BOX issues Area Forecast Discussion (AFD) at Aug 20, 7:23 PM EDT381
FXUS61 KBOX 202323
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
723 PM EDT Tue Aug 20 2024
.SYNOPSIS...
Low pressure over the Canadian Maritimes and high pressure over the
Great Lakes will provide unseasonably cool weather into Thursday,
about 10 degrees cooler than normal. A few scattered afternoon
showers and possibly an isolated thunderstorm is in the forecast
Wednesday, but by no means a washout. Dry weather prevails
Thursday and into the weekend, along with a warming trend.
&&
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
710 PM Update:
Variable amounts of cold-air stratocumulus around Southern New
England, greatest towards the north and east. However decreasing
trends noted in satellite imagery, with a more gradual decrease
in clouds towards mostly clear skies to continue. Cloud cover
could linger into early in the overnight for eastern and
southeast coastal New England but should trend mostly clear for
these locations by the predawn hrs. A gradual decrease in NW
wind speeds are anticipated too, although the NW gradient is
still pretty robust across central and eastern NY and suspect NW
speeds around 5-10 mph may still continue until midnight before
becoming light NWly for the overnight hrs. Lows should approach
dewpoint temps tonight under good radiational cooling, in the
mid 40s to mid 50s.
Previous discussion:
* Fall-like Temps through Wed night
Very cool airmass has overspread the region, at least by
August 20th standards, with 3 pm temps only in the upper 60s
and lower 70s, despite dry weather prevailing. Diurnal clouds
and gusty WNW winds will both dissipate with sunset/loss of
diurnal heating. Thus, decreasing clouds and diminishing winds
this evening and overnight. This combined with a dry airmass
(dew pts in the upper 40s/low 50s) in place will result in
radiational cooling and temps falling into the upper 40s and
lower 50s, mid to upper 50s in the urban areas and coastline.
These temps are about 10 degs cooler than normal, definitely
providing a fall-like feel to this airmass. Given the setup
mentioned above, derived mins from the colder MOS guidance.
&&
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
4 PM update...
* Cool weather continues with temps running about 10 degs
cooler than normal
* Scattered afternoon showers, isolated thunder possible
Sunshine to start the day but quickly gives way to diurnal
CU/SCU and becoming broken to overcast at times given cold
cyclonic flow flow aloft. Anomalous short wave and cold pool
(-20C) currently over southwest Quebec, advects eastward across
SNE during peak heating Wed afternoon and early evening. Not
expecting a washout by any means, just scattered diurnal
showers. Given in the anomalous cold air aloft (-20C at 500 mb)
a few of the more robust showers may contain small hail or
graupel (aka dippin dots) and possibly lightning, as cross
section show saturation possible up to the -10C isotherm.
Otherwise, dry weather prevails with highs once again only in
the upper 60s and lower 70s (about 10 degs cooler than normal).
Not quite as breezy as today, with west winds 10-15 mph.
Wednesday night...
Any early evening scattered showers dissipate by late evening
along with decreasing clouds. Departing short wave delivers a
reinforcing shot of cool air overnight, with lows once again in
the upper 40s and lower 50s, mid to upper 50s in the urban area
and coastline. These temps are about a month ahead of scheduled.
&&
.LONG TERM /THURSDAY THROUGH TUESDAY/...
4 PM update...
Highlights:
* Mix of clouds and sun with unseasonably cooler weather continuing
into Thurs. Hit or miss showers mainly north of the Mass Pike.
* Dry weather with a warming trend Fri into the weekend, with temps
trending above normal by the weekend.
* Next best chance for widespread showers/t-storms around
next Monday but details are still unclear at the time.
Details:
Upper level low associated with a shot of unseasonably cool
temperatures reminiscent of early-Fall will still remain over the
interior Northeast on Thurs, then slowly egress toward the northeast
into northern ME/eastern Quebec on Friday. Rising 500 mb
heights/subsidence aloft Fri into the weekend, with sfc high
pressure parked to our south allowing for a warming trend to temps
closer to seasonable and then slightly above normal. Pattern then
continues into at least later Sun or Mon, with indications in
ensembles of an amplifying upper trough re-developing over the
Northeast, bringing our next best chance for showers and t-storms.
With upper low still in the vicinity on Thurs, expect temps
continuing to run cooler than normal (mid 60s to low-mid 70s highs)
with variable amts of cumulus cloudiness associated with the cool
pocket of air aloft. Couldn't rule out a shower north of the Mass
Pike nearest the cold pocket aloft but dry weather should prevail
more often than not. Thereafter warming trend with dry weather
supporting highs warming back into the 70s to mid 80s Fri into the
weekend, with lower to mid 80s being more common by Sat and Sun.
Overall a pretty nice stretch of weather!
Looks like we do turn more unsettled either late Sun or Mon as a
cool front and parent upper trough approach the region. Differences
in the models regarding timing and amplitude of the trough energy,
so at this point it is still unclear which day(s) may have better
chances for showers or t-storms and what impacts, if any, we could
see from this unsettled period. Maintained slight chance PoP mention
for now and can then adjust up or down with subsequent guidance.
&&
.AVIATION /23Z TUESDAY THROUGH SUNDAY/...
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-OVC VFR (bases 035-050) should steadily decrease in
coverage. NW winds around 8-12 kt to gradually decrease to
under 5 kt overnight.
Wednesday...High Confidence.
VFR then VFR/MVFR cloud bases developing in the afternoon along
with scattered showers. An isolated low top thunderstorm is
possible, along with small hail and gusty winds given such
anomalous cold air aloft. Activity will be focused 18z-22z across
northern portions of MA/CT/RI. Otherwise WNW winds 10-15 kt.
Most of the day remains dry. Brief seabreeze possible 15z-18z
and then west winds developing.
Wednesday night...high confidence.
Any early evening showers/isolated -TSRA will dissipate with
sunset, giving way to VFR, dry weather and let west winds.
KBOS TAF...High confidence in TAF thru 12z Wed. Then some
uncertainty on a possible short duration seabreeze 15z-18z Wed.
Wind direction would briefly shift to the SE, then west after
18z. Also, marginal MVFR/VFR cigs 18z-22z along with VCSH. Low
risk (10-20%) of an isolated -TSRA with higher probability
across northwest MA.
KBDL TAF...High confidence in TAF. SCT-BKN VFR cloudiness,
greatest coverage during Wed afternoon. Hit or miss aftn SHRA,
possible rogue TS 17z Wed-00z Thu but drier weather for many hrs.
Outlook /Thursday through Sunday/...
VFR.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
4 PM update...
Thru Wed night...
SE swells from distant Ernesto finally eroding, therefore have
cancelled the SCA. Otherwise, dry weather with good vsby with
WNW winds 10-15 kt, up to 20 kt near shore Tue afternoon/early
evening. Chance of a shower/thunderstorm near shore Wed
afternoon/evening.
Outlook /Thursday through Sunday/...
Winds less than 25 kt.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.
&&
$$
SYNOPSIS...Loconto/Nocera
NEAR TERM...Loconto/Nocera
SHORT TERM...Nocera
LONG TERM...Loconto
AVIATION...Loconto/Nocera
MARINE...Loconto/Nocera
Source:
BOX issues Area Forecast Discussion (AFD) at Aug 20, 7:23 PM EDT----------------
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