Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 291821

Area Forecast Discussion
National Weather Service Pendleton OR
1021 AM PST Thu Feb 29 2024

Updated Aviation Discussion

.AVIATION...18Z TAFS...Rain and snow will be the
highlights for most sites due to the cold front having passed
through the PacNW, except for KYKM. Though, rain may be expected to
continue through afternoon as well but confidence is low on that due
to coverage (30-40%). KRDM and KBDN are currently varying between
MVFR and IFR/LIFR during the morning with low VSBYs and CIGs because
of snow. However, conditions could improve later in the afternoon
for both sites but with snow continuing at KBDN. Moderate winds with
gusts at 20-30kts will be prevailing for most sites with the
exception of KDLS where they decrease later in the afternoon.


Current forecast looks on track overall, but made some adjustments
to temperature based on current observations and latest guidance.
Otherwise, all winter storm warning headlines remain in effect
unchanged, and several wind advisory headlines were canceled
earlier with others remaining until 4 PM this afternoon. Will look
at additional information and determine if any of those advisories
can be adjusted.


.PREV DISCUSSION... /issued 211 AM PST Thu Feb 29 2024/

SHORT TERM...Today through Saturday… Current radar shows the bulk of
the precipitation to still be along the mountains to the west of the
Cascades. Current web cameras across the Blues show bare pavement
and ground observations show very little precipitation has fallen.
Much of the precipitation is across the Cascades ahead of the
incoming cold front. Ground observations show the max wind gusts
across portions of the area to be well within the advisory domain
with locations showing 45 plus mph gusts occurring. Winds will
remain elevated overnight and through tomorrow. There will be a lull
in precipitation across the forecast area through the early morning
ahead of the cold front however, once the cold front passes, not
only will there be another increase in the winds across the area but
an increase in snow accumulations across both the Cascades and then
the Blue Mountains. Winter storm warnings remain in effect along
the Cascades as well as the Blue mountains and wind advisories
remain across central, north central OR, the foothills of the
northern and southern Blues, Yakima Valley, lower Columbia Basin
and the Grande Ronde Valley through the end of the day.

Models are in firm agreement with the cold front making its way
across the Cascades bringing with it precipitation. Looking at the
raw ensembles, over 80% show an additional 5-7 inches along the
Cascades with higher amounts at the peaks and over 70% show the
higher peaks of the Blue Mountains seeing and additional 5-6 inches.
70% of the ensembles show the I-84 corridor will see another 2-3
inches. Snow levels will remain above 4500 ft across the Blues to
start and will begin to decrease through the day to below 2000 ft
thanks to the cold front bringing cooler temperatures behind it.
Temperatures today will be in the low to mid 40s with over 50% of
the raw ensembles in agreement, the Basin will see mid to upper 40s
with over 70% agreement, central and north central OR will see mid
to upper 30s with 65% agreement and lastly, the peaks will see low
to mid 30s with 55% agreement. The highest temperatures have
actually occurred late this evening thanks to the southerly flow
aloft causing downsloping winds. Adiabatic warming is causing a rise
in temperature this evening. Ground obs show the current temperature
to be 56 here at the office. Winds will also continue to be windy
through the day affecting primarily the southern and northern Blues,
John-Day Basin, Grande Ronde Valley and Wallowa County with the
strongest winds occurring at the base of the mountains with
sustained winds of 25-35 mph with gusts to 55 mph. Confidence in the
winds materializing is high (80-90%).

