Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 230957
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
157 AM PST Sat Feb 23 2019

.SHORT TERM...Today through Monday...A very complex and wintry
weather pattern is shaping up for the short term period. A weak
disturbance is currently moving through the Blue Mountains and some
of the Foothills of the Northern Blues this morning. It is bringing
heavy snow amounts to the Northern Blue Mountains this morning, with
KMEH already having reported more than .35 tenths of an inch, as of
1 AM, of liquid equivalent precipitation so far. There have been
light rain and snow with no accumulation over the Foothills of the
Blue Mountains as well. This disturbance is expected to move off to
the east later this morning. A winter Storm Warning for this initial
weather disturbance for the Northern Blue Mountains will remain in
effect though, as the wintry pattern will persist for the Northern
Blues without much of a break. The steady wintry precip will not get
going for the rest of the CWA until either late this afternoon or by
late this evening. Have decided for now to leave the Winter Storm
Watches/Warnings as is for now and wait for the next model run or
two to decide whether to upgrade them to warnings or advisories. One
issue to consider is that frontogenesis with thickness/temperature
gradients tightening along this front develops tonight and Sunday.
North of this boundary will be cold air that is cold enough to
support mostly all snow for all locations. South of this front snow
levels rise sharply to near 4000 feet which will turn the snow to
rain in the lower valleys such as the John Day Basin and Grande
Ronde Valley. This front will sag southward until late Sunday
evening and then it is forecast to stall, and then slowly move back
northward as a warm front after that. Depending on where this front
stalls, and for how long, between its sagging southward and then
retreating back northward will determine where the heaviest snow
will fall. In any case it looks like the central portion of the CWA
(mainly the Blue Mountains) will receive the greatest amounts of
snow with areas north and south of the boundary will receive less
snow. North of the boundary will probably see warning amounts of
snow, but there is much more uncertainty south of the boundary due
to the much higher snow levels and warmer temperatures. This is
another reason to wait for newer model runs before upgrading the
Watches. Feel that the warnings already in place are good and should
remain as warnings. This will be a long duration and high impact
winter storm event beginning today or this evening, and ending
Monday night or possibly in the extended period on Tuesday. 88

.LONG TERM...Monday night through Saturday.  A frontal boundary will
meander north and south across the forecast area through Wednesday
with several rounds of precipitation across the area.  Models
continue to struggle with the day to day details and timing. Current
thinking is that a warm front will lift out of Oregon into southern
Washington on Tuesday.  There is the potential for some heavy
mountain snow, while some warmer surface temperatures in the lower
elevations will see a mix of rain and snow, but very dependent on
where boundary reaches.  There looks to be a break on Thursday and
Friday before the next system approaches the region on Saturday. 93

&&

.AVIATION...12z Tafs.  MVFR conditions with sct-bkn clouds 025-050
k ft agl will prevail through the day with some snow showers moving
into central Oregon by late day. Snow will continue over the
mountains.  Snow will spread north over most of Oregon and into
southern Washington overnight tonight with IFR cigs and vsby in
light snow. 93

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  36  25  31  24 /  20  60  80  50
ALW  36  24  33  25 /  20  30  60  40
PSC  34  25  34  24 /   0  30  50  30
YKM  33  24  33  20 /  20  40  60  40
HRI  36  27  34  24 /  10  40  70  40
ELN  35  22  33  18 /  30  50  60  30
RDM  40  30  39  24 /  40  70  70  80
LGD  34  26  37  26 /  50  70  80  70
GCD  35  29  39  31 /  60  80  90  70
DLS  39  30  37  27 /  30  70  80  70

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning from 4 PM this afternoon to 4 AM PST
     Wednesday for ORZ503-508>511.

     Winter Storm Watch from this afternoon through late Tuesday
     night for ORZ044-505>507.

     Winter Storm Warning from 10 PM this evening to 4 AM PST
     Wednesday for ORZ041-050.

     Winter Storm Warning until 4 AM PST Wednesday for ORZ502.

     Winter Storm Watch from this evening through late Tuesday night
     for ORZ049.

WA...Winter Storm Warning from 10 PM this evening to 4 AM PST
     Wednesday for WAZ024-520-521.

     Winter Storm Warning until 4 AM PST Wednesday for WAZ030.

     Winter Storm Watch from this evening through late Tuesday night
     for WAZ026>029.

&&

$$

88/93/93


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