Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kbox 230900 
afdbox

Area forecast discussion
National Weather Service Taunton Massachusetts
400 am EST Thu Feb 23 2017

Synopsis...
high pressure centered offshore southeast of New England will
bring dry and unseasonably warm conditions today and tonight. A
cold front stalls over southern New England tonight and then
moves north as a warm front Friday. A strong cold front will
cross the region late Saturday afternoon and night, bringing
areas of rain and patchy fog. There will be a low chance for
isolated thunderstorms as the front passes. Near seasonable
temperatures will return early next week, with blustery
conditions on Sunday and Monday. There may be another chance for
precipitation around the middle of next week.

&&

Near term /until 6 PM this evening/...
high pressure centered offshore is bringing a light southwest
flow to the region. This moved higher dew point air onshore
along the South Coast and brought low clouds and dense fog to
the region. After sunrise the clouds and fog should retreat out
over the water. A dense fog advisory will continue along the
South Coast of Rhode Island and Massachusetts through the morning rush hour.

Low pressure passes across Ontario and Quebec today, while the
high pressure remains just offshore. This will create a better
defined gradient to aid southwest winds. A 50 knot southwest jet
is expected to move up the St Lawrence Valley, while a secondary
southwest jet will move across srn New England at 2000-3000
feet. Speeds in the secondary jet are forecast at 30-35 knots,
and may spin up gusts of 20-25 knots at the surface.

Warm advection in the southwest flow should limit the mixing
depth, but temps at 925 mb reach 9-12c which would support Max
sfc temps in the lower 60s, roughly 60-64. If we mixed all the
way to 850 mb we would tap 7-8c, which would support Max sfc
temps in the lower 70s. A mixed layer up to either 950 or 925 mb
looks more reasonable. The southwest flow off the ocean should
keep readings cooler along the South Coast. Ocean temps are in
the low 40s, so daytime highs should be in the upper 40s and
lower 50s.

Note the climate section at the end of this discussion. Based on
expected temps, pvd and orh stand a chance of tying/breaking the
Max temp record today. Bos has an outside chance, but we think
they will fall just short. Bdl would need to mix above 900 mb to
have a chance, and this would seem too much.

&&

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

Cold front trailing the Canadian low will drift into or near
southern New England tonight, but becomes parallel to the upper
flow by midnight and should stall by that time. Digging
shortwave over the plains will eventually turn the upper flow
more southwest and push the stalled front north as a warm front.

Although placement of the front when it stalls will determine
our overnight weather, it seems likely that most of our area
will remain south of the front...certainly the areas south of
the Mass Pike. This will mean another night of moist air with
fog and low clouds again moving ashore from the south. Dense fog
may again be a concern overnight. Dew points in the 40s point to
min sfc temps in a similar range.

Friday...

Cold front slowly lifts north of our area during the day.
Southwest flow will increase through the day, eventually
generating lift across the front and resulting in light rain or
showers. The best chance of this will be in areas north of the
front, northern Massachusetts.

Clouds will work against similar temps to Thursday. But temps at
1000 mb continue to support Max sfc temps near 60. The southwest
flow will again work to keep South Coast areas several degrees
cooler.

&&

Long term /Friday night through Wednesday/...

Highlights...

* mild with widespread showers likely Sat into Sat night
* blustery and cooler sun/Mon
* more active pattern for next week

Pattern overview...

00z guidance is in general agreement synoptically, still have some
several mesoscale features to resolve. Synoptically potent plains
trough will move towards New England on Saturday pushing a cold
front through by Saturday night. Chilly and blustery conditions for
Sunday and Monday as zonal flow takes shape. Guidance diverges
beyond Sunday leaving a low confidence forecast. Zonal flow to start
but the GFS is more progressive and develops a quick moving system
on Monday while the ec is dry until Tuesday. Timing issues need to
still be resolved. Next system to watch is Wednesday/Thursday
timeframe but model sensitivity to this system is high as the ec is
more progressive than the GFS. Regardless, looks like precip during
the mid-week with cooler temperatures once again by Thursday.
Trended the next weeks forecast towards a blend of the ensembles as
well as the ec which appears to be inline with the UKMET.

Details...

Saturday into Saturday night...

Potent shortwave will move through the flow and approach southern
New England on Saturday. This wave will drag a cold front across the
region ending the chances for above average temperatures.

During the morning, appears to be enough low level moisture trapped
under an inversion to keep low clouds and drizzle across a portion
of the area. Highest confidence is across the South Coast, but this
area can be greater as surface southerly winds will continue to
advect higher dewpoint into the region.

Ahead of the front, anomalous southerly flow with low level jet increasing to
35-45 kts as 925 mb temps warm to 11c. This will result in above
average temperatures for the region as well as gusty winds. Precipitable water
values also increase near 2 Standard above normal as southern stream
moisture is fed into the system. Along the front, a secondary low
will develop but appears it will be to far north and east and will
to keep southern New England out of the heavy qpf. This appears to
be inconjunction with the gefs as well as the ec ensembles which has
just a 20 percent prob of qpf over 0.5 inch. Will need to continue
to watch this secondary low and see where it will eventually develop
during this system.

