Thursday, July20, 2017 L-36.com


Marine Weather and Tides
Siasconset, MA

Version 3.4
What's New / NOTES
6/25/2017 - NOAA is having a major issue that impact the 7 day forecast load times. Many users are reporting problems. The issue has been reported.
5/23/2017 - Worked with NOAA again to speed up the 7 day forecast load times. Thanks to them for being responsive.
5/19/2016 - There were issues with the 3 day airport observation history. I switched to another data source. Let me know if you see any issues with the data feeds.

Sunrise 5:28AMSunset 8:15PM Thursday July 20, 2017 6:36 PM EDT (22:36 UTC) Moonrise 2:42AMMoonset 5:18PM Illumination 8% Phase: Waning Crescent; Moon at 27 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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ANZ005 622 Pm Edt Thu Jul 20 2017
Synopsis for eastport me to stonington me out 25 nm.. A cold front will approach the waters on Fri and cross the waters late Fri afternoon. High pres will build in on Sat.

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 201953
afdbox
area forecast discussion
national weather service taunton ma
353 pm edt Thu jul 20 2017

Synopsis
After some wet weather tonight, one more day of hot and humid
weather for Friday. Cooler and drier air moves in for Friday
night. Warm and dry Saturday. Cooler, and more humid but with
unsettled weather follows for Sunday through Tuesday.

Near term until 6 am Friday morning
330 pm update...

* highlights...

- late afternoon scattered showers and thunderstorms expected
mainly for N E portions of ma through evening. There's a low
risk of storms becoming strong to severe.

- into this evening, complex of showers and thunderstorms out
of W ny pushes S e. Expecting rain to clip S W portions of s
new england with the possibility of some embedded thunder.

* discussion...

scattered showers and thunderstorms forecast in association with
a moist, unstable boundary layer being acted upon mid to upper
level ascent. However a limiting culprit across the region of mid-
level dry air.

With favorable ascent across N new england associated with the
mid-level vortmax and lfq of an upper level jet through the
cyclonic flow acting upon a destabilized surface-h8 boundary
layer, already seeing shower and thunderstorm activity initiating
along the high terrain with better convergent focus. Some of
that mid to upper level ascent should lobe S far enough to spark
some activity as suggested by the hrrr, especially over N E areas
of ma where chance pops are presently forecast this evening. But
after more thorough analysis, the strong to severe chances are
limited by the presence of mid level dry air. Even the ncar
ensembles show low probability of lightning in concert with a
present area of low k-indices.

Meanwhile S w, monitoring the upstream parallel-leading stratiform
mesoscale convective system (mcs). S-flank is anchored to the low
level SW inflow of better moisture. However as the complex drops
s, it will depart from areas of more favorable venting and shear.

The modification of the environment looks to weaken lessening
the maintenance of low level inflow as W winds become SW during
the evening period over upstate ny pa. Thinking that S W areas
of new england will see widespread rain with the leading stratiform
from the MCS as it weakens. Perhaps some embedded thunder. But two
issues, 1.) cloud shield associated with the mcs, and 2.) mid-
level dry air. Hrrr is suggesting some heavier precipitation with
the parent outflow boundary acting on the destabilized airmass
over S W ct, but not totally sold on it.

In all, will limit the thunder threat across the region, opt out
of any strong to severe wording, and mainly focus on chance pops
for scattered to widespread rain over N E ma and S W ct. In-between
may see little if anything.

Heat diminishing, lows dropping down to around the upper 60s to
low 70s. The W SW flow prevailing allowing the maintenance of
higher dewpoints along the S SE coast, likely to see the return
of low clouds and fog. If anything dense, mainly over nantucket.

Will issue another special weather statement highlighting the
threat along with the potential of a dense fog advisory.

Short term 6 am Friday morning through Friday night
Friday...

one more day of heat and humidity. Little if any lifting and
forcing mechanisms, looking like a quiet day beneath a fairly
dry airmass. The boundary layer mixing out to around h85 where
temperatures of +16-17c still reside, should see scattered
cumulus develop as both drier air and faster westerlies mix down
to the surface. Highs upper 80s to low 90s with mid to upper 60s
at first quickly mixing out to upper 50s to low 60s. This will
limit heat indices from climbing into the mid 90s. No heat
advisory headlines are being considered with this forecast.

Friday night...

turning cooler and drier. Low to mid level cool-dry front sweeps
s e. Winds shifting NW ushering in drier air with a slightly cool
airmass aloft. Humidity dropping beneath some scattered to broken
cloud decks. Lows dropping into the low to mid 60s with a few
spots N W in the upper 50s.

Long term Saturday through Thursday
Highlights...

