Clifton, Virginia Weather

371
FOUS30 KWBC 132237
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
637 PM EDT Thu Mar 13 2025

Day 1
Valid 01Z Fri Mar 14 2025 - 12Z Fri Mar 14 2025

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

Roth


Day 2
Valid 12Z Fri Mar 14 2025 - 12Z Sat Mar 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE LOWER TO MID MISSISSIPPI VALLEY INTO PARTS OF THE OHIO AND
TENNESSEE VALLEYS...

...2030Z Update...

Prior discussion reviewing the synoptic setup and caveats on the
more limited potential for a flash flooding threat compared to a
severe threat remain on track. Expect a line of convection to
develop along the cold front by early evening, first for more
northern areas across the Middle Mississippi Valley with additional
storms extending southward through the Lower Ohio and Tennessee
Valleys through the night. Updated 12Z hi-res guidance indicates
the combination of strong dynamics, moist southerly return flow,
and sufficient instability could lead to some locally heavier
rainfall amounts around 2" supported by quick downpours with rain
rates of 1-1.5" per hour. However, this potential appears to remain
rather limited given the quick progression of the storms/cold
front, and thus only a few isolated instances of flash flooding
mainly for urban areas is expected.

Putnam

A strong mid-to-upper level shortwave crossing the Southwest on
Day 1 is expected to move east of the Rockies, with a negatively-
tilted low developing over the central Plains early in the period.
Powerful forcing is forecast to interact with what is expected to
be a relatively modest plume of moisture advecting north ahead of
the system. Storms are forecast to develop initially over the lower
to mid Mississippi Valley Friday afternoon before moving east into
the Tennessee and Ohio valleys during the evening and overnight.
Cell motions will likely be quite progressive given the very strong
wind fields in place. Therefore, this convection will likely pose
more of a severe risk than a flash flood threat. However, given the
strong dynamics, along with sufficient instability for deep
convection, expect that rainfall rates will be briefly intense
enough to produce localized amounts that exceed current model
forecasts (maybe locally over 2 inches). Still, this appears to be
a lower-end flood threat, and probably confined to localized
impacts over more sensitive urban or low lying areas that are
impacted by a quick burst of intense rainfall.

Pereira

Day 3
Valid 12Z Sat Mar 15 2025 - 12Z Sun Mar 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
TENNESSEE AND OHIO VALLEYS...

Even as the previously noted low lifts to the north through the
Great Lakes into Ontario, the upper pattern will remain amplified
across the central U.S. as an upstream shortwave dives southeast
into the southern Plains on Saturday morning and spreads eastward
over the Lower Mississippi Valley into Saturday afternoon/evening.
A surface wave developing along the leading system`s trailing cold
front will help focus deeper moisture tapped by strengthening
southerly winds and with increasing upper-level dynamical support
as the southern shortwave approaches. This will help lead to the
continued development and maintenance of an intense line of
thunderstorms pushing eastward along the front. The general
consensus of the most recent 12Z guidance indicates that widespread
accumulations of 2-4 inches centered over parts of the Tennessee
and lower Ohio Valleys are likely. A large Slight Risk was
maintained across the region, reflecting the higher probabilities
for 2 inches or more shown by the GEFS/ECENS where this favorable
combination of deeper moisture, interacting with strong forcing,
along a relatively slow moving front, is expected to raise the
potential for heavy amounts late Saturday into early Sunday. This
remains a higher-end Slight Risk for parts of the area, and a more
focused corridor with the potential for an upgrade to a Moderate
Risk is becoming apparent where the potential exists of pre-
frontal/warm air advection forced convection on the leading edge of
returning higher theta-e air. The latest 12Z guidance indicates
this potential is currently highest from northeast
Mississippi/northwest Alabama northeast through central Tennessee
into south-central Kentucky where locally higher totals of 5-6"
could be realized. However, have opted to remain at a higher-end
Slight Risk for now given that the placement of similar corridors
in these setups often initially has a northern bias in the
guidance, and that once the period moves within the hi-res window
the placement of the heaviest rain rates/amounts will become more
clear.

Putnam/Pereira

Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt