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FXUS61 KBOX 281955

Area Forecast Discussion
National Weather Service Taunton MA
355 PM EDT Sun May 28 2017


Isolated spot showers mainly across central and northern
Massachusetts will come to an end early this evening. Otherwise,
dry weather is expected tonight, but a fast moving low pressure
system will bring a period of widespread rain and unseasonably 
cool temperatures to the region on Memorial Day. Upper low and 
cold pool linger during the mid and late week over the Great 
Lakes and Northeast USA while surface high pressure builds in. A
couple of weak cold fronts are possible during this time 
bringing showers and possibly thunderstorms. Otherwise fair 
weather with near seasonable temperatures.



350 pm update...

Just enough diurnal heating coupled with low level moisture has
allowed for a few spot showers to popup this afternoon, mainly
across central and northern MA. Areal coverage will be quite 
limited and expect these brief isolated showers to come to an 
end early this evening with the loss of daytime heating. 

Otherwise, dry and tranquil weather in store for the region
tonight with just an abundance of clouds. Low temps should
bottom out between 50 and 55 in most locales.



***Period of widespread rain overspreads the region from west to
 east through early afternoon on Memorial Day with unseasonably
 cool temps***

Monday /Memorial Day/...

A shortwave approaches the region on west to southwest flow
aloft, which increases the forcing for ascent. This coupled with
a modest ESE low level jet and Pwats 1+ standard deviations
above normal, will allow rain to overspread the region. Timing
still uncertain given model differences, but a period of
widespread rain should overspread the region Monday morning
through early afternoon from west to east. The rain should
taper off to scattered light showers/drizzle late Mon 
afternoon/early evening. Elevated instability parameters look 
marginal for thunder, but there is a low risk for an isolated 
t-storm or two in our southern zones mainly along the south 

It also will be an unseasonably cool Memorial Day as high
pressure over the Canadian Maritimes will result in cool easterly
surface winds, coupled with clouds and rain. High temps will 
only be in the 50s to near 60 and it will be breezy on the 

Monday night...

Shortwave and deeper moisture will have exited the region by
early Monday evening. However, moist northeast low level flow will
probably allow scattered light showers/drizzle and fog to 
persist into the evening across eastern New England. While most 
of the scattered light showers/drizzle should come to an end by 
midnight, areas of low clouds and patchy fog may persist longer as
low level moisture may remain trapped below the inversion. Low 
temps will mainly be in the upper 40s to the lower 50s.



Big Picture...

Longwave scale maintains a ridge west/trough east pattern for much 
of the long term period.  Shortwave scale shows a closed low slowly 
moving from the Great Lakes into Eastern Canada, maintaining a 
cyclonic flow over the Northeast USA and especially New England 
through Saturday. Several shortwaves move through this flow. One 
additional shortwave dives south from the Canadian Arctic and over 
the Northeast USA Sunday as the closed low moves off. 

Mass fields are similar among the long-range models through 
Thursday, but differ in handling the Sunday shortwave. Thermal 
fields are similar through Thursday. This brings moderate-high 
confidence in the overall synoptic pattern through Thursday. Low 
confidence in events for next weekend.


Tuesday through Friday...

Upper low and associated cold pool remain to our west Tuesday but 
move over us Wednesday through Friday. Multiple shortwaves move 
through the flow Tuesday through Friday, and exact timing at this 
stage is difficult. Already some model timing differences from the 
12Z suite yesterday. At this time, the best chance of shortwave 
passages along with associated surface fronts/troughs would be 
Wednesday and Friday. Convection firing over Upstate NY and PA 
Tuesday could work into our area later Tuesday. 

Precipitable water values are highest Tuesday, then diminish 
Wednesday and Thursday. PW values return in surges Friday afternoon 
and Sunday afternoon. The cold pool will aid in destabilizing the 
airmass each day, with expected low level heating on Wednesday 
bringing the greatest destabilization. Convective parameters show 
increasing instability on Tuesday, greater instability Wednesday, 
stable air Thursday, and returning instability Friday.  This 
suggests scattered showers and a few thunderstorms Tuesday, 
Wednesday, and Friday.

