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Area Forecast Discussion (AFD)

Issued by Pendleton, OR (PDT)

                            
000
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