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Area forecast discussion 
National Weather Service Taunton Massachusetts
400 PM EDT Sat Jul 12 2014

Synopsis...

Scattered showers/thunderstorms will develop Sunday afternoon across
far western New England and overspread the rest of the region by
Monday/Tuesday and perhaps even continuing into Wednesday. Some of
the storms may be strong to severe along with a localized flash
flood threat. A trend toward drier and less humid weather follows by
middle to late in the week.

&&

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

Marginal instability across far western New England may trigger a
spot shower or two through early this evening. Otherwise...another
dry/tranquil night of weather in store for southern New England.

High pressure continues to move off the coast allowing low level
moisture to gradually return to the region. Therefore...lows will
only bottom out to between 60 and 65 across most locales by daybreak
Sunday. Some patchy fog may develop in some typically prone
locations late...but nothing widespread.

&&

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

Sunday...

Anomalous closed upper level low will drop south towards Great
Lakes. However...dynamics/forcing will still be far enough west to
result in one more dry day across much of our region. The exception
will be southwest New Hampshire/western Massachusetts and northern CT...as these locations
will be on the edge of the instability axis. Convective available potential energy on the order of
500 j/kg along with 25 to 30 knots of shear will be enough to
trigger a few showers/thunderstorms. Now were certainly not
expecting a washout in this region...but a few hit and miss
showers/storms possible mainly during the afternoon hours.
Instability/shear combination does not look to be enough for any
severe weather...although can/T rule out an isolated strong
thunderstorm. Best shot for that will be along the east slopes of
the Berkshires.

High temperatures will be in the middle to upper 80s...except a few degrees
cooler on the immediate South Coast/cape/islands. It will be more
humid than the last few days...but not oppressive.

Sunday night...

Increasing low level moisture and decent jet dynamics in association
closed low over the Great Lakes will allow the threat for scattered
showers/thunderstorms to increase as the night wears on. Given
precipitable waters on the order of 2+ inches...locally heavy rainfall will also
be an increasing concern. It will be muggy with low temperatures only
bottoming out in the upper 60s to lower 70s.

&&

Long term /Monday through Saturday/...
highlights...

* showers and thunderstorms likely Sun night through Tuesday with
strong storms possible along with a threat for flash flooding
* drier and less humid weather returns Thursday and Friday.

Synoptic overview and guidance evaluation...

Ensembles and deterministic guidance continue to show good
continuity on an evolving highly amplified pattern across North
America beginning this weekend and continuing into next week. The
long wave pattern will feature two high amplitude ridges...one
across western Canada attaining heights + 3 South Dakota. The other ridge will
be located over the northwest Atlantic. Between these two ridges an
anomalous closed low dives southward into the Great Lakes with
heights reaching -3 South Dakota Tuesday over the Ohio Valley. This high amplitude
meridional flow will be accompanied by a strong frontal zone with
tropical moisture to the east and a Spring-like cool airmass to
the west. This frontal zone will also be accompanied by strong jet
dynamics...yielding a risk for strong to severe thunderstorms Monday and Tuesday
along with a threat for flash flooding.

00z gefs ensembles and its operational 00z GFS are more progressive
with the upper trough and frontal passage than the 12z ecens
ensembles and new 00z European model (ecmwf). These are typical model biases we see
with frontal passages... European model (ecmwf)/ecens slower than GFS/gefs. Given the
time range here best course of action is to follow a model blend to
minimize model biases. Although would not be surprised to see the
slower European model (ecmwf)/ecens solutions verify given the high amplitude
meridional flow.

Daily details...

Monday...lead short wave trough and attending prefrontal trough
should be sufficient to trigger scattered showers/T-storms across
the region with a more of a focus over western New England given
proximity to trough. Precipitable waters + 2 South Dakota combined with at least modest
instability of 1000-1500 ml convective available potential energy support T-storms with potential
heavy rain and wind. Warm and muggy conditions as well.

