FOUS30 KWBC 221736
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1236 PM EST Thu Jan 22 2026
Day 1
Valid 16Z Thu Jan 22 2026 - 12Z Fri Jan 23 2026
The probability of rainfall exceeding flash flood guidance is less
than 5 percent.
A mesoscale cyclone appears to have formed near the intersection
of a weak surface trough/front east to northeast of Biscayne Bay.
This combination has led to thunderstorm development with heavy
rainfall, which up until this point has only impacted southern
portions of Key Biscayne though some cells recently are
threatening to move ashore a little farther north across Key
Biscayne and near Fisher Island. The airmass along and east of the
coast is sufficiently moist and unstable for thunderstorms with
heavy rainfall, and effective bulk shear supports the formation of
random mesocyclones. The low-level inflow to the east north of the
mesocyclone runs counter to the westerly flow aloft, with the
combination leading to minimal cell movement. The overall threat of
heavier rainfall materializing over urban areas of the I-95
corridor still appears to be fairly isolated. The overall threat
appears to wane after 19z/2 pm EST when the guidance implies that
the mesocyclone near South Florida drifts eastward. A non- zero
threat of flash flooding exists, but convective coverage and the
brevity of the thunderstorm risk precludes any addition of Marginal
areas at this time.
Isolated showers across southern California may also impact
portions of the Transverse and Peninsular Ranges as well, with
brief heavy rain occurring near burn scars across the area. The air
mass should be sufficiently moist, with precipitable water values
in the 0.75-1" range. Bubbles of 100+ J/kg of MU CAPE lie offshore
at the present time. This should maximize hourly rain amounts in
the 0.4" neighborhood. The 12z HREF probabilities of 0.5"+ in an
area are below 15%, also implying that lesser hourly amounts are
expected. The threat for flash flooding here is also less than 5%
although an isolated instance of excessive runoff cannot be
completely ruled out.
Roth/Cook
Day 2
Valid 12Z Fri Jan 23 2026 - 12Z Sat Jan 24 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE TEXAS
HILL COUNTRY...
Gulf inflow ahead of an incoming upper level trough across the=20
Northern Plains/West brings overrunning moisture into South-Central
TX, with precipitable water values rising to 1.25" within a cool=20
atmosphere with 5610 m 1000-500 hPa thickness, implying complete=20
saturation. RAP forecasts show MU CAPE rising to 500+ J/kg,=20
implying a heavy rain threat. The 12z HREF/06z REFS agree, showing=20
high enough probabilities of 0.5"+ an hour and 3"+ in 24 hours to=20
be of concern to the Hill Country, where there is limited topsoil
to prevent runoff. This new Marginal Risk was added in=20
collaboration with the EWX/New Braunfels TX, SJT/San Angelo TX,=20
and FWD/Fort Worth TX forecast offices.
Roth
Day 3
Valid 12Z Sat Jan 24 2026 - 12Z Sun Jan 25 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL NEAR THE
NORTHWEST GULF COAST...
An upper level trough phasing as it moves through the Rockies lures
sufficient Gulf moisture into Southeast TX/the Upper TX Coast and
southwest Louisiana, with precipitable water values rising to
1.25-1.75". Considering the coolness of the environment, this
should lead to atmospheric saturation. The region is diffluent=20
aloft and does not appear to be capped...700 hPa temperatures are
forecast to be below 6C. MU CAPE rises above 1000 J/kg, at times.=20
Inflow at 850 hPa/effective bulk shear appears sufficient for=20
convective organization. Hourly rain amounts to 2.5" with local=20
totals to 5" are possible, given the above ingredients. The 12z=20
UKMET, 12z Canadian Regional/RDPM, and 00z ECMWF have a signal for=20
heavy rainfall in this region, though the 12z GFS does not. Enough=20
of a signal exists for a Marginal Risk area to be hoisted this=20
cycle. Over the past week, it has been wet across portions of
Jefferson, Orange, & Galveston Counties in TX as well as portions=20
of southwest LA south of I-10. Isolated to widely scattered issues=20
would be mostly confined to urban areas.
Roth
Day 1 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7ESEwQjP6l0ddiDKpbckZF5M_vqB9TFPzru7FR97hUey= 5dUOGGWskzC0YIGgmkt-EaGb8qB8wTebH-iyp29l6AT6ucg$=20
Day 2 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7ESEwQjP6l0ddiDKpbckZF5M_vqB9TFPzru7FR97hUey= 5dUOGGWskzC0YIGgmkt-EaGb8qB8wTebH-iyp29lx_Wf7Vc$=20
Day 3 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7ESEwQjP6l0ddiDKpbckZF5M_vqB9TFPzru7FR97hUey= 5dUOGGWskzC0YIGgmkt-EaGb8qB8wTebH-iyp29llAcGhKw$=20
=3D =3D =3D
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