Area Forecast Discussion
Issued by NWS Pendleton, OR

Home |  Current Version |  Previous Version |  Text Only |  Print | Product List |  Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
134
FXUS66 KPDT 150543
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
943 PM PST Fri Feb 14 2025

.Updated Aviation Discussion.


.AVIATION...06Z TAFS...VFR conditions currently experienced at all
sites, with most sites degrading to either MVFR or IFR toward the
end of the period as a result of an incoming weather system. The
only exception will be for KRDM/KBDN, which should stay VFR through
the period. Light snow will be impacting the remaining sites during
the mid-to late afternoon as ceilings drop to 1.5-3kft with
visibilities of 2-4SM. IFR conditions are expected at KALW toward
the end of the period as visibilities drop to 2SM. Elsewhere
(KDLS/KPDT/KYKM/KPSC) conditions will drop to MVFR with visibilities
of 3-4SM and ceilings of 1.5-2.5kft. Winds will stay light and
below 10 kts for all sites through the period. 75


&&

.PREV DISCUSSION... /issued 304 PM PST Fri Feb 14 2025/

SHORT TERM...This afternoon through Sunday night...A flattening
shortwave trough is exiting the Pacific Northwest to the east this
afternoon, leaving a northwesterly flow aloft and some isolated to
scattered upslope snow showers across the Blue Mountains and their
adjoining foothills. Winter Weather Advisories remain in effect
for the Blue Mountains through 10PM this evening, where confidence
is high (70-90%) in an additional 1-3" of snow accumulation
beneath snow showers. Elsewhere, cancelled the winter weather
products for the foothills of the northern Blue Mountains of OR/WA
early since accumulating snowfall tapered off late this morning;
confidence is high (80%) that additional accumulations in snow
showers will be light at 0.5" or less.

This evening through Saturday morning, an upper-level shortwave
ridge will push east over the Pacific Northwest, bringing upslope
snow to an end.

The break in precipitation will be brief as the next upper-level
low and attendant weak frontal system is slated to arrive by
Saturday afternoon. While the warm frontal boundary looks weak
with a shallow, weak warm nose aloft, this will pose some
potential for light freezing rain or mixed wintry precipitation
(rain/snow/freezing rain) for sheltered valleys along the east
slope of the OR/WA Cascades, the Columbia River Gorge, lower
Columbia Basin, and Blue Mountain foothills. Probabilities are
low-medium (20-50%) in accumulating freezing rain (0.01" or
greater) for the aforementioned areas Saturday night through
Sunday. Additionally, there is a medium-high probability (40-80%)
in measurable lowland snow in Washington, with a low-medium
probability (20-60%) for the lowlands of Oregon. Of note, there is
up to a 30% probability of advisory-level snowfall (2" or more)
for the lowlands of OR/WA Saturday afternoon through Sunday night.
Have held off on issuing any winter weather products for the
lower elevations due to medium-high (50-70%) confidence in
forecast ice and snow (below the required 80% threshold).

Snow in the mountains of eastern Oregon and eastern Washington
will likely reach advisory levels between Saturday afternoon and
Monday morning, with the best chances for the OR/WA Cascade crest
(70-90%) and northern Blue Mountains. Probabilities of warning-
level snow are below 80%, so opted to issue advisories for the
Cascades. Held off on issuing for the Blue Mountains since
existing highlights are in effect. Plunkett/86

LONG TERM...Monday through Friday...An active weather pattern is
in store for the region through the extended forecast as a series
of shortwave troughs bring periods of mountain snow and
potentially a mix of precipitation types in the lowlands.

Ensemble cluster guidance is in great agreement Monday of a
shortwave trough swinging across the PacNW and exiting southeast
of the region with a transitory ridge moving inland Tuesday. While
snow levels are expected to be 2.5kft to 4kft across the forecast
area, the cooler temperatures Monday morning will result in a
rain/snow mix in portions of the WA Columbia Basin. As the day
progresses and temperatures warm-up in the lowlands, any
precipitation will fall as light rain into the early evening hours
(confidence 60-70%). Light to moderate snowfall accumulations
between 5 to 8 inches will develop across the OR Cascades and the
northern Blues through Monday, with snowfall amounts up to 2
inches along the WA Cascade crest and higher ridges of the eastern
mountains (confidence 60-80%). Drier conditions will develop into
Tuesday as the ridge pushes inland, however, northwest flow aloft
on the lee side of the ridge will continue to produce light snow
across the mountains through Tuesday night.

Wednesday through Thursday, disagreement amongst the ensemble
cluster guidance greatly increases on timing and strength of an
incoming shortwave trough that will flatten the ridge Wednesday
and exit to the southeast sometime late Thursday. That said,
confidence is mod-high (60-80%) in area-wide precipitation
chances returning to the forecast area with another round of light
to moderate snow chances in the mountain zones. As for the
lowlands, the cluster solutions with the stronger shortwave trough
will result in higher chances of precip and precip amounts, while
the lower 500mb heights will result in snow levels at or below
the surface. At this time, confidence is low (20-30%) in
precipitation type for the lower elevations, which has translated
to chances of a rain/snow mix in the forecast. Confidence in
timing of precipitation tapering off is also low (20-30%) as well,
as cluster solutions are split between the shortwave exiting in
the morning, afternoon, or evening Thursday. Behind the shortwave
exit, guidance is in good agreement in a ridge building back into
the PacNW with dry conditions Friday, though one cluster solution
(25% of members) keeps light snow chances across the mountains.
Lawhorn/82

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  22  38  27  41 /  30  30  80  90
ALW  24  36  30  38 /  40  20  90  90
PSC  18  35  29  39 /  10  20  70  70
YKM  20  36  27  38 /   0  30  70  50
HRI  20  37  29  41 /  10  30  70  80
ELN  22  36  26  38 /   0  40  80  60
RDM  15  41  27  46 /   0  20  30  50
LGD  24  36  29  40 /  50  30  90  90
GCD  19  38  29  43 /  30  30  80  90
DLS  29  41  32  43 /  10  40  80  90

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 10 PM Saturday to 10 AM PST Monday
     for ORZ509.

WA...Winter Weather Advisory from 4 PM Saturday to 10 AM PST Monday
     for WAZ522.

     Winter Weather Advisory from 4 PM Saturday to 4 AM PST Monday
     for WAZ523.

&&

$$

SHORT TERM...86
LONG TERM....82
AVIATION...75