647
FXUS66 KPDT 071528
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
828 AM PDT Tue May 7 2024

.UPDATE...A broad trough remains over the area though it is
rapidly moving off to the east while a ridge builds offshore. A
weak wave that brought snow to the mountains is also departing but
radar shows some showers continuing over the Blue Mountains. The
overnight shift extended the Winter Weather Advisory for the
Northern Blue Mountains to noon. Will keep that for now but trends
are downward and may expire it early. Winds in the Kittitas
Valley are increasing and model guidance is confident that the
current wind advisory through 11 PM tonight is valid. Will keep
that in effect as well. Changes to the current forecast were
minimal but did adjust POPs over the eastern mountains slightly
and also adjusted a few temperatures today a degree or two upward.
Forecast update already out. Perry/83

&&

.PREV DISCUSSION... /issued 459 AM PDT Tue May 7 2024/

UPDATE...After reviewing web cams and latest radar, it was
decided to extend the Winter Weather Advisory for the east slopes
of the Oregon Cascades and the northern Blue Mtns until noon
today. Web cams show steady snow in several locations, and WSR-88D
has shown little decrease in the shower activity. Additional
accumulations up to 3 inches are forecast for this morning.

PREV DISCUSSION... /issued 408 AM PDT Tue May 7 2024/

SHORT TERM...Today through Thursday night...The winter event for
the mountains is coming to an end, although winds will remain a
concern for some of the lower elevations. The longwave trough is
shifting eastward in response to an upper ridge building along the
coast, and this will provide a northwest flow aloft today and a
drier northerly flow aloft tonight. Current winter weather
advisories for the east slopes of the OR Cascades and the northern
Blue Mtns will be allowed to expire at 5 AM. However, there will
continue to be scattered orographic mountain snow showers over
the northern Blues through the morning hours that will bring an
additional inch or two of snow above 5000 feet. The 10:1 ratio
from the HREF shows around 80% chance of at least 1" but only 20%
for 2" or more in the Tollgate and Ski Bluewood areas. The WA/OR
Cascades will also observe scattered light snow showers, mainly on
the western slopes and in far northwest Kittitas County
associated with the Puget Sound Convergence Zone in the northwest
flow aloft.

Winds are locally breezy early this morning, and it will be
another breezy to windy day today. Surface gradients will be tight
for the next 18-24 hours, and surface winds won`t decouple from
winds aloft until W&&

.SHORT TERM...

.LONG TERM...


&&

.AVIATION...ednesday morning. A Wind Advisory is in effect
for the Kittitas Valley from 8 AM to 11 PM today. NBM and HREF
both indicate around a 75% probability for gusts greater than 45
mph and 25-35% for gusts greater than 50 mph at ELN (less than 20%
for greater than 55 mph gusts). A tight cross-Cascade gradient
will also result in localized wind gusts 35-45 mph through the
Cascade gaps and the eastern Columbia River Gorge.

It will be chilly tonight under a dry northerly flow aloft, but
breezy winds this evening and a southwest surface gradient through
the night will keep lows from falling below freezing in the
areas that normally are in growing season--the Lower Columbia
Basin and surrounding valleys. Temperatures are forecast to fall
into the mid to upper 30s in these area, and there will be patchy frost
but not a hard freeze. Other locations will observe lows tonight
in the 20s to lower 30s.

A warming trend begins Wednesday. Temperatures will be slow to
warm at the start as the ridge remains to the west, leaving
eastern WA/OR under a northeast flow aloft. A rex block begins to
form Thursday, and the upper ridge will strengthen over the
PacNW. Wister/85

LONG TERM...Friday through Tuesday...A quiet and dry period is in
store for the extended period with POPS less than 15% through
Tuesday. The latest GEFS ensemble shows an upper ridge over the
region through Saturday which gradually transitions to flat westerly
flow Monday and Tuesday. The GFS has a more pronounced shortwave
trough moving across the Pacific Northwest on Monday and Monday
night but this is not supported by the ensemble clusters. It will be
warm Friday with high temperatures 75-85 in the lower elevations,
and even warmer on Saturday with highs 83-93 across the lowlands.
The NBM probabilities of 90+ degree temperatures peak on Saturday at
30-70% across the Columbia Basin and Yakima Valley. As the ridge
flattens Sunday and the flow becomes more westerly a weak cold front
will move across the area. This will begin a slight cooling trend
and also cause an increase in west winds through the Cascade gaps.
The upper bound of the winds will be limited by the absence of
strong low to mid level jets. The latest NBM is forecasting peak
wind gusts at KELN of 31 mph on Sunday and 33 mph on Monday. At KDLS
the peak wind gusts are forecast to be 29 mph both Sunday and
Monday. High temperatures will cool to the mid 70s to mid 80s in the
lower elevations for Monday and Tuesday. With the warm weather the
recent snow in the mountains will melt and will contribute to some
rises on area rivers. Significant flooding is not forecast at this
time but the current forecast from the Northwest RFC has the Naches
River near Cliffdell reaching action stage early Saturday morning.
78

AVIATION...12Z TAF&&

.SHORT TERM...

.LONG TERM...


&&

.AVIATION...S...VFR conditions will prevail through the
period. SCT-BKN clouds at 040-070 AGL and some mid clouds above
today with a clearing trend this evening becoming SKC tonight. Winds
will increase this morning and become 15-20 kt sustained and gusts
25-30 kt decreasing after sunset. 78

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  57  35  62  39 /  20   0   0   0
ALW  60  38  64  42 /  20   0   0   0
PSC  66  40  71  45 /   0   0   0   0
YKM  63  36  72  42 /   0   0   0   0
HRI  63  38  68  41 /  10   0   0   0
ELN  58  37  69  42 /   0   0   0   0
RDM  52  27  60  33 /  10   0   0   0
LGD  51  32  57  37 /  40   0   0   0
GCD  47  30  58  32 /  30  10   0   0
DLS  60  40  70  45 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until noon PDT today for ORZ502-509.

WA...Winter Weather Advisory until noon PDT today for WAZ030.

     Wind Advisory until 11 PM PDT this evening for WAZ026.

&&

$$

MORNING UPDATE...83
SHORT TERM...85
LONG TERM....78
AVIATION...78