Tuesday...timing differences here regarding arrival of trailing
short wave trough and attending surface cold front. GFS and its
ensembles faster than the European model (ecmwf) and ecens. Nevertheless stronger jet
dynamics with this trailing short wave trough as gefs anomalies
suggest 250 mb jet reaching + 3 South Dakota over New York state with rrq across
southern New England. This will provide strong qg forcing. These
synoptic scale features combined with model quantitative precipitation forecast signal heavy
rainfall potential with new 00z European model (ecmwf) storm total of 1-3" across the
region...heaviest amounts western CT/MA. 00z GFS not far behind with
up to 2.5" across the Berkshires. The more progressive 00z gefs
indicate areas of low probability of 2-3" rains from New Jersey northeast to
downeast ME. Thus a moderate risk of heavy rain and localized
flooding here Monday and Tuesday. Warm and muggy conditions continue as
well.

Wednesday...lots of uncertainty here given model spread on timing of
frontal passage. A model blend suggest this will be our transition
day with a risk of showers/T-storms across eastern Massachusetts and Rhode Island early
in the day...followed by a trend toward drier/less humid conditions
from west to east as frontal passage works across the region.

Thursday and Friday...mid/upper level trough remains west of New
England Thursday however the upper air pattern begins to deamplify as
short wave trough lifts northeast into southeast Canada Friday. Overall
this supports a trend toward drier and less humid weather for
southern New England.

&&

Aviation /20z Saturday through Thursday/...
forecaster confidence levels...

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

Short term /through Sunday night/...

This afternoon and tonight...high confidence. VFR other than
perhaps a touch of very late night/early Sun morning patchy ground
fog in the typically prone locations. Sea breezes will come to an
end by early evening.

Sunday...high confidence in mainly VFR conditions. A few
showers/thunderstorms may affect our far western zones mainly in the
afternoon...resulting in localized lower conditions. However...this
activity will likely remain west of all our forecast terminals for
most of the day.

Sunday night...moderate confidence. MVFR-IFR ceilings/visibilities over spread
the region as deep low level moisture works into the region. The
risk for scattered showers/thunderstorms increases as Sunday night
wears on.

Kbos taf...high confidence in taf. Easterly sea breeze becomes
southeast through late afternoon and then finally south by 00z this
evening.

Kbdl taf...high confidence in taf.

Outlook...Monday through Wednesday...

Moderate to high confidence on MVFR/IFR at night in areas of fog
along with scattered showers/tstms. Conditions may improve to low
end VFR during the afternoon hours. However risk of showers/thunderstorms
increase during this time. Low probability of some improvement Wednesday
from west to east.

&&

Marine...
forecaster confidence levels...

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

Short term /tonight through Sunday/...high confidence.

Tonight...winds/seas to remain well below Small Craft Advisory thresholds.

Sunday and Sunday night...increasing southwest flow and good mixing
over the land should allow southwest wind gusts of 25 to 30 knots to
develop late Sunday morning and particularly during the afternoon
across the near shore waters. In addition...long southwest fetch
should allow Small Craft Advisory seas to develop on the outer-waters Sunday night.
Therefore...Small Craft Advisory headlines posted for all waters for the above
concerns.

In addition...some fog may develop Sunday night and we can/T rule
out a few thunderstorms particularly toward daybreak Monday.

Outlook...Monday through Wednesday...

Moderate to high confidence on modest south-southwest winds 15-20 knots with gusts
up to 25 possible. Visibility lowering at times in areas of fog along with
tropical downpours Sun night through Tuesday. Some improvement possible Wednesday
as frontal passage may sweep across the waters.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
New Hampshire...none.
Rhode Island...none.
Marine...Small Craft Advisory from 11 am to 11 PM EDT Sunday for
anz230>234-236-251.
Small Craft Advisory from 11 am Sunday to 8 am EDT Monday for
anz235-237.
Small Craft Advisory from 2 PM Sunday to 8 am EDT Monday for
anz250.
Small Craft Advisory from 11 PM Sunday to 8 am EDT Monday for
anz254>256.

&&

$$
Synopsis...Frank
near term...Frank
short term...Frank
long term...nocera
aviation...Frank/nocera
marine...Frank/nocera

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