Area Forecast Discussion Issued by NWS Boston, MA
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000
FXUS61 KBOX 160714
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
314 AM EDT Sat Mar 16 2024
.SYNOPSIS...
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A mixture of clouds and sunshine with unseasonably mild temperatures
today, but it will be noticeably cooler along portions of the
immediate coast with sea breezes. A round of brief showers overnight
into Sunday morning will be followed by another mild Sunday
afternoon along with breezy conditions developing. Temperatures
trending near to cooler than seasonable for much of the
upcoming week. Isolated showers possible Monday through
Wednesday along with gusty winds. Drier on Thursday and Friday.-- End Changed Discussion --
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.NEAR TERM /UNTIL 6 PM THIS EVENING/...
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315 AM Update...
* A mixture of clouds/sun today with highs upper 50s/near 60, but it
will be cooler along parts of the immediate coast with sea breezes
Lingering cyclonic flow continued to result in an abundance of low
clouds across central/eastern New England very early this morning.
There was also some very localized patchy ground fog in the typical
low-lying locations where some partial clearing has occurred...but
any of this should burnoff quickly after sunrise. Guidance indicates
some subtle upper level ridging building into the region today. This
should allow some of the stratus to dissipate across central/eastern
New England later this morning. That being said...expect more strato-
cu to develop with diurnal heating. So overall...a mixture of clouds
and sunshine are on tap for today. 925T on the order of +5C/+6C by
this afternoon should yield afternoon highs mainly in the upper 50s
to near 60 inland from the coast. These temps are about 10 to 15
degrees above normal for this time of year. A weak pressure gradient
will allow for localized sea breezes and cooler high temps in the
upper 40s to the lower 50s along parts of the immediate coast.-- End Changed Discussion --
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.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
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Key Points...
* Brief scattered showers after midnight into Sun AM
* Partly sunny & breezy Sun afternoon with perhaps a spot shower
* Highs Sunday in the upper 50s/near 60...cooler high terrain/Cape
Details...
Tonight into Sunday...
An approaching shortwave trough will induce a modest southwest LLJ
overnight into Sun am. While we expect dry weather to prevail this
evening...the forcing for ascent will increase along with low level
moisture overnight. This should result in a brief band of showers
crossing the region after midnight into Sunday morning. Overnight
low temps will only drop into the upper 30s to the lower 40s.
These showers will be short-lived in a given location with the bulk
of them over by Sunday afternoon. Still may have a few spot showers
Sunday afternoon with some diurnal heating...but generally Sunday
afternoon will be dry & unseasonably mild. Highs should top out
mainly in the upper 50s to near 60...but cooler in the high terrain
as well as the Cape/Islands. It will be a bit breezy too with
southwest winds shifting to the west with some gusts of 20 to 30 mph.-- End Changed Discussion --
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.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
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Highlights
* Dry for most on Mon and Tue with temps trending near to below
normal. Could have some isolated showers in western MA/CT on Mon.
Should see a bit more coverage in the shower activity on Tue.
* A quick moving front/system slides through on Wed bringing more
spotty showers.
* Drier on Thu and perhaps for much of Fri.
Monday through Tuesday...
Will have cyclonic flow in place through this timeframe. An
elongated trough digs into the eastern Great Lakes/Mid Atlantic on
Mon. This lifts into the Gulf of Maine/Nova Scotia by early Tue. In
its wake a shortwave ridge builds into New England, but quickly
shifts offshore on Tue. Another shortwave digs into New England on
Tue. A weak cold front slides through on Mon and a surface trough
rotates through on Tue.
Think out of these two days that Mon will be dry for most of the
region. The only exception is across western MA/CT where could see
some PoP up showers as a -20 to -30 degree 500 hPa airmass slides
in. Think we remain a bit drier and warmer further to the E/SE given
the W to WNW flow at 850 hPa and PWATs of roughly 0.2 to 0.25
inches. Looks also like we will have excellent mixing within the
boundary layer perhaps mixing down -20 to -30 degree Celsius dew
points at the top of the PBL during the day. Due to this have
lowered our RH/Td values to account for mixing down drier air. Given
the W/WNW flow will be near to slightly warmer than seasonable on
Mon until that front slides through.
