NWS Boston/Norton, MA wrote its last area forecast discussion before the first event at Feb 13, 4:09 AM EST, 51 minutes earlier.
Area forecast discussion, Feb 13, 4:09 AM EST, 51 minutes before
Area Forecast Discussion
National Weather Service Taunton MA
409 AM EST Mon Feb 13 2017
.SYNOPSIS...
* Updates to long-term portions only...
Low pressure was intensifying E of Nantucket early this morning.
Snow increasing over E MA, diminishing and becoming showery in
western areas. Rain changing over to some snow in SE MA and S RI.
Otherwise this intense low will bring a threat of damaging winds
across much of the region, especially when combined with snowfall
already on trees and wires. High pressure and cold conditions
prevail Tuesday. Another storm system is forecast Wednesday into
Thursday. A renewed period of cold weather is forecast Friday into
the weekend, however there is a moderating warmer trend into next
week.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
*** Mixed precipitation in southeast sections changes over to
some snow overnight ***
*** Icy roadways as temperatures drop ***
*** Strong winds and numerous power outages Monday ***
1 AM update...
Surface low is rapidly deepening as expected. Now down to
991 mb. It was already east of Nantucket, with winds having
switched to the NW at Nantucket.
Snow was increasing across eastern MA and this will continue
for the overnight hours...then should be confined to the
immediate coast after daybreak. Rain and sleet in southeast MA
and RI should change over to some snow as colder air works its
way southeastward. As temperatures fall to below freezing,
watch out for very icy spots on roadways and sidewalks in
eastern MA, RI, and northeast CT.
Scattered snow showers were working their way across eastern NY
and these could affect CT and western MA overnight... in
association with the upper low.
No changes to our snowfall accumulation forecast at this point.
Still looks like an additional 1 to 4 inches in eastern MA with
locally up to 5 more inches in northeast MA.
We have been receiving many reports of damage from snow-laden
trees. As temperatures fall below freezing the snow on the trees
will ice up. When the high winds develop toward daybreak and
throughout the region on Monday (highest in the east), numerous
power outages are likely to occur. Be alert for low hanging
wires and trees!
Winds... Winds will begin to increase after 3 AM reaching
sustained values of 15 to 25 with gusts 40-50 mph inland and
25-35 mph sustained with gusts 50-60 mph along immediate coastal
areas, especially Cape Ann, Cape Cod and Nantucket. High Wind
Warnings are in effect for RI and eastern MA with Wind
Advisories in northern CT and western/central MA.
Discussion of Marine and Coastal Flood headlines can be found
below.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
Although snowfall will be ending by mid day, the peak of the
winds will be ongoing well into the evening hours across the
area. This will lead to some areas of blowing snow where the
snow was the fluffiest. However, more importantly is the
combination of these strong winds (see above for expected wind
speeds) and the snow laden trees yielding a higher risk for tree
damage and power outages even well after the snowfall ends.
Therefore, both wind and marine headlines will linger much
longer.
&&
.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
*/ Highlights...
- Dry and chilly weather for Tuesday
- Another storm system for Wednesday into Wednesday night
- Seasonable conditions for the end of the week
- Warming trend into next week
*/ Overview...
Indications of a pattern shift pointing towards a moderating warmer
temperature trend into late February. Trying to make sense of it,
perhaps a result of what appears to be cyclonic wave breaking over
the CONUS related to the phase shift of the MJO (7 to 8 to neutral)
or rather the stratospheric polar low shifting from N Canada into N
Asia with more the better region of cross-polar flow situated over W
Europe. Either which way signals of +2 standard deviation H5 heights
along with a considerable H85 temperature anomaly, up to +20C, over
the N-Central CONUS into Canada stretching NE across our area with
time. No surprise to see above-average temperature CPC forecasts out
for 6-10/8-14 days. Keep in mind that's averaged out for the period.
More surprising though is the 3-4 week above average forecast. The
end of winter? Not ready to think so quite yet. Just looking at the
latest forecast teleconnections, purely speculating, it would appear
into late-Feb that the NAO/AO/PNA become fairly neutral. Perhaps we
see a return of the EPO/WPO becoming the dominant influence of the
downstream pattern. If either turn negative, climatologically the NE
CONUS falls beneath a more of a troughing pattern and below average
temperatures. Just thinking off the cuff. In the meantime, focusing
on next week into the early half of the following week. Details and
targets of opportunity noted below.
