BOX issues Area Forecast Discussion (AFD) at Oct 9, 7:18 PM EDT004
FXUS61 KBOX 092318
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
718 PM EDT Wed Oct 9 2024
.SYNOPSIS...
A cold front will be moving through Southern New England tonight
into early Thursday morning. Other than a low chance at passing
showers, the cold front should be dry but will usher in a rather
cool air mass. This will set the stage for a breezy Thursday
with cooler than normal temperatures. Warm dry weather persists
Friday and Saturday. Area of low-pressure brings rain and
unsettled weather to the region Sunday night into Monday. Cooler
air mass settles in behind the departing low-pressure system by
the middle of next week.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
315 PM Update:
Still a nice afternoon across Southern New England currently,
governed by surface high pressure, with a modest west breeze and
temps in the lower to mid 60s. Cold pool aloft with daytime heating
is helping to create an increasing coverage of cumulus clouds this
afternoon; however greater coverage along with scattered showers
were more common across NY and portions of VT, associated with
increasing dynamic support tied to a pretty strong midlevel
shortwave trough seen on WV imagery nearing the northwestern shore
of Lake Ontario.
So for rest of the afternoon into tonight, the approach of the
midlevel trough should bring about a continued increase in cloud
cover, although considerably more cloudiness north and west compared
to areas south and east. Past several HRRR runs as well as some of
the 12z CAMs continued to show widely scattered passing showers in
the westerly flow late this aftn into the late evening. I did add a
low chance (15-20% chance) of a shower given the strength of the
shortwave trough and its history of generating showers to our north
and west, although temperature-dewpoint spreads of 20-25 degrees
would make it difficult for rain to reach the ground. Vast majority
of the time is expected to be dry. Passage of the shortwave and its
associated cold front will bring about strong cold advection (925 mb
temps falling to +1 to +4C) and a breezy NWly windshift, along with
decreasing cloud cover. Toward daybreak we could see some ocean
effect stratocumulus streamers over the Cape and Islands, but the
vast majority of the area will be otherwise cloud-free. The
northwesterly breezes should keep temps in the low 40s tonight
despite the cool advection.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
315 PM Update:
Thursday and Thursday Night:
Cold pool aloft settles over the Northeast states, with strong high
pressure over MI bringing ridging into Southern New England and the
mid-Atlantic states. The low level cold air is one of the coolest
airmasses we've seen to this point in the Fall. Despite wall to wall
sunshine (outside of the morning hours over the Outer Cape where
ocean effect stratocu is likely), it will be a rather breezy day
once mixing begins, with NWly gusts around 20-25 mph. With 925 mb
temps around +2 to +5C, highs may struggle to reach into the lower
50s across the higher terrain, and into the mid 50s to around 60 for
the remainder of Southern New England.
For Thurs night, the airmass begins to gradually modify, but clear
skies will favor good radiational cooling. Temperatures should fall
pretty quickly once the sun goes down, although there will still be
a pretty noticeable NW breeze of around 10 mph into the evening
hours. I did lean low temps toward some of the cooler MOS guidance
with lows in the low 40s, and the areas which typically radiate well
could see low temps in the mid/upper 30s. Those are temps which
would support potential for frost, but the expected strength of
sustained northwest breezes should mitigate the risk for frost.
&&
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Highlights
* Warm and sunny Friday and Saturday
* Increasing cloudiness Sunday afternoon ahead of a low-pressure
system that will bring precipitation to the Northeast Sunday night
into Monday
* Trending toward cooler temperatures by the middle of next week
Friday and Saturday
Deep northwest flow will continue to support sunny/dry conditions
across southern New England on Friday afternoon. 925 hPa temps near
10 Celsius will support above normal surface temperatures in the mid
to upper 60s on Friday. Friday night into Saturday, flow aloft
becomes more zonal with westerly winds advecting a warmer air mass
over the northeast. 925 hPa temps approaching 15C will support well
above normal temperatures for mid-October with some locations in
southern New England perhaps experiencing high temperatures in the
mid 70s. This is about 10 degrees above the climatological normal
high temperatures for Boston for October 12th. While substantial, we
won't be coming close to any records.
