BOX issues Area Forecast Discussion (AFD) at Jul 9, 10:28 AM EDT388
FXUS61 KBOX 091428
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
1028 AM EDT Tue Jul 9 2024
.SYNOPSIS...
Oppressive heat and humidity are expected to continue today and
tomorrow with isolated shower/thunderstorm chances in the
afternoon/evening hours, mainly across western and northern
Massachusetts. Quite warm and very humid weather will continue
through the end of the work week. While at least isolated
showers and thunderstorms are possible at anytime, it appears
the main risk for more widespread activity with torrential
rainfall/localized flash flood potential will be sometime
Friday/Friday night along a frontal boundary.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
No major changes to the ongoing forecast this morning. Main
changes were to cloud cover and accounting for the area of
showers moving across MA this morning. Latest SPC mesoanalysis
showed most-unstable CAPE values around 1,000 J/kg across
southern New England with 30-40 kt of effective shear. Mid level
lapse rates were not even moist-adiabatic, which will hinder
thunderstorm development, at least for now.
Still expecting more showers and thunderstorms this afternoon
and evening. Minor tweaks to temperatures to account for
existing cloud cover over the next few hours.
655 AM Update...
Previous forecast is on track. We can not rule out a brief
elevated spot shower/t-storm this morning across west and
northwest MA...but dry weather will generally prevail through
mid-afternoon. The main risk for isolated to scattered
thunderstorms will be mid-late this afternoon into this evening
across northern and western MA...which the prior forecast
discusses below.
Fog and low-stratus persists over the south coast and
southeastern MA. A dense fog advisory remains in effect for
these areas through 11AM. Expect fog/low stratus to lift by mid
to late morning giving way to partly sunny skies. Heat and
humidity continues today as a broad Bermuda High Pressure system
continues to support a southwest stream of warm/moist air into
The Northeast. Heat indices peak in the upper 90s to near 100
across portions of interior MA this afternoon. Also, with steady
southwest winds likely to fend off a sea-breeze, heat advisory
criteria may be reached all the way to the coast with
consecutive days of 95+ heat indices possible today and
tomorrow. Thus, the heat advisory has been expanded to the coast
to include the rest of Plymouth, Suffolk, and Essex counties.
In addition to potentially dangerous heat this afternoon, there
is also a marginal risk for a strong to severe thunderstorms
mainly across northern and western MA. Surface temperatures in
the upper 80s/low 90s and dewpoints in the low 70s will result
in surface based CAPE values between 1000 and 2000 J/Kg.
Additionally, an increasing pressure gradient aloft will support
a stronger wind field with a 40 to 50 knot jet developing at
500 hPa. This will support deep layer shear values between 30
and 40 knots which would be sufficient to sustain organized
convection. Moisture values will surge this afternoon as well
with PWATs rising above 1.75 inches. The lacking ingredient
today will be lift as only modest forcing for ascent is in the
forecast with a weak upper-level disturbance moving across the
northeast. The greatest forcing looks to be focused just north
of southern New England, but hi-res model guidance suggests this
feature will sag far enough south to trigger some showers and
storms across northern and western MA, mainly along route 2.
Damaging wind gusts and heavy rainfall/flooding would be the
primary risks as weak mid-level lapse rates will limit hail
growth potential. Nonetheless, some small hail can't be ruled
out either. Timing for storms would be the typical 2 to 8 PM
time frame when the most instability will be available.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
Tonight
Persistence forecast tonight with very little change in the air
mass. Thus, we can expect another round of fog/low stratus
developing across the south coast, Cape, Islands, and portions
of southeast MA. Another dense fog advisory may be needed. No
relief from the heat overnight as low temperatures will be
bounded by dewpoints in the low 70s. Light south/southwest
winds.
