Area Forecast Discussion
Issued by NWS Boston, MA

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813 FXUS61 KBOX 221742 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 142 PM EDT Wed Mar 22 2017 .SYNOPSIS... An arctic cold front crosses the region this morning, followed by dry, windy conditions as well as very cold temperatures into Thursday. Wind chills will drop to between 0 and 10 below zero tonight into early Thursday morning. High pressure will build west of New England on Thursday, then push off the mid Atlantic coast Thursday night. Temperatures will moderate late in the work week, before another system arrives with the potential to bring a variety of precipitation types to the area over the weekend into early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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140 PM update... Arctic front offshore with unlimited sunshine as very dry air has overspread the region with dewpoints falling through the single numbers and teens. Temps ranging through the 20s in the interior and will fall to near 30 in the coastal plain by late afternoon. Wind chills falling into the single numbers and teens. Impressive cold for late March. The strong cold advection and near dry adiabatic low level lapse rates will promote excellent momentum transfer with mixing likely to the top of the PBL. Peak of the wind will be mid afternoon into early evening with gusts to 40-50 mph.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Tonight... Gusty northwest winds slowly diminish later this evening. Clear skies for the most part, so expecting a very cold night. Low temps will generally range from 5 to 15 above zero. This will result in wind chills of 0 to 10 below zero, which is not enough for a Wind Chill Advisory. Regardless, if will feel quite cold. Thursday... Large high pressure moves toward the Mid Atlantic coast. Dry weather continues. Gusty winds continue, but not nearly as strong as today. Temperatures moderate some as well, but still should only be a few degrees higher than our normal low temperatures. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Highlights... * Snow to rain showers on Friday as temps warm near average * Above average temps on Saturday with a few showers * Low confidence next Sun-Tues with unsettled weather possible at times with some rain, ice and/or snow possible Pattern Overview... 00z models and ensembles are in agreement with the general synoptic pattern for the long term. Uncertainty increases in the extended do to mesoscale and thermal issues. Mid-level ridge axis will move through the region on Friday as high pressure slides to the south. Split flow aloft with closed low over the southern Plains and northern stream across southern Canada. The initial closed 500 mb will slowly move into the Midwest over the weekend. The low comes into confluent flow and weakens into an open wave as it comes towards the Northeast early next week. Due to the confluent flow aloft, high pressure persists over northern New England keeping surface temperatures cool, resulting in mixed precip at times for the weekend into early next week. The models have slowed compared to 21.00z guidance. However, the EC is a bit faster compared to the GFS/GEFS mean in the forward progression of the upper trough for early next week. Still a lot of uncertainty with this timeframe. Details... Thursday night...High confidence. Mid-level ridge will build overhead Thursday night allowing for WAA to develop. Temps will radiate out during the first half of the night thanks to light winds and clear skies. Clouds will build into the area during the later half limiting radiational cooling. While overnight lows will fall, appears that they may hold steady during the later half of the night within the strong WAA pattern. Friday...Moderate confidence. Surface high pressure shifts eastward resulting in warm/moist advection in the mid-levels. Tighten pressure gradient will result in gusty winds near 30 MPH. Ascent due to isentropic lift will eventually saturate the column, resulting in periods of precipitation during the day and into the night. A weak shortwave in the mid-levels will help increase precipitation chances. P-type will be dependent on timing of precip as well as mid-level warmth as surface temps will start out below freezing especially across the higher terrain. Model guidance and BUFKIT data shows warm nose inching in at 800 and 850 mb with cooling at 925mb. This will help support a transition from snow to sleet to eventually rain during the day on Friday. Low confidence on if freezing rain will occur, something to watching in the coming days. Saturday...Moderate confidence. A bit tricky forecast is in store for this timeframe. Used a non- diurnal trend in the Friday night into Sat morning forecast thanks to increasing WAA. 850 mb temps Saturday morning will be close to 8C but drop through the day. Surface temperatures will reach into the mid 50s, cannot rule