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000
FXUS66 KPDT 130947
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
247 AM PDT Sat Apr 13 2024

.SYNOPSIS...Multiple weather concerns are anticipated for the
short term period:  (1) thunderstorms with a marginal threat of
isolated severe today; (2) strong winds associated with a
vigorous cold front beginning late Sunday then more widespread
windy conditions on Monday; (3) patchy blowing dust associated
with the winds; and (4) cold air lowering snow levels Monday and
Monday night. Other than light mountain snow showers on Tuesday,
the long term period that extends to next Saturday is looking dry.
There will be a gradual warm during this time.

&&

.SHORT TERM...Today through Monday night...A large closed low has
developed off the CA coast with the center a little over 200
miles west of the SF Bay area. Meanwhile, a strong westerly flow
is currently over southern Canada. This has left our forecast area
between both synoptic features. A southerly flow aloft on the
front side of the trough will set the stage for numerous showers
and scattered thunderstorms this afternoon and evening over most
of Oregon. SPC continues to show central and north central OR
under a marginal risk for severe weather today. HREF mean SBCAPES
are between 300-600 J/kg with 40-50kt of shear between 0-6km which
means thunderstorms are capable of sustained updrafts. The
diffluent flow is particularly disconcerting, as storms could
train with heavy rainfall and localized flooding. MFR 00Z RAOB
shows 0.73" PWATs which is a good indicator for heavy rain
potential. Overall confidence for today`s forecast is very high
for showers (100%) and thunderstorms (70%), moderate for heavy
downpours (40%), and low for large hail and damaging winds
(5-10%). Otherwise, it will be unseasonably warm today due to an
inverted surface thermal trough over the region, and today`s highs
will be about 10-15 degrees above seasonal average.

Sunday will be another warm day, and a few record highs may be
reached. Showers and thunderstorms will once again develop. On
Sunday, the highest probability of thunderstorms (60%) will be
over south central and southeast OR.The parent low off the CA
coast will move south and way out of any concern. However, a
secondary upper low will pinwheel around the main low and set up
over northern NV. This will not have as much impact in terms of
moisture and instability in our forecast area, but our far eastern
zones which includes Wallowa, Union, Grant, Wheeler and Crook
Counties will observe showers and a chance (40-60%) of
thunderstorms. I can`t rule out a strong or even severe storm, but
the threat is minor. The westerly flow over southern Canada will
lower to the south across northern WA. A tight cross Cascade
gradient will set up, resulting in a strong marine push late
Sunday. Deterministic models are showing 5-7mb differences between
SMP-ELN by late Sunday. Confidence is high that the Cascades gaps
which includes the Kittitas Valley and the eastern Columbia River
Gorge will observe very windy conditions, and this may warrant a
Wind Advisory. Due to strong winds that are also forecast for
Monday, will highlight the concerns in wx graphics which still
gives time to analyze both days for any wind highlights.

Monday`s winds continue to look strong and more widespread due to
the approaching cold front moving south across the PacNW. The
marine push will tighten surface gradients for widespread windy
conditions in the lower elevations. There are also signs of
isentropic descent pushing winds aloft to the surface. However,
the factors that may keep winds from reaching high wind warning
criteria are the winds at 850mb and 700mb that models show between
30-35kt. For now, confidence is about 80% for winds reaching
advisory (45-55 mph gusts) but confidence decreases to around 50%
for some areas to have stronger than 55 mph gusts. This is also
supported by the NBM probability for winds.

There will be around a 10-15 degree drop in temperatures from
Sunday to Monday, and snow levels will lower to around 2500-3000
feet Monday night. Despite the lowering snow levels, drier air
behind the front will limit snow accumulations with little to no
accumulations for most of the forecast area. Latest model runs
have trended lower on snow amounts in the Cascades and northeast
mountains. It will be a chilly Monday night with lows in the 20s
and 30s along with a bitter wind chill due to sustained winds of
10-20 mph overnight. Wister/85


.LONG TERM...Tuesday through Saturday...The long term is finally
bringing a stretch of quieter weather, with some lingering
mountain precipitation during the middle of next week giving way
to dry and clear conditions with temperatures a few degrees above
normal.

Tuesday will be the most active day of the long term forecast
period as an upper low swings across Canada. With the front
associated with this feature already east of our region, expect
that most appreciable precipitation will occur due to orographic
lift across the mountains of our forecast area. With limited QPF
to begin with and snow levels between 3000-5000 feet, the bulk of
any activity will be light rain or snow. By Wednesday, clouds
begin to clear and precipitation exits with the eastward
progressing low, bringing benign conditions as we lie between
systems with an offshore ridge that may begin moving over by the
end of the period. This should help to slowly raise temperatures,
with highs for our population centers on Tuesday in the upper 50`s
to mid 60`s, raising a couple of degrees each day with upper 60`s
to upper 70`s by a week from today.

Overall there is moderate confidence (60%) in the long term
forecast. There does lie some uncertainty in regards to the
overall pattern after the Canadian low departs, with discrepancies
lying in the placement of the offshore ridge plus some possible
shortwave activity that may move across late next week. Ensemble
guidance overall seems to favor a lack of significant shortwave
activity and ridging encroaching but not quite moving directly
over the PacNW, which is reflected in the above forecast, but the
outliers do pull forecast confidence down for our temperatures.
Goatley/87


&&

.AVIATION...06Z TAFS (previous discussion)...VFR is favorable for
all sites for the remaining TAF period with cloudy skies (FEW to
OVC, 050-250 kft) sticking around. KRDM and KBDN are still
expected to have rain Saturday night, along with wind gusts
between 20-30 kts (>70% confidence). Other than that, winds will
remain light. Feaster/97


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  72  47  73  43 /   0  10  10  10
ALW  77  49  77  46 /   0  10  20  10
PSC  77  51  81  48 /   0   0   0   0
YKM  75  46  79  42 /   0   0   0   0
HRI  76  49  79  46 /   0  10  10   0
ELN  74  47  74  43 /   0   0   0   0
RDM  65  44  64  35 /  50  70  20  10
LGD  73  47  70  41 /  10  10  40  30
GCD  74  45  69  38 /  20  30  60  30
DLS  75  53  71  46 /   0  10   0   0

&&

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

$$

SHORT TERM...85
LONG TERM....87
AVIATION...97