Tomorrow
Warm/moist air mass remains in place tomorrow with an uptick in
surface dewpoints to the mid 70s. This will be accompanied by
increased deep layer moisture as PWATs are likely to exceed 2
inches across much of southern New England. With the increased
moisture will come increased cloud cover, but the overall
tropical air mass will continue to support heat advisory
conditions despite less sunshine. Confidence in this aspect of
the forecast is on the moderate to high side. The lower
confidence portion of tomorrow's forecast resides with scattered
shower/thunderstorm potential. There will remain a suitable
environment for thunderstorms tomorrow afternoon with sufficient
deep layer shear (30+ knots), 1000 to 2000 J/kg of CAPE, and a
surplus of moisture. Forcing for tomorrow will be associated
with a surface warm front lifting north with the remnants of
what is now Tropical Depression Beryl lifting into The Midwest.
The strongest atmospheric forcing will reside near the remnant
circulation, but model guidance supports shower/thunderstorm
activity across portions of southern New England. Similar to
today's forecast, hi-res model guidance is hinting at the
greatest shower/thunderstorm potential generally along and north
of I-90/. Once again damaging wind gusts and heavy downpours
would be the primary threat with hail being a secondary threat.
Areas south of I- 90 can expect hot/muggy conditions with modest
south winds and more clouds than sun.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Key Points...
* Quite Warm & Very Humid Thu & Fri
* Very Warm Sat/Sun/Mon with above normal temps continuing and
still humid but a bit of an improvement from Thu and Fri
* Main threat for widespread showers/t-storms with torrential
rainfall & localized flash flooding will be sometime Fri/Fri
night
Details...
Thursday and Friday...
Strong upper level ridging across the Atlantic will direct the
remnant circulation of Beryl across the eastern Great Lakes and
then into northern New England on Thu. This will result in Thu
being a very humid day with dewpoints in the 70s as deep
tropical moisture continues to be dragged northward. Highs
should be well into the 80s to the lower 90s Thu depending on
the amount of solar insolation realized. So certainly may need
to expand Heat Advisories into Thu for a good portion of the
region.
Thinking that the main focus for showers and thunderstorms on Thu
will be to the north and west of our region...in the vicinity of
the forcing from the remnant circulation of Beryl. That being
said...enough heating/instability will be around for the threat
for at least an isolated convective threat at least in our
western and northern zones. While forcing will be rather limited
in our region...any storm that is able to develop will be
capable of producing torrential rainfall and a very localized
flood threat.
Appears though that the main risk for more widespread showers/t-
storms will be sometime Fri and/or Fri night as shortwave energy
gets pulled up from the south and a surface frontal boundary
drops down from the north. These two factors combined with
Pwats in excess of 2 inches will bring the potential for showers
and t-storms with torrential rainfall. We certainly will need
to watch for a localized flash flood potential given the above
factors...but that will depend upon the mesoscale factors which
are unknown at this point in the forecast.
Sat/Sun/Mon...
If the frontal boundary slows down a bit, Sat could feature
another decent risk for showers and t-storms. At this time
though, the consensus of the guidance shifts the main forcing
with the shortwave off the coast. Regardless, modest
instability will result in at least an isolated convective risk
at times but thinking the majority of the weekend into Mon
features dry weather. It still will be very warm and humid, but
dewpoints will be a bit lower than what we are expected Thu/Fri
as upper level flow turns somewhat more westerly. Still looking
at above normal temps though with highs well into the 80s to
the lower 90s away from the south coast.
&&
.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Today...Moderate confidence.
Fog/low stratus across southeast New England will lift by mid-
late morning...but may still flirt at times with parts of the
very immediate south coast & Cape. As for ACK, IFR/LIFR
probably hang tough for most of the day but there may be a brief
window where conditions temporarily scour out. Elsewhere expect
VFR conditions with a chance for thunderstorms west of I-495 at
BED, ORH, and BAF. Thinking BDL may be displaced far enough
south to escape thunder chances, so didn't include a PROB30
group in BDL TAF due to a lack of confidence. Similarly, while a
thunderstorm reaching BOS is not out of the realm of
possibility, confidence is currently not high enough to include
a PROB30 group for -TSRA with this update. Southwest winds
increasing to between 10 and 15 knots with some 20+ knot gusts
possible by afternoon.
Tonight...Moderate confidence.
