874
FXUS66 KPDT 150510
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1010 PM PDT Fri Jun 14 2024

.UPDATED AVIATION...VFR conditions will prevail through the
forecast period. Primary concerns will continue to be the winds
across all TAF sites. BDN/YKM are the only TAF sites that are
below 10kts at the moment, but winds are expected to increase
there between 14-16Z. All remaining sites are seeing westerly
winds between 12-15 kts and gusts to 20 mph increasing to 15+ kts
and gusts to 30 kts later in the period. Bennese/90


&&

PREV DISCUSSION... /issued 236 PM PDT Fri Jun 14 2024/

SHORT TERM...Tonight through Sunday...

Key Points:

1) Very cool temperatures expected this weekend, with highs 10-13
degrees below normal.

2) Overnight lows similarly cool, with a chance at near to below
freezing for Central Oregon and all mountain zones.

3) Rain, thunderstorms, and breezy winds expected with the weekend
system, but significant weather concerns unlikely.

A deep upper low is moving along the Canadian coastline and will
slide inland between the US and Canada tonight into Saturday,
bringing significantly cooler weather, particularly for this time
of year, along with breezy winds and a chance at precipitation.
The jet will find itself just south of us, keeping us on the cool
side of the system with temperatures the first major article with
this system. The forecast calls for highs 10-13 degrees below
normal Saturday and Sunday, with highs in the 60`s to low 70`s for
our population centers - a likely last hurrah at Spring-like
conditions for the region. The NBM even suggests there is nowhere
in the region that could see 80 degrees, with probabilities for
temperatures greater than or equal to 80 at zero widespread.
Meanwhile overnight lows will be very chilly - in the low 40`s to
mid 30`s. Portions of Central Oregon and all mountain zones are
expected to even see freezing temperatures yet again. Widespread
frost for these areas seems certain, but moving onto a freeze
risk remains much more uncertain. Confidence is low to moderate
(30-40%) that we will see lows reaching 32 for Deschutes County,
and if we do it`s unlikely that they`ll be widespread enough to
warrant a freeze warning.

Moving onto winds, probabilities are low (<30%) that gusts will be
strong enough to reach wind advisory levels on Saturday (45+ mph)
for a widespread enough region to justify any issuance. The NBM
shows a 30-60% chance for portions of the Lower Columbia Basin,
Foothills of the Blues, Simcoe Highlands, and Kittitas Valley,
with the highest percentage chances in the Simcoes. If any gusts
do reach this level, the expectation would be that the higher
terrain of these areas and perhaps a localized site or two could
reach this threshold, but not enough to warrant the issuance at
this time.

Finally precipitation does move back into the region, including
the return of mountain snow! For snowfall - amounts are light, and
limited to only the highest terrain. Several inches may occur for
the highest peaks and crests, but expecting little to none by the
time you reach the mountain passes and valleys. Showers and some
thunderstorms will also be present with this system on Saturday,
but ingredients for storms including instability and shear will be
lacking in the best environment (generally the Washington side of
the CWA), and anticipating at best some thunder in the mountains
on Saturday due to orographic enhancement. Finally, QPF just won`t
be present to warrant significant rainfall outside of the
mountains. Rain shadowing from the Cascades will limit significant
accumulations on Saturday outside of the mountains themselves,
and then as wrap around moisture brings a bit more widespread
chances late Sunday into Monday, PWAT values generally at or below
normal (0.25-0.75 inch) won`t promote much in the way of
noteworthy accumulations for general late night/early morning
showers from Central Oregon up through the Wallowas and foothills
of the Blues. Six hour QPF chances from 06-12Z Monday of 0.1 inch
or greater are 10% or less. So although we will be active and
unusually cool, no other major impacts are anticipated at this
time. Goatley/87

LONG TERM...Monday through Friday...Cool and wet conditions
continue into Monday as broad troughing envelops the region. This
system will provide for enough moisture advection and instability to
support showers and potentially thunderstorms across primarily the
eastern mountains of Oregon and Washington, while the western half
of the forecast area is left under the trough`s dry slot. Current
thinking is that showers will prevail more so than thunderstorms due
to how cold the air mass will be, however did leave mention in given
the time of year and the trough axis being located right overhead.
The colder air pulled down into the PacNW via this trough will allow
for more chilly nights, with low temps Monday and Tuesday morning
diving down into the 40s and 30s for the entire forecast area. Zones
must vulnerable to freezing temps would be central Oregon and the
Wallowa Valley, however confidence in this occurring is low (20-30%)
as cloud cover and ambient moisture may help prevent temps from
bottoming out too much.

Ensembles suggest troughing will persist into the midweek, however
temps will slowly start to rebound back toward seasonal averages as
mid-level flow becomes more zonal, thus cutting off further cold air
advection. NBM suggests light PoPs during the afternoon hours for
primarily our mountain zones Tuesday into Wednesday as troughing
supports instability and the opportunity for weak orographic
showers and isolated t-storms to develop, however NBM PoPs waver
around 15-25% and the best chances for rain look to be on Monday
across the entire period.

Ensembles generally depict more benign flow moving in by the end of
the work week, either in the form of zonal flow or troughing weak
enough to preclude any precip threats. NBM produces a warming trend
as a result, with high temps inching back towards the 90s by the end
of the period. Confidence in these temps is only low to moderate (40-
45%), however, due to the discrepancies depicted across ensemble
members. Evans/74

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  49  66  40  66 /  10  10   0  10
ALW  52  69  43  69 /  20  30   0  10
PSC  55  71  45  72 /   0  10   0   0
YKM  46  68  38  69 /   0  10   0  10
HRI  52  71  43  72 /  10  10   0  10
ELN  45  64  41  67 /   0  10   0  10
RDM  41  61  33  64 /   0   0   0   0
LGD  46  61  37  62 /  10  20   0  10
GCD  43  64  35  64 /   0  10   0  10
DLS  52  66  46  70 /  10  20   0  10

&&

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

$$

SHORT TERM...87
LONG TERM....74
AVIATION...90