We note that SPC shows a marginal risk of severe wx just to our west 
on their Day 3 outlook for Tuesday. Conditions do seem more 
favorable to our west and less favorable over our area. But Western 
Mass and adjacent CT are close to the outlooked area and will need 
to be monitored as Tuesday gets closer. It is possible a squall line 
or bow could develop to our west and then move into the adjacent 
areas late in the day. In such a case, the concern would be for 
straight-line winds late in the day.

The Friday cold front stalls south of New England Friday night/early 


High pressure brings a brief break in unsettled weather Saturday. 
Upper low sweeping south from the Canadian Arctic approaches 
our area on Sunday. This in turn generates a wave along the 
stalled cold front. The rain shield with this wave moves across 
our area on Sunday. As noted above, low confidence in this 
solution due to run- to-run variations.


Forecaster Confidence Levels...

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

Short Term /through Monday Night/...

Tonight...Low confidence. We kept things mainly VFR, but some 
of the guidance brings in a lot of IFR to even LIFR conditions.
Certainly possible, but just did not have enough confidence to 
go that pessimistic given easterly flow and best moisture to our
southwest. Later shifts will have to monitor trends closely 
this evening as confidence is rather low.

Monday and Monday night...Moderate to high confidence. MVFR to 
IFR conditions overspread the region through the morning and 
into the early afternoon in a period of widespread rain. There 
also is a low risk for an embedded t-storm or two, mainly near 
the south coast on Mon. Easterly wind gusts around 20 knots are 
expected on the coast, with up to 25 knots across portions of 
the Cape/Islands.

The rain will taper off to light showers/drizzle from west to 
east late Monday afternoon/early evening. However, MVFR- IFR 
conditions may persist for much of Mon night with the lowest 
conditions most likely on the coast.

KBOS TAF...Moderate confidence in TAF.

KBDL TAF...Moderate confidence in TAF.

Outlook /Tuesday through Thursday/...Moderate confidence.

Generally VFR. Potential for brief IFR in early morning fog. 
Potential for MVFR cigs/vsbys in afternoon/evening showers and 
scattered t-storms. Best chance for the latter will be in 
Western/Central Mass and Northern Connecticut. Least chance for 
showers/tstms will be Thursday.

South winds Tuesday, becoming southwest Wednesday, west Thursday, 
and southwest Friday. All winds should be less than 20 knots.


Forecaster Confidence Levels...

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

Short Term /through Monday Night/...

Tonight...High confidence. The ridge of high pressure will
continue to move east of the waters. However, pressure gradient
will remain weak enough to keep winds/seas below small craft
advisory thresholds for most of the overnight hours.

Monday...Moderate to high confidence. High pressure building 
across the Canadian Maritimes coupled with a wave of low 
pressure passing to our south will generate easterly wind gusts 
around 25 knots for many waters on Monday. Therefore, small 
craft headlines posted for many of our waters. Easterly fetch 
will also build seas between 3 and 6 feet across our open 
waters. The strongest wind gusts/seas will be across our 
southern waters. Rain and patchy fog is also expected to develop
and an isolated t-storm or two can not be ruled out Monday 
across our southern waters.

Monday night...Moderate to high confidence. Winds and seas will
begin to diminish later Monday evening and especially after
midnight as disturbance moves away from the region and pressure
gradient weakens. Areas of fog may persist into early Tue am
reducing vsbys for mariners.

Outlook /Tuesday through Friday/...Moderate confidence.

Tuesday through Friday...

Winds less than 25 knots and seas less than 5 feet through the 
period. Scattered afternoon showers possible. Water temps may weaken 
most thunderstorms that approach the coastline, but one or two 
storms could briefly affect the waters. 



Latest observations continue to show a storm surge just over a
half foot along the eastern MA coast. Another high astro tide of
12.0 feet occurs just after 2 am in Boston. While that is a bit
lower than the last two nights, there will be a little more of 
an onshore component and probably a storm surge of a half foot
or even a bit more. While no significant problems are expected,
very minor nuisance coastal flooding is possible along the most
vulnerable shore roads along the eastern MA coast. Therefore,
have opted to go with another coastal flood statement.


MARINE...Small Craft Advisory from 9 AM to 8 PM EDT Monday for 
     Small Craft Advisory from 11 AM Monday to 2 AM EDT Tuesday for 
     Small Craft Advisory from 6 AM Monday to 2 AM EDT Tuesday for 



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