Any isolated to scattered convection that is able to
develop...mainly in western and northern MA should diminish by
mid-late evening. Otherwise...IFR/LIFR conditions in low
clouds and fog likely return to the south/southeast coast
tonight as the boundary layer cools. But the northward extent
of the MVFR-IFR conditions remain uncertain...but thinking
primary risk will be near and especially south of I-90.
Wednesday...Moderate Confidence.
Any lower cigs/vsbys should improve to mainly VFR away from the
south coast. MVFR/IFR may linger into the afternoon near the
immediate south coast, Cape and Islands. A few showers or
t-storms are possible again Wed with the main risk probably
across western and northern MA again. Winds becoming more
south/SSW at 10 to 15 knots.
KBOS TAF...Moderate to High confidence in TAF.
High confidence in VFR conditions today and that strong
southwest winds will fend off the sea breeze today. Scattered
showers and thunderstorms are expected west of I-495 today, so
there is a low chance that a storm could make it to the terminal
this evening (22-01Z). Confidence in this actually occurring is
too low for any mention of thunder in the latest TAF update.
KBDL TAF...Moderate to High confidence in TAF.
High confidence in VFR conditions today, but brief lower
conditions possible if thunderstorms/heavy downpours impact the
terminal. Confidence in thunderstorm activity is higher across
north/west MA and less so for CT, so there is no mention of
thunder in the latest TAF update, but there is a low risk.
Mentions of -TSRA may appear in future updates if confidence
increases.
Outlook /Wednesday Night through Saturday/...
Wednesday Night: MVFR/IFR conditions possible. Breezy. Slight
chance SHRA, slight chance TSRA.
Thursday: Mainly MVFR, with local IFR possible. Breezy. Chance
SHRA, chance TSRA.
Thursday Night: Mainly VFR, with areas MVFR possible. Breezy.
Slight chance SHRA, slight chance TSRA.
Friday: Mainly VFR, with areas MVFR possible. Breezy. Chance
SHRA, chance TSRA.
Friday Night: Mainly MVFR, with local IFR possible. Breezy.
Chance SHRA, chance TSRA.
Saturday: Mainly MVFR, with areas VFR possible. Breezy. Chance
SHRA, isolated TSRA.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Today through Tomorrow
Warm/humid air mass will support areas of fog over the coastal
waters, especially during the overnight hours. Otherwise expect
winds to prevail out of the south/southwest with modest seas up
to three feet over the outer marine zones. Can't rule out an
isolated afternoon/evening storm over the eastern marine zones
both Tuesday and Wednesday afternoons.
Outlook /Wednesday Night through Saturday/...
Wednesday Night: Winds less than 25 kt. Seas locally
approaching 5 ft.
Thursday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft. Slight chance of rain showers,
slight chance of thunderstorms.
Thursday Night: Winds less than 25 kt. Local rough seas. Slight
chance of rain showers, slight chance of thunderstorms.
Friday: Winds less than 25 kt. Seas up to 5 ft. Slight chance
of rain showers, slight chance of thunderstorms.
Friday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of
rain showers, chance of thunderstorms.
Saturday: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers, slight chance of thunderstorms.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 8 PM EDT Wednesday for CTZ002>004.
Air Quality Alert until 11 PM EDT this evening for CTZ002.
MA...Heat Advisory until 8 PM EDT Wednesday for MAZ005-006-011>013-
017-018.
Air Quality Alert until 11 PM EDT this evening for MAZ005>007-
010>016.
Heat Advisory until 8 PM EDT Wednesday for MAZ007-014>016-019.
Dense Fog Advisory until 11 AM EDT this morning for MAZ020>024.
RI...Heat Advisory until 8 PM EDT Wednesday for RIZ001>004.
Dense Fog Advisory until 11 AM EDT this morning for RIZ006>008.
MARINE...None.
&&
$$
SYNOPSIS...Frank/RM
NEAR TERM...Belk/RM
SHORT TERM...RM
LONG TERM...Frank
AVIATION...Frank/RM
MARINE...Frank/RM
Source:
BOX issues Area Forecast Discussion (AFD) at Jul 9, 10:28 AM EDT----------------
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