Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 162301 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 701 PM EDT Tue Oct 16 2018 .SYNOPSIS... A cold front moves through the region Wednesday followed by the coldest air of this young fall season invades Wednesday night and Thursday. However the cold weather is short lived with moderating temps Fri and Sat but a chance of showers ahead of a cold front Saturday. Colder air returns Sunday and Monday behind the frontal passage. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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7 PM update... Only change to the forecast was to include potentially patchy frost given dew pts are in the 30s, light winds and mostly clear skies. Otherwise previous forecast verifying nicely and on track for the remainder of the night. Earlier discussion below. ================================================================= Clear skies will prevail tonight, with some increase in mid/high clouds late tonight across western New Eng as mid level trough moves into the Gt Lakes. Enough gradient tonight will maintain modest wind over the higher terrain and coastal areas which will limit radiational cooling. Lows will range from the mid 30s to lower 40s.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... Wednesday... Robust mid level trough and shortwave moves into New Eng with attending cold front sweeping across the region during the afternoon. Steep low level lapse rates approach dry adiabatic in the 0-3km layer which will lead to broken clouds developing given some low and mid level moisture. Can`t rule out a few showers, especially interior given modest forcing but overall moisture is a limiting factor and will limit areal coverage. Gusty SW winds in the morning will shift to W in the afternoon with gusts to 25-35 mph developing in the cold advection pattern. Moderating low level temps will lead to a miler day with highs into the lower 60s in the coastal plain with mid 50s over the interior higher terrain. Wednesday night... Strong cold advection will bring anomalous cold airmass for this time of year with gusty W/NW winds. -10C air at 850 mb moves into SNE by 12z Thu. Lows will range from the upper 20s higher terrain to low/mid 30s elsewhere away from the outer Cape/Islands. Wind chills late Wed night into Thu morning will drop to the upper teens to mid 20s. No frost expected given wind and very dry air, but freeze headlines likely needed for portions of the interior where growing season is still active. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Highlights... * Brief surge of winter cold Thursday * Moderating temperatures Friday and Saturday * Return to colder than normal Sun & continuing into early next week * Mainly dry this period with just scattered showers Fri ngt/Sat Synoptic Overview and Model Preferences. GEFS and ECENS continue to support a persistent eastern Pacific trough/western Canada ridge this period which fits teleconnections of a -EPO and + PNA. This favors downstream trough over eastern Canada into New England. Given the NAO remains positive the flow remains somewhat progressive so these cold surges will be short lived. However central-northern Atlantic ridge coupled with the western Canadian ridge will support eastern Canadian/New England trough to reload resulting in temperatures at or colder than normal much of this period. Thursday... High amplitude mid level trough over the Maritimes advects a winter- like airmass into New England with 850 mb temps down to -10C to -8C. This will only support highs in the 40s which is about 15-18 degs colder than normal! These highs are more typical of early Dec, thus running way ahead of schedule. It will feel even colder courtesy of NW winds gusting up to 20-30 mph which will yield wind chills in the 30s. So definitely a winter chill in the air Thu. Wed night will be the colder night for the urban areas given the strong CAA however Thu night will be colder for the suburbs. This will be a result of a very dry airmass with dew pts in the teens combines with diminishing wind and mostly clear skies. Leaned toward the colder MOS guidance here with lows in the 20s across many of the suburbs and 30-35 in the cities including much of the immediate coastline. Friday... Upper air pattern remains progressive so anomalous cold trough exits with rising heights/warming temps aloft offering a nice rebound in temperatures. In addition anticyclonic mid level flow and associated subsidence should yield mostly sunny conditions. Increasing southwest winds will erode/modify leftover cold air with 925 mb temps recovering to about +5C by Fri afternoon, supporting highs well into the 50s. Weekend... WAA pattern ahead of next northern stream trough and attending cold front. 925 mb temps warm to about +9C Sat afternoon so highs in the lower 60s seem reasonable. Thus leaned toward the warmer EC MOS for highs. Models have trended a bit faster with this short wave/attending front with greatest risk for scattered showers Fri night into Sat morning with possible drying trend Sat afternoon given quicker FROPA. Post frontal airmass overspreads the area Sat night into Sun. Cold cyclonic flow aloft will yield diurnal clouds and perhaps a spot rain/snow shower especially over the interior. Otherwise dry weather prevails. However it will be cold with 12z ECENS 850 mb temps ranging from -4C to -6C, supporting highs from the upper 40s to lower 50s. It will feel colder given blustery NW winds. This will be followed by another chilly night (Sunday night) as winds diminish and lows dip into the 20s and 30s. Early next week... Persistent long wave trough hangs tough over eastern Canada into New England with colder than normal temps Monday with highs only in the 40s. Some moderation Tue ahead of next short wave and attending cold front, however looks like this just reloads the long wave trough with a reinforcing surge of cold air for mid week. Mainly dry this period other than low risk of scattered showers with short wave and attending cold front around Tue. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 7 PM update... VFR, dry and light WSW winds overnight. Earlier discussion below. ============================================================== Short Term /through Wednesday Night/...High confidence. Through tonight...VFR. Light W/SW wind. Wednesday... VFR. sct-bkn cu 5-6k ft developing in the afternoon, greatest coverage in the interior where a few showers possible. Gusty SW winds in the morning becoming west with 25-30 kt gusts developing in the afternoon. Wednesday night... VFR. W/NW gusts 20-30 kt early in the evening, then diminishing but remaining gusty along the immediate coast. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Thursday through Sunday/...Moderate-High confidence. Thursday: VFR. Windy with gusts to 35 kt. Thursday Night: VFR. Windy with local gusts to 30 kt. Friday: VFR. Breezy. Friday Night: Mainly VFR, with areas MVFR possible. Windy with areas gusts to 30 kt. Chance SHRA. Saturday: Mainly MVFR, with areas VFR possible. Windy with gusts to 30 kt. Chance SHRA. Saturday Night through Sunday: VFR. Breezy.
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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 Wednesday Night/...High confidence. West winds mostly below SCA tonight. Increasing SW winds Wednesday morning, then gale force west wind gusts developing Wed afternoon and continuing through Wed night in strong cold advection behind the cold front. Gusts to 35-40 kt expected. Outlook /Thursday through Sunday/...Moderate to High Thursday: Low risk for gale force winds with gusts up to 35 kt. Areas of rough seas. Thursday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Friday: Winds less than 25 kt. Areas of seas approaching 5 ft. Friday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Chance of rain showers. Saturday: Low risk for gale force winds with gusts up to 35 kt. Areas of rough seas. Chance of rain showers. Saturday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Slight chance of rain showers. Sunday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. && .CLIMATE... Record Low Maximum Temperatures for Thursday October 18 BOS 45 in 1898 ORH 36 in 1989 BDL 44 in 2009 PVD 46 in 1939 && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Gale Warning from 2 PM Wednesday to 8 AM EDT Thursday for ANZ232>235-237-254>256. Gale Warning from 4 PM Wednesday to 4 AM EDT Thursday for ANZ230. Gale Warning from 4 PM Wednesday to 8 AM EDT Thursday for ANZ231-250-251. Small Craft Advisory from 10 AM Wednesday to 8 AM EDT Thursday for ANZ236. && $$ SYNOPSIS...KJC/Nocera NEAR TERM...KJC/Nocera SHORT TERM...KJC LONG TERM...Nocera AVIATION...KJC/Nocera MARINE...KJC/Nocera CLIMATE... is the U.S. government's official web portal to all federal, state and local government web resources and services.