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Area Forecast Discussion (AFD)

Issued by Pendleton, OR (PDT)

FXUS66 KPDT 220613 CCA

Area Forecast Discussion
National Weather Service Pendleton OR
958 PM PST Thu Feb 21 2019

updated the aviation discussion

.UPDATE...High pressure dominates the regions weather with dry 
conditions and mostly clear skies allowing for good radiational
cooling. Overnight temps are expected to fall into the teens with
single digits across the higher elevations. A storm system will
approach the two state area and light snow is expected along the
wa/or cascades tomorrow morning. The system will migrate east and
increase the chances for showers further inland by afternoon.
Minor snow accumulations can be expected with this before another
stronger storm system effects the region on Saturday that has
prompted a winter storm watch. Otherwise minor changes were done 
to temps and sky and pops and now the short term forecast appears 
more on track.

.AVIATION...lcl mvfr conditions can be expected at most taf sites 
except for taf site kpsc that could experience areas of mvfr and lcl 
ifr conditions until 15z. Otherwise a return to mostly vfr until 
after 18z when a disturbance creates areas of mvfr due to lowering 
ceilings and vsby especially in snow showers.


.PREV DISCUSSION... /issued 235 PM PST Thu Feb 21 2019/ 

SHORT TERM...Tonight through Sunday...A cold and dry northerly 
flow will remain over the region through Friday. Clearing skies 
overnight will allow for temperatures to drop into the teens and 
even single digits or below zero in the colder prone areas. The next 
weather system is already dropping south along the west coast of 
Canada and will be moving into the Pacific Northwest on Friday. It 
will begin to spread precipitation into the forecast area Friday 
afternoon and overnight. However, the northwest to southeast track 
of this system means very little precipitation in most of the Lower 
Columbia Basin region while the higher terrain will see some snow 
accumulations but at expected below advisory criteria levels. The 
heart of this system begins to stall off the Coast of Washington and 
remains there through the first of next week. What this will do is 
turn the flow more westerly and tap into some eastern Pacific 
moisture that will spread across mainly Oregon Saturday night 
through Tuesday. This will set up a situation where areas of eastern 
Oregon could see some significant snowfall accumulations during this 
time period. As such, a Winter Storm Watch has been issued to alert 
the public of the potential long duration of this event and 
significant snow accumulations. There remains some slight model 
differences during this time that could result in the area of 
significant snow fall shifting north or south of the current 
expected forecast track over Oregon and will be monitored in 
subsequent forecast updates over the next couple of days. 
Regardless, the potential is there for this to have a major impact 
on travel across portions of eastern Oregon.  

LONG TERM...Sunday night through Thursday...The models are in good 
agreement with a mostly zonal flow undercutting a blocking high in 
AL. The jet stream will be around the WA/OR border through at least 
Tuesday. A surface front will remain stalled over OR, keeping a 
prolonged period of snow near the frontal boundary (mainly over the 
southern half of the CWA). Any waves moving along the front will 
enhance the snow near it. While there is high confidence in the 
broad pattern, I have very low confidence in timing of any waves 
along the front which will divide the cold air north in Washington 
and warmer air from central Oregon southward and shift the front 
north or south. Since the weather (particularly pops and snow 
levels) is very dependent on the location of the frontal boundary, I 
kept likely pops in OR south of the Columbia Basin and chance/slight 
chance in WA through Tuesday. If the front shifts north into the 
Lower Columbia Basin cold air trapped at the surface may produce 
freezing rain in addition to rain and snow. Wednesday and Thursday 
ridging will build into WA and OR. The ECMWF develops the ridge near 
ID while the GFS builds a ridge offshore Wednesday and shifts it 
east Thursday. Either way drier air will move into the CWA. Coonfield


PDT  12  37  27  36 /  10  10  60  30 
ALW  14  36  28  35 /  10  10  70  20 
PSC  17  37  25  35 /   0  10  30  10 
YKM  15  36  22  34 /   0  30  10  30 
HRI  15  38  27  38 /   0   0  40  10 
ELN  15  36  18  34 /   0  60  10  30 
RDM  14  41  28  40 /  10   0  20  50 
LGD  11  35  25  35 /  10  10  70  60 
GCD  11  37  27  36 /  10   0  60  60 
DLS  22  41  31  40 /   0  30  50  40 


OR...Winter Storm Watch from Saturday afternoon through Tuesday 
     afternoon for ORZ503-505-506-508>511.

     Winter Storm Watch from Saturday evening through Tuesday 
     afternoon for ORZ049-050-502.