NWS Burlington, VT wrote its last area forecast discussion before the first event at Jul 10, 12:45 PM EST, 15 minutes earlier.
Area forecast discussion, Jul 10, 12:45 PM EST, 15 minutes before
Area Forecast Discussion
National Weather Service Burlington VT
145 PM EDT Mon Jul 10 2023
.SYNOPSIS...
Multiple rounds of moderate to heavy rain is ongoing. Expect
storm rainfall totals across much of Vermont and northeastern
New York to reach 2 to 5 inches of rain with locally 7 inches
through Tuesday. With saturated soil and elevated river levels
from recent rainfall, widespread significant to potentially
catastrophic flash flooding are expected overnight tonight into
Monday night. The heavy rainfall will also lead to sharp river
rises, leading to widespread area and river flooding through
Tuesday. Muggy and unsettled conditions continue through the
rest of the week. The next system to bring rain will be Thursday
into Friday.
&&
.NEAR TERM /THROUGH TUESDAY/...
As of 150 PM EDT Monday...
Forecast remains largely on track. Earlier this morning, we noticed
a potent 572 Dm low trying to close off over Rochester, NY with
the upper level trough increasingly taking on a negative tilt
along with upper level diffluence over our region. The 12z HRRR
and NAM 3km picked up on this development and backs/blossoms
the precipitation over the populated Winooski River valley from
Montpelier to Burlington through the afternoon hours. WPC has
also highlighted the concern in their Mesoscale Discussion 0688.
By early afternoon, the favorable left exit region of the 250mb
jet streak is now nosing into Connecticut. So updated the 6 hour
QPF for this afternoon using some of the hi-res 12z CAM
guidance. In addition, WPC now has most of VT under the High Day
1 Excessive Rainfall Outlook, which means that widespread flash
floods are likely with significant to potentially catastrophic
impacts. The existing Flash Flood Warnings across northern VT
might need to be updated/upgraded in severity. Stay tuned and
always remember turn around, don't drown.
PREVIOUS DISCUSSION...
* Expect significant to potentially catastrophic widespread
flash flooding through Monday evening, with possible impacts
not seen since Irene.
* Widespread heavy rainfall of 2-5 inches with localized 7+
inches will be exacerbated by the saturated soil and elevated
river levels from all the recent rainfall.
* Scattered strong storms are possible Monday afternoon with the
risk of an isolated downburst.
With people waking up, we're now getting reports of how bad the
flooding is in central Vermont. Evacuations have been taking
place, all routes leading into a couple small mountain towns and
villages have been closed off, and multiple road washouts and
field flooding are ongoing. The latest radar scans show another
mass of rain headed into these areas. Be on the alert and know
higher ground that you can reach. Heed all road closures; turn
around, don't drown. Stay safe and have all electronics charged
and set to receive alerts.
Deep, moist convergence is ongoing across the region. The first
wave of vort maxes is starting to lift north, and there some
breaks of rain, but there's another vort swinging through and
the dynamical forcing is expected to be more intense than this
first wave that's going through, and when we will have some
diurnal destabilization. That's bad news. Confidence remains
very high that this will be a high end to locally extreme event
for the region that will be a danger to life and property. This
is because forecast probabilities of exceeding 5 inches are
nearly 80 percent in parts of central Vermont, and the updated
forecast reflects localized 6 inch reports along the mountain
summits. The idea of rainfall totals in excess of 7 inches is
still on the table along the spine of the Greens. We remain in
a High risk ERO for much of our CWA (Monday 8 AM to Tuesday 8
AM), which means that widespread flash flooding is expected.
The gradient of precipitation is fairly sharp moving east of the
Adirondacks. St. Lawrence County remains out of the Flood Watch
at this time, with rainfall amounts between 0.33" to 1.33" with
locally higher amounts possible. Did add a mention of ponding
possible in the area, but impacts appear to remain minimal for
St. Lawrence County.
The one change to the forecast was to increase wind gusts on
Tuesday. In the Northeast Kingdom, we will have to monitor the
potential for a low-level jet of 35 to 45 knots lifting north
across the region as the upper low intensifies. Forecast
guidance suggests mid-level cooling may allow some of these
winds to mix to the surface of the Northeast Kingdom. With such
saturated soils, felling trees would be easier than normal. For
now, have started the trend up to 20 to 30 mph across parts of
central Vermont into the Northeast Kingdom, but this may need to
be watched as a post-storm impact Tuesday afternoon.
Please take this flooding event seriously, have multiple ways
to receive real-time NWS weather alerts and have contingency
plans in place.
&&
.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY/...
As of 355 AM EDT Monday...Shower chances will continue as we head
into the middle part of the week. Some brief shortwave ridging may
allow for a brief break Tuesday night, but things should redevelop
on Wednesday as an upper shortwave skirts by just to our northwest.
A frontal boundary will attempt to push through the forecast area.
