WPC Day 3 Excessive Rainfall Outlook
Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
Updated: 0809 UTC Wed Jun 23, 2021
Valid: 12 UTC Jun 25, 2021 - 12 UTC Jun 26, 2021
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
412 AM EDT Wed Jun 23 2021
Valid 12Z Fri Jun 25 2021 - 12Z Sat Jun 26 2021
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE MIDWEST AND UPPER GREAT LAKES...
...Midwest/Upper Great Lakes...
A trough anchored from the Northern Plains into the Rockies will
become more amplified through the forecast period. Mid-level
impulses will round the base of the trough moving atop existing
surface/outflow boundaries which will promote widespread showers
and thunderstorms within the region. At the surface, a low will
lift through the Plains and toward the Upper Great Lakes region
which will usher in rich moisture and instability into the region.
Precipitable water values will climb above 2.25 inches (which is
over 2.5 standard deviations above the mean) aided by 30-40 knot
southwesterly flow. With ample warm air advection, instability
will surpass 2000 J/kg allowing rain rates to exceed 2 inches per
hour. Given the propagation vectors and mean wind profiles,
anticipate training to occur across a portion of the region. As a
result, areal average precipitation will range between 2-4+ inches
with locally higher amounts possible, especially across IL,
northern IN and into southern MI.
Model spread continues through Friday, but there is enough
multi-model signal to highlight the potential for robust rain
rates over modest flash flood guidance. Therefore, isolated to
scattered flash flooding is likely. If consensus grows in terms
of QPF amounts and placement, especially over vulnerable soils,
anticipate the need for an upgrade. However, a lot depends on the
precipitation observed on Day 1 and 2 as well as the residual
boundaries left over from prior convection. While the
precipitation activity should also be driven by large scale
synoptic forcing, there may be enough mesoscale features that need
to be taken into consideration for the QPF and associated risk
areas. We will continue to evaluate the flash flood potential
through the coming days.
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt