Flood in Oregon, February 16 to 17, 2017

Area Forecast Discussion
National Weather Service Medford OR
302 PM PST Thu Feb 16 2017

.SHORT TERM...A surface low is moving into the northern Oregon
coast this afternoon and a weak upper shortwave trough is over the
region. As these features gradually lifts northeastward, expect
some continued showers into the evening, with activity decreasing
tonight. Gusty south to southwest winds are continuing on the east
side today. However, these winds are forecast to lower after
sunset as the mid level jet weakens and daytime mixing decreases.

Another low pressure system is forecast to approach the northern
and north-central California coast on Friday. This low is forecast
to gradually moves southward Friday night with an upper trough
moving over the Pacific Northwest. With the low remaining south of
the area, expect mostly light to moderate showers to move into the
CWA. Model solutions show some variability on how far south the
low will be positioned as it nears the California coast on Friday.
This will position will factor into how widespread showers are on
Friday. Have leaned towards the ECMWF which brings the surface
low just off the San Francisco Bay area Friday morning and then
shifts the low slightly southward Friday evening. The GFS model
continues to show a slightly more northerly position and as a
result, spreads showers into southern Oregon by Friday afternoon.
Meanwhile the ECMWF keeps most the showers in Northern California
and to the south on Friday and spreads showers into Southern
Oregon Friday evening and night as the upper trough moves into
place. The NAM is forecasting a much more southerly track with the
low and keeps a drier pattern in place over southern Oregon. Will
need to monitor these forecasts as the low moves into the coast
tomorrow. Overall, precipitation amounts are expected to be light
to moderate though. Snow levels are forecast near 4000 feet
elevation Friday morning, rising to 5000 to 5500 feet Friday
afternoon and evening.

On Saturday, a shortwave trough remains over the area with
lingering showers. This trough is forecast to shift to the east
Saturday afternoon and evening. So expect decreasing shower
coverage over the area by Saturday evening.

Another Pacific low and frontal system then will approach the
coast Saturday night. Models show good agreement with this front
moving inland on Sunday morning and afternoon. Of note, the ECMWF
is slower to shift the front inland and lingers it near the coast
through Sunday. While there is variability on the details of this
front, overall, expect some moderate rain along the coast with
light to moderate precipitation inland over the area. Snow levels
are expected to start out 3000 feet west of the Cascades and
around 3500 to 4500 feet from the Cascades east. Snow levels will
rise slightly during the day Sunday to around 4000 to 5000 feet by
late Sunday afternoon. Light snow accumulations are expected over
the mountains and for some areas east of the Cascades, especially
Sunday morning. Current forecasts support amounts of 2 to 4
inches of snow in the Cascades on Sunday. Winds will also increase
some on Sunday with generally breezy south to southwest winds
over the area and some gusty winds along the coast and into the
mountains. Another low is then forecast to move up from the
southwest Sunday evening into Sunday night bringing the potential
for increasing wet and windy weather.

.LONG TERM...Late Sun night, Feb 19 into Fri morning, Feb 24...
This period will be characterized by continued wet weather, with
snow levels initially a little above normal near 6 kft,
transitioning to colder, more showery conditions with snow levels
and temperatures below normal, near 2-3 kft. Of note will be wind
headline potential late Sunday night through Tuesday morning, minor
flood potential Tuesday, and snow headlines Tuesday into Wednesday.
The focus for storm activity will again be across Northern
California, with the Medford Forecast area being most affected
Monday through Wednesday.

More specifically, a frontal system will arrive on southwest flow
late Sunday into Sunday night. Snow levels have varied a fair
amount in the model guidance for this time period, probably in
part due to timing, but also because of evaporational cooling
effects of a southeast flow on the front side of the weather
system. Thus, snow levels will begin in the 4500 to 6500 foot
range, surging to 5500 to 7500 feet about Monday morning before
trending back down. Thus, appreciable mountain snow is likely to
be above 6kft Sunday night through Monday. Areas that get
appreciable southeast through southwest winds will again ahead of
this front Sunday night into Monday.

Monday night into Tuesday snow levels fall into 3-5kft range. There
are model differences in this time frame regarding details,
specifically precipitation amounts. The bulk of the ensemble
guidance indicates southwest flow energy continuing precipitation
through much of Tuesday, but some guidance ends the precip by
Tuesday afternoon. Tuesday night into Wednesday showers and lower
snow levels in the 2-4kft are expected. A showery northwest to north
flow then lingers. Moisture appears limited for Thursday into Friday
as high pressure begins to settle in. BTL

&&

.AVIATION...16/12Z TAF CYCLE...A strong cold front move east of the
Cascades late this morning. A mixture of IFR and MVFR cigs will
continue until late morning with mountains obscured. Moderate to
strong south winds will continue at KLMT until the front passes, and
strong winds aloft will continue to produce low level wind shear as
well as mountain wave turbulence over the entire area. Conditions
will improve after the front passes. Gusty winds and showers with
potential for isolated thunderstorms are expected over much of the
area again this afternoon.  /FB

&&

.MARINE...Updated 230 PM PST Thursday 16 February 2017...Current
satellite image shows the low just starting to move onshore just
south of Astoria. winds will be on the decrease early this evening,
but seas are expected to remain elevated enough for small craft
conditions to continue. Seas will start out in the 10-15 foot range
this evening, then gradually diminishing to around 11 feet by Friday
morning.

A surface low is expected to move south of the waters Friday
afternoon with increasing north winds that could approach at least
small craft in the southern waters and portions of the northern
outer waters. There's even an argument winds could approach low end
gales in marine zone 376 Friday afternoon and evening. We'll look at
this more carefully and determine if a gale watch or warning will be
needed.

Calmer weather is expected Saturday with north winds decreasing in
the morning. Another front will move through the waters late
Saturday night or Sunday morning. The models are still showing
different solutions with respect to the strength of the front.
Either way, winds are expected to reach small craft Saturday night
and stay there through Sunday afternoon.

We still need to keep a close watch on Monday. The models have not
shed anything significantly different from yesterday. The models
show low pressure developing again inside of 130W. The 12z GFS run
still shows a stronger low. The ECMWF also shows the low deepening,
but it's much quicker and it's not as strong as the GFS. Both models
track the low northeast inside of 130W as it moves northeast. The
worst case scenario could be storm force winds for most of the
waters Monday. The best case would be high end small craft or gales
Sunday night into Monday morning. Given this is still a ways out,
details will likely change, so watch for updates on this developing
situation. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 7 PM PST this evening for ORZ030-031.

CA...Wind Advisory until 7 PM PST this evening for CAZ085.

Pacific Coastal Waters...Small Craft Advisory until 4 PM PST this afternoon for
     PZZ350-356-370-376.
     Small Craft Advisory for hazardous seas until 10 PM PST Friday
     for PZZ350-356-370-376.

CC

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MEDFORD OR
423 PM PST THU FEB 16 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0400 PM     HEAVY RAIN       4 NNE TAKILMA           42.11N 123.58W
02/16/2017  M2.72 INCH       JOSEPHINE          OR   TRAINED SPOTTER

            .

&&

NWS MEDFORD OR
IRIS SYSTEM