Area Forecast Discussion
Issued by NWS Boston, MA

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332 FXUS61 KBOX 251942 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 342 PM EDT Tue Apr 25 2017 .SYNOPSIS... Low pressure will slowly track up the east coast tonight into Wednesday morning bringing periods of rain along with a few embedded thunderstorms. Low clouds along with some drizzle and fog are expected to linger Wednesday night into Thursday especially along the coast. Very mild to warm afternoons should return Friday and Saturday with the low risk for a few showers/thunderstorms. Much cooler weather follows Sunday especially on the coast. Another cold front will likely bring more showers to the region sometime Monday into Tuesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 215 PM Update... Southerly plume of moisture combined with easterly low level flow contributing to showers moving through southern New England, and advancing towards our area from the south. Could still have a a rumble of thunder within RI/southeast MA prior to 00Z. East/Northeast winds continue through this afternoon, with gusts 25 to 30 mph along east coastal MA, southeast MA and southern RI. Overall temps remaining nearly steady in the mid 40s to low 50s this afternoon, with some mid 50s in the CT River Valley region from Springfield thru Hartford. Early Morning Discussion follows... High confidence in trends, moderate confidence in timing. A low pressure off the Mid Atlantic coast will try to move north today. However, a weak surface ridge over southern New England will prevent it from making much northward progress today. Despite that, moisture will stream north into our region, resulting in plenty of clouds, and eventually periods of rain, across all of our region. Precipitable water values approach 1.25-1.50", which is about 2-3 standard deviations above normal. Rainfall could be heavy at times, especially late this afternoon. Not thinking this rainfall will lead to river flooding, but will need to monitor the poor drainage areas, especially the urban centers. Dew point depressions across northern MA remain large early this morning, which means it will be a while longer before significant rainfall reaches the ground. Previous forecast had this covered well, so only tweaked the onset timing by an hour or so to reflect observed trends. Still thinking at least light rainfall will develop over the region by 9-10 AM. East winds will mean another raw spring day, especially along the coasts. Max temperatures today are expected to be around 10 degrees below normal. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Tonight...High confidence. Widespread rainfall will fall tonight as weak ridge over southern New England breaks down. A strong southeast low level jet will also approach, especially after midnight. Not a lot of instability, but marginal mid level lapse rates could result in a few thunderstorms tonight into Wednesday morning. The most likely area where this could occur remains the Cape and islands, due to their proximity with the low level jet. Temperatures should remain steady or slowly rise tonight, especially across RI and SE MA. Gusty easterly winds will continue tonight along the coast. Wednesday...Moderate confidence. Low pressure continues to move slowly north along the coast. Still expecting this low to remain south of our region through Wednesday evening. Despite that, the mid level low associated with this system should be overhead, opening the door for mid level drying to bring an end to the widespread rainfall. Thinking this is more likely to happen during the afternoon hours, but do not have a lot of confidence in the exact timing. Even so, scattered areas of rain, or perhaps drizzle, may persist for much of the afternoon. Low risk for thunderstorms continuing, mainly across the Cape and islands, and the adjacent coastal waters. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... Highlights... * Low clouds/spotty drizzle Wed night+Thu with cool temps on coast * Mild to warm afternoons Fri/Sat with a low risk for a few t-storms * Backdoor cold front brings much cooler temps by Sun * Period of showers which may be briefly heavy sometime Mon/Tue Details... Wednesday night and Thursday... Closed upper level low will linger off the southern New England coast Wed night into Thu. Model cross sections indicate a fair amount of low level moisture lingering below the subsidence inversion. Given overall setup and time of year, feel low clouds will linger Wed night into Thu afternoon even across much of the interior. There also should be areas of fog and drizzle, especially on the coast Wed night and Thu am along with the risk for a spot shower or two. With that said, guidance is probably too warm with forecasted high temps on Thu given expected low cloud cover. High probably remain in the 60s for most of the region and perhaps stuck in the mid to upper 50s along the coast. Now if more sun is realized than expected it still would be possible for portions of the interior to break 70, but hedging cooler for now. Friday and Saturday... Upper level ridge of high pressure building off the southeast coast will be pumping higher height fields into southern New England. Decent shot for high temps to reach the 70s to lower 80s away from any marine influence along the coastline, especially the south coast with south to southwest flow. Most of this time should feature dry weather, but a few