< Day 1 Outlook Valid Through 12Z Today
Day 2 Outlook >
WPC Day 1 Excessive Rainfall Outlook
Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
Updated: 0806 UTC Wed Jul 28, 2021
Valid: 12 UTC Jul 28, 2021 - 12 UTC Jul 29, 2021
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
405 AM EDT Wed Jul 28 2021
Valid 12Z Wed Jul 28 2021 - 12Z Thu Jul 29 2021
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE UPPER GREAT LAKES INTO THE UPPER MIDWEST...
...Upper Midwest/Great Lakes...
The next shortwave trough makes its way across the area during the
period with sufficient instability and PW values reaching 1.75 to
2.0 inches. Soils have been primed through previous days rainfall.
Soil moisture is already sitting in upwards of the 98th percentile
and with previous days QPF, the day 1 periods will see much lower
FFG than what is currently seen, which is already low. Flash
flooding concerns are on the higher end confidence wise. The
Slight Risk area has been adjusted for portions of WI into MI to
better align with latest QPF forecast and model guidance. The
Marginal Risk area already in play for this region was expanded
slightly to account for differences among the models and latest
...Great Basin/Intermountain West...
Monsoonal moisture continues to surge north across the region with
weak mid-level impulses helping to focus convection farther north.
This becomes no more evident than by the precipitable water values
remaining above 1.25 inches in some locations under broad
southerly low level flow. With plenty of diurnal heating,
anticipate MUCAPE to climb above 1000 J/kg allowing for
differential heating across the terrain. Therefore, afternoon
convection will largely be tied to the mountains and eventually
shift off into the valleys/deserts through the late
afternoon/evening. Hourly rain rates could reach between 0.5-1
inches, though isolated higher amounts are possible, especially
with slow moving convection. Given the complex terrain, wet
antecedent conditions across the Southwest/Central-Southern
Rockies, and burn scars, localized flash flooding could occur and
the Marginal Risk area has been maintained.
A boundary should stall near the FL/GA line extending west to the
central Gulf Coast. Convergence of tropical air along this
boundary should allow heavy enough rainfall to locally exceed the
currently high flash flood guidance and combined with previous
days QPF, the Marginal Risk area was kept in play.
Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt