Wednesday, November25, 2020
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Marine Weather and Tides
Siasconset, MA

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Sunrise 6:44AMSunset 4:20PM Wednesday November 25, 2020 6:15 AM EST (11:15 UTC) Moonrise 3:15PMMoonset 2:52AM Illumination 77% Phase: Waxing Gibbous; Moon at 10 days in cycle
NOTE: Some of the data on this page has not been verified and should be used with that in mind. It may and occasionally will, be wrong. The tide reports are by xtide and are NOT FOR NAVIGATION.
Marine Forecasts
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7 Day Forecast for Marine Location Near Siasconset, MA
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location: 38.84, -69.85     debug


Area Discussion for - Boston, MA
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FXUS61 KBOX 250854 AFDBOX

Area Forecast Discussion National Weather Service Boston/Norton MA 354 AM EST Wed Nov 25 2020

SYNOPSIS.

Low pressure approaching from the west will result in mainly cloudy weather today with the threat for showers increasing later tonight. Periods of showers with pockets of heavy rainfall are on tap for Thanksgiving. Gradually improving conditions into Thursday night. Cooler and generally unsettled Friday into Saturday though with mainly dry weather. High pressure brings sunny conditions for Sunday. While details are still a bit unclear, a significant precipitation maker is in the cards for early next week. Temperatures trend near to above normal Sunday into early next week.

NEAR TERM /UNTIL 6 PM THIS EVENING/.

350 AM Update .

* Spotty Freezing Drizzle Possible This AM Across Interior SNE

High pressure will continue to slowly shift east of the Canadian Maritimes today. Modest warm advection aloft will result in a rather cloudy day, but with limited deep moisture most of the day will be dry. That being said there is enough low level moisture and shallow forcing for spotty very light showers/sprinkles today. Across the interior, temperatures are cold enough to support flurries, but there also is the concern for spotty freezing drizzle. Shallow cold air trapped at the surface coupled with a lack of ice nuclei/warming temps aloft might be the culprit. While any amounts of -Fzdz will be generally on the order of a trace, that is all it takes for hazardous travel. A special weather statement remains in effect to highlight this concern.

As for temperatures, we leaned towards the high resolution 3 KM NAM/HREF which almost always out perform the global/MOS guidance in these cases. Temps will be slow to rise across portions of interior SNE, perhaps not breaking freezing in a few locations until late morning or early afternoon. In fact, some areas across the interior may not get out of the 30s. Meanwhile, the coastal plain should recover well into the 40s and even reach the 50 to 55 degree range near the south coast.

SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/.

* Thanksgiving will feature periods of showers with pockets of heavy rainfall and perhaps a few embedded t-storms

Tonight .

A rather dynamic closed upper level low will move east across Ohio tonight. This will increase the forcing for ascent along with a modest southwest LLJ. So while a few showers will be possible this evening, expect the activity to become rather widespread toward daybreak near and northwest of the Boston to Providence corridor. A surface front will keep temps in the upper 30s to lower 40s across much of the region, while areas near the south coast will be milder in the upper 40s and lower 50s. This surface boundary will also result in areas of fog, which may be locally dense especially on the cool side of the boundary.

Thanksgiving .

A rather dynamic system will bring periods of showers with pockets of heavy rainfall on Thanksgiving. In fact, a few embedded t-storms will be possible especially during the afternoon and early evening.

Low pressure will approach from the west with secondary development expected near the I-95 corridor. This coupled with a modest southerly LLJ and Pwats 2+ standard deviations above normal will set the stage for periods of showers with pockets of heavy rainfall. Rainfall amounts on the order of 0.50 to 1.25 inches are reasonable for much of the region. However, localized higher amounts of up to 2 inches are possible across eastern CT/RI and eastern MA. This is in the vicinity of a surface trough, where low level convergence will be maximized. There also may be locally higher rainfall amounts if a few embedded t-storms develop. Highest risk for this will be during the afternoon and early evening as a dynamic closed upper level low will steepen mid level lapse rates to between 6.5 to 7.0 C/KM.

