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000
FXUS66 KPDT 180507
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1007 PM PDT Wed Apr 17 2024

Updated Aviation Discussion

.AVIATION...06z TAFs...VFR conditions expected. Clear skies are
will prevail overnight, with light, terrain-driven winds less
than 10 kts. Winds will then shift more north and east during the
day Thursday. Evans/74

&&

PREV DISCUSSION... /issued 217 PM PDT Wed Apr 17 2024/

SHORT TERM...Tonight through Friday... Forecast area will remain
under a cool cyclonic flow through Thursday due to a closed low
pressure centered over south central Canada. There will be some
instability showers this afternoon and evening over portions of SE
Washington and NE Oregon which will dissipate towards sunset. Then
expect clearing skies and light winds overnight that will allow
temperatures to lower to around freezing through early Thursday
morning in the cold prone areas around the Lower Columbia Basin. A
Freeze Warning has been issued encouraging the protection of plants
that would be susceptible to damage due to cold temperatures.

Conditions Thursday will be very similar with temperatures being a
couple of degrees warmer. Some shallow convective showers remain a
very low chance (less than 15%) over the SE WA and NE Oregon
mountains through the late afternoon and evening hours. Thursday
night into Friday morning will also see temperatures lowering to
around freezing in portions of the Lower Columbia Basin and further
Freeze Warnings may be needed.

By Friday the low pressure over Canada moves eastward allowing a
ridge of high pressure over the eastern Pacific to begin moving into
the Pacific Northwest. Again, will see slightly warmer temperatures
bring us back to near normal temperatures heading into the weekend.

LONG TERM...Saturday through Wednesday...The long term period will
see a ridge over the area early Saturday give way as a weak system
crosses along the Washington/British Columbia border Saturday
afternoon through Sunday afternoon. Sunday night through Tuesday
morning, another ridge will be over the area for dry and warmer
weather. By Tuesday afternoon, models are in agreement about an
upper low and trough affecting the area though there are substantial
differences about the strength and location of the upper low and
trough.

On Saturday, models are in excellent agreement in having the
arriving system bring precipitation to the Cascades in the afternoon
(30-40 percent increasing to 60-80 percent in the evening) and then
to the eastern mountains Saturday night (30-50 percent chance). Snow
levels will start out at 5000-7000 feet and drop to 3500-5000 feet
overnight, so mainly rain is expected at pass levels. Rain amounts
of 1 to 2 tenths of an inch are possible. A few model ensemble
members put some light rain into the Blue Mountain Foothills
Saturday evening, so a couple of hundredths of an inch is possible
there. Temperatures will be a few degrees above normal with highs in
the 60s and lower 70s. As the system arrives Saturday evening,
tighter pressure gradients will bring 15 to 25 mph winds to the
lower elevations which will continue into Sunday morning in the
Columbia Basin.

A few light showers will linger Sunday in the higher mountains but
otherwise dry conditions are expected Sunday and Monday. Cooler air
brought in by the system will knock temperatures down a few degrees
Sunday with highs in the upper 50s and 60s. The ridge will
strengthen and build on Monday as an upper low and trough approaches
out in the eastern Pacific. Temperatures will warm to the mid 60s to
lower 70s with mainly lower to mid 60s in the mountains.

Models diverge on Tuesday as the ECMWF and Canadian have a deep low
and front approaching the central British Columbia coast and the GFS
has a weaker low and front approaching the southern Oregon and
northern California coast. By Wednesday, the ECMWF and Canadian have
the low at or near the central British Columbia coast. The Canadian
is weaker and the low is located over northern Vancouver Island
while ECMWF is stronger and the low is further northwest. The GFS
has a weakening low come ashore near the Oregon/California border.
Models agree in having a chance of very light rain over the Cascades
and eastern mountains with snow above 5000 feet. Amounts will be
just a few hundreths of an inch. A southwest flow Tuesday will keep
temperatures above normal with highs in the mid 60s to mid 70s with
upper 50s to mid 60s in the mountains. Wednesday will be a degree or
two cooler. Perry/83

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  30  61  32  63 /  10   0   0   0
ALW  32  64  35  66 /  10   0   0   0
PSC  34  66  39  68 /  10   0   0   0
YKM  31  64  34  65 /  10   0   0   0
HRI  32  66  35  68 /  10   0   0   0
ELN  31  60  33  60 /  10   0   0   0
RDM  27  60  27  61 /   0   0   0   0
LGD  28  58  29  61 /  20   0   0   0
GCD  28  60  29  66 /   0   0   0   0
DLS  36  67  40  67 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Freeze Warning from 2 AM to 9 AM PDT Thursday for ORZ044-507.

WA...Freeze Warning from 2 AM to 9 AM PDT Thursday for WAZ026>029.

&&

$$

SHORT TERM...91
LONG TERM....83
AVIATION...74