BOX issues Area Forecast Discussion (AFD) at May 31, 1:51 AM EDT423
FXUS61 KBOX 310551
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
151 AM EDT Sat May 31 2025
.SYNOPSIS...
A strong low pressure will bring a round of widespread showers
and scattered thunderstorms with locally heavy rainfall late
tonight into Saturday morning. A period of drier weather is
possible late morning into Saturday afternoon, before another
round of scattered showers arrives later Saturday into Saturday
night, with a few embedded thunderstorms possible too. Drier
weather follows Sunday into Monday. Dry weather much of next
week, except Thu and/or Fri, with the risk for scattered showers
& thunderstorms. A warming trend is likely too, with a 40-50%
chance of highs in the 80s mid to late in the week.
&&
.NEAR TERM /THROUGH TODAY/...
Key Messages:
* Scattered evening showers and possibly a t-storm across interior
Partial sunshine and temps warming into the 70s with dewpoints near
60 have contributed to marginal instability with SBCAPES around 500
J/kg. Scattered showers have developed across CT through interior MA
and can't rule out a t-storm through the afternoon, north and west
of I-95. Weak surface boundary stalls across western MA this
evening and guidance continues to highlight interior MA and CT for
scattered showers and perhaps a t-storm into this evening while it
remains mostly dry near the coast through about midnight.
&&
.SHORT TERM /TONIGHT THROUGH 6 PM SUNDAY/...
Key Messages:
* A period of showers and thunderstorms move in late tonight into
Sat morning. Locally heavy rainfall and some street flooding
possible, especially western MA/CT
* Drying out late morning into the afternoon, but a few late day
showers or a t-storm possible
Quite an interesting scenario unfolding for late tonight into
Sat morning as a rather anomalous mid level trough/shortwave
acquires neg tilt as it lifts NE across SNE. Closed low
develops at 700 mb as it moves into western New Eng with a sub
980 mb surface low which is outside the CFSR climatology for
SLP for this time of year. This is quite impressive for almost
early June. Winter type dynamics combined with late spring
moisture will result in heavy rainfall across the NE as this
system moves through late tonight and Sat morning. Decent
elevated instability combined with strong forcing will support
scattered t-storms as well. Surface instability is minimal so
not expecting any severe weather, but will have to monitor
instability trends very closely as any surface instability will
result in a risk of severe weather. HREF is indicating some
updraft helicity tracks indicative of a strong forcing and
kinematic environment.
Heavy rainfall is the more likely risk from this system. Based on
interior track of 700 mb low would expect heaviest rainfall
across western MA/CT, but could see a secondary QPF max further
east near the coast where elevated instability and low level jet
dynamics are more robust. PWATs briefly increase to 1.25-1.5"
which only about 1-2SD above normal so rainfall probably will
not be as significant as it otherwise could be if moisture were
more anomalous. Still, the potential exists for localized 3-4
inch rainfall amounts focused across western MA/CT. In fact, EMC
HREF indicating low probs of 3 hr QPF exceeding FFG over the
Berkshires and also show 10 percent probs of 5 inches in western
MA. The rest of the area will depend on coverage and duration
of convection so rainfall will be variable with some areas
seeing less than an inch while other areas get more.
As shortwave and mid level low lift to the north after 15z, expect
showers to exit the region with a period of dry weather late morning
into the afternoon. In fact, decent dry slot ahead of the mid level
low may lead to some breaks of sunshine across eastern New Eng.
However, secondary shortwave passage and cold front may trigger a
few late day showers or perhaps a t-storm. Winds shift to SW in the
morning then W in the afternoon and become gusty with potential for
30 mph gusts. Highs mostly in the mid 60s to around 70.
&&
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Key Messages:
* Scattered showers & isolated thunderstorms possible Saturday
evening
* Mainly dry Sunday, but cooler than normal, with highs in the 60s
and lows in the 40s
* Dry much of next week along with a warming trend
Saturday night...dry slot overspreads the region Saturday afternoon,
followed by a secondary short wave pivoting across SNE. Models
struggling with the amplitude, moisture and track of this feature.
However, cooling temps aloft will support steepening mid level lapse
rates combined with cyclonic flow to yield a round of scattered
showers with possible embedded thunder. Not expecting severe storms,
but a low risk of lightning (10-20%) could briefly impact outdoor
events. Timing of low top convection is roughly 20z-02z. Not a
washout given short duration and small areal coverage. Strong CAA
for this time of year will advect 850 mb temps down to +3C by 12z
Sun. This will support lows 45-50 for most locations.
Sunday...dry westerly flow, but cold (-20C at 500 mb) cyclonic flow
aloft, will yield lots of diurnal clouds. Given mid/upper level
trough is deamplifying (rising heights) with time, this should limit
any diurnal shower activity to isolated in coverage with the highest
probability (10-15%) across the hilly terrain of MA and CT. Thus, by
no means a washout with mostly dry weather prevailing. Most breaks
of sunshine will be early and again late in the day, with the loss
of daytime heating. This cold air aloft will translate to highs only
in the 60s (only +3C at 850 mb), perhaps near 70 at the coast given
downslope west winds. Although, it will feel cooler given breezy
conditions, west winds 15 to 20 mph. Two cool nights as well, with
lows in the 40s for most locations Sunday morning and again Monday
morning.
Next week...long wave trough exits New England Mon/Tue and is
replaced by ridging thereafter from the west. This should deliver a
warming trend for the region beginning Tue and persisting into late
in the week. A few of the ECMWF members pinch off some of the
northern stream energy rotating through the long wave trough Mon
across the northeast, forming a closed low off the Mid Atlc coast.
These few members then track this feature and its moisture across
SNE Wed and Thu. However, not much support for this solution from
other model guidance, including the GFS and UKMET. Also, the ECMWF
ensembles have a 40-50% chance of 80+ deg temps here Wed thru Fri.
Thus, will hedge the forecast towards mainly dry and warmer this
period. Chance of showers/tstms Thu or Fri with approaching short
wave/frontal boundary. Otherwise, next week features lots of dry
weather with warming temps each day!
&&
.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06z TAF Update...
Today...Moderate confidence.
IFR/LIFR cigs with areas of fog near the south coast.
Widespread showers and sct t-storms will continue, then lift to
the north after 15z. Locally heavy rainfall possible.
Conditions improving to VFR during the afternoon after wind
shift to W. Gusts to 25-30 kt developing during the afternoon,
locally higher over the Cape and islands, especially Nantucket.
A few late day showers or a t-storm possible.
Tonight...High confidence.
VFR. W winds 10-15 kts.
Sunday...High confidence.
VFR. W winds 10-15 kts, gusting to 20-25 kts in the afternoon,
locally higher to 30 kts over the Cape and Islands.
BOS TAF...High confidence in trends. Lower confidence in vsby
potential and timing.
BDL TAF...High confidence in trends. Lower confidence in exact
timing and specific details.
Outlook /Sunday Night through Wednesday/...
Saturday Night: VFR. Breezy. Chance SHRA, slight chance TSRA.
Sunday through Sunday Night: VFR. Breezy.
Monday: VFR.
Monday Night through Wednesday:
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Through Saturday...
Increasing S/SE winds tonight, becoming SW 12-18z Sat followed
by gusts to 25-30 kt developing. Seas building to 8-10 ft over
southern waters. SCA in effect for all waters. Showers and sct
t-storms moving over the waters late tonight and Sat morning
with poor vsbys in fog, with some improvement developing during
the afternoon.
Outlook /Sunday Night through Wednesday/...
Saturday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. Slight chance of rain
showers.
Sunday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of seas approaching 5 ft.
Sunday Night: Winds less than 25 kt. Areas of seas approaching
5 ft.
Monday: Winds less than 25 kt. Seas locally approaching 5 ft.
Monday Night through Wednesday: Winds less than 25 kt.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from noon today to 10 PM EDT this evening
for ANZ230-231-236-251.
Small Craft Advisory from 8 AM this morning to 8 AM EDT Sunday
for ANZ232>235-237-254>256.
Small Craft Advisory from noon today to 8 AM EDT Sunday for
ANZ250.
&&
$$
SYNOPSIS...KJC/Nocera
NEAR TERM...KJC
SHORT TERM...KJC
LONG TERM...Nocera
AVIATION...BW/Dooley
MARINE...KJC/Nocera
Source:
BOX issues Area Forecast Discussion (AFD) at May 31, 1:51 AM EDT----------------
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