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

Synopsis...
scattered showers/thunderstorms will develop Sunday afternoon across
far western New England...slowly moving across the rest of the
region by Monday. The rainfall chances could continue into early
Wednesday. Some of the storms may be strong to severe along with a
localized flash flood threat. A trend toward drier and somewhat less
humid weather follows by late in the week.

&&

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

1000 PM update...
upper level cloud debris from Great Lakes convection will spill
into southern New England overnight. This will limit any
radiational cooling conditions overnight. A few spotty showers
across upstate New York are weakening allowing for a dry forecast to
continue. Aside from some minor tweaks...forecast remains on track
for the overnight hours.

Previous discussion...
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 Monday and Tuesday...strong
storms possible along with a threat for flash flooding
* unsettled conditions may linger into Wednesday...slow
improvement pushes in late
* drier and less humid weather returns Thursday and Friday

Overview and model preferences...

Medium range models and their ensembles continue to show
amplification of middle to upper level pattern across the west Pacific and
lower 48. Anomalous cold pool moves across central and eastern
Canada while ridging builds across the western U.S. Into the
middle of next week. Positioning of this upper level cutoff system
and surface front lying across the northeast U.S. To the Middle Atlantic
States appears to show relatively good continuity...tapping
tropical airmass from the Gulf of Mexico. This will yield
continued threat of flash flooding Monday and Tuesday due to slow
movement of the front and training of rainfall along it. Could
also see some strong to possibly severe storms with good
instability with SW flow in place and increasing dewpoints.

Models and ensembles diverge on the progression...or lack thereof...
of northern stream systems during Wednesday. 12z GFS op run
continues its faster progression though slowing the progression of
the front somewhat...and the 12z ggem op run is also closer to this
solution. However...both the 00z and 12z ec run are slower as one
would expect with meridional upper level pattern. Plan on leaning
toward a blend of available models and ensembles due to uncertainty
of timing this far out. Looks like the Upper Cutoff tends to
retreat into eastern Canada late next week with flattening of the
upper flow. Conditions look drier with seasonable temperatures.

Details...

Monday through Tuesday...broad 500 mb trough across the Great Lakes
will set up a SW wind flow at the surface and aloft. This will
open the tropical connection from the Gulf of Mexico as the front
runs parallel to the upper flow. Precipitable waters increase to 2.1 to 2.2
inches... around 2 South Dakota above normal for middle July...during this
timeframe. Highest concern is the potential of flash flooding with
excellent moisture transport at all levels...especially as weak
short waves move along the slow moving front. Quantitative precipitation forecast forecast
continues to signal average rainfall of 1-3 inches...highest
across west CT and Massachusetts. Some spots could receive more in localized
heavy downpours or if training of heavy cells move across.
Continued moderate risk for heavy rainfall and localized flooding.

Also see potential for strong to possibly severe thunderstorms during
this timeframe...but looks like best shot occurs during Tuesday.
Good jet dynamics in place with rrq of a 120 knots 300 mb jet passes
across Quebec on Tuesday. Also noting k indices in the middle to
upper 30s along with lifted indices below zero. Carried chance to
likely probability of precipitation through this timeframe along with enhanced wording for
heavy rainfall. Dewpoints will be in the middle 60s to around 70...so
warm and muggy conditions in place.

Wednesday...still a lot of questions as to timing the front across
the region. For now...expect the front to ever so slowly move across
during the day. Will still see continued risk for thunderstorms.
Even though the core of 120 knots 300 mb jet is in NE Quebec by this
time...will still see some effects for expansive rrq of this jet
across interior areas. Have carried chance showers/thunderstorms through
most of the day...then should diminish around or after sunset.
Dewpoints start to drop across SW New Hampshire/west Massachusetts by evening.

Thursday...could still see some widely scattered showers across east Massachusetts Thursday
morning as front continues its slow trek off the coast. Improving
conditions inland expected...which should shift east during the
afternoon. 500 mb trough remains west of the region...so can not rule
out widely scattered diurnal showers developing across north Massachusetts/S New Hampshire where
coolest air aloft is in place. Dewpoints drop to the middle-upper 50s
across the CT valley...but may linger in the lower 60s over
eastern areas. Expect seasonably high temperatures.

Friday-Saturday...models continue to signal deamplification of the
upper trough to the west...but rather low confidence during this
portion of the forecast due to previous timing issues. Should be dry
and comfortable on Friday...with dewpoints creeping up again during
Saturday. Very low probability of a diurnal shower well inland.

&&

Aviation /02z Sunday 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/...

Tonight...high confidence. VFR. Perhaps a touch of very late
night/early Sun morning patchy ground fog in the typically prone
locations.

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.

Kbdl taf...high confidence in taf.

Outlook...Monday through Thursday...

Monday and Tuesday...moderate to high confidence. MVFR-IFR
ceilings/visibilities at night in areas of fog along with scattered
showers/tstms. Conditions may improve to low end VFR during the
afternoon hours. Expect showers and scattered thunderstorms anytime during this
timeframe.

Wednesday...low confidence due to timing. MVFR conditions to
start...then slow improvement from NW-se. Conditions appear to
linger across east Massachusetts/Rhode Island through most of day. Patchy late night/early
morning fog with local IFR conditions.

Thursday...low confidence due to timing. May see local MVFR
conditions across east coastal Massachusetts early with any leftover
showers...otherwise VFR.

&&

Marine...
forecaster confidence levels...

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

Short term /tonight through Sunday night/...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 Thursday...

Monday-Tuesday...moderate to high confidence. Expect S-SW winds
gusting up to 20 knots over the outer waters...low probability of a few gusts
to 25 knots on the southern outer waters. Small craft seas will likely
continue...up to 5-6 feet on the outer waters. Reduced visibilities in areas
of fog. Showers/scattered thunderstorms through this period.

Wednesday...moderate confidence. SW winds and seas diminish. Still
chance for scattered showers/thunderstorms and patchy fog reducing visibilities.

Thursday...moderate confidence. Winds and seas below small craft
criteria. Leftover patchy fog with reduced visibilities early Thursday morning.

&&

Tides/coastal flooding...
very high astronomical high tides with Boston at 12.0 feet just
before midnight and then 12.2 feet around midnight Sunday night.
However...south to southwest winds will prevent any problems along
the eastern Massachusetts coast. Along the South Coast...winds will not be
strong enough to cause any issues. No coastal products are
anticipated over the next 36 hours.

&&

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/evt
near term...Frank/dunten
short term...Frank
long term...evt
aviation...Frank/evt
marine...Frank/evt
tides/coastal flooding...

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