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Area forecast discussion 
National Weather Service Taunton Massachusetts
355 am EDT Sat may 30 2015

Synopsis...
dry weather will continue for today thanks to an area of high
pressure. A cold front will slowly move across the region
Sunday...then stall south of New England early next week. This
will bring a chance of showers and a few thunderstorms
Sunday...and a period of rain early next week. High pressure
brings dry weather for the latter part of the week.

&&

Near term /until 6 PM this evening/...

4 am update...

Southwest flow will continue to advect in moisture into the region.
Stratus and fog have spread across the South Coast/cape and islands
and is beginning to move northward. Biggest question is how far
north and how dense will visibilities drop. Currently have the South
Coast/cape and islands in a dense fog advisory and will add Plymouth
County and the rest of Bristol County as well. Fog is also
developing across some of the Lower Valley regions...anticipate this
fog to remain 1sm as temperatures/dewpoint spread decreases.

Otherwise temperatures have dropped into the middle 50s to low 60s. Expect
them to drop another degree or two...but then rise once the sun
rises.

Today...

High pressure will slowly shift offshore today allowing for the
southerly flow to dominate the region. Dewpoints will be on the
increase allowing for another warm and muggy day. Anticipate good
mixing today so SW wind may gust between 20-30 kts.

In the latter half...cold front will move across the Great Lakes
region allowing for showers and thunderstorms to develop. The better
dynamics and forcing will be well to the west of the
region...however because we are in a very warm and moist airmass
cannot rule out a few pop-up showers and thunderstorms out ahead of
this front. Therefore kept the slight chance pop across the western
zones...which is in conjunction with Storm Prediction Center convective outlook.

Otherwise believe that most of the region will remain dry for today
with high temperatures reaching into the middle to upper 80s away from the
south coastline.



&&

Short term /6 PM this evening through 6 PM Sunday/...
tonight...

Noticed guidance continues to slow down the frontal passage...so
have adjusted the forecast to account for this trend.

The cold front will begin to approach the region
tonight...bringing some much need rainfall to the region. As the
front approaches guidance indicates that showalters will be below
0 with k values above 30c. Therefore cannot rule out some
embedded thunder overnight. Area that will see the higher rainfall
amounts will be north of the Pike...especially north of Route 2.

Since the front will still be northwest of the region...anticipate
another round of fog to develop along the South Coast/cape and
islands as moisture pools along the front. Low confidence if it will
be dense or not.

Tomorrow...

Timing of the cold front is still in question as latest guidance
trend is to slow down the front. Regardless believe that the front
will cross southern New England on Sunday bringing some much needed
rain. Guidance still shows elevated thunder parameters...so will
continue to mention thunder in the forecast...but strong to severe
storms are not expected.

Both the NAM and GFS indicate good boundary layer moisture along the
front as is begins to stall over the region. With precipitable water values around
1.6 inches and the front becoming aligned with the upper flow
aloft...could see the potential for heavy rain and flooding due to a
slow storm motion. Because of the uncertainty on where the front
will stall...held off on issuing any sort of Flood Watch at this
time. Right now believe that locations along and north of the Mass
Pike will see the higher precipitation amounts on Sunday. Perhaps it will
push Worcester out of the top 5 driest Mays on record.

&&

Long term /Sunday night through Friday/...
big picture...

Changeable pattern through the week. Upper ridge moves offshore
Sunday. Upper trough slowly crosses the northeast USA early week.
Upper ridge from the western USA then shifts east over the eastern
USA late week.

Differences among the models regarding timing with the upper trough
early week with the ggem the fastest and European model (ecmwf) slowest. We used a
model consensus in timing.

The dailies...

Sunday through Tuesday... cold front either over or just north of
northern mass Sunday morning will move south across the region
during the day. Precipitable water values along and ahead of the
front will be 1.50 to 1.75 inches which is around 2 Standard dev above
normal. Totals of 47-49 and showalters of 0 to -2. All of this
suggests sufficient moisture for showers and enough instability over
the low level convergence to support a few thunderstorms.