Sunday and Monday
By the second half of the weekend, short-wave energy from Canada
will dig south over The Great Lakes and support the development of a
surface low-pressure system over The Midwest. Latest forecast
guidances suggests this system will approach The Northeast Sunday
evening bringing unsettled weather to the region. The fine details
still need to be worked out at this time range, but the consensus is
for modest warm frontal precipitation Sunday night, followed by a
more robust round of precipitation ahead of the associated cold
front on Monday. Ensemble mean 24 hour precipitation forecasts are
ranging from 0.1 to 0.3 inches across the southern New England
between Sunday night and Monday. 90th percentile guidance gets as
high as 0.75 inches, so even in the wetter forecast scenario, this
looks to be a modest rain event to end the holiday weekend.
Next Week
A cooler air mass settles over The Northeast behind a departing cold
front next Tuesday. This will support chilly temps in southern New
England with highs/lows on Tuesday and Wednesday in the mid
50s/upper 30s respectively. No signals for any substantial
precipitation, but a large cold pool aloft characterized by 500 hPa
temps near -30C may support some cloudiness or sporadic instability
showers during the afternoon hours.
&&
.AVIATION /23Z WEDNESDAY THROUGH MONDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
00Z TAF Update:
Tonight: High confidence.
SCT-BKN VFR ceilings. Cold front moves through between 07-11z
Thursday and brings a windshift to NW around 10-15 kt with
sub-20 kt gusts.
Thursday: High confidence.
Mainly VFR, though out on the Outer Cape during the morning
hours we could see ceilings get near MVFR levels due to ocean
effect. NW winds 10-15 kt with gusts 20-25 kt.
Thursday Night: High confidence.
VFR. Gusts should ease after sundown with NWly sustained winds
decreasing to around 6-10 kt.
KBOS TAF...High confidence in TAF.
KBDL TAF...High confidence in TAF.
Outlook /Friday through Monday/...
Friday through Saturday: VFR. Breezy.
Saturday Night: VFR.
Sunday: VFR. Chance SHRA.
Sunday Night: Mainly VFR, with local MVFR possible. Breezy.
Chance SHRA.
Columbus Day: VFR. Breezy. Slight chance SHRA.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
315 PM Update:
Forecast confidence is rated as high, though becomes moderate
to high for Thursday and Thursday night.
Conditions to remain below SCA criteria through most of the evening
and overnight hours, with west winds 15-20 kt and seas 4 ft or less.
Passage of a cold front and cold air aloft over the milder waters
should permit NW gusts into the SCA range starting around the pre-
dawn hours Thursday on all waters. It looks as though the gusts over
the waters may occur in two surges: one in the immediate few hrs
after cold frontal passage, and then again for Thurs evening and
overnight especially over the eastern waters. SCAs have been issued
for all waters through at least noontime Thursday on all waters.
Since gusts could be on the borderline to SCA levels Thurs aftn and
evening, opted to keep the SCAs on the southern waters thru noon;
later shifts may need to revisit if the SCAs on the southern waters
should be extended further in time. Better confidence on SCA level
gusts through Thurs night on the eastern marine zones led to SCAs
going until pre-dawn Friday for these areas. Waves and seas 4 ft or
less through Thurs, though will increase a bit to around 4-6 ft on
the eastern outer waters Thurs night.
Outlook /Friday through Monday/...
Friday: Winds less than 25 kt. Seas locally approaching 5 ft.
Friday Night through Saturday: Low risk for Small Craft
Advisory winds with gusts up to 25 kt. Areas of seas
approaching 5 ft.
Saturday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft.
Sunday: Winds less than 25 kt. Slight chance of rain showers.
Sunday Night: Winds less than 25 kt. Local rough seas. Chance
of rain showers.
Columbus Day: Winds less than 25 kt. Areas of rough seas.
Chance of rain showers.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 4 AM to noon EDT Thursday for ANZ230-
232>237-255-256.
Small Craft Advisory from 4 AM Thursday to 5 AM EDT Friday for
ANZ231-250-251-254.
&&
$$
SYNOPSIS...Loconto/RM
NEAR TERM...Loconto
SHORT TERM...Loconto
LONG TERM...RM
AVIATION...Loconto/RM
MARINE...Loconto/RM
Source:
BOX issues Area Forecast Discussion (AFD) at Oct 9, 7:18 PM EDT----------------
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