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Day 2 Outlook >
WPC Day 1 Excessive Rainfall Outlook
Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
Updated: 1559 UTC Sun Apr 14, 2024
Valid: 16 UTC Apr 14, 2024 - 12 UTC Apr 15, 2024
Day 1 Excessive Rainfall Forecast
Forecast Discussion
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1157 AM EDT Sun Apr 14 2024
Day 1
Valid 16Z Sun Apr 14 2024 - 12Z Mon Apr 15 2024


...Coastal Southern California...
Only cosmetic changes were made for the 16Z Day 1 ERO update to
the previous Marginal Risk area across the Transverse range and
the southern portions of the central California Coast Range. A
second area of showers is developing early Sunday morning along the
central California Coast Range ahead of the strong closed low
along the central California coast. This upper center is expected
to rotate southeastward along the central California coast and
through the Transverse Range day 1. An organized area of showers
will accompany this upper low, supporting additional moderate to
locally heavy precip totals day 1. Hourly rainfall totals from the
hi res guidance suggests .10-.25"+ amounts are possible. HREF
neighborhood probabilities are rather low for any hourly totals
greater than .50". Isolated runoff issues possible where additional
moderate to locally heavy rains fall over regions that received
rain over the past 24 hours.

...Northern Mid-Atlantic into the Central Appalachians...
For the 16Z update, we removed the northern portion of the Marginal
Risk area that had extended into southern NY. Despite the 850-700
mb kinematic and moisture transport anomalies and steepening
700-500 mb lapse rates, lower (sub 850 mb) tropospheric dry air,
which is not currently being handled well by the models (including
13Z NBM), is a big mitigating factor for the overall flash flood
threat (in all aspects...real extent, duration, and intensity).
Believe the drier ARW, HRRR, and RRFS are having a better handle on
the evolving situation, vs. the much wetter ARW2, FV3, and NAM
CONUS-Nest. Have opted to maintain a portion of the Marginal Risk
area (over PA, far eastern OH, and northern WV), however from an
excessive rainfall/flash flood threat, expect the risk to be on the
lower end of the marginal risk scale -- i.e. closer to 5% vs. near

...Previous Discussion...

A surface frontal boundary expected to sink southward
late Sunday afternoon into Sunday night across the Northern Mid-
Atlantic. A narrow axis of instability, LIs 0 to -4, MUCAPE
200-500 j/kg, and increasing PW values .75-1"+, expected along and
ahead of this front. HI res model consensus is for a line of
showers/thunderstorms to form along and ahead of this front across
the Northern Mid- Atlantic Sunday afternoon and sink southward into
early Sunday evening. Recent heavy precipitation from the Central
Appalachians into the Northern Mid- Atlantic has resulted in
saturated soils and high stream flows. Hi res model consensus is
for potential of .25-50"+ hourly amounts along this front. With
soils saturated, much of this will runoff, possibly resulting in
isolated flash flooding. No significant changes made to the
previous Marginal Risk across this region.



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