Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Taunton Massachusetts
653 PM EDT sun Mar 9 2014
an active polar jet stream will bring a few bouts of clouds and snow
showers to the region Monday morning and again late Monday night.
Cool temperatures will be the theme early this period but then the
polar jet lifts northward allowing milder weather to overspread
southern New England Tuesday with temperatures rising into the
50s! A winter storm is likely Wednesday into Thursday...but the
details of how much rain or snow will fall is uncertain. Cold and
dry weather follows...but a warmup is possible next weekend.
Near term /until 6 am Monday morning/...
650 PM update...
Satellite loop shows high clouds streaming into southern New
England this evening...but will remain thin enough early tonight
to allow for good radiational cooling conditions. Adjusted
temperatures to allow for more of a temperature drop before
thicker clouds arrive...especially across interior. Otherwise
forecast in good shape and no changes made.
Overnight...latest water vapor satellite imagery clearly shows a
robust northern stream short wave trough-pv anomaly moving across
Ontario this afternoon. This feature races southeast late tonight
with its moisture and lift entering northern Massachusetts and southwest New Hampshire.
This will result in light snow showers overspreading this area after
06z and especially toward 09z. For the remainder of the
region...CT/RI and southeast Massachusetts should remain dry with just
increasing clouds ahead of approaching short wave trough. Not as
cold given increasing clouds and warm advection pattern ahead of
Short term /6 am Monday morning through Tuesday/...
Short wave trough moves across the region during the morning. Good
model agreement on a lack of lift and deep layer moisture with this
feature...as all model guidance only offering a few hundreds to 0.05
inches of quantitative precipitation forecast. Strongest lift occurs across northern New England.
Thus only expecting a dusting to perhaps low probability of up to an inch
of snowfall in a few spots. Some areas may just see some flurries.
This quantitative precipitation forecast will also be spread out over a 6 hour window from about 09z
to 15z. Therefore not expecting an inch of snow in a short period of
time. Hence should be little if any impact on the morning commute.
For the remainder of the day tsections suggest lots of low and middle
level moisture linger. However some weak short wave ridging develops
across the area behind the departing jet impulse. So a few breaks of
sunshine are possible...but clouds will likely dominant. Not much
wind tomorrow along with temperatures climbing to near seasonal levels...
u30s to l40s.
Another northern stream short wave approaches from the northwest.
Models suggest stronger synoptic scale forcing with this feature
than tonight/S. However it does track north of the region. Best
chance of snow showers late Monday night will be over northeast Massachusetts and
southern New Hampshire. A minor accumulation possible. Elsewhere just some
Behind departing short wave...ridging develops across the northeast
in response to digging trough upstream. This results in a warmer
airmass overspreading the region. This combined with west-northwest wind
downsloping low level flow will yield a mild afternoon for the
region. In fact could be a real nice day with temperatures well into the
50s. Model soundings not showing much blyr mixing but this is a
typical bias. Given surface pressures over the area only around
1000mb /weak subsidence inversion/ coupled with strong March
sun...blyr should be fairly deep promoting good mixing along with
west-northwest downsloping surface winds. 2 meter temperatures from the European model (ecmwf) are
the warmest of the guidance and leaned in this direction. MOS may be
too cool given its still operating on cool season equations through
3/31...then switching to warm season equations thereafter.
Long term /Tuesday night through Sunday/...
* still need to work out details of winter storm Wednesday into Thursday.
* Mainly dry/seasonable next weekend.
Wednesday into Thursday...moderate confidence.
Starting to see some trends in ensembles and operational models...
and although they are coming into better agreement with their
surface and upper features...it is still early to lock onto one
solution just yet. It is important to note Pacific short wave will
not reach West Coast until Monday morning...so its interaction with
northern stream energy is still in somewhat of a doubt in day 3-4
time frame until it becomes better sampled.
