Area Forecast Discussion
Issued by NWS Boston, MA

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178 FXUS61 KBOX 250913 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 513 AM EDT WED MAY 25 2016 .SYNOPSIS... An upper level high pressure ridge will bring very warm to borderline hot weather to most of the region Today through Saturday, except for cooler temperatures at times along the immediate coast. A backdoor cold front will bring cooler weather to the region sometime on Sunday, but temperatures should rebound to at or above normal by early next week. A few showers and thunderstorms are possible Thursday night into Friday, and again this weekend but the vast majority of this time will be dry. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... ***Summer temperatures push in today across the region*** H5 cutoff low continues to push E to the Gulf of Maine. Low clouds and areas of fog have developed across most of the region, lowest across portions of the CT valley into NE CT and interior E MA. Light/variable or calm winds in place along with low temp/dewpt spreads at 08Z. Expect the fog to linger through sunrise then, as winds start to pick up, CIGS/VSBYS should improve. Some fog may linger through 13Z-14Z in deeper valleys where winds may take a bit longer to stir. Weak ridging at the surface and aloft will cross the region by midday through the afternoon with NW winds aloft. Warm core H925 temps will push across the region, up to +19C to +22C by this afternoon. Once skies become mostly sunny by midday, temps will rise quickly with excellent low and mid level mixing in place. Expect temps to top off in the mid-upper 80s with a few spots touching or surpassing 90. However, dewpoints will remain rather low, in the mid 40s to around 50 so humidity levels will be low. High clouds will start to push in from the NW during the mid and late afternoon ahead of H5 short wave across far northern New England. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Tonight... Most of the energy from a weak H5 short wave trough will remain across northern New England. NW flow keeps dry conditions across the region tonight. The mid and upper level clouds will dissipate overnight as SW winds shift back to W-NW and diminish. It will remain mild, with temperatures only bottoming out from the mid 50s well inland to lower-mid 60s across the coastal plain. Thursday... A cold front will slowly push S across the region during the day. Clouds will push in from the W as the front moves in during the afternoon. Short range models vary in their solutions, with mainly dry conditions through the day offered by the ECMWF, but the GFS tens to bring some moisture with a weak H5 short wave in the W-NW flow aloft. Have mentioned only slight chance POPs moving into W MA/N Central CT during the mid and late afternoon hours. Have noted marginal instability with this system, plus another day of warm temperatures, so have mentioned widely scattered showers/isolated thunderstorms. It will be another warm day, with somewhat higher dewpoints making it feel a bit more humid. Highs will again be in the mid-upper 80s away from the immediate coast, with a few spots possibly hitting 90 again. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Highlights... * Friday: Very warm w/highs mid-upper 80s northwest of Bos-Pvd but a bit cooler across Southeast MA/RI * Saturday: Hot and a bit humid w/highs mainly upper 80s to lower 90s away from the immediate south coast * Sunday: Temps uncertain depending on timing of cold front, warmest readings likely CT River Valley w/coolest across Eastern MA coast * A few showers/t-storms possible Thu night/Fri and again Sat/Sun but the vast majority of this time will be dry * At or above normal temperatures likely return early next week Details... Thursday night...Shortwave energy and a burst of elevated instability may result in a few showers/t-storms Thursday night, mainly northwest of a Boston to Providence line. If any activity is able to develop it will be short-lived with the majority of the night ending up dry. Low temps mainly in the upper 50s to the lower 60s. May see some patchy ground fog develop late in the typically prone locations. Friday...Surface winds shift to the south southwest behind the warm front as 850T rise to around +14C. Plenty of sunshine should allow highs to warm into the middle to upper 80s northwest of a Boston to Providence line. Southeast of this line...a cooling marine layer may hold highs in the upper 70s to the lower 80s. Dry weather will dominate on Friday...but enough instability combined with a pre-frontal trough may allow a few showers/thunderstorms to develop across Western MA/Northern CT Fri afternoon and evening. Not sure if this activity gets into our region or stays to our west...but highest risk will be across northwest MA. Shear is rather weak so even if we see a few thunderstorms in our western zones...overall severe weather threat is rather low. Saturday...A hot and somewhat humid day is on tap to kick of the Memorial Day Weekend. 