Area Forecast Discussion
Issued by NWS Boston, MA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
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
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KBOX 142309 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 709 PM EDT Mon May 14 2018 .SYNOPSIS... Warmer and more humid conditions move in ahead of a cold front Tuesday. The front will likely bring a round of showers and thunderstorms Tuesday afternoon and evening which may be accompanied by strong winds and brief heavy rainfall. Much cooler temperatures arrive Wednesday and will need to keep an eye on showers to the south of our region before dry and significantly warmer temperatures return Thursday. Unsettled weather with rounds of showers and locally heavy rainfall may arrive sometime Friday and especially by the weekend. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
-- Changed Discussion --
705 pm update... Previous forecast pretty much on track. Dry weather for most of the night, but will have to watch for weakening convection spilling into the region toward daybreak as a shortwave approaches combined with steepening mid level lapse rates. There is some weak elevated instability but best instability is to the SW so probably just a few showers, but can not rule out a rumble or two of thunder. Otherwise, expect stratus and patchy fog to redevelop along the south coast with low clouds gradually spreading inland overnight given SW flow and increasing dewpoints. Lows will range through the 50s.
-- End Changed Discussion --
&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... *** Scattered strong to severe t-storms possible Tue afternoon and early evening *** The main forecast issue for Tuesday is the potential for severe weather as a cold front moves south across the region in the afternoon and early evening. Mid level shortwave passage will be accompanied by increasing mid level jet with 500 mb winds increasing to near 70 kt. This is quite impressive and 0-6km shear values will increase to 50-55 kt. There will be some low clouds to start the day across much of the region and there is a low risk for a few morning showers moving through. However, we do expect the low clouds to erode leading to partial sunshine as SW flow increases ahead of the cold front. With 925 temps increasing to 20C, temps may soar into the 80s away from the south coast with sufficient sunshine. Dewpoints expected to rise into the lower 60s which will result in CAPES increasing to 1000-2000 J/kg with best instability in the interior. In addition, mid level lapse rates are quite impressive at 7-7.5 C/km ahead of the front which will help to produce robust updrafts with any storms. Most favorable environment will likely remain to the SW where instability is greatest. However, scattered showers/t-storms expected to develop and move into northern and western MA by early afternoon with increasing forcing ahead of the cold front which is expected move into NW MA by 18z. Given the strong and unidirectional deep layer shear, hi-res guidance is indicating storms will organize into a line and intensify as it moves south with embedded bowing segments. Best chance of severe weather likely will be confined to central and western MA into CT where main instability axis is located. However, given the strong shear, showers and t-storms should reach the south coast in a weakened state toward evening. Damaging wind gusts will be the primary threat but heavy rainfall also a concern given high PWATs approaching 2 inches pooling ahead of the front. Also, while a low probability, can`t rule out a brief tornado given impressive shear values, especially in vicinity of backed surface winds which will locally enhance low level helicity. Showers and embedded t-storms expected to dissipate Tue evening near the south coast. The cold front will stall just south of the coast so the risk for a few showers may continue through the night near the south coast. Turning cooler Tue night as winds shift to north then NE. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Highlights... * Much cooler Wed especially along the coast and will need to watch a cluster of rain showers to our south * Probably dry Thu with a return to much warmer temperatures * Unsettled weather may arrive by Fri and especially the weekend with rounds of showers along with locally heavy rainfall * Low risk of flooding this weekend Details... The frontal boundary sinks south of our region Wed resulting in easterly winds and much cooler temps. Highs probably stay in the mid to upper 50s along the coast and mainly 60s elsewhere with the onshore flow. Most of the models keep over running showers to our south...but the ECMWF and even UKMET indicate some shower potential in portions of our region so it is something will have to watch. At this time it appears that a ridge of high pressure will keep us dry on Thu with partial sunshine. 850T rising to around +12C would support highs in the upper 70s to the lower 80s away from any localized sea breezes. Unsettled weather may arrive by Friday and especially this weekend. This the result of strong upper level ridging off the Atlantic coast and some shortwave energy diving towards the Great Lakes. This will allow tropical moisture to work northward into the region. GEFS are showing Pwats 3+ standard deviations above normal over the weekend...which is quite an impressive signal this far out. Rounds of showers and even isolated thunderstorms are expected with locally heavy rainfall. When ever you have a signal for these anomalous Pwats at this time range there is at least a low risk of flooding. That will depend on many mesoscale factors such as where any local boundaries setup etc. Nonetheless...something to watch in the coming days. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday Night/... Tonight...Moderate confidence. IFR/LIFR stratus and fog expected to redevelop along the south coast through midnight. Lower cigs down to MVFR/IFR will spread inland overnight. Tuesday...Moderate confidence. IFR stratus and fog will gradually dissipate and become VFR through morning. Low cigs may linger over ACK. SW gusts to 25 kt developing by afternoon, especially in the coastal plain. Scattered to numerous showers/t-storms expected to develop across western MA by early afternoon and move to the coast by evening. Lower cigs/vsbys along with heavy rain and strong winds may accompany any t-storms. Tuesday night... Lingering showers and a few t-storms near the south coast in the evening. Otherwise, IFR stratus and patchy fog possible over the Cape/Islands with mainly VFR elsewhere. KBOS Terminal...Moderate confidence in TAF. MVFR cigs expected late tonight with low risk for brief IFR. Sct t-storms possible mid/late afternoon Tue. Brief heavy rain and gusty winds possible. KBDL Terminal...Moderate confidence in TAF. MVFR cigs expected late tonight with moderate risk for brief IFR. Sct t-storms possible by mid/late afternoon Tue. Brief heavy rain and gusty winds possible. Outlook /Wednesday through Saturday/...Moderate confidence. Wednesday: Mainly VFR, with areas MVFR possible. Breezy. Slight chance SHRA. Wednesday Night: Mainly VFR, with local MVFR possible. Thursday: VFR. Thursday Night: Mainly VFR, with local MVFR possible. Chance SHRA. Friday: Mainly MVFR, with areas VFR possible. Breezy. Chance SHRA. Friday Night: Mainly MVFR, with local IFR possible. Breezy. SHRA likely. Saturday: Mainly MVFR, with areas IFR possible. Breezy. SHRA likely.
-- End Changed Discussion --
&& .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday Night/... Through Tuesday night...Moderate confidence. Winds remain below SCA through tonight, then increasing pre- frontal SW flow developing Tue. Gusts to 25+ kts expected by afternoon over nearshore waters where mixing will be best. Building seas to 5+ feet expected over outer southern waters late Tue/Tue night. Winds shift to N Tue night then increasing NE flow toward daybreak Wed, especially over eastern MA waters. SCA issued for some nearshore waters and outer southern waters. Poor vsbys developing tonight into early Tue in areas of dense fog. Also, afternoon/evening showers and thunderstorms are also possible. Outlook /Wednesday through Saturday/...Moderate confidence. Wednesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Wednesday Night: Winds less than 25 kt. Slight chance of rain showers. Thursday: Winds less than 25 kt. Thursday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers. Friday through Friday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Rain showers likely. Saturday: Winds less than 25 kt. Seas locally approaching 5 ft. Rain showers likely. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from noon to 7 PM EDT Tuesday for ANZ233>235. Small Craft Advisory from 10 AM to 7 PM EDT Tuesday for ANZ230- 236. Small Craft Advisory from 4 PM Tuesday to 8 AM EDT Wednesday for ANZ255-256. && $$ SYNOPSIS...KJC/Frank NEAR TERM...Frank/KJC SHORT TERM...KJC LONG TERM...Frank AVIATION...KJC/Frank MARINE...KJC/Frank

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