Area Forecast Discussion
Issued by NWS Boston, MA

Current Version | Previous Version | Text Only | 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
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
315 FXUS61 KBOX 190203 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1003 PM EDT Mon Jun 18 2018 .SYNOPSIS... Heat and humidity will come to an end tonight as a cold front from the northwest pushes through. A few strong thunderstorms are possible especially across western MA and northern CT. A much nicer day is on tap for Tuesday behind the cold front with plenty of sunshine and much lower humidity. Low pressure passes off the South Coast Wednesday, with a chance of showers along the coast. High pressure from Canada brings dry weather Thursday and Friday. a cold front them brings a chance of showers over the weekend, followed by dry weather early next week. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 10 pm update... Strong to severe thunderstorms have concluded. Only the chance of thunderstorm activity continues overnight. No longer any appreciable threats other than occasional lightning, brief heavy downpours, enough to wake you out of bed given a renewed threat along and ahead of a cold front pushing S across the NE CONUS presently, expected offshore by morning. Evaluation of latest SPC / RAP near-term high-res mesoscale guidance, convective-supporting parameters by way of instability have for the most part diminished. Only a chance of a thunderstorm through the remainder of the overnight hours. However, still a deep, moist airmass in place with precipitable waters on up to 2 inches. Confluent low-level SW jet along and ahead of the forcing cold frontal boundary beneath mid-level energy through the digging weak H5 trof boundary and some favorable diffluence aloft, can`t rule out heavy rainers through the overnight hours. Beneficial rains for certain given how dry it has been as of late, the lack of rain. Best chance of rain across S/W areas of S New England associated with energy out of Upstate NY into N PA, moving with a more WNW mean wind. Accompanying decent K-indices. Additional rainfall amounts upwards of around 0.50 inches possible. Low risk of nuisance flooding issues in the way of urban / poor-drainage. Dewpoints remaining sticky right on through morning with values in the 60s, will keep overnight temperatures stable and mild. Looking at lows down around the upper 60s. Fog and low marine stratus remain an issue along the S-coast and likely so through the early morning hours till frontal passage. Will be looking at visibility as low as a quarter of a mile, presently ongoing at Nantucket. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... Tuesday... A few lingering showers early Tuesday as a cold front finally pushes offshore. Dewpoints and K values will be quickly dropping in the late morning into afternoon and thus expect clearing skies and dry weather. Northwest winds will be gusty in the morning before high pressure moves into the area. Gusts to near 20-25 MPH are possible. Otherwise a pleasant weather day. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... Big Picture... Longwave pattern shows above normal heights across the western and southern USA with a persistent trough over the Great Lakes and Northeast USA. Northern stream jet flows from far northern Canada southeast across New England eventually moving north of us by the weekend. A shortwave embedded in this flow moves across New England Wed night or Thursday. A weaker southern flow across the central USA carries a closed low from the Northern Rockies to the Western Great Lakes. The low then ejects into the northern stream and crosses New England during the weekend. Mass fields over the Eastern USA are similar through Saturday, then diverge. Thermal fields agree on cooler temps Thursday-Friday followed by warming temps over the weekend, then trending cooler again early next week. Forecast confidence is high through Friday, trending to moderate over the weekend. Concerns... Tuesday night-Wednesday... High pressure builds over the region Tuesday night, then shifts offshore Wednesday. Northern stream shortwave dives southeast into New England. This shortwave will be supported by a 105 knot jet and drive a surface cold front toward our area. The jet may also provide enough upper divergence and lift to support a developing low along the Mid Atlantic coast late in the day Wednesday or Wednesday night. W values climb to 1.5 inches along the South Coast Wednesday evening before drier air pushes south across New England overnight. Expect dry weather Tuesday night and Wednesday. The Mid Atlantic system mostly passes offshore, but the upper lift may allow for rain to graze the South Coast. Thursday-Friday... High pressure builds over the region with dry weather and cooler temperatures. Saturday through Monday... Midwest upper low and associated surface system eject into the Northern stream by Saturday, then cross New England Sunday. Rain out ahead of the system arrives Saturday, with rain along the cold front Sunday afternoon or night. PW values increase again, with 2 inch values possible Saturday night and Sunday. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/...Moderate confidence. Tonight... SCT SHRA continue, renewing over S/W MA and CT towards 5z. Lesser threat of TSRA, rather RA/+RA threats along with IFR CIGs and VSBYs, especially along the S-coast with ACK reporting 1/4SM FG presently and likely to continue so through midnight, gradually improving towards morning. Otherwise VFR. SW winds through early morning, LLWS for S-coast along with MVFR-LIFR CIGs and VSBYs in fog and stratus, before winds shift NW by Tuesday morning. Tuesday through Wednesday... VFR conditions expected. Breezy out of the NW Tuesday, SW on Wednesday. KBOS Terminal... RA threat concluding. Can`t rule out brief lower CIGs and VSBYs towards MVFR, otherwise BKN low-end VFR into early morning. KBDL Terminal... SCT -SHRA/SHRA redeveloping shortly after midnight and then concluding into the early morning hours. TEMPO MVFR-IFR possible with CIGs and VSBYs, otherwise BKN low-end VFR. Outlook /Wednesday Night through Saturday/...Moderate confidence. Wednesday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA. Thursday through Friday Night: VFR. Saturday: Mainly VFR, with local MVFR possible. Breezy. Slight chance SHRA. Saturday Night: Mainly MVFR, with local VFR possible. Chance SHRA. Sunday: Breezy. 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/...High confidence. Tonight... Seas starting off low, however should build with persistent SW flow around 15 kts and gusts upwards of around 25 kts. Small Craft headlines persist. Dense fog is the bigger issue with visibility as low as 1/4 of a mile down around the S-coast including the Cape and Islands. Some SCT showers, otherwise lower conditions and wet weather threats conclude into early morning behind a sweeping cold front and a NW wind shift. Tuesday through Wednesday... Lingering small craft swell across our southern most outer-waters diminishes by late morning. Otherwise...winds/seas should remain below small craft advisory thresholds. Outlook /Wednesday Night through Saturday/...Moderate confidence. Wednesday Night: Winds less than 25 kt. Chance of rain showers. Thursday: Winds less than 25 kt. Slight chance of rain showers. Thursday Night through Friday Night: Winds less than 25 kt. Saturday: Winds less than 25 kt. Slight chance of rain showers. Saturday Night through Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Air Quality Alert until 10 PM EDT this evening for CTZ002>004. MA...Air Quality Alert until 11 PM EDT this evening for MAZ003>007- 009>016-026. RI...None. MARINE...Small Craft Advisory until 10 PM EDT this evening for ANZ230>237-251. Small Craft Advisory until 4 AM EDT Tuesday for ANZ250. Small Craft Advisory until 10 AM EDT Tuesday for ANZ254>256. && $$ SYNOPSIS...WTB/Dunten NEAR TERM...Dunten/Sipprell SHORT TERM...Dunten LONG TERM...WTB AVIATION...WTB/Dunten/Sipprell MARINE...WTB/Dunten/Sipprell is the U.S. government's official web portal to all federal, state and local government web resources and services.