134
AWUS01 KWNH 030626
FFGMPD
CAZ000-ORZ000-WAZ000-031400-

Mesoscale Precipitation Discussion 0382
NWS Weather Prediction Center College Park MD
225 AM EDT Mon Jun 03 2024

Areas affected...Pacific Northwest

Concerning...Heavy rainfall

Valid 030625Z - 031400Z

SUMMARY...A strong late season atmospheric river will continue to
bring heavy rainfall into the Pacific Northwest overnight with a
break in the activity then expected by early Monday morning.

DISCUSSION...The latest GOES-W Airmass RGB satellite imagery in
conjunction with CIRA-ALPW and experimental LVT products shows a
very well-defined and impressive atmospheric river continuing to
advance inland across the Pacific Northwest as an upper-level
trough and associated frontal zone prepares to cross the region.

IVT values are forecast to generally max out over the next 3 to 6
hours across the coastal ranges of western OR and down into
northwest CA just ahead of the approaching cold front. IVT
magnitudes are forecast to reach locally 750 to 1000 kg/m/s and
this coupled with strong warm air advection aided by a strong deep
layer trans-Pacific jet will maintain heavy rainfall rates.

Enhanced upslope flow/orographics will favor these heavier rates
between now and 12Z occurring over the southwest-facing slopes of
the southwest OR/northwest CA coastal ranges and into the upslope
areas of the OR Cascades where they are expected to peak into the
0.50" to 0.75"/hour range.

The nose of a strong 110+ kt 250 mb upper-level jet should drive
this latest atmospheric river well inland by early Monday morning
along with the passage of a cold front that will regionally allow
for the rainfall rates to then decrease, but there will continue
to be post-frontal shower activity lingering through the morning
hours with the persistence of onshore flow.

Expect additional rainfall amounts by early Monday morning of 2 to
3 inches across the coastal ranges of southwest OR/northwest CA
and into windward slopes of the OR Cascades. This is consistent
with the 00Z HREF guidance. Meanwhile, additional amounts of 1 to
2 inches can be expected farther north over the orographically
favored terrain of western WA.

Orrison

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...EKA...MFR...PDT...PQR...SEW...

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

LAT...LON   48592186 48102123 46792134 45692146 44352167
            43162187 42832192 42452225 42322312 41992315
            41692309 41252328 40792357 40792417 41072450
            41712464 42502464 43812425 45132410 46252414
            47592442 47992415 47972344 47522299 47672248
            48512240