052
FXUS66 KPDT 191729
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1029 AM PDT Sat Oct 19 2024


.UPDATED AVIATION DISCUSSION...

.AVIATION...18Z TAFS...VFR conditions will prevail throughout this
period. Winds at KPSC will elevate to 15 kts with gusts up to 25kts
due to increased westerly flow. Conditions will improve starting
this evening. Otherwise, winds will be less than 12 kts for the
remaining sites. Feaster/97

&&

.MORNING UPDATE...Radar reveals a region of light -RA across
much of Morrow, Umatilla, Benton, Franklin, and Walla Walla
counties early this morning, likely facilitated by subtle
mid-level WAA coupled with weak upper-level PVA. Updated the
forecast to include a slight chance (15%) mention of -RA for the
aforementioned area since the PSC ASOS and web cameras indicate
some precipitation is reaching the ground. Elsewhere, reduced PoPs
in the lee-side valleys of Yakima and Kittitas counties to
exclude anything above a slight chance (15-24% PoPs) mention of
-RA. Plunkett/86

&&


.PREV DISCUSSION... /issued 323 AM PDT Sat Oct 19 2024/

.SHORT TERM...Today through Monday night...No major concerns are
anticipated in the short term period...at least nothing that
requires highlights. Rain and high elevation snow will bring
additional relief to some of our current wildfires, and the
Cascades and Blue Mtns will have moderate rainfall amounts with a
quasi-stationary cold front Sunday night and Monday (confidence
80%).

Western WA and northwest OR are observing widespread
precipitation, and some of the showers have spread to the
Cascade east slopes. In the Kittitas County, several RAWS have
measured 0.2-0.3" of precipitation over the past 24 hours.
Additional amounts up to 0.10" are likely (60%) in northwest
Kittitas County, but the probabilities decrease significantly for
amounts greater than 0.1". This is associated with a warm front
lifting north today with precipitation north of the forecast area
by the afternoon. Doppler Radar is also detecting isolated showers
over the northern Blue Mtns associated with orographic lift in a
westerly flow aloft, and this will be included in the forecast for
the early morning hours. Otherwise, it will be a dry day and
warmer compared to yesterday due to weak ridging taking place over
WA/OR.

The westerly flow over the eastern Pacific will buckle in response
to a developing trough over the Gulf of Alaska. A southwest flow
will increase over the forecast area tonight and Sunday. Sunday
will be partly to mostly cloudy and unseasonably warm due to
increasing heights and the southwest flow aloft. Meanwhile, a
fairly strong surface low off the WA coast will send a warm front
over northwest WA and into BC with little effect for our forecast
area. However, a cold front will sag southward Sunday night and
Monday for the next round of precipitation. PoPs will be 60-90%
for nearly all forecast zones on Monday. The upper level support
associated with the left exit region of an upper level jet and a
weak AR advertised by both the ECMWF ENS and GEFS increase
confidence that wetting rainfall (i.e. 0.1") will be widespread.
In a nutshell, moderate rainfall amounts of 0.25-0.5" are forecast
for the Cascade east slopes and the Blue Mountains, but 0.5-0.75"
of rain cannot be ruled out. NBM shows 80% of 0.25" or more along
the Cascade Range and the Blue Mountains...40-60% in Wallowa
County and along the Blue Mtn Foothills. There is a 60% chance for
0.5-0.75" and a 30% probability for amounts greater than 0.75"
along the Cascade crest and the Blue Mtns north of Ukiah.

No wind concerns are anticipated, but it will be locally breezy
with gusts 20-30 mph during the short term. The Grande Ronde
Valley will have continuous southerly winds gusting to 25-35 mph
as a lee side low sets up on the west side of the northern Blue
Mtns.  Wister/85


.LONG TERM...Sunday through Saturday...

Bottom Line Up Front

1.  Mostly dry conditions to start the period

2.  Precipitation returns Friday

3.  Seasonal temperatures through the period

Remnants of the the upper level system will allow for some high
mountain showers Tuesday while the remainder of the forecast area
will be under dry conditions. Models show an upper level low
beginning to build off the coast. This is shifting the upper level
flow to a more westerly to southwesterly flow. Clusters are in
decent agreement with the main variance being in the positioning
of the upper level low. Models show the low to begin to shift
south allowing a ridge to begin to build in over the PacNW. Models
begin to diverge from one another beginning Tuesday night with
regards to the amplitude of the ridge. ECMWF has the upper level
flow flattening and becoming westerly while the GFS and Canadian
keep the ridge in place overhead. Confidence in the solution is
moderate (50- 60%). Regardless of the solution of westerly flow or
the ridge, models and ensembles show the solution to be dry.

Models continue to diverge from one another through the remainder
of the period. Clusters are struggling with the timing and
positioning of the incoming system with regards to whether it will
be a closed low or an open wave and when the precipitation will
essentially occur. With that, NBM has been populated and shows
precipitation to be over the region beginning Thursday morning.
Confidence in the solution is low (30-40%). 10-20% of the raw
ensembles show precipitation reaching the Cascade crests Thursday
afternoon with light precipitation amounts of near 0.01 inches of
rain. 60-70% of the ensembles show that by Friday afternoon, the
Cascades will see near 0.20 inches of additional rain, 30-40% show
the lower Columbia Basin, foothills of the Blues, central OR and
portions of the Ochoco- John Day Highlands will see near 0.05
inches of rain. Again, confidence in the forecast that far out
remains low.

Temperatures through the long term are expected to remain seasonal
with the EFI showing temperatures to be at or near seasonal. 66%
of the raw ensembles show the majority of the region seeing
temperatures in the upper 50s with a few isolated locations in the
Basins seeing near 60 Tuesday. As the ridge settles overhead,
temperatures will increase ever so slightly with nearly 50% of the
ensembles putting the majority of the norther portion of the
region in the 60s, while the souther and south eastern portions
seeing near the 70s. By Friday, ensembles become spread and show
almost equal chances of temperatures being in the upper 40s or
50s. Confidence in the temperatures beginning Friday is again low
(30-40%) as the solutions vary which will ultimately cause
temperatures to vary greatly as well. Bennese/90

&&


.PRELIMINARY POINT TEMPS/POPS...
PDT  72  44  75  46 /  20   0   0  60
ALW  75  49  79  48 /  20   0   0  60
PSC  74  50  77  53 /  20   0   0  60
YKM  70  40  73  41 /  20  10  10  70
HRI  74  47  77  50 /  20   0   0  60
ELN  68  43  72  41 /  20  20  20  70
RDM  73  41  75  44 /   0   0   0  50
LGD  68  43  71  43 /  10   0   0  40
GCD  71  41  76  45 /   0   0   0  20
DLS  72  46  75  50 /  20  10  20  90

&&

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

$$

MORNING UPDATE...86
SHORT TERM...85
LONG TERM....90
AVIATION...97