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Area forecast discussion
National Weather Service Taunton Massachusetts
642 am EDT Tue may 30 2017

Synopsis...
weak high pres will build across the region today, bringing dry
weather but with temperatures remaining below normal. An
approaching cold front may bring a few strong thunderstorms to
the northwest of a Boston to Providence corridor late Wednesday
afternoon and evening. Dry and seasonable weather follows
Thursday, but unsettled weather with showers at times may return
Friday into early next week but plenty hours of dry weather
will be mixed in too.

&&

Near term /through tonight/...

Overall trend in the forecast remains on track for this morning.
Low clouds, areas of fog and patchy drizzle to start. Conditions
will dry out by the late morning but clouds will remain to be
pesky.

Initial line of thunderstorms developing across upstate New York will
continue to move to the northeast this morning just missing the
region. The second impulse later today will be the one to watch.



Previous discussion...

A strong mid level low remains north of the Great Lakes today.
This should place southern New England well within a southwest
flow aloft. This will trend temperatures higher. However, a high
pressure nearby over the North Atlantic will prevent this
southwest flow from reaching its maximum impact. Surface winds
should not turn southerly until late this afternoon. As such,
still expecting Max temperatures to remain about 10 degrees
below normal.

This high pressure should also prevent many showers from moving
east into southern New England through most of today. There is a
chance for some showers and isolated thunderstorms to move into
the western half of southern New England this evening.

&&

Short term /Wednesday/...
tonight...

Mid level low remains north of the Great Lakes. Mid level lapse
rates are slightly better than moist adiabatic across southern
New England. Still not expecting any surface-based instability.
So, while isolated thunderstorms cannot be ruled out entirely,
not thinking any thunderstorms which do develop will be very
strong. The most likely scenario is for convection to develop to
our west, then move east into our region, becoming less
widespread the farther east they travel.

Southwest flow aloft should finally take hold, resulting in near
normal low temperatures.

Wednesday...

The main concern form Wednesday remains the potential for
strong convection. Persistent cold pool aloft to our northwest
would continue to Foster an environment of fairly steep mid
level lapse rates. There is also expected to be a sufficient
amount of shear within the lowest 6 km where stronger, more
organized convection would be possible.

The greatest uncertainty still revolves on how how much of a
contribution surface-based instability can make. This will
depend mostly on how quickly clouds break up in the morning.
As previously mentioned, the greatest risks would be strong
damaging winds and large hail. The greatest threat remains to
the northwest of the Boston to Providence corridor, particularly
across western and northern Massachusetts closer to the more supportive
synoptic dynamics.

&&

Long term /Wednesday night through Monday/...
highlights...

* near seasonable and dry for Thursday
* unsettled conditions continue Friday into early next week
* seasonable temps likely into Sat with a return of below normal
temps early next week

Pattern details...

The model guidance remains relatively agreeable in showing
persistent troughing across the northwest and northeast through
the period. However, the specifics at the surface remain
uncertain as various pieces of guidance are showing occasional
timing and strength issues which has lead to a spread in the
surface low tracks. Regardless the pattern continues to be
seasonable to below average in temperatures with unsettled
conditions.

Details...

Wednesday night into Thursday...high confidence.

Remaining showers and thunderstorms on Wednesday evening will
come to an end during the overnight hours as mid-level trough
pushes through the area.

Thursday will be the pick of the week as weak mid-level ridging
moves over the region in response to building high pressure to
the west. Very steep lapse rates as surface temps warm into the
upper 60s to low 70s as temps aloft continue to cool. Mid-level
lapse rates are near 7 c/km and with some mid-level moisture,
believe diurnal clouds will develop. May need to watch for a
rogue thunderstorm but confidence is low as k values are quiet
low as well as pwats.

Breezy conditions will develop in response to the steep lapse
rates on Thursday with gusts near 25 to 30 miles per hour.

Friday into Sunday...moderate confidence.

Upper level trough will begin to take hold as another digging
shortwave from southern Canada moves overhead. This will swing a
surface low pressure system from the Great Lakes into the
northeast. A warm front associated with this system will try to
move into the northeast on Friday with its cold front passing
through sometime on Saturday. Still some timing differences with
this system but right now it appears a more active pattern is
taking hold with a chance for iso thunder each day as warm air advection and
higher dewpoints moves into the area.

Sunday and beyond...low confidence.

Cold front will stall somewhere near the region resulting in
either dry but cool weather north of the front and wet,
seasonable weather south of the front. The GFS is more amplified
pushing the front through where the ec keeps it over southern New England.
Continued with a blend in the guidance for now until details can
be resolved. Thus while the forecast looks wet, there will be
dry weather mixed in each day.

&&

Aviation /12z Tuesday through Saturday/...
forecaster confidence levels...

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

Short term /through Wednesday/...moderate confidence.

Today...MVFR/IFR cigs will lift to VFR/MVFR this afternoon. A
few showers or an isolated thunderstorm possible across western
Massachusetts by late afternoon.

Tonight...more MVFR/IFR conditions with scattered showers and
isold thunderstorms moving across the region.

Wednesday...MVFR-IFR conditions early may improve to MVFR-VFR
by afternoon. A few strong thunderstorms possible late afternoon
and evening, mainly northwest of a Boston to Providence
corridor. Lower confidence in timing.

Kbos taf...moderate confidence in taf.

Kbdl taf...moderate confidence in taf.

Outlook /Wednesday night through Saturday/...moderate confidence.

Wednesday night...lingering MVFR conditions in showers and
thunderstorms. Conditions improve to VFR from west to east
overnight.

Thursday...mainly VFR conditions. Gusty westerly winds near
25 kt.

Friday and Saturday...a period of MVFR-IFR conditions possible
in some low clouds and some showers, but timing uncertain.
Greatest risk for lower cigs/vsbys late Fri into early Sat.

&&

Marine...
forecaster confidence levels...

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

Short term /through Wednesday/...high confidence.

Winds and seas expected to remain below Small Craft Advisory
thresholds through Wednesday. The greatest concern for mariners
will be reduced visibility from areas of fog today into
Wednesday morning. Low risk for isolated thunderstorms tonight
into Wednesday.

Outlook /Wednesday night through Saturday/...moderate
confidence.

Wednesday night and Thursday...pressure gradient should be weak
enough to keep winds and seas below Small Craft Advisory thresholds.
Main concern for mariners will be for some fog, especially across
our southern waters during the late night/early morning hours.

Friday and Saturday...moderate confidence. Persistent long
southwest wind ahead of a cold front may result in seas building to
between 4 and 7 feet across our southern waters later Fri into Sat.
Some showers and fog patches also may impact mariners at times. Small Craft Advisory
may be needed.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...none.

&&

$$
Synopsis...Belk/dunten
near term...Belk/dunten

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