Cstar ensemble sensitivity plots indicate northern stream will be
more of a driver with this system...so possibilities still range
from a trend even farther north if upper trough sharpens more...or
farther S and offshore if it remains more progressive. There are
also fairly significant timing differences as well with some of
guidance having most of precipitation Wednesday and early Wednesday night...as
opposed to others Wednesday night into Thursday. Forecast continues to utilize
blend of model guidance to dampen out these differences.
That said...there has definitely been more of a northern trend with
track of surface low and there is rather tight clustering among
ensemble means and operational runs. Forecast is based upon track
just off S coast /near Cape Cod and islands/ which would mean more
in way of rain Wednesday and early Wednesday night except for higher elevations
of western/north central Massachusetts and SW New Hampshire. There is plenty of cold air
lurking just to our north...and this should surge southward late Wednesday
night and Thursday morning as low heads to Gulf of Maine. Therefore we
expect a change to snow from northwest to southeast during that time...giving
potential for accumulating snow all way down to S coast...Cape Cod
and islands /although how much is in question/. There are also hints
of wrap-around snows as system departs Thursday morning...but models seem
to be backing off on strength and resulting amount of precipitation.
We will need to see if these trends continues before locking in
further...but for now it appears that higher snow accumulations will
be confined to locations north of Mass Pike and outside I-495...
especially across higher elevations. Cips analogs /based off GFS/
help put this event in context. Probability of 6 or more inches of
snow /based upon top 15 analogs/ is highest roughly along and north of
Route 2 corridor.
Friday through sun...moderate confidence.
High pressure builds over northeast Friday...but presence of cold air
aloft should result in at least diurnal cloudiness and perhaps
scattered rain/snow showers. Warm front should lift through Sat which
will bring milder airmass...before cold front brings a return to
seasonable temperatures sun. Upper pattern looks only to support
widely scattered rain/snow showers with frontal passage.
Aviation /00z Monday through Friday/...
low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Short term /through Monday night/...high confidence.
Tonight...MVFR ceilings develop across northern Massachusetts and southern New Hampshire
toward 09z along with scattered snow showers. Elsewhere VFR and
Monday...areas MVFR ceilings in scattered snow showers 09z-15z. Snow
accumulations from a dusting to perhaps an inch. Improvement to
VFR late morning and afternoon.
Monday night...marginal MVFR-VFR in another round of snow showers.
Minor accumulation possibly especially northeast Massachusetts and southern
Tuesday...VFR and dry along with a modest northwest wind.
Kbos terminal...high confidence in taf.
Kbdl terminal...high confidence in taf.
Outlook...Tuesday night through Thursday...
Tuesday night...moderate confidence. VFR ceilings at or above 080.
Wednesday into Thursday...moderate confidence. IFR in rain and snow...with snow
more likely across western/north central Massachusetts and SW New Hampshire Wednesday. Rain changes
to snow Wednesday night into Thursday morning from northwest to southeast before ending. Low level wind shear
possible Wednesday night along S coast...Cape Cod and islands due to
southerly low level jet of 50-60kt. Northwest wind gusts to 30kt possible
Friday...moderate confidence. VFR.
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
diminishing west-northwest wind and becoming SW toward morning. Leftover east-southeast
swells diminish as well. Snow showers possible toward morning.
snow showers possible early...then good visibilities. Light SW winds.
modest SW wind with possibly snow showers northern waters.
front moves offshore with a modest west-northwest wind overspreading the
waters. Good visibility and dry weather.
Outlook...Tuesday night through Friday...
Moderate confidence through the period.
Diminishing winds and seas Tuesday night as high pressure moves off the
Low pressure is forecast to strengthen Wednesday/Wednesday night as it tracks
from middle Atlantic to Gulf of Maine Thursday morning. Still plenty of
uncertainty in its track with envelope of possible solutions ranging
from S coast Rhode Island/Massachusetts to southeast of Nantucket...which would impact
conditions on coastal waters. More northern track would bring period
of strong S winds Wednesday/Wednesday night while more offshore track would
result in somewhat weaker east/NE winds.
Marine...Small Craft Advisory for hazardous seas until 11 PM EDT this
evening for anz250-254>256.