538 
FXUS66 KPDT 020336
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
736 PM PST Fri Jan 1 2021

.EVENING UPDATE...Surface cold front and upper level shortwave
trough are currently pushing a line of showers across the 
forecast area this evening, with some locations briefly reporting
breezy conditions ahead and behind the frontal passage. Lower
elevation light rain will quickly diminish behind the frontal 
passage tonight, while shortwave and westerly flow will continue 
to support upslope snow showers in the mountains through tomorrow
morning. Another upper level shortwave and surface cold front will
impact the forecast area tomorrow afternoon, with another round of
rain and mountain snow showers developing. Expect breezy to windy
conditions to develop late Saturday as tight surface gradient
develops with cold front approach. Winter weather advisories are
still looking good for the WA Cascades east slopes and the
northern Blue mountains in WA/OR as this series of weather systems
bring periods of moderate to heavy snow above 4,000ft. Made minor
adjustments to evening forecast package to adjust for current
trends. Lawhorn/82


&&

.PREV DISCUSSION... /issued 209 PM PST Fri Jan 01 2021/ 

SHORT TERM...Tonight through Monday...Active weather pattern in 
store for the weekend and into next week as a series of systems 
impact the region with rain and mountain snow. A shortwave trough 
will move across the region tonight pushing a frontal system through 
the area. Rain and mountain snow will accompany the front through 
Sunday morning with modest amounts of QPF. Behind the front a fast 
westerly flow of moist air will become established with moderate 
rain and snow redeveloping mainly over the mountains late Saturday. 
Snow levels will be mainly 4000-5000 feet. A strong cold front will 
sweep through Saturday night and early Sunday bringing a period of 
gusty southwest winds to the region. It is quite possible that wind 
advisories may be needed during this time period. This is 
supported by the HREF mean wind gust product...and the HREF max 
wind gust product is showing large areas of winds exceeding 50-60
mph early Sunday morning. This could be a little aggressive but 
definitely bears watching. Will be issuing a winter weather 
advisory for the Northern Blues and East Slopes of the Washington 
Cascades above 4000 feet with this forecast package valid until 
18Z Sunday mostly for the higher passes and ski areas. There looks
to be a brief break in the rain/snow on Sunday afternoon then a 
warm front is forecast to lift northward across the region Sunday
night and monday with more precipitation. Winds have become strong 
and gusty in the southern Grande Ronde Valley this afternoon so a 
wind advisory has been issued until 11 pm this evening. 
78

LONG TERM...Monday through Friday...Global forecast guidance not 
relenting on an active synoptic pattern consisting of progressive
westerly flow aloft with embedded trough activity every couple of
days. Ensembles disagree slightly on the timing of the arrival of
each wave, but little disagreement on the overall large-scale 
pattern. Deterministic GFS and ECMWF have been more aggressive 
with depicting a well-organized trough passing through the PacNW 
late Monday into Tuesday. QPF ensembles from the GEFS and EPS 
suggest a couple tenths of an inch from this system in the lower 
elevations. Given the moist Pacific westerly upper-level flow, 
snow levels will be high enough to keep precipitation type at rain
in the valleys through the week. Monday starts off at around 5000
ft, bottoming out to 3000 ft for most areas by the end of the 
week. 

GFS and ECMWF also agree on another system arriving late Wednesday,
bringing another chance of valley rain and mountain snow. A bit 
more spread across ensemble members for this system, with the EPS 
a bit more aggressive with QPFs than the GEFS. Temps will be mild,
with highs in the low 50s in the lower elevations, down to the 
mid 40s by the end of the week, with lows in the mid to upper 30s.
​​​​​​​74

AVIATION...00z TAFs...Cigs will decrease this evening as a weak 
front moves through the area and brings a chance of light rain 
showers for all sites. MVFR conditions possible during rainfall, 
while YKM expected to remain at or near MVFR through the period due 
to lingering low stratus. Cigs around 5 kft or less through the 
period, becoming ovc for all sites by early Saturday morning. Winds 
will increase out of the SW by Saturday afternoon, gusting up to and 
over 20kts at times. Light showers possible for PDT/PSC/ALW Saturday 
afternoon as strong jet passes overhead. 74​​​​​​​

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  36  49  41  51 /  30  30  50  50 
ALW  39  51  43  52 /  40  40  70  50 
PSC  36  52  44  53 /  20  20  30  20 
YKM  31  48  36  50 /  50  40  60  40 
HRI  37  53  42  53 /  30  20  40  30 
ELN  30  42  33  44 /  50  40  60  40 
RDM  34  48  38  49 /  50  20  60  50 
LGD  31  40  36  44 /  50  40  80  70 
GCD  32  44  37  47 /  30  40  60  50 
DLS  37  49  40  50 /  80  60  90  60 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 10 AM PST Sunday for ORZ502.

     Wind Advisory until 11 PM PST this evening for ORZ049.

WA...Winter Weather Advisory until 10 AM PST Sunday for WAZ030-520.

&&

$$

EVENING UPDATE...82