BOX issues Area Forecast Discussion (AFD) at Aug 9, 5:30 AM EDT333
FXUS61 KBOX 090930
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
530 AM EDT Fri Aug 9 2024
.SYNOPSIS...
Widely scattered to scattered showers today, with a focus on
greater rain/storm chances this evening and overnight. The
passage of the remnants of Debby's bring showers with pockets of
heavier rains and a low risk for severe weather across interior
southern New England. Other than a period of light to moderate
rains Friday night into Saturday morning, little to no impacts
are expected for eastern MA and RI. Rapid improvement Saturday
afternoon. We then enter into an extended spell of pleasant
midsummer weather with seasonable temperatures and low humidity
levels starting Sunday into the middle of next week. Other than
a limited risk for showers or thundershowers Monday into early
Monday evening, dry weather
&&
.NEAR TERM /THROUGH TONIGHT/...
Update 5:30 AM - Areas of locally dense fog continue to expand
along the coast, have issued a Dense Fog Advisory for coastal
Rhode Island, south coast of Massachusetts; includes Cape Cod
and the Islands, as well as coastal Plymouth County. This
advisory will run through 9am as visibilities are falling to
1/4 mile in locations with many others reporting less than 1
mile.
Updated: 3:30AM
Today:
Debby is now a tropical depression and as of the time of writing, is
located over northern North Carolina/southern Virginia. As the system
moves north it is interacting with the frontal boundary that moved
south of our region earlier this week, which is lifting north as a
warm front. With this warm front dew points are increasing and will
return to the 70s, so rather humid air mass en route.
Given the low level moisture there are low ceilings and areas or
reduced visibility. Right now, only a small number of sites are
reporting dense fog, less than 1/4 mile. Given dense fog is not
widespread, will hold off on issuing a Dense Fog Advisory.
This morning and much of today will feature widely scattered to
scattered showers and embedded thunder. Have kept the highest POPs
to the west, closer to the center of T.D. Debby. Given high PWATs at
2.0 inches, there will be tropical downpours within any shower. We
feel that the bulk of the activity and impacts arrive late afternoon
to early evening, around 8pm, to western New England.
Low clouds remain today and result in high temperature in the 70s, a
few spots in the lower CT River Valley may approach 80F.
Late Afternoon into Overnight:
Remnants of Debby are caught up in a mid-level trough and races
east across New England generally 22z-10z, but could exit
earlier than 12z. The type of impacts include; heavy rains,
severe weather, and marine/beach impacts. Let's break down those
below...
Heavy rainfall and localized flood potential:
Guidance continues to support the passing of the surface low to the
west of southern New England, which continues to reduce our risk for
flooding. However, given that we expect up to 2.0 inches of rain to
fall over far western MA/CT, locations that end up beneath prolonged
downpours could see some localized street flooding. Far western
southern New England, areas west of the CT River continues to be in
a Slight Risk (level 2 of 4) of excessive rainfall, so something to
keep an eye on. Rain comes to an end for our western zones by 4AM
and for the eastern coast of MA by mid-morning. Though, a few
showers may linger into the coast waters, Cape Cod, and Islands
through later morning to early afternoon.
Severe Weather:
Not much has changed with the potential of severe weather. As we
mentioned, the environment this afternoon/evening is favorable for
short-lived tornadoes as remnants of Debby track to the west of New
England. These situations often feature very high shear in lowest
levels and low LCLs (cloud bases) but in order to support tornado
formation we need instability in lowest levels (0-3km CAPE) and
either surface boundary or mesolow to focus low level spin.
In this case, we're seeing several favorable signals in model
guidance, especially for western thirds of MA/CT. First, there is
sufficient 0-3km CAPE (over 200 J/kg) as warm front lifts through
during late afternoon and early evening. Local CSTAR research has
shown that we only need to see values of 25-75 J/kg in tropical
remnant environments so that should easily be attainable. Second,
environment itself favors high amounts of shear in lowest levels and
in this case we have over 200 m2s2 of 0-1km shear, much of which is
focused in 0-500m layer. Research has also shown the 0-500m layer
can be a good discriminator for tornadoes vs non tornado
environments (values of 95 or higher). Lastly, LCL heights are down
to 500m which is below the typical height of about 700m.
While these factors line up very well and have support from SREF
Tornado Ingredients, it's not always a lock in these situations.