High temperatures on Thanksgiving are also tricky and we once again leaned strongly towards the high resolution 3 KM NAM. While temps across RI/SE MA should reach the upper 50s to the lower 60s, portions of the interior may be jammed up in the 40s north of the surface boundary. Areas of fog will also once again impact the region, particularly in the cool sector.

LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/.

Highlights .

* Heavier showers/possible thunder Thursday night, then clearing overnight.

* Unsettled Fri and Sat, though generally dry with slowly cooling temps. Sunny conditions Sunday.

* Complex weather pattern early next week, potentially bringing an impactful and mainly wet system to our area Monday and/or Tuesday. Strong winds and building seas also possible. Stay tuned!

Details .

Thursday Night:

Heavier showers, possibly embedded with thunder from Thanksgiving Day will continue to translate eastward into the waters Thursday night, though it may take much of the night to clear rain chances. Steadiest precip mainly for eastern and southeastern New England. Still looks cloudy even in the wake of the frontal system with fairly high RH progged for the overnight. Will show low temperatures only dropping into the mid to upper 40s under mostly cloudy skies.

Friday into Sunday:

Split flow pattern aloft then evolves across CONUS, with weather in this period for our area being mostly dominated by fast-moving northern stream trough energy. Initial 500 mb height rises on Fri weaken late Fri into Sat as a progressive 500 mb trough skirts across the Great Lakes into northern New England. Outside of some Great Lakes moisture, weak surface features and lack of deeper moisture shouldn't really result in much precip as this feature passes through. Appears best chance for precip is mainly to our north, but will carry limited/lower Chance PoPs. Surface ridging then builds in later Sat into Sunday.

All in all, Fri thru Sat are generally unsettled but nothing too significant as far as precipitation goes, with the best chance again being on Sat. Thermally, 925 mb temps undergo weak cold advection on Fri, with lowest 925 mb temps set to take place on Sat (around +2 to -2C). Fri features milder temperatures (mid 50s) but will generally partly to mostly cloudy skies. Highs mainly in the 40s on Sat, with chilly nighttime lows in the 20s to lower 30s under good radiational cooling. Sunday is looking like the pick of the weekend with full sun and warming 925 mb temps supporting highs in the mid/upper 40s, perhaps a few 50s and lows around the freezing mark.

Monday into Tuesday:

A highly amplified, complicated/complex 500 mb pattern then develops across CONUS early next week. While the specific details and impacts are still unclear, confidence is increasing on storminess centered around Monday and/or Tuesday.

On the large-scale, deterministic and ensemble guidance point to phasing of stronger northern stream energy from the northern Rockies with ejecting shortwave energy in the southern branch of the jet on Sunday. This results in a full-latitude 500 mb trough across the nation's midsection by late Sunday into early on Monday. An initial sfc cyclone near the Gulf Coast moves northward and rapidly occludes into the Great Lakes on Monday. Its associated cold front/frontal- occlusion will likely slowly approach the eastern US seaboard into our area later Monday and/or into Tuesday. Southerly flow becomes significantly enhanced ahead of this feature (some guidance has 850 mb winds of 60-70 kt!), with a subtropical moisture connection resulting in ECMWF ensemble-progged PWATs of 1" to 1.2", which are about 2 to 3 standard deviations above climo. Orientation of the southerly flow parallel to the frontal zone could set the stage for a prolonged and potentially heavy QPF event, perhaps with some convective elements. In fact, ECMWF ensemble 24-hour QPF over 1" are quite sizable for what amounts to a Day-6/Day-7 forecast at around 50-70%. That's quite a signal for that time range! The biggest uncertainties revolve around timing the onset of precip and the complex phasing of the two energy streams; specific to the latter point, most of the guidance suggests any colder air would be more underneath the upper level cyclone well to our southwest with current odds appearing more tilted towards a wetter vs wintry outcome. This would especially be the case if the front translates slower and allows for pre-frontal southerly flow to persist for a longer period of time.

