Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 261412 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1012 AM EDT THU MAY 26 2016 .SYNOPSIS... Warm weather will continue through Saturday, except at times on the immediate coast. A backdoor cold front will bring cooler weather to eastern MA Sunday with warm weather continuing elsewhere. Dry weather dominates through Sunday other than isolated showers/thunderstorms at times. Near or above normal temperatures continue for much of next week and there is the potential for a period of more widespread showers Monday and/or Tuesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1015 AM Update...Temperatures have jumped quickly into the upper 70s to low 80s this morning. Exceptions are along the immediate coast where onshore winds have kept temperatures a few degrees lower. The 10 AM observation from Logan indicates the sea breeze has moved onshore there, which means last hours temperature of 77 is the highest we`ll see possibly for the day, but certainly until late this afternoon/evening. Made minor adjustments to the temperatures and sky cover forecasts for the day to try to better incorporate the sea breeze at the coast as well as some scattered clouds over the area. Otherwise, the forecast is on track. Previous discussion... As high pressure ridge builds S of the region, expect a general light pressure gradient. This will allow sea breezes to develop along the coast by mid morning. H5 ridging also builds E today, with H5 heights increasing to 580 to 582 dm by this afternoon. With W-SW winds aloft, H85 temps will increase to +14C to +16C this afternoon, and up to +22C across western areas at H925! Very warm airmass indeed. Expect temps to rise to 85-90 away from the coast, but held down to the 70s along the immediate coast with the sea breezes. With weak surface convergence across the region, there may be just enough lift along with the diurnal heating to cause a few isolated afternoon showers and perhaps even a t-storm. If anything is able to develop areal coverage/duration should be rather limited. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Tonight...The weak stalled front should also lift N-NE as winds become more S-SW and the ridge pushes offshore. Noting a weak mid level short wave in the SW flow at the surface and aloft. Some timing issues on the short range models in moving this E out of the Appalachians and mid-Atlantic states. Have kept similar timing going from the previous forecast and kept mention of slight chance to low chance PoPs, with only an isolated mention of thunder, though think this will be very spotty. With ocean temps mainly in the lower-mid 50s and the onshore winds, expect overnight lows to fall back to 55-60 across eastern and central areas, ranging to the lower-mid 60s across the CT valley. Friday...Expect another warm day with continued S-SW winds on back side of high pres ridge over the western Atlc. With the high in place to the E, weak trough will remain across western areas. Also noting rather good instability with CAPEs rising to 1200-1400 J/kg as well as K indices in the low-mid 30s and surface based LIs around -1 to -2. So have kept chance PoPs going from the interior Merrimack Valley across central MA to the CT Valley, with the best shot from late Friday morning through the afternoon. Temps will be in the 80s away from the immediate coast, holding in the 70s along S coastal areas with the onshore winds. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Highlights... * Hot Sat w/highs mainly 90-95 away from the immediate coast. * Near or above normal temperatures through much of next week * Mainly dry Sat/Sun other than iso showers/t-storms but activity could be a bit more organized Sun afternoon across interior * More widespread area of showers may affect the region Mon and/or Tue but that remains highly uncertain Details... Friday night...While it remains uncertain if any isolated convection will affect the region late Friday it should diminish during the evening hours. Otherwise, dry weather with upper level ridging in control. Low temps will only drop to between 60 and 65 in most locations. Some patchy ground fog will likely develop in the typically prone locations given increasing low level moisture. Saturday...Unseasonably hot weather anticipated and record highs may be challenged. 850T around +16c with plenty of sunshine and a well mixed atmosphere should yield highs between 90 and 95 in most locations away from the immediate coast where localized sea breezes may develop. Dewpoints in the lower to mid 60s will make it feel a bit muggy. The majority of Saturday will be dry, but there is the risk for some isolated to widely scattered convection Saturday afternoon and evening. As usual, mesoscale processes will dictate what happens and its not clear cut. A weak pre-frontal trough combined with modest instability with CAPEs increasing to between 1000 and 2000 J/KG. Upper level ridging and lack of forcing will certainly be limiting factors. Sea breeze convergence and terrain impacts might be enough to trigger isolated to widely scattered convection Sat afternoon and evening. 