233
FXUS66 KPDT 101123
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
422 AM PDT Fri May 10 2024

Updated aviation discussion

.SHORT TERM...Today through Sunday night  A ridge of high pressure
continues to dominate over the region and will continue through the
majority of the weekend. A weak shortwave will make its way across
the upper level ridge breaking it down slightly bringing more
seasonable temperatures back to the forecast area. Dry conditions
will dominate even under the influence of shortwave makes its way
across the WA Sunday evening.

Models are in firm agreement with the upper level ridge over the
forecast area with an upper level low still over the Four Corners
remaining in tact through Sunday evening. This synoptic pattern has
caused and will continue to cause the ridge to strengthen into what
is called a Rex blocking pattern. This will bring dry and warming
conditions through Saturday with temperatures reaching 15-20 degrees
above normal by Saturday. High confidence in the forecast for
temperatures cresting 90s with raw ensembles showing a 80%
probabilities for the Columbia Basin and adjacent valleys, 60-70%
for the lower Columbia Basin and the foothills of the Blues and the
Gorge seeing temperatures in the mid to upper 80s.

Sunday evening the models begin to show a weak shortwave making its
way across the upper level ridge. This will cause a slight breakdown
shifting the upper level flow to a more westerly component and
increasing the winds, cooling the temperatures slightly and bringing
a less 20% probabilities of rain to the far northern portion of WA
Cascades. Otherwise, the remaining portions of the region will
remain under dry and warm conditions with over 90% of raw ensembles
showing the temperatures to be in the mid to upper 80s across the
majority of the CWA with the higher elevations in the mid 60s to
70s. Winds are expected to increase as the cross Cascade gradient
increases with the shift of the upper level flow. Ensembles show a
greater than 60% probability of the lower Columbia Basin seeing
sustained winds of 25 mph, 75-85% for the Simcoe Highlands and the
Gorge, and over 90% for the Kittitas and Yakima Valleys.

With the rise in temperatures, guidance has begun to pick up on a
slight heat risk for Saturday through portions of the Columbia
Basin. If you are outside on Saturday enjoying the warmth, please be
mindful and wear sunscreen, drink plenty of fluids and remember that
the rivers will be fast flowing and still dangerously cold.
Bennese/90

.LONG TERM...Monday through Friday...Model agreement looks good
through the first of the week with a weak shortwave passage Monday
followed by the rebuilding of the ridge in the wake of its
departure. However, from midweek onward uncertainty increases in
both the ensemble and deterministic models as to whether the ridge
will persist or a westerly flow develops and allows another trough
passage late in the week. 00Z deterministic models highlight this
uncertainty by having flipped in the past 24 hours. The GFS now
builds a ridge over the western USA while the EMCWF has a trough
passage occurring on Thursday which is the exact opposite from
yesterday. Ensemble models also showing the differing solutions but
to a lesser degree in the amplitude of the trough on Thursday.
Overall this is causing the NBM to play middle of the road
forecasting. Example, Thursday high temperatures probabilities range
from mid 60s to mid 80s with actual forecasted highs in the mid 70s.
Same for the chance of precipitation as it could either be dry or
chance of precipitation, the NBM splits the difference with a slight
chance of precipitation.

So, current extended forecast will see cooler temperatures on Monday
by 5 to 10 degrees as the trough passage ushers in some cold air
advection. This produces some breezy to windy conditions which could
reach wind advisory levels across portions of the Lower Columbia
Basin. Could also see a few showers along the crest of the Cascades.
Tuesday will see a reduction of the winds to just breezy and overall
dry conditions as the trough departs and ridging begins to rebuild
over the region. Beyond this point the high degree of uncertainly
brings forecast confidence level to low. Will hold onto the NBM`s
middle of the road temperature forecast but have under cut the NBM
POPs restricting it to just a slight chance of showers along the
Cascade crest late Wednesday through Friday.


&&

.AVIATION...06z TAFS...Little to no aviation impacts through the TAF
period as clear skies and light winds are expected.


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  79  51  84  55 /   0   0   0   0
ALW  82  55  87  60 /   0   0   0   0
PSC  85  55  91  57 /   0   0   0   0
YKM  85  52  90  52 /   0   0   0   0
HRI  85  53  90  58 /   0   0   0   0
ELN  84  53  87  54 /   0   0   0   0
RDM  78  46  82  47 /   0   0   0   0
LGD  76  49  80  50 /   0   0   0   0
GCD  77  48  81  49 /   0   0   0   0
DLS  86  57  90  57 /   0   0   0   0

&&

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

$$

SHORT TERM...90
LONG TERM....91
AVIATION...80