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000
FXUS66 KPDT 181016
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
316 AM PDT Wed May 18 2022

.SHORT TERM...Today through Friday Night...
The pattern will be quite active at the start of the near term
period as a compact, but potent area of low pressure pivots across
northern Washington into southern British Columbia. This will
bring a band of strong westerlies aloft and a fast moving,
unseasonably strong cold front through the Pacific Northwest today
into tonight. Thereafter, a northwesterly flow pattern looks to
set in, chances for convection shutting down by Friday.

For today, The frontal passage will result in strong gusty winds.
Latest Hi-res ensembles (HREF) continue to support this,
depicting ensemble mean gusts of 40 to 50 mph across much of the
Columbia Basin, Kittitas Valley, and Columbia Gorge. the ECMWF
Extreme Forecast Index (EFI) also supports this with values of 0.8
to 0.9, supporting a climatologically unusual wind event. Winds
of this intensity typically result in blowing dust, and while this
will certainly be the case across portions of the Upper Columbia
Basin and where fields have recently been plowed, recent rains
should mitigate this threat somewhat. Still, folks should be on
the lookout and be prepared for localized visibility reductions
within blowing dust this afternoon and evening.

In addition to the wind, precipitation is expected to spread
mainly over the Cascades and mountains of eastern Oregon and
southeast Washington. Initially much of this will fall as rain,
but as snow levels tumble later today, a transition to snow is
expected above 4000 to 5000 ft. this will likely result in some
light snow accumulations, especially over the Washington Cascades,
where precipitation is expected to be heavier and more prolonged.
While amounts don`t look terribly high, accumulations of 1 to 4
inches are expected through White and Snoqualmie Passes, which
could certainly lead to some travel issues over the next 24 hours.

As the upper low continues east and south on Thursday, the flow
will become more northwesterly, this will usher in some colder
air, making it feel noticeably cooler than today. Highs will
generally be 10 to 15 degrees below climatological normals in the
50s and low 60s in the lower elevations. Despite these cooler
temperatures, much colder air aloft will result in afternoon
instability, particularly across northeast Oregon and southeast
Washington. This is where showers and a few afternoon
thunderstorms can be expected. Severe storms are not expected, but
gusty winds, lighting, heavy downpours and small hail may
accompany any storm, especially given the colder airmass overhead.

Chilly temperatures can be expected on Friday as high pressure
settles in with radiational cooling. This will lead to frost and a
light freeze, particularly for higher elevation valleys and cold
prone areas. Given we will be past mid May and well into growing
season, care should be taken to ensure sensitive plants are
protected. Thereafter, a gradual warming and drying trend is
forecast heading into the weekend. Austin/79

.LONG TERM...Saturday through Wednesday...
Models continue to struggle in the long term period as they deal
with a few weak disturbances affecting our area. Not only do they
disagree with each other, they have substantial changes from run
to run. Fortunately, the Extreme Forecast Index shows no unusual
weather is expected and the ECMWF and NAEFS Situational Awareness
Tables agree with this. Cluster Analysis shows that model
ensembles are showing a greater than usual spread among its
members. The GFS and ECMWF deterministic runs are generally close
to their ensemble means through Monday then begin to deviate from
the mean. The Canadian model continues to have its deterministic
run as something of an outlier among its ensemble members during
several periods. Overall forecast confidence is below average and
worsens by Tuesday and Wednesday.

On Saturday models agree in having a ridge offshore and a broad
trough over our area. Both the GFS and ECMWF have a wave moving
through the area with the GFS a little further south than the
ECMWF. Have a chance of rain and afternoon thunderstorms over the
northeast Oregon mountains and dry elsewhere. Rain amounts will be
less than a tenth of an inch and showers will taper off rapidly
after sundown. On Sunday the latest model runs show the ridge
pushing off to the east and the GFS brings a secondary wave
through the trough while the ECMWF doesn`t show much of a wave.
Have kept a slight chance of showers over the Washington Cascades
and the higher mountains of eastern Oregon. Rain amounts will be
very light. Do not see enough instability for any thunderstorms
Sunday. The rest of the area will remain dry.

On Monday models show the offshore ridge over our area with a
west to northwest flow. Latest models runs look dry but previous
runs had a disturbance moving through, so have held on to a slight
chance of light rain showers in the mountains for now. Models
then show a front moving over the ridge and through the area. The
ECMWF and Canadian have it arriving late Tuesday afternoon and
night with showers continuing Wednesday. The GFS holds off its
arrival until Wednesday afternoon. Given the timing differences,
have a slight chance of rain in the mountains, central Oregon and
Blue Mountain Foothills both days with the rest of the lower
elevations dry. Temperatures Saturday through Monday will be in
the mid 60s to mid 70s with mainly mid 50s to mid 60s in the
mountains. Monday and Tuesday will be 3-5 degrees cooler. Perry/83

&&

.AVIATION...Previous discussion...06Z TAFs...VFR conditions to
prevail through the period. A low pressure system will push a cold
front across the region with rain possible at site DLS and VCSH at
sites RDM/BDN/YKM in the late morning and early afternoon. CIGS will
become sct-ovc AOA 5kft to 10kft AGL with bkn-ovc AOA 20kft AGL and
will persist through the evening. Winds will be less than 12kts
through early tomorrow morning, before increasing to 15-20kts with
gusts 25-35kts possible as the frontal passage impacts sites.
Strongest winds will develop after 19Z. Sites DLS/PDT/ALW will
continue to see strong westerly winds through tomorrow evening, with
all other sites 10-15kts with gusts 20-25kts possible. Lawhorn/82

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  65  40  59  36 /  20  10  30   0
ALW  66  43  59  38 /  40  10  30   0
PSC  69  46  65  41 /  10   0  10   0
YKM  67  37  62  35 /  30  10  10   0
HRI  68  43  64  41 /  10   0  10   0
ELN  62  38  56  38 /  40  10  20   0
RDM  65  33  57  28 /  10  10  30   0
LGD  64  37  51  33 /  30  20  50   0
GCD  69  37  51  33 /  10  10  40   0
DLS  66  45  61  42 /  50  20  40   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from noon today to 10 PM PDT this evening for
     ORZ041-044-507-508-510.

WA...Wind Advisory from noon today to 10 PM PDT this evening for
     WAZ024-026>029-521.

&&

$$

SHORT TERM...79
LONG TERM....83
AVIATION...82