Certainly we'll be on the eastern edge of more favorable area
(region closer to the actual remnant low itself). But we have to
watch its warm front extending eastward as well as possibility of
mesolow formation along boundary to help enhance spinup. It's also
possible to have all of this occur without any lightning.
It's important to stress that these types of circulations, while
potentially supportive of tornadoes, tend to be very shallow in
nature and do not last very long. Radar detection can be difficult
especially at farther distances from the radar. These situations are
usually handled by issuing Severe Thunderstorm Warnings with the
"Tornado Possible" tag since it is difficult to track these
transient couplets. However, any longer-lived couplets that do
manage to form can be handled with Tornado Warnings.
Marine/Rip Currents:
Southerly winds will be on the increase Friday night and Saturday
morning leading to some gusty winds, mainly over the waters. A Gale
Warning is in effect for the southern waters starting late this
afternoon with Small Craft Advisories elsewhere. Building wave
heights and the southerly flow will lead to a risk for increased
surf and rip currents for south-facing beaches Friday night into
Saturday. Have issued Rip Current Statement for today and a High
Surf Advisory for the same locations on Saturday.
&&
.SHORT TERM /SATURDAY/...
Updated: 3:30AM
Rain wraps up shortly after sunrise on Saturday, where the showers
may linger is near the Cape and Islands with the weak surface trough
nearby. This will be short-lived as surface high pressure builds in
from the southwest. Clouds clear rapidly from west to east early
morning into the afternoon, but clouds could be stubborn in far
southeast Massachusetts through mid-afternoon. Wind direction shifts
and becomes west, this will lead in drier air and lowering the
humidity from the mid 70s to the low/mid 60s by end of day. As for
winds, those will remain gusty during the first-half of the day in
eastern Massachusetts and Rhode Island, but quickly subside into the
afternoon. All in all a nice day expected with highs climbing into
the lower and middle 80s.
&&
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Highlights:
* Extended spell of dry weather with seasonable temperatures and low
humidity levels Sunday through midweek.
* Other than spotty showers/t-shower late Mon into Mon evening,
dry weather prevails for the vast majority of the time.
Details:
00z ensembles remain in good agreement in indicating cyclonic flow
aloft will govern our weather pattern through this portion of the
forecast period. Initially, a rather potent and anomalous mid/upper
level shortwave disturbance over the eastern Gt Lakes is expected to
gradually progress into the Northeast states starting later Sunday
and Monday. As this feature moves eastward, broad troughing aloft is
maintained and reinforced by additional more subtle disturbances
progressing southeastward from the Upper Midwest region.
Despite the presence of cyclonic flow aloft, much of this forecast
period is generally dry under a drier W/WNW flow, and may only lead
to some enhancement to diurnal cloudiness. The one exception looks
to be later Mon into Mon night, associated with the passage of the
initial shortwave disturbance moving through the Northeast. The
various global coarser-resolution models vary some in the depictions
in the placement of shower/possible t-storm coverage Mon and Mon
night. Looked at model forecast soundings and because of the cooler
profiles aloft, wet bulb zero heights as are low as 10,000 ft, which
for midsummer is very uncommon. Carried a greater mention of cloud
cover and indicated 15-20% PoP for isolated showers and t-storms
mainly for the southern third of Southern New England, exiting
quickly offshore Mon night/early Tue.
On the whole though, it is a rather pleasant and dry midsummer
weather pattern with comfortable humidity levels and temperatures in
the mid 70s to lower-mid 80s; these are generally seasonable or
slightly cooler than normal.
&&
.AVIATION /10Z FRIDAY THROUGH TUESDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Through 12z...Moderate Confidence.
IFR to LIFR, scattered rain and locally dense fog. Light east
to northeast winds 5 to 10 knots.
Today...Moderate Confidence.
Slight improvements from south to north, with a brief period of
MVFR conditions possible this afternoon, 18z to 00z. There will
be scattered rain showers throughout the day, but not an all day
washout. Winds veer from the east to the southeast by 18z, then
south by late afternoon. Wind speed increasing throughout the
day generally 10 to 15 knots with gusts 20 to 25 knots.
Tonight...Moderate Confidence.
Lower end MVFR to IFR, with localized LIFR within heavy rain as
remnant moisture of Debby moves from west to east across
southern New England, between 00z to 10z. Winds are south to
southwest 15 to 20 knots, higher gusts 25 to 30 knots are
possible.
Saturday...High Confidence.
