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Area forecast discussion 
National Weather Service Pendleton or
822 am PST Wednesday Nov 25 2015

Short term...upper low over northern Nevada slowly moving
southeast away from the forecast area today. Cloudy skies with
scattered snow showers over central and northeast Oregon will
gradually clear during the day. Further north into the Washington
Columbia Basin and Yakima Valley skies will remain mostly sunny
through the day as upper ridge builds in. Temperatures mainly in
the 20s and 30s. Some locations will have brisk north winds
through the afternoon. New snow cover over Oregon will result in
cold overnight low temperatures the next few days. 94


Previous discussion... /issued 450 am PST Wednesday Nov 25 2015/

Short through Friday...the upper low was over extreme
southeast Oregon at 1:30 this morning and was slowly drifting to the
southeast. The snow has come to an end for the most part in
northeast Oregon. In central and east central Oregon the snow has
tapered off to light snow showers. No additional accumulation is
expected anywhere in the forecast area this morning. Therefore all
warnings and advisories have been cancelled. Drier air is filtering
southward from the north into southeast Washington and northeast
Oregon. Low clouds can be seen dissipating from north to south with
the drier air as seen on infrared satellite imagery. Once skies clear out
temperatures will drop rapidly as modified Arctic air filters into
the region. The exception may be the Blue Mountain foothills
southward where low clouds may persist for the rest of the night and
much of today resulting in warmer than expected minimum temperatures
this morning. Today will be a transition day from low pressure to
high pressure aloft as an upper ridge builds over the region from
the west. A cold northerly flow will keep temperatures from rising
much during the day but can expect maximum temperatures to range
from the lower to middle 30s across the lower Columbia Basin to the 20s
to near 30 in the mountains. Tonight will be drier with clear skies
and light winds over the two state area resulting in much colder
minimum temperatures. As such maximum temperatures on Thursday will
be a few degrees cooler than today. After that cold air and moisture
will become trapped in the basin and adjacent valleys resulting in
the formation of patchy freezing fog or low clouds there. May
eventually need freezing fog highlights as this scenario unfolds.
Fair but cold weather will persist on Friday. 88

Long term...Friday night through Wednesday...cold and dry
conditions will prevail through Monday. The biggest forecast
challenge during this period is how much fog will develop. Friday
night through Sunday a dry northeasterly flow wrapping around the
low to the south should keep the lower atmosphere mixed enough to
preclude fog. But on Sunday night the low will move off to the
east...and high pressure will allow the low level inversion to
strengthen...trapping moisture near the surface...allowing fog and
low stratus to form. This could be short-lived though...since the
GFS has been consistent in forecasting the arrival of a wet weather
system on Monday night and Tuesday that would bring rain and snow to
the region. However...the European model (ecmwf) holds the high pressure ridge over
the area and sends the low into the southwest U.S.. needless to
say...the models have been having a hard time resolving what will
transpire with the split flow in the eastern Pacific at the
beginning of next week. They do come back in to better agreement on
Wednesday however...with a deep broad trough approaching the
coast...sending warm frontal precipitation inland. It is too soon to
be confident...but there is some indication that this could result
in a freezing rain event along the east slopes of the Cascades. Cobb

Aviation...12z tafs...snow has ended at all taf sites...but low
clouds are still present at kpdt...krdm...kbdn and kalw...causing
MVFR or worse conditions. Meanwhile kdls and kpsc are VFR with
ceilings 5-6k feet...and kykm is clear. Conditions are expected to
continue to improve...and all sites will eventually clear out either
this afternoon or evening. The one site of concern is kalw...where
upslope flow could fuel low clouds through most of the next 24
hours. Breezy north winds can be expected today...but will decrease
later tonight. 82


Preliminary point temps/pops...
PDT 32 16 28 16 / 0 0 0 0
alw 33 19 31 19 / 0 0 0 0
psc 39 19 33 18 / 0 0 0 0
ykm 39 16 38 18 / 0 0 0 0
hri 38 17 31 17 / 0 0 0 0
eln 34 16 35 18 / 0 0 0 0
rdm 27 6 26 7 / 30 0 0 0
lgd 30 15 27 13 / 20 0 0 0
gcd 29 10 30 7 / 40 0 0 0
dls 41 22 37 23 / 0 0 0 0


PDT watches/warnings/advisories...

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