New Day 1 Outlook >
WPC Day 1 Excessive Rainfall Outlook Valid Through 12Z Today
Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
Updated: 0821 UTC Fri Aug 14, 2020
Valid: 01 UTC Aug 14, 2020 - 12 UTC Aug 14, 2020
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
855 PM EDT Thu Aug 13 2020
Valid 01Z Fri Aug 14 2020 - 12Z Fri Aug 14 2020
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
the UPPER MISSISSIPPI VALLEY AND THE ARKANSAS RIVER VALLEY INTO
...Northern Plains and Upper Mississippi Valley...
Convection has initiated this evening across portions of northwest
MN. Would expect this activity to exhibit some backbuilding and
training characteristics over the next several hours, with weak
Corfidi vectors and deep layer mean flow parallel to the boundary.
Overnight cells should begin propagating eastward across central
and northern MN...however by this time things should be
progressive enough to keep the flash flood threat low. Thus the
greatest flash flood risk is likely over the next several hours
from far eastern ND into northwest MN...where some totals over 3"
appear likely. The Slight risk was confined to this corridor of
training/backbuilding...as a Marginal should suffice further east
given the expected forward speed of cells by that time.
Additional convective development is likely tonight over southwest
ND as a strong wave and upper jet moves into the region. This
appears to be a good setup for intense convection given the degree
of instability, wind shear and deep layer forcing present. However
the flash flood threat should not be all that great given the
expected quick forward motions of cells. Thus a Marginal risk
should suffice to cover the localized risk that may result from
the short duration intense rainfall rates.
...Oklahoma and Arkansas...
A Slight risk was maintained from portions of eastern OK into
southwest AR. Will likely see convection develop here around 06z
on the nose of an increasing axis of lower level moisture
transport, where convergence will be maximized. These cells will
exhibit some northwest to southeast training parallel to the
aforementioned convergence axis. This should be enough to get some
3" amounts later tonight. Although recent HRRR runs do suggest a
fairly quick southeastward progression of the convective
complex...so even though we should see some training
initially...the duration of the event does not appear all that
long...which should help prevent a more extreme rainfall event.
The extent/magnitude of the moisture transport axis and the degree
of upstream instability, both also seem to suggest the duration of
the event will be somewhat limited. This may keep the flash flood
risk more isolated in nature...although portions of southeast OK
and southwest AR saw very heavy rainfall amounts just a couple
days ago...so these areas should be more susceptible to additional
flash flooding. Some question remains as to the exact location of
this threat tonight...but if it does overlap with this earlier
rainfall axis then a more concentrated flash flood risk could
evolve...and thus think the Slight risk remains warranted.
...Southeast and Mid Atlantic...
A localized flash flood risk continues across portions of the
Southeast into the Mid Atlantic. In general the threat should
continue to gradually decrease through the evening hours...however
some instances of cell collisions and locally enhanced rainfall
will persist for at least the next several hours across the
Marginal risk area.
Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt