267
FXUS66 KPDT 200927
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
227 AM PDT Mon May 20 2024

.SHORT TERM...Today through Wednesday...Cool, breezy, and wet
conditions continue across the forecast area as a series of upper-
level lows trek through the region. This trend will unfortunately
continue through most of the week, so those hoping for clear and
warm late-spring weather will have to hold on for just a little bit
longer.

The first of this series of lows is actually a departing trough that
has been centered over western Canada over the last several days.
This trough has developed a positive tilt and will invite northerly
flow into the forecast area, as well as weak instability. This
northerly flow is quite dry, however, and latest guidance has
actually backed off a bit on PoPs this afternoon as models pick up
more on the dry incoming airmass. The ingredients are there for weak
showers to develop over Wallowa County, and perhaps even some
isolated thunderstorms, however confidence is low (30%) on anything
substantial materializing as mid-level moisture just isn`t there to
support more widespread development. Bulk shear is also pretty weak,
so convective cells would be weak and short in duration. Elsewhere,
expect generally clear skies and mildly breezy conditions, except
for the Cascade Gaps, where windy conditions will continue.

Widespread showers become more likely Tuesday into Wednesday as
another upper-level low dives down from Canada and envelops the
forecast area through most of the midweek. Showers are expected to
become widespread more towards the latter half of Tuesday, with t-
storms not being of particular concern due to the cold, northerly
origin of this system. Guidance has actually backed off quite a bit
on storm chances for the period, even for Wednesday, when the low is
directly overhead and lift is maximized. Even then, NAM shows very
unimpressive CAPE, and lapse rates are weak as well. Did leave
chances for storms Wednesday afternoon for primarily the eastern
mountains, where mechanical lift over the mountains may help trigger
an isolated storm, but overall expect showers more than anything
through the midweek.

This train of systems will unfortunately keep the ongoing breezy
conditions ongoing, however headline-worthy winds are not
anticipated at this time. Northerly flow will also invite colder air
into the forecast area, with temps dropping to as much as 15 degrees
below average by Wednesday as highs struggle to climb into the 60s
even for our lowest elevations. Fortunately, freeze concerns appear
to be limited, as moisture and cloud cover are expected to insulate
the area from temps really bottoming out overnight. Evans/74

.LONG TERM...Thursday through Sunday...Thursday looks to be mainly dry
across the region in northwesterly flow. There could be some
lingering showers over the eastern Oregon mountains, though the
deterministic models are less supportive of this than the NBM. By
later Thursday into THursday night, all of the guidance has dry
weather everywhere.

By Friday, there continues to be uncertainty with regard to the next
trough/low approaching the Pacific Northwest.  The GFS is a bit
stronger and considerably further south with the low position than
the ECMWF.  However, each model does bring some showers to the area
into Saturday, but exactly where and how much will be dependent on
the track and strength of the low.  The good news is the precip does
look less than yesterday.  With the deeper low, the GFS does bring
ridging in behind its passage on Sunday while the ECMWF has dry west
to northwesterly flow followed by ridging.  Wile uncertainty
remains, at this point, the second half of the holiday weekend does
look better than the first.

The ensemble clusters continue to support the ECMWF (more northern)
solution.  On Friday and Saturday, the GFS solution is only
preferred by 18% of the solutions, while the ECMWF is preferred by
39% and 46% respectively.  Additionally, the ECMWF continues
ensemble mean continues to be in better agreement with its
deterministic run at 500 mb giving more confidence to its solution.

Depending on the ultimate low track, Friday afternoon into Friday
evening could be breezy.

High temperatures look to be below normal in central Oregon Thursday
and near normal elsewhere.  Friday will see highs near normal.
Saturday`s highs will be about 5 or so degrees normal everywhere
with a return to near normal on Sunday.

&&

.AVIATION...12Z TAFS...High confidence (90-100%) in VFR conditions
through the period. Gusty winds to around 25 kts are expected to
redevelop at DLS and 15 to 20 kts at PDT, BDN, RDM and YKM. All
winds should become 10 kts or less during the late afternoon/evening
except at DLS where the decrease will happen later...during the
late evening/overnight.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  68  42  65  45 /   0   0  20  80
ALW  70  47  67  49 /   0   0  30  80
PSC  76  49  68  51 /   0   0  20  50
YKM  75  42  66  42 /   0   0  30  20
HRI  75  46  67  48 /   0   0  20  50
ELN  68  45  62  42 /   0   0  30  20
RDM  64  34  63  42 /   0   0  20  40
LGD  62  37  65  44 /  10   0  20  90
GCD  63  35  64  44 /  10   0  20  90
DLS  71  47  64  49 /   0   0  40  40

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

$$

SHORT TERM...74
LONG TERM....77
AVIATION...77