* sat: dry and very warm afternoons but with lower humidity
* Sun into tue: cooler than normal + unsettled with showers at times
* drying trend likely by the middle of next week
overview and model preferences... Noting that the time-mean jet
remains firmly entrenched across new england through the long term
period. This generally has two consequences, one being the
inability to get true subtropical warmth into new england and the
second being the continuation of a relatively active pattern. As
the previous forecaster noted, this by no means suggests a washout.

The first canadian vortex shifts from the ungava bay region offshore
of newfoundland-labrador by the end of the weekend. This will
initially yield more zonal flow, but it is short lived as a second
wave phases and re-deepens the longwave trof in place across the ne
conus. This trof remains the key synoptic player in sensible wx
details across the region through much of next week, and its trof
center's location with respect to S new england will determine
whether the active, wet pattern continues or drier air is allowed to
move in.

Details...

sat...

current indicators suggest that with the vortex to the N shifting
e, this allows a ridge of high pres to move into new england,
keeping the slow moving frontal boundary well to the S and
limiting destabilization somewhat thanks to subsidence and a dry
air intrusion which lower overall lapse rates and moisture
(lowered k- indices). Therefore, will maintain a mostly dry
forecast for the day on sat. The ridging and afternoon mixing
will provide a bit of relief in afternoon dewpoints, possibly
mixing them down into the upper 50s. H85 temps, should be
reached, and given they run around +16c, afternoon highs could
be as warm as near 90 where downsloping is maximized, mid-upper
80s elsewhere.

Sat night into sun...

will need to watch another MCC develop in the great lakes
region and gradually shift along and S of the stalled frontal
boundary through the oh valley to the mid atlantic states. Given
the better thermodynamic parameters remain S of this stalled
front, and weak lapse rates remain in place, am not too keen on
nocturnal convection, as this is a typical case where the best
instability moisture will pull the MCC to the SW of new england.

However, one factor to consider as we approach will be the
remnant cold pool and whether a weak cold pool low pres could
allow the remnants of the system to slide e, or re-form
convection in situ. Will keep pops mainly S through the
overnight hours, but will still need to monitor this as we
approach given the close proximity. Otherwise, noting an attempt
to lift the front N on sun, and with the additional moisture
load could see a round of shra develop but given weak lapse
rates remain and better CAPE remains to the s, only looking at a
spot TS if at all. Still relatively unsettled, and should the
front shift further N than currently progged, it has the
possibility of being more active. Generally cooler (mainly 70s
to around 80 for highs) with more clouds to contend with, but
dewpoints will generally be higher thanks to the increase in
column moisture.

Mon into tue...

with deepening trof move in aloft, am noting guidance in favor
of developing weak slow moving low pres which will gradually
pivot across the region during this 48-hour period. Given some
cooling aloft with the trof, am noting a slight increase in
lapse rates along with CAPE values. Shear does increase too
thanks to cyclonic curvature yielding stronger directional
shear. Overall, a window of potential continuing unsettled wx
with a mix of showers and occasional t-storms. Not a washout, as
dry air will rotate into the region at times as the low pres
moves. However, some heavy rain possible given pwats hover near
1.50 inches. Not a great setup for severe wx, but given the
shear slightly higher lapse rates this still may need to be
watched. Another, mitigating factor may be clouds, which are
likely to be dominant (with generally a few breaks of sun).

Highs likely remain at or below normal thanks to the cloud cover
while overnight mins should rest in the 60s thanks to sustained
dwpts. More to come given the uncertainty in development of the
weak low pres.

Wed into late next week...

base of trof finally shifts E of the region allowing for
ridging and attendant NW flow. This drying and influence of high
pres associated with the ridge should allow for a trend of
drying less unsettled wx for the late week period. Will trend
dwpts down suggesting more comfortable conditions and mainly
dry nil pops.

Aviation 19z Thursday through Tuesday
Forecaster confidence levels...

low - less than 30 percent.

Moderate - 30 to 60 percent.

High - greater than 60 percent.

Short term through Friday night ... High confidence.

Through tonight...

vfr. W SW winds with gusts up to 20 kts diminishing. -ra
possible mainly N E ma and S W ct with a lower risk of tsra.

Ifr-lifr CIGS and vsbys advecting back in along the s-coast and
along the CAPE and islands with ack seeing 1 2sm fg again.

Friday...

s-coast ifr CIGS and vsbys eroding, especially over ack. W sw
winds continuing with gusts up to 20 kts.VFR with sct cigs
around 4-5 kft.

Friday night...

continuedVFR. Winds veering out of the W NW with time early on.

Kbos terminal...

low risk of shra tsra activity into evening. OtherwiseVFR.

