745 FXUS61 KBOX 061046 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 546 AM EST Sat Feb 6 2021 .SYNOPSIS... Dry and seasonable weather is on tap for today and tonight, but it will be windy for a time later this morning and afternoon. A short duration snowstorm will impact the region on Sunday with the highest amounts near and especially southeast of I-95. Drier weather returns on Monday. Active weather pattern for mid to late in the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 430 AM Update... A mixture of sun and clouds is on tap for today, but it will become somewhat windy by afternoon. 850T drop to between -10C and -12C early this morning behind a cold front. This combined with a modest west to southwest jet will bring good mixing with the colder temps aloft moving into the region. The result will be southwest wind gusts on the order of 25 to 35 mph developing by afternoon, but a few gusts around 40 mph are possible across the Cape and Islands. High temperatures should range from the middle 30s in the higher terrain to the upper 30s/lower 40s elsewhere. It will feel colder though given the windy conditions. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... Highlights... * Snowstorm Sunday with uncertainty on NW extent of higher amounts * Greatest concern is across RI/SE MA where heavy wet snow may result in the risk of some power outages Details... Tonight... A rather quiet but cold night is in store for the region as a ridge of high pressure passes to our south. Light winds along with mainly clear skies during the first half of night will allow for good radiational cooling, especially northwest of I-95 where a deep snowpack was still in place. Low temps should bottom out in the teens to lower 20s and may even see a few high single digit readings in the normally coldest outlying areas of northwest MA. Low pressure developing off the mid Atlantic states will result in a significant increase in mid/high level cloudiness after midnight. This will result in temps leveling off or even rising a few degrees toward daybreak. Sunday... Low pressure developing off the Carolina coast early Sunday morning will rapidly lift northeast and pass near the Benchmark Sunday afternoon/early evening. Snow will rapidly overspread the region from southwest to northeast Sunday morning and continue Sunday afternoon. Ptype on this one should pretty much be all snow, except perhaps for parts of the outer-Cape and Nantucket where some rain and sleet may mix in at times. This will be a very progressive/fast moving coastal storm with the snow pretty much exiting the coast by early to mid Sunday evening. While we are confident in a plowable snow across most of southern New England, the uncertainty exists on whether or not higher amounts advertised by certain models will be realized. Also, the northwest extent of the heavier amounts is also uncertain. There is a battle amongst a lot of the global vs. high resolution model guidance. The tendency is for a lot of the high resolution data to be heavier with the snow amounts and also further northwest compared to the global models. It is quite evident even comparing the 3 KM to 12 KM NAM model. Given the differences we somewhat blended the guidance together. While we think some of the high resolution guidance may be too heavy with the QPF & as well as being too far northwest; there are a few things we need to consider. There are some indicates of a band of pretty intense 700 mb frontogenesis and good snowgrowth on the northwest side of the storm. We also should mention there are decent mid level lapse rates and a -EPV signature. This may result in 1-2 inch per hour snowfall rates for a time especially late Sunday morning and Sunday afternoon. In addition, a period of good SLR/s would occur in this band especially if it is able to reach northwest of I-95, where surface temperatures will be colder. We opted to issue a Winter Storm Watch for northern CT, northwest RI and most of MA except for the northwest portion of the state. While we are uncertain if heavier banding will be able to make it this far northwest; a watch just requires 50 percent confidence in criteria being met and given colder temps SLR/s will be better than 10 to 1. Hopefully, the differences between some of the guidance will be sorted out with the 12z runs and later shifts can upgrade to warnings or go with winter weather advisories. Regardless, confidence is fairly high in a plowable snow across this region. Went ahead and converted the Winter Storm Watch to a warning for central and southern RI as well as southeast MA including Cape Cod. There is a good 700 mb banding signature in this region, which should lead to a period of 1 to 2 inch per hour snowfall rates. Our thinking is that 5 to 9 inches of snow seem reasonable for this region. This will also be a wet snow with surface temperatures right around freezing, so some power outages will be possible if the higher amounts are realized. We did opt to keep the Winter Storm Watch for Nantucket given the mixing potential. Lastly, given the track of this system and lack of strong high pressure to our north winds will not be much of a problem for most of the region. We do expect wind gusts of 30 to 45 mph across the Cape and Islands, which is not that strong for their standards but could be somewhat more of an issue with the wet snow. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... * Progressive pattern through the extended. Drier weather for Monday and Wednesday. * Snow and rain for the region on Tuesday into Wednesday as a Clipper moves through. Still need to hammer down the track of the low moving through as this will impact where there is more snow or rain. * Active pattern continues with a coastal system possible late in the week. Could see some arctic air filtering in Wednesday into Thursday. Sunday night through Monday... Will initially have a northern stream trough over Quebec and southern stream over southern New England while a weak mid level ridge is over the TN/OH Valley. The troughs will lift northeastward into northern New England and Nova Scotia, while the ridge builds into the Mid Atlantic. The quick moving low associated with the southern stream will lift into Nova Scotia. High pressure will nudge in as it builds into the eastern Great Lakes/Mid Atlantic Sunday night. The high builds over southern New England on Monday as the ridge builds into New England. Snow will taper off during the evening as the low lifts out and skies will clear from west to east. Lowered temperatures as northwest winds advect -10 to -15 degree Celsius air in. Lows generally in the teens across much of the region, but it will be a bit cooler along the south coast with readings in the low to mid 20s. High pressure builds over southern New England on Monday. The ridge flattens a bit as the next