Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 161050 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 650 AM EDT Fri Mar 16 2018 .SYNOPSIS... Mainly dry but unseasonably cold weather is anticipated through early next week. Another coastal storm may impact the region Wednesday or Thursday, although there is low confidence on exact timing. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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650 AM Update... Obs and satellite pix show mainly clear skies over Southern New England. Patch of clouds is developing over/west of the CT River Valley, and obs from BAF and BDL suggest some mid-level clouds. Water Vapor loop shows one shortwave moving offshore, another shortwave approaching through Western NY. Small adjustments made to temperatures and sky cover, but no changes in forecast logic from earlier this morning. Previous discussion... WV loop suggests core of a vort-max centered in the core of a longwave trof is shifting S of the region early this morning, while a very weak/dry cold front approaches from the W. This should pivot across S New England between 12Z and 18Z this morning as it is already approaching E NY per latest OBS (particularly the dropping dwpts). This front will pass with little to no fanfare outside of a few low-mid clouds, diminishing dwpts (into the teens) and a resurgence in winds in its wake thanks to low lvl CAA. Expecting another day with wind gusts once again 25-35 mph, particularly strong this afternoon and evening with the peak CAA. H85 temps drop to an avg near -13C (H92 near -9C) through the afternoon. This should yield highs around 30 in NW MA, 35-40 across SE MA and RI. Generally a bit cooler than yesterday.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Overnight... A bit of a meteorological squeeze play as secondary robust shortwave/H5 cutoff approaches from the N while slight low-mid lvl warm advection occurs to the S. This results in mid lvl confluence and a slight rise in heights. However, it also increases the pres gradient. This will enhance near sfc cold advection. In spite of the clearing implied by the slight rise in heights, these winds should allow min temps to drop into the upper teens to mid 20s, one of the colder nights of this week. Sat... The robust H5 shortwave rotates S, but given the rising heights to the S the core should remain to the N during the daylight hours as it rotates toward the Maritimes. Still, weak low-mid lvl cold front should pass across the region early. While these feature, like the many before it s moisture starved, lift is a bit stronger thanks to enhanced baroclinicity already in place. Also, noting a well mixed BL to nearly H7, with a pool of moisture around the top of the mixed layer. Lapse rates from the sfc to the top of the mixed layer are also quite high, nearly 7C/km. Therefore, could see some flurries/sprinkles develop through the morning as this wave makes its closes pass. Expect little if any accumulation. Otherwise, with the core of the cold associated with the cutoff approaching H85 temps drop as low as -15C by afternoon. However as mentioned above mixing should exceed this. Therefore, expecting highs similar to Fri, low to upper 30s. Winds continue, but more northwesterly, expecting gusts 25-35 mph. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Big Picture... Large scale pattern shows troughs lingering over New England/Maritimes and just off the Pacific Coast. Two jet streams are embedded in this pattern. The northern one extends from the northern territories of Canada to New England, the southern jet from California to the Carolinas. A jet segment also feeds down the Pacific Coast into the southern jet. Mass and thermal fields among the various models are similar through Tuesday morning, showing the New England/Maritime trough slowly lifting northeast to near Greenland. The trough over the west coast lingers near the Western USA through the weekend, then ejects east through the southern jet early next week. Fields are similar in a broad sense Wednesday-Thursday, but show noticeable smaller scale differences during that period. Several shortwaves move through the northern and southern flows during this period. Most are rather weak with limited moisture. One shortwave just off the Pacific Northwest coast sweeps south to California this weekend, then east to the Mid Atlantic coast by Tuesday. The second shortwave ejects from Alaska, digs over the Plains early next week, and covers the Eastern USA by Wednesday. Run-to-run trends have shifted south over the past four model runs. The GGEM keeps some precip over CT-RI-SE Mass Tuesday afternoon/evening as the first shortwave approaches, but the others have shifted it offshore. These trends now bring most precipitation into our area on Wednesday. Forecast confidence is moderate to high through Monday. Because of the changing solutions next midweek, confidence in the forecast for that period remains low. Details... Saturday night through Monday... A shortwave in the northern stream sweeps through the cyclonic flow around the Maritime low. This shortwave, supported by a 100-knot jet, crosses Southern New England on Sunday. Limited moisture with this feature...the GFS indicates more, the ECMWF less. Expect increased sky cover for a time but no precipitation. Mixing both days should reach at least 925 mb and possibly 900 mb. Temperatures at these levels will support high temperatures in the 30s each day. Winds in the mixed layer suggest northwest gusts to 20 knots Sunday. Tuesday through Thursday... As noted above, the shortwave that was projected to affect us Tuesday has suppressed farther south with each model run. Current runs keep precip south of New England, except for the GGEM which brings light precip values to CT-RI-SE Mass overnight. The turning of the upper flow from the south on Wednesday is a much more logical time to expect precipitation to move north into our area. We have adjusted pops to reflect a chance of precip starting late Tuesday night and continuing through Thursday. Temperature profiles are mixed, with mainly snow in the interior and a mix of rain and snow in the coastal plain. This is a low confidence forecast, with the run-to-run changes of the models and the differences in details leaving open several scenarios ranging from major storm to complete miss. Confidence should not improve much until both predecessor shortwaves, as described above, move over land later this weekend. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/...
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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 Saturday/...High confidence. Today... VFR. Occasional low-mid clouds. NW winds increase during the day, with gusts 20-30 kt, highest along the coast. Tonight... VFR. Slight increase in winds. With a few more gusts around 30 kt during the evening and early overnight. Saturday... VFR. Winds turn more NW, gusts 20-25 kt. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Saturday Night through Tuesday/... Moderate confidence. Saturday Night through Monday: VFR. Breezy. Monday Night through Tuesday: VFR.
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&& .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday/...High confidence. Today into tonight... W-NW wind gusts will gradually increase across the waters through the day. Peaking first on the S waters late this afternoon and evening with gusts around 35 kt on the open ocean waters. The E waters then follow, with gusts also around 35 kt. Near shore waters will be slightly weaker, therefore Gale Warnings will be issued late this afternoon/evening for the outer waters with Small Craft Advisories mostly close to shore. Seas peak early Sat AM around 10-12 ft on the outer waters. Sat... NW Gales continue mainly across the E waters with Small Craft Conditions lingering across the S waters. The Gales drop off by afternoon, with Small Craft Advisories following all waters thanks to both gusts/seas. Outlook /Saturday Night through Tuesday/...Moderate confidence. Saturday Night: Winds less than 25 kt. Local rough seas. Sunday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. Sunday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of seas approaching 5 ft. Monday: Winds less than 25 kt. Seas locally approaching 5 ft. Monday Night through Tuesday: Winds less than 25 kt. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT Saturday for ANZ230-232. Small Craft Advisory until 5 PM EDT Saturday for ANZ233>237. Gale Warning from 5 PM this afternoon to 2 AM EDT Saturday for ANZ231-255-256. Gale Warning from 5 PM this afternoon to 2 PM EDT Saturday for ANZ250-254. Gale Warning from 8 PM this evening to 2 PM EDT Saturday for ANZ251. && $$ SYNOPSIS...WTB/Doody NEAR TERM...WTB/Doody SHORT TERM...Doody LONG TERM...WTB/Frank AVIATION...WTB/Doody MARINE...WTB/Doody is the U.S. government's official web portal to all federal, state and local government web resources and services.