Flood in Oregon, January 20, 2019

Area Forecast Discussion
National Weather Service Medford OR
403 AM PST Sun Jan 20 2019

.Updated Aviation Discussion.

...Heavy rain, possible flooding to continue for the next few
hours. Remember to turn around, don't drown...

.DISCUSSION...Radar and Satellite observations are showing bands
of moderate precipitation occurring across portions of southern
Oregon and western Siskiyou County in northern California. This is
part of the same atmospheric river and stalled frontal boundary
that have brought copious rainfall amounts to the area. 2-day
storm total rainfall amounts as of 2 AM include 2.22 inches at the
Medford Airport, 4.69 inches at the Brookings Airport, 7.9 inches
of rain at Redmound, 2.27 inches at the Roseburg Airport, 0.54
inches at Klamath Falls, and less the farther east you go.
Additionally, the Ash Creek Raws in siskiyou County received 1.3
inches of rain. Unfortunately, the ASOS at Mt. Shasta City stopped
reporting, so we don't have a clear picture of precipitation in
that area. Areas in the Shasta Valley, where things were windy,
seemed to get much less rain, with the Weed Airport RAWS seeing
less than a tenth of an inch of rain. This seems reasonable, as we
expect areas that see winds to get less rain due to terrain
effects.

Additionally, some of our recent burn scars received several
inches of rain--namely the Natchez fire in northern California,
and the Chetco Bar/Klondike Fires in southern Oregon. So far we
have not received any reports of debris flows, but they will be
possible as more rain falls. Please, if you encounter water on
roadways, find an alternate route. Turn around, don't drown.

Antecedent conditions are extremely wet, and there have been
several reports of water ponding on roadways through the day
today. Have extended the urban and small stream flood advisory
through 8 AM as another round of heavy precipitation is poised to
move through our area and the frontal boundary nudges back one
more time before moving eastward. Am also continuing the areal
flood watch for southern Coos, Curry, Josephine, and western
Siskiyou Counties for now.

Furthermore, a few of our rivers have come risen quite rapidly
over the last several hours, and we are keeping a close eye on
these areas. This includes the Rogue River at Agness and the
Coquille River at Coquille. These areas currently have river flood
watches in effect, and feel comfortable continuing these watches
as the rivers will get close to seeing some minor impacts of roads
and homes. Additionally, we're keeping a close eye on the Little
Butte Creek near eagle point. We've already reached "action stage"
with this creek, which means that it is getting close to
bankfull. The current thinking is that creek will not overflow its
banks, but since homes are pretty close, will continue to
monitor. Please stay tuned to your local media/NOAA weather radio
for updates and any possible warnings that may come from our
office.

This front will finally begin advancing again, and it will make
the precipitation more showery in nature. Current model guidance
is indicating that this could happen as early as 5 AM, but things
could be delayed a couple of hours. Once the front moves through,
snow levels will drop to around 4000 feet. Web cameras are already
showing snow along Highway 97 near La Pine and highway 138 near
Diamond Lake. This is normal as the front has that wobble. The
snow should turn back into rain at some point tonight for an hour
or two, then turn back to snow showers later this morning. Of
course, the guidance has not handled the intricacies of this storm
very well, so these areas could see only snow. Thus, a winter
weather advisory goes into effect at 4 AM for areas above 4000
feet in the Cascades, Siskiyous, and the Marble Mountains. This
advisory is only in effect for the higher passes, like Lake of the
Woods. Will need to continue to monitor US 97 via communication
with ODOT and web camera to determine if an advisory is needed
there too.

Finally, the last threat associated with this system will be winds
from the south in the Shasta Valley and the Summer Lake area and
higher terrain areas east of the Cascades. Some of our wind gusts
have already risen to 40 mph, and could see wind gusts to 55 mph.
This can make travel difficult for high profile vehicles, and
could cause loose objects to be blown away. The wind advisory will
continue for the aforementioned areas until 10 AM once things
start calming down.

The showers will continue through today becoming a bit more
sporadic. Meaning there will be increasing periods where it is not
raining. This transition day will continue through Monday before a
ridge of high pressure builds in over the Pacific Northwest and
California. This means we will be returning to the fog and low
clouds next week for many areas west of the Cascades with cold
overnight low temperatures also returning.

One exception to this pattern is that a weak front will move
northward over the ridge on Wednesday. This will bring some light
precipitation to areas north of the Umpqua Divide, but this system
is not expected to be as impactful as the currently ongoing
system.

In summary, lots of rain has fallen over the past two days.
Moderate will continue through today becoming showery in nature.
Make sure you remain aware of high water, possible debris flows,
and any flooding. Stay near your weather radio, or stay tuned to
local news media who will relay any additional warnings from our
office. -Schaaf

&&

.AVIATION...For the 20/12Z TAFs...MVFR with local IFR ceilings are
expected along a frontal boundary this morning for inland westside
locations. The front will push east during the morning and there is
a chance for ceilings to improve to VFR for a brief time, but
confidence is not high enough to show improving conditions in the
TAF at Medford. Post frontal showers behind the front could bring
MVFR and local IFR ceilings to locations along and west of the
Cascades from mid to late morning through this afternoon.

Gusty winds could develop in the Shasta Valley and over the east
side for a few hours in advance of the front. There could also be
isolated thunderstorms over the coastal waters and immediate coast
as the upper trough moves onshore this afternoon into this evening.
Conditions are expected to remain unstable enough tonight to prevent
IFR/LIFR ceilings and visibility from developing, but it could
materialize if there's enough clearing. Right now, there is not
enough confidence there will be sufficient clearing, so kept the
lower conditions out of the TAF's. Later shifts will need to take
another look at this. -Petrucelli

&&

.MARINE...Updated 200 AM PST Sunday 20 January 2019...Seas will
lower some today, but due to a combination of a northwest and
southwest swell, they are expected to remain small craft into Monday
afternoon. Therefore the end time of the small craft advisory for
seas has been extended until 4 pm pst Monday. Please see MWWMFR for
more details.

Low pressure will move into the waters Sunday night, then south of
the waters Monday. North winds will increase some, but they should
remain below small craft. However as previously mentioned the
combination of northwest and southwest swell will be enough to cause
small craft conditions for seas.

A warm front will move north of the waters Tuesday bringing
increasing south winds mainly over the northern outer waters, but
they should remain below small craft. Elsewhere, calmer conditions
are expected. There's good agreement a west swell will increase
Wednesday afternoon, but right now they are only projected to be
between 9-10 feet. Meanwhile, high pressure will remain over the
waters Wednesday through the end of next week. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 10 AM PST this morning for ORZ030-031.
     Winter Weather Advisory until 4 AM PST Monday above 4000 feet in
     the for ORZ025-027-028.
     Flood Watch until 10 AM PST this morning for ORZ021-022-024.

CA...Winter Weather Advisory until 4 AM PST Monday above 4000 feet in
     the for CAZ080>083.
     Flood Watch until 10 AM PST this morning for CAZ080.
     Wind Advisory until 10 AM PST this morning for CAZ081.

Pacific Coastal Waters...Small Craft Advisory for hazardous seas until 4 PM PST Monday
     for PZZ350-356-370-376.