400
FXUS66 KPDT 031111
AFDPDT

KEY POINTS

1. Lingering snowfall in the WA Cascades becoming widespread rain
beginning Monday morning.

2. Persistent wet weather pattern through the week

3. Breezy winds Wednesday through end of the week

DISCUSSION...Monday through Monday night...Current satellite shows
some mid level clouds moving across the northern and southwest
portion of the CWA. Clouds will continue to build through the day as
models show the leading edge f the upper level system continuing to
move closer to shore.

Models show the leading edge of the upper level system to begin to
affect the WA Cascades beginning after 10AM. NBM shows snow levels
to reach as low as 2500 feet with models showing precipitation
accumulations of up to 2 inches along Snoqualmie Pass over the
course of the day today (Monday). Raw ensembles show between 50-70%
probabilities of up to 2.5 inches of snow expected along Snoqualmie
Pass with Stampede and Chinook Passes seeing 80% or greater
probabilities of 3 to 4 inches over the next 24 hours. Models show
the system continuing to push onshore bringing southwest flow aloft
to the region and pushing across the area from the northwest bring
probabilities of widespread rain after 5PM with almost the locations
seeing at least 0.10 inches of rain. 40-60% probabilities of 0.15
inches through the Columbia Basin, Gorge, foothills of the southern
and northern Blues and north central OR. 70-90% probabilities of
near 0.20 inches through Yakima and Kittitas Valley as well as below
2500 feet on the eastern slopes of the WA Cascades.

Tuesday through Wednesday afternoon...Models continue to be in firm
agreement through Tuesday night with the progression of the system.
Models show the system to begin to flatten out to a more zonal or
westerly flow aloft Tuesday with lingering showers across the
western portion of the CWA affecting mostly the eastern slopes of
the OR & WA Cascades through the western potion of the Columbia
Basin, central OR and portions of the Ochoco-John Day Highlands
Tuesday and continuing through Wednesday morning before becoming
mainly mountain showers with light lower elevation rain. Raw
ensembles show the aforementioned areas will see 40-70% chances of
near 0.20 inches of rain while the remaining areas will see light
rain both Tuesday and Wednesday with ensembles showing 30-60%
probabilities of near 0.10 inches Tuesday and again through
Wednesday afternoon.

Accompanying the next system will be a surface front that will bring
breezy conditions across the region Tuesday and will persist through
Wednesday. Tuesday, breezy winds of near 20 mph sustained will be
through central OR becoming a bit more widespread Wednesday and the
models show the front to lift across the region. Raw ensembles show
30-50% chances across central OR and across portions of the Ochco-
John Day Highlands before becoming more widespread Wednesday through
north central OR and along the foothills of the Blues. Continued 30-
50% probabilities of sustained winds of 20-25 mph.

Lastly, models remain in relatively good agreement with this system
persisting through Thursday with persistent rainfall. Amounts are a
bit more out of sync with the clusters struggling when it comes to
the arrival of the next heavier rain amounts.  Regardless, models
are in agreement that a wet pattern will continue to persist over
the region through at least Saturday. 90

AVIATION...12Z TAFs...VFR conditions will persist through the
forecast period with CIGs beginning to move in across the region and
remaining 5-10kft. Winds will be below 10kts through the period and
mostly terrain driven. Rain is expected to impact TAF sites
DLS/YKM/PSC beginning 18-19Z fro YKM/DLS respectively and after 22Z
for PSC as the system moves across the region. Put Prob30 elsewhere
as models are uncertain of timing and if rain will reach the far
eastern portions of the region. The system is moving in a more NW to
SE direction and will likely miss RDM/BDN only allowing for mainly
drizzle so a Prob30 was also added at those sites beginning late in
the period. 90
.