*/ Discussion...
Tuesday...
Quiet weather. Dry. Ridging pattern in place and a region of greater
subsidence between the exiting Sunday / Monday storm system and the
approaching storm system for Wednesday. Overall light winds. Perhaps
some scattered to broken pancake-like cloud decks associated with a
fairly-flat mid level disturbance skirting across the region. Still
a chilly airmass aloft and a fairly deep snow pack across the area,
going to be a chilly day with highs up around the low 30s.
Tuesday night through Wednesday night...
Continued uncertainty. Evaluating the 13.0z forecast guidance suite
there remain subtle differences in how the models handle the morph-
ology of cyclonic troughing of N-stream energy across the region.
Subsequent variations on strongest QG-forcing beneath broad upper-
level diffluence which in turn alter low to mid level features, for
example, location of the H85/7 lows as well as the attendant mid-
level dry slot.
Wanting to make a decision as to model preference, am leaning more
towards a blend between the 12.12z and 13.0z EC with the double-
barrel surface low and parent frontal boundaries slowed up against
colder air and a recent deep snow pack over E/SE NH and up across
Maine. Greater confidence of the energy transfer from the Great
Lakes region over Appalachia into regions of greater baroclinicity
in the Gulf of ME will occur more closer in proximity to the N MA
border rather than over VT, NH and S ME. Not absolutely clear but
perhaps we'll see an inverted trough / norlun trough setup.
So going into detail top-down, cyclonic troughing, QG-forcing, and
upper level diffluence invoke cyclogenesis from the N Great Lakes
region into the Gulf of ME. With amplification of conveyer belts,
anticipate mild above-freezing H925 air associated with a convergent
nose of H85-925 S/SW-flow ascending shallow cold air maintained
initially by interior NE-flow Tuesday night into early Wednesday. An
over-running setup, depending on thermal profiles, looking at a
mixed precipitation event, however rather light given moisture
origin is more continental rather than sub-tropical / maritime.
Precipitation eroding as deeper surface low pressure develops over
the Gulf of ME with drier air wedging in aloft during late Wednesday
into Wednesday night. However, cold air advection proceeding, lapse
rates steepen considerably up as high as H7. Instability along with
continued ascent through the column with mid to upper level features
sweeping the region, can not rule out snow squalls as mentioned by
the previous forecaster, however, greater focus is upon regions of
significant low level convergence along a potential inverted/norlun
trough the later half of Wednesday into Wednesday night collocated
with aforementioned steep lapse rates, instability, and low-level
moisture. Such a trough may develop close to NE MA however consensus
of signals has it mainly W-E across ME.
Tough to nail down snowfall amounts. CIPS analogs suggest a general
2-4" event, mainly across the interior within the I-95 corridor, if
anything heavier, over the N/W high terrain within colder air. Yet
forecast amounts half that, a general coating to 2" event with the
higher amounts over the N MA border, especially NE MA. Confidence is
low given the uncertainty noted earlier. Could end up less. What
we're considering here is a more continental-airmass associated with
the N-stream ultimately deepening while becoming intertwined with
warm and dry conveyer belts. Both precip-type and column drying are
an issue that play into snowfall totals. The specifics difficult to
nail down. Again, a low confidence forecast. The associated energy
as noted earlier is way up in the northern portions of the Northwest
Territories of Canada. Poorly sampled, even by satellite. Run-to-run
model guidance has exhibited inconsistencies with heights.
Blustery conditions late Wednesday into Wednesday night given the
low deepening offshore and steep lapse rates. Perhaps some initial
blustery S winds as the low transitions while deepening across New
England. Greater confidence of strong NW flow behind the system as
it continues to deepen across the Gulf of ME with high pressure
building in from the W, albeit the couplet of pressure falls/rises
is not as robust as the system presently ongoing, seemingly though
from consensus of latest forecast guidance.
Thursday onward...
Preference towards ensemble means with respect to trends. NE CONUS
finds itself within the NW flow regime associated the backside of
the H5 trough and within the NE periphery of the +2SD ridge over the
N-Central CONUS. Thursday into Friday there is the possibility of
some shower activity given the cyclonic flow, through which weak
impulses rotate, and continued steep low level lapse rates. Maybe
another chance of showers along a lifting warm frontal boundary
Saturday into Sunday ahead of a ridge of high pressure shifting E.
Will forecast quiet weather for now with a moderating temperature
trend towards seasonable to above-seasonable conditions brought
about by more S flow with time.
&&
.AVIATION /09Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06z update...
Overnight...Moderate confidence.
IFR-LIFR in a wintry mix of precip across RI and southeast
MA...changing to some snow. Snow elsewhere, ending in western MA
and CT by 10Z. Areas of MVFR in northern CT overnight. Winds
shift to NNW and will increase dramatically with gusts over 50kt
possible eastern MA especially Cape Ann to Cape Cod to
Nantucket towards 12Z.
Monday...
IFR-LIFR early gradually improves to MVFR however very strong to
damaging NNW winds 50+ kt possible Cape Ann to Cape Cod to
Nantucket. A period of moderate to heavy snow may continue 12z-
16z from Cape Ann to Cape Cod. Conditions slowly improve
during the afternoon from west to east.
KBOS TAF...Moderate confidence in TAF.
Mix of SN and RA back to SN after 06Z, with periods of SN/+SN
possible from 08Z thru 13Z...possibly 15Z. Winds shift to the NW
after 06Z, becoming NNW and increase in speed to between 35-45
kt at times during the day Mon (a few gusts near 50 kt can't be
ruled out). Categories are likely to be predominantly IFR/LIFR
thru the morning, improving to VFR around 18Z.
KBDL TAF...Moderate forecast confidence.
IFR conditions with -SN lingering during the evening, and may
have brief periods of -FZRA until about 03Z. As winds shift to
the NW towards 12Z tomorrow they will increase with 30-40 kt
gusts continuing thru the day. Also, a chance for -SN during the
morning hours, but the main issue will be the wind with VFR
conditions expected during the day.
Outlook /Tuesday through Friday/...Moderate confidence.
Tuesday...
VFR. Breezy NW winds diminishing. Perhaps some SCT low-end VFR cigs.
Wednesday into Wednesday Night...
Potential -SN with IFR-LIFR impacts. Mixing with -RA for the S/SE
terminals. Light winds during the event turning out of the NW and
becoming blustery as -SN concludes.
Thursday and Friday...
VFR. Initial breezy NW winds diminishing. SCT-BKN MVFR to low-end
VFR cigs with perhaps some SHSN/SHRA.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
*** Dangerous Coastal Storm impacts the waters Tomorrow ***
No major changes to marine headlines or issues through tomorrow.
Overnight...
Low pressure was intensifying east of Nantucket and by 7 AM,
a sub-980 mb low is expected. Gale force winds late tonight
approach storm force by morning. Rain and snow limit vsby.
Monday...
Powerful/dangerous sub-970 mb low over Georges Bank! NNW winds
50+ kt likely along with rapidly building seas. Snow heavy at
times lowering vsby. Strongest wind and largest seas over
eastern MA waters.
Outlook /Tuesday through Friday/...Moderate confidence.
Tuesday...
Breezy NW winds diminishing with time. Falling below 25 kts into
Tuesday morning. Seas undergo a period of subsiding initially 8 to
12 feet on the outer waters to 5 to 6 feet by Wednesday morning. The
threat of freezing spray diminishing early on.
Wednesday into Wednesday night...
Rain forecast. Breezy S winds Wednesday turning out of the NW and
remaining breezy overnight. Still uncertainty with this forecast as
a storm center traverses from the Great Lakes region into the Gulf
of ME expected to strengthen. Wind and wave action amplifying in
response, though the magnitude is not yet clear. Right now, near
gale force gusts possible along with waves building 8 to 10 feet on
the outer waters.
Thursday into Friday...
NW winds continue with the potential of gusts up to 25 kts. With
colder air initially early Thursday there is the threat of freezing
spray over the E waters. Waves 5 to 8 feet on the outer waters a
good chunk of the forecast timeframe.
&&
.TIDES/COASTAL FLOODING...
