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Area forecast discussion
National Weather Service Pendleton or
410 am PST Thu Nov 23 2017

Update...a Flood Watch was issued for Washington zone 520--the east
slopes of the Washington Cascades--in effect through this evening.
Automated sites have measured 1.5-2.0 inches of rain over the past
couple of days. A weather spotter submitted photos on facebook of
Trout Lake creek running high and fast. Sharp rises have also
occurred on the Klickitat river near Glenwood. Additional rainfall
amounts near 0.5 inch today may cause minor flooding.

&&

Short term...today through Saturday. Happy Thanksgiving!
Temperatures yesterday were about 15-20 degrees above seasonal
average. It will be warm again today with highs ranging from the
mid 50s to mid 60s for most of the area--not quite records but
close. It will be another day with a moist southwest flow aloft and
widespread rain. The lower Columbia Basin and the Yakima Valley may
miss out on the precipitation due to rain shadowing off the
Cascades. Rainfall amounts will range from a few hundredths to a
quarter of an inch--locally 0.25-0.5 inch along the east slopes of
the Cascades and the Blue Mountains. The Naches River has risen to
near bankfull, and other rivers and streams have likely experienced
sharp rises as well. Precipitation will taper off tonight, and snow
levels will lower to 4000-5000 feet, limiting additional snowmelt
runoff. The cold front tracking south-southeast across Washington
and Oregon late this afternoon and evening will have strong winds
aloft associated with it. Because the winds are mainly parallel to
the cold front with no strong indication of isentropic descent, I do
not expect winds to meet advisory criteria. Surface winds today
will be 20-30 mph gusting to 40 mph for many areas, but exposed
ridgetops will have stronger wind gusts.

No major weather concerns are anticipated Friday and Friday night.
Western Washington will see numerous showers, and some of the
precipitation will spill over to the east slopes. Snow levels will
be around 3500 feet Friday and Friday night in this area. I-90
through Snoqualmie Pass is mainly 2000-2700 feet from Easton
eastward to Ellensburg, therefore Holiday travelers will likely
experience rain rather than snow. On Saturday, the next front will
arrive from the southwest associated with a strong surface low
tracking north along the coast. Rain and mountain snow will be
widespread across central and north central Oregon during the day
with a chance of rain and mountain snow elsewhere. Snow levels will
increase during the day, and any snow during the afternoon will
mainly occur in the higher elevations. The Grande Ronde Valley and
a few areas along the Blue Mountain foothills and near Long Creek
will observe southerly winds gusting to 40-45 mph. Wister

Long term...Saturday night through Thursday...long range models are
in fairly good agreement in the weather pattern of troughs and
ridges through Tuesday. An upper ridge will persist over the region,
with the ridge axis just east of the County Warning Area Saturday night through
Sunday night. There will be an abundant amount of moisture riding up
and over the ridge across the County Warning Area for periods of rain. The best
chances for rain will be over western areas of the County Warning Area Saturday
night and then the best chance will shift eastward to the eastern
portions of the County Warning Area on Sunday with a warm front moving across the
County Warning Area. Can expect a decent amount of quantitative precipitation forecast from this warm front...along
with mild temperatures for late November. After that an upper trough
off the coast will move inland with a cold front on Monday. There
will be a period of rain or rain showers with this cold front. Will
need to keep an eye on rivers and streams in case of possible
flooding or high water. After this cold front an upper ridge will
rebuild over the region, which will bring drier conditions from
Monday night Onward. However the long range models begin to differ
from each other during this later time. Due to the uncertainty will
leave at slight chance to chance of rain over the mountains through
the rest of the long term period. It will be breezy to windy at
times...especially over the ridge tops with above normal
temperatures through the period...though snow levels will lower
during the latter part of the extended period...but still above
normal. 88

&&

Aviation...12z tafs...MVFR and possibly IFR conditions may occur
over the area...especially at tafs krdm...kbdn...kpdt and kalw due
to lowered cigs and visibility in rain...fog or mist. Conditions
will improve by late tonight as an upper ridge builds over the
region...though during this time of year under a ridge there may be
areas of fog or low stratus which may continue to cause MVFR or IFR
conditions at times and colder temperatures. It will be breezy to
windy today into this evening...and then diminishing wind late
tonight. However winds will remain just below advisory speeds...at
least at this time. 88

&&

Preliminary point temps/pops...
PDT 64 41 53 36 / 70 40 0 0
alw 64 42 54 39 / 80 30 0 10
psc 65 40 55 36 / 20 10 0 10
ykm 59 36 51 33 / 20 10 10 10
hri 63 39 55 35 / 30 20 0 0
eln 56 34 48 32 / 40 10 10 10
rdm 62 33 52 32 / 50 40 10 0
lgd 60 37 50 36 / 70 70 10 0
gcd 61 39 50 37 / 50 70 10 0
dls 62 40 55 38 / 70 40 10 10

&&

PDT watches/warnings/advisories...
or...none.
Washington...Flood Watch through this evening for waz520.

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