From
Mike Powell@454:3/105 to
All on Sat Nov 29 09:05:37 2025
FOUS30 KWBC 290800
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Sat Nov 29 2025
Day 1
Valid 12Z Sat Nov 29 2025 - 12Z Sun Nov 30 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHEAST TEXAS...
A cold front moving south down the Plains will run into a plume of
Gulf moisture moving into eastern Texas tonight. The clash of these
two air masses is expected to result in some limited thunderstorm
development this evening across portions of east central Texas and
northern Louisiana. Overnight tonight, the line will press
southward. As the line encounters ever increasing amounts of Gulf
moisture, convective coverage is likely to also increase across
southeastern Texas. Since the plume will continue northeastward up
the front, additional convective development is also expected
across central Louisiana. However, both due to increased distance
from the Gulf and poor instability (values broadly have come down
to at most 500 J/kg of MUCAPE), the storms further north and east
into Louisiana are likely to remain as a progressive skinny line of
convection. Meanwhile, in the Marginal Risk area across southeast
Texas, closer proximity to the Gulf should allow for a bit of pre-
frontal convection to form before the more organized line of storms
moves through. Given the lack of instability, progressive movement
of the storms, time of day (overnight tonight), and very dry soils
present along the Gulf Coast, the thinking as regards coverage of
flooding remains the same... only very isolated flash flooding=20
possible where any prefrontal storms train over urban or other low-
lying, flood-sensitive areas. This remains a lower end (near 5%)
flood risk. For the most part, the rain expected tonight will be=20
beneficial. The line will move through the Houston metro around=20
midnight local time, then both weaken and move into the Gulf beyond
that.
Wegman
Day 2
Valid 12Z Sun Nov 30 2025 - 12Z Mon Dec 01 2025
The probability of rainfall exceeding flash flood guidance is less
than 5 percent.
Wegman
Day 3
Valid 12Z Mon Dec 01 2025 - 12Z Tue Dec 02 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
CENTRAL GULF COAST TO THE SOUTHERN APPALACHIANS...
A fast-moving progressive shortwave trough that extends from an
expansive upper level low over Canada will provide the upper level
forcing for cyclogenesis along a potent cold front that will
roughly parallel the Gulf Coast and Eastern Seaboard. The low will
begin to form along the Texas Gulf coast during the day Monday,
then track ENE across the Deep South, ending the period near the
South Carolina/Georgia border. As the low tracks along the Gulf
Coast, it will continually add Gulf moisture to its circulation,
while also thriving on the baroclinicity brought on by a=20
reinforcing cold air mass moving southeast from the Midwest. PWATs
in the warm, moist Gulf air mass will exceed 1.75 inches in some
areas. However, any instability will likely remain along the
immediate coast, with very little instability inland. This supports
an overrunning rainfall scenario, rather than an overly convective
one. A prolonged period of light to moderate rain is expected
across much of the South as a result. The heaviest rain is forecast=20
from near New Orleans northeast to the southern Appalachians. It's=20
in this corridor that the highest probability of flash flooding=20
exists. The qualifier to this statement however is that FFGs across
the Deep South are quite high as a result of recent dry weather=20
and therefore very dry soils. This will favor most of the rainfall=20 associated
with this low being beneficial to affected areas.=20
Isolated flash flooding is most likely in urban or flood-prone=20
areas, as well as in the flashier streams that drain the Southern=20 Appalachians.=20
Wegman
$$
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From
Mike Powell@454:3/105 to
All on Sat Jan 3 10:51:00 2026
FOUS30 KWBC 030823
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
323 AM EST Sat Jan 3 2026
Day 1
Valid 12Z Sat Jan 03 2026 - 12Z Sun Jan 04 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN THE UPSLOPE
REGIONS OF THE SIERRA AND THE SHASTA OF NORTHERN CALIFORNIA...
The axis of anomalous 850-700 mb moisture flux values...2 to 4+
standard deviations above the mean...along and ahead of the inland
moving frontal boundary early Saturday will impact the upslope=20
areas of the Sierra, northward into the Shasta of northern
California and spread through the Transverse Ranges of Southern=20
California. The primary change from the previous outlook was to
expand the slight risk area along all of the upslope regions of the
Sierra and expand it northward into the upslope of the northern CA
Shasta Range. HREF and RRFS neighborhood probabilities are high in
the slight risk area along the Sierra into the Shasta for 1, 2 and
3"+ totals and high along the Transverse Range for 1 and 2"+=20
totals day 1. In the slight risk area along the Sierra and Shasta,
hourly rainfall totals of .25-.50"+ are possible through the day 1
period and along the Transverse Range primarily during the first=20
half of day 1. This is resulting in HREF and RRFS probabilities of 3
hour precip exceeding 3 hour FFG values being well defined in the
upslope area of the Sierra and Shasta through day 1 and over the
Transverse Range during the fist half of day 1. Soils remain fairly
saturated in the slight risk areas from recent heavy rains at the
end of 2025 with runoff issues possible as additional heavy
rainfall occurs over these saturated soils.
Oravec
Day 2
Valid 12Z Sun Jan 04 2026 - 12Z Mon Jan 05 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
NORTHERN SIERRA...
Additional shortwave energy expected to rotate through the mean
trof position along the West coast and inland across California day
2. This will support a continued wet showery pattern with=20
additional moderate to locally heavy precip totals along much of=20
the California coast Ranges and into the upslope of the Sierra. A
small slight risk area was introduced in the upslope of the northern
Sierra where model consensus is for potential of additional 1 to 2"
of rain. While rainfall rates are expected to be less than day 1,
generally .10-.25, there will be overlap with the day 1 qpf axis in
places with 48 hour totals of 3-6" in the slight risk area. Much=20
of the day 2 precip will occur during the first half of day 2. HREF
and RRFS 12 hour precip ending 0000 UTC Mon are high for 1 and 2"+
totals. Otherwise, no changes made to the broad marginal risk area
for much of coastal and northern California.
Oravec
Day 3
Valid 12Z Mon Jan 05 2026 - 12Z Tue Jan 06 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG THE CENTRAL
TO NORTHERN CALIFORNIA COAST AND NORTHERN CALIFORNIA...
The mean trof position is maintained day 3 off the West coast with
model consensus for amplification of a new closed low in the base
of the mean trof off the Central to Southern CA coast. The low=20
level southerly flow on the east side of this developing closed low
will not be as strong as the day 1 and 2 low level south=20
southwesterly flow, resulting in 850-700 mb moisture flux values=20
only 1 to 1.5 standard deviations above the mean. PW values also=20
expected to be lower than day 1 and 2, with anomalies only 1 to=20
1.5 standard deviations above the mean. Model consensus is for=20
additional .50-1"+ rainfall amounts along the Central to Northern=20
CA coast and into the upslope of the Northern Sierra. At the=20
moment, these amounts warrant keeping the Excessive Rainfall=20
Outlook threat level at marginal for the day 3 period, with no=20
significant changes made to the previous outlook.
Oravec
$$
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