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< Day 1 Outlook Day 3 Outlook >
 
WPC Day 2 Excessive Rainfall Outlook
Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
 
Updated: 2008 UTC Mon Apr 15, 2024
Valid: 12 UTC Apr 16, 2024 - 12 UTC Apr 17, 2024
 
Day 2 Excessive Rainfall Forecast
 
Forecast Discussion
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
747 PM EDT Mon Apr 15 2024
Day 2
Valid 12Z Tue Apr 16 2024 - 12Z Wed Apr 17 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS EASTERN
PORTIONS OF THE NORTHERN PLAINS SOUTHWARD THROUGH MUCH OF THE
MISSISSIPPI VALLEY...

20z Update:
We considered a Slight risk upgrade across portions of northeast IA
into southern MN and southwest WI. It is here where the heaviest
rainfall rates and totals are expected on Tuesday. Enough
instability is forecast to support 1-2"/hr rainfall over this area,
which will likely exceed 1hr FFG in spots. One limiting factor for
flash flooding will be the expected quick movement of cells,
limiting the duration of heavy rates. Some periodic
training/backbuilding is possible near the warm front, which
supports some areas exceeding 3" of total rainfall. However HREF 5"
exceedance probabilities drop to near 0, likely indicative of the
overall progressiveness of the system. Antecedent conditions and
streamflows are also generally below average across most of the
region. Thus despite the likelihood of some 1hr and 3hr FFG
exceedance, the coverage and magnitude of impacts are expected to
remain below Slight risk levels. The main threat will be to urban
areas, where the intense rates may lead to localized flash
flooding. Outside of urban areas the dry ground and limited green
vegetation may allow for some excess runoff, however these impacts
are expected to remain isolated as well. After coordination with
local WFOs, the consensus was to stick with just a Marginal risk
for now.

There may be an ongoing flash flood threat over southeast SD to
begin the period, but will let the day 1 Slight risk over that
area handle this threat for now. Pending observations later
tonight we may need to extend the Slight into this day 2 period.

Otherwise, did expand the Marginal risk into WV, where some slow
moving convection near a warm front may result in localized heavy
rains over an area that already has elevated soil saturation and
streamflows.

Chenard

...Previous Discussion...

The closed low and trailing cold front will advance from the High
Plains into the Upper Mississippi Valley while an west-east
orientated warm front extends across the Upper Midwest to the Mid-
Atlantic region. An axis of anomalous precipitable water values up
to 2 standard deviations above the mean, will persist along and ahead
of the well defined cold front while pooling along the warm front.
Organized convection will likely fire up in proximity to this
anomalous moisture axis. Like the previous day, the convection is
expected to be fairly progressive that continues to limit the
potential for heavy rainfall and associated areas of localized
flooding.

Locations along and north of the warm front have the greater
potential for organized precipitation to span from the Northern
Plains to the Upper Mississippi Valley/Upper Midwest. Heavy rain
will likely spread across locations north of the warm front and
maintain for longer durations as the moisture surging
northward from the Gulf of Mexico over the frontal boundary
persists. Consensus suggests broad areal averages of 1 to 2 inches
with locally higher amounts certainly possible. This region has
been relatively dry over the past few weeks, resulting in dry soils
and below average stream flows.

Campbell

 

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