Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 211729

Area Forecast Discussion
National Weather Service Pendleton OR
930 AM PST Thu Jan 21 2021

.Updated Aviation Discussion.

.SHORT TERM...Today and tonight...A band of steady light
precipitation will continue to impact the northern portion of the
forecast area through this morning. Observations around the Basin
show a mix of snow and rain with some very light accumulations
occurring generally above 1000 to 1500 feet. The precipitation will
shift to more over northeast Oregon and southeast Washington this
afternoon where the mountains could see 2 to 4 inches of snow. The
low causing the precipitation is currently off the Washington coast
and dropping southward where it will clip southwest Oregon tonight
before moving into northern California on Friday. There will
continue to be some light precipitation overnight mainly across
Oregon which will lingering into Friday then ending Friday night.
Most of the precipitation will fall as snow but with light
accumulations of around an inch or 2 in the lower elevation and 2
to 4 inches in the mountains. Nothing worth of issuing advisories.


AVIATION...18Z TAFS...Variable conditions currently across all
sites as PDT/YKM/ALW are LIFR, PSC is at IFR, DLS is MVFR, and
RDM/BDN are VFR. Conditions should continue to degrade, dropping all
sites to IFR or LIFR between 19Z-04Z. Moisture will linger in the
area, keeping light rain and snow showers in the vicinity through
the period. Conditions should stay IFR/LIFR through the end of the
period as the main system slowly slides down the Pacific coast.
Overnight fog likely to develop for ALW and possibly PDT during the
morning hours on Friday. 75


.PREV DISCUSSION... /issued 228 AM PST Thu Jan 21 2021/

SHORT TERM...Today through Saturday...Water Vapor satellite
imagery showing an upper low continuing to push south along the
BC coast this morning with westerly flow aloft into the PacNW.
This has pushed some light showers across the Cascades and into
the forecast area, while areas that have been saturated by precip
have seen patchy fog develop. The upper low will continue south
along the coast today before moving into northern CA by early
Friday morning. As center of low passes south of the WA/OR border
today, westerly flow aloft will transition to a cold northerly
flow aloft, allowing colder air to advect into the intermountain
west this afternoon and evening. Snow is expected in higher
elevation valleys and portions of foothill locations this
morning, with a rain/snow mix possible in the lower elevations
through this afternoon. As colder air advects into the
intermountain west this afternoon, any lower elevation
precipitation still occurring will transition into snow by
tonight. Winter highlights are not anticipated with this system as
snow accumulations in the lower elevations will be light while
mountain areas will generally see 2-4 inches.

Upper level shortwave trough in northerly flow will follow quickly
behind the upper low tonight and pull the upper low further south
into CA tomorrow. Light snow showers will diminish from north to
south as upper low moves further south into CA tomorrow, leaving
the forecast area under a dry northerly flow aloft by tomorrow
evening. Drier air advecting into the region will help to clear
skies by tomorrow evening and limit any potential fog development
overnight. Friday afternoon highs likely to be the coldest in the
short term period, while cold air advection and clear skies
overnight Friday will bring the coldest night through the next

Saturday will see mostly clear skies and calm conditions as
northerly flow aloft persists over the region through the
afternoon. Late Saturday, flow aloft will turn northwesterly in
response to the next weather system approaching the region, with
mid to high level clouds increasing late in the evening.

LONG TERM...Sunday through Thursday...Quite active and continued
cooler for the long term with a combo of upper level lows projected
to drop south along the West Coast. The first low is expected to
drop south along western WA/OR into CA/NV Sunday into Monday. Cold
front will drag south across the CWA Sun/Sun night before weakening
on Monday. Expect mainly snow, even in the low elevations as temps
aloft are much colder, with light accumulations possible. A few
showers could continue into Monday with moisture wrapping around the
low as it drops south of the region. Tuesday looks to be dry in
between systems. The next upper low is expected to drop south along
the west coast Tues night into Thursday. Model differences in
timing, location and strength much more pronounced with this system
with GFS stronger with better surge of Pacific moisture feeding into
the region, while the EC is weaker and further south, keeping region
mostly dry. Ensemble means lean more towards GFS with a decent shot
of snow for Cascades and eastern/central OR mountains. Seasonably
cooler temps with highs in the 30s to low 40s. Lows in the upper
teens to around 30. 84


PDT  35  29  34  21 /  80  30  20  10
ALW  36  31  36  23 /  80  20  20  10
PSC  38  30  41  23 /  70  20  10   0
YKM  39  28  41  20 /  60  20  10   0
HRI  39  30  41  23 /  70  20  20   0
ELN  37  27  38  19 /  60  10  10   0
RDM  46  27  35  19 /  10  50  40  10
LGD  36  28  34  19 /  70  30  30  20
GCD  42  29  38  20 /  30  20  30  20
DLS  42  34  42  27 /  60  30  20   0




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