NWS Medford, OR wrote its last area forecast discussion before the first event at Jan 6, 8:00 PM PST, 4 hours earlier.
Area forecast discussion, Jan 6, 8:00 PM PST, 4 hours before
Area Forecast Discussion
National Weather Service Medford OR
800 PM PST Fri Jan 6 2017
.DISCUSSION...07/00Z NAM in. 07/00Z GFS in through 84hr.
Not much happening over the Medford CWA at the moment...just
increasing cloud cover. All that will change later tonight though
as a storm moves into the area. The day shift team did a bang up
job describing the plethora of weather events that will be
occurring over the next few days, and their AFD has been appended
below with a few minor edits.
There has been one change made in the forecast this evening...
winds have been increased in the Shasta Valley later tonight
through Saturday. The minimum temperatures forecast for tonight
will also be updated soon.
&&
.AVIATION...07/00Z TAF CYCLE...Precipitation and areas of MVFR are
expected to reach the coast after midnight, and IFR conditions
will spread inland through Saturday. Trapped low level cold air will
make for a mix of precipitation types with rain, snow, and periods of
valley freezing rain that could arrive as early as 12Z Saturday. Most
guidance change precipitation type to rain by noon, but low level
winds remaining under 20 knots, confidence is not high that we will
have enough winds to scour our cold air at KMFR.
Confidence is also moderate to high that IFR will return to KLMT
tonight as a warm front approaches from the south but does not quite
move through. As a result, we could see a prolonged period of IFR
conditions due to both low cigs and poor vis from snow and blowing
snow. -BPN/FB
&&
.MARINE...Updated 200 PM PST Friday 6 January 2017...Southerly winds
will increase to advisory strength this evening ahead of a warm
front. Winds will remain gusty through the morning, and will
peak in the afternoon with the possibility of gusts briefly reaching
gale force. Meanwhile, seas will remain steep and dominated by
wind wave and fresh swell, with very steep and hazardous seas
expected beyond 10 nm form shore tonight through Sunday. The next
front on Sunday will bring another round of gusty winds to the
coastal waters, and may also produce gales as it sweeps east
to northeastward. While gales are possible, confidence is low.
However, confidence is much higher in very steep and hazardous
seas spreading to all areas, so the Hazardous seas watch was
upgraded to a warning.
The pattern looks to remain active through the week, with a series
of fronts producing periods of strong winds and very steep seas.
-BPN
&&
.PREV DISCUSSION... /Issued 325 PM PST Fri Jan 6 2017/
DISCUSSION...Tonight through Sunday...Very cold surface temperatures
are in place this afternoon, with sub-zero readings currently
observed in Lakeview, 3 degrees at Klamath Falls, and 7 degrees in
Yreka. To give perspective on how poorly the models are handling
this cold air mass, MOS guidance is 10 to 20 degrees too high
compared to actual observations. We have made adjustments to this,
and we expect another very cold night with only some high cirrus
clouds moving in right now and temperatures dropping. Temperatures
are already dropping in Medford and now are at 24 degrees with a
very dry 16F dew point temperature.
Tonight, moisture associated with a developing storm system over the
Pacific waters will overrun these very cold temperatures, and snow
is expected in most places. Any snow is expected to stick to roads
readily given the cold surface conditions, so travel will turn
dangerous quickly. We have upgraded Winter Storm Watches to Warnings
for most inland areas. There is some uncertainty regarding how long
sub-freezing temperatures will linger on Saturday, and we have
pushed the Warning out to noon for the Rogue, Applegate, and
Illinois Valleys. Some high-resolution models show gusty southeast
winds affecting the southern portion of the Rogue Valley near
Ashland late tonight, and there is a chance this area switