Area Forecast Discussion
Issued by NWS Boston, MA

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207 FXUS61 KBOX 201948 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 348 PM EDT Mon May 20 2019 .SYNOPSIS... Warm, summer-like day ahead of a sweeping cold front this afternoon into evening with isolated to scattered showers and thunderstorms, some of which may be strong to severe. Dry, cool air building in overnight. Seasonable weather with windy conditions Tuesday. Dry weather continues Wednesday into Thursday with less wind, then a period of showers will likely impact the region sometime late Thursday into early Friday. Summer like warmth may return by the end of next weekend. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 4 pm update ... */ Highlights ... - Isolated to scattered showers and thunderstorms - Strong to severe threat expected to be very isolated, if any - Biggest threat of strong to damaging winds with any strong to severe - Exiting this evening */ Discussion ... Now (4 pm update) ... Isolated to scattered showers have developed, struggling to mature further into thunderstorms with decent reflectivity above -10C given marginal lapse rates aloft and pronounced dry air above H7. With any updrafts, more than likely they are being choked off, keeping activity low-topped. Despite the instability and effective shear, confident that we`ll not see widespread strong to severe, rather very isolated. Perhaps lift along the sweeping cold front will push storms higher, in an environment of SW-NE uni-directional shear yielding a potential strong to severe wind threat along with heavy rain, frequent lightning. But low confidence. HREF and especially NSSL WRF have the right trends in mind with isolated to scattered activity, some of it multi-cellular mini-clusters given the environment and anticipated pulsing storm-mode. Will hold with SEVERE THUNDERSTORM WATCH 198 for the time-being, see if something gets going. Likely a pulse will go up here and there, then come down, and with the model forecast inverted-V soundings, could see some localized wind damage. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Tuesday into Tuesday night ... Cool, dry airmass in place. Scattered cloud decks developing as the boundary layer becomes well mixed with highs getting up to around 70 degrees. Momentum mix down along with drier air, looking at dewpoints in the 30s and NW wind gusts up around 20 to 25 mph. Should winds subside during the evening and overnight periods, then perhaps radiational cooling could proceed, especially over N/W MA and CT sheltered valleys allowing temperatures to drop into the upper 30s. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Highlights... * Dry and pleasant Wed into Thu with less wind * A period of showers possible late Thu into early Fri * Summer like warmth may return next Sunday-Monday Details... Wednesday... Pleasant day Wednesday as surface high pressure moves in with a building ridge at the mid levels. Winds come down from Tuesday and should be light with a relaxed pressure gradient. Plenty of sun to be had, and high temperatures expected to climb into the upper 60s. Thursday and Friday... Thursday will be mostly dry as the ridge axis crosses southern New England, but our next shot of rain comes late in the day through the overnight hours. A shortwave riding over the ridge moves through Thursday night bringing increased moisture in the form of clouds during the day Thursday, and increasing risk of showers Thursday evening through at least early Friday. Ahead of the low, PWATs top 1.5" with plenty of low level forcing given a 35-40kt LLJ at 925mb. System moves off to the southeast and rain comes to an end later Friday. Placement of the low over SNE or just to the east will bring easterly winds Friday and cooler than average temps in the low 60s (50s along the coast). Saturday through Monday... Behind Friday`s departing system we see building high pressure and the return of mid level ridging. This should lead to a dry and sunny Saturday before a low over QC swings a cold front through Saturday night into Sunday bringing another chance of rain. Uncertainty increases for the far extended forecast, but trends are toward a warmer and mostly dry forecast late Sunday into Monday under building high pressure. Temps look to reach into the 70s each day. && .AVIATION /20Z MONDAY THROUGH SATURDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday Night/...High confidence. Today and Tonight... Low-end VFR SCT-BKN CIGs. FEW-SCT SHRA, lower threat TSRA, so will not make any mention and keep with VCSH. With any -RA/RA, localized MVFR 010-030 possible. Otherwise, winds around 20015G20KT. Improving 1z-6z especially along the S/SE-coast. W/NW winds at around 28015G25KT, strongest along the high terrain. Tuesday into Tuesday night ... VFR. SCT 040. NW sustained 15 to 20 kts, highest gusts around 30 kts, strongest along the high terrain. Winds diminishing evening and overnight. KBOS Terminal... FEW-SCT SHRA threat, lower risk TSRA through 1z. KBDL Terminal... FEW-SCT SHRA threat, lower risk TSRA through 0z. Outlook /Wednesday through Saturday/... Wednesday: VFR. Breezy. Wednesday Night: VFR. Thursday: VFR. Breezy. Chance SHRA. Thursday Night: Mainly VFR, with local IFR possible. Breezy. Chance SHRA, isolated TSRA. Friday: Mainly VFR, with local IFR possible. Windy with local gusts up to 30 kt. Slight chance SHRA. Friday Night: VFR. Saturday: VFR. Chance SHRA. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday Night/...High confidence. 4 pm update ... Today... SW winds sustained around 15 kts with gusts around 20 kts. Seas of 3 to 6 feet. Isolated to scattered showers and thunderstorms approaching the waters towards evening. Keep with present SMALL CRAFT headlines, dropping Boston Harbor and Massachusetts Bay with the expectation of remaining just below criteria. Tonight... Isolated to scattered showers and thunderstorms along a sweeping cold front. Some could be strong, especially for the E-waters off of MA. Frequent lightning. SW winds continuing with sustained around 15 kts, gusts around 20 kts, backing out of the NW behind the cold front pushing through this evening. Seas around 3 to 6 feet. Maybe some renewed fog along the S/SE coast before the cold front sweeps through. Tuesday into Tuesday night ... Breezy NW winds. Gusts up to 30 kts possible over the E waters. Can`t rule out attendant wave heights 5-7 feet. Outlook /Wednesday through Saturday/... Wednesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Wednesday Night: Winds less than 25 kt. Thursday: Winds less than 25 kt. Chance of rain showers. Thursday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers, isolated thunderstorms. Friday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Chance of rain showers. Friday Night: Winds less than 25 kt. Local rough seas. Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 AM EDT Tuesday for ANZ231>237-250. Small Craft Advisory until 8 AM EDT Wednesday for ANZ254>256. && $$ SYNOPSIS...Sipprell/BW NEAR TERM...Sipprell SHORT TERM...Sipprell LONG TERM...BW AVIATION...Sipprell/BW MARINE...Sipprell/BW is the U.S. government's official web portal to all federal, state and local government web resources and services.