out a few 60s if the mid-level ridge continues to build. Surface cold front will push through the region during the day. Could see a few rain showers but not expecting widespread rainfall as heights continue to build overhead. Sunday into Tuesday...Low confidence. While guidance is in agreement synoptically, still a lot of details to work out for this portion of the forecast. Biggest uncertainties will be the placement of the upper level low and how quickly it will diffuse over the weekend into early next week. Already have seen a slower track and could see northern High pressure strengthen moreso leaning towards a slower precip time on Sunday. Right now, 00z guidance shows stalled boundary draped across southern New England on Sunday with a few shortwaves moving through the flow. High pressure building in from the north has the potential to push the front farther southward on Sunday which could leave the first half of it dry. Diffusing closed low will become an open wave and track through southern New England early next week with another wave right behind it. Believe timeframe where we will see the heaviest precip is when the open wave approaches Sunday night into Monday. As mentioned before, still a lot of uncertainty as to the thermal profiles. Looking at the latest EC, it has trended a warmer in the mid-levels versus the GFS with both models indicating surface temps near freezing. Believe that there could be a period where the region could see a mixed bag of precip. Still a lot of uncertainty with this timeframe as thermal profiles will change. Will continue the mentioning of snow, sleet, ice and/or rain for the forecast until thermals come better in alignment. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday night/... High confidence. VFR. NW gusts to 30-40 kt into early evening will gradually diminish but still gusts to 25 kt overnight along the coast. NW wind gusts to 20 kt Thu becoming light Thu night. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Friday through Sunday/... Friday...Moderate confidence. VFR to MVFR conditions in snow to rain showers during the day. Cannot rule out the potential for sleet across western terminals in the morning. Gusty southwest winds near 30 kts are possible. Saturday into Sunday...Low to moderate confidence. A period or two of showers along with some MVFR cigs are possible at times. Saturday night into Sunday has the better chance for wintry precip.
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&& .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/...High confidence. Today and Tonight...Northwest wind gusts of 30 to 40 knots expected under very strong cold advection. Strongest of those wind gusts will occur through this evening. Gale warnings are posted for all our waters. Freezing Spray Advisories also continue for most of the coastal waters into mid morning Thursday. Thursday...High confidence. NW winds gusting to 25-30 kt, highest over the outer waters, diminishing below Small Craft Advisory during the evening. Light freezing spray will continue through midday, then ends as winds drop off. Seas up to 5-6 ft on the outer waters. Outlook /Thursday Night through Sunday/... Friday...Moderate confidence. Southwest wind gusts of 20 to 30 knots may develop ahead of frontal passage. Small craft headlines may be required. Low chance for gales across the outer eastern waters. Saturday...Moderate confidence. Cold frontal passage Saturday will help increase seas and winds. SCA may be needed. Sunday...Low confidence. Cold front will be south of the waters as surface high pressure moves northeast of the region. && .CLIMATE... Record lows for Wednesday, March 22: Boston (BOS) 8/1885 Hartford (BDL) 12/1934 Providence (PVD) 15/1988 Worcester (ORH) 8/1988 Record cold highs for Wednesday, March 22: Boston (BOS) 24/1885 Hartford (BDL) 29/1960 Providence (PVD) 28/1914 Worcester (ORH) 25/2002 Record lows for Thursday, March 23: Boston (BOS) 6/1934 Hartford (BDL) 9/1934 Providence (PVD) 8/1934 Worcester (ORH) 4/1934 && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Wind Advisory until 6 PM EDT this evening for CTZ002>004. MA...Wind Advisory until 8 PM EDT this evening for MAZ004>007- 012>024-026. Wind Advisory until 6 PM EDT this evening for MAZ002-003- 008>011. RI...Wind Advisory until 8 PM EDT this evening for RIZ001>008. MARINE...Freezing Spray Advisory from 7 PM this evening to 9 AM EDT Thursday for ANZ231>235-250-251-254>256. Gale Warning until 2 AM EDT Thursday for ANZ232-251-255-256. Gale Warning until 1 AM EDT Thursday for ANZ233>235-237. Gale Warning until midnight EDT tonight for ANZ230-236. Gale Warning until 3 AM EDT Thursday for ANZ231. Gale Warning until 5 AM EDT Thursday for ANZ250-254. && $$ SYNOPSIS...Belk/Dunten NEAR TERM...KJC SHORT TERM...Belk LONG TERM...Dunten AVIATION...KJC/Dunten MARINE...Belk/Dunten CLIMATE... is the U.S. government's official web portal to all federal, state and local government web resources and services.