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Area forecast discussion...updated
National Weather Service Pendleton or
428 am PDT Thu Oct 19 2017

Updated aviation discussion

Short term..today through Saturday...a very active weather pattern
will continue through the short term period. For today, a cold front
is slowly sliding south and east across the forecast area. This
front is already bringing rain along the east slopes of the Washington
Cascades early this morning. By midday, the rain will increase along
the Oregon east slopes and begin to spread into the eastern Columbia
Gorge, Yakima and Kittitas valleys. For the afternoon commute, rain
will be as far east as a line from about Richland--Boardman--Condon
and Prineville...the rain will continue to spread east over the rest
of the forecast area through the evening hours. 24 hour
precipitation amounts by 5am Friday will range from 1-3 inches along
the Cascade east slopes, one third to two thirds of an inch in the
Blue Mountains...with a general tenth to third of an inch in the
lower Columbia Basin and surrounding valleys. A Flash Flood Watch
remains in effect until early this evening for the east slopes of
the Washington Cascades, specifically the Jolly Mountain and Norse
Peak burn scar areas. Upwards of 0.50-0.75 inches of rain has
already fallen in these areas. The other story today will be the
increasing southwest winds just ahead of the front. Winds are
already gusting over 35 mph in the Yakima Valley early this morning,
with gusts to around 50+ mph reported along the higher ridgetops
nearby. An additional area of strong winds is expected to develop
across south-central Oregon into the ochoco-John Day Highlands. This
includes locations such as Bend, Sunriver and Paulina...as well as
the US-20 corridor in southeast Deschutes County. Winds in this area are
forecast to 20-30 mph, with gusts up to 45 mph this afternoon. This
could make travel difficult for high profile vehicles and could also
create localized patchy blowing dust. At this time, do not think
winds will reach High Wind Warning criteria...but this will need to
be watched closely in case conditions change. During the day on
Friday the County Warning Area will be under the upper level trough and associated
cold pool of air. This will cause instability showers to develop in
the strong, westerly upslope flow over the Blue Mountains and along
the Cascade crest. For the lower Columbia Basin and surrounding
valleys, expect mainly dry conditions, partly to mostly cloudy skies
and gusty west winds. Winds will be 20-30 mph, with gusts 35-40 mph
Friday afternoon for much of the area. A Wind Advisory may
eventually be needed for parts of the forecast area, if confidence
grows that these stronger winds will materialize. Temperatures will
be much cooler, with lower snow levels behind the departing cold
front. Look for highs only in the 50s to lower 60s...except upper
30s and 40s in the mountains. Snow levels will be around 4500 feet
in the afternoon, falling to 3500-4000 feet Friday night. The next
weather system quickly approaches and moves into the western half of
the County Warning Area late Friday night and early Saturday morning. This system
will bring a warm front through the region...allowing snow levels to
eventually rise in the late afternoon. However, as mentioned above
snow levels will be holding between about 3500-4500 feet Saturday
morning, as precipitation chances rapidly increase. This will mean
periods of rain and higher elevation snow will be likely through the
day Saturday, areawide. The cold wedge of air will become trapped
over the northern and eastern parts of the area. With a good shot of
warm air advection precip moving through, several inches of snow
will be possible in the mountains above 3500-4000 feet in Washington
and above 4000-4500 feet in Oregon. If temperature and snow levels
are indeed low enough, its possible some winter weather highlights
(advisories) may be need for some of our mountain zones. Again, this
situation will be closely monitored with future forecast updates.
The good news is, with the colder temperatures and lower snow
levels, this may at least delay any additional hydrologic concerns
into Saturday afternoon. 77

Long term...Saturday night through Wednesday...a warm front will
be moving northwest through the northeast part of the County Warning Area Saturday
night. Rain shadowing will begin in central or and south central Washington.
Snow levels will be 8000-9000 feet so precipitation will be mainly
rain. Sunday a cold front will move southeast across southeastern Washington
and eastern or. Saturday night and Sunday will be very wet over the
Cascades and eastern mountains where one to two inches or more of
rain will be possible. Sunday night moist westerly flow will
transition to drier northwest flow as an upper level ridge begins to
develop offshore. Rain will taper off during this period. The upper
level ridge will slowly shift east over Washington and or Monday night
through Tuesday evening or Wednesday. Subsidence from the ridge will
bring dry and warmer daytime conditions over the area. Light winds
and clear night will provide good radiational cooling at night.
Patchy late night and early morning is possible in the Columbia
Basin. Early Wednesday the European model (ecmwf) has flat westerly flow as a weak
front moves through the area. The GFS maintains the ridge. The GFS
ensembles range between the two solutions. I left the forecast dry
but the split in the models lowers confidence. Coonfield

&&

Aviation...12z tafs. Increasing clouds with cigs lowering
through the day. Rain spreading across area. Winds 10-25 knots except
at kdls 5-15 kt. 76

&&

Preliminary point temps/pops...
PDT 66 44 60 39 / 20 100 20 10
alw 68 48 62 43 / 20 100 30 10
psc 64 48 63 41 / 50 80 10 10
ykm 60 39 61 35 / 40 20 10 10
hri 63 45 63 39 / 50 90 10 10
eln 58 37 56 35 / 50 20 10 10
rdm 64 37 52 33 / 70 80 20 40
lgd 69 42 52 37 / 10 90 50 30
gcd 68 41 52 35 / 10 90 50 20
dls 59 45 62 43 / 80 50 10 20

&&

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

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