FOUS30 KWBC 050814
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
314 AM EST Thu Nov 5 2026

Day 1
Valid 12Z Thu Nov 05 2026 - 12Z Fri Nov 06 2026

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

B Hurley
 

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...

...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 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...

Generally maintained the inherited Marginal Risk area from
yesterday's Day 4 ERO, though shifting a bit farther east based on
the latest guidance trends.

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 4 and Day 5
Valid 12Z Sun Nov 08 2026 - 12Z Tue Nov 10 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL SUNDAY ACROSS
PARTS OF SOUTH TEXAS...

Day 4: Continued with the Marginal Risk area from yesterday's Day 5
ERO, which is essentially an extension (slight migration) of the
Marginal Risk area on Day 3 (Sat-Sat night). Upper trough and
attendant southern stream upper jet support and deep subtropical
moisture will gradually shift east of TX, but not before another
day of potentially heavy rainfall across South TX, particularly
along the TX Gulf Coast. Used a blend of the AI GFS and ECMWF
guidance in outlining the Marginal Risk area, though it should be
pointed out that both the 00Z operational GFS and ECMWF show a
narrow corridor of 3-6" along and near the Lower-Middle TX Coast.
There is some areal spread however with these higher totals, along
with the overall high spread with the rest of the operational
global and AI guidance. Because of this, have maintained the
Marginal Risk, however could certainly see an upgrade to a Slight
Risk in future forecasts if/when the models show better clustering
with the heavier totals.

B Hurley
$$
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