Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus66 kpdt 261626 

Area forecast discussion
National Weather Service Pendleton or
926 am PDT Wed Apr 26 2017

Short and tonight...a fast moving zonal flow over the
region today with a weather system passing. This system will bring
rain to the forecast area through the morning then we will see
increasing westerly winds from midday through overnight.
Precipitation will taper off when the winds kick in but continue to
see some upslope showers into the Blue Mountains through the night.
Snow levels will be 4000 to 5000 feet today lowering to 3000 to 3500
overnight. This will mean 1 to 3 inches of snow for portions of the
mountains overnight. The west winds will begin to increase midday
and continue into the overnight period when they will reach their
peak. Wind advisories have been issued for the Simcoe Highlands and
the Kittitas Valley but may need to add some other zones. Will make
this decision after the complete set of morning model runs come in.


Previous discussion... /issued 440 am PDT Wed Apr 26 2017/

Short through upper level storm system
is moving out of the County Warning Area this morning and another one is expected to
move into central or this morning. This will bring another round of
precipitation to eastern Washington and or. The precipitation will be
heaviest in Oregon. The snow levels will be 4500-6000 ft so most of
the precipitation will be rain. It will become windy/very windy
after the cold front passage this afternoon. Wind advisories have
been issued for the Kittitas Valley and Simcoe Highlands for gusty west-
northwest winds. Models have backed off on wind speeds across the lower
Columbia Basin, but I kept the wind speeds similar to the previous
forecast because models frequently underestimate how much winds mix
to the surface after a cold front passage. Upper level flow will
turn northwest this afternoon as a ridge builds offshore. Multiple
waves in the northwest flow will keep showery precipitation over the
area tonight and Thursday. Upslope regions of the eastern mountains
will get the most rain/snow. Snow levels will drop to 2500-3000 ft
by Thursday morning. However the showery precipitation will probably
not produce enough widespread snow to justify a winter advisory
though local accumulations may reach advisory criteria. This will
need to be monitored. Friday a drier northerly flow will develop
with decreasing chances for showers. Coonfield

Long term...Friday night through Tuesday. A weak transitory ridge
will push inland Friday night...and showers will end after midnight.
A dry forecast is in store Saturday...but showers will return
Saturday night when the ridge flattens and allows a Pacific front to
gradually travel south across WA/OR. A westerly flow will remain on
Sunday for continued showers but also breezy winds.
Models...particularly the European model (ecmwf)...are having some difficulty with a
shortwave trough progged to move south on Monday. The European model (ecmwf) has
been flip flopping on the strength...and the latest run dampens the
wave with little to no precipitation. Leaning towards the more
consistent GFS and Canadian with a stronger wave. However, rain and
mountain snow showers (snow levels around 4000-5000 feet) will
mainly develop along the Cascades and far northeast Oregon and
southeast Washington. The models are in agreement with an upper
level ridge building Tuesday and a highly amplitude ridge on
Wednesday. People wanting more sun and less rain will likely get
their wish Tuesday and Wednesday. Wister

Aviation...12z tafs. The forecast area is between fronts at this
time with the next front spreading precipitation across eastern or
this morning then southeast Washington this afternoon. Ceilings are currently
VFR with bases around 4k-10k ft above ground level. Confidence is fairly high that
light to moderate rain will occasionally bring ceilings/visibility down to
MVFR at kalw and kpdt...and this was included in the 12z tafs. Kdls,
kykm and kpsc may see little to no rainfall with this upcoming front
and will remain VFR for the next 24 hours. Krdm and kbdn should
remain VFR but light rain may briefly lower ceilings to MVFR. The main
aviation concern will be the increasing wind. SW-west winds increasing
to 15-25 knots with gust 25-35 knots are expected at all taf
sites this afternoon and evening...possibly overnight. Wister


Preliminary point temps/pops...
PDT 56 41 55 37 / 80 20 30 30
alw 58 44 58 42 / 80 30 30 30
psc 63 44 63 41 / 40 10 10 20
ykm 62 40 61 37 / 30 0 10 10
hri 61 43 60 41 / 60 10 20 20
eln 58 39 56 38 / 20 10 10 10
rdm 52 29 51 24 / 90 10 30 30
lgd 51 38 50 35 / 100 50 40 40
gcd 49 34 48 28 / 100 30 50 60
dls 59 44 58 42 / 80 10 30 20


PDT watches/warnings/advisories...
Washington...Wind Advisory until 9 PM PDT Thursday for waz026-521.

National Weather Service Glossary of Abbreviations