Otherwise appears that the bulk of the heavy precip will be across
upstate New York and Vermont including The East Slope of the Berks. This area
is where the better dynamics will be as well as enhancement due to
upslope. May need to watch river levels after this system because of
the heavy rainfall potential and snow melt up north. Right now
ensembles are pointing towards a few sites near action stage.

As the cold front approaches, does appear that profiles turn moist
adiabatic. This may help mix some of the higher winds to the
surface. So cannot rule out a few gusts above 40 miles per hour. Also guidance
continues to show some elevated instability with tt above 50 and Li
below 0. Because of the steep pressure falls with this system,
cannot rule out the potential for a rumble of thunder and have
continued to mention the potential in the forecast.

Frontal passage will be quick as temperatures plummet behind the front. Could
see some wet flakes on the backside depending on how much moisture
is left as front moves through. Right now cannot rule out an inch
across far northwest mass.

Sunday into Tuesday...

Chilly and blustery northwest flow will take over the region by Sunday into
Monday. Temperatures difference between Saturday and Sunday could be
close to 15-20f. Wind gusts could also increase close to 30 miles per hour as
the region mixes well above 850mb. This will result in wind chill
values in the 30s. A Stark contrast from the previous several days.

Guidance mesoscale issues come to light by Monday as a weak wave
appears to move through the flow. 24 hour timing difference between
the GFS and ec with the ec pushing the system through on Tuesday.
The latest ecens and gefs are leaning closer to the ec keeping the
high pressure over the region on Monday. However there are still a
few members that are on the fast side. Whether this system comes in
on Monday or Tuesday we could see some rain/snow showers for the
region. Low confidence on timing.

Wednesday and beyond...

Large spread in the guidance for this period. Synoptically mean
upper level ridge over the Atlantic will help temps warm above
average. However potent shortwave moving through the Great Lakes
will push a warm and cold front towards southern New England. A lot
of issues to be resolved in exact placement of the low and if any
secondary low pressure systems develops. But right now models are in
agreement on the timing with this system coming through Wed
PM/Thursday with another cold snap behind it.

&&

Aviation /09z Thursday through Monday/...
forecaster confidence levels...

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

Short term /through Friday/...

Today...moderate confidence.

IFR and LIFR cigs/vsbys along the South Coast and islands, while
VFR conditions farther north. Patchy MVFR vsbys possible in
patchy fog before sunrise away from the coast. The South Coast
fog will retreat offshore this morning, with all areas becoming
VFR.

Tonight...moderate confidence.

Low clouds and fog will again move ashore along the South Coast
and islands. Expect conditions to return to IFR/LIFR in fog.
Potential for MVFR and patchy IFR in lighter fog farther north.

Friday...low-moderate confidence.

A cold front will stall over southern New England by Friday
morning and then slowly lift north. Still quite a bit of
uncertainty as to where this will stall. Expect IFR cigs and
MVFR vsbys in morning fog. Areas of MVFR cigs/vsbys expected in
showers Friday afternoon near or north of the front...so the
best chance for this would be in northern Massachusetts.

Kbos taf...moderate confidence in taf.

Kbdl taf...moderate confidence in taf.

Outlook /Friday night through Monday/...

Saturday...moderate confidence. Fog and drizzle to start the day in
MVFR/IFR conditions. Potent cold front will move through Sat PM
brining heavy rain, gusty winds near 30 kts and the potential for
thunder. Behind the front could see some wet flakes across the northwest
terminals. All of this could drop conditions to IFR/LIFR overnight,
but anticipate a rapid improvement near dawn Sunday.

Sunday...moderate confidence. Improving conditions with blustery northwest
wind gusts near 30 kts.

Monday...low confidence. Still a large spread in guidance. Mainly
VFR conditions with northwest gusts near 25kts. Could see some sct showers
across the South Coast.

&&

Marine...
forecaster confidence levels...

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

Short term /through Friday/...high confidence.

Today...

Areas of dense fog will linger through mid morning and then
shift farther offshore. This means poor vsbys early, but then
improving. Southwest winds will increase today with gusts of
20 to 25 knots, especially on the eastern outer waters. Seas
remain below 5 feet. Winds will need to be monitored, but
currently look to remain below small craft thresholds.

Tonight and Friday...

Cold front moving south will stall overnight or Friday morning,
then move slowly north. The Massachusetts North Shore may spend
a few hours north of the front with winds shifting from the east
or southeast. Areas south of the front will maintain southwest
winds through the period.

Outlook /Friday night through Monday/...

Saturday...moderate confidence. Increasing southerly flow with the
potential for Small Craft Advisory gusts. Waves will also increase in response. Vsbys
reduced in developing rain and fog. Low potential for thunder late
in the day.

Sunday...high confidence. Northwest winds will keep seas up and
increase wind gusts near 30 kts. Low probability for gales across
the outer waters.

Monday...low confidence. Large spread in the guidance but gusty northwest
winds will continue keeping seas up for sometime.

&&

Climate...
record highs for Thu Feb 23

Bos...65/1990
bdl...68/1990
pvd...60/1990
orh...61/1990

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...dense fog advisory until 9 am EST this morning for maz020>024.
Rhode Island...dense fog advisory until 9 am EST this morning for riz006>008.
Marine...none.

&&

$$
Synopsis...wtb/dunten
near term...wtb
short term...wtb

National Weather Service Glossary of Abbreviations