Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 211800
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1000 AM PST Tue Nov 21 2017

.SHORT TERM...Today...This morning, satellite water vapor imagery
and the height contours of the 400mb pressure surface indicate a
longwave trough and ridge couplet over the NE Pacific and the
interior Pacific Northwest. The trough is between 140-150W and the
ridge axis is along the Idaho/Oregon/Washington border. This
pressure pattern has southwest flow aloft on the eastern flank of
the trough steering an atmospheric river of moisture into the
Pacific Northwest. The atmospheric river has brought a warm front
and attendant rain to the region this morning. Composite radar
imagery from several NWS Doppler weather radars in western sections
of  Washington and Oregon show widespread rain has spread to the
Cascades and areas east of the Casdcades this morning. KPDT radar
shows bands of light rain moving across the Lower Columbia Basin to
the Blue Mountains and the Grandce Ronde Valley yielding a trace of
rain thus far in the Tri-Cities, Walla walla and Hermiston.
Pendleton Airport has received 0.01 inch of rain and Meacham 0.02
inch. Snow levels will be well above normal today resulting in rain
expected at pass levels through tonight and Wednesday.

The current forecast looks good, except that the new 12Z mesoscale
model runs (NAM12 and MM5 with GFS input) show very little
measurable rainfall today in central Oregon. As such central Oregon
will likely have some sprinkles and intermittent light rain, which
may accumulate to 0.01-0.03 inch of rain from 9 AM this morning
through this afternoon. As such I will decrease PoPs and QPF amounts
for today in central Oregon.  Polan

&&

.AVIATION...18Z TAFs...VFR conditions will generally prevail for the
next 24 hours with mainly mid level OVC expected. Prevailing rain
with periods of lighter showers is expected for the next 24 hours
though KBDN and KRDM may not see much rain after 12Z. With the
heavier rain, MVFR ceilings and visibility will be possible,
especially at KYKM after 12Z and KALW after 06Z. Rain will begin
decreasing after 15Z. winds will generally remain below 12 kts
though KBDN and KRDM will have gusts to 20 kts this afternoon and
early evening. Perry

.PREVIOUS DISCUSSION... /issued 243 AM PST Tue Nov 21 2017/

SHORT TERM...Today through Thursday night...The weather pattern
will remain active with a couple of warm and cold fronts moving
across the region through the period. The next warm front will move
into the region by tonight with temperatures and snow levels rising
to much above normal levels for the latter part of November. There
will be an abundant amount of moisture in a southwest flow aloft.
The result will be a chance to likely precipitation across the
entire CWA which will decrease over central Oregon and the valleys
along the Cascades east slopes to due to a westerly downslope flow
later today. Then another weather system....though not as strong
will move into the region by Thursday and Thursday night. This
seccond system will not be as strong or as wet as today and/or
tonight. It will be breezy to windy at times...especially over the
ridges and in the higher elevations. 88

LONG TERM...Friday through Monday...Medium range models continue to
be in agreement with the large scale pattern late week into early
next week. A cold front will exit to the southeast early Friday,
with low amplitude ridging providing for little/no precipitation
Friday/Friday Night, thus will cap PoPs at slight chance for most
areas. Snow levels of 4000-6000 feet Friday will rise to 5000-7500
feet Friday Night as a warm front approaches the area. The warm
front will cross the area Saturday with the systems cold front
crossing on Sunday. Some model differences exist with liming and
amount of deep moisture, so will use high end chance to likely PoPs
for the mountains with lesser chances for the lowlands. Snow levels
of 6000-9000 feet Saturday/Saturday Night will fall to 5000-7000
feet Sunday. A weaker shortwave behind the trough axis is progged to
move across the area Monday for chance of rain with high elevation
snow. With relatively high snow levels through the extended period,
winter traveling conditions are not likely. Temperatures will be
cooler than Wednesday/Thanksgiving Day, but will be 4-7 degrees
above normal.

AVIATION...12Z TAFs...VFR conditions will generally prevail for the
next 24 hours, with mid deck BKN/OVC expected. Rain will move in
from the south, with prevailing rain beginning around 12Z at
RDM/BDN, spreading north to near the WA/OR border by late morning,
and into southern WA in the afternoon. Areas of MVFR will be
possible in the heavier precip. Rain will gradually diminish in
coverage tonight. Winds will remain under 12 KT, except for RDM/BDN
where winds will increase to around 15 KT this afternoon.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  51  49  63  49 /  80  60  40  10
ALW  52  51  63  51 /  70  70  40  20
PSC  48  47  60  47 /  90  60  40  20
YKM  47  43  57  43 /  90  60  40  30
HRI  50  48  61  47 /  80  60  40  20
ELN  45  41  53  40 /  90  60  50  30
RDM  56  50  64  47 /  60  60  20  10
LGD  53  49  59  51 /  80  80  50  20
GCD  53  49  61  49 /  70  70  30  10
DLS  50  49  60  49 /  90  70  50  40

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

$$

99/88/80



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