Kbdl terminal...

ra possible this evening. Will continue with vcsh. Lower risk
of tsra.

Outlook Saturday through Tuesday ...

sat... High confidence.

MainlyVFR. A spot shower or thunderstorm possible late, mainly
overnight.

Sun through tue... Low confidence.

Vfr will likely dominate especially inland, however a complex
mix of clouds, occasional shra and isolated tsra could lead to
occasional dips to MVFR ifr. Otherwise, some clouds and fog may
lead to low CIGS vsbys (especially along the coast) to yield
periodic ifr MVFR conditions as well. Timing uncertain.

Marine
Forecaster confidence levels...

low - less than 30 percent.

Moderate - 30 to 60 percent.

High - greater than 60 percent.

Short term through Friday night ...

through tonight...

breezy W SW flow continues. Scattered showers and thunderstorms
possible off the waters off NE ma and S ct. Waves below 4 feet.

Renewed fog forecast along the near-shore s-coast, especially
around nantucket.

Friday through Friday night...

w SW winds through the day dissipating fog. Will shift W nw
overnight ushering in drier air. Gusts below 20 kts. Seas below
4 feet.

Outlook Saturday through Tuesday ...

sat and sun... High confidence.

Mainly quiet boating weather expected. Winds although shifting from
mainly w-sw to the E on sun, should remain below 20 kt. Seas too,
remain low, mainly 3 ft or less on the ocean waters. Only caveat
could be a localized shower or thunderstorm, which may exhibit
stronger winds higher seas locally.

Mon and tue... Moderate confidence.

With a risk for low pres slowly approaching then moving over the
waters seas may build in response to nearly 5 ft on the ocean
waters. Winds are likely to generally remain below small craft
advisory thresholds, but given the risk for higher seas, headlines
may be needed for a time during this period.

Box watches warnings advisories
Ct... Heat advisory until 6 pm edt this evening for ctz002>004.

Ma... Heat advisory until 6 pm edt this evening for maz017>021.

Ri... Air quality ALERT until 11 pm edt this evening for riz001>008.

Heat advisory until 6 pm edt this evening for riz001>004-006.

Marine... None.

Synopsis... Doody sipprell
near term... Sipprell
short term... Sipprell
long term... Doody
aviation... Doody sipprell
marine... Doody sipprell


Weather Reporting Stations
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Airport Reports
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AirportDistAgeWind ktVisibilitySky/WeatherTempDewPtHumidityPressure
Nantucket, Nantucket Memorial Airport, MA168 mi43 minSSW 108.00 miFair76°F72°F88%1011.4 hPa

Wind History from ACK (wind in knots)
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Last 24hrSW10SW8SW6SW6SW5SW6SW6SW8W10W8W7W6W5W6W4W7SW6SW8SW10SW10SW9SW12SW11SW10
1 day agoS5S5CalmS5S5SW6SW4S5SW5S7S10S9SW9S8SW7SW6SW11SW11SW12SW11SW10S10SW10SW8
2 days agoSE6SE6SE7SE6SE7SE6SE5SE7SE4CalmS4--CalmSW3SW4SW6S7SW8S6S6S8S6S8S6

Tide / Current Tables for
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Weather Map and Satellite Images
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IR Satellite Image from GEOS
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Wind Forecast for Boston, MA (18,4,5,8)
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Ground Weather Radar Station Upton, NY
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The information on this web site has not been checked for accuracy. It is for entertainment purposes only and should be independently verified before using for any other reason. There are five sources. 1) Documents and manuals from a variety of sources. These have not been checked for accuracy and in many cases have not even been read by anyone associated with L-36.com. I have no idea of they are useful or accurate, I leave that to the reader. 2) Articles others have written and submitted. If you have questions on these, please contact the author. 3) Articles that represent my personal opinions. These are intended to promote thought and for entertainment. These are not intended to be fact, they are my opinions. 4) Small programs that generate result presented on a web page. Like any computer program, these may and in some cases do have errors. Almost all of these also make simplifying assumptions so they are not totally accurate even if there are no errors. Please verify all results. 5) Weather information is from numerious of sources and is presented automatically. It is not checked for accuracy either by anyone at L-36.com or by the source which is typically the US Government. See the NOAA web site for their disclaimer. Finally, tide and current data on this site is from 2007 and 2008 data bases, which may contain even older data. Changes in harbors due to building or dredging change tides and currents and for that reason many of the locations presented are no longer supported by newer data bases. For example, there is very little tidal current data in newer data bases so current data is likely wrong to some extent. This data is NOT FOR NAVIGATION. See the XTide disclaimer for details. In addition, tide and current are influenced by storms, river flow, and other factors beyond the ability of any predictive program.