Heavy Snow in Oregon, March 4 to 5, 2024

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
311 PM PST Mon Mar 4 2024

.SHORT TERM...Tonight through Wednesday...Satellite imagery this
afternoon shows a weak upper low starting to push into the Olympic
Peninsula, while organized showers are developing and pushing into
western WA and northwest OR. Zooming out, a broad upper trough
continues to sit over western Canada and the northern half of
western CONUS, while keeping cool air advection into these areas
today.

The weak upper low just offshore the Olympic Peninsula is expected
to swing east across WA this afternoon into tomorrow morning,
bringing with it an increase of snow shower activity across the
mountainous terrain in the forecast area. Meanwhile, a stationary
front extending east to west is expected to develop between 43N
and 44N latitudes overnight, with snow showers associated with
this frontal boundary extending north into portions of Jefferson,
Deschutes, Crooks, and Grant counties. Snow amounts of 3 to 6
inches in the OR Cascade east slopes and Ochoco-John Day Highlands
is expected through late tomorrow morning, and 2 to 4 inches in
the Redmond/Bend/Prineville areas with light snow flurries further
north possible.

Tuesday, the stationary front and the moderate snowfall associated
with it will meander south of the forecast area as another
shortwave rounds the broad upper trough. This shortwave passage
tomorrow will help to keep light snow showers going across the
eastern mountains and the southern portion of the forecast area.
By Tuesday night, a cool and dry northwest flow will develop over
the PacNW, resulting in shower activity decreasing area-wide.
These drier and cooler conditions will continue through Wednesday
as northwest flow prevails aloft. Temperatures will remain below
normal through the middle of the week, with afternoon temperatures
ranging from mid 30s (mid-elevation valleys) to upper 40s
(Columbia Basin)...except 20s to lower 30s mountains. Lawhorn/82

.LONG TERM...Thursday through Monday...The long term period will see
a few days of quieter weather as a ridge build overhead before the
weather pattern becomes more active this weekend into early next
week as a trough and pair of fronts move through the area.

The Extreme Forecast Index shows little in the way of unusual
weather aside from breezy winds Saturday along the Blue Mountain
Foothills and in central Oregon. This fits with the forecast of
south to southwest winds of 15 to 25 mph with gusts to 35 mph in
those locations as well as the Grande Ronde Valley. There is a small
Shift of Tails area in the Pendleton area suggesting the potential
for a southerly downsloping wind event along the base of the Blue
Mountains. This is something that will have to be watched in the
upcoming days.

Thursday will see the trough that had been over the area moving off
to the Rockies while a drier northwest flow from an offshore ridge
will move overhead. This will give us dry weather and slightly
warmer temperatures with highs in the 40s and in the mid 30s to
lower 40s in the mountains. This will still be several degrees below
normal for early March. Thursday night through Friday night, models
continue to be in excellent agreement in having the ridge come ashore
and move through the area. This will keep us dry and give us
temperatures rising to near normal with highs in the upper 40s to
mid 50s in the lower elevations and in the 40s in the mountains.

The weather pattern will change Saturday as the ridge departs to the
east and a weakening frontal system will move ashore and into our
area. There will be a chance of rain and snow in the mountains on
Saturday afternoon and evening while the lower elevations will just
have a slight chance of rain with a few hundredths of an inch at
most. Snow amounts in the mountains will be on the order of an inch
or two along the Cascade crest. There is a 65-70% chance of an inch
of snow along the crest and a 40% chance of 2 inches but values drop
of significantly at higher snow amounts. In the eastern mountains,
the probability of an inch of snow is 35-45%. Temperatures Saturday
will be similar to Friday. Taking a closer look at the winds
mentioned above, The Grande Ronde Valley has an 85-95% chance of
wind gusts to 39 mph and the southern Grande Ronde Valley has an 80%
chance of gusts to 47 mph but the chances drop off sharply at higher
wind speeds. In the Blue Mountain Foothills, there is a 70-80%
chance of 39 mph wind gusts from Pendleton to Milton-Freewater, but
drops to about 40% for 47 mph gusts. Chances are much lower
elsewhere in the Blue Mountain Foothills. It's far too early to make
a decision, but a wind advisory for the southern Grande Ronde Valley
and the Blue Mountain Foothills looks possible if the models stay
consistent with these wind speeds.

After a break late Saturday night and Sunday morning, models bring
in a stronger frontal system, though there are differences about the
timing and strength of the system. The ECMWF is weakest and fastest
with the system and the GFS is strongest and slowest. The NBM has a
chance of mountain snow developing Sunday afternoon with a slight
chance of rain in the lower elevations. This becomes likely mountain
snow and a chance of lower elevation rain Sunday night and Monday.
This looks like a good compromise between the models and the NBM
solution was used. The NBM has a 75-85% chance of 4 inches of snow
along the Cascade crest though it drops off to about 25% for 6
inches. The eastern mountains have a 40-60% chance of 2 inches of
snow but only about a 30-40% chance of 4 inches in the highest
portions of the mountains. Rainfall in the lower elevations are a
tenth of an inch or less on Sunday and Monday. Winds will remain
breezy on Sunday but significantly lower than on Saturday.
Temperatures will remain in the mid 40s to mid 50s in the lower
elevations and in the upper 30s to mid 40s in the mountains.
Perry/83

&&

.AVIATION...00Z TAFs...VFR conditions will be prevalent across most
TAF sites for the next 24 hours. However, a disturbance moving
through the area will bring snow showers with MVFR/IFR conditions to
KRDM and KBDN through 16Z tomorrow morning. Snow will end and vsby
will improve to VFR after 16Z but MVFR cigs are expected to
continue. Have also added a PROB30 for snow showers with MVFR
conditions to KALW and KPDT from 09Z-13Z. Otherwise, VFR conditions
are expected with cigs at 4K-8K feet AGL. KDLS will have light rain
showers from 00Z-07Z through cigs will remain around 5k feet AGL.
Winds continue at 10-15 kts with gusts to 25 kts at KALW, KPDT and
KPSC but should drop below 12 kts by 02Z. Otherwise winds will
remain below 12 kts for the next 24 hours. Perry/83

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  28  43  25  44 /  30  20   0   0
ALW  29  44  26  46 /  30  20   0   0
PSC  30  48  28  48 /  10  10   0   0
YKM  25  46  23  47 /  10   0   0   0
HRI  30  48  27  48 /  20  10   0   0
ELN  23  42  20  43 /  10   0   0   0
RDM  26  37  18  41 /  60  40  10   0
LGD  25  39  18  42 /  50  30  10   0
GCD  25  38  19  42 /  70  50  20  10
DLS  31  49  27  47 /  40   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 10 AM PST Tuesday for ORZ506-511.

     Winter Weather Advisory until 10 AM PST Tuesday for ORZ509.

WA...None.
&&

SHORT TERM...82
LONG TERM....83
AVIATION...83