Area Forecast Discussion
Issued by NWS Pendleton, OR

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000
FXUS66 KPDT 190518
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1018 PM PDT Mon Mar 18 2024

Updated Aviation Discussion

.AVIATION...06Z TAFs...VFR conditions expected over the next 24
hours. SKC or some rare high clouds possible. Winds 10 knots or
less overnight, becoming breezy DLS tomorrow afternoon with gusts
briefly up to around 20-25 knots possible. Other sites may see
some gusts 10-15 knots but shouldn`t be frequent. Goatley/87


&&

PREV DISCUSSION... /issued 226 PM PDT Mon Mar 18 2024/

SHORT TERM...Tonight through Wednesday...The strong upper level
ridge of high pressure over the region will begin to weaken and move
southward on Tuesday. Conditions will stay dry and well above normal
temperatures through Tuesday. By Wednesday what`s left of the ridge
will stretch from the western Great Basin back up into the Pacific
Northwest leaving the forecast area under a southwest flow aloft.
Meanwhile, a series of weather systems in the eastern Pacific Ocean
will begin to consolidate into an upper level trough. One of these
small systems will get caught up in the southwest flow and approach
the Pacific Northwest Wednesday. The main focus for precipitation
will be from the Cascade westward late Tuesday and overnight.
However, models are indicating some instability over far eastern
Oregon in the late afternoon through evening that will produce some
showers along with a low chance (10-15%) of thunderstorms. This
system will also increase the west to east pressure gradient across
the region Wednesday resulting in some breezy winds and temperatures
cooler by 5 to 10 degrees but still above normal.

LONG TERM...Thursday through Saturday...Starting Thursday morning
into Friday morning, a upper-level ridge exits eastward over
PacNW as the closed low continues moving near the Oregon coast
with widespread precipitation. By Saturday morning, that closed
low will be near the Oregon coastline as precipitation impacts the
forecast area. Breezy conditions may develop for Thursday morning
into Thursday night in the Columbia Basin (70% confidence). The
ECWMF continues to favor wet conditions sooner Thursday into
Friday morning while GFS shows mainly dry conditions until
Saturday morning when the GFS becomes wetter than ECWMF. That
being said, confidence remains low due to difference in timing
with precipitation (50%).

Small uncertainty within the models showing a prominent ridge
whereas the cluster analysis shows a weak ridge that is appearing
zonal. But overall, both ensemble means and deterministic models
remain in good agreement with the evolution and direction of the
trough (70% confidence). Temperatures will remain above normal with
high EFI of 0.7-0.90, showing an anomalous event for maximum
temperatures within the forecast area for Thursday. Snow levels will
be upwards to 3900-5200ft by Thursday morning but increases to 4000-
6000ft Friday into Saturday morning while the closed low moves near
PacNW with widespread precipitation. This is also due to the
southwesterly flow aloft bringing in moisture advection. Feaster/97

Saturday through Monday...Cooler and wet conditions will prevail
next weekend as ensemble guidance is in strong agreement on the
region being enveloped by low pressure. This low will emerge from
the central Pacific before merging with a trough over BC, allowing
for cooler temps to advect in and widespread PoPs to prevail through
the period.

NBM probabilistic QPF this far out it actually suggesting a decently
wet system, with about a 50-65% chance of 24-hr QPF exceeding 0.1
inches by Sunday morning across the lower Basin and even central
Oregon, and about 25-40% for over a quarter of an inch by the end of
the weekend. Snow levels will generally be on the warmer end at
around 3500-4500 on Saturday and 2500-3500 ft on Sunday. As a
result, not expecting much in the way as far as snow impacts are
concerned at pass level, but some accumulations may occur during the
latter half of the period when temps are cooler (confidence around
30%).

Once the low passes through, ensembles start to diverge in solutions
as the pattern turns more progressive. Overall trend, however,
appears to favor cooler than average temps (low 50s for highs across
our population centers) and persistent chances for PoPs through the
weekend heading into early next week, with Saturday looking to be
the wettest day of the period. Evans/74

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  39  71  43  68 /   0   0   0  10
ALW  41  74  50  70 /   0   0   0  10
PSC  41  77  48  72 /   0   0   0   0
YKM  40  76  42  70 /   0   0   0   0
HRI  40  77  47  69 /   0   0   0   0
ELN  37  74  41  67 /   0   0   0   0
RDM  36  73  40  64 /   0   0   0  10
LGD  37  72  44  70 /   0   0   0  20
GCD  37  72  42  70 /   0   0   0  20
DLS  43  76  47  66 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

$$

SHORT TERM...91
LONG TERM....74/97
AVIATION...87


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