Area forecast discussion
National Weather Service Taunton Massachusetts
700 am EDT Tuesday may 21 2013
Synopsis...
a backdoor cold front will drop south across the region late
tonight and Tuesday resulting in briefly cooler weather across
eastern New England and chance of thunderstorms in western New
England. Warm and humid conditions continue into Thursday and
Friday with scattered showers and strong thunderstorms possible. A
cooler and less humid air mass is expected for the coming weekend.
&&
Near term /through tonight/...
700 am update...
forecast is generally on track for this morning. Made updates to
account for current conditions. Locally patchy dense fog has
spread across much of the region this morning per latest observation and
webcams. Will continue the dense fog advection until 10 am this morning.
Have pushed back timing of precipitation as showers over New Hampshire will remain
north of the region...and expect precipitation to develop by late
morning/early afternoon hours.
Previous discussion...
still trying to nail down the location of a back-door cold front
across eastern Massachusetts this morning. Winds are very light across most
of southern New England. Latest mesonet wind data indicated this
front had moved onshore across the North Shore. Farther south...
especially south of Boston...this front has apparently not made
much progress.
The location of this frontal boundary will play a crucial role in
our weather today. Significantly lower temperatures will be felt
east of this front...with another day of Summer-like warmth well
to the west. Cloud cover will also play a major role as well.
Marine stratus and patchy dense fog will take a while to dissipate
this morning.
These temperatures in turn will influence how much convective
instability is generated today. Latest Storm Prediction Center mesoanalysis had
1000-200 j/kg of most unstable cape. Mixed-layer cape was non-
existent. Marginal middle-level lapse rates this morning should mean
the broken convective line moving east across New York state should
weaken as it moves east of the CT River Valley across southern New Hampshire.
That said...still maintained at least an isolated threat of
showers and thunderstorms north of Route 2 in Massachusetts and southern New Hampshire
this morning.
As for later this afternoon...thinking airmass will destabilize to
result in mixed layer convective available potential energy of 750-1250 j/kg. Marginal middle-level
lapse rates should continue. Greatest threat of showers and
thunderstorms should be across the interior. However...cannot rule
out the possibility of elevated convection moving farther east
over the surface marine layer. Should this happen...thinking
convection would be weakening as it does so.
Temperatures were a blend of the MOS guidance.
&&
Short term /Wednesday/...
back-door cold front should move farther north late tonight into
Wednesday as a warm front. This should allow for a warmer day
across eastern Massachusetts. Still not convinced synoptic flow will be
strong enough to prevent local seabreezes from developing...so
temperatures will be tricky along the immediate coastlines.
Am currently expecting a brief diminishment of any convection
late tonight into Wednesday morning...as suggested by climatology.
Instability regenerates Wednesday afternoon...so kept at least a
chance of showers and thunderstorms in the forecast. The lowest
risk for showers and thunderstorms will be across the cape and
islands...where another round of low clouds and fog will keep
temperatures lower.
Used a blend of MOS guidance once again for temperatures.
&&
Long term /Wednesday night through Monday/...
highlights...
* scattered showers and thunderstorms Thursday into Friday
* cooler and less humid for the weekend
Confidence level/model guidance...moderate confidence in the
overall forecast...yet low confidence on model performance. The
00z GFS/NAM significantly slowed down the digging trough for the
northeast. The rest of the model guidance followed suit but not as
drastically. Leaned forecast towards ec/UKMET which where in
between the 12z and 00z guidance as well as previous forecast. Overall
have high confidence that precipitation will occur Thursday and moderate
confidence for Friday. High confidence in a cool down for the week
with moderate confidence for seasonal temperatures and dry forecast for
beginning of the work week.
Details...
Thursday into Friday...
Approaching upper level trough will bring a round of precipitation and
thunder to the region. Still some timing issues as models still
differ on exact location and mesoscale parameters.
