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Area forecast discussion..updated 
National Weather Service Pendleton or
930 PM PST Thursday Jan 29 2015

Updated aviation discussion

Update...a weak upper level low has formed near The Dalles. This
low will drift south overnight as an upper level ridge builds into
Washington. Some light drizzle is possible in central Oregon
overnight as the low drifts south. The low has weakened the surface
inversions over the lower Columbia Basin so that the base of the
stratus lifted this afternoon. This has kept the fog patchy this
evening. As this low moves south overnight the surface inversions
will strengthen again tomorrow morning. However the fog will
probably remain patchy I do not expect to issue any
dense fog advisories. As the ridge rebuilds tomorrow fog will
become more widespread. Coonfield


Aviation...06z tafs...low stratus and mist is currently affecting
all taf sites and will continue to do so over the next 24 hours.
Ceilings/visible are expected to lower slightly overnight with LIFR/IFR
conditions possible at all taf sites. Worst conditions will be at
kbnd and krdm Friday morning. There will likely be some fluctuations
in the ceilings/visible at krdm and kbdn as weak disturbance moves south.
Kbdn and possibly krdm may break out of the fog/stratus Friday
afternoon. Other taf sites will have some gradual improvement after
18z Friday...with most taf sites rising into high end IFR or low end
MVFR ceilings between 800-1800 feet above ground level. Winds are forecast to remain
light. 76


Previous disc... /issued 340 PM PST Thursday Jan 29 2015/

Short term...tonight through Sunday. Low clouds and fog will
persist across the lower Columbia Basin and surrounding areas and
also over valley locations. Meanwhile a ridge of high pressure will
continue to build into the two state area with dry conditions
expected into Saturday. Locations where there are no clouds
afternoon high temperatures will be above normal. Otherwise a low
pressure system will approach the pacnw this weekend with increasing
clouds and showers are expected Sunday afternoon.

Long term...Sunday night through Thursday night...the period starts
off rather active with several storm systems bringing periods of
rain and mountain snow for Sunday night through Tuesday
morning...went high chance to lower end likely probability of precipitation for this time.
Snow levels are forecast to be between 3500 to 5500 feet during
the day...and 2000 to 4000 feet at night from Sunday night through
Tuesday...therefore higher elevation accumulating snow is a
possibility. After this a weak...transient upper ridge builds into
the region Tuesday afternoon into Wednesday...this should bring a
drier northwest flow into the area. By the middle of next week model
differences become more apparent...with both the timing and strength
of the next potential system in question. The 29/12z European model (ecmwf) is faster
bringing more moisture into the region associated with a warm front
by Wednesday afternoon while the 29/12z GFS allows this system to
pass by too far into the Pacific with just some scattered showers
arriving Wednesday night into Thursday. With the uncertainty decided
to take a blend of the guidance which yielded slight chance probability of precipitation in
the lower elevations and chance probability of precipitation for rain/snow in the mountains.
Through much of the extended period temperatures are forecast to
remain at above average any Arctic or modified Arctic
air remains along and east of the Continental Divide. 77


Preliminary point temps/pops...
PDT 32 39 30 41 / 10 0 0 10
alw 35 40 33 41 / 10 10 0 10
psc 33 40 31 41 / 0 10 0 10
ykm 31 40 29 40 / 0 0 0 10
hri 33 41 31 42 / 0 0 0 0
eln 30 40 29 41 / 0 0 0 10
rdm 29 48 27 50 / 0 0 0 0
lgd 29 46 28 45 / 10 0 0 10
gcd 29 49 27 49 / 10 0 0 0
dls 36 44 34 45 / 10 0 0 10


PDT watches/warnings/advisories...

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