Area Forecast Discussion

from: NWS Pendleton, OR

FXUS66 KPDT 180212

Area Forecast Discussion
National Weather Service Pendleton OR
712 PM PDT Sat Apr 17 2021

.SHORT TERM...Skies will remain clear tonight with lows mostly in
the 30s to lower 40s and light winds. Satellite indicating a
short wave and cold front moving south through BC this evening.
This system will be approaching the Pacific northwest Sunday. Main
impact will be increasing westerly winds ahead of the front in
the afternoon. It will be another mostly sunny warm day with highs
in the 70s to lower 80s. The cold front will move through the
forecast area Sun night with partly cloudy skies and gusty north
winds. May have a few showers over the Blues and Wallowa county in
the upslope flow. Also could see patchy blowing dust in the
Columbia basin. Much cooler Mon with highs in the 60s.


.PREV DISCUSSION... /issued 530 PM PDT Sat Apr 17 2021/

SHORT TERM...TONIGHT THROUGH MONDAY...An upper level ridge of
high pressure will continue to be over the region tonight through
tomorrow afternoon before weakening tomorrow evening. Warming and
dry conditions will continue into tomorrow afternoon, with
temperatures peaking in the upper 70s to mid 80s. Skies will
continue to be mostly clear tonight and through tomorrow
afternoon, though expect cloud cover to increase late Sunday ahead
of an approaching system.

The upper level ridge will weaken Sunday afternoon as an upper
level shortwave coupled with a dry back door cold front slides
south from Canada into the northern Plains and Rockies late Sunday
and Monday. Breezy westerly winds will develop tomorrow afternoon
in response to the approaching cold front, then turn to the
northeast behind cold front passage overnight Sunday. Most of the
precipitation with this system will be further east over ID/MT,
however, if any precipitation does occur it will likely be over
the Wallowas as the frontal boundary clips northeastern OR.
Frontal passage will also usher in cooler air into the region with
Monday afternoon temperatures 10 to 15 degrees cooler than

Monday, northeasterly winds will continue to be locally breezy
across the Columbia Basin and into central OR as surface pressure
gradients are slow to relax. Behind system passage early Monday, a
shortwave ejected from a deep low over the northern Pacific will
march west and approach the PacNW. This will continue to subdue
the upper level ridge over the eastern Pacific, while the inter-
mountain west will likely see increasing mid to high level cloud
cover increasing from west to east Monday evening through the
overnight hours. Lawhorn/82

LONG TERM...TUESDAY THROUGH FRIDAY...The extended period is
dominated by a large upper level low off the Aleutian Peninsula,
and its interaction with the ridge sitting offshore of the PacNW. A
couple shortwaves are able to sneak through as the ridge elongates
north-to-south Tuesday and Wednesday. There are some discrepancies
between models, mainly in the form of intensity and location of
incoming shortwaves. The GFS is the stronger result, bringing
slightly more moisture onshore and further north than that of the
ECMWF. The ECMWF instead slides all precipitation, albeit light, to
our south and west, keeping our area dry Tuesday and Wednesday.
Precipitation gets closer when viewing the GFS outcome, but stays
just to our south. The GFS moves the shortwave onshore along the OR
coast whereas the ECMWF pushes it onshore along the northern CA
coast. GFS ensembles also hint at some lingering moisture Wednesday
and early Thursday, especially in the mountains. However, this
precipitation is dialed back and not nearly as prevalent in the
deterministic product. Observing the ensemble clusters, the ECMWF
ensembles are fairly consistent at an increased influence from the
CONUS upper level trough to allow a steeper axis associated with the
offshore ridge. This is the reasoning behind a wetter GFS outcome,
as a more west-northwest flow occurs instead of a north-northwest
flow with the ECMWF. The cluster phase space also shows less of an
ensemble spread and closer ensemble and deterministic means with the
ECMWF versus the GFS. The shortwave trough then continues east,
keeping precipitation to our south as it moves into the Wasatch

The upper level ridge then builds in from offshore Thursday,
providing dry and warm conditions. A warming trend commences Tuesday
before cooler temperatures return Thursday and bottom-out over the
weekend. 75

AVIATION...00Z Tafs. Clear skies tonight into Sunday
morning. Cirrus increasing in the afternoon. Winds 5-10kt tonight
increasing to 10-15kt Sun morning and 15-25kt by afternoon.


PDT  40  79  41  64 /   0   0   0   0
ALW  41  80  42  66 /   0   0  10   0
PSC  35  83  47  69 /   0   0  10   0
YKM  37  82  45  68 /   0   0  10   0
HRI  37  83  45  69 /   0   0   0   0
ELN  37  78  40  64 /   0   0  10   0
RDM  32  77  37  66 /   0   0   0   0
LGD  34  73  40  60 /   0   0   0   0
GCD  35  74  42  64 /   0   0   0   0
DLS  42  82  48  71 /   0   0   0   0





NWS PDT Office Area Forecast Discussion