Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Taunton Massachusetts
225 PM EST Wednesday Mar 4 2015

Synopsis...
weak low pressure will push along the stalled front with another
round of snow tonight into Thursday. High pressure will build in
for Friday through this weekend...bringing dry conditions with
colder than normal temperatures. A weakening front may bring some
light snow showers on Monday.

&&

Near term /through tonight/...
225 PM update...

* trending forecast a bit lower for snowfall totals
* Winter Storm Warning remains posted for islands...converting
watch to Winter Weather Advisory along S coast
* northern extent of snow remains questionable

Radar mosaic shows patches of light rain /or sprinkles/ heading
along S coast this afternoon. Expect this to continue through this
evening as additional activity across PA/New Jersey heads in our
direction. Some breaks or thinning in cloud cover has allowed
temperatures to rebound this afternoon into 30s and 40s...a
testament to early March sun which we often underestimate this
time of year. In fact it is more reminiscent of Spring as coolest
temperatures are along S coast...Cape Cod and islands where fog/
low clouds prevail.

Cold front continues to make slow progress through southern New
England and will head off S coast tonight. This will set stage for
our next round of snow as column cools from northwest to southeast during night.
Confidence is medium at best given concerns about how fast this
cooling takes place near S coast which affects timing of
changeover to sleet/snow as well as how much can accumulate.

Our thinking is change to snow will occur from Hartford to Boston
between 9 PM and 11 PM...Providence to Plymouth closer to
midnight...and on cape/islands around 2 or 3 am. Cross sections
show potential for decent burst of snow overnight...which is
mainly focused S of Mass Pike /and especially near S coast/.

Consensus of 12z models have nudged things a bit farther S from
earlier runs...especially high-res models which show sharp cutoff
to northern edge of precipitation shield which has to be taken
into consideration. 12z European model (ecmwf) remains a bit farther north with its
axis of quantitative precipitation forecast which prevents US from taking everything too far
offshore. In coordination with wpc and neighboring offices... we
will nudge snowfall totals down a tad with focus of highest
amounts along S coast/Cape Cod and especially islands.

We will maintain Winter Storm Warning for islands /4 to 7 inches/.
Our highest confidence is on lower end of that range based upon
model consensus. We will convert Winter Storm Watch on S coastal
Rhode Island/Massachusetts to Winter Weather Advisory /2 to 5 inches/ with higher
totals focused on coast and Cape Cod and lower end of range closer
to Providence.

There are several red flags to consider against going with overly
high amounts including being able to overcome initially warm low
level temperatures...continued southward nudge on models and fact
that best lift in maximum snow growth zone is limited to late tonight
and early Thursday morning near S coast. Fact that high-res models show
little if any snowfall north of Mass Pike makes sense given we expect
a sharp gradient on northern edge of system...so if anything
snowfall totals along and north of Mass Pike may be a bit overdone.

Note probabilistic snow forecasts will show rather large range
/ie few inches to nearly a foot on Nantucket/ due to uncertainty
in temperature profile and to some degree how far close or
offshore does axis of heaviest quantitative precipitation forecast lie. This leads US to play
forecast more conservatively due to reasons mentioned above.

For those wondering about bos snowfall record...we need 1.9 inches
to tie 1995-96. Our latest forecast has about 0.7 inch at bos.

&&

Short term /Thursday through Thursday night/...
focus for steadier snowfall will be over southeast New England Thursday
morning with rapid drying from northwest bringing clearing to interior by
afternoon. Expect additional 2 to 4 inches during day across S
coastal Rhode Island/Massachusetts and Cape Cod/islands with less than inch as far north as
Mass Pike. Definitely colder day ahead with highs only in 20s
except near 30 on cape and islands.

Clearing sets in across all of region Thursday night as system heads
farther out to sea and high pressure builds in. Another shot of
bitterly cold air arrives with lows from about 5 below to 5 above
across interior to teens closer to coast.

