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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Tuesday
• 
• High: 64 °
• Low: 52 °
• Chance of Rain

• Wednesday
• 
• High: 72 °
• Low: 57 °
• Thunderstorm

• Thursday
• 
• High: 68 °
• Low: 55 °
• Chance of Rain

• Friday
• 
• High: 68 °
• Low: 52 °
• Chance of T-Storms

• Saturday
• 
• High: 64 °
• Low: 48 °
• Chance of Rain

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