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Area forecast discussion 
National Weather Service Taunton Massachusetts
635 PM EST sun Nov 29 2015

high pressure over Quebec Sunday afternoon builds slowly south into
the Gulf of Maine yielding dry and chilly weather through Monday
night. The exception will be tonight and early Monday over southeast
Massachusetts where scattered snow showers are expected. A storm
coming out of the western USA will bring rain to New England later
Tuesday into Wednesday. There is a low risk of freezing rain at the
onset in northwest Massachusetts. High pressure then brings dry and
seasonable weather for the late week.


Near term /until 6 am Monday morning/...

630 PM update...

No major changes to the forecast for this evening. Temperatures
continue to drop across the interior thanks to radiational
cooling. Another chilly night with lows in the teens to middle 20s.
Across the eastern Seaboard will see ocean effect clouds keeping
temperatures warmer...especially with the northeast flow off the warmer water later
tonight. Appears that there is still the chance for ocean effect snow
across the immediate East Coast. Only change that is Worth noting
is the middle-level deck across up state New York and Vermont...which continue
to move south. May increase cloud cover for northwest mass. Have
increased sky cover to account for this latest trend. Otherwise
forecast remains on track.

Previous discussion...
short wave trough over Quebec Sun afternoon moves southeast into the
Maritimes. Behind this trough cold air advection increases across southern New
England with h850 temperatures falling from 0c Sun afternoon to -10c by 12z Monday.
This will yield lows mainly in the 20s overnight. Dry weather
prevails except across southeast Massachusetts as cold air is delivered on NE
winds as 1034 mb high advects into Maine overnight.

This setup will yield ocean effect snow showers across southeast Massachusetts.
Increased probability of precipitation from model guidance given GFS/NAM/rgem/arw and nmm
all generate some light quantitative precipitation forecast in this area. Always difficult to
project exact quantitative precipitation forecast in these events given the mesoscale aspect.
Despite low level lapse rates /SST to top of blyr/ on the order of
17c/18c ocean induced convective available potential energy peak at around 300j/kg and ncape
0... is below the desired minimum threshold of 400 j/kg and
0.18 ncape. Nevertheless expecting scattered snow showers mainly
from 05z to 14z across southeast Massachusetts. While ocean temperatures are near 50
temperatures aloft /-5c to -6c at 925 mb/ tonight are very cold and should
support mainly snow showers. Not expecting much if any snow
accumulation by can/T rule out a dusting or a decorative coating in
spots with coastal Plymouth County likely the greatest risk for any
minor accumulation.


Short term /6 am Monday morning through Monday night/...
Monday ...

Scattered snow showers likely continue in the morning across
southeast Massachusetts. Elsewhere dry weather prevails but lots of
ocean effect strato-cumulus across the entire region as moisture becomes
trapped beneath inversion. Thus limited sunshine tomorrow. In
addition chilly airmass associated with 1032 mb high over the Gulf
of Maine will limit blyr mixing given low subsidence inversion. This
will result in highs tomorrow colder than normal with maxes from
only the u30s to l40s. One of the few colder than normal days this

Monday night...

Decreasing clouds will give way to a chilly night as surface ridge
lingers over the area. Thus light winds and a dry airmass results in
another night with temperatures in the 20s. Any precipitation from the next
weather system should hold off until sometime Tuesday.


Long term /Tuesday through Sunday/...

* precipitation overspread the region on Tuesday lasting into Wednesday night
* dry and seasonable temperatures likely next Thursday/Friday


12z model guidance as well as their ensembles are in good synoptic
agreement for this forecast. However differences arise in the
mesoscale especially for the middle-week system. An approaching low
pressure system will move across the Great Lakes and swing a warm
front through the area late Tuesday followed by a cold front
Wednesday. This could bring some appreciable rain to the region for
the mid-week. As mentioned there appears to be some guidance issues.
Biggest question is surface temperatures at the onset of precipitation on Tuesday.
Also have low confidence on where the axis of heavy precipitation will set
up as guidance pushes the developing coastal low either over the
cape /NAM and ec/...over 95 corridor /UKMET/ or the outlier...south
of the benchmark /GFS/. Otherwise the ec is faster in precipitation
compared to the GFS/NAM but is align with the UKMET and CMC. Because
of the model spread...have a low confidence in the middle-week system.
Behind this system expect strong high pressure to remain over the
eastern Continental U.S. Through next weekend.


Tuesday into Wednesday...lower confidence.

Warm front will begin to approach from the southwest on Tuesday.
This front will warm the middle-levels above 0c...however at the
surface especially with such a cool start on Tuesday morning...surface
temperatures will be close to 32f. Most of the guidance keeps precipitation from
coming to the region Tuesday morning...with a better shot during the
15-18z hours. However if the atmosphere decides to moisten up
earlier and precipitation falls in the morning then we could see some
freezing drizzle/rain at the onset of precipitation especially across the
western zones of Massachusetts and CT. There are also some indications that the
CT valley may experience cold air they may struggle to
warm up on Tuesday as well.