Models continue to be in firm agreement on Friday with the upper
level system still making its way across the forecast area. Snowfall
will continue as the moisture continues to be ushered into the
region. Southwest flow aloft will aid in the moisture transport
along the eastern mountains. Ensembles continue to show another 4-6
inches of snow along the Blue mountains with near 2 inches along the
I-84 corridor with over 55% agreement. 75-95% along the Cascades
showing an additional 4-6 inches with 90% showing an additional 3
inches along Snoqualmie Pass. Snow levels will vary from west to
east with the lowest levels along the WA Cascades steadily
increasing to only 1600 ft along the south eastern portion of the
region and temporarily increase to between 1600-2000 ft during the
day before decreasing to below 1200ft. 55% of the raw ensembles show
high temperatures Friday to be in the low to mid 40s across the
region with isolated locations in the Basin seeing low 50s while the
upper terrains see mid to upper 20s. Winds will continue to be
breezy but will no longer reach advisory criAVIATION...12Z
TAFS...Expecting mainly VFR conditions to prevail through the
period. A cold front passage will take place this morning producing
some light rain with rain becoming snow at RDM/BDN between 14-18Z.
CIGS of bkn-ovc will mostly be AOA 4kft to 7kft AGL during cold
frontal passage and then improving. RDM/BDN could see brief time
with MVFR-IFR cigs and VIS due to light snow. Southerly winds of 12-
25kts with gusts 25-35kts will continue to impact sites through the
morning then transition to SW-W through the day. Lawhorn/82teria.

Models remain in agreement with the upper level system still
affecting the region sending rippling shortwave across the region.
This will continue to bring snow showers across the mountains and 30-
40% probabilities of low elevation rain to start the day before a
brief period of low level reprieve from precipitation. Saturday 70-
90% of the raw ensembles show snow accumulations along the Cascades
as well as the Blues to be between 2-3 additional inches with higher
amounts along the peaks. However, QPF amounts are very light with
little to no accumulations in the lower elevations. Snow levels will
be relatively low to start with below 600ft along the foothills of
the Cascades and 600-1000 ft across the Basin and the foothills of
the Blues through the western edge of Wallow County before dropping
below 500 ft region wide. Temperatures will be a bit cooler than
days past with over 60% of the raw ensembles showing much of the
region in the upper 30s to low 40s with some scattered upper 40s
through the Basin. Bennese/90

LONG TERM...Sunday through Thursday...Models continue to show good
agreement early in the long term but then timing and system
placement issues start to arise days 5 and 6 and periods beyond.

A large upper level trough will continue over the western USA Sunday
through Monday as it continues to slowly transition to the east
before the flow transitions to a westerly Tuesday through Friday.
Sunday and Monday will primarily be a cool and showery pattern with
some weak impulses passing through the trough helping to trigger and
enhance showers at times. Snow levels will remain low at roughly
1000 to 2000 feet but showers mean any significant snowfall would be
limited and confined to mountains with brief burst of heavy snowfall.
As mentioned, flow aloft transitions to westerly Tuesday following
the departure of the upper level trough. This transition will be
good for continued upslope showers into the Cascades and eastern
mountains but an overall decrease in showers across the rest of the
forecast area. However, it is during this time that models begin to
show differing solutions with placement and timing of features thus
lowering forecast confidence going into Wednesday and beyond.
Ensemble models continue to show a progressive westerly flow
Wednesday and Thursday with a some semblance of a flat trough.
However, deterministic models show varying amplitude of this trough
with the GFS dropping storm energy all the way south into southern
California by late Wednesday and Thursday while the ECMWF does the
same but about 24 hours later. The NBM does its best to stay on top
of this by maintaining some low pops Wednesday and Thursday which
seems reasonable.


PDT  47  31  45  30 /  80  20  40  40
ALW  50  33  45  33 /  90  30  50  50
PSC  54  34  49  34 /  60  10  30  30
YKM  45  28  44  27 /  20  30  40  30
HRI  49  34  49  32 /  70  10  30  40
ELN  45  27  40  26 /  30  40  50  30
RDM  40  27  37  24 /  90  40  50  50
LGD  46  27  41  28 /  90  50  60  60
GCD  47  27  38  25 /  80  40  70  70
DLS  45  32  44  29 /  80  60  60  50


OR...Wind Advisory until 4 PM PST this afternoon for ORZ049-050-505.

     Winter Storm Warning until 4 PM PST this afternoon for ORZ502.

     Winter Storm Warning until 4 AM PST Friday for ORZ509.

WA...Winter Storm Warning until 4 PM PST this afternoon for Waz030-



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