207
FXUS66 KPDT 191125
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
425 AM PDT Wed Mar 19 2025

.Update for Aviation...


SHORT TERM...Today through Friday night...Back-to-back shortwave
troughs will facilitate active late-winter/early-spring weather
across our forecast area through the remainder of the week.
Mountain snow, lowland rain/snow, and widespread breezy to windy
conditions are the main points of discussion.

Current water vapor imagery shows an upper-level ridge of high
pressure overhead with an offshore upper-level shortwave trough
approaching the Pacific Northwest. The ridge will migrate eastward
through the day with the trough pushing onshore late afternoon
through tonight. Surface pressure gradients will increase today,
and winds aloft will strengthen as the trough approaches and
swings overhead. Have opted to expand our Wind Advisories to
include the foothills of the northern Blue Mountains of Washington
due to high confidence (70-90%) in areas reaching advisory-level
sustained winds (30 mph or greater) and/or gusts (45 mph or
greater) late this afternoon along the base and slopes of the
northern Blue Mountains with downslope winds, and then this
evening into tonight across the whole zone as the trough punches
across the Columbia Basin and winds switch to southwesterly.

The 00Z HREF shows a 35-45 kt jet at 850 mb stretching over the
Columbia Plateau from north-central and northeast Oregon through
south-central and southeast Washington this evening through early
Thursday morning. Confidence is medium-high (40-70%) that
sufficient momentum transfer from aloft will occur with the
shortwave passage to reach advisory-level winds across forecast
zones in the aforementioned region, but would like to have higher
confidence (80%) to issue additional wind highlights so have held
off for now.

With regard to winter highlights, after collaboration with
surrounding offices, have held off on issuing any for the
Washington Cascades. Confidence is medium-high (50-90%) in
reaching 6 inches or more of snow for Snoqualmie and White passes
through Thursday night. An advisory may be needed with the next
forecast package on the day shift. Elsewhere, have lowered the
advisory for the Oregon Cascades to 4000 feet as forecast snow
totals and snow levels are supportive. Moreover, NBM probabilities
suggest Santiam Pass has a high chance (~85%) of reaching
warning-level totals. Considered upgrading the advisory to a
warning, but after collaborating with PQR/MFR have held off in
favor of letting the incoming day shift make any changes.

Looking ahead, a weak warm front will push onshore late Thursday,
followed by the next shortwave trough on Friday. Another couple
rounds of widespread breezy to windy southwesterly to westerly
winds is expected with medium-high probabilities (40-70%) of
needed additional wind highlights for much of the Columbia Plateau
Thursday and Friday.

Lastly, the next round of forecast snowfall may warrant additional
winter highlights for the mountains Friday through Friday night.
Plunkett/86

LONG TERM...Saturday through Tuesday...A weak trough will move
across the Pacific Northwest on Saturday, and will bring another
round of precipitation, mainly for the mountains. By Saturday
night the flow becomes more northwest and additional precipitation
is expected in the northwesterly flow, again mainly for the
mountains.

By Sunday night into Monday, a ridge will begin to build over the
western CONUS. Precipitation will end except for the Cascades and
eastern mountains, and by Monday night dry conditions are expected
everywhere.

Snow levels early on Saturday will range from below 2500 feet for
the Washington Cascades to 4500 feet for the Oregon Cascades. Snow
levels will rise to 3000 to 3500 feet for the Washington Cascades
by Saturday afternoon, 3500 to 3500 feet for the Blue Mountains
and 5000 to 5000 feet for the Oregon Cascades. Snow levels will
continue to rise into Sunday. with snow levels between 6000 and
7000 feet by Sunday afternoon.

QPF amounts Friday through Sunday will be over an inch for the
crest of the Cascades and Blue mountains with lower amounts
elsewhere. The nearby higher terrain will see 0.25 to 0.50 inches.
Most of the lower elevations will see 0.15 inches or less with
the Columbia Basin, Yakima Valley, Kittitas Valley and Central
Oregon only see a few hundredths.

Snow amounts through Saturday will be upwards of 6 inches in the
Washington Cascades except probably 8 to 10 along the crest. For
the Oregon Cascades, a few inches below 4000 feet and upwards of
a foot above 4000 feet, along the crest. For the Blue Mountains,
perhaps a couple of inches below 4000 feet and 6 to 10 inches
above 4000 feet along the crest.

Sunday through Monday, will see another 0.75 to 1 inch along the
crest of the Washington Cascades, though much less in the Oregon
Cascades, only maybe 0.25 inches. About 0.25 inches is expected in
the Blues as well, and 0.25 to 0.50 inches in the higher terrain
around the Washington Cascades and not much elsewhere. Due to the
higher and rising snow levels Sunday into Monday, little in the
way of significant accumulations are expected, outside of possibly
the crest of the Washington Cascades.

High temperatures will climb from near normal on Saturday with
highs in the 50s to near 60 degrees to 15 to 20 degrees above
normal by Tuesday with all lower elevation locations into the 70s.
The ECMWF EFI shows the anomalously warm temperatures with values
of 0.8 to 0.9 over much of the region by Tuesday.

With the warm temperatures by early next week and new snow and
then rain on snow, we will need to keep an eye on rivers and
streams as we go into next week.

AVIATION...
12Z TAFS...VFR conditions are expected through the period. The
next system will move onshore later this afternoon/evening and
bring rain to most TAF site this evening/tonight. Rain is expected
generally form west to east and then will continue for the
remainder of the period.

BDN/RDM/ALW will see wind gust in the 25 to 30 kt range beginning
later this afternoon. PSC and PDT will see winds around 15 kts,
with some higher gusts possible.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  58  37  54  41 /  10  60  60  50
ALW  56  38  53  42 /  10  80  70  70
PSC  58  38  58  42 /  10  40  20  20
YKM  49  32  55  38 /  20  60  20  30
HRI  59  37  57  42 /  10  40  30  30
ELN  47  31  52  34 /  40  80  30  40
RDM  53  29  49  34 /  10  70  40  30
LGD  47  32  47  35 /  10  80  80  80
GCD  49  29  46  34 /  10  80  80  80
DLS  52  37  54  41 /  20  90  80  70

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 8 AM this morning to 2 AM PDT Thursday for
     ORZ049.

     Winter Weather Advisory from 5 PM this afternoon to 11 PM PDT
     Thursday for ORZ502-509.

     Wind Advisory from 5 PM this afternoon to 5 AM PDT Thursday for
     ORZ507.

WA...Winter Weather Advisory from 5 PM this afternoon to 11 PM PDT
     Thursday for WAZ030.

     Wind Advisory from 5 PM this afternoon to 5 AM PDT Thursday for
     WAZ029.

&&

$$

SHORT TERM...86
LONG TERM....77
AVIATION...77