850T around +16C, plenty of sunshine, and a westerly component to the surface winds should allow for high temps to reach into the upper 80s to the lower 90s away from the immediate south coast. Dewpoints between 60 and 65 across most of the region will make it feel a bit humid. While most of the day will be dry...a few showers and thunderstorms may develop Saturday afternoon and evening with a pre-frontal trough and Cape values between 1000 and 2000 J/KG. This will be mainly to the northwest of a Boston to Providence line. Forcing will be rather weak, so areal coverage of any activity that develops may remain limited. Severe weather threat also looks rather low at this time with rather weak 0 to 6 km shear...but too early to rule out a strong thunderstorm or two given decent instability. Sunday...Low confidence on high temperatures given a subtle change in timing of the backdoor cold front will make a big difference in the exact outcome. We can say that the warmest readings will be across the Lower CT River Vally and coolest along the Eastern MA coast. Good shot though at the CT River Valley seeing high temps reach well into the 80s...while the Eastern MA coast has afternoon temps falling into the 60s. A few showers will remain possible and perhaps even a couple of t-storms across the interior if enough instability develops during the afternoon. Monday and Tuesday...Backdoor cold front does not appear as strong on the latest model runs. It looks to washout across the region early next week. GFS washes out on Monday while the ECMWF waits until Tuesday. Probably should see the return to above normal temps by Tue with rather warm temps aloft. && .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through 12Z...Moderate confidence, though lower in timing of improving conditions toward daybreak. Areas of IFR-LIFR CIGS and mixture of VFR to IFR VSBYS in patchy fog, lowest across interior E MA and portions of CT valley into NE CT. Local LIFR VSBYS in dense fog patches. Should start to see conditions improve to VFR across CT valley after 08Z, then slowly progressing E after daybreak. Calm or light/vrbl winds. Today...Moderate confidence this morning, then high confidence. IFR-LIFR CIGS and areas of MVFR-IFR VSBYS should improve by 14Z- 15Z. Otherwise, VFR. W-SW winds 10 kt or less. Tonight...High confidence. VFR conditions. W-NW winds 10 kt or less. Thursday...High confidence. VFR. Light W-NW winds, except sea breezes possible late morning/afternoon along the coast. KBOS TAF...Moderate confidence. IFR-LIFR CIGS through 12Z then should improve to VFR. KBDL TAF...Moderate confidence. Occasional IFR CIGS/MVFR VSBYS through 13Z, then VFR. Outlook /Thursday Night through Sunday/... Thursday night and Friday...Moderate to high confidence. VFR conditions likely dominate but some brief MVFR conditions possible in a few brief showers/t-storms mainly across the interior. Also, some patchy ground fog possible in the typically prone locations very early Fri am. Saturday...Moderate to high confidence. VFR conditions likely dominate but a brief period of MVFR-IFR Cigs/Vsbys possible in a few afternoon and evening showers/thunderstorms. Sunday...Low confidence. MVFR-IFR conditions may develop from east to west behind a backdoor cold front. A few thunderstorms also possible Sun afternoon across the interior. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through 12Z...High confidence. Light N-NW winds increase up to 10 kt by 12z. Visibility restrictions in patchy fog, locally dense in some locations. Today...High confidence. W winds up to 10 kt will back to SW 10-15 kt this afternoon with gusts up to 20 kt on the southern outer waters. Seas 4 ft or less. Lowered visibilities in patchy fog through mid morning then improving. Tonight...High confidence. Light southwest winds become west, gusting up to 20 kt on the southern outer waters this evening. Seas 4 ft or less. Thursday...High confidence. Light W winds shifting to S in the afternoon. Seas remain below 5 ft. Outlook /Thursday Night through Sunday/...High Confidence. Winds and seas will generally remain below Small Craft Advisory thresholds through the period. The main concerns are a period of near shore southwest wind gusts of 20 to 25 knots Saturday afternoon which will result in some choppy seas for mariners. May also see some brief easterly wind gusts between 20 and 25 knots on Sunday behind a backdoor cold front. && .FIRE WEATHER... Today...Expect temperatures will rise quickly, soaring well into the 80s to near 90 across most locations except cooler along the immediate south coast. These temperatures will combine with dewpoints in the mid 40s to mid 50s to result in minimum afternoon RH values down to between 25 and 30 percent. A few hours of westerly wind gusts up to 20 mph are anticipated. Given Tuesday`s rainfall and marginal criteria, will fall short of needing fire weather headlines. Many locations are close to or already at full green-up. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Air Quality Alert from 11 AM this morning to 11 PM EDT this evening for MAZ020>024. RI...Air Quality Alert from 11 AM this morning to 11 PM EDT this evening for RIZ003-004-006>008. MARINE...None. && $$ SYNOPSIS...Frank/EVT NEAR TERM...EVT SHORT TERM...EVT LONG TERM...Frank AVIATION...Frank/EVT MARINE...Frank/EVT FIRE WEATHER...EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.