Area Forecast Discussion
Issued by NWS Boston, MA

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857 FXUS61 KBOX 271103 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 603 AM EST Mon Feb 27 2017 .SYNOPSIS... High pressure centererd south of New England today moves out to sea Tuesday. This brings back a mild flow of air with above normal temperatures. A couple of weather systems will bring periods of wet weather later Tuesday into Wednesday night. Colder air returns late this week into next weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 6 AM Update... Chilly start to the day as temperatures are back to seasonable for this time of year. Plenty of sunshine will help temps rebound in the 50s. Aside from a few minor updates the overall forecast remains on track for today. Previous Discussion... High pressure centered south of New England. Flow around the high has brought west-southwest winds to our area, which will continue through the day. Dry airmass will mean mostly sunny skies, possibly some thin cirrus. Vertical profile shows potential for mixing up to 850 mb. Winds aloft in this mixed layer are 25-30 knots. So this means potential surface wind gusts reaching 25-30 knots. The mixing will tap temps aloft of -3C to -4C, which would support max sfc temps in the low to mid 50s. Given past behavior of model temperatures and the potential for mixing higher than model forecast, we added 2-3F to the max temps. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... Tonight...Moderate-High confidence. West-southwest flow diminishes near the surface. But high pressure offshore maintains dry weather for much of the night. Weak cold front is indicated moving south from Canada into Northern New England. A weak airflow makes it difficult to determine how far south the front makes it, but pressure pattern suggests it gets no farther south than the Massachusetts border. Shortwave ejecting from a trough over the Pacific Southwest reaches the Great Lakes by Tuesday morning. Models do show a broad cloud area moving across New England, and the GFS is aggressive with measureable pcpn while the ECMWF is generally dry. We agree with increasing clouds, but tend more toward the drier ECMWF solution for pcpn. Most of the dynamics and low level inflow remain well to our west. Temperatures should cool off early, but warm advection remains weak through the night so at most temps would level off overnight with a range in the mid 20s NW to mid 30s coast. Tuesday...Moderate-High confidence. Increasing southwest flow, especially during the afternoon. This will bring an increasing potential for lift over us and so a chance of pcpn especially in the afternoon/evening. The airmass looks similar to today but with a few more clouds in place. So we expect another mild day with temperatures near 50 or in the low to mid 50s. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights... * Above average temperatures for Wednesday * Showers and thunderstorms Wednesday into Thursday * More seasonable conditions return on Friday Pattern Overview... 00z models and ensembles remain in generally good agreement and a consensus approach was used. Overall, frontal boundary is forecast to progress through the East during the Wed-Thur timeframe. Upper level trough will remain over the region in the weekend resulting in more seasonable conditions. The pattern will then begin to transition to a more quasi-zonal flow by the beginning of next week. Details... Tuesday night...High Confidence. Warm sector will begin to push through the region as upper level warm front passes northward. This pushes southern New England into a higher theta-e region. A weak mid-level wave will develop and bring showers to the area overnight. Temperatures will remain steady and/or rise a few degrees by morning. Low confidence on any thunder for Tuesday night as some models are indicating elevated instability. Wednesday into Thursday... Moderate confidence. Main weather producer will occur Wednesday into Thursday. Still some issues on the timing of the cold frontal passage. The NAM appears to be on the slower end of the guidance compared to the rest of the solutions. Will need to watch if this slow down will continue as some of the ensemble members are also hinting at this as well. Temperatures will be well above normal on Wednesday and thus went above guidance by several degrees. If full mixing occurred some locations would be in the mid-70s. However lots of low and mid-level moisture due to clouds so have gone down the middle for temperatures with highs nearing 70F. Overall, southern New England will remain in the warm sector starting Wednesday as upper level trough approaches from the west. This low pressure system will drag a cold front across the region by Thursday. There is the potential for a few waves to develop along the front. A head of the system, stout southwesterly LLJ near 60-70 kts will develop. This southwest flow will tap into Gulf moisture, pushing PWAT values 3 STD above normal for this time of year. Moisture flux will be on the increase as the frontal system approaches so anticipate a period of moderate to perhaps heavy rain on sometime Wednesday into early Thursday. There is a risk for thunderstorms on Wednesday into Wednesday night as lapse rates will steepen to 7 C/KM as well as LI dropping below 0. Models are even producing some surface CAPE near the area and so have upped the chances for thunderstorms. Can`t rule out a few strong storms as 0-6 km shear values will be close to 40-50 kts. While the entire period don`t be wet, as dry air intrudes in the mid- levels at times, appears that a good slug of rain can fall especially within any thunderstorms. Main threat for these storms will be heavy rain and strong gusty winds. The cold front will sweep through during the first half of the day on Thursday resulting in temperatures falling. Looks like another scenario of high temps occurring at midnight. There is still some timing issues on FROPA but appears that gusty winds will follow suite as model sounding indicating good mixing behind the front. Friday and beyond... Moderate confidence. As the cold front passes through, northwest winds take a hold of the region. Models continue to indicate the potential for a clipper system on Friday/Saturday. This will bring reinforcing cold air to the region allowing temperatures to fall back towards seasonable. The GFS is a bit more robust then other guidance with the clipper so leaned towards an ensemble approach. Good mixing and cold air over the ocean may result in ocean effect snow showers over the weekend before another clipper system comes through towards the end of the weekend. && .AVIATION /12Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/... Today... High confidence. VFR. Increasing high clouds especially in the afternoon/evening. W-SW winds start the day light near the surface and at 25-30 knots in the lowest 5000 feet AGL. Expect some of this wind to mix to the surface in gusts during late morning and afternoon, then diminish toward evening. Tonight... High confidence. VFR. Increasing high clouds before midnight. Cloud bases lower to around 4500 feet overnight. Tuesday...Moderate confidence. VFR most of the day. Chance of MVFR cigs developing during the afternoon, but this could hold off until evening. There is a chance of reduced vsbys in showers in the afternoon but the better chances will hold off until night. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Tuesday Night through Friday/... Wednesday...Moderate confidence. Periods of -RA through the period will result in MVFR/IFR conditions. Cannot rule out LIFR in fog during the overnight hours. Thursday...Moderate confidence. VFR conditions from west to east during the morning. Blustery westerly winds. Friday...Moderate confidence. Mainly VFR, with MVFR possible toward the south coast in -SHSN. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/...High confidence. Today... High pressure offshore moves east tonight and Tuesday. West southwest flow actually increases for a time late morning and afternoon, bringing a chance of 25-30 knot winds during that time. Winds then diminish this evening. A Small Craft Advisory will be in effect on all waters for this wind. Meanwhile 5 foot seas will linger on the outer waters. Tonight and Tuesday... Winds and seas remain below Small Craft Advisory levels. Clouds do move in from the west later tonight. Vsbys may lower below 3 miles in showers along the southern waters, mostly Tuesday afternoon/evening. Outlook /Tuesday Night through Friday/... Tuesday night...Moderate confidence. Warm frontal passage Tuesday night could drop vsbys in rain and fog. Wednesday into Thursday...Moderate confidence. Approaching system from the west will push a cold front through on Thursday, increasing both seas and winds during this period. Heavy rain and a few thunderstorms are possible, lowering vsbys. There is the potential for southerly gales across the waters Wed night, with the better chance for northwesterly gales on Thursday behind a cold front. Friday...Moderate confidence. Gusty west winds continue. Small Craft Advisories likely will be needed for some of the coastal waters. && .FIRE WEATHER... Dry and blustery conditions will persist today pushing minimum relative humidity values at or below 30 percent for a good portion of interior Southern New England as southwesterly flow gusts 25 to 30 mph. Over the weekend much of Western and Central MA and CT saw around 0.50-0.75" of liquid, with around 0.10-0.25" to the east, there`s some concern of potential fire weather conditions over Northeast CT, RI and Eastern MA as temperatures warm into the mid and possibly upper 50s. && .HYDROLOGY... Rising water levels, partly from weekend rain but also from snowmelt in Northern New England. There is still plenty of water moving downriver from the snowpack. We will need to monitor water levels across southern New England for a while this week. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EST this evening for ANZ231>235-237-251. Small Craft Advisory until 6 PM EST this evening for ANZ230- 236. Small Craft Advisory until midnight EST tonight for ANZ250-254. Small Craft Advisory until 8 PM EST this evening for ANZ255- 256. && $$ SYNOPSIS...WTB/Dunten NEAR TERM...WTB/Dunten SHORT TERM...WTB LONG TERM...Dunten AVIATION...WTB/Dunten MARINE...WTB/Dunten FIRE WEATHER...staff HYDROLOGY...staff

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