Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 280844 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 443 AM EDT SAT MAY 28 2016 .SYNOPSIS... Hot weather is on tap for all but portions of the immediate coast today. While the majority of the region will remain dry, isolated showers/thunderstorms will occur early this morning and again this afternoon. A backdoor cold front will bring cooler temperatures to eastern MA Sunday but it will remain very warm across the interior, where scattered showers and thunderstorms likely develop during the afternoon. Tropical moisture will bring showers with locally heavy rainfall very late Sunday night into Memorial Day. Dry conditions with warm afternoons follows Tuesday into Wednesday, but unsettled weather may return by the end of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1150 PM Update... A few spotty showers, one with a quick rumble of thunder, have crossed into far NW Mass at 03Z. Expect these to weaken as they shift E over the next few hours. 00Z high resolution models as well as the GFS/NAM are all indicating the development of scattered showers/thunderstorms around or after 06Z as a strong W-SW low level jet moves near and just S of the S coast. Starting to note a few showers developing on the twin forks of Long Island on latest KBOX 88D radar. Will also see fog redevelop across the southern waters, possibly reaching the S coast, Cape Cod and the islands overnight. GOES-E experimental aviation MVFR/IFR/LIFR percentages, and start to see at least MVFR conditions could move into the Cape and islands overnight as the low clouds and fog develop. Remainder of the forecast looks in pretty good shape, but have updated to bring conditions current. Previous Discussion... With light winds and increasing moisture in the air, we are likely to have another round of fog. This will favor coastal areas as well as typical inland fog spots. The fog may be locally dense, and may require a dense fog advisory once confidence is higher in its location. Otherwise, mins only fall into the low-mid 60s again tonight thanks to high crossover temps and lingering clouds. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... Saturday... Mid lvl ridging continues with rising heights across the region and plenty of sunshine. No trouble mixing to at least H85 where temps will approach +16C by afternoon peak heating. Weak return flow will limit sea breezes to mainly the south coast. Therefore, still expecting probably the hottest day we have seen thus far with highs topping out in the low-mid 90s across much of the region away from S coastal areas. Dwpts will remain elevated as well, mainly in the low-mid 60s even during peak mixing. The other issue will be convective potential. Plenty of SFC/mixed lvl CAPE would be available, except the rising heights and modest subsidence it/s associated with is likely to yield a slight capping inversion and limit updraft development. Lapse rates are modest, mainly approaching 6.0C/KM in the mid lvls, but this is most likely a reflection of the mid lvl dry air. Even the latest 12Z ECMWF now is almost NIL for QPF during the afternoon and evening hours. Definitely not going NIL given the rising PWATs and potential energy available if the cap is broken, but will limit it mainly to slight and low end chance across the terrain and along developing sea breezes where at least some lift will be available. T-storms will be mainly airmass-type as shear is also quite limited. Saturday night... Continued increase in low-mid lvl moisture will actually help to erode the cap and allow for some maintenance of any shra/t-storms that develop, so will be slow to drop overnight POPs. Otherwise, the increase in moisture beneath the inversion increases the risk for overnight fog development which once again has the risk of being locally dense at times and may require headlines. Otherwise, another mild night with mins only falling back into the 60s. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Highlights... * Heavy rain showers Memorial Day with localized flooding possible * Mainly dry w/near or above normal temps Tue/Wed * Unsettled weather may return late Thu/Fri or next weekend Details... Sunday night and Memorial Day... Any left over scattered convection across interior southern New England will quickly diminish early Sunday evening with the loss of daytime heating. The rest of the evening will mainly be dry other than perhaps a spot shower or two, but some fog may develop. Things then become quite interesting very late Sunday night into Memorial day. Tropical depression 2 currently several hundred miles southeast of Charleston South Carolina is expected to become Tropical Storm Bonnie today. This storm is then expected to track northwest and approach the Carolina coast Sunday, then move very slowly northeast through the middle of next week remaining well south of our region. This tropical storm will not have a direct impact in southern New England, and none of Bonnie`s winds/storm surge will affect our region. While a direct impact will not occur, an approaching cold front will pull a plume of its tropical moisture northward into southern New England. PWATS