Rapid clearing from west to east early Saturday morning, with
VFR conditions as early as 10z across western terminals and 15z
across the eastern terminals. IFR/MVFR conditions linger for the
Cape and Island terminals through 16z/18z, then become VFR.
Winds are west at 10, while south coast, Cape, and Island
terminals are southwest 15 knots with gusts to 25 knots.
KBOS TAF... High confidence in trends, but moderate confidence
in timing.
IFR to LIFR this morning with periodic light showers.
Visibilities improve through the mid-morning, but low ceilings
remain. Brief period of MVFR conditions this afternoon, but
will return to IFR tonight. Overnight a line of heavy rain and
low risk for embedded thunder. Rapid clearing Saturday as system
moves off shore.
KBDL TAF... High confidence in trends, but moderate confidence
in timing.
IFR to LIFR this morning with periodic light showers. Slight
improvements mid to late morning to MVFR late morning and should
remain through late afternoon, before returning to IFR or LIFR
with a line of heavy rain and low risk for embedded thunder.
Rapid clearing Saturday as system moves off shore.
Outlook /Saturday Night through Tuesday/...
VFR.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Gale Watches that were in effect for today into Saturday were
converted to Gale Warnings over the southern waters, while small
craft advisories were maintained over much of the eastern waters.
SE to S winds will steadily increase today on all waters, but reach
into the 30 to 35 kt range tonight and into Saturday as a low level
jet of 40 to 50 kt moves over the waters. The degree of mixing does
add an element of uncertainty but felt gusts have the best chance at
reach gale force over the southern waters, and may fall into the
solid SCA range (around 30 kt) over the eastern waters. Wave heights
will be steadily building today into Saturday given a lengthy
southerly fetch, into the 5-7 ft range by late this afternoon, then
increase further into the 7-10 ft range on the outer waters tonight
into early on Sat, then slowly decrease into Sat aftn/night. Showers
and areas of marine fog are expected through this afternoon, with
light to moderate showers tonight into early in the day on Saturday
before decreasing rapidly as cold front moves offshore.
For the beaches/surf zone...today into Saturday are far from ideal
weather conditions for those looking to head to the beach with
overcast and periods of showers. With the building wave heights
today and especially tonight and the first part of Saturday, that
will raise the risk for dangerous rip currents and building surf.
We've opted to issue a Rip Current Statement for south-facing
beaches today into early tonight given wave heights building to
around 5-7 ft. For tonight into Saturday, with wave heights more
commonly in the 7 to 10 ft range and southerly flow increasing, that
will continue to generate rip currents but also lead to high surf,
with a High Surf Advisory being raised tonight and continuing into
Saturday for south-facing beaches.
Outlook /Saturday Night through Tuesday/...
Saturday Night: Winds less than 25 kt. Local rough seas.
Sunday: Winds less than 25 kt. Seas locally approaching 5 ft.
Sunday Night through Monday: Winds less than 25 kt. Isolated
rain showers.
Monday Night through Tuesday: Winds less than 25 kt.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Dense Fog Advisory until 9 AM EDT this morning for MAZ019>024.
High Risk for Rip Currents through this evening for MAZ020>024.
High Surf Advisory from 8 PM this evening to 8 PM EDT Saturday
for MAZ020>024.
RI...Dense Fog Advisory until 9 AM EDT this morning for RIZ006>008.
High Risk for Rip Currents through this evening for RIZ006>008.
High Surf Advisory from 8 PM this evening to 8 PM EDT Saturday
for RIZ006>008.
MARINE...Small Craft Advisory from 5 PM this afternoon to 10 AM EDT
Saturday for ANZ230-236.
Small Craft Advisory from 5 PM this afternoon to 2 PM EDT
Saturday for ANZ231-250-251.
Gale Warning from 5 PM this afternoon to 2 PM EDT Saturday for
ANZ232>235-237-254>256.
&&
$$
SYNOPSIS...Loconto/Dooley
NEAR TERM...Dooley
SHORT TERM...Dooley
LONG TERM...Loconto
AVIATION...Loconto/Dooley
MARINE...Loconto
Source:
BOX issues Area Forecast Discussion (AFD) at Aug 9, 5:30 AM EDT----------------
If I'm using your data in a way that is against your terms please email the team at "threatweb@pupswoof117.com"! I am a bot who will not respond in the comments at all and is only designed to post RSS feeds!
