474 
FXUS66 KPDT 061809
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1009 AM PST Sun Nov 6 2022

.Updated Aviation Discussion.

AVIATION...18Z TAFs..VFR conditions are forecast to continue
through the morning. By late this afternoon through the evening, 
conditions are expected to degrade to MVFR as lowering ceilings
and -RA impacts most terminals, with -SN at BDN/RDM and possibly 
a mix at YKM. HREF probabilities indicate low chances of IFR 
conditions (<10%) at all terminals except BDN/RDM later this 
afternoon and evening as the band of precipitation goes through. 
IFR probabilities are 20-30% for BDN/RDM this evening. Confidence 
is also lower than average on the onset of MVFR conditions and 
this timing may have to be adjusted in subsequent issuances.

Winds are forecast to be around 10 kts or less through the 
period, except for BDN/RDM/ALW which will see some gusts to around
25-35 kts at BDN/RDM and 20 kts at ALW today. Plunkett/86

&&

MORNING UPDATE...Main concern for today continues to be snow 
across the Cascades, with precip eventually spreading eastward 
later today as the flow aloft shifts more SW. Webcams around the 
OR Cascades are showing a respite in snow showers, while snow 
continues to fall across the WA Cascade crests. Expecting snow to 
resume later today in the OR Cascades as the flow makes its SW 
shift, supporting more moisture influx into the area, where snow 
will spill over a bit more into the foothills, but still looking 
like the bulk of this system's snow will impact primarily the 
crests and mountain passes rather than the foothills. Latest Hi- 
res guidance has a band of precip sweeping across the rest of the 
forecast area east of the Cascades beginning around 5 PM, however 
current radar does show light showers in the WA Basin running 
ahead of the precip falling over the Cascades. Expect snow levels 
to run around 3500 to 4500 ft east of the Cascades for much of the
day. Any precip east of the Cascades and foothills looks to be on
the lighter end - less than a tenth of an inch. 

Made some minor tweaks, otherwise most of the morning forecast 
package remains intact. Evans/74

PREV DISCUSSION... /issued 326 AM PST Sun Nov 6 2022/ 

SHORT TERM...Today through Tuesday...Current radar imagery is 
showing that the current precipitation is in Wa moving to the 
Northeast. The short term models HRRR/SREF/NAM12 and RAP are in 
strong agreement that the low will continue to dig south and a 
little eastward through the day bringing the moisture over the 
Cascades later this morning and moving farther east by the 
afternoon. Snow levels are expected to drop to as the system digs 
in bringing cold air in behind it. As the system moves over the 
Cascades, expect snowy conditions, especially in the the mountain 
passes. The ECMWF EFI forecast of 0.88 for Sunday into Monday is 
signaling above average snowfall over the Cascades and some higher
terrains. Showers are expected in the Basin with a chance 
(30-50%) of showers elsewhere. A Winter Weather Advisory is in 
affect for both the Or and Wa Cascades until 4 pm today. Please 
check road conditions through the passes before traveling. 

The HRRR/SREF/NAM and Rap models continue to forecast the low 
traversing farther south through the period, it will deepen and 
the moisture is then shifted out of the region. The deepening of 
the low will allow for cold air to move in over the region 
bringing cold temperatures. The NBM is showing highs today will be
in the low 50s in the Gorge and Basin, 40s for the foothills and 
Central Or and 30s for the higher terrains. The ECMWF EFI is again
signaling a below average temperatures through the short term, 
mostly in the higher terrains and Central Or. Again, the NBM is 
showing temperatures will decrease by about 5 degrees each day 
through Wednesday when high temperatures will bottom out in the 
20s for the higher terrains and 30s elsewhere. Bennese/90

LONG TERM...Wednesday through Saturday...A large trough will be
making its way onshore in California beginning Wednesday and 
then will progress north and east across the Great Basin on 
Thursday and end up in the northern plains on Friday as ridging 
returns to the west. The models are in very good agreement through
about Friday, with only minor timing differences on the low as it
ejects northeastward. By Saturday, there is another low off the 
Pacific Northwest coast and there are model differences that 
develop with respect to this feature.

As far as sensible weather goes, it is going to be unseasonably
cold through the week, with high temperatures generally in the 
mid to upper 30s...at best. There is some disagreement win the 
models as to how high the temperatures will be, with the ECMWF 
generally warmer. Regardless, these temperatures are 15 to 20 
degrees colder than normal. Overnight lows will be in the teens 
and 20s which are also about 10 to 20 degrees below normal.

As the axis of the trough crosses the region on Wednesday, there 
could be some snow showers, mainly over the mountains, but after 
that the balance of the forecast looks dry.

The ECMWF EFI shows the anomalous cold well.  Beginning Wednesday 
There is a large swath of values -0.7 to -0.7 over the entire
region with some embedded -0.8 to -0.9 Thursday and Friday are 
quite similar, with perhaps some slight moderation by Saturday. 
Low temperatures don't show up as extreme until Thursday when 
there is a large swath of -0.8 to -0.9 from the Columbia Basin in 
Washington northward. By Friday and Saturday, most of the area is 
indicated in -0.7 to 0.8.

Examining the ensemble clusters toward the end of the period, while 
certainly not definitive, there is some support for the ECMWF 
solution over the other models on Saturday, but there is not great 
agreement between the clusters either.  However, the cluster phase 
space shows that the ECMWF ensembles are most cluster together 
compared to the other models and are also more clustered around the 
deterministic run, which would lend additional credence to the ECMWF 
solution during this time.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  51  30  46  22 /  20  70  10  20 
ALW  51  33  48  25 /  20  70  20  10 
PSC  53  36  48  30 /  50  60  10  20 
YKM  45  25  40  22 /  70  50  20  30 
HRI  55  33  50  27 /  40  60  10  20 
ELN  42  24  38  22 /  80  60  20  30 
RDM  46  22  43  21 /  50  80  20  30 
LGD  41  29  41  20 /  10  70  20  10 
GCD  47  25  43  22 /  10  80  10  10 
DLS  48  33  49  32 /  80  50  30  30 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 10 PM PST this evening for ORZ509.

WA...Winter Weather Advisory until 4 PM PST this afternoon for WAZ520.

&&

$$

MORNING UPDATE...74
SHORT TERM...90
LONG TERM....77
AVIATION...86