Regardless...southern New England will be located in the warm sector
of the system allowing higher dewpoints and therefore muggy
conditions. Temperatures will warm into the 80s. Believe diurnal precipitation
will be the main treat for this day...with strong storms possible.
Main threat of these storms will be hail...strong winds and heavy
downpours. A cold front will begin to approach the region Thursday
night and move through the area on Friday. This will change the
convective Mode to more of a possible squall line on Friday.
Convective parameters appear to be more in line due to the slow down
of the overall system. Only thing truly lacking is the amount of
instability as cloud debris will be around from the previous nights
showers/thunder. If storms do develop then believe the main threat
will be strong winds and heavy downpours as precipitable waters reach close to 1.5
in.
This weekend...
Upper level trough will push through over the week...cold air advection will
bring a thermal trough into the region. This will drop temperatures well
below seasonal average. Am not anticipated any frost/freeze headlines
at this time but may need to monitor in the future as the entire
area is now in the growing season. Expect mainly dry weather for
the weekend and temperatures in the middle to upper 60s.
Monday and beyond...surface high pressure will be in control for
the first half of next week. This will help temperatures reach seasonal
conditions. Appears that there is limited moisture...however
cannot rule out a spot shower or two...especially if sea breeze develops.
&&
Aviation /12z Tuesday through Saturday/...
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Overview...moderate confidence in timing and areal coverage of
stratus and fog both this morning and Wednesday morning.
Patchy IFR/MVFR conditions due to fog have spread north across
southern New England this morning. Expect fog to dissipate and
conditions to lift to VFR by this morning.
Today...showers and thunderstorms are possible this
afternoon...especially across the CT River Valley.
Tonight...widespread IFR/LIFR in stratus and fog redevelop.
Wednesday...pretty much a repeat of Tuesday. Gradual improvement
to VFR/MVFR from west to east.
Kbos terminal...moderate confidence...mainly due to timing of VFR
improvement.
Kbdl terminal...moderate confidence...mainly due to timing of VFR
improvement.
Outlook...Thursday through Saturday...
Thursday into Friday...low to moderate confidence.
Moderate confidence on sea breeze developments. Very unsettled
pattern with variability between VFR conditions and MVFR/IFR
conditions in shra/tsra/fog. Improving conditions late Friday
night into Saturday morning.
Saturday...high confidence. VFR.
&&
Marine...
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
High confidence through Wednesday.
Winds and seas expected to remain below Small Craft Advisory
criteria most of today. Leaned more heavily upon the Swan wave
guidance as the wna wave guidance appears to be too high. Still
expecting areas of fog to persist through today before expanding
once again tonight.
Increasing southwest winds Wednesday may lead to development of
marginal 5 feet seas across the southern outer coastal waters of Massachusetts
and Rhode Island. Will hold off on issuing another Small Craft Advisory
right now to avoid confusion with existing advisory.
Outlook...Thursday through Saturday...
Thursday into Friday...high confidence. Approaching storm system
will increase seas above 5ft during this time period...Small Craft Advisory will be
needed. Expect low visibilities in heavy showers and some thunder as well.
Believe Friday is the better day for thunderstorms across the waters as
cold front will push through New England on Friday.
This weekend...moderate confidence. Seas will remain above Small Craft Advisory
for most of the weekend especially for the outer waters. Gusty northwest behind
the front will bring gusts close to gale force Sat into Sat night.
&&
Box watches/warnings/advisories...
CT...none.
Massachusetts...dense fog advisory until 10 am EDT this morning for maz020>024.
New Hampshire...none.
Rhode Island...dense fog advisory until 10 am EDT this morning for riz006>008.
Marine...Small Craft Advisory for hazardous seas until 8 am EDT this
morning for anz255-256.
&&
$$
Synopsis...Belk/dunten
near term...Belk/dunten
short term...Belk
long term...dunten
aviation...Belk/dunten
marine...Belk/dunten
