Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 151528 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1128 AM EDT Thu Mar 15 2018 .SYNOPSIS... Cool dry and breezy conditions continue into the weekend. Another coastal storm may impact the region sometime next Tuesday, although there is low confidence on exact timing. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1125 AM Update... Have updated the marine forecast to lower the Gales on the southern near shore waters to Small Craft Advisories. Gales continue on the southern outer waters. Previous Discussion... Expect a few lingering snow showers across portions of the CT valley through midday as a weakening mid level short wave passes across western areas. Otherwise, will see a mixture of sun and clouds in the W-NW flow aloft around the H5 cutoff low over the Maritimes which will continue to slowly lift NE through the remainder of the day. Temps at 14Z have recovered through the 30s. W-NW winds continue with gusts up to 25 to around 30 kt, highest along the coast and across the higher inland terrain. May see gusts as high as 35 kt into early this afternoon, then will diminish as the pressure gradient slowly relaxes. Near term forecast in good shape with only a few minor adjustments to bring conditions current. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Overnight... H5 trof rotates SSE, which will likely yield an increase in overnight cloud cover, but mostly SCT-BKN. This is thanks to enhanced Great Lake moisture streaming through the column. Any remnant streamers, should remain generally to the SW of the BOX CWA thanks to steering flow mainly out of the NW aloft. This increase in moisture combined with the gradient, will limit overnight temp decline. Therefore mins remain in the upper 20s to low 30s. Fri... With the final vort-max associated with longwave trof rotating through, the core of the coldest air should settle across S New England with H85 temps dropping as low as -12C and H92 temps nearly -7C. This will once again limit diurnal warming, with highs stalling in the 30s across most of the area. Breezy conditions continue with NW winds gusting 25-35 mph throughout the day. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Big Picture... Longwave scale shows trough east/ridge west, although this pattern decreases in amplitude next week. Shortwave scale shows two jet streams. The northern jet runs from Northern Canada southeast to New England. The southern jet runs from Baja California to the Carolinas. An additional jet segment flows from the Gulf of Alaska south down the coast to feet into the southern jet. Mass fields are similar through Monday. The behavior of the upstream shortwaves then diverges among models Tuesday and Wednesday. In particular, the GFS is about 18 hours faster than the ECMWF in moving a weather system past us...Tuesday on the GFS and Wednesday on the ECMWF. The 00Z GFS moisture field for Tuesday and Wednesday shifted south by 100-150 miles from previous runs of the model. Confidence in the Friday night through Monday forecast is moderate to high. Confidence in the Tuesday-Wednesday forecast remains low due to spatial and timing differences among the models. Details... Friday night through Monday... As noted, multiple shortwaves move through over the weekend. Each one has the potential to produce some lift. Cross sections of moisture show a layer between 800 and 900 mb through Saturday evening, then drier air all levels Sunday. But they also show drier air near the surface. Expect at least partly cloudy skies Saturday and mostly sunny skies Sunday and Monday. Mixing reaches to around 900 mb this weekend, and temperatures at that level support max sfc temps in the upper 20s and 30s. Winds in the mixed layer are northwest 25-30 knots Saturday, northwest 15-20 knots Sunday, and are light southwest Monday. Expect wind gusts in these ranges. Tuesday-Wednesday... Shortwave currently over the Gulf of Alaska west of Juneau is projected to move south in the feeder flow mentioned earlier, then sweep east in the southern jet starting Sunday. A second shortwave currently near the Aleutian Islands will move into the northern stream, dive south from northern Canada, and dig a trough over the Great Lakes/Midwest. This will turn the upper flow over us from the south, and if that southern stream system is in place at that time, then it will move up the coast and bring us -gulp- another coastal storm. If the timing is off, then we will see the southern system scamper out into the Atlantic. Operational models favor the stormier scenario. Temperature profiles favor snow inland and a rain/snow mix in the coastal plain, with potential for several inches inland should all of this develop. The model differences, run-to-run changes, and the uncertainty inherent in a Day 6 forecast continue to suggest caution in being too detailed in this part of the forecast just yet. So we will continue with chance pops for both days. && .AVIATION /16Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/...High confidence. Through this afternoon... VFR. CIGS mainly 050-080 SCT-BKN. May see brief local MVFR CIGS through 18Z-19Z across higher terrain. W Winds gusting 25-35 kt, highest mainly at terminals along the coast and across the Worcester hills and E slopes of the Berkshires. Tonight into Fri... VFR. The lower VFR CIGS break toward early Fri AM, with mainly high clouds thereafter. W winds shift to the NW on Fri. Gusts 20-25 kt at times. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Friday Night through Monday/... Friday Night through Saturday: VFR. Windy with gusts to 30 kt. Saturday Night through Sunday Night: VFR. Breezy. Monday: VFR. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/...High confidence. 1125 AM Update Winds across the southern near shore waters have diminished so have lowered the Gales to Small Crafts there. Gales continue across the southern outer waters through this evening. After the Gales are lowered there, expect a long period of Small Craft Advisories to follow into Friday given little change in the expected wind speeds and elevated seas as a result. Low risk for Gales to return by late Fri evening, which may require a Gale Watch. Outlook /Friday Night through Monday/...Moderate confidence. Friday Night: Low risk for gale force winds with gusts up to 35 kt. Areas of rough seas. Saturday: Low risk for gale force winds with gusts up to 35 kt. Local rough seas. Saturday Night: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Local rough seas. Sunday through Sunday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. Monday: Winds less than 25 kt. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 AM EDT Friday for ANZ230>235-237- 250-251. Small Craft Advisory until 8 PM EDT this evening for ANZ236. Gale Warning until 10 PM EDT this evening for ANZ254-255. Gale Warning until 8 PM EDT this evening for ANZ256. && $$ SYNOPSIS...WTB/Doody NEAR TERM...EVT SHORT TERM...Doody LONG TERM...WTB AVIATION...WTB/Doody/EVT MARINE...WTB/Doody/EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.