Area Forecast Discussion
Issued by NWS Boston, MA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
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
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KBOX 131018 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 427 AM EST Sat Jan 13 2018 .SYNOPSIS... Heavy rain ends this morning as a bit of ice across western MA with a flash freeze the main story across the rest of the region as temperatures crash today. Mainly dry but very cold weather follows tonight through Monday. Mainly dry but cold weather is expected Sunday and Monday. Low pressure diving south from the Canadian Arctic will bring a chance of snow Tuesday and Wednesday. Dry weather may return Thursday and Friday. We will be watching a potential coastal storm that could change that Thursday forecast. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --
***Heavy Rain/Urban Street Flooding Threat Ends By Mid Morning*** ***A bit of ice across western MA this morning but the main story will be a flash freeze today as temperatures crash*** 1) Heavy Rain/Flooding And Coastal Wind Early This Morning... Heavy rain impacting eastern MA/RI where 80+ knot low level jet was impinging on Pwats 4-5 standard deviations above normal. Significant urban street flooding will continue to be an issue in this region through daybreak. In addition...the heavy rain and associated convective elements were tapping some of that low level jet allowing 40 to 50 mph wind gusts along and southeast of the BOS-PVD corridor. Will continue wind advisory but should see these winds diminish from west to east by mid morning...as low level jet exits the region. As the low level jet shifts east of the region...precipitation will decrease in areal coverage/intensity dramatically by mid morning. 2) Western MA Light Icing With Flash Freeze The Main Story Today: Temperatures were mainly in the upper 50s to the lower 60s very early this morning...but have dropped into the 30s along the east slopes of the Berks early this morning behind a very strong cold front. This cold front will cross western MA by 12z...reach the Boston to Providence corridor by 15 or 16z and then off the southeast New England coast by 18z. Enough precipitation will remain for a brief period of light freezing rain/sleet across western MA. For the rest of the region...the cold air should come in pretty much after the precipitation has ended. However...may still see an hour or two of spotty -fzdz as the surge of cold air initially comes in shallow and there is some left over low level moisture for a 1 to 3 hour period. The main concern though is the expected Flash Freeze and dramatic drop in temperatures today. Most of our flash freezes occur when our winds turn north northeast which prevent drying. In this case...the winds will turn northwest which should allow for at least some drying. However...given the dramatic temperature drop from readings in the upper 50s to lower 60s very early this morning and into the 20s in most locations by mid afternoon is quite unusual in this part of the country. Given all the recent rain/street flooding/standing water think will see some icing issues and will continue the winter weather advisory along and northwest of the Boston to Providence corridor.
-- End Changed Discussion --
&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/... Tonight... Very cold air will be ushered in on north to northwest winds. Although we won/t be extremely cold at 850 mb this airmass will come down shallow and expect overnight low temps to mainly be in the single digits to lower teens in most locations. We may even flirt with wind chill advisory conditions along the east slopes of the Berks...but it was too marginal to issue at this time. Meanwhile on the outer-Cape...NNW winds may allow for some ocean effect snow showers to develop overnight but with accums of only a dusting to less than 1 inch are expected. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Highlights... - Cool and mainly dry except light snow across extreme SE MA. - Advisory or even winter storm snow possible Tue into early Thu depending on track. - Seasonable late week. Overview and model preferences... The formation of an upstream Rex-block, signaling a strong positive PNA, combined with blocking cutoff high pres at H5 near the Azores, allows meandering cutoff to settle near the Great Lakes early in the week. This is a PV lobe associated with a current Baffin Island vortex, so it will carry with it another round of arctic influenced air as it settles just upstream. The primary focus associated with this cutoff will be a clipper system initially. However, there is some indication of secondary development as the trof begins to transition toward a negative tilt along the coast. While the ECMWF and many of its ensembles lead the charge, there remains enough uncertainty that a blend of ensembles from both the ECENS and GEFS is preferred as it will take into account both the more progressive and more amplified solutions. As the trof shifts ENE, will maintain this blend into the weekend. Details... Sun through Mon... Arctic airmass once again settles just to the W of New England, but not without its impacts. H92 temps dip as low -13C by early Mon morning. This suggest cool highs each day, mainly in the 20s, although with high pres cresting wind chills should be limited. Overnight lows, however are primed for radiational cooling, but will be mitigated by the now lack of a snowpack. Still will likely see mins fall as low as the single digits in sheltered valleys to the teens elsewhere. Strong subsidence is implied in soundings, which suggests mainly dry conditions. H85 temps are warmer under this inversion than temps below. With NNW flow gradually shifting toward the NNE, the delta-T values from SST to H85 hovers around 15C, while to H9, it is closer to 20C. Therefore, although shallow will likely see light (given only moisture is at the top of the mixed layer) snow showers across mainly the outer portions of Cape Cod and possibly Plymouth county Sun night into Mon as the winds take on a slight E component. Accums should will remain light. Tue into Thu... As cutoff sets up near the great lakes and its attendant longwave trof continues to dig, the final depth and tilt will ultimately determine the possibility of secondary coastal development