Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 130517
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1016 PM PDT Tue Mar 12 2024

Updated aviation discussion

Update...A northwest flow continues over the region as the upper
level trough slowly moves off to the east. Showers are decreasing
with the loss of the suns heating and confined mainly to the
mountains where a winter weather advisory for the Cascades remain in
effect until 11pm. Winds remain breezy but will gradually decrease
overnight. An upper level ridge will begin building into the region
Wednesday as we head into some warm Spring conditions through the
rest of the week. Just expecting some lingering showers over the far
eastern mountains through Wednesday afternoon.

.SHORT TERM...Tonight through Friday night...Main concerns exist
over the next 6-12 hours between snow and convective rain showers.
Latest radar display shows convective showers with a cloud flash
reported by ground-based networks and GLM denoting lightning
activity across the Northern Blues near the WA/OR border over the
last 30 minutes. Roughly 250+ J/kg of MUCAPE in place per the
latest mesoanalysis. Current thinking is the threat for any
lightning will be confined to this area, Northern Blues south to
northern Grant county east, owing to best supporting orographic
ascent and the best mid-level lapse rates in excess of 7 C/km.
Still a concern that we could see a convectively enhanced wind
gust in excess of 45 mph if a storm can be realized farther west
where the best synoptically forced winds are. However, confidence
in that outcome is low (20-30%) and shrinking based on trends.

No change in headline with winter weather advisories ongoing
through 11 pm tonight. That said, the heaviest period of
accumulating snow has passed with an addition 1-4 inches possible
at Snoqualmie and Santiam passes, the latter likely on the lower-
end of that range. Confidence is high that cessation of meaningful
snow (using QPF > 0.05” per hour) will end around 03Z-06Z tonight
based on HREF probs (less than 30%).

Wind forecast for today appears on track. Moderate winds with
gusts of 30-40 mph ongoing at lower elevations. The only elevated
gusts have been at Rattlesnake mountain at around 3.5 kft with a
peak gust of 59 mph. The only other noteworthy gust was at a CWOP
in the southern foothills of the Blues that reported a peak gust
of 49 mph.

Looking ahead, PoPs will decrease appreciably over the small
hours tonight with dry conditions tomorrow through Friday night.
As the current upper trough over the PacNW dives southeast across
the Northern Intermountain West tonight, a amplifying upper-level
ridge is expected to take hold and dominant the sensible weather
Thursday onward. Weak ridging already apparent on water vapor
imagery will continue with a strong anomalous ridge expected to be
in place by Thursday. Of note, the mean EPS 500 mb forecasts
exceeds the 99th percentile and is greater than all values in
the model climate centered on a 3-week period over the offshore
waters of British Columbia. This anomalous upper ridge continues
to build with the highest heights centered over Vancouver Island
Friday extending north, and still exceeding all values in the
model climate. This will begin a warming and drying trend that
will persist into the next work week with highs near seasonable to
slightly above normal by Friday area-wide.

.LONG TERM...Saturday through Tuesday...The extended period is
characterized by a strong upper level ridge that extends across
the area through Monday, before beginning to weakening as an upper
level trough slides south along the British Columbia coast. This
provides dry conditions across the Pacific Northwest as a warming
trend will commence, with high temperatures likely pushing into
the low 70s for lower elevations of the Columbia Basin, Yakima
Valley, Eastern Gorge, Central Oregon, and along the Blue Mountain
foothills early in the workweek. The only other weather concern
during this period resides with breezy winds Tuesday afternoon and
evening along the Simcoe Highlands and the Blue
Mountains/foothills as pressure gradients tighten associated with
the approaching upper level trough.

Guidance and ensembles are in good agreement with the overall
pattern of a persistent ridge of high pressure over the area through
Monday, but differences do arise regarding the ridge`s strength and
how quickly it weakens into the beginning of the workweek. This is
visualized via the 500mb EOF Patterns, which depict a 35-44%
ensemble variance primarily related to the ridge`s strength over the
weekend. The largest ensemble difference occurs on Saturday, with
the ECMWF depicting a stronger ridge and area of high pressure than
the GFS or the CAN. This is associated with warmer conditions with
the ECMWF as the flow aloft would be more from the northeast rather
than from the north as with the GFS or CAN. This discrepancy
continues into the early part of the workweek as east and eventually
southerly flow is more enhanced with the stronger synoptic features
of the ECMWF. This also looks to keep the incoming trough on Tuesday
weaker and further north to allow continued warming midweek. The
cluster phase space shows additional confidence in the ECWMF
scenario, as ensemble members are more in-line with one another and
better represented by the deterministic solution. The NBM also
aligns with this warmer outcome as depicted by the ECMWF, with an 70-
90% chance of high temperatures of 70 degrees or higher along the
northern Blue Mountain foothills of Oregon, the Bend/Redmond/Madras
area, and across the southern Yakima Valley on Monday. The NBM also
shows a 60-70% chance of high temperatures reaching 70 degrees or
greater over Hermiston and the Tri-Cities area Monday afternoon.
Normally, our first high temperature of 70 degrees or higher is
attained in late March (March 23rd for Tri-Cities and March 26th for
Pendleton), so we are right on track to see that come to fruition.
75


&&

.AVIATION...06Z TAFS...Mostly clear around the Columbia Basin
but ramming partly cloudy over the mountains with a few showers
through late Tuesday afternoon then overall clearing Tuesday evening
and night. Some remaining SW winds 10-20Kts gusting 20-30Kts but
overall winds are on the decrease and will be 5-15kts by morning and
through the day.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  31  49  29  53 /  30   0   0   0
ALW  34  52  32  56 /  40   0   0   0
PSC  34  57  31  58 /  10   0   0   0
YKM  28  55  30  58 /  10   0   0   0
HRI  33  55  30  58 /  10   0   0   0
ELN  31  50  29  55 /  10   0   0   0
RDM  27  46  24  52 /  20   0   0   0
LGD  29  44  25  52 /  40   0   0   0
GCD  26  43  22  52 /  40  20   0   0
DLS  36  53  33  59 /  20   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 11 PM PDT this evening for ORZ509.

WA...Winter Weather Advisory until 11 PM PDT this evening for WAZ522.

&&

$$

SHORT TERM...80
LONG TERM....75
AVIATION...75


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