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000
FXUS66 KPDT 250518
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1018 PM PDT Wed Apr 24 2024

Updated Aviation Discussion

.AVIATION...06Z TAFs...Skies are currently SCT-BKN with variable
bases 8-15 kft, and clouds will thicken to BKN-OVC early Thursday
morning. After 17Z, CIGS will lower to less than 10 kt as
precipitation increases from the west. Latest model runs are
coming in about 2-3 hours slower on timing of precipitation. In
addition, latest guidance does not show CIGS lowering below VFR at
DLS. Therefore, will back off a couple of hours on
precipitation and will have VFR (3.5 kft in some sites) for all
terminal airports. Winds are decreasing to 15 kt or less for most
TAF sites, although it remains breezy with NW winds gusting to 25
kt at DLS. By early morning and most of Thursday, winds will be
westerly at 12 kt or less.  Wister/85

&&

.PREV DISCUSSION... /issued 445 PM PDT Wed Apr 24 2024/

SHORT TERM...
Tonight through Friday night...An upper level trough will move
across the Pacific Northwest tonight. Behind the front, Precip
chances will increase from west to east beginning tonight. The
Cascades will begin to see precipitation first generally through
morning. During the morning hours, precipitation will move east of
the mountains into central Oregon, the Yakima and and Kittitas
Valleys and portions of the Columbia Basin and further east
during the afternoon and evening hours. Precipitation should come
to an end by later Friday over all areas except that mountains,
where it will linger into Saturday morning.

Snow levels are fairly high 5000-6000 feet, lowering to 4000-5000
feet by Saturday morning. So, the majority of the precipitation
will be in the form of rain except at the higher terrain, where
snow could occur with some accumulations. Along the highest
elevations of the Oregon Cascades, there could be a few inches
but in most locations, less than an inch.

QPF values THursday into Friday are 0.50 inches or more along the
Oregon Cascade Crest. 0.25 inches to 0.50 inches in the higher
Washington Cascades and parts of the Wallowas. Generally 0.25
inches or less else where along the higher terrain and 0.10
inches or less in the lower elevations. QPF Friday into Saturday
morning is lower. Generally 0.25 inches or less in the Oregon
Cascade crest and .10 inches or less elsewhere and a not much if
anything in central Oregon, the Columbia Basin, and Yakima Valley.
The ECMWF EFI continues to highlight and area of 0.8 to 0.9 along
the Oregon Cascades.

Today`s breezy winds will remain through the evening, then
decrease through the morning. Thursday looks to have relatively
light winds, but renewed breeziness odf 20 to 30 mph, possibly as
high as 35 mph is possible again on Friday mainly across the
Columbia Basin and Simcoe Highlands. NBM wind gust probabilities
of >=39 mph on Friday are generally 50 to 60% across the Columbia
Basin and Simcoe Highlands.

On Friday, there is also a low (20%) chance of thunderstorms
mainly in the eastern Oregon mountains. the Storm Prediction
Center has included portions of Wallowa, Union, Grant and Crook
and Deschutes COunties in its Day 3 Outlook.

CAPE is generally 400 J/kg or less in this area Friday afternoon
and rapid decreases after 00Z Saturday. LI values are between
about 0 and -2 degrees C. So there there is at least some threat,
albeit low at this time and we can see how this threat evolves
over the next two days.

With the trough moving through temperatures will be at or below
normal through the period.

LONG TERM...
Saturday through Wednesday...Models are in reasonable agreement
through the long term period in having a progressive and unsettled
weather pattern though most precipitation will be confined to the
mountains. Despite the progressive and unsettled pattern, the
Extreme Forecast Index indicates no unusual weather through the
period. Typical showery spring weather is expected. The main area
of concern in the models are timing differences as to when various
shortwaves will arrive but confidence is good in the overall
weather pattern.

Saturday will see a departing trough and closed low over the Rockies
while a trough and cold front in the Gulf of Alaska approaches the
Pacific Northwest coast. Ahead of the front, a weak transitory ridge
will be crossing the area which will give us slightly warmer
temperatures with highs in the upper 50s to mid 60s and in the lower
to mid 50s in the mountains. A westerly flow aloft will bring a
slight chance of very light rain showers to the mountains. The
greater concern will be west to southwest winds of 15 to 25 mph in
the Columbia Basin in the afternoon, though at this point it doesn`t
look like it will reach wind advisory levels.

On Sunday, the upper low and trough will move to the central British
Columbia coast and the front will move into our area though impacts
will again be mainly breezy winds of 10 to 20 mph in the afternoon.
The mountains will again have a chance of very light rain showers
with snow levels at 6000 feet. Temperatures will be a degree or two
warmer than Saturday.

Monday through Wednesday, models are in general agreement in having
the upper low and trough sink south offshore from British Columbia
to the Washington coast, though model ensemble clusters have
differences as to the timing and location of the closed low and
trough and for the timing and strength of the shortwaves moving into
the area each day. The shortwaves, aided by daytime heating, will
give the mountains a 30-60 percent chance of showers each day while
lower elevation rain will be confined to a 15-30 percent chance in
the Blue Mountain Foothills. Showers will taper off during the
overnight hours. Snow levels will be 4500-5500 feet. The mountains
will get a tenth of an inch of rain or less each day while the
amounts in the Blue Mountain Foothills will be barely measurable.
Temperatures on Monday will drop to the mid 50s to mid 60s with
upper 40s to mid 50s in the mountains then warm a degree or two each
day Tuesday and Wednesday. Breezy winds will return Monday afternoon
but will be lighter on Tuesday and Wednesday. Perry/83

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  41  60  45  61 /   0  60  70  40
ALW  46  65  48  64 /   0  60  80  60
PSC  46  65  48  68 /   0  50  30  20
YKM  41  60  41  66 /   0  50  20  10
HRI  45  64  46  67 /   0  50  40  20
ELN  40  58  41  62 /   0  50  30  20
RDM  36  55  39  55 /   0  60  50  30
LGD  39  60  43  56 /   0  50  90  70
GCD  37  61  41  56 /   0  70  80  80
DLS  47  58  48  61 /  10  80  60  30

&&

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

&&

$$

SHORT TERM...77
LONG TERM....83
AVIATION...85