Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 270543 AAA

Area Forecast Discussion
National Weather Service Pendleton OR
1034 PM PDT Mon Jul 26 2021

updated the aviation discussion

.UPDATE...The latest radar was showing a few showers south of
Pendleton moving ne into the blue mountains along with some
showers in and near the Wallowas and the forecast was updated to
reflect this. Further south isolated showers and a thunderstorm is
possible overnight in a plume of moisture streaming into the area.
Otherwise minor changes were done to overnight temps and the
short term forecast appears on track.

A challenge could be with the coverage of showers and
thunderstorms tomorrow. The rap model was generating showers over
central Oregon tomorrow morning that could stretch into portions of
south central Washington by midday and remain persistent into the
afternoon. Meanwhile the models were moving additional mid level
moisture into central Oregon and into Grant county Tuesday
afternoon. The rap and the hrrr models were developing an area of
convection in this region after 20z with moderate to high confidence.

.AVIATION...Mainly vfr conditions can be expected at all taf sites.
However an isolated shower may approach any taf site until 12z
except for taf sites kykm and kpsc. Meanwhile isolated tsra may
develop near taf sites krdm and kbdn between 22z-04z and lvl mvfr
conditions may be approached.


.PREV DISCUSSION... /issued 441 PM PDT Mon Jul 26 2021/

SHORT TERM...Tonight through Wednesday...Light showers moving
northeast continues across portions of central OR and the
northeast mountains this afternoon, with only a couple of
lightning strikes being recorded in the last hour or two. Cloud
cover and smoke aloft have helped to limit daytime warming across
the eastern half of the forecast area, with many of these
locations struggling to warm into the low to mid 90s.

A slight chance of showers with thunder possible will continue
into this evening, and linger over portions of the Ochoco-John Day
Highlands and central OR into early tomorrow morning. Overnight,
flow aloft will begin to turn to the south as a sub-tropical low
moves west into the eastern Pacific. This will help to advect more
monsoonal moisture into the region, and help to keep temperatures
in the low to mid 90s in the afternoon. Impulse rounding the upper
level high pressure over central CONUS will help to increase
instability across the mountains in central and northeastern OR
Tuesday, with slight chance to chance of thunderstorms possible
through Tuesday evening. Though thunderstorm chances will be
better tomorrow, fire weather concerns will be below marginal as
any thunderstorm will be capable of producing moderate to heavy
rain. Wednesday, upper high pressure will begin to amplify over
the region while a slot of dry air advects into the region. This
will lead to storm chances diminishing across the central OR and
the northeast mountains by early Wednesday, and for temperatures
to warm into the 90s, though portions of the Basin may hit the
triple digit mark with enough clearing overhead. Winds through the
next couple of days will generally be light to locally breezy in
the afternoons, and become diurnally driven in the nighttime
hours. Lawhorn/82

LONG TERM...Thursday through Sunday...Above average heat into the
triple digits, areas of thunderstorms, and then a cooling trend
are all possible in the extended forecast period.

Ensembles remain in solid agreement that the deep ridging over the
majority of the Western/Central US will continue to extend up into
our region with a deep low offshore of Canada and a trough off of
California. This pattern will continue to increase our
temperatures to end the week and begin the weekend, with upper
90`s likely for much of the forecast region into triple digits for
the Columbia Basin. If current trends follow, some local records
could be threatened by this weekend`s heat wave, along with the
need for some heat advisories to possible excessive heat warnings
later this week.

Divergence between the ensembles then occurs on the strength of
the the ridging, but still agree on the eventual breakdown of the
ridge and subsequent retreat back to the Four Corners.
Temperatures should begin to fall, but are likely to remain above
average for the area. The ECMWF ensembles have better agreement
between the deterministic and the mean based on cluster analysis,
which would favor their solution of a weaker ridge and more
progressive pattern from SW`ly flow from deeper troughing off the

Meanwhile, embedded shortwaves within the overall flow and enough
moisture including anomalously high PW values of 1-1.3" are
expected to produce scattered thunderstorm activity from South-
Central through Eastern OR over the majority of the extended
period. Because of the high moisture content, any storms that
form look to be wet and shouldn`t aid in fire weather concerns.
With a daily risk across this region, above average precipitation
values for this time of year are present across the Eastern half
of Oregon, which may be the sign of relief this area has been
looking for. Goatley/87


PDT  66  91  66  95 /  20  10  20   0
ALW  70  93  70  97 /  10  10  20   0
PSC  71  96  70  98 /   0   0  10   0
YKM  66  96  65  97 /   0   0   0   0
HRI  69  96  69  99 /  10  10  10   0
ELN  64  92  63  95 /   0   0   0   0
RDM  60  87  58  93 /  20  20  30  10
LGD  65  91  64  92 /  20  10  20  10
GCD  66  92  62  94 /  20  20  30  10
DLS  69  93  68  98 /   0   0   0   0




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