Gale Warning from 4 PM this afternoon to 4 PM EST Tuesday for ANZ233>237. Storm Warning from midnight tonight to 1 PM EST Tuesday for ANZ250-254. && $$ SYNOPSIS...Belk/BL NEAR TERM...Belk/BL/Gaucher/JWD SHORT TERM...BL LONG TERM...Belk AVIATION...Belk/BL/Gaucher/JWD MARINE...Belk/BL TIDES/COASTAL FLOODING...