543
FXUS66 KPDT 172235
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
235 PM PST Sun Nov 17 2024

.SHORT TERM...Today through Tuesday...A particularly active period
is in store for the forecast area, with everything from rain, heavy
mountain snow, and strong winds slated for the next 72 hours.

For today, a cold front is swinging through the forecast area,
bringing with it gusty conditions, rain, and eventually, mountain
snow. Yesterday`s system provided us with a shot of warm air that
lifted snow levels above our major mountain passes, but as this cold
front moves through, colder, northerly air will rush in behind and
drop snow levels down to around 2000 feet. A Winter Storm Warning
remains in effect for our Cascades and northern Blues zones, with
the expectation being that warning-level snow will primarily fall
between the writing of this discussion and early morning Monday.
Light snow will persist into the day Monday, but only expecting a
couple of inches at best to fall at pass level between daybreak
Monday and midnight heading into Tuesday. Elsewhere, rain showers
will occur along the cold front, before drier conditions prevail
across the lower elevations late tonight through most of the day
Monday. Breezy winds will continue amidst this active pattern.

Looking ahead to Tuesday, a potentially significant low pressure
system is shaping up off the coast of the PacNW. Global models are
suggesting that this low could have a central pressure as low as 945
mb, which is quite strong for the region. This low will circulate a
warm front through the forecast area during the latter half of
Tuesday, while keeping us in a persistent band of wet, SW flow aloft
through the remainder of the work week. Warm fronts lifting through
from the southwest are typically conducive for downsloping wind
events, and given how strong this low looks to be, did opt to issue
a High Wind Watch for the base of the Blue Mountains of Oregon, as
well as central and north central Oregon. Don`t think models are
quite capturing the potential wind threat this far out, but would
not be surprised if CAMs start depicting wind gusts exceeding 60 mph
for these areas Tuesday night into Wednesday.

Moisture advection will be robust with this low as well,
particularly for the Cascades. Models are currently suggesting that
the foothills of the Cascades, particularly in Washington, could see
heavy snow exceeding 6 inches above 2500 feet, with several inches
of snow potentially extending down toward Cle Elum and even into the
Kittitas Valley. Much is still subject to change with the forecast
over the next few days, but particular interest will be kept on the
Tuesday night into Wednesday time period in terms of monitoring the
potential for a significant weather event. Evans/74

.LONG TERM...Wednesday through Sunday...Southwesterly flow aloft
will be dominant in the long term as a very strong low pressure
system sits just offshore of the PacNW, bringing plentiful
precipitation in the form of an atmospheric river with
temperatures warm enough to keep most of the region as rainfall
rather than snow, but with this will come concerns of localized
persistent rainfall and possibly isolated flooding.

Wednesday starts with a deep and stacked low from the surface to
500 mb just offshore of the US/Canada. Strong winds will have
already been occurring overnight from Tuesday into Wednesday, with
a high wind watch currently in effect from Central Oregon up
through the foothills of the Blues. By later Wednesday morning
winds will still be breezy, but should be relaxing by the
beginning of the afternoon. With winds lessening, our main
concerns with this system will become precipitation as the low
continues to sit just offshore and spin moisture across the region
daily. Southwesterly flow should help to bring rising snow levels
though, above 4-7k feet by Thursday. This means the majority of
falling precipitation will be rainfall outside of the highest
elevations, limiting impactful winter conditions for us. That
being said, some localized areas of flooding may occur as we see
daily rain alongside melting of any snow that did fall prior to
this. A widespread flood event isn`t expected currently, as daily
QPF amounts will be around 0.1-0.5 inch outside of the mountains,
but the NBM does show a near daily 50-100% probability of QPF
amounts of 0.1 or more for our entire CWA. Look for localized
rises on rivers for our region to be possible due to this
rainfall.

Overall there is moderate to high confidence in the forecast.
Ensembles are in very good agreement on the forecast pattern,
indicating the stalled low will drive our weather pattern through
most of the next week or so. Differences primarily arise right at
the end of the period, when clusters show a very varying solutions
on how quickly this system finally decides to move inland.
Otherwise, any uncertainty will be in the exact placement of the
moisture and the potential low-end (at least for our area)
atmospheric river event, but ensembles agree we`ll be sitting
around 150-200% of normal PWAT values for this time of year, so
expect a soaker come later next week. Goatley/87

&&

.AVIATION...00Z TAFs...A mix of VFR to MVFR conditions expected
due to rain moving through the region. Rain should persist until
this evening and lessen overnight. Next round of precipitation
moves in tomorrow morning, and could include snow for BDN/RDM.
Once again MVFR conditions will be possible due to this
precipitation and snow and could locally impact flight categories.
Breezy winds continue through tomorrow DLS/PSC/ALW/PDT, with gusts
20-30 knots possible. Finally with the precipitation exiting this
evening, cloud decks should lift to medium to high CIGs and
become SCT to BKN, but will drop again with the next round of rain
back between 5-10k feet, possibly lower at times with
precipitation. Goatley/87


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  33  45  28  46 /  70  30  20  10
ALW  36  47  30  47 /  80  50  30  20
PSC  39  50  34  48 /  30  10  20  10
YKM  26  47  24  41 /  20  10  20  30
HRI  36  49  31  50 /  40  10  20  20
ELN  26  43  22  39 /  40  20  20  40
RDM  27  41  24  44 /  70  50  20  10
LGD  27  38  21  37 / 100  60  40  20
GCD  26  38  20  41 /  90  60  50  30
DLS  35  49  31  46 /  60  50  50  50

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning until 10 PM PST Monday for ORZ502-509.

     High Wind Watch from Tuesday afternoon through Wednesday morning
     for ORZ507-508-510-511.

WA...Winter Storm Warning until 10 PM PST Monday for WAZ030-522.

&&

$$

SHORT TERM...74
LONG TERM....87
AVIATION...87