NWS Pendleton, OR wrote its last area forecast discussion before the first event at Nov 8, 1:24 PM PST, 5 hours 36 minutes earlier.
Area forecast discussion, Nov 8, 1:24 PM PST, 5 hours 36 minutes before
Area Forecast Discussion
National Weather Service Pendleton OR
124 PM PST Mon Nov 8 2021
.SHORT TERM...Tonight through Wednesday night...A weak upper
ridge is keeping this afternoon mostly clear with just some high
clouds. Conditions will change significantly beginning tonight. A
broad upper trough with a warm front will move into the region
off the Pacific tonight into Tuesday morning. This system will
bring with it substantial rainfall, and more importantly strong
southerly winds in mostly the southern portions of the forecast
area (mainly from the Blue Mountain Foothills south and eastward
as well as central and north central OR). There are High Wind
Warnings in effect for central OR, the east slopes of the OR
Cascades, the southern, northern and northwest Blue Mountains.
Wind advisories are in effect for all of the Blue Mountain
Foothills, portions of central OR...near Redmond and Bend, north
central OR, the John Day Basin, and Wallowa County. Expect strong
gusty, and probably damaging winds in these areas tonight into
Tuesday morning. The warnings and advisories are both in effect
from 7 PM PST this evening until 10 AM PST Tuesday morning.
Expect rainfall amounts to range from one to two tenths of an inch
in the Lower Columbia Basin and adjacent valleys as well as
central and north central OR. Rainfall amounts of up to 0.3 to 0.7
of an inch can be expected in the John Day Highlands, all of the
Blue Mountains, much of Wallowa County and the Cascade east slopes
of both OR and WA. The deterministic models along with their
ensembles are in good agreement for this scenario of both
precipitation and wind. The ECMWF EFI index is almost 1.0 for
strong winds tonight and Tuesday, which results in high
confidence that the strong winds will occur.
The upper trough axis with this weather system will move to the
east of the CWA Tuesday evening, with mainly upslope showers
lingering over the Cascades and Blue Mountains as the flow aloft
becomes northwest, and surface winds become westerly. Snow levels
with this system are expected to rise enough to negate heavy
snow, except for the highest peaks. Therefore there will not be
a need for any winter weather highlights. However, there will be
some cold air damming along the Washington Cascades, and there
could be a few inches there tonight, with snow levels generally
starting out at 2000-3000 ft MSL this evening before they rise on
Tuesday morning. Snow levels will then drop again behind the cold
front with this system Tuesday night and Wednesday. However, the
precipitation will have already moved to the east of the CWA, and
only upslope snow showers can be expected in the eastern
mountains, and spill over show shwoers over the Cascades.
On Wednesday and Wednesday night a broad upper ridge will build
over the region with warming temperatures again, as heights and
850 mb temperatures rise going into the extended forecast period.
However, there will also be another surge of moisture riding over
the top of the building ridge, which may bring possibly some more
substantial rainfall amounts for most of the forecast area. Snow
levels will rise significantly during this period, so winter
highlights will likely not be needed.
Temperatures for tonight and Tuesday will be mainly in the 50s in
the lower elevations and mostly mid 30s to mid 40s in the
mountains for highs. Night time lows will be mainly in the 40s
over the lower elevations, and mid 20s to mid 30s in the
mountains. On Wednesday temperatures will be a few degrees cooler
for both the day time and night time behind the cold front with
this next weather system. 88
.LONG TERM...Thursday through Monday...Much of the long term period
continues to be dominated by large-scale ridging across much of the
western CONUS. The overall trend as a result will be warmer
temperatures, relatively light winds, and increased snow levels,
with the primary change in the forecast in the last 24 hours being
an increased chance for area-wide precip Thursday into Friday.
The synoptic pattern will transition after a shortwave moves through
the area and begins to deepen over the eastern CONUS during the
midweek. This will allow ridging to build over the west, but a NW
flow pattern will set up as the trough pushes eastward, allowing for
some moisture transport over the forecast area and thus a chance for
showers primarily for Thursday. Previous model runs had pinned the
strongest of the NW flow more to our north over northern WA, but
the deterministic models are now more in favor of a northwesterly
jet a bit more south, just enough to provide decent POPs during
the day Thursday. Lesser chances exist for the southern CWA,
including central OR and the John Day Highlands, but even the
ensembles seem to be converging on more of a wet Thursday and
early Friday. Trend continues to be that the ensembles are wetter
than the NBM, but even the NBM probabilistic guidance suggests at
least a chance (30-40%) of a quarter inch QPF in the lower Basin.
Will monitor future runs to see if NBM trends more toward global
ensembles or vice versa, but overall messaging is a wetter shift
in the forecast for the end of the work week.
Beyond Friday, the amplitude of the ridge builds, before flattening
to our north Saturday. The result would be increased rain chances
north of our area, but the forecast could shift as it has in the
last day or so. As this jet of westerly flow deepens into a trough
to our east, ridging will once again prevail Sunday into Monday.
Of this, ensembles look to be in decent agreement, with main
discrepancies stemming from the positioning of the ridge axis.
Look for temps to climb toward the low 60s for some areas by the
weekend, with snow levels higher than 6000-7000 ft through much of
the period. 74
&&
.AVIATION...00z TAFs...VFR conditions are expected until around
midnight, when an oncoming frontal system will bring gusty winds and
rain across all sites. Areas along the east slopes of the Cascades
will see the first of the rain, before it spreads eastward toward
the eastern mountains by the middle of the night. Could see vsby
reductions in light rain and strong S/SE wind gusts, which could
exceed 30 kts at times. CIGs will be clear this evening, before
increasing clouds overnight, and CIGs falling to OVC 5 Kft, down
to MVFR/IFR within rain showers. Rain will exit by early Tuesday
morning, leaving gusty W/SW winds 15-20 kts sustained by the
afternoon. 74
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 41 53 34 50 / 50 80 10 10
ALW 43 55 37 52 / 50 90 10 10
PSC 43 55 40 54 / 70 80 0 0
YKM 33 51 29 50 / 80 80 10 10
HRI 42 55 38 53 / 60 70 0 10
ELN 33 47 30 47 / 70 90 10 10
RDM 39 50 30 49 / 80 30 10 20
LGD 36 48 29 45 / 60 90 20 20
GCD 37 52 31 49 / 80 70 20 10
DLS 42 54 41 52 / 90 80 30 20
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning from 7 PM this evening to 10 AM PST Tuesday
for ORZ502-503-506-509.
Wind Advisory from 7 PM this evening to 10 AM PST Tuesday for
ORZ049-050-505-507-508-510-511.
WA...High Wind Warning from 7 PM this evening to 10 AM PST Tuesday
for WAZ030.
Wind Advisory from 7 PM this evening to 10 AM PST Tuesday for
WAZ029.
&&
SHORT TERM...88
LONG TERM....74
AVIATION...74