849
FXUS66 KPDT 221614
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
914 AM PDT Wed May 22 2024

.UPDATE...Several advisory level wind gusts have occurred at the
Pendleton airport this morning, which has warranted the extension
of the Wind Advisory to include the foothills of the Northern Blue
Mountains of Oregon through 5 PM this afternoon. The pressure
gradient is forecast to tighten as guidance is in agreement with
increasing winds through the early afternoon along the foothills
as gusts of up to 50 mph will be possible. Otherwise, the early
morning forecast package is on track and few edits were done with
this morning`s update in regards to wind speeds along the
foothills. 75


&&

.PREV DISCUSSION... /issued 412 AM PDT Wed May 22 2024/

SHORT TERM...Today through Friday...Satellite and radar imagery
tonight shows the remnants of a warm front exiting into ID, with
the associated broad band of precipitation draped across far
eastern WA/OR. Behind this band of precip, cloud cover is becoming
partly cloudy as water vapor shows a dry slot at the bottom of a
closed upper low working it`s way into north central OR and south
central WA.

Today, the aforementioned upper closed low will drop southeast
across the PacNW then exit into central ID later this evening,
providing another active weather day across the forecast area.
While precipitation yesterday was more stratiform, the combination
of the upper low overhead and increasing surface instability will
result in mostly showers through the evening hours. In the
mountains, snow levels will be dropping to between 4.5kft-5kft,
allowing showers at and above these elevations to consist of
mostly snow or a rain/snow mix. Heaviest snow amounts (6+ inches)
will be concentrated along the higher peaks across the Strawberry
mountains, Wallowas, and the peaks along the Cascade
crest(confidence 50-60%). Lighter amounts between 2-4 inches will
accumulate in areas of the northern Blues from Tollgate north, as
well as the central WA Cascades(confidence 40-50%). Increasing
surface based instability and modest low level lapse rates will
also provide enough forcing for isolated thunderstorms to develop
in the Columbia Basin and the eastern mountains by the afternoon.
Also to note, the cold core of the low aloft will also allow for
graupel to be mixed in with the rain showers in the lower
elevations. Westerly winds will be increasing through this
morning into the afternoon across the much of the forecast area
today, with high confidence (75-85%) of wind speeds 20-35mph and
gusts 30-50mph, in which the strongest winds will be felt through
the OR Columbia Basin and southern Blue mountain foothills where
wind advisories are in effect.

Late tonight through Friday morning, a drier northwest turning
west flow will be settling across the PacNW resulting in
widespread dry conditions through this period. That said, wrap-
around moisture from the departing low will continue to aid in
development of light rain/snow showers across Wallowa county into
Thursday morning.

Precipitation chances will return to the PacNW throughout Friday
as a shortwave trough slides along the BC coast and across the
region. Shower chances will mainly be confined to the mountain
areas and immediate foothills throughout the day, while dry
conditions will persist across the lower elevations. Rain amounts
will be fairly light for Friday, with NBM probabilities only
showing a 40-50% chance of 0.1 inches across the Cascade crest,
northern Blues, and Wallowas. Modest cross-Cascade pressure
gradients will result in breezy winds between 15-25mph and gusts
up to 35mph developing through the Cascade gaps Friday, and
locally breezy conditions across the lower elevations. Lawhorn/82

LONG TERM...Saturday through Wednesday...The forecast starts out
with some uncertainty on Saturday in the location/track of an upper
level low that will have an impact on the Pacific Northwest Weather.
The GFS moves the low across Oregon while the ECMWF keeps it in
southern Canada. The ensemble clusters favor a track more across
Washington. Utilized the NBM for this forecast and it is producing a
30-40% chance of mountain showers for Saturday and 5-15% POPS
elsewhere. There is a slim chance of thunderstorms (10-15%)over the
eastern mountains Saturday afternoon but this chance will fluctuate
based on the eventual track of the upper low, with higher
probabilities with a more southern track. Regardless of the scenario
surface based CAPE will be rather low (200 J/kg or less) so strong
storms are not expected. QPF outside of locally heavier showers
will be light with 50th percentile amounts from the NBM averaging
05-.10 inches.

There is also the potential for breezy to windy west winds across
the lower elevations especially the Cascade gaps on Saturday
afternoon and evening. The NBM has a 20-40% chance for winds
exceeding 45 mph in these areas Saturday afternoon. One of the
windiest areas will be the Kittitas Valley. Most of the the 50 ECMWF
ensemble members are forecasting peak wind gusts of 35-45 mph with a
mean value of 40 mph Saturday afternoon at KELN.

Once this weather system exits the region dry westerly flow will be
over the region on Sunday and then the ensemble clusters are in
general agreement that an upper level ridge will build northward
centered roughly over the Rockies through Tuesday. This will result
in a warming trend with high temperatures peaking Tuesday in the mid
to upper 80s in the Columbia Basin. By Tuesday night and Wednesday
there is considerable uncertainty in the pattern over our region
with the clusters ranging from flat SWLY flow to a deep upper trough
along the PACNW coast. The NBM increase pops to 10-20% across the
lowlands and 20-30% across the mountains beginning Tuesday night.

AVIATION...12Z TAFS...VFR conditions will prevail through the
period with CIGS BKN-OVC 035-070 AGL. Beginning around 18Z and
lasting until 03-05Z -SHRA will impact the KPSC, KALW, and KPDT
terminals. Latest HREF guidance is showing a 50% chance of TSTMS at
KPDT so have included VCTS in the TAF from 22-02Z. Winds will
increase quickly at all sites after sunrise with 15-22 kt sustained
winds and gusts 25-32 kt. Winds will tend to decrease late this
afternoon and evening. 78

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  55  41  65  42 /  70  70   0   0
ALW  57  44  68  47 /  70  40  10   0
PSC  63  49  73  50 /  50  30   0   0
YKM  60  43  73  45 /  30  20  10   0
HRI  60  45  72  46 /  60  60   0   0
ELN  55  43  68  43 /  30  10  10   0
RDM  51  32  64  38 /  20  10   0   0
LGD  51  39  61  39 /  80  60  10   0
GCD  50  37  60  38 /  80  80  10   0
DLS  60  47  70  48 /  50  10   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 5 PM PDT this afternoon for ORZ044-507-508.

WA...None.
&&

$$

UPDATE...75


&&

.SHORT TERM...

.LONG TERM...


&&

.AVIATION...
SHORT TERM...82
LONG TERM....78
AVIATION...78