Trending cooler on Tue with more cloudiness. Should have a better
shot for isolated showers across the interior. An anomalously cold
airmass will be overhead at 500 hPa. Both the NAEFS/EPS situational
awareness tables indicate -2 to -2.5 STD below model climo, which
are values of roughly -30 to -40 degrees Celsius. Given the core is
parked more over us will have a fair amount of cloudiness,
especially with diurnal heating. Have kept slight chances of precip
given limited moisture, but based on experience have seen these
setups result in spotty shower activity. Could actually see spots
where there is graupel.
Wednesday through Thursday...
Bit of a pattern change setting up as flow shifts from cyclonic to
quasi-zonal. A fast moving shortwave slides through the Great Lakes
and New England on Wed. A ridge axis begins building over the
Low/Mid Mississippi River Valley on Thu. A frontal system swings
through on Wed through on Wed before high pressure nudges in on Thu.
Still a bit of uncertainty on how things exactly evolve for the
middle of the week, but models are a bit more consistent with a
shortwave digging in. Though there are questions on how strong a
wave digs in. A frontal system slides through, which will bring
spotty showers. Still thinking that the NBM slight chances of precip
handles this well, so have stuck with it. High temps range from the
mid 30s across the high terrain to the 40s elsewhere.
Dry on Thu as high pressure nudges into the region. Temperatures
still trending cooler than seasonable. Highs top out in the mid 30s
across the higher terrain to the 40s elsewhere.
Friday...
At this point still appears dry and quiet on Fri with a ridge axis
building into the Mid Atlantic. Could have our next trough lift in
from the Mississippi/TN Valley later in the day, but there are
timing/intensity differences. At this point appears the risk is
greater more for Sat than Fri, but have stuck with the NBM for now
given the run to run differences.-- End Changed Discussion --
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.AVIATION /07Z SATURDAY THROUGH WEDNESDAY/...
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Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06z TAF Update...
Today...High Confidence.
Any lingering MVFR ceilings should dissipate across eastern New
England through 12z...but may persist a few hours longer across
the Cape/Nantucket. Otherwise...VFR with winds becoming SW at
5-10 knots and localized sea breezes developing in the afternoon
along parts of the very immediate coast.
Tonight and Sunday...Moderate Confidence.
Mainly VFR conditions this evening. A period of MVFR with brief
localized IFR conditions possible overnight into Sunday
morning with a few brief showers also possible. Conditions will
tend to improve to mainly VFR by the middle of Sunday
afternoon...but this process may be delayed several hours across
parts of the Cape/Islands. S winds up to 10 knots or so tonight with
some 20 to 25 knot gusts developing toward daybreak across the
Cape/Islands. Winds shift to the west by mid afternoon Sunday with
gusts of 20-25 knots.
KBOS TAF...High confidence in the overall TAF...but uncertainty
if we do see an period of ESE sea breezes during the afternoon.
KBDL TAF...High confidence in TAF.
Outlook /Sunday Night through Wednesday/...
Sunday Night through Monday: VFR. Breezy.
Monday Night: VFR. Windy with local gusts up to 30 kt.
Tuesday: VFR. Windy with local gusts up to 30 kt. Isolated
SHRA.
Tuesday Night: VFR. Breezy.
Wednesday: VFR. Breezy. Slight chance SHRA.-- End Changed Discussion --
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.MARINE...
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Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Today through Sunday...High Confidence.
Lingering 5 foot seas across our southeast outer-waters will
diminish by daybreak. Therefore...will let the small craft headlines
expire at 10z for these locations. Winds/seas will then remain below
small craft advisory thresholds today into this evening. Approaching
shortwave trough will induce a modest southwest LLJ overnight into
Sunday. This should generate SW wind gusts of 20 to 30 knots
overnight into Sunday eventually shifting to more of a W direction.
A new set of small craft headlines will be needed once the current
headlines over our southeast outer-waters expire.
Outlook /Sunday Night through Wednesday/...
Sunday Night through Monday: Winds less than 25 kt. Areas of
seas approaching 5 ft.
Monday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft.
Tuesday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Local rough seas.
Tuesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft.
Wednesday: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers.-- End Changed Discussion --
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.BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 7 AM EDT this morning for ANZ254-
255.-- End Changed Discussion --
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$$
SYNOPSIS...Frank/BL
NEAR TERM...Frank
SHORT TERM...Frank
LONG TERM...BL
AVIATION...Frank/BL
MARINE...Frank/BL