Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 231918 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 318 PM EDT Sun Jul 23 2017 .SYNOPSIS... Cooler, damp conditions are forecast for Monday and Tuesday. High pressure Wednesday will bring dry and pleasant weather, probably through much of Thursday, too. Another low pressure will likely bring showers/isolated thunderstorms to the region Thursday night and/or Friday, perhaps lingering into Saturday. Temperatures will be below normal for most, if not all, of the coming week. && .NEAR TERM /THROUGH TONIGHT/... Rather tranquil weather continues into the early evening. Band of low clouds from this morning continued to slowly dissipate this afternoon. Elsewhere, mid and high level clouds associated with our next weather-maker had already started to move in from the west. Minor tweaks to bring the afternoon forecast back in line with observed trends. Increasing clouds tonight, with rain arriving from west to east, most likely after midnight and especially toward daybreak Monday. 23/12z guidance has rather good agreement on the track and timing of a low pressure passing by to our south, so have high confidence in this timing. Continuing onshore flow and increasing clouds should prevent temperatures from lowering too far below normal. && .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... Impressive 5 to 6 standard deviation easterly flow at 925 mb Monday. Very rare event for late July. Precipitable water values also about 2 standard deviations above normal. Thinking a widespread rain will result, despite the strongest lift staying over the south coast of New England during the morning. Locally heavy rain will be possible at times, especially toward the south coast of New England. Generally thinking one half to one inch of rainfall, with locally higher amounts. The steadier rain should taper off to showers Monday afternoon into Monday night. This should be forced mainly by a cold pool aloft and a trailing mid level shortwave. Rainfall amounts expected to be quite a bit less that what happens Monday morning and early afternoon. With our region remaining on the north side of this low pressure, expecting temperatures to remain generally below normal. && .LONG TERM /TUESDAY THROUGH SATURDAY/... Highlights... * Dry and pleasant Wed and probably into much of Thu afternoon * Unsettled/wet weather likely returns by Thu night and/or Fri * Temps will remain below normal through the end of the week Details... Tuesday through Tuesday Night... Cool and damp Tuesday as the mid-level dynamics sweep the region with stronger mid-level forcing acting upon remnant, available moisture, though more continental rather than sub- tropical. Light showery weather is to be expected along with an abundance of low clouds, perhaps some patchy fog. Clearing out Tuesday night in wake of the H5 trough. Subsidence prevailing as cooler, drier air settles S brought in by N flow becoming light with increasing high pressure up to around 1025. As model solutions vary, especially with respect to the magnitude of low level convergent forcing along the frontal profile from the NE with the GEFS suggesting +3-4 standard deviation above normal and both the EC/NAM hinting at least a 30 mph inflow, will keep it conservative and keep close to the latest SREF output. Upstream convective elements transitioning along the quasi-stationary boundary S at the start of the forecast period late Sunday into Sunday night, indications of mesoscale convective systems across PA and NY, but then it would appear the pattern across the NE CONUS becomes more synoptic with energy pinwheeling. Chance to likely PoPs, highest Monday. Will hint at the chance of thunder towards SW CT Monday. No special wording just yet on heavy rain given the uncertainty and low confidence spatially as to where heavy rain will occur. Wednesday into Thursday afternoon... High pressure will build across the region Wed and slide east of our area by Thu. The result will be dry weather Wed and probably into most of Thu afternoon. Temperatures should rebound from early in the week, but still average a bit below normal for late July. Highs should mainly be in the middle 70s to lower 80s Wed and Thu afternoons with comfortable humidity. Thursday night through Saturday... A rather impressive shortwave for late July will dive southeastward from the Great Lakes and carve out another Northeast trough. The approaching shortwave will likely bring a period of showers and perhaps isolated thunderstorms to the region. Specific timing is uncertain with most guidance currently focused on Thu night/Fri, but it is possible some activity lingers into Sat. Temps should remain below normal with highs mainly in the 70s to the lower 80s. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/... Through 00Z...VFR. east to northeast winds continue. Tonight...High confidence. CIGs lowering SW to NE towards MVFR- IFR as -RA begins to spread across the region. Continued E flow with gusts up to 25 kts towards the south coast. Monday...Moderate confidence. MVFR-IFR CIGs. Impacts to the AM push possible with RA/+RA. VSBY restrictions expected. Continued breezy NE flow with gusts up to 25 kts. Monday Night...Moderate confidence. MVFR-IFR CIGs linger with -SHRA/DZ. LIFR conditions possible towards the Cape and islands. NE winds continue with gusts up to 25 kts possible during the evening, especially across E MA. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Tuesday through Thursday/... Tuesday...Moderate confidence. MVFR-IFR CIGs linger with -SHRA/DZ. Tuesday Night...Moderate confidence. Improving towards VFR. Winds backing N remaining breezy. KBOS Terminal...VFR. NE wind gusts of 20 to 30 knots diminish this morning, but gusts to between 15 and 20 knots will be possible into early afternoon. Wednesday and Thursday...Moderate confidence. Mainly VFR conditions into Thursday afternoon. Potential for deteriorating cigs/vsbys Thursday night but timing of showers, low clouds, and fog patches are uncertain at this time. && .MARINE... FORECASTER CONFIDENCE LEVELS... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/... A more winter-like low pressure is expected to travel south of New England Monday morning. This will result in an increasing easterly flow with gusts up to 30 kt at times. Its possible for a brief period of gale force gusts around the Cape and islands Monday morning, but have low confidence it will persist long enough to warrant a Gale Watch or Warning at this time. Will be issuing a Small Craft Advisory for some of the waters, soon. Outlook /Tuesday through Thursday/... Tuesday and Tuesday Night... Winds diminish some, but rough seas continue across the outer coastal waters. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Belk/Frank NEAR TERM...Belk SHORT TERM...Belk LONG TERM...Frank AVIATION...Belk/Frank MARINE...Belk/Frank is the U.S. government's official web portal to all federal, state and local government web resources and services.