system to impact our region begins developing over the Mid Mississippi River Valley. Expect this to bring some mid to high clouds across western parts of the CWA, but elsewhere skies should be relatively clear due to downsloping with NW flow. May be a bit breezy for the first half of the day until the high relaxes the pressure gradient as it builds in. Highs generally in the 20s across the region. Could see some low 30 degree readings along the south coast. Tuesday into early Wednesday... Next shot for impactful weather across southern New England as the progressive pattern continues. A trough will lift from the Upper Mississippi River Valley/Northern Plains late on Monday into northern New England/eastern Quebec by late Tuesday/early Wednesday. A clipper system will slide into southern New England from the Great Lakes. Should see a secondary low develop nearby the region. Still have a decent amount of spread amongst deterministic guidance in where the secondary low develops and tracks. The operational GFS and UKMET are more in line with the majority of the latest EPS/GEFS members, which feature a broad low developing over New England and deepening over the Gulf of Maine. The ECMWF/ICON and CMC develop a deeper low just south of southern New England which tracks over the Cape and offshore. This will have implications on how much warm air will get into the region and thus where the rain/snow line develops. In addition, the GFS and company are a bit more progressive than the ECMWF, which would continue precipitation into early Wednesday. Given the uncertainty this far out have kept with the NBM guidance as would like to see a bit more run to run and model to model consensus before jumping onto a particular solution. Regardless it does appear there will be accumulating snow for southern New England, but it is too early to get into specific details at this point in time. High temperatures range from the 20s across the higher terrain to the 40s across Cape Cod and the Islands. Wednesday through Friday... Mid level ridge axis builds in for Wednesday bringing drier weather. A weak surface high will build into southern New England. After this models really spread out with how to handle the next system for Thursday or Friday. A trough will lift in from the Plains. Lots of differences in the timing and amplitude of this feature as it lifts in. This may bring a coastal storm into the region, but lots of uncertainty given we are talking 6-7 days out. Confidence highest in the drier weather on Wednesday as high pressure builds in. May see a touch of arctic air into Thursday AM as northwest winds at 850 hPa advect colder air into the region. Still a bit uncertain on how cold it will get as there are some differences amongst guidance. Right now 850 hPa temperatures range from -8 to -15 degrees Celsius. Highs on Wednesday will be in the 20s across the interior and 30s along the coastal plain. Lows heading into Thursday will be in the single digits above zero across the higher elevations and the low 20s for Cape Cod and the Islands. Given the differences amongst guidance have leaned on the NBM for Thursday and Friday. This keeps chances of precipitation and as stated earlier there may be a coastal storm that impacts the region. Will need to see how things evolve with guidance over the next couple of days. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent 06z TAF Update... Today...High Confidence. Localized patchy ground fog should burnoff in most by 9z or 10z. Otherwise, VFR conditions are on tap for today. SW wind gusts of 25 to 30 knots develop by afternoon with gusts to around 35 knots possible across the Cape and Islands. Tonight...High Confidence. VFR conditions with an increase in mid/high level cloudiness late. Winds becoming light. Sunday...High Confidence. IFR to LIFR conditions develop from southwest to northeast during the morning and continue through the afternoon. This in response to widespread snow that will fall heavy at times, especially along and southeast of a Hartford to Worcester to Boston line. Ptype should be snow for most of the region, except the outer-Cape and Islands where there may be some rain and sleet at times. NNE winds will gust to between 15 and 25 knots along the I-95 corridor and 25 to 35 knots across the Cape/Islands. We may even see a few gusts around 40 knots across Nantucket. KBOS TAF...High Confidence in TAF. KBDL TAF...High Confidence in TAF. Outlook /Sunday Night through Wednesday/... Sunday: Mainly VFR, with areas MVFR possible. Breezy. Chance SN. Sunday Night through Monday: VFR. Breezy. Monday Night: Mainly VFR, with areas MVFR possible. Chance SN. Tuesday: Mainly MVFR, with local VFR possible. Breezy. Chance SN, chance RA. && .MARINE... Today...High Confidence. Modest WSW low level jet coupled with good mixing should yield southwest wind gusts of 35 knots by afternoon across our open waters. We converted the Gale Watches to Warnings across all waters except small craft headlines for Boston Harbor and Narragansett Bay. Seas will be quite choppy and high. Tonight...High Confidence. Winds diminish to small craft advisory levels by early evening and below that by or shortly after midnight. This is response to a brief ridge of high pressure building to our south. However, seas will remain rather high given lingering southerly swell. Sunday...High Confidence. A fast moving low pressure system will lift northeast from the mid Atlantic and pass near the Benchmark Sunday afternoon and early evening. NE small craft wind gusts of 25 to 30 knots expected across our northern waters, but 35 to 40 knot gusts in our southern waters seem reasonable. Another set of Gale Headlines will likely be needed for our southern waters. Outlook /Sunday Night through Wednesday/... Sunday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain, chance of snow. Sunday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Monday: Winds less than 25 kt. Seas up to 5 ft. Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain, slight chance of snow. Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain, patchy fog. Local visibility 1 to 3 nm. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Winter Storm Watch from Sunday morning through late Sunday night for CTZ002>004. MA...Winter Storm Warning from 7 AM Sunday to 1 AM EST Monday for MAZ017>023. Winter Storm Watch from Sunday morning through late Sunday night for MAZ004>016-024-026. RI...Winter Storm Warning from 7 AM Sunday to 1 AM EST Monday for RIZ002>008. Winter Storm Watch from Sunday morning through late Sunday night for RIZ001. MARINE...Gale Warning until 7 PM EST this evening for ANZ231>235-237- 250-251-254>256. Small Craft Advisory until 7 PM EST this evening for ANZ230- 236. && $$ SYNOPSIS...Frank NEAR TERM...Frank SHORT TERM...Frank LONG TERM...BL AVIATION...Frank/BL MARINE...Frank/BL