Timing of this frontal passage differs between models, which has
implications for convective potential on Wednesday. Note the NAM has
SB CAPE values of 1000-2000+ J/kg along with 30-35 kt of 0-6km
shear, which would point toward organized strong storms. Meanwhile,
the GFS is not as aggressive, keeping CAPE below 1000 J/kg and shear
less than 30 kt. Trends will need to be watched. Otherwise, expect
highs in the lower to mid 80s, potentially into the upper 80s in
southern sections.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 355 AM EDT Monday...Overall expect to stay in a fairly active
and warm/muggy pattern as remain on the periphery of upper low
pressure gyrating around near the Hudson Bay. Shortwave troughs will
periodically rotate around this low, lifting across our region on
southwest flow. Timing of these features and their associated
precipitation is often to nail down more than just a couple days
ahead of time, though there is some consensus in the Thursday night
into Friday timeframe. Less agreement heading into the weekend, so
have stayed pretty close to the NBM to account for model
differences. Temperatures will remain near to slightly above normal,
though they will ultimately depend upon precipitation and sky cover,
especially daytime highs. Overall, highs should be in the 80s and
lows in the 60s.
&&
.AVIATION /18Z MONDAY THROUGH SATURDAY/...
Through 18Z Tuesday...TAFs range from VFR to LIFR with mixes of
fog and rainfall reducing visibilities with highly variable
ceilings. Winds are calm for the most part, but will trend
southeast and then north and northwest. Overall, intervals of
IFR ceilings and visibilities is likely to prevail as heavy rain
expands northwards. There could be brief pockets of lighter
rain that improve visibilities. After 18z, another swath of
very heavy rain and embedded thunder will lift north into the
region as surface low lifts north. Northwest winds will become
favored after 21z, though still with some variability possible
depending on the low track. This will likely cause decreasing
ceilings at most sites back below 1000 ft agl. Rain will trend
towards KSLK, KBTV, and KEFK after 21z as the low lifts
northwards. Towards 00z Tuesday, increasing 1500-2000 ft agl
winds out of the northwest at 35 to 40 knots. So have introduced
some LLWS for the latter portions of TAFs for several terminals,
including KRUT and KSLK.
Outlook...
Tuesday: VFR. Chance SHRA, Slight chance TSRA.
Tuesday Night: VFR. Slight chance SHRA.
Wednesday: VFR. Slight chance SHRA, Slight chance TSRA.
Wednesday Night: VFR. Slight chance SHRA.
Thursday: Mainly MVFR, with areas VFR possible. Chance SHRA,
Slight chance TSRA.
Thursday Night: Mainly MVFR, with local IFR possible. Chance
SHRA, Slight chance TSRA.
Friday: Mainly VFR, with areas IFR possible. Chance SHRA, Slight
chance TSRA.
&&
.HYDROLOGY...
** WPC has updated their Day 1 Excessive Rainfall Outlook and
most of VT is now in their Day 1 High risk ERO, which means
that widespread flash flooding is expected/likely.
We remain in a Moderate Risk from the Adirondacks east, with an
embedded High Risk ERO along the eastern slopes of the
Adirondacks, Champlain Valley, and across the spine of the Green
Mountains. This indicates numerous flash flooding is likely.
There will be two rounds of widespread heavy rainfall. One is
ongoing, which is producing rainfall amounts between 0.50" and
2.50", locally up to 3.50" of rain. After a brief lull, rainfall
will once again blossom during the day, peaking this afternoon
into evening. There is even potential for a third round of
moderate rainfall overnight hours as wrap around precipitation
develops behind an upper low. Given the saturated ground and
antecedent high river/creek levels, bottom line is that it will
not take a whole lot of rain to cause widespread issues.
Overall, we continue to forecast widespread 2 to 5 inches of
rain with locally 7+ inches especially along and near the spine
of the Green Mountains. Expect washed out roads and culverts,
fast- responding creeks spilling out of their banks, as well as
widespread poor drainage urban area flooding. Even outside of
the stratiform widespread rainfall, convective elements will be
possible this afternoon, leading to locally enhanced rainfall
with a quick inch or two in as little as an hour. By this
evening into overnight hours, and heading into Tuesday, the
flooding mode will transition from flash flooding to more of
area and main stem river flooding. Typically vulnerable basins
including the Mad River in Moretown, Otter Creek in Center
Rutland, Winooski River in Essex Junction and Ausable River at
Ausable Forks are expected to reach minor and moderate flood
stage on later today, Tuesday, and even into Wednesday.
The main takeaway is that if you are in a Flood Watch, please take
this flooding event seriously, have multiple ways to receive real-
time NWS weather alerts and have contingency plans in place.
&&
.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Flood Watch through Tuesday evening for VTZ001>011-016>021.
NY...Flood Watch through Tuesday evening for NYZ027-028-030-031-034-
035.
&&
SYNOPSIS...Haynes
NEAR TERM...Chai/Haynes
SHORT TERM...Hastings
LONG TERM...Hastings
AVIATION...Chai/Haynes
HYDROLOGY...Chai/Hastings