Small Craft Advisory 102, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
1033 AM PST Fri Dec 21 2018

.Updated aviation discussion.

.DISCUSSION...Updates were made earlier to accounted for some
isolated showers west of the Cascades this morning. Some shortwave
energy is moving across the forecast area this morning and this is
generating some very light isolated showers. These showers won't
last long and drier air will move in later this afternoon. We'll
be in a break between systems today and for the first part of
Saturday. Clearing skies this afternoon and evening will lead to
fog and freezing fog developing in the interior valleys tonight
into Saturday morning. Then by Saturday afternoon, the next front
will move onshore bringing another round of gusty winds, rain, and
mountain snow. We'll be focusing on any needed headlines for wind
and snow for the afternoon package. In addition we'll be taking a
closer look at expected weather during weekend/holiday travel
period and any potential impacts. For more details on this, see
the previous discussion below. /BR-y

&&

.AVIATION...For the 21/18Z TAFs...Areas of IFR/LIFR out there this
morning, affecting most terminals. Conditions are expected to
improve to VFR late morning to early afternoon, then areas of
IFR/LIFR redeveloping tonight and continuing into Saturday morning.
Confidence is moderate to high for LIFR conditions in valleys west
of the Cascades tonight due to high surface moisture levels and
partly to mostly clear skies. Spilde/Keene

&&

.MARINE...Updated 730 AM PST Friday 21 December 2018...
North winds will be relatively light today then transition to
southerly tonight through Saturday. Seas will remain steep and
elevated today, but should drop below 10 feet tonight. Another
frontal system will arrive midday Saturday, with gales likely
Saturday afternoon and very steep seas possible Saturday evening
through Sunday. Seas are also expected to increase to around 18 feet
Saturday evening, then a heavier west swell could bring seas up to
22 feet by Sunday morning.

A couple of low pressure systems are then likely to affect the area
Sunday through Christmas Day. Given the fast flow across the
Pacific, models are still struggling with the timing and strength of
these features. Best estimate is the first front and surface low
move into the area late Sunday/Sunday night followed quickly by
another on Monday. Overall, seas should gradually lower following
the peak on Sunday, but will remain elevated through Christmas Day
along with periods of stronger winds, possibly gales. -Spilde/Keene

&&

.PREV DISCUSSION... /Issued 403 AM PST Fri Dec 21 2018/

SHORT TERM...Some light scattered showers are occuring this
morning, mainly in Modoc and southeast Lake counties. Showers will
taper off this afternoon. Fog and low clouds has filled in many
western valleys this morning and will slowly clear this afternoon
and a weak high pressure ridge will build over the area late today
and remain in place through Saturday morning. Additional fog is
expected tonight and Saturday morning, especially across western
valleys. Then an active pattern is expected Saturday afternoon
through Christmas day as a series of weather systems move into
the area and bring rain and snow and periods of gusty winds.

On Saturday, a low pressure will move towards the British
Columbia bringing a trailing cold front towards the Pacific
Northwest coast. This front will spread precipitation into the
area Saturday afternoon through Saturday night as is gradually
pushes inland. Although Saturday will start off cold, models show
good agreement that snow levels will rise late in the day to
around 4000 feet for inland areas late Saturday afternoon and
evening. Snow levels of 4000 to 4500 feet will continue Saturday
night for areas for the Cascades east and will be around 4500 to
5500 feet for areas west of the Cascades. As precipitation
continues overnight, a few inches of snow is possible over the
higher passes in the Cascades, including at Lake of the Woods and
Diamond Lake and a couple inches of snow is possible across
northern and central Klamath county. Given the holiday travel, may
need to consider snow advisories for the higher passes.

Winds aloft will increase as well Saturday evening and night.
This will result in gusty south to southwest winds over the
mountains. Some strong winds are possible over the higher
mountains east of the Cascades and in the Summer Lake area. Will
need to monitor this portion of the forecast with future model
runs.

A low is then expected to move into the area Sunday and spread
additional precipitation inland during the day Sunday and into
Sunday night. Although models are in general agreement that this
low will move into the area from the west late in the day Sunday
into Sunday evening, there remains significant variability in the
strength and timing. The main concern with this low will be the
amount of rain and snow that may occur. Snow levels may be  down
near high pass levels, around 4500 to 5000 ft. So holiday travel
may be impacted by light to locally moderate snow Sunday into
Sunday night, especially over the higher passes in the Southern
Oregon Cascades.

On Monday, another low will approach the area and is expected to
move inland during the day Monday and into the evening. Models
show a high degree of variability in the details of this low and
how strong it will be as it moves into the area and whether it
will track directly overhead or be positioned further south. So
confidence is low in the rain/snow forecast. Snow levels are
forecast to be near higher pass levels, around 4500 to 5000 feet
on Monday and may lower to 3500 to 4000 feet Monday night. This
combined with precipitation, may bring additional travel impacts
from rain and snow. However, there is considerable variability
between models on the amount of rain/snow that may occur Monday
and Monday night. The ECMWF indicates a stronger low and brings
the low inland over the area with moderate to locally heavy
precipitation possible, and continued rain/snow Monday night. The
operational GFS and GEFS mean show a somewhat weaker system
moving into the area though. So will need to continue to monitor
future model runs to refine the details of the forecast for this
system.

LONG TERM...By late Christmas day, expect decreasing chances for
precipitation as an upper level ridge builds into the region. A
low pressure system moving over the ridge and into the region
late Wednesday into Thursday may weaken the ridge and bring
additional rain and snow to the area though.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.

CA...None.

Pacific Coastal Waters...Gale Watch from Saturday morning through
Saturday evening for      PZZ350-356-370-376.      Small Craft
Advisory for hazardous seas until 10 PM PST this      evening for
PZZ350-356-370-376.

MNF/CC/MAS

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MEDFORD OR
952 AM PST FRI DEC 21 2018

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

0950 AM     HEAVY RAIN       2 SSE PISTOL RIVER      42.26N 124.39W
12/21/2018  M2.41 INCH       CURRY              OR   TRAINED SPOTTER

            8 AM TO 8 AM.

&&

KS