This is a somewhat complex scenario for the Monday early afternoon
high tide given wind direction, speed, wave height and fetch, and
pressure rise factors. We have not changed our thinking too
dramatically over the past 24 hours. We are anticipating minor to
moderate coastal flooding along exposed NE and E facing shorelines
from Salisbury to Plymouth and the Nantucket Harbor area. From
Sandwich to Eastham, we anticipate widespread moderate coastal
flooding with a risk of pockets in the moderate to major coastal
flooding range. Will break out reasoning and potential impacts by
location below:
Salisbury to Plymouth... Minor to moderate coastal flooding possible
with greatest impact along the exposed ocean shorelines such as
Hull...Scituate...Marshfield, and Duxbury. Although the wind
direction is expected to be NNW or even NW, waves of 15 to 20 feet
just offshore may compensate for a partial offshore component of the
wind. Some wave overwash is possible along the exposed shoreline,
and significant erosion may occur Salisbury to Rockport, including
and especially Plum Island, as well as Hull to Plymouth. We went
with a warning rather than advisory for the exposed shorelines to be
safe given what we think will be very robust wave action.
Sandwich to Eastham... This is the area of greatest concern.
Moderate coastal flooding is expected with pockets of moderate to
major coastal flooding possible due to a combination of a potential
surge around 3 feet and waves around or even slightly higher than 15
feet in Cape Cod Bay. Erosion along this stretch of coastline may be
severe and some low spots may have 3 to 4 feet of inundation. A few
of the most vulnerable homes and other structures could be damaged
by wave action along this stretch of coastline. What is significant
for this stretch of coastline is that a NNW wind with gusts near 60
mph leading up to the high tide will be aligned with a significant
fetch channeling waves generated over the Gulf of Maine into Cape
Cod Bay and right up to the shoreline. The eventual severity of the
event will depend upon direction/speed of the surface wind flow, how
close to the coast the low pressure center will be, and to what
extent pressure rises may dampen the surge. This could be a
dangerous situation for this particular stretch of coastline.
Ocean side of Cape Cod and the East Side of Nantucket...The issue
for these areas will likely be the potential for severe erosion from
waves of 20 to 25 feet approaching the shoreline.
Nantucket Harbor area...A surge of 2 to possibly 2.5 feet held in by
a NNW wind potentially gusting near 60 mph will likely cause minor
to moderate coastal flooding with low areas possibly experiencing 1
to 3 feet of inundation.
Later High Tide Cycles...We anticipate the potential for minor
coastal flooding in a few ocean exposed shoreline areas for one or
two additional high tide cycles due to a significant lingering
swell. The ETSS guidance is particularly aggressive while the ESTOFS
guidance goes negative. We plan to hold off on any headlines for
these later high tide cycles until we get past the Monday early
afternoon event.
Guidance...As is typically the case, we have gone above both wave
and storm surge deterministic guidance with the SWANGFS and ETSS
guidance being the best starters but still probably a little too
low. We think that both the ETSS and ESTOFS surge guidance may be
significantly too low for Nantucket harbor. Experimental wave run up
guidance is showing a risk of erosion and some overwash at the Hull
and Scituate hot spots, reflecting our wave forecast. We appreciate
continued special support from the National Hurricane Center on
experimental surge and inundation guidance, which have
factored into our latest thinking.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Wind Advisory until 7 PM EST this evening for CTZ002>004.
MA...Wind Advisory until 7 PM EST this evening for MAZ002>004-
008>012-026.
High Wind Warning until 7 PM EST this evening for MAZ005>007-
013>024.
Coastal Flood Warning from 11 AM this morning to 4 PM EST this
afternoon for MAZ007-019-022-024.
Coastal Flood Advisory from 11 AM this morning to 3 PM EST
this afternoon for MAZ015-016.
Winter Storm Warning until 1 PM EST this afternoon for
MAZ005>007-014.
RI...Wind Advisory until 7 PM EST this evening for RIZ008.
High Wind Warning until 7 PM EST this evening for RIZ001>007.
MARINE...Storm Warning until 11 PM EST this evening for ANZ231-232-250-
251-254>256.
Storm Warning until 7 PM EST this evening for ANZ230-233>235-
237.
Gale Warning until 1 AM EST Tuesday for ANZ236.
&&
SYNOPSIS...Sipprell/GAF
NEAR TERM...Doody/GAF
SHORT TERM...Doody
LONG TERM...Sipprell
AVIATION...Doody/Sipprell/GAF
MARINE...Doody/Sipprell/GAF
TIDES/COASTAL FLOODING...Thompson