approach or possibly exceed 2 inches, which will be near record high levels based on historical upper air data for this time of year. The guidance also signals the development of a SSW 30 to 40 knot low level jet by 12z Monday which is 2+ standard deviations above normal. This all means we should see bands of heavy rain showers develop very late Sunday night/early Monday morning. Given the anomalously high PWATS combined with the low level jet, there will be a risk for localized flooding. While the models do a very good job these days in indicating potential for heavy rainfall/localized flooding, they often struggle with the location. At this time, appears that a lot of the guidance is indicating an initial band of heavy rain showers across eastern NY state towards 12z Monday, close to the shortwave/better dynamics. Western MA and Northern CT may be on the eastern edge of this band, so this will have to be watched. It then appears that a second band may develop later Monday morning/afternoon across southeast MA/RI on the nose of a 40+ knot low level jet. Some of the guidance has this lingering into Monday evening, while other data dries us out by then. So in a nutshell, expecting numerous showers with locally heavy rainfall. Given the above parameters, it is certainly possible that a narrow swath may see 2+ inches of rain in less than an hour. So while widespread flooding is not expected...there certainly is potential for localized flooding especially if a heavy rain band sets up in one of our more vulnerable urban centers. Greatest risk for that appears to be in our far western zones and perhaps southeast New England on the nose of the low level jet, but again that certainly is subject to shift. Tuesday and Wednesday... Dry weather with warm afternoon highs into the 80s are anticipated away from the immediate coast Tue/Wed as a ridge of high pressure builds over the region. Dewpoints will drop back into the 50s though so will get rid of the humidity. Thursday into Saturday... Forecast confidence becomes quite low over this time. Upper level ridge will eventually break down by the end of next week. Whether that happens later Thu or holds off until next weekend is uncertain, but once that occurs unsettled weather will return. && .AVIATION /09Z SATURDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Tonight...Moderate confidence. Mainly VFR through about 06Z inland, then patchy fog possible especially at typically prone airports with localized MVFR/IFR conditions. Another risk for LIFR along Cape Cod and Island terminals overnight into Saturday morning. Saturday and Saturday night...Moderate confidence. Mainly VFR. Local MVFR-IFR conditions in patchy fog through mid morning. Low probability of brief MVFR conditions in SCT afternoon SHRA/TSRA across the interior. Another risk for overnight fog tomorrow night. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Sunday night through Wednesday/... Sunday night and Memorial Day...Moderate to high confidence. MVFR- IFR Cigs/Vsbys likely develop late Sunday night and continue into Memorial Day. This the result of low clouds...fog patches and heavy rain showers. Isolated thunderstorms are also possible. Monday night through Wednesday...Moderate to high confidence. Lingering MVFR-IFR conditions possible Monday evening, but improvement to VFR Tue continuing Wed. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday/...High confidence. Overnight... Winds and seas remain below small craft criteria. There will be some fog to contend with. The fog could be quite dense at times and may take some time to burn off even after sunrise. Saturday and Saturday night... Seas on the southern outer waters may briefly reach 5 feet at times but should diminish again at night. South to southwest winds will remain less than 20 knots. More fog may develop Saturday night. Outlook /Sunday night through Wednesday/... Sunday night through Monday night...Moderate to high confidence. Quiet Sunday night on the waters other than some fog. We may see some southwest wind gusts to 25 knots develop Monday morning and continue into the afternoon with the aid of a low level jet along with heavy showers/isolated thunderstorms. Marginal 5 foot seas may also develop across our southern waters late Mon into Mon night. Tuesday and Wednesday...Moderate to high confidence. Lingering 5 foot swell possible across our southern waters Tue, but should diminish by late Tue night. Otherwise, a ridge of high pressure will keep winds/seas below small craft advisory thresholds with good visibility into Wed. && .CLIMATE... Some record highs may be challenged as temperatures will be the warmest on Saturday. 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 from 11 AM this morning to 11 PM EDT this evening for CTZ003-004. MA...Air Quality Alert from 11 AM this morning to 11 PM EDT this evening for MAZ004>007-009>018-026. RI...None. MARINE...None. && $$ SYNOPSIS...Frank/EVT NEAR TERM...EVT-Coming Soon SHORT TERM...EVT-Coming Soon LONG TERM...Frank AVIATION...EVT/Frank MARINE...EVT/Frank CLIMATE...Staff is the U.S. government's official web portal to all federal, state and local government web resources and services.