Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 191122
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
422 AM PDT Mon Oct 19 2020

.UPDATED AVIATION DISCUSSION...

.AVIATION...12z TAFs...VFR conditions expected through the next 24
hours. Gusty westerly winds up to 20 kts gusting to over 30 kts
expected again today, especially for the Kittitas Valley. Low-level
clouds early will give way to high clouds in the afternoon into the
evening, with overcast conditions expected for central Washington.
Patchy blowing dust also possible for the Washington Columbia Basin,
particularly around PSC. Winds will decrease to around 10 kts for
most areas by the overnight.

&&

.PREV DISCUSSION... /issued 245 AM PDT Mon Oct 19 2020/

SHORT TERM...Today through Wednesday night...A strong northwest
flow aloft will remain over the Pacific Northwest through
Tuesday. This persistent pattern has resulted in breezy to windy
conditions over most of the forecast area, and this will continue
again today. In fact, winds will be stronger today than yesterday
due to a tighter pressure gradient east of the Cascades. A low
level jet with 850mb winds around 40 kts will cause winds to meet
advisory criteria in the Kittitas Valley this afternoon and
evening, and a Wind Advisory will be issued during the morning
forecast package. Scattered orographic mountain showers can be
expected along the WA Cascades north of Mt. Adams through this
evening, and the remainder of the forecast area will be partly to
mostly cloudy. Little change in the synoptic pattern over the
Pacific Northwest on Tuesday means little change in the weather
elements, although winds will not be as gusty.

A strong cold front will dive south across British Columbia
Tuesday night then over WA/OR Wednesday. Although the front is
limited in moisture, snow levels will plummet from around
5000-7000 feet Tuesday night to 3500-4500 feet on Wednesday. The
GFS is more bullish with precipitation compared to the NAM and
believe the GFS is more realistic in the areas likely to
experience low level upslope along the Blue Mountains and Wallowa
County. 1-3 inches of snow are forecast for areas north of Meacham
and over the Wallowa Mountains Wednesday and Wednesday night.
Wednesday night will be COLD for all of the forecast area, as
temperatures drop into the 20s to lower 30s for most of the
region. A few of the colder mountain valleys such as Bear Valley,
Ukiah, and near LaPine will observe lows in the teens. The cold
temperatures that are in the forecast will likely warrant freeze
warnings for many of our lower elevations zones that will
experience the first hard freeze of the season. Wister

LONG TERM...Thursday through Monday...A trough departing our area
after Wednesday night will leave the region under dry and cold NNW
flow aloft. This shift in the upper-level pattern will mark the
start of a cooling trend that will last through early next week, as
Friday will see the potential of a strong trough digging into the
Pacific NW, bringing with it a surge of cold arctic air and the
chance for the first snowfall of the season.

Global guidance coming into better agreement over the last few days
on depicting a building ridge over the Gulf of Alaska kicking a deep
trough south through British Columbia into the Pacific NW. Main
disagreement across the models stems in the magnitude and location
of the trough axis, which will greatly influence temperature and
precipitation forecasts. As of now both the GFS and its ensemble
guidance favors a negatively tilted trough axis right through our
CWA, which would favor higher precip values and colder temps. ECMWF
deterministic similar to GFS on magnitude, but puts the trough a
little more to our east. Many members of Euro ensemble also favor a
more broad trough, which would still usher in colder air but keep
things a bit drier. Obviously too far out to commit to precip type,
amount, and temperatures, but global guidance agreeing this far out
suggests something resembling an unseasonable cold blast and the
chance for mountain snow. Will have to see what solution the global
guidance converges to over the next few days.

Beyond the weekend, models in good agreement over a return to NW
flow aloft before ridging settles in over the western CONUS by the
middle of next week. Guidance suggests a warming up period beyond
the extended period as a result.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  63  43  59  42 /   0   0   0  10
ALW  65  46  60  43 /  10  10   0  20
PSC  69  45  62  43 /  10   0   0  10
YKM  67  40  61  35 /   0   0   0  10
HRI  67  44  63  43 /   0   0   0  10
ELN  61  42  58  37 /  10  10   0  10
RDM  65  36  64  37 /   0   0   0  10
LGD  62  40  58  39 /  10  10  10  20
GCD  68  41  64  41 /   0   0   0  10
DLS  65  48  63  46 /  10   0   0  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Wind Advisory from 3 PM this afternoon to 9 PM PDT this evening
     for WAZ026.

&&

$$

SHORT TERM...85
LONG TERM....74
AVIATION...74



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