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WPC Met Watch

Mesoscale Precipitation Discussion: #0939 (2019)
(Issued at 400 PM EDT Mon Oct 21 2019 )

MPD Selection

Graphic for MPD #0939

Mesoscale Precipitation Discussion 0939
NWS Weather Prediction Center College Park MD
400 PM EDT Mon Oct 21 2019

Areas affected...Western WA

Concerning...Heavy rainfall

Valid 212000Z - 220800Z

Summary...An atmospheric river will bring a period of moderate to
locally heavy rainfall to the Olympics and central Cascades of WA.
Hourly rainfall magnitudes up to 0.5", and total rainfall as high
as 3-6" will result in some minor flooding concerns through the
overnight hours.

Discussion...Rain rates are expected to increase across the
Olympics and central Cascades over the next several hours as the
core of the atmospheric river (AR) moves across the region. This
system does appear to meet AR criteria, but is rather progressive,
meaning the duration of the heaviest rainfall rates will not be
all that long. Also, while IVT, 850-700mb U wind components into
the terrain, and PWs are all anomalous...none of these components
are that extreme (nothing near record levels). So for AR standards
this is generally an average event...and a lack of instability
should also keep rainfall rates in check. With all this said, this
event will still produce some hefty rainfall totals across the
Olympics and the central Cascades through tonight...and over the
past two weeks precipitation is as much as 150-300% above normal
across this region. Thus this additional heavy rainfall may result
in some minor flooding concerns across these areas into tomorrow

The 17z HRRR and 12z HREF are in good agreement with the timing of
heavier rainfall rates and event total rain. Rates should pick up
around 23z and remain up through around 06z...with hourly
magnitudes peaking around 0.5" for a few hour window. Thereafter
the better rates will begin shifting southward over the Cascades
with a lightening of rain across the Olympics and central
Cascades. Through 12z Tuesday we should end up with 2-4" of total
rain over the Olympics, and closer to 3-6" over the western slopes
of the central Cascades.




LAT...LON   48942259 48902184 48592105 48082087 47442093
            46732164 46252332 46662411 47992462 48562451

Last Updated: 400 PM EDT Mon Oct 21 2019

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Page last modified: Wednesday, 13-May-2015 19:29:02 GMT