&&

Long term /Friday through Tuesday/...
* high pressure builds in Thursday night...passing S Friday
* moisture starved cold front moves through this weekend
* uncertain forecast early next week

Models are in fairly good agreement going into the weekend. There
are some minor discrepancies in timing of a cold front through the
weekend. Then next week they diverge a bit...with European model (ecmwf) attempting
to bring a coastal low up over the benchmark Tuesday and the GFS
bringing in a strong high pressure just south of southern New
England. At this point...will opt for a blend of available guidance
for the weekend into early next week to take care of some of the
timing errors.

Friday...the high pressure becomes suppressed to the south as low
pressure moves into Quebec. This will keep chilly
temperatures...well below normal for early March... in place for
southern New England.

This weekend...a shortwave pushes low pressure through Quebec...
allowing a cold front to move through southern New England. At this
point...this frontal passage appears to be fairly moisture starved
so little if any precipitation will accompany this front. Temperatures
moderate a bit but remain well below normal.

Early next week models diverge with radically different solutions
for southern New England. Given the time frame...this is not
completely unusual...so will take either model with a grain of salt
at this time. Regardless of the model...it does look like
temperatures continue to moderate into next week.

&&

Aviation /19z Wednesday through Monday/...
forecaster confidence levels...

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

Short term /through Thursday night/...moderate confidence.

MVFR/IFR persists along S coast...Cape Cod and islands through
this evening with isolated light showers. Ceilings may improve
slightly after 00z but overall trend is to maintain persistence in
conditions. VFR ceilings elsewhere.

MVFR/IFR spreads north in light snow tonight...probably as far north as
bdl-sfz-bos mainly due to visibility. Light rain changes to sleet and
snow closer to S coast after 06z where LIFR expected through
daybreak Thursday. VFR ceilings farther north and west.

Conditions slowly improve Thursday from northwest to southeast...with Cape Cod and
islands last to improve 16z-20z.

Snow accumulations...
bos/baf/bed/orh...1 inch
bdl/pvd...2 inches
fmh/hya...3-4 inches
ack...5-7 inches

Kbos taf...high confidence. Coordinated taf with cwsu zbw.

Kbdl taf...high confidence.

Outlook...Friday through Sunday...

Moderate confidence. Mainly VFR through this period. Brief MVFR
conditions are possible Thursday night as snow comes to an end.

&&

Marine...
forecaster confidence levels...

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

Short term /through Thursday night/...moderate confidence.

Maintaining Small Craft Advisory on outer waters and Block Island/Rhode Island sounds
primarily due to seas through Thursday or Thursday night.

Cold front slowly drops S tonight with wind shift to northwest and
possibly a few gusts to 25 knots. Spotty light rain will give way to
sleet and snow late tonight...with lowest visibility from midnight into
Thursday morning.

Snow should mainly affect S coastal waters Thursday before heading
offshore Thursday night. High pressure building in to region may bring
period of 25kt northwest wind gusts Thursday night...mainly on outer waters.

Outlook...Friday through Sunday...

High confidence. Winds and seas slowly diminish Friday as high
pressure builds over the waters. They then increase but only
modestly over the weekend as a cold front approaches then crosses
the waters. Small craft advisories will likely be necessary on the
outer waters for a portion of this time.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...Winter Storm Warning from 7 PM this evening to 7 PM EST
Thursday for maz023-024.
Winter Weather Advisory from 7 PM this evening to 7 PM EST
Thursday for maz020>022.
Rhode Island...Winter Storm Warning from 7 PM this evening to 7 PM EST
Thursday for riz008.
Winter Weather Advisory from 7 PM this evening to 7 PM EST
Thursday for riz003>007.
Marine...Small Craft Advisory until 6 am EST Friday for anz235-237-250-
254>256.
Small Craft Advisory until 3 PM EST this afternoon for anz251.

&&

$$
Synopsis...Belk/jwd
near term...jwd
short term...jwd
long term...rlg
aviation...Belk/jwd
marine...Belk/jwd

National Weather Service Glossary of Abbreviations