0 to 6 KM shear is weak, so if anything develops the overall severe weather threat would be low. However, an isolated strong thunderstorm or two can not be ruled out with decent instability and potentially large temp/dewpoint spreads. Very localized heavy rainfall would also also be possible given any storm that is able to develop will be slow moving. In a nutshell, much of the region will likely remain dry Saturday but isolated slow moving showers/t-storms with very localized heavy rainfall can not be ruled out. Sunday...The backdoor cold front pushes across the region from east to west. Timing of the front remains uncertain and a 6 hour shift in either direction will make a huge difference in high temperatures. Overall, thinking interior gets very warm while cooler air works into eastern MA. A few showers may accompany the cold front, but will have to watch for a bit more organized area of scattered showers/thunderstorms with very localized heavy rainfall across western MA/northern CT Sunday afternoon. This will depend upon how much instability develops ahead of the backdoor front and its exact timing. Monday and Tuesday...A disturbance currently northeast of the Bahamas will track northwest and probably not directly impact our region. However, a plume of its tropical moisture may get pulled north into southern New England ahead of a cold front. Low confidence on how this all plays out, but there is at least a risk for a more organized/widespread area of rain showers. Temps will remain near or above normal and exact temps be determined by timing of potential clouds/showers. Wednesday...Low confidence this far out but do not see any organized precipitation threat. Temps near or above normal. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Today...High confidence. VFR. Expect sea breezes to develop by mid to late morning on both coasts. Tonight...Moderate confidence. VFR conditions likely for much of the period. Brief MVFR conditions possible in SCT -SHRA/-TSRA mainly across W MA/N central CT, but briefly may reach into NE CT/central MA this evening. Patchy fog with MVFR-IFR conditions after 07Z-08Z across interior valleys. Friday...Moderate to high confidence. Mainly VFR. Local MVFR conditions with low risk of a few brief scattered SHRA/TSRA mainly across the interior. Also, patchy ground fog possible in the typically prone locations through mid morning. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Friday Night through Monday/... Friday night and Saturday...Moderate to high confidence. Mainly VFR other than a few hours of patchy ground fog toward daybreak Sat in the typically prone locations. Isolated showers/t-storms may also result in brief/localized lower conditions. Sunday...Low to moderate confidence. May see some MVFR CIGS work into northern and eastern MA behind the backdoor cold front. Otherwise, mainly VFR outside of any widely scattered convection. Monday...Low confidence. Potential for a period of MVFR-IFR conditions in low clouds and some showers but that remains highly uncertain. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/...High confidence. Today and tonight...Expect S-SE winds less than 15 kt and seas 4 ft or less. May see some visibility restrictions in patchy fog late tonight along the coast. Friday...S-SW winds 15 kt or less. Some gusts may approach 20 kt on the near-shore waters during the afternoon. Seas remain 4 ft or less. May see local visibility restrictions in patchy early morning fog. Outlook /Friday Night through Monday/...High confidence. Winds and seas will generally remain below small craft advisory thresholds through the period. Biggest concern is Saturday afternoon along the south coast, where some near-shore lower 20 knot wind gusts may occur resulting in choppy seas. && .CLIMATE... Warmest day of the week appears to be Saturday and some record highs may be challenged. Record highs for Saturday May 28... Boston...92 set in 1931 Providence...91 set in 1931 Hartford...93 set in 1977 Worcester...88 set in 1911 and 1929 Milton/Blue Hill...90 set in 1929 && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Air Quality Alert until 11 PM EDT this evening for CTZ002>004. MA...Air Quality Alert until 11 PM EDT this evening for MAZ002>005- 008>014-017-018-020-021-023-026. RI...Air Quality Alert until 11 PM EDT this evening for RIZ001>008. MARINE...None. && $$ SYNOPSIS...Frank/EVT NEAR TERM...Frank/RLG/EVT SHORT TERM...EVT LONG TERM...Frank AVIATION...Frank/EVT MARINE...Frank/EVT CLIMATE...Staff

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