Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 071718
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
917 AM PST Wed Dec 7 2016

Updated aviation discussion

.SHORT TERM...Forecast is on track for today. Only update was to
increase the cloud cover over southeast WA and far northeast OR
this morning where a large band of stratocumulus is blanketing the
region. The clouds will begin to break with the afternoon
sun...and these areas will go from overcast to scattered. The
cloud cover kept overnight temperatures from plummeting over most
of southeast Washington with lows in the 20s while eastern Oregon
was substantially colder last night with lows in the single
digits and teens and several colder valleys falling below zero.
The coldest spot noted in our forecast area was a RAWS site in the
Deschutes National Forecast (Tepee Creek--elevation 4735 feet)
that fell to -17F last night. A light northerly surface gradient
and a dry northwest flow aloft will keep the region cold with
highs in the mid teens to upper 20s. Enjoy the tranquil weather
because the winter weather will hit hard beginning late tonight
and over the next several days. Details on this can be found in
the previous discussion.  Wister

.AVIATION...18Z TAFs...VFR conditions are expected through the day
and most of tonight at all TAF sites. The exception will be at KRDM
and KBDN late tonight after 06Z when the next system spreads snow
into central Oregon which will create MVFR or IFR conditions at
times due to lower visibility and cigs in snow. Will also see a
persistent stratocumulus cloud deck over the Columbia basin with
ceilings nearing MVFR conditions at KDLS and KYKM. Winds will be
light and mostly 10 kts or less at all TAF sites.

&&

.PREV DISCUSSION... /issued 250 AM PST Wed Dec 7 2016/

SHORT TERM...Today through Thursday night...The next system will
approach the OR coast this evening and move into central OR
overnight. With cold air in place at the surface the warm front
will spread snow across the area Thursday. All areas will have
some snow accumulation. Multiple Winter Storm Watches have been
issued for Thursday through Friday. Central and southeast Oregon
snow levels will increase late Thursday and precipitation will
change to rain below 3500-4500 feet. However...there may be a
period on Thursday when the Bend and Redmond areas have some sleet
or light freezing rain before changing to rain.

LONG TERM...Friday through Thursday...An active extended period is
in store for the forecast area. A major winter storm will exit the
region by late Friday but there will still be some snow or mixed
precipitation over mainly the Lower Columbia Basin northward through
the day Friday. Central Oregon and north Central Oregon will likely
warm up enough for the precipitation to change over to rain, but
elsewhere precipitation type will either be snow or a mix of snow
and freezing rain. The best chance for freezing rain will be over
the Lower Columbia Basin while areas north will stay all snow
(Yakima and Kittitas Valley). The Blue Mountain Foothills will
likely see a change over to either freezing rain or rain too on
Friday due to a southerly downslope wind off the Blue Mountains. The
latest models keep colder air in the CWA Friday night and most areas
will have snow showers, which will change back to a mixture of
freezing rain and snow...or just rain due to warming on Saturday.
Temperatures along the Blue Mountain Foothills on Saturday are
expected to rise to the mid 30s to around 40 so the snow will likely
change over to rain there. There will be a break in the weather on
Saturday night with drying in the north central areas of the CWA but
then another system will move in on Sunday with more mountain snow
and lower elevation rain or mixture. This will be a warmer system
with a southerly low level flow causing mainly rain in the Blue
Mountain Foothills and the Oregon Lower Columbia Basin. Will have to
watch the basin though for trapped cold air in case freezing rain
becomes a possibility there. There will be another break on Tuesday
and then another system will move in on Wednesday and Thursday of
next week. The latest GFS backed off on the colder air that was
supposed to move in with this latter system next week, but the ECMWF
stayed cold, so confidence is low for precipitation type and if
snow, and how much snow will accumulate and where, and how cold it
will be. 88



&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  21  12  27  23 /   0  10  90  80
ALW  24  15  28  25 /   0  10  90  80
PSC  26  16  27  22 /   0  10  90  80
YKM  29  13  25  17 /   0  10  90  80
HRI  25  15  26  22 /   0  10  90  80
ELN  26  12  23  18 /   0  10  90  90
RDM  26  13  30  25 /   0  40  80  50
LGD  22  11  28  26 /   0  10  90  80
GCD  24  13  33  28 /   0  10  80  70
DLS  32  25  29  23 /   0  10 100  90

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Watch from late tonight through Friday morning for
     ORZ510.

     Winter Storm Watch from Thursday morning through Friday morning
     for ORZ041-044-507-508.

WA...Winter Storm Watch from Thursday morning through Friday morning
     for WAZ026>029-521.

     Winter Storm Watch from Thursday morning through Friday morning
     for WAZ024.

     Winter Storm Watch from Thursday morning through Friday
     afternoon for WAZ520.

&&

$$

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