Flooding in Washington, March 13 to 17, 2017

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
1109 AM PDT Mon Mar 13 2017

Updated AVIATION Discussion

.SHORT TERM...A large plume of moisture is pointed at northern
Oregon and much of Washington this morning. Periods of rain and very
high elevation snow are already occurring along the East Slopes of
the Cascades, mainly in Washington. The latest radar shows some
isolated to scattered showers developing across southern Washington
this morning, mainly from the Tri-Cities eastward. Adjusted PoPs and
QPF up a bit for later this afternoon and tonight across the
northern tier of Oregon and much of south central and SE Washington.
This was based largely on the latest RAP, HRRR, and NAM model
guidance. Central Oregon looks to stay mainly dry, but cloudy over
the next 24 hours or so, therefore adjusted PoPS/QPF down here,
mainly into the slight chance or lower category. Overall, look for
QPF amounts through Tuesday morning of 1 to 2 inches along the East
Slopes of the Washington Cascades, 0.50 to 0.75 inches for the
Northern Blue Mountains and the East Slopes of the Oregon Cascades
north of US 20, and a general 0.10 to 0.25 inches for the lower
elevations of northern Oregon and southern Washington, including the
Lower Columbia Basin and surrounding valleys. Lower totals, of under
a quarter inch are expected in the Southern Blue Mountains, and
Wallowa County...with under a tenth of an inch for Central Oregon
and the Ochoco-John Day Highlands. These rainfall amounts, combined
with higher elevation snow melt will cause continued stream/river
rises across northern Oregon and much of southern Washington,
through at least the next several days. Some area rivers and streams
will approach bankfull, and perhaps even minor flood stage. Standing
water in low lying areas will also continue to be an issue,
especially in the Yakima and Kittitas Valleys, where flood
advisories remain in effect. Expect that the current flood advisory
for portions of Kittitas County will need to be extended later this
morning. Otherwise, temperatures will remain mild today, with highs
in the mid 50s to lower 60s in the valleys/basins and 40s to lower
50s in the mountains...snow levels will rise to 8000-9000 feet this
afternoon and evening. 77

&&

.AVIATION...18Z TAFs...CIGS AOA 10-12K ft AGL for remainder of this
morning will lower this afternoon to 5K-8K ft AGL, then decrease to
4K-7K ft AGL tonight. Light rain will develop across SE WA and NE OR
this afternoon. VFR conditions over the next 24 hours, except at
KYKM where conditions will become MVFR by midnight and then to
IFR/LIFR by around 10Z/14th. KRDM and KBDN will remain dry through
the period. Winds will be less than 10 knots for the next 24 hours,
except at KRDM and KBDN, which will see winds of 10-12 kts gusting
to around 20kts today.  Polan

&&

.PREVIOUS DISCUSSION... /issued 405 AM PDT Mon Mar 13 2017/

SHORT TERM...Today through Wednesday. Upper level ridge that
brought fair weather Sunday will give way to an approaching
frontal boundary today. Satellite shows thicker clouds overspreading
the region and this will continue. Rain will develop over the
Cascades this morning and spread east through the day. Best
chances for rainfall will be the Cascades and northeast Oregon
mountains northward into Washington. Central Oregon will have
limited precipitation today. The frontal boundary will remain
nearly stationary over the Pacific Northwest through Wednesday. A
southwest flow aloft will occasionally enhance the front as short
waves move along it. These waves will cause the front to move a
bit north and south which will shift the focus of heavier rain.
Overall appears the Cascades will see the heaviest rainfall with
1-2 inches likely. The northeast Oregon mountains should see at
least 1 inch. This will cause rivers and streams to rise again
this week. Temperatures will be mild with highs in the 50s to
lower 60s. Snow levels will be 6-8k feet. 94

LONG TERM...Wednesday night through Sunday. A cold front Wednesday
night will bring widespread rain during the evening hours followed
by scattered to numerous rain and mountain snow showers overnight.
Snow levels will fall from 5000-7000 feet ahead of the front to 2000-
3500 feet behind the front.  Several inches of snow are possible in
the mountain zones overnight.  Precipitation will taper off Thursday
morning...and only lingering mountain showers are expected Thursday
afternoon.  Dry conditions are forecast for Thursday night.  It will
be a chilly night with lows in the upper 20s to mid 30s...but partly
to mostly cloudy skies will keep temperatures from lowering
significantly.  The next warm front late Friday will bring another
round of rain with snow levels increasing to around 6000-8000 feet.
There are some model differences in the latest runs...and both the
ECMWF and Canadian models are faster and farther north with the
offshore surface low compared to the GFS.  The differences do not
play a huge role in the overall forecast...and the models advertise
a cold front Saturday night that could lower the snow levels back
down to the mountain passes Saturday night.  Drier air will follow
the front...and Sunday should be a tranquil weather day with cool
temperatures and  isolated to scattered mountain snow showers. Wister

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  56  46  62  47 /  40  60  60  40
ALW  58  49  61  49 /  50  80  60  50
PSC  56  46  60  46 /  60  70  60  50
YKM  53  42  56  41 /  60  70  60  50
HRI  58  47  62  47 /  40  60  40  40
ELN  48  38  51  38 /  70  60  70  50
RDM  60  42  63  42 /  20  30  30  30
LGD  55  45  58  45 /  30  60  50  40
GCD  57  40  61  42 /  10  30  30  30
DLS  53  45  60  43 /  60  60  70  60

&&

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

77/99/94/85