Area Forecast Discussion
Issued by NWS Boston, MA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KBOX 221739 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 139 PM EDT Sun Apr 22 2018 .SYNOPSIS... High pressure remains in control through Tuesday bringing dry weather with moderating temperatures. Wet weather returns Wednesday into Thursday as low pressure moves through our region. Unsettled weather continues into the weekend, but not a washout. && .NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
Just about as quiet as it gets around here weatherwise with high pressure in control. Satellite imagery shows clear skies around region with nearest (high) clouds in PA and southern NJ. Deep mixing to nearly 850 mb has prevented sea breezes from developing so far this afternoon. However, model guidance suggests winds aloft will weaken just enough to allow a weak sea breeze to develop along E MA coast and a slightly stronger SW sea breeze along south coast from mid to late afternoon. Mixing has also brought drier air to surface, as dewpoints have fallen into teens and lower 20s, resulting in relative humidity values dropping to less than 20 percent. Dewpoints will gradually recover through this evening as mixing subsides. Otherwise, clear skies and light winds tonight with patchy valley fog. Leaned closer to MOS for lows which tend to perform well in these situations. Lows drop back into 30s to around 40 with some patchy frost inland.
-- End Changed Discussion --
&& .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
-- Changed Discussion --
High pressure becomes centered over SNE Monday. Once again plenty of sunshine with light winds, and coastal sea breezes will get underway by their usual late morning time frame. This will give way to S/SW flow Monday night as the high shifts offshore, with some increase in high clouds late. Stayed close to MOS with highs in the 50s/60s Monday, perhaps approaching 70 in CT valley, and lows falling back into 30s to near 40 Monday night.
-- End Changed Discussion --
&& .LONG TERM /TUESDAY THROUGH SATURDAY/... */ Highlights... - Wet and breezy midweek - Perhaps a reprieve Friday - More showers possible Saturday Overview and model preferences... Phasing S stream and Pacific waves will lead to gradual height falls and reduction of the ridge across NE throughout the day on Tue and into Wed. Another longwave trof gradually develops across the CONUS as a result during the latter half of the week. Following the initial development, a second stronger wave connected to the Aleutian vortex will likely deepen the trof by next weekend, yielding a return to cooler, and maintaining the unsettled and wet conditions that look to begin on Wed. Noting a better agreement between deterministic runs in the phasing process and deepening of the wave for mid week than previous runs. Therefore, although ensemble means will still be used, will blend in more operational guidance with this forecast update. Details... Tue... High pres slips E but remains in control through the day and much of the evening. However, a combination of developing return flow, and increased moisture loading aloft will likely yield increasing clouds. Dry WX prevails. H85 temps near +4C should be mixed too, so expecting another day in the 60s in spite of the clouds. S shore sea breezes likely, with a risk on the E coast as well, but increase pres gradient may preclude this. Wed and Thu... Low pres develops out of the remnant cold pool from convection across the SE, as S stream wave develops. Guidance in fair agreement on track, E of the spine of the Appalachians as low pres deepens enough to draw it more N of E. With it, PWATs increase to nearly 200 percent of normal. As the low deepens, an LLJ of 40 kt also develops through the morning Wed. This will lead to a period of rain, potentially heavy at times as K indices exceed 30 and soundings become conditionally unstable. Initial overrunning followed by mid low and mid lvl convergence will lead to rain most of the day. With the wave continuing to deepen, the low pres will deepen and slow, leading to wet conditions persisting into the overnight hours, with wrap around SHRA possible into Thu, but with some improvement. Probs of QPF exceeding 1.00 inches rather high. Clouds along with a dip in H85 temps will yield cooler temps each day, with highs mainly in the 50s and lows in the 40s. Fri and Sat... Although trof remains in place, a brief period of rising heights looks possible ahead of a secondary/acute wave traversing the CONUS from the Aleutian low and NW Territory origins. Therefore, a period of more dry-than-wet conditions looking more likely per ensemble/operational guidance. Still with cyclonic flow and some moisture clouds and a spot shower can be ruled out. Temps near seasonal normals, although potentially cooler if more cloud than sun is observed. Early next week... The aforementioned wave reinforces the trof across the E, with a return to cooler and wetter wx possible. Still several details to iron out, but confidence rises based on ensemble means/operational runs showing at least some synoptic agreement. && .AVIATION /17Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/...High confidence. Sea breeze potential still questionable along E MA coast this afternoon as winds aloft have been just strong enough to maintain W/NW flow. However, there should be some weakening in winds later this afternoon to allow sea breeze to develop between 20z-23z. Confidence is higher for south coastal sea breeze which should get underway around 20z as well. VFR. Light W/NW winds prevail tonight with local MVFR/IFR visibility in patchy valley fog. Higher confidence in sea breezes along both coasts Mon. KBOS Terminal...Moderate confidence in TAF. E sea breeze expected 20z-23z but if it does not occur, winds will veer to N. KBDL Terminal...High confidence in TAF. Outlook /Tuesday through Thursday/...High confidence. Tuesday: VFR. Tuesday Night: MVFR/IFR conditions possible. Breezy. Chance RA. Wednesday: Mainly MVFR, with areas IFR possible. Breezy. RA. Wednesday Night: Mainly MVFR, with areas IFR possible. Breezy. Chance SHRA, chance RA. Thursday: Mainly MVFR, with areas VFR possible. Breezy. Chance SHRA.
-- End Changed Discussion --
&& .MARINE...
-- Changed Discussion --
Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/...High confidence. High pressure builds over waters with light winds, flat seas, and good visibility. Only concern for recreational boaters is for sea breezes along South Coast this afternoon with 15-20kt gusts and choppy seas near shore, especially when opposing outgoing tide. Similar conditions Monday. Outlook /Tuesday through Thursday/...High confidence. Tuesday: Winds less than 25 kt. Tuesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain. Wednesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Rain. Wednesday Night: Winds less than 25 kt. Rough seas up to 12 ft. Chance of rain showers, chance of rain. Thursday: Winds less than 25 kt. Rough seas up to 9 ft. Slight chance of rain showers.
-- End Changed Discussion --
&& .EQUIPMENT...
-- Changed Discussion --
NOAA Weather Radio transmitters serving Providence and Hyannis are out of service due to phone line problems. The phone company has prioritized the issues and is working to get the weather broadcast back on the air as soon as possible.
-- End Changed Discussion --
&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Belk/JWD NEAR TERM...JWD SHORT TERM...JWD LONG TERM...Doody AVIATION...Belk/JWD MARINE...Belk/JWD EQUIPMENT...Staff

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.