231
FXUS66 KPDT 222124
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
224 PM PDT Tue Sep 22 2020

.SHORT TERM...Today through Thursday Night...
A noted pattern change will take place over the next couple of
days as a powerful upper trough impacts the region. this will
bring waves of mountain and valley rains, occasionally breezy
conditions, and cooler temperatures through late week.

Mild and partly cloudy conditions will persist through the
remainder of the day and into tonight ahead of the storm system.
Clouds will be on the increase overnight as mid level moisture
overspreads the Pacific northwest. This will tend to keep
temperatures a bit warmer than on prior nights with lows mainly in
the upper 40s to mid 50s in the lower elevations, and upper 40s
to mid 40s in the mountains.

From Wednesday into Thursday, the upper trough will gradually
move into British Columbia, bringing strong onshore flow and a
cold front through the region. The result will be bands of light
to moderate rain spreading from northwest to southeast. Activity
will first affect portions of central Washington, especially the
Cascades, before spreading southward into Oregon into the
afternoon and evening hours Wednesday. The heaviest rains look to
occur from Wednesday afternoon through late Thursday morning.
During this timeframe, mountainous areas may see upwards of 1 to 2
inches of rain, with the highest amounts near the Cascade Crest.
Elsewhere, expect amounts ranging from around a tenth of an inch
up to a half inch with the lowest amounts in the Columbia Basin.
Still, any wetting rains will be welcomed given the extended dry
spell we have seen over the last couple of months. The increased
cloud cover and shower activity will act to suppress daytime
highs, keeping them near seasonal averages for a change.

lingering showers will remain likely through Thursday night given
the strong persistent onshore flow. The highest chances will be
over the mountains, though some showers may also affect the
Columbia Basin.

.LONG TERM...Friday through Tuesday...
Rain chances will linger through Friday evening into Saturday,
mostly in elevated areas, as a broad trough sweeps through the
Pacific NW. Global guidance shows the trough digging into the
eastern CONUS as it passes through our area by the start of the
weekend. This will lead to some embedded shortwaves in the upper-
level pattern, creating light precip chances over the WA Cascades
and NE OR mountains into the early weekend. Any amounts look to be
light at this time given the weak upper-level forcing. Locally
breezy conditions also possible, especially in the Basin, as a
tight pressure gradient associated with the exiting trough could
lead to gusts over 20 mph at times.

Sunday and beyond, a strong ridge pattern will set up over the
western CONUS, as our mild, more seasonal conditions will yield to
much warmer temperatures compared to the climatological norm in
late September. Early guidance suggests highs climbing into the
mid 80`s in the Basin by the middle of next week, with mid to
upper 70`s in the mountains. Winds look to decrease as high
pressure builds, which could lead to further daytime warming,
although the enhanced nightime cooling as we enter autumn may
offset any substantial heating. Guidance begins to diverge on
upper-level pattern after Tuesday, but expect mostly dry and warm
conditions from the end of the weekend through the middle of the
next work week.

&&

.AVIATION...18z TAFs...
VFR conditions expected to persist through the period with passing
high clouds. Winds to increase slightly this afternoon with gusts
15 to 20 knots possible KDLS/KRDM/KBDN. Otherwise expect mainly
light diurnal winds. 79/Austin

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  50  81  53  69 /   0  10  80  50
ALW  54  81  55  71 /   0  10  80  60
PSC  57  81  58  72 /   0  10  80  30
YKM  53  75  50  70 /  10  30  90  40
HRI  55  83  57  73 /   0   0  80  40
ELN  49  70  47  65 /  10  50  90  50
RDM  48  79  48  67 /  10   0  80  50
LGD  49  80  51  67 /   0  10  50  80
GCD  50  83  53  70 /   0   0  40  70
DLS  58  80  58  71 /  10  20 100  60

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

$$

SHORT TERM...79
LONG TERM....74
AVIATION...74

NWS PDT Office Area Forecast Discussion