Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
725 PM EST Thu Nov 5 2026
Day 2
Valid 12Z Fri Nov 06 2026 - 12Z Sat Nov 07 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
SOUTHEASTERN NEW ENGLAND...
...Southeast New England...
The prior forecast reasoning for southeastern New England remains
on track. Only some minimal edits to the inherited Slight Risk
covering portions of Rhode Island into southeastern MA were needed
based on the now available hi-res guidance. Both the 12Z HRRR and
suite of RRFS guidance support the potential for areal average
rainfall over 3" and locally higher totals of 5"+. This guidance
trended a bit to the north and east of the inherited Slight Risk
leading to an extension further into southeast Massachuesetts to
the northern tip of Cape Cod. While FFGs are higher closer to the
coast through this region, the locally heavy totals of 5"+ would be
more than enough to still lead to scattered flooding concerns.
...Southeast VA into Northeast NC, the DelMarVa, and coastal NJ...
Further south, considered introducing a targeted Slight Risk
across portions of southeastern VA and northeastern NC based on the
hi-res guidance which shows the potential for some locally heavier
totals in the 3-5" range. Modest instability (~1000 J/KG CAPE)
should lead to some more robust storms with waves along the front
potentially helping to slow its progression and allow for at least
brief training potential, both contributing to higher totals. This
would result in a greater concern for scattered flash flooding
particularly for the more urban areas around Norfolk/Virginia
Beach. However, given the generally overall progressive nature of
the front and drier relative conditions through the region, have
left a Marginal Risk for now. The Marginal Risk has also been
expanded northward to include portions of the southern DelMarVa
peninsula as well as coastal New Jersey based on the hi-res
guidance. While there is some concern the eastward progression of
the front may clear the coast before storms develop/expand in
coverage especially with northward extent, there is enough of a
signal for the potential of 2-3"+ through the region that at least
isolated flooding will be a concern.
...Southeastern AZ...
A targeted Marginal Risk has been added across southeastern
Arizona. A developing upper-wave in the southern stream will pass
over the region Friday leading to at least isolated to scattered
thunderstorm development. While not quite as anomalous as recent
events, increasing moisture as well as modest instability could
lead to a few more robust downpours producing ~1" or so of rain,
which could be enough to lead to some isolated flash flooding
concerns.
Putnam
...Previous Discussion...
...Eastern Portions of LI and CT into RI and Eastern MA...
Trimmed the western portion of the Marginal Risk area inherited
from yesterday's Day 3 ERO across southern New England, based on
the guidance trends (continued eastward shift in the rainfall
axis). Mid-upper level trough takes on a more neutral tilt, with
the large-scale ascent becoming enhanced within the right-
entrance region of the 90-110kt upper level jet streak. Low- level
flow (1000-850 mb) backs towards the south while increasing to ~30
kts, strengthening the low-level moisture flux/transport off the
Gulf Stream. This will bring PWs of 1.5-1.75 across the outlook
area, which is 2-2.5 standard deviations above normal for early
Nov. Instability, even elevated, is expected to be fairly minimal
per the guidance (MUCAPEs ~200-400 J/Kg), however given the axis of
favorable deep-layer moisture/theta-e, the bulk of the guidance
continues to show peak 24hr rainfall between 3-5+ inches across
parts of southeastern New England, particularly from Newport and
Providence RI to Plymouth MA. Given the latest REFS exceedance
probabilities over this area, including 40-50% of >5"/24hrs, EAS
40-45% probabilities of >3"/24hrs, and 30-40% probs of exceeding 2
year ARI amounts, have opted to include a targeted Slight Risk area
in the Day 2 ERO.
...Southeast VA into Northeast NC...
Have included a Marginal Risk area across coastal portions of the
Mid Atlantic, including Hampton Roads. Degree/duration of favorable
dynamics are not as favorable compared to southeastern New England,
however the guidance does show a bit more instability to work with
(higher probs of at least 750-1500 J/Kg), which translates to
higher 1+ in/hr rainfall rates Friday afternoon into early evening.
Areal-average QPF within this region is between 1.5-3.0" per a
multi-model blend (including the AIGFS and ECMWF AIFS).
B Hurley
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
725 PM EST Thu Nov 5 2026
Day 3
Valid 12Z Sat Nov 07 2026 - 12Z Sun Nov 08 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS SOUTH-CENTRAL
AND SOUTH TEXAS...
...2030 UTC Update...
Only minimal adjustments were needed for the Marginal Risk across
south-central/south Texas based on the latest guidance. This
included a northwestward extension into portions of the southern
Hill Country where there remains a concerning signal from the GFS
for heavier rainfall across the more sensitive terrain. As noted
below, a Slight Risk may eventually be needed with more confidence
in the location of the heaviest rainfall, particularly if it were
to focus on portions of the Hill Country or where there would
expectedly be more convergence/forcing along the coast. However,
there remains too much spread in the guidance to have enough
confidence in a risk area for now.
Putnam
...Previous Discussion...
Model guidance is beginning to converge on a synoptic evolution
that would favor areas of heavy rain over southern TX this weekend.
A mid-upper low is forecast to dive southeast out of AZ and into
northern MX late Friday/Fri night, then gradually progress
eastward towards West TX by Sunday. This feature will provide ample
ascent for rainfall, with a strong upper level jet providing
additional lift. Anomalous moisture will advect northward ahead of
this system, and while PWs will likely not be as high as recent
events, it is still forecast to exceed the climatological 90th
percentile. In the low levels we should have east to northeasterly
flow, which will aid in isentropic ascent over the region, but
should also act as a stabilizing factor. Thus the degree of
instability, which will impact rainfall rates and the flash flood
potential, remains a question.
In terms of the latest guidance, the ECMWF AIFS continues to be the
most persistent model showing the heavy rainfall threat, and is
gaining more support from the operational ECMWF, GFS, and CMC.
If/where sufficient destabilization is able to occur to drive
higher rainfall rates, a future Slight risk upgrade may be
necessary. Best chances for this at the moment appear to be along
the south TX coast where instability advecting in off the water and
coastal convergence could focus higher rainfall magnitudes.
B Hurley/Chenard
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
