AWUS01 KWNH 250750
FFGMPD
ORZ000-WAZ000-252000-

Mesoscale Precipitation Discussion 0052
NWS Weather Prediction Center College Park MD
250 AM EST Tue Feb 25 2025

Areas affected...Lower Foothills of Western Washington & Far
Northwest Oregon...

Concerning...Heavy rainfall

Valid 250800Z - 252000Z

SUMMARY...Reducing rainfall rates to .25-.3"/hr and spots of
additional 2-3" adds to streamflows/ongoing river flooding within
western facing foothills of Cascades/Olympics, as well as much of
the Coastal Range.

DISCUSSION...GOES-W WV shows an textbook symmetric deep layer
fairly broad cyclone just west of the entrance to the Juan de Fuca
strait, which is accompanied by a sub 985mb surface low.  While
the cyclone is starting to fill well past peak maturity, a subtle
lobe of vorticity and associated jet streak is rounding the base
of the cyclone resulting in broadening diffluent/divergent
downstream flow across W WA increasing westerly surface to 700mb
flow.  Given onshore surface winds are gusting over 50 mph that
increase to 70kts by 700mb slowly veering from WSW to W over the
next few hours, is solidly orthogonal to the SW slopes of the
Olympics and while moisture is limited due to the deep cold air
through depth, total PWats of .75" and the strength of winds will
continue to result in solid rainfall rates of .25 to .3"/hr in the
lower slopes before the freezing levels about 3Kft. 

The upper-low will continue to spin down but approach the coastal
range maintaining the strong moisture flux with very slow
reduction with the winds.  The Willapa Hills will take the
greatest brunt of flux closer to the track of the low and best
orthogonal flow to support .25-.3"/hr for about 9-12 hours which
will allow for an additional 2-3"+ though spots along the NW
Oregon Coastal Range in Clatsop and Tillamook counties will see
slightly reduced rates, but still potent for 1-2.5" totals.  Given
soil conditions are already nearly fully saturated per NASA SPoRT
LIS product suggesting 85-95% saturation through 40cm, most will
continue to run off and maintain already increased stream rates
and flooding conditions in downstream rivers, yet rates are not
likely to result in rapid rises.

Downstream into the Cascades, the slopes increase rapidly with
only limited areas of the lower foothills below freezing levels,
with much of the moisture above to fall as snow. Still, similar
1-3" totals in the lower foothills extend mainly north of the
Columbia river in the Washington Cascades with best rates up to
.25"/hr likely as the core of the upper-level low crosses later
this morning into early afternoon (15-20z), ending the prolonged
atmospheric river event. 

Gallina

ATTN...WFO...PQR...SEW...

ATTN...RFC...NWRFC...NWC...

LAT...LON   48942200 48742184 48432150 47742151 47592157 
            47042186 46692232 46322237 46232248 46172269 
            45992307 45572326 44912345 44722383 45082410 
            46302409 47572444 48352474 48232423 47882394 
            47502371 47432326 46852323 46682282 46812275 
            47032231 47492197 48092192 48412207 48792219 
            
$$
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