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Area forecast discussion 
National Weather Service Boston/Norton Massachusetts 
653 am EDT sun may 20 2018 


Synopsis... 
a warm front warm front lifts north through the region tonight, 
allowing a warm and humid airmass to overspread the area. A 
cold front triggers scattered showers with brief heavy rainfall 
and isolated thunder this afternoon. Drier this evening into 
Monday with passing showers during the mid-week. Cooler, drier 
air follows for Thursday into Saturday. 


&& 


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


700 am update... 


Upper level trough continues to approach the region from the 
west while surface cold front is currently draped across the 
eastern Great Lakes into northern New England. This front will 
be the focus of convection that develops today. 


Still a lot of clouds across the region with areas of fog and 
drizzle. These clouds may limit temperatures and instability 
today. Have noticed in area webcams that the dense fog has 
pushed back in across the South Coast as vsbys are at or below 
1/4sm. Will wait for the top of the hour obs but may issue a Special Weather Statement 
for the patchy dense fog. 


Still have a good low level jet over the region and with high precipitable water values 
cannot rule out a few isolated showers during the morning hours. 
Timing from the cams suggest that the front will approaching 
between 11 and 1 PM and move across southern New England through 
the day. As mentioned before, there is the potential for some 
embedded thunder but any severe weather appears unlikely at this 
time. The front will move offshore by 7-8 PM leading to a quick 
drying trend as winds will turn out of the northwest and 
Canadian high pressure builds into southern New England. 


Aside from the rain and fog, winds across southeast Massachusetts have 
increased to 20-25 kts. Expect these type of gusts to continue 
into the morning hours as low level lapse rates begin to 
steepen and we mix out per BUFKIT soundings. 


Previous discussion... 


Low clouds and fog will be prevalent this morning. Widespread 
showers early this morning across Rhode Island and southeast Massachusetts will move 
offshore by mid morning. 


Clouds will be key to the realized weather later this afternoon. 
A cold front will move through this afternoon and evening. 
Instability will be very dependent upon the amount of sunshine. 
Forecast cape values in some of the high resolution guidance of 
500-1,000 j/kg persist. The longer the clouds linger, the lower 
the cape values will likely be, and the fewer thunderstorms 
would result. In either case, not expecting severe weather 
because many other ingredients are missing. 


Precipitable water values of 1.50-1.75 inches will mean locally 
heavy rainfall is possible, too. Still looks like the window for 
the greatest risk for showers, after daybreak, will be between 
10 am and 5 PM. 


Modest southwest winds will push warmer and more humid air into 
our region. This should make for a more Summer-like feel today. 
High temperatures generally in the 70s away from the coasts, 
perhaps a little higher where sunshine breaks out for a while. 


&& 


Short term /6 PM this evening through 6 PM Monday/... 
high pressure building into the Great Lakes tonight and Monday 
will send drier weather our way. Mainly clear skies will permit 
the sunshine to boost temperatures well into the 70s Monday away 
from the immediate coast. Local seabreezes possible. Not nearly 
as humid as today, with comfortable dewpoints mainly in the 
40s. 


&& 


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


* passing showers Tuesday and Wednesday 
* potential for dry weather but below avg temps for the end of 
this week 
* potential for wet weather Memorial Day weekend 


Details... 


Monday night...high confidence. 


Dry weather will prevail as high pressure slides into the Gulf 
of Mexico. Approaching warm front to the south will help 
increase dewpoints and leave temperatures cool but mild. Lows in 
the mid 50s. 


Tuesday into Wednesday... moderate confidence. 


Bermuda high pressure remains while upper level trough 
continues over the northeast Canada. This puts the region in a 
more zonal pattern. Weak wave moving through the flow will slide 
along a stalled front south of southern New England. This could 
bring showers across the area and keep the region on the cool 
side of the front. Still a spread on how far north precip will 
get, but right now highest confidence is south of the Pike. 


Behind this disturbance, an approaching cold front will move in 
from the northwest. This front is associated with the upper 
level trough digging into the northeast. Could see some showers 
along this front but moisture is a bit marginal. Models are even 
hinting as some sb cape, so if showers develop cannot rule out 
a rumble of thunder. Temperatures will be more seasonable with 
highs in the mid 70s. 


Thursday into Saturday...moderate confidence. 


Drier but breezy conditions looks to be in store for the end of 
the week due to a northwest flow pattern. Lots of dry air will 
dominate on Thursday, but appears that a weak disturbance will 
move through the area on Friday. For now trended the 
temperatures below avg and kept with a dry forecast. 


Sunday and beyond...moderate confidence. 


Digging trough over the Great Lakes will move into the 
northeast, resulting southwest flow aloft. Good moisture plume 
moving up from the Gulf could result in wet weather Sunday into 
Monday. Still a lot of uncertainty in regards to the weekend so 
stay tuned. 


&& 


Aviation /12z Sunday through Thursday/... 
forecaster confidence levels... 


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


Short term /through Monday/... 


Today...high confidence in trends. Moderate confidence in 
timing. IFR/LIFR lifts to MVFR by midday, slightly longer South 
Coast. Drizzle and areas of morning fog erode by midday but give 
way to a broken line of showers along and ahead of an 
approaching cold front. Low probability of isolated 
thunderstorms, but showers will contain locally heavy rain from 
about 15z-21z from west to east. Breezy southwest winds 15 to 20 
kt with a few gusts up to 25 kt possible. 


Tonight...high confidence in trends. Moderate confidence in 
timing. Any leftover IFR/MVFR early evening over Cape Cod 
improves rapidly to VFR. Otherwise VFR and dry weather. 


Monday...high confidence. VFR. 


Kbos terminal...moderate confidence in taf. Low risk for iso 
thunder between 17-21z. 


Kbdl terminal...moderate confidence in taf. 


Outlook /Monday night through Thursday/...moderate confidence. 


Monday night: VFR. 


Tuesday: VFR. Chance rain showers. 


Tuesday night: mainly VFR, with local MVFR possible. Chance 
rain showers. 


Wednesday: VFR. Slight chance rain showers. 


Wednesday night through thursday: VFR. 


&& 


Marine... 
forecaster confidence levels... 


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


Short term /through Monday/...moderate confidence. 


Areas of fog will lead to restricted visibility, less than 1 nm 
at times. Increasing SW winds ahead of a cold front today. Gusts 
up to 25-30 kt. Showers with locally heavy rain this afternoon 
and early evening. Winds become northerly behind a cold front 
tonight and quickly diminish. Rough seas will take a little 
longer to subside, especially across the outer coastal waters. 


Outlook /Monday night through Thursday/...moderate confidence. 


Monday night: winds less than 25 kt. Seas locally approaching 
5 ft. 


Tuesday through Tuesday night: winds less than 25 kt. Chance of 
rain showers. 


Wednesday: winds less than 25 kt. Slight chance of rain 
showers. 


Wednesday night through thursday: winds less than 25 kt. Seas 
locally approaching 5 ft. 


&& 


Box watches/warnings/advisories... 
CT...none. 
Massachusetts...none. 
Rhode Island...none. 
Marine...Small Craft Advisory until 6 PM EDT this evening for 
anz232>234-250. 
Small Craft Advisory until noon EDT today for anz230-251. 
Small Craft Advisory until 3 PM EDT this afternoon for anz231. 
Small Craft Advisory until midnight EDT tonight for anz236. 
Small Craft Advisory until 6 am EDT Monday for anz235-237-254. 
Small Craft Advisory until 1 PM EDT Monday for anz255-256. 


&& 


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



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