near the mid Atlantic, after a weakening clipper impacts the region. At this time, ensemble low locations for the potential coastal low range from non-existent, to an inside runner to close to Bermuda, with some clustering near the 40/70 benchmark. However, this much spread is likely to continue into Sun, until the PV anomaly currently wrapped up the arctic becomes better sampled. The clipper does ingest some moisture on Tue as it approaches the Atlantic. This does yield decent moisture in the DGZ, however overall lift is weak, so SLRs are unlikely to be maximized. So a more progressive solution favored by the GFS, with QPF ranging only between 0.1-0.25 inches could stay below advisory criteria. Meanwhile, the more robust solution would quickly follow the clipper with influence of coastal low pres Wed-Thu with better lift in the DGZ and overall more latent-heat energy. There is some precedent for this solution given some of the ensembles and overall amplification of the pattern, and should it verify, it has closer to 0.5-1.00 inches of QPF which may warrant winter storms. Too early to call on totals at this time, especially since the more amplified solution also introduces warmer air (H92 temps average +3C across SE MA). Elsewhere, with H92 temps generally between -2C and -6C, mainly SN is expected, along with highs closer to seasonal normals in the upper 20s to low 30s and lows in the teens to mid 20s. Something to watch especially late weekend into Mon. Fri into the weekend... Enough breakdown of the upstream Rex to signal a transition. As opening wave transitions E and moderates, temps look to return to more seasonable levels, along with mainly dry air. && .AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/... Through 12z This Morning...Moderate to high confidence. Low end MVFR to IFR conditions in rain through 12z. LLWS along with southerly wind gusts of 35 to 40 knots expected along and southeast of the BOS-PVD corridor. Strong cold front should be through western MA by 12z allowing Ptype to change to -FZRA/IP. After 12z Today...Moderate to high confidence. IFR to MVFR conditions should improve to mainly VFR from west to east this afternoon. Strong cold front reaches the BOS-PVD corridor by 15z-16z and probably off the southeast New England coast by 18z. Most of the light -FZRA/IP should be confined to western and north central MA...but a brief period of spotty -fzdz may occur for an hour or two behind the front across the rest of the region. Main issue will be a Flash Freeze as temperatures tumble below freezing and into the 20s in most locations by mid afternoon. KBOS Terminal...Moderate to high confidence in TAF. KBDL Terminal...Moderate to high confidence in TAF. Outlook /Sunday through Wednesday/... Sunday: VFR. Breezy. Sunday Night: VFR. Martin Luther King Jr Day: Mainly VFR, with local IFR possible along extreme southeast MA in some light SHSN. Breezy. Monday Night: Mainly VFR, with local IFR possible along extreme southeast MA in some light SHSN. Tuesday: MVFR/IFR conditions possible. Chance SN. Tuesday Night: Mainly IFR, with local MVFR possible. Chance SN. Wednesday: Mainly VFR, with areas IFR possible. Breezy. Chance SN.
-- 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 Tonight/... Today...Moderate to high confidence. Potent southerly low level jet was allowing for SSW wind gusts up to 40 knots on many of our waters early this morning...especially in heavier rain which was allowing some of the stronger winds to mix down. Winds should drop below gale force wind gusts from west to east by mid morning as low level jet exits the region. However, strong cold front cross the waters later this morning and early afternoon with NW wind gusts around 25 knots. Gales will need to be converted to small craft headlines. Tonight...High confidence. NNW wind gusts around 20 knots in the cold air advection pattern...but seas will remain above small craft thresholds even though swell will be on the downward trend. Outlook /Sunday through Wednesday/... Sunday: Winds less than 25 kt. Areas of rough seas. Local visibility 1 to 3 nm. Sunday Night: Winds less than 25 kt. Seas up to 5 ft. Slight chance of snow showers. Local visibility 1 to 3 nm. Martin Luther King Jr Day: Winds less than 25 kt. Seas up to 5 ft. Slight chance of snow showers. Areas of visibility 1 to 3 nm. Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Tuesday: Winds less than 25 kt. Local rough seas. Chance of snow, chance of rain. Visibility 1 to 3 nm. Tuesday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of snow. Visibility 1 to 3 nm. Wednesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of snow. Visibility 1 to 3 nm. && .CLIMATE... Record high temps set yesterday: BOS 61 in 2017,1975 PVD 62 in 2018 BDL 60 in 2018 ORH 59 in 2018 && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Flood Watch until 1 PM EST this afternoon for CTZ002>004. Winter Weather Advisory from 9 AM this morning to 4 PM EST this afternoon for CTZ002>004. MA...Flood Watch until 1 PM EST this afternoon for MAZ002>024-026. Dense Fog Advisory until 5 AM EST early this morning for MAZ020-021. Winter Weather Advisory from 11 AM this morning to 4 PM EST this afternoon for MAZ005>007-013>019. Wind Advisory until 9 AM EST this morning for MAZ018>024. Wind Advisory until 6 AM EST early this morning for MAZ013- 015>017. Winter Weather Advisory until 4 PM EST this afternoon for MAZ002-003-008>011. Winter Weather Advisory from 9 AM this morning to 4 PM EST this afternoon for MAZ004-012-026. Dense Fog Advisory until 9 AM EST this morning for MAZ022>024. RI...Flood Watch until 1 PM EST this afternoon for RIZ001>008. Dense Fog Advisory until 5 AM EST early this morning for RIZ006>008. Winter Weather Advisory from 11 AM this morning to 4 PM EST this afternoon for RIZ002>005. Wind Advisory until 6 AM EST early this morning for RIZ002-004- 006-007. Winter Weather Advisory from 9 AM this morning to 4 PM EST this afternoon for RIZ001. MARINE...Gale Warning until 9 AM EST this morning for ANZ231>234-250- 251-254>256. Gale Warning until 7 AM EST this morning for ANZ230-235-236. Small Craft Advisory until 7 PM EST this evening for ANZ237. && $$ SYNOPSIS...Frank/Doody NEAR TERM...Frank SHORT TERM...Frank LONG TERM...Doody AVIATION...Frank/Doody MARINE...Frank/Doody CLIMATE...staff

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