shortwaves will result in the low risk for a couple of showers/t-storms. Greater chance of development would occur if energy moves through closer to the time of peak heating on Fri and Sat. Saturday night and Sunday... Despite abnormally high height fields, strong high pressure will be building across eastern Canada. This will likely send a backdoor cold front south of the region late Sat or Sat night. Much cooler temps are likely for Sunday especially along the coast where they should remain in the 50s. Perhaps a few spot showers, but high pressure may suppress most of the activity to our southwest. Monday and Tuesday... Timing uncertain, but an approaching cold front will likely bring a period of showers. GEFS anomalies signaling decent low level jet coupled with fairly high Pwats so the showers may be heavy for a brief period of time. Again, timing uncertain and not expecting both days to be total washouts. Temperatures also uncertain given timing/wind direction. && .AVIATION /20Z TUESDAY THROUGH SUNDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday/... This Afternoon and Tonight...High confidence in trends. Moderate confidence in timing. Conditions deteriorating to IFR/LIFR during this afternoon with showers and fog. Potential exception of BDL/BAF vicinity, where MVFR conditions are expected into early evening, then deteriorating to IFR. E wind gusts 25 to 30 kt over Cape/Islands with winds veering to SE tonight with similar gusts. LLWS developing Cape/Islands this evening as SE/S low level jet at 50+ kt develops, especially after midnight. LLWS may extend as far north as BOS. Isolated TSRA possible tonight. Wednesday...Moderate confidence. MVFR-IFR CIGS continue with areas of -RA/RA and patchy fog, especially across the eastern half of southern New England. Reduced VSBYS likely, down to IFR in spots. May see areas of LIFR CIGS across the higher inland terrain and along the coast. SE winds gusting up to around 25 kt across Cape Cod and the islands. Low risk of TSRA early in the day, especially the S coastal terminals. LLWS impacts for the Cape and islands, and possibly as far north as BOS, during the morning hours. KBOS TAF...Moderate confidence in TAF. Potential for LLWS 08Z- 14Z with SE low level jet. KBDL TAF...Moderate confidence in TAF. Outlook /Wednesday Night through Sunday/... Wednesday night into Thursday...Moderate to high confidence. IFR to even LIFR conditions likely Wed night into part of Thu am along with some fog, drizzle and a spot shower. Lower conditions most likely on the coast. Conditions may improve to mainly MVFR by late Thu morning and afternoon. Thursday night and Friday...Moderate confidence. MVFR/IFR conditions likely in areas of low clouds and fog patches Thu night into early Fri am. Improvement to VFR likely by Fri afternoon with the low risk for a few showers and perhaps a t-storm. Saturday and Sunday...Moderate confidence. VFR conditions probably dominate. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday/...High confidence. Persistent easterly flow across the coastal waters this afternoon into tonight. Gusts 25 to 30 kt possible, especially across the southern coastal waters. Widespread rain continues this afternoon, and is expected to be heaviest tonight into Wednesday morning. Plenty of visibility restrictions in both rain and fog expected. Low risk of thunderstorms, mainly on the southern waters. Extended Small Craft Advisories across most waters through Wednesday. Outlook /Wednesday Night through Sunday/... Wednesday night through Friday...Moderate to high confidence. Despite wind gusts mainly 20 knots or less, left over southeast swell will result in small craft seas persisting through Friday across many of our outer and southern waters. In addition, areas of fog may result in poor vsbys for mariners especially during the overnight and early morning hours. Saturday and Sunday...Moderate to high confidence. West to southwest wind gusts to 20 knots Saturday will shift to the northeast by late Sat or Sat night behind a backdoor cold front. Overall, expect winds and seas to remain below small craft advisory thresholds. && .TIDES/COASTAL FLOODING... * Potential minor flooding impacts during astronomically high tides Tonight through Wednesday along the east and south coasts Not anticipating any flooding impacts for the high tide later today, as winds, surge and seas will not have built up enough. Minor flooding possible during the high tide cycles tonight and Wednesday along both coastlines. A storm surge around 1 ft with low risk of 1.5 ft surge on top of high astronomical tides and building seas may lead to minor inundation of vulnerable shoreline roads. Some beach erosion is also possible, especially for east and southeast facing beaches. Boston High Tides (flood stage 12.5 feet)... 11.47 feet / Tuesday 11:20 pm 11.15 feet / Wednesday 11:50 am Providence High Tides (flood stage 7 feet)... 5.98 feet / Tuesday 8:11 pm 5.53 feet / Wednesday 841 am && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 3 PM EDT Wednesday for ANZ231>234. Small Craft Advisory until 8 PM EDT this evening for ANZ230- 236. Small Craft Advisory until 8 PM EDT Wednesday for ANZ235-237- 250-251-254>256. && $$ SYNOPSIS...Frank NEAR TERM...Belk/Dunten/NMB - update coming soon SHORT TERM...Belk - update coming soon LONG TERM...Frank AVIATION...Belk/Frank/NMB MARINE...Belk/Frank TIDES/COASTAL FLOODING...Update coming soon

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