541
FXUS66 KPDT 311050
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
250 AM PST Fri Jan 31 2025

.SHORT TERM...
Today through Sunday night...Widespread precipitation will
gradually overspread the entire region today after some light
precipitation this morning. The precipitation this morning will be
rain or freezing rain, especially over portions of the Columbia
Basin, but only a light glaze is expected, due to marginal
temperatures. More widespread precipitation is expected by
afternoon. Snow levels are quite high and will rise as a warm
front moves through, so generally all rain is expected by later
this morning/afternoon as freezing levels increase to over 5000
feet in most locations and over 4000 feet in the Washington
Cascades, except possibly right along the crest. Snow levels will
then decrease by Saturday morning, though with the exception of
the mountains, most precipitation will be over by then. SNow
levels will drop to between 2500 to 3500 feet in the Oregon
Cascades and Blue Mountains to basically ground level in the
Washington Cascades. Snow levels will fall even further by
Saturday afternoon, with all areas below 2000 feet.

Winter storm warnings and winter weather advisories have been
issued and will remain unchanged for now. With the high snow
levels to start, that will limit accumulations at first and some
of the numbers guidance was giving seem high as a result. However,
it is possible that the advisories may need to be upgraded to
warnings if snow is heavier than forecast.

ANy precipitation begins to taper off later Saturday into Sunday,
though there sill be some lingering light snow in the mountains.
The region will be in westerly flow between an upper low near
British Columbia and an atmospheric river to our south over
northern California and Nevada. Precipitation chances will
increase for the mountains later Sunday into Sunday night for the
mountains as a strong shortwave moves through. At this point,
another few inches are anticipated.

Winds will be quite breezy today, especially across the Grande
Ronde Valley and portions of the Columbia Basin and central
Oregon, where winds could gust 30 to 40 mph. NBM probabilities of
wind gusts >= 39 mph in these areas are 60-90 percent. NBM
probabilities of wind gusts >= 47 mph is generally 30 to 50
percent. On Saturday, winds will be similar to today.


.LONG TERM...
Monday through Friday...Deterministic models and ensemble
clusters are in good agreement on depicting a large upper level
trough/low anchored just offshore through Wednesday with moist
SWLY flow aloft over the area. Wednesday through Friday there are
some subtle differences on the evolution of the upper low as it
opens up and moves across the region...but expect a gradual
transition from SWLY flow aloft to NWLY by Friday. It will be cold
through the period with high temperatures as much as 15 degrees
below normal from Tuesday onward. This will result in snow levels
down to the basin floor and any precipitation falling as snow.

The most impactful period looks to be Monday night through Tuesday
evening. The NBM has 30-70% POPS with highest values over the
mountains. The deterministic models show an axis of moderate QPF of
.25 -.75 inches across Oregon but the NBM is much lighter. The QPF
clusters are favoring closer to .10 to .25 inches with heavier
amounts directed farther south into northern California.
Still the NBM probabilities of exceeding one inch of snow Tuesday
are 30-50% across the lower elevations of Oregon and GFS and ECMWF
ensemble plumes show several members with higher amounts. Thus it
appears that there will be at least some snow in the lower
elevations of mainly Oregon on Tuesday.

Wednesday through Friday will be unsettled with a chance of snow but
POPS will gradually decrease as the upper low weakens. POPS will
generally be in the 30-50% range in the mountains and 15-30% across
the lowlands. Threat for heavy or impactful amounts of snow looks
rather low during this period (10%). Overnight temperatures will be
quite cold with the coldest morning on Thursday. Thursday morning
lows will be in the single digits in the mountain valleys with teens
in the lower elevations. 78


&&

.AVIATION...
06Z TAFs...MVFR to VFR conditions expected through the
period. A weather system arriving to the region tonight will
produce precipitation impacts at all sites, with precipitation
expected to end at all sites around 00Z. Sites DLS/PDT/RDM/BDN/ALW
will see rain through this period, site YKM will see a rain/snow
mix with a prob30 of freezing rain between 11Z and 16Z, and site
PSC will see rain with a prob30 of freezing rain between 10Z and
16Z. CIGs of bkn-ovc at most sites will drop to between 1.5kft to
3kft with precipitation, but will increase to 3kft to 6kft after
precipitation exits the area. Precipitation will also produce vsby
impacts at most sites, though confidence is low (20-30%) in
periodic dips into MVFR conditions. Winds will be light through
the morning hours, then increasing to 12-20kts with gusts 20-30kts
developing tomorrow afternoon through the evening. Lawhorn/82

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  50  33  42  26 /  80  70  20  10
ALW  49  36  44  28 /  90  80  40  20
PSC  48  34  47  29 /  80  50  10   0
YKM  43  26  44  20 /  70  50  30  20
HRI  50  35  46  28 /  70  50  20   0
ELN  40  25  38  18 /  70  50  40  20
RDM  48  29  40  21 /  80  70  10  10
LGD  40  33  39  22 /  80  90  50  20
GCD  45  35  42  24 /  80  70  40  20
DLS  47  34  46  29 /  80  80  70  40

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 10 AM PST this morning for ORZ044.

     Winter Weather Advisory until 4 PM PST Saturday for ORZ502.

     Winter Weather Advisory until 4 PM PST Saturday for ORZ509.

WA...Winter Weather Advisory until 10 AM PST this morning for
     WAZ026>028.

     Winter Weather Advisory until 4 PM PST Saturday for WAZ030.

     Winter Storm Warning until 4 PM PST Saturday for WAZ522.

&&

$$

SHORT TERM...77
LONG TERM....78
AVIATION...78