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000
FXUS66 KPDT 192201
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
301 PM PDT Fri Apr 19 2024

.SHORT TERM...Today through Sunday Night...

Key Messages:

1. Cold overnight temperatures tonight across the Kittitas Valley.

2. Breezy winds Saturday evening through Sunday morning.


Current radar and visible satellite imagery showing sunny skies and
dry conditions as an upper level ridge approaches the coast and
infiltrates into the area overnight into early Saturday morning.
This will lead to a slight increase in cloud cover as we proceed
into the early morning hours on Saturday as flow aloft turns from
the southwest, which should inhibit radiational cooling enough to
keep morning temperatures at or above freezing across the Kittitas
Valley. The slight increase in mid-and high level clouds will come
in from the south, filing into south and central Washington shortly
after 3 AM. Sustained winds are also expected to stay between 4-8
mph before 3 AM, which will also help to slow cooling down by
keeping the lower levels of the atmosphere mixed. Thus, the timing
of these two parameters look to keep morning temperatures above
freezing. Additional confidence in gleaned from the NBM, which
highlights a 43% chance of Ellensburg reaching 32 degrees or
below, which is down from a 49% chance 24 hours ago. Thus,
confidence is moderate to high (60-70%) that morning low
temperatures will stay above freezing across the Kittitas Valley
Saturday morning.

The upper level ridge is closely followed by an upper level trough
and an associated cold front that will allow a pressure gradient to
develop along the Cascades as winds shift from offshore to onshore
flow. These conditions will attribute to an increase in winds across
the east slopes of the Washington Cascades and the Lower Columbia
Basin with gusts of up to 40 mph possible Saturday night into Sunday
morning. Confidence in these wind values is moderate (50-70%) as the
NBM highlights a 40-60% chance of portions of the Basin (primarily
south of Hermiston and north of Pendleton) receiving wind gusts of
39 mph or greater. The NBM suggests a better chance of wind gusts
reaching 39 mph or greater over the Simcoe Highlands, with a 50-70%
chance. Confidence is moderate to high (70-80%) of winds staying
below advisory criteria, as the NAM, SREF, and GFS all keep the
pressure gradient between Portland and Spokane in the 10-11.5mb
range, which is below the normal advisory threshold of 12mb.
Guidance has also continued to trend downward, as the GFS (11.5mb)
has decreased by 1 mb over the last 12 hours. Wind speeds will peak
between 10 PM Saturday through 4 AM Sunday, with winds slowly
tapering off through the morning hours.

Mountain precipitation will also accompany the cold front, beginning
along the Cascade crest late Saturday afternoon before including the
east slopes of the Washington Cascades, northern Blue Mountains and
foothills, and areas of higher terrain in the Basin through the
evening. This is a quick moving cold front, so precipitation will
taper off over the northern Blue Mountains early Sunday morning,
with drier conditions along the Washington Cascade crest anticipated
through Sunday afternoon. Limited moisture is present with this
front, as only a trace of rain is anticipated along the Blue
Mountain foothills and 0.10 - 0.20 of an inch at higher elevations
along the Cascades and northern Blue Mountains. High temperatures
will be increasing 2 to 6 degrees from Friday to Saturday, but drop
back down 3 to 7 degrees Saturday to Sunday behind the cold front.
75


.LONG TERM...Monday through Friday...Models in fair agreement
through the period. However, they do differ in their evolution of an
upper level trough that begins impacting the area Tuesday and
possibly through the rest of the period. In general terms, GFS is a
little deeper but develops it into a broad upper level trough over
the Pacific Northwest by late Thursday while the ECMWF is a little
weaker and pushes it east of the area late Thursday into Friday. In
addition, GEFS spaghetti plot shows a chaotic pattern (no members
agreeing) by Thursday and Friday which leads to high confidence that
nailing down these two periods at this time is going to be extremely
difficult.

Monday is expected to be dry, but precipitation is expected to
develop in our southwest CWA and spread eastward Tuesday afternoon.
Precipitation will be mainly confined to the mountains until
Thursday and Friday. At this time, the best chance for widespread
precipitation up to a 0.10 of an inch will be Friday, especially
over the mountains. However, probabilities remain pretty low (10-
20%) in the basin and foothills and higher (35-50%) in the
mountains. There are large discrepancies in the models during the
Thursday/Friday timeframe, especially given the ECMWF ensemble
paints more of a shortwave ridge over the area Friday which would
imply a drier forecast. In summary, unsettled weather is expected
through much of the period with timing difficult to pin down at this
time.

Confidence is moderately high (60-80%) we`ll see breezy conditions
over the Simcoe Highlands and Kittitas valley Wednesday.

Temperatures will remain near to above normal through the period.
Earle/81


&&

.AVIATION...18Z TAFs...VFR conditions will
prevail through the period. Some mid/high clouds will stream into
the area overnight. Winds will be 8-13 kts with higher
afternoon/early evening gusts. Winds will decrease overnight to 8
kts or less. Earle/81


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  34  66  38  59 /   0   0  20   0
ALW  37  68  42  62 /   0   0  30   0
PSC  41  70  45  66 /   0   0  10   0
YKM  36  66  36  63 /   0   0  10   0
HRI  36  69  42  65 /   0   0  10   0
ELN  33  64  36  58 /   0   0  20   0
RDM  33  69  30  58 /   0   0   0   0
LGD  33  68  36  55 /   0   0  20   0
GCD  36  72  36  58 /   0   0  10   0
DLS  41  68  42  62 /   0  10  10   0

&&

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

$$

SHORT TERM...75
LONG TERM....81
AVIATION...81