843
FXUS66 KPDT 031026
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
326 AM PDT Mon Jun 3 2024

.SHORT TERM...Today through Wednesday...

Key Messages:

1. Windy through this evening. *Wind Advisories in Effect*

2. Widespread rainfall through this morning.

3. Slight rises on area rivers.

Current radar and infrared satellite imagery showing light to
moderate returns extending across the Basin and mountain zones
under cloudy skies. These conditions are associated with an upper
level trough and cold front that will pass through the area this
morning, leading to persistent rainfall through the morning and
elevated winds through this evening. The main weather concern
associated with this system resides with windy conditions across
the Basin, Gorge, Simcoe Highlands, Northern Blue Mountain
foothills, east slopes of the Cascades, and the Yakima/Kittitas
Valleys, where wind gusts between 45 and 55 mph are anticipated.
This is a result from the upper level trough tightening isobars at
mid-and upper levels, coupled with the frontal system allowing a
surface pressure gradient to develop along the Cascades. These
features will work in tandem in order to bring sustained winds of
25 to 35 mph primarily out of the west. Confidence in these wind
values is high (90%), as the NBM suggests an 80-100% chance of
wind gusts reaching advisory criteria (>45 mph) over the
aforementioned areas. Additional confidence in gleamed via the 850
mb winds, which the GFS and ECMWF both showcase values between
50-60 knots (57-69 mph), and consistency in the forecast pressure
gradient between Portland and Spokane, which the GFS, SREF, and
NAM all highlight a gradient of between 11-14.5 mb - well above
the normal advisory threshold of 11 mb. These sustained winds and
gusts have warranted the issuance of a Wind Advisory across the
aforementioned areas from 8 AM through 11 PM.

Widespread rainfall will continue to occur through the morning
hours as the upper level trough and associated frontal system
continue to pass through the area, exiting to our east through the
afternoon and evening. Periods of moderate to heavy showers will
ensue through the morning as this system is supplied by a moderate
atmospheric river (AR), which is bringing precipitable water
amounts of 0.75-1.50" (150-225% above normal) via the GFS and
ECMWF. An additional 0.50-1.00" is expected over the Cascades and
eastern mountains, 0.20-0.40" over Wallowa County, 0.05-0.25"
along the northern Blue Mountain foothills and the John Day-Ochoco
Basin, 0.01-0.10 for lower elevations of the Basin, Simcoe
Highlands, and the Eastern Gorge, and a trace to 0.01" for Central
Oregon and the Kittitas/Yakima Valleys through the remainder of
the day. There is also a slight chance (5-15%) of developing
isolated thunderstorms across Wallowa, Union, eastern Umatilla,
and northeast Grant counties late this morning through the early
afternoon as a weak boundary of drier air follows closely behind
the earlier exiting cold front. This may provide enough forcing
over a saturated lower atmosphere to allow discrete storm cells
to develop. However, confidence is low (10%) as surface CAPE of
between 100-150 J/kg is forecast via the HREF, and overcast skies
will inhibit varying warming to help trigger any additional lift.
If a cell or two does develop, the main concern would be heavy
rainfall and gusty winds.

Significant rainfall will also lead to the potential for rivers to
rise, especially as higher rain amounts are anticipated to occur
over mountainous terrain. At this time, there are no rivers that
are forecast to reach action (bankfull) stage through the period.
This was a different story just 24 hours ago as the Naches River
near Cliffdell and near Naches were both forecast to reach action
stage later today. Even though there is still a 38% chance that
the reach near Cliffdell will reach action stage, the official
forecast keeps it just shy at 28.95 feet overnight tonight into
Tuesday morning (29 feet is action stage). The reach near Naches
is now forecast to peak Tuesday morning at 15.68 feet, which is
well below the action stage of 16 feet. Furthermore, the chances
of reaching action stage for the Naches River near Naches is less
than 5% via the forecast from the Northwest River Forecast
Center.

An upper level ridge begins to build in the wake of today`s system
Tuesday and Wednesday, but not without a weak shortwave riding
over on Tuesday. This will lead to breezy winds again across the
Simcoe Highlands and over portions of the lower Basin, with
sustained winds of 15-25 mph and gusts of 30-40 mph primarily out
of the west. High temperatures will be on the rise through
the period, bumping up 5 degrees both Tuesday and Wednesday as
values reach near normal. Clearing skies overnight tonight and
Tuesday night will drop morning temperatures into the upper 40s
to low 50s for lower elevations of the Basin. Afternoon humidities
will also drop considerably on Wednesday, as upper teens encroach
into areas of Central Oregon and into the Basin. 75


.LONG TERM...Thursday through Monday...While much of the period
looks hot and dry, a few sticklers across ensemble guidance continue
to hinder forecast confidence, especially for next weekend onward.
Confidence is high that the first stretch of the period will see the
warmest temperatures we`ve seen this year thus far, with NBM
probabilistic guidance suggesting an 80 to 90% chance of highs on
Saturday eclipsing 90 degrees across our lower elevations, but
confidence is low to moderate on what will happen after that.

High pressure ridging will prevail for the tail end of the work
week, albeit a bit dirty in nature, before ongoing model
discrepancies start to show up around late Friday onward. The GFS
wants to introduce more amplified SW flow into the region around
then, stemming from the influence of a broad low centered just off
the BC/Alaskan coast, while the ECMWF keeps a negatively tilted
ridge overhead. Ensembles continue to lean more towards the ECMWF,
but so long as the GFS continues to introduce this moisture
advection, the NBM will continue to depict light PoPs and even
thunderstorm chances across our eastern mountain zones and the
Oregon Cascades. We`ll continue to monitor how models trend in the
coming days, but should note that even the GFS is starting to delay
PoPs a bit more as ensembles continue to converge toward a drier
solution. Either way, expect warming conditions for Thursday through
at least Saturday, with the forecast Sunday onward still a bit up in
the air. Evans/74


&&

.AVIATION...12z TAFs...Rain showers are largely expected to end for
all TAF sites early this morning, before very windy conditions
prevail for the remainder of the day. Wind Advisories are in effect
across most of our sites, with gusts over 40 kts possible,
especially at PDT, PSC, and DLS. VFR conditions are expected
otherwise, with cigs generally clearing through the day, starting at
around bkn-ovc 5-10 kft, becoming sct-bkn at mid-level by the
afternoon, before clouds build back in overnight heading into
Tuesday. Evans/74


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  64  48  71  49 /  50  30  20   0
ALW  66  50  71  52 /  80  30  40  10
PSC  70  54  76  51 /  40  30  20   0
YKM  67  47  72  42 /  20  20  20  10
HRI  68  52  75  50 /  40  40  10   0
ELN  61  44  67  44 /  30  20  20  10
RDM  61  45  73  45 /  20  10  10   0
LGD  61  44  71  49 /  80  20  30  20
GCD  65  46  76  48 /  60  10  10   0
DLS  65  52  71  52 /  30  20  30  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 8 AM this morning to 11 PM PDT this evening
     for ORZ041-044-507-508-510.

WA...Wind Advisory from 8 AM this morning to 11 PM PDT this evening
     for WAZ024-026>029-521.

&&

$$

SHORT TERM...75
LONG TERM....74
AVIATION...74