404
FXUS66 KPDT 192330
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
430 PM PDT Sat Apr 19 2025

.Updated for Aviation...


.AVIATION...
00Z TAFS...VFR conditions are generally expected through the TAF
period. Gusty winds this afternoon will decrease though the
evening and overnight at all sites expect DLS. Winds should
decrease to 10 kts or less. Winds will increase again on Sunday
and will gust to around 20 kts. There is a small chance (<25%) of
MVFR CIGS Sunday morning at BDN/RDM/PDT and ALW.

&&

.PREV DISCUSSION... /issued 236 PM PDT Sat Apr 19 2025/

SHORT TERM...today through Tuesday morning...

Radar and satellite indicate most of the activity has pushed over
to the eastern part of our CWA. The rest, if not most, of the
activity will move out of the region by early Sat evening,
leaving for a cool, dry overnight starting the week. Low
temperatures overnight will drop to the mid 30s to low 40s for
much of the area, with low 30s in the higher elevations.

Key messages for the rest of the short term:

1) Possible freezing temperatures Tues AM
2) Dry, breezy conditions for lower elevations for the rest of
the period
3) Another chance of precip Monday AM for the mountain regions

Moving forward, a trough from British Columbia will eventually
make its way down into the PacNW Sunday night going into Monday
morning. Conditions remain fairly dry for the lower elevations
since the EURO/GFS wants to place the trough just to the east
which in return will shift our upper level winds from a more zonal
form into a NW direction aloft. Moisture advection will remain
limited, thus only giving PoP chances in the mountain regions
while keeping everywhere else dry. Notably, the highest QPF
amounts are located near Snoqualmie Pass at up to an inch and up
to a half inch for other parts of the Cascades and the Northern
Blue Mountains. Snow levels will be around 3000 to 3500 feet
(on the lower range in the Cascades and on the higher range in the
Blue Mountains) on Sun AM, but will drop to around 2500 to 3000
feet as the trough digs into the area heading into Monday morning.
Pressure gradients will tighten in the same time frame,
forecasting breezy gusts across the Basin, Gorge, and Kittitas
Valleys at around 25 to 35 knots. Nothing to suggest at this time
a Wind Advisory is needed for this event.

The trough will eventually prograde to the east as we progress
through the short term. Skies will clear out, leading to some
effective radiation cooling at night. NBM currently displays mid
30s for Tues overnight but will need to monitor for trends for
possible freezing in the Foothills of the Blues and parts of the
Kittitas Valley. If confidence increases by tomorrow, a freeze
watch may be issued for these areas and any other regions that
may deem necessary. Other than that, not expecting any more precip
for the CWA in the short term after Monday mornings snow showers
in the mountain regions.

LONG TERM...Tuesday through Saturday...NWP guidance
suggests predominantly dry weather through much of Thursday. While a
weak shortwave trough is advertised for Tuesday, shortwave ridging
is the likely scenario Wednesday afternoon through most of Thursday.
Late Thursday through Saturday, ensemble guidance is favoring a
troughing pattern for the PacNW, but analysis of ensemble clusters
and current deterministic runs shows notable differences in pattern
details.

Near- or sub-freezing morning low temperatures appear possible
Tuesday, and to a lesser extent Wednesday and Thursday, across many
of our low-elevation areas. The highest chances will be in cold-
prone locations within the Yakima and Kittitas valleys as well as
the foothills of the Blue Mountains of OR/WA, and lower Columbia
Basin. NBM probabilities of freezing morning lows are highest for
Tuesday in the Kittitas Valley and portions of the foothills of the
northern Blue Mountains of OR (broadly 20-40% chance) with lower
chances elsewhere (5-15%). While a cool (ensemble-mean 850-mb temps
of -2 to +1C), dry (ensemble-mean PWATs of 0.2-0.4") air mass is
forecast for the region, the presence of the aforementioned
shortwave trough does introduce more uncertainty in efficient
radiational cooling. While NBM probabilities are currently quite low
(<10%) for freezing morning lows Wednesday and Thursday across the
lower elevations of our forecast area, shortwave ridging, mostly
clear conditions, and the dry air mass should present a locally
higher chance of freezing for cold-prone locations.

Uncertainty in details of the 500-mb pattern grows Friday and
Saturday, but some flavor of an upper-level trough is likely (>80%
chance) with locations ranging from just offshore of northern
California to inland northern Washington. Will note that the ECMWF
EFI does not show any signal climatologically atypical events at
this time. Plunkett/86

AVIATION...18Z TAFs...VFR conditions are likely (>70% chance) for
all sites through the period. A cold frontal passage this morning
has brought light rain to the region. This front, and any rain
chances, will push east of all sites by afternoon. Widespread gusty
westerly winds are forecast today before slackening overnight
through Sunday morning. Of note, there is a low chance (<30%) that
stratus will produce MVFR CIGs Sunday morning at BDN/RDM/PDT/ALW,
Plunkett/86

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  39  60  39  60 /   0   0  10  10
ALW  42  59  41  58 /   0  10  40  20
PSC  41  65  40  65 /   0   0  10   0
YKM  38  64  35  63 /   0   0   0   0
HRI  41  64  39  63 /   0   0  10   0
ELN  40  58  36  58 /   0   0  10   0
RDM  31  59  29  60 /   0   0   0   0
LGD  34  58  36  55 /   0   0  30  10
GCD  33  59  36  57 /   0   0  10   0
DLS  42  61  41  61 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Wind Advisory until 8 PM PDT this evening for WAZ026.

&&

$$

SHORT TERM...95
LONG TERM....86
AVIATION...77