829
FXUS66 KPDT 051608
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
908 AM PDT Sun May 5 2024

.MORNING UPDATE...Water vapor imagery shows the center of an
upper-level low over southeast Oregon. Meanwhile, satellite and
radar both show a robust deformation band across north-
central/northeast Oregon into south-central/southeast Washington.
The main upper low is forecast to remain nearly stationary
through morning before pulling southeast through the afternoon and
evening, bringing a gradual end to precipitation to the lower
elevations. Upslope snow will continue for the mountains tonight
for the northern Blues and Wallowas with lesser amounts for the
Cascade crest.

The main update to the forecast this morning was to
increase forecast snow amounts for the southern Blue Mountains
today. ODOT and public reports show areas of 4-6, perhaps up to 8
inches have fallen overnight into this morning along OR-207 and
US-395, especially along upslope areas under the deformation band.
Have issued a Winter Weather Advisory for the southern Blue
Mountains until 2AM Monday morning; the bulk of forecast
additional snowfall amounts (3-7 inches below 4500 feet and 4-9
inches above 4500 feet) are expected this morning and afternoon
with precipitation tapering off this evening into the early
morning hours. Plunkett/86

&&

.PREV DISCUSSION... /issued 511 AM PDT Sun May 5 2024/

AVIATION...12Z TAFs...A mix of VFR to MVFR with isolated IFR
expected as SHRA continues across the region. Rain will linger the
longest across PSC/PDT/ALW, exiting by around 06Z. CIGs remain
between 1-5k feet, and will lift to around 3-5k feet as the
precipitation exits. Gusty winds all sites between 15-30 knots,
strongest PDT where gusts 30-35 knots expected. Winds should
weaken by around 06-09Z for DLS/BDN/RDM/YKM, but will remain gusty
for PSC/ALW/PDT through the entire period. Goatley/87

PREV DISCUSSION... /issued 326 AM PDT Sun May 5 2024/

SHORT TERM...Today through Tuesday...The center of the closed
upper level low is moving through NW Nevada this morning and will
be over SW Idaho by this afternoon. Moisture continues to wrap
around the low coming into eastern Oregon from Idaho mainly
impacting NE and north central Oregon and portions of southern
Washington. This will continue through the morning but as the low
moves towards SW Idaho this afternoon this moisture flow gets cut
off and leaving leftover moisture lingering over the forecast
area. As the low moves into Idaho this will allow a northwest flow
to push into the Pacific Northwest and begin to push the
lingering moisture eastward beginning this afternoon and
continuing overnight. This flow will maintain some showers along
the Cascade crest and portions of the east slopes. Meanwhile this
flow will place the Blue mountains under a favorable upslope flow
enhancing precipitation over the eastern mountains that begins to
taper off late tonight. This event is still on track to produce
some significant and beneficial precipitation amounts to the
forecast area today and overnight with the main focus now shifting
to the eastern portion of the forecast area, the Blue Mountain
Foothills and eastern mountains. Snow levels over central Oregon
will remain around 3000 to 4500 feet today with some more
accumulation snow accumulations in the mountains for which Winter
Weather Advisories continue. Snow levels over the eastern
mountains will lower tonight to around 3500 feet by Monday morning
meaning there will be some minor accumulation snow as well.

A shortwave in the northwest flow is expected to arrive on Monday
which will once again increase precipitation across the forecast
in the form of showers with a slight chance of thunderstorms
over the eastern mountains. This will be followed by linger
mountains showers on Tuesday that come to an end Tuesday night as
a ridge of high pressure begins to build into the region from the
west.

Other concern for today will be the increasing westerly winds
associated with exiting low pressure system and the developing
northwest flow. Expect westerly windy conditions to reach wind
advisory levels of 25 to 35 mph with gusts up to 50 mph across
north central Oregon from the Columbia River Gorge eastward to
the Foothills of the Blue Mountains. Winds will decrease slightly
tonight but still remain breezy to windy through Monday and
Tuesday with further issuances or extension of wind advisories
being possible..

LONG TERM...Wednesday through Sunday...Significant weather
concerns in the long term will be limited to warming temperatures
and dry conditions as high pressure becomes the primary weather
feature across our region.

In regards to the overall synoptic pattern, aforementioned high
pressure will be the primary feature of our region, though the low
pressure and troughing currently moving across today will have an
influence as well. Ensemble guidance indicates a ridge of high
pressure will begin moving over the PacNW on Wednesday, while low
pressure moves into the middle of the US. As the ridge continues
to stretch into the Northern Rockies and Canada on Thursday and
Friday, part of the low will separate from the primary source and
retrograde into a separate, weaker low over California/Nevada.
This will allow the ridge to continue strengthening over the PacNW
and possibly over the entire West Coast by the weekend. Primary
discrepancies in ensemble guidance revolve around the weak low
that moves back over California, as around 60% of the GFS members
have this low stronger than other ensemble guidance, even bringing
a portion of it into Southern Oregon, which would be a cooler
solution compared to other ensembles, but with the majority of
members including the multi-model ensemble indicating strong
ridging for the majority of the PacNW, this remains an outlier
solution.

With this synoptic pattern, expect a quick warming trend and dry
conditions through the long term. Temperatures on Wednesday should
still be on the cooler side, around 2-5 degrees below normal, but
rapidly become 2-5 degrees above normal on Thursday, and by the
weekend could be reaching as high as 10-20 degrees above normal.
The NBM indicates a 30-90% chance of highs greater than or equal
to 80 degrees next Saturday for our lower elevation zones, and a
30-50% chance of highs greater than or equal to 90 degrees for the
Columbia Basin by next Sunday. NWS HeatRisk values still only
show around a category 1, or minor, level of heat for our area,
primarily affecting those extremely sensitive to heat, especially
when outdoors, and heat-related highlights remain very low (less
than 5%). Goatley/87

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  49  41  57  38 / 100  70  70  30
ALW  52  43  59  41 / 100  90  70  30
PSC  59  46  64  44 /  90  40  30  10
YKM  62  39  62  37 /  20   0  20   0
HRI  56  43  62  42 / 100  40  40  10
ELN  58  41  56  37 /  10  10  20  10
RDM  49  34  52  30 /  10  20  60  30
LGD  46  37  52  36 / 100  90  90  60
GCD  43  34  51  33 / 100  80  90  80
DLS  58  45  57  44 /  10  40  60  20

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 11 PM PDT this evening for ORZ041-044-507-
     508-510.

     Winter Weather Advisory until 2 AM PDT Monday for ORZ503.

     Winter Weather Advisory until 11 PM PDT this evening for ORZ506.

     Winter Weather Advisory until 11 AM PDT this morning for ORZ509.

WA...Wind Advisory until 11 PM PDT this evening for WAZ024-026-521.

&&

$$

MORNING UPDATE...86
SHORT TERM...91
LONG TERM....87
AVIATION...87