Differences among the models on timing the frontal passage but all move it
south of the coast by Sunday evening. The front is then aligned with
the upper flow and stalls. Shortwave moving through the Great Lakes
is forecast to generate a wave along the front which crosses the
Appalachians Monday and passes south of New England Tuesday. This
along with high pressure in eastern Canada should bring a cool
northeast flow to the region Monday and Tuesday. Meanwhile a
southwest flow continues above 5ooo feet above ground level and suppies lift and
moisture over the top. We will maintain likely probability of precipitation Monday
diminishing to chance probability of precipitation during the day Tuesday as the low moves
east.

Wednesday through Friday... high pressure builds surface and aloft
bringing dry weather to southern New England. With the demise of the
northeast marine flow...mixing should return with heights reaching
at least 875 mb Wednesday and at least 850 mb Thursday and Friday.
Temperatures at the top of the mixed layer each day suggest maximum surface
temperatures in the middle 60s to low 70s Wednesday...70s to near 80
Thursday...and 75-85 Friday.

&&

Aviation /08z Saturday through Wednesday/...
forecaster confidence levels...

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

Tonight...moderate confidence. IFR stratus/fog moving in from the
South Coast dropping visibilities below 1/4sm. This should dissipate by
morning.

Today...moderate confidence. Any low clouds/fog patches south of
Pike probably scour out by late morning...lingering across the
Cape/Island by early afternoon. Dry weather expected...although
there is a low risk of a spot shower/thunderstorm across northwest
Massachusetts late in the afternoon/early evening.

Tonight into Sunday...moderate confidence. VFR to start with
conditions deteriorating by late tonight into Sunday due to
widespread -shra/-tsra. Fog and stratus may fill back in along the
South Coast overnight tonight. Otherwise could see some low level wind shear
across the southern sites on Sunday.

Kbos terminal...moderate confidence in taf. Uncertain on if fog
will fill back in overnight.

Kbdl terminal...moderate confidence in taf.

Outlook...Sunday night through Wednesday...moderate confidence.

Monday through Tuesday... MVFR/IFR ceilings and visibilities with best chance
over the coastal plain and eastern slopes of the Worcester Hills.
Showers possible through both days.

Wednesday... VFR with a north-northwest wind.

&&

Marine...
forecaster confidence levels...

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

Short term /today through Sunday/...

Today...moderate to high confidence. Excellent mixing over the
land will generate near shore small craft wind gusts of 25 to 30
knots this afternoon. In addition...southeast swell will generate
5 foot seas across the outer-waters. Therefore...small craft
headlines posted for all waters. Areas of fog should improve
somewhat by afternoon.

Tonight...moderate to high confidence. Near shore small craft
wind gusts should diminish by the evening. However...5 foot swell
will continue across the outer-waters. Areas of dense fog
possible tonight.

Sunday...moderate confidence. May need to extend Small Craft Advisory for cold air advection
behind a passing cold front from the north. Otherwise expect
showers with embedded thunder could occur ahead of the front during
the afternoon hours.

Outlook...Sunday night through Wednesday...moderate confidence.

Monday-Tuesday...Small Craft Advisory may be needed especially on
the eastern waters. Northeast winds gusting 20 to 25 knots each day.
Seas 5 to 8 feet on the eastern mass waters...and 3 to 5 feet on the
southern waters.

Wednesday...a Small Craft Advisory may be needed...mainly on the
eastern waters. Diminishing northeast to north winds. Seas of 5 feet
may linger on the eastern waters.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...dense fog advisory until 8 am EDT this morning for maz017>024.
Rhode Island...dense fog advisory until 8 am EDT this morning for riz002>008.
Marine...Small Craft Advisory from noon today to 10 PM EDT this evening
for anz230>237-251.
Small Craft Advisory from 2 PM this afternoon to 3 PM EDT
Sunday for anz250-254>256.

&&

$$
Synopsis...wtb/dunten
near term...dunten
short term...dunten
long term...wtb
aviation...wtb/dunten
marine...wtb/dunten

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