Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 180621 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 121 AM EST Sun Feb 18 2018 .SYNOPSIS...
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Fast moving low pressure will bring a plowable snow to portions of southern New England overnight. The snow will end by daybreak with rapidly improving conditions and temperatures rising well above freezing. Warm frontal showers lift north across the region for Monday, followed by a warm up for the mid week period with potential record breaking warmth. A return to more seasonable conditions by late week.
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&& .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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1250 AM Update... KBOX 88D Dual Pol continues to show correlation coefficient (CC) values of around 0.8, indicative of wet snow and/or rain across SE RI and S coastal Massachusetts including the mid and lower Cape and Martha`s Vineyard. Also noting bright banding on the 0.5 degree reflectivity where the mixed precip lies. Temps in those areas ranged from 33 degrees from KPVD-KPYM, up to 39 degrees at KACK at 05Z where it continues to lightly rain. Winds have shifted back to light N across the CT Valley where temps remain in the upper 20s to near 30, while heavier snow was reported across N central and NE Mass down to the Route 128 where visibilities were between 1/2 and 1 mile. Noting snow amounts of 3-5 inches across N Central CT into NW RI on Public Information Statement at 1217 AM. With the mix and change over to rain across S coastal areas, have ended the the Winter Storm Warnings and Winter Weather Advisories across those areas. Noting back edge of precip working into SW CT, moving into the southern Berkshires as deepening low pressure pushes ENE early this morning. Have updated to bring conditions current, including headlines to be in line with the conditions especially across S RI/S coastal Mass.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/... The storm tonight will quickly depart within the progressive mid level flow. High pressure will build into the Mid Atlantic states, bringing drier and warmer conditions to southern New England during this period. Expecting a decent amount of snow melt Sunday afternoon. Good radiational cooling conditions Sunday night could lead to the formation of black ice on untreated surfaces. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... */ Highlights... - Showers on Monday - Above average temperatures Tuesday and Wednesday - Following some rain, return to seasonable conditions late week */ Overview... Split flow parked out across the N-Central Pacific. S-stream dipping towards Hawaii into the ITCZ where anomalous westerlies prevail with a lingering phase 7 MJO. N-stream ridging into Alaska. The two under- going confluence into Western N America. N-stream energy sheared S capturing S-stream mild, moist westerlies before ejecting NE. A sub- tropical ridge builds off the SE CONUS as does the integrated water vapor transport into SE Canada, an anti-cyclonic Rossby wave break emerges into the N Caribbean. On the warm side of the thermal wind profile, looking at a surge of warmer than average conditions, shots of wet weather suppressed by mid-level subsidence, blustery SW winds throughout. Will hit on the targets of opportunity below. */ Discussion... Monday... Warm frontal light to moderate rain late and overnight. Isentropic ascent, convergent forcing. Precipitable waters +1-inch, expect higher outcomes N/W along SW-facing high terrain slopes, away from the building H5 sub-tropical ridge. Cold air eroding with breezy SW winds, gusts up to 30 mph initially before warmer air aloft inverts mixing to off. Both clouds and dewpoints increasing, potential fog issues given colder waters, ground. Non-diurnal temperature trend towards Tuesday morning as H925 temperatures warm above +10C. Tuesday into Wednesday... Potential record-breaking warmth, especially Wednesday. Please see the CLIMATE section below for record highs established on February 21st and for all of February since records began. H925 temperatures warming to +12-16C, H85 temperature anomalies +20C. Going with the cold front holding off till Wednesday night. A question of clouds hampering sunshine. Dry above H9, fair amount of low-level moisture to mix out below that given higher dewpoints. Breezy SW winds aiding in mechanical mixing along with anticipated daytime heating, expect cloud breaks over the interior while socked-in along the S/SE coast, especially evening and overnight periods. It`s amazing you only have to look back 1-year to get an idea on potential outcomes. Not the same synoptic pattern but can gain insight as to possible impacts. Stay conservative, hold highs in the 60s. SW gusts 30 to 35 mph possible. Wednesday night into Thursday Night... Showers at first along a sweeping cold front, suppressed in with its intensity by the sub-tropical ridge. Expect light outcomes. Then a cool down to more seasonable temperatures beneath high pressure. It could be into Friday morning we`ll see our coldest temperatures more so if radiational cooling materializes. Friday onward... If the sub-tropical H5 ridge weakens, thermal wind profiles shifting S/E, will be watching waves of energy out of the confluent base of a H5 trof over the W CONUS. On what side of the envelope and specific timing of individual waves, all pertinent on potential outcomes that at this time are uncertain. Preference to the EC ensemble mean. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/... Overnight...Moderate confidence. Conditions deteriorating with onset -SN/SN, possible +SN for BDL to BOS and interior terminals S/E away from the coast. Some mixed -RA/-SN along S coastal terminals, with mainly RA at KACK. Lowering LIFR-VLIFR with 1/4SM SN VV002 for some toward midnight, but some question where the band of heavier snow will set up. IFR-LIFR for S coastal terminals with mix with, possible changeover to rain. Light/variable winds through 07Z-08Z become N-NW toward daybreak. Today... Brief leftover MVFR-IFR CIGS through 14Z, then VFR. NW wind gusts up to 25-30 kt this morning, highest across higher inland terrain and along the coast, then diminish during the afternoon. Tonight... VFR. KBOS Terminal...Moderate confidence. IFR conditions in -SN, may see conditions briefly lower to LIFR in occasional periods of SN through 08Z-09Z. Snow accumulations along runways of around 2-3 inches. Conditions improve to VFR by around 12Z-14Z. KBDL Terminal... Snow begin reported, will increase in intensity going towards midnight, diminishing a couple of hours after, light into the early morning hours. Looking for snowfall accumulations on the runways potentially up around 6 inches. Airport weather warnings may be needed for snowfall rates of 1-2 inches per hour. Outlook /Monday through Thursday/...Moderate to High Confidence. Washingtons Birthday: VFR. Breezy. SHRA likely. Monday Night: Mainly VFR, with areas IFR possible. Breezy. SHRA likely. Tuesday: Mainly VFR, with areas IFR possible. Breezy. Slight chance DZ. Tuesday Night: Mainly VFR, with local IFR possible. Breezy. Slight chance DZ. Wednesday: Mainly VFR, with local MVFR possible. Breezy. Wednesday Night: VFR. Chance SHRA. Thursday: VFR. Slight chance SHRA.
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&& .MARINE...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/... Poor visibility with gusty E-SE winds expected tonight in snow and rain. Gusts could approach 30 kt. Rough seas expected to build once more across the outer coastal waters Sunday. Gusty NW winds develop in the wake of a departing low pressure, too. Small Craft Advisories posted for all the waters at some point tonight into Sunday. Outlook /Monday through Thursday/...Moderate to High confidence. Washingtons Birthday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Monday Night: Winds less than 25 kt. Seas up to 5 ft. Rain showers likely. Tuesday: Winds less than 25 kt. Local rough seas. Slight chance of drizzle. Tuesday Night: Winds less than 25 kt. Areas of rough seas. Slight chance of drizzle. Wednesday: Winds less than 25 kt. Areas of rough seas. Slight chance of rain showers. Wednesday Night: Winds less than 25 kt. Local rough seas. Chance of rain showers. Thursday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers.
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&& .CLIMATE... Record Highest Observed Temperature for February... (since records began) Boston.........73 (02/24/2017) Hartford.......73 (02/24/1985) Providence.....72 (02/24/1985) Worcester......69 (02/24/2017) Record High Temperatures (Tuesday 20th / Wednesday 21st)... February.......20th......21st..... Boston.........68 (1930) 63 (1906) Hartford.......69 (1930) 63 (1930) Providence.....69 (1930) 63 (1930) Worcester......65 (1930) 59 (1930) Record Warmest Low Temperature... February.......20th......21st..... Boston.........46 (1930) 45 (1994) Hartford.......50 (1981) 49 (1981) Providence.....48 (1981) 50 (1981) Worcester......47 (1981) 43 (2002) && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...Winter Storm Warning until 7 AM EST this morning for CTZ002>004. MA...Winter Storm Warning until 7 AM EST this morning for MAZ005>007-011>019. Winter Weather Advisory until 7 AM EST this morning for MAZ002>004-008>010-026. RI...Winter Storm Warning until 7 AM EST this morning for RIZ001>006. MARINE...Small Craft Advisory from 7 AM this morning to 2 PM EST this afternoon for ANZ231>234. Small Craft Advisory from 8 AM this morning to 1 PM EST this afternoon for ANZ230. Small Craft Advisory from 7 AM this morning to noon EST today for ANZ236. Small Craft Advisory from 7 AM this morning to 1 PM EST this afternoon for ANZ235-237. Small Craft Advisory until 6 PM EST this evening for ANZ250- 256. Small Craft Advisory until 1 PM EST this afternoon for ANZ251. Small Craft Advisory until 10 PM EST this evening for ANZ254- 255.
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&& $$ SYNOPSIS...Belk/Sipprell NEAR TERM...Sipprell/EVT SHORT TERM...Belk LONG TERM...Sipprell AVIATION...Belk/Sipprell/EVT MARINE...Belk/Sipprell/EVT CLIMATE...Staff

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