Mesoscale Precipitation Discussion 0030
NWS Weather Prediction Center College Park MD
440 AM EST Sun Feb 28 2021
Areas affected...OH Valley
Concerning...Heavy rainfall...Flash flooding possible
Valid 280940Z - 281540Z
SUMMARY...Heavy showers and thunderstorms should tend to increase
in coverage and general organization going through the mid-morning
hours. The concerns for runoff problems and some flash flooding
will likely increase with time.
DISCUSSION...A mid-level trough is seen approaching the Midwest
which is seen facilitating an axis of deep layer southwest flow
downstream over the OH Valley. Strong warm-air advection and
enhanced moisture transport as aided by the approach of a 40 to
50+ kt low-level jet are already driving a broken axis of heavy
showers and thunderstorms along and near the OH River and this
activity is likely to become a tad more expansive in nature with
somewhat greater convective organization favoring heavier rainfall
rates going through 12Z to 15Z this morning.
This will be fostered by an expected increase in instability
pooling along a warm front seen lifting gradually north across the
OH Valley. Already MUCAPE values are locally 500 to 1000 j/kg
across the areas of southeast MO and southern IL given the strong
southwest low-level jet, and this pool of instability will be
advancing off to the east with time.
MRMS data shows some of the rainfall rates across northwest KY and
far southern IN already approaching 1 inch/hr and with greater
instability arriving toward and after 12Z, these rainfall rates
should increase and expand in coverage as well.
The environment is likely to be conducive for repeating rounds and
localized training of convective cells given the orientation of
the showers and thunderstorms to the deep layer steering flow and
proximity to the aforementioned warm front. The 00Z/06Z HREF
guidance and recent runs of the HRRR support localized swaths of 2
to 3 inches of rain going through 15Z. However, some isolated
heavier amounts will be possible given the training cell threat
and uptick in rainfall rates.
As a result, there should be a gradual increase in runoff concerns
and some flash flooding going through the early to mid-morning
hours.