Heavy Snow in Oregon, February 3 to 4, 2019

Area Forecast Discussion
National Weather Service Pendleton OR
731 PM PST Sat Feb 2 2019

.UPDATE...A band of rain is moving up with a warm front across the
Blue Mountain Foothills and the Lower Columbia Basin. Rain has
begun to fall at most locations in these areas. There is also
patchy fog, some locally dense fog at KYKM, ahead of the rain
shield that is working its way northward. This weather system will
continue to bring rain and showers to the forecast area overnight.
Then on Sunday cooler air will begin to move into the Pacific
Northwest as a cold front moves southward behind this system with
lowering snow levels down to the valley floors by Monday
afternoon. The precipitation type will change over to snow Sunday
night, even down to the basin floor Sunday night into Monday.
Winter Storm Watches are posted for significant accumulations for
all of our Oregon zones and a couple of the Washington zones for
the time being. These will likely either be lowered to an
advisory, dropped or upgraded to a warning as the coming snow
event unfolds. After that can expect cold weather (the coldest of
the season) for the rest of the week with perhaps another shot of
cold air and more snow by the end of the week. 88

&&

.AVIATION...06Z TAFs...mainly VFR conditions will prevail through
the next 24 hours. However, there will be some areas with MVFR or
IFR conditions, such as at KYKM, which has IFR conditions in dense
fog during last hour. Rain and rain showers may also cause MVFR
conditions overnight and then as the rain changes over to snow
Sunday night there could be more MVFR or even IFR conditions
Sunday night. Winds will be light and will shift to mostly north
to northwest by late Sunday. 88

&&

.PREV DISCUSSION... /issued 237 PM PST Sat Feb 2 2019/

SHORT TERM...Tonight through Tuesday night...Upper level low
pressure system off the California coast will move inland and open
up which will spread moisture and precipitation back across most of
the forecast area tonight and Sunday. Snow levels will initially be
4000 to 6000 feet overnight but begin to lower on Sunday in response
to another low pressure system dropping south out of British
Columbia and setting up off the Washington coast. This will increase
the moist southwest flow over the mountains of eastern Oregon late
Sunday and overnight with the lowering snow levels and the beginning
of a prolonged snow event so have issued a winter storm watch for
the eastern mountains through Tuesday. The low off the Washington
coast will continue dropping south Sunday night and Monday spreading
more moisture across the forecast area. It will also begin to pull
colder air southward into the forecast area resulting in snow levels
dropping to the surface of the Columbia Basin by late Sunday night
and Monday. Models continue to indicate a prolonged northerly
surface flow associated with the cold air which coincides with a
stalled moisture band over northern Oregon that could result in some
significant snow fall Monday through Tuesday. For this several other
zones will be added to the winter storm watch covering Monday
through Tuesday.

LONG TERM...Wednesday through Saturday. Cold northerly flow will be
over the area Wednesday with a few snow showers over the mountains.
The mainly dry and cold conditions will continue Thursday as a ridge
of high pressure move across the area.  Models are a little
different in the next low to affect the area Friday and Saturday
with the GFS dropping a low down the coast and then slowly into
Oregon next weekend.  The EC pushes a frontal band across the area
Friday with the low retrograding offshore and then down the Oregon
coast.  They converge back together by the end of the period with
moisture wrapping around the low and spreading across Oregon. This
will mean some differences in precipitation placement and timing so
have continued with some chance of snow showers Friday and Saturday,
mainly over Oregon.  Temperatures will be about 10 to 12 degrees
below normal and depending on snow cover and clearing, may end up
even a few degrees colder. 93

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  37  41  32  31 /  70  50  50  80
ALW  37  42  33  34 /  60  50  40  60
PSC  36  44  32  34 /  20  20  20  40
YKM  32  41  29  32 /  10  20  20  40
HRI  37  44  32  33 /  40  40  20  60
ELN  30  38  27  30 /   0  20  20  20
RDM  36  42  27  34 /  70  40  30  80
LGD  37  42  30  35 /  80  80  80  80
GCD  39  45  30  37 /  80  70  80  80
DLS  36  44  32  34 /  20  20  20  70

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Watch from late Sunday night through Tuesday
     afternoon for ORZ041-044-505-507>511.

     Winter Storm Watch from Sunday afternoon through Tuesday
     afternoon for ORZ049-050-502-503-506.

WA...Winter Storm Watch from late Sunday night through Tuesday
     afternoon for WAZ024-029-521.

     Winter Storm Watch from Sunday afternoon through Tuesday
     afternoon for WAZ030.

&&

88/93/88