Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 211131 AAA

Area Forecast Discussion
National Weather Service Pendleton OR
330 AM PST Thu Feb 21 2019

Updated Aviation Discussion

.SHORT TERM...Today through Friday Night...Although snow has tapered
off across most of the forecast area, WSR-88D is picking up on 20-25
dBZ returns over the Blue Mountains and foothills.  Scattered snow
showers have been observed early this morning, and web cams are
showing snow-covered roadways that were earlier plowed.  The center
of the upper low is over SE Oregon and Nevada with continued wrap-
around moisture.  The HRRR forecasts QPF up to 0.1 of an inch for
areas east-southeast of Pendleton and the Oregon Blues through 18Z.
Forecast will reflect scattered morning snow showers with
accumulations up to 1.5 inches. Typically, these wrap-around
patterns can cause snow to accumulate fast in Wallowa County but the
web cam at Joseph is showing very light accumulations since
midnight. Snow has also tapered off or ended over central Oregon. No
winter highlights are planned for this morning, but we will keep a
close eye on precipitation over the Blue Mtn Foothills.

Snow showers will taper off to isolated mountain snow showers over
eastern Oregon this afternoon and end everywhere tonight.  Clearing
skies will cause temperatures to plummet into the single digits and
teens for most of the area.  Clouds will increase from the west
Friday morning and will be mostly cloudy and cold Friday afternoon.
The next front will bring snow to the Washington and northern Oregon
Cascades Friday afternoon then over the remainder of the forecast
area Friday night.  Frontogenesis begins to develop south of the
Washington border after midnight with the front forming a line from
Walla Walla to Heppner to Madras by 12Z Saturday.  More details on
this upcoming system can be found in the long term discussion. There
will be weak warm air advection ahead of the front increasing snow
levels to around 1500 feet, therefore some of the lowest elevations
will have a rain/snow mix Friday evening.  Wister

.LONG TERM...Saturday through next Friday...The models are in good
agreement to start with a mostly zonal flow with a northwest to
southeast direction. This is where the jet stream will be, which
will divide the cold air north of it in Washington and warmer air
from north central Oregon southward. A weather system will move into
the region again by Sunday. This next system will affect mostly the
southern CWA with the cold/warm air boundary over north central
Oregon. 1000-850 thicknesses are marginal for snow for elevations
below 1500 feet MSL, but precipitation will be widespread this
system will eventually bring a little light snow as the colder air
moves into the CWA on Sunday. This wet pattern will persist for and
through the beginning of the extended period, which will be around
Monday. After conditions will dry out fast.  Then a short visit with
an upper ridge will develop over the Pacific Northwest. Cold air
will be trapped at the surface in the Lower Columbia Basin south
through central Oregon. This time of year, the mixing out of warmer
air under a ridge may transport warmer air and may cause rain or
freezing rain through Wednesday and the rest of next week. 88


.AVIATION...12Z TAFs...Conditions vary from VFR at YKM and PSC, MVFR
at DLS, to MVFR/IFR at BDN, RDM, ALW, and PDT. No major changes in
CIGs/VSBYs are expected this morning as the Blue Mtn Foothills and
Central OR will have periods of light snow.  This afternoon, most
sites will be VFR and only SCT mid-level clouds at YKM and PSC.
Radiational fog may reduce visibilities tonight, particularly along
the Blue Mtn Foothills. A northerly gradient may cause stratus
clouds to develop at BDN and RDM.  There is some uncertainty for the
overnight forecast so will not reduce anything less than MVFR at
PDT, ALW, RDM and BDN. Wister


PDT  28  14  35  27 /  40  10   0  40
ALW  29  16  36  28 /  30  10  10  50
PSC  31  19  36  26 /  10   0  10  10
YKM  34  18  35  22 /  10   0  30  10
HRI  31  17  37  28 /  10   0   0  20
ELN  34  15  33  19 /  10   0  60  20
RDM  32  15  40  28 /  20  10   0  30
LGD  30  12  34  25 /  20  10  10  60
GCD  31  13  36  27 /  20  10   0  50
DLS  37  23  39  31 /  10   0  30  40





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