FOUS30 KWBC 030806
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
406 AM EDT Thu Sep 3 2026

Day 1
Valid 12Z Thu Sep 03 2026 - 12Z Fri Sep 04 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
EASTERN TEXAS...

...Texas, Gulf Coast and Florida...

An axis of training convection and backbuilding located to the
south and Southeast of the remnant circulation of Edouard will be
persist from the overnight hours and should weaken towards 15z.
The Moderate risk may be able to be removed with the 16z update
tomorrow, but the expectation is for a locally significant flash
flood risk to be ongoing to start the period Thursday morning. Some
models indicate another possible uptick Thursday night into Friday
morning, but this is lower confidence given more uncertainty
regarding the state of the remnant vort center by this time.

Elsewhere onshore flow within the pooled high PW values and
stalled boundary could trigger convection along the coastline and
across the Florida Peninsula leading to isolated areas of flash
flooding/ponding. A Marginal Risk spans from eastern Texas to Florida.

...Southwest...

Moisture will be increasing over the region during this period to
help fuel diurnal convection across Arizona and New mexico, leading
to a scattered flash flood risk. This region will continue to be
monitored over the coming days. A Slight Risk is in effect for
southeast Arizona and extreme southwest New Mexico while a Marginal
covers portions of eastern Arizona and nearly the western half of New Mexico.

...Upper Midwest to Mid-Atlantic...

One or more rounds of organized convection is forecast to track
trough the region today and into the overnight hours. Antecendant
rains have left portions of the area sensitive to additional
rainfall/high rainfall rates. The axis of heaviest precipitation
will likely focus over Wisconsin. A Marginal Risk is in effect from
North Dakota to southern New England/northern Mid-Atlantic.

...California into the Intermountain West...

A strong synoptic system will bring an axis of heavy rainfall to
to the region. Not much instability, but just enough showing up in
model forecasts to suggest some potential for localized higher
rates and an isolated flash flood potential. A Marginal Risk is in
effect for northern California, eastern Oregon, eastern Washington,
Idaho and far western Montana.

Campbell/Chenard
 

Day 2
Valid 12Z Fri Sep 04 2026 - 12Z Sat Sep 05 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
ARIZONA AND NEW MEXICO...

...Southwest...

PW anomalies raise back to 2-2.5 standard deviations above normal
during this period. Still remains to be seen how much influence
the eventual tropical system that ultimately pulls west of Baja
will have in terms of the upper level moisture (potential uptick in
the PW anomaly). A Slight Risk was maintained for Arizona while a
broad Marginal covers southeast California the Four Corner as this
is where the signal for better moisture/instability axis aligns.
Isolated to scattered flash flooding is expected.

...Gulf states...

Lingering moisture and instability along this corridor could
result in a continued localized flash flood risk. A Marginal Risk
was maintained from eastern Texas to southern Georgia and Florida.

...Upper Midwest/Ohio Valley/Central Appalachians...

Additional organized/widespread convection to develop downwind of
the upper ridge axis today. Precipitable water values are high
enough with sufficient instability that embedded cells could
produce local downpours and isolated flooding. This will likely
start over eastern portions of the Upper Midwest, where the upper
jet streak to the northeast is expected to strengthen as the
pivoting northern stream trough impinges on the broad-scale ridge
to the south. Have essentially traced the Marginal Risk area
southeast along the mean 850-300 mb thickness fields, where the
upper level forcing along/ahead of the surface front will be most
supportive of more organized activity. A Marginal Risk is in effect
from Wisconsin to Virginia and eastern North Carolina.

Campbell/Chenard
 

Day 3
Valid 12Z Sat Sep 05 2026 - 12Z Sun Sep 06 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
THE SOUTHWEST...

Moisture southwesterly flow will be directed into the Southwest
between a deep upper low/trough over the Pacific Northwest and a
strong upper high centered over the Southern Plains. A suppressed
moisture and instability axis will likely be positioned from southern
California through central New Mexico. There is connection to a
tropical moisture plume from Marie so this area will continue to
be closely monitored. For now, a Marginal Risk covers the level of
threat for excessive rainfall and spans from southern California
across southern Nevada, Arizona and New Mexico.

Campbell/Jackson
 

Day 4 and Day 5
Valid 12Z Sun Sep 06 2026 - 12Z Tue Sep 08 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM SOUTHERN
CALIFORNIA, ACROSS THE SOUTHWEST, GREAT BASIN, INTO THE NORTHERN
ROCKIES AND EASTWARD INTO THE NORTHERN PLAINS/UPPER MISSISSIPPI
VALLEY AND ACROSS PORTIONS OF THE SOUTHEAST...

...Southern California/Southwest, Great Basin into the Northern Rockies...

The anomalously strong western mid to upper level trof will
continue to be very slow moving during the upcoming day 4 and 5
period. There is consensus that this trof will be able to transport
anomalous PW values in the vicinity of Marie northeastward from
Southern CA/Southwest, into portions of the Great Basin, and
Northern Rockies. Widespread scattered convection, locally heavy
rains and localized flash flooding possible across this area. A
more widespread qpf and excessive rainfall footprint expected day
4, with a decrease in threat area day 5, confined to eastern
AZ/western to central NM into southwest CO. A slight risk area is
possible in future updates when confidence in details of potential
heavy rain axes increases.

...Northern Plains into the Upper Mississippi Valley...
Shortwave energy moving northeastward in the broadly diffluent
upper flow pattern across the Northern Plains/Upper MS Valley
region will also support potential for organized convection along
and to the northeast of the northwest to southeast oriented frontal
zone across the Northern Plains. Anomalous PW values, 2-3+
standard deviations above the mean, expected across this region,
supporting potential for heavy rains and isolated runoff issues
both day 4 and day 5.

...Southeast/North Florida...
Widespread scattered convection likely both day 4 and 5 in the
vicinity of the slowly southward moving frontal boundary across
the Southeast/North Florida. Low confidence in qpf details in the
vicinity of this front, but with PW values 1.75-2.00", locally
heavy rains and isolated runoff issues possible.

Oravec
$$
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