Offered high likely PoPs and went significantly above NBM guidance on winds/wind gusts to indicate the potential. Will also side temperatures toward above-normal levels.

There is still a lot to be ironed out on the details. Despite the haziness on the specifics, the potential exists for an impactful system Monday and/or Tuesday that may bring significant QPF, strong winds and building rough seas/possible coastal flooding. Stay tuned!

AVIATION /08Z WEDNESDAY THROUGH SUNDAY/. Forecaster Confidence Levels .

Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.

06Z Update .

Today . Moderate Confidence. A broken to overcast deck of mainly VFR ceilings are expected today, but a few hours of localized MVFR cigs are possible too. Dry weather dominates today, but spotty sprinkles/very light showers are possible. Across portions of the interior, flurries/sprinkles and of more concern spotty -fzdz will be possible through early afternoon. While any precipitation should be extremely light and spotty, a brief period of -fzdz will be possible at KBAF, KORH and KBDL terminals. Winds will become S at 5 to 15 knots by afternoon across the coastal plain, but may remain very light and even from a N direction in the interior and especially CT River Valley.

Tonight . Moderate Confidence. VFR conditions may dominate early in the evening but will lower to mainly MVFR to even IFR as the night wears along. A few showers possible this evening, but widespread showers will overspread much of the region at least near and NW of the BOS-PVD corridor between 6z and 12z. Areas of fog are also expected too.

Thanksgiving . Moderate Confidence. Mainly IFR to localized IFR conditions in periods of showers with pockets of heavy rainfall. A few embedded t-storms are possible too especially across CT/RI and eastern MA. SE wind of 5 to 15 knots expected over the coastal plain, but winds may be light and variable in the interior. In addition, fog is also expected which may be locally dense especially across portions of the interior.

KBOS TAF . Moderate Confidence in TAF.

KBDL TAF . Moderate Confidence in TAF.

Outlook /Thursday Night through Sunday/ .

Thursday Night: MVFR/IFR conditions possible. Breezy. Chance SHRA, isolated TSRA, patchy BR.

Friday: Mainly VFR, with local IFR possible.

Friday Night: VFR.

Saturday through Saturday Night: VFR. Breezy.

Sunday: VFR.

MARINE.

Today through Thanksgiving . High Confidence.

A developing modest southerly LLJ will result in building SCA seas and southerly wind gusts of 25 knots by this afternoon. We have hoisted SCA headlines for most waters into this evening. While we may see a bit of a lull in the winds/seas for a time tonight, expect more SCA seas and south wind gusts of 20 to 25 knots again on Thanksgiving. In addition, showers and fog will increase overnight into Thanksgiving. A few embedded t-storms will also be possible especially during the afternoon and evening.

Outlook /Thursday Night through Sunday/ .

Thursday Night: Winds less than 25 kt. Local rough seas. Chance of rain showers, isolated thunderstorms, patchy fog.

Friday: Winds less than 25 kt. Seas up to 5 ft.

Friday Night through Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft.

Saturday Night: Winds less than 25 kt. Seas up to 5 ft.

Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft.

BOX WATCHES/WARNINGS/ADVISORIES. CT . None. MA . None. RI . None. MARINE . Small Craft Advisory from 8 AM this morning to 7 PM EST this evening for ANZ231>235-237-251. Small Craft Advisory until 10 PM EST this evening for ANZ250- 254. Small Craft Advisory from 8 AM this morning to 10 PM EST this evening for ANZ255-256.

SYNOPSIS . Frank/Loconto NEAR TERM . Frank SHORT TERM . Frank LONG TERM . Loconto AVIATION . Frank/Loconto MARINE . Frank/Loconto


Weather Reporting Stations
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Airport Reports
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AirportDistAgeWind ktVisibilitySky/WeatherTempDewPtHumidityPressure
Nantucket, Nantucket Memorial Airport, MA168 mi22 minSE 910.00 miOvercast43°F30°F63%1031.5 hPa

Link to 5 minute data for KACK

Wind History from ACK (wind in knots)
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