Coastal low develops across the Delaware-Maryland-Virginia Tuesday and move up the
eastern Seaboard late Tuesday afternoon/evening. As mentioned earlier
believe the GFS is an outlier keeping the coastal south of the
benchmark while the remainder of the model consistent is near or
over the cape. Regardless appears that precipitation will over spread the
region late Tuesday morning into the afternoon hours. As the surface
low deepens...we could see some locally heavier downpours across
portions of the region Tuesday night into Wednesday morning. In fact...
precipitable water values increase 1.5 inches which is 2-3 Standard deviations
above normal. This helps support the potential for heavier

Guidance shows that the surface warm front will push through on Wednesday
which will allow for a warm up in temperatures. As mentioned by previous
forecaster...could be a lull in precipitation before second round starts up
when the cold front passes through from west to east late Wednesday into
Wednesday night. We could see a few show showers on the back side across
the Berkshires Wednesday night. Although there is still a lot of
uncertainty anticipate a damp Tuesday and especially Wednesday.

Thursday into Saturday...high confidence.

Dry weather will prevail for Thursday and especially Friday into
Saturday. Only issue is cold core low/cyclonic flow will remain over
the region on Thursday morning. This could trigger a few snow
showers across the northwest portion of mass with the higher terrain
having the best shot. As the low moves towards the Maritimes...a
secondary cold front will swing through increasing westerly winds to
20-30 miles per hour. Winds should begin to decrease after sunset on Thursday.

Thursday into Saturday temperatures will be seasonable with highs
into the middle to upper 40s each day.


Aviation /00z Monday through Friday/...
forecaster confidence levels...

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

Short term /through Monday night/ ... high confidence.

Tonight ...

Overall VFR and dry weather. The exception is across southeast Massachusetts
including Cape Cod and the islands where MVFR ceilings will become
common along with scattered snow showers. Not expecting much if
any snow accumulations...possibly a dusting. NE winds increase to
15 to 20 knots with a few gusts up to 25 knots possible.

Monday ...

Marginal MVFR/VFR ceilings with scattered snow showers possible in the
morning across southeast Massachusetts. Low risk a few snow showers could
come close to bos/Logan Monday am. Gusty NE winds over Cape Cod and
islands early diminish quickly. Light winds elsewhere.

Monday night ...

Any MVFR ceilings early give way to VFR. Dry weather and light winds

Kbos terminal ... VFR with MVFR ceilings moving in toward 12z. Low
risk of a few snow showers accompanying the MVFR ceilings. North wind
becomes NE late tonight. High confidence in taf.

Kbdl terminal ... VFR with patchy MVFR ceilings beginning Monday afternoon.

Outlook /Tuesday through Friday/...

Tuesday into Wednesday...moderate confidence. VFR to start with
conditions quickly dropping into approaching rain system. Could see
MVFR/IFR ceilings with visibilities dropping within heavy rain through most of
this period.

Thursday and Friday...high confidence. VFR with gusty westerly winds
near 20-30 kts on Thursday. SW winds around 10 kts on Friday.


forecaster confidence levels...

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

Tonight ...

North wind becomes northeast and increases to 15 to 20 knots with a few
gusts to 25 possible. Scattered snow/rain showers develop over the
waters near Cape Cod and Nantucket.

Monday ...

NE wind 15 to 20 knots in the morning slackens as high pressure builds into
the Gulf of Maine. Seas will slowly subside as well. Scattered snow
showers early will taper off by midday.

Monday night ...

Light winds as high pressure remains over the Gulf of Maine and extends
westward into New England.

Outlook /Tuesday through Friday/...

Tuesday into Wednesday...moderate confidence. High pressure over the
waters for much of Tuesday. However approaching warm and cold front
will switch the winds to the south and eventually in a westerly
direction by Wednesday night. Seas will build in response and could see
low visibilities in heavy rain and fog. Small Craft Advisory will be needed.

Thursday...high confidence. Winds will increase out of the west
keeping seas up through Thursday. Wind gusts will breach between 25-
35 kts. Low confidence on gales. Seas will remain up with outer
waters close to 8-10 feet.

Friday...high confidence. High pressure will build allowing for seas
and winds to relax below Small Craft Advisory.


Box watches/warnings/advisories...
Rhode Island...none.
Marine...Small Craft Advisory until 1 PM EST Monday for anz231-250-251.
Small Craft Advisory until 4 PM EST Monday for anz254>256.


near term...nocera/dunten
short term...nocera
long term...dunten

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