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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS66 KPDT 201514
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
814 AM PDT Sat Apr 20 2024

.UPDATE...
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Dry weather expected for the balance of the day today, as a cold
front approaches from the west. Current forecast looks reasonable
and few changes were made. Winds will increase during the evening
and overnight hours, especially for the Simcoe Highlands,
portions of the Columbia Basin, Kittitas Valley, and Foothills of
the Blue Mountains.
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&&

.PREV DISCUSSION... 
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/issued 447 AM PDT Sat Apr 20 2024/

AVIATION...12Z TAFS...VFR for this period with cloudy skies (FEW to
OVC, 080-250 kft). All sites will be breezy this afternoon into
tonight with wind gusts between 20-30 kts (>60% confidence)as the
cold front moves across the region. Pre-frontal winds might be
lighter. Rain showers might occur but confidence is very low (<20%).
Feaster/97

SHORT TERM...Today through Monday night...Deterministic models
and ensembles are in excellent agreement on moving an upper level
shortwave across Washington tonight. This will be followed by WNW
flow aloft on Sunday and then the flow will turn SWLY on Monday.
Most of the forcing for upward motion with the WA shortwave will
be north of the area but light showers and high elevation snow
showers are highly likely along the WA Cascade east slopes
tonight (60-90% chance)...with around a 60% chance along the
Oregon crest and a 30% chance for the northern Blue Mountains.
Snow levels will lower from 5-7 thousand feet AGL early this
evening to 2500-3000 feet AGL by 12Z Sunday. NBM probability of
TSTMS for the WA Cascades is less than 10% this evening and near
zero elsewhere so the threat for thunderstorms is very low.
Precipitation amounts will be light. 50th percentile QPF amounts
along the Washington east slopes is .10-.20 inches with less than
10 inches for the Oregon crest and only a few hundreths of an
inch for the Blues.

A cold front will move across the region this evening bringing
gusty west winds for most of northern Oregon and southern
Washington. Winds will be 15 to 25 mph with gusts 30-35 mph. The
probability of winds exceeding 45 mph is near zero except for
10-40% in the Simcoe Highlands. With this in mind will not be
issuing any wind highlights with this forecast package.

Today will be the warmest of the next three days with high
temperatures in the upper 60s to lower 70s lower elevations. Mid
50s to mid 60s are forecast for highs on Sunday with temperatures
warming up 3-5 degrees on Monday. The chance for precipitation
Sunday night through Monday night will be near 0%. 78

LONG TERM...Tuesday through Saturday...Overall, confidence in
forecast details next week is low due to significant variance among
model ensemble members. Broadly speaking, near- to above-normal
temperatures are forecast through the period, and Tuesday evening
through Saturday, a slight chance (15-24%) to chance (25-54%) of
showers is forecast for the mountains with reduced chances (<15%)
for the lower elevations except (15-35%) Thursday afternoon through
Friday afternoon. NBM probabilities are not suggesting high
confidence in any wind, winter, or freeze highlights at this time
(<40% chance), and latest forecasts from the NWRFC are not
indicating any hydrological concerns.

Confidence in the longwave pattern is high (>70% chance) Tuesday
morning with upper-level ridging over the PacNW shifting east across
the Rockies through the day. Meanwhile, an incoming trough from the
Pacific turns flow aloft southwesterly and ushers in a modest
increase in PWATs by afternoon and evening. Some guidance is
depicting modest instability Tuesday afternoon, though confidence in
any thunderstorms developing is currently low (<10% chance). The NBM
paints a slight chance (15-24%) of showers across the mountains with
lower PoPs elsewhere.

Wednesday onward, confidence in pattern details degrades as ensemble
clusters are presenting a range of solutions with regard to the
evolution of the longwave pattern. Broadly speaking, troughing is
favored over the West through Friday, though clusters exhibit
differences in timing and/or amplitude of features, and the best
chance of precipitation area-wide will be Thursday afternoon through
Friday afternoon. By Saturday, clusters are presenting a more
amplified longwave pattern over the West with roughly half of
members showing a ridge overhead with the other half favoring
troughing for the forecast area. Plunkett/86
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&&

.PRELIMINARY POINT TEMPS/POPS...
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PDT  66  39  59  34 /   0  20   0   0
ALW  70  41  62  37 /   0  20   0   0
PSC  71  43  66  39 /   0  20   0   0
YKM  68  35  63  32 /   0  10   0   0
HRI  70  41  64  36 /   0  20   0   0
ELN  65  35  57  32 /   0  20   0   0
RDM  70  31  57  29 /   0   0   0   0
LGD  68  38  56  30 /   0  20   0   0
GCD  72  38  58  31 /   0  10   0   0
DLS  69  41  62  37 /   0  10   0   0
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&&

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

$$

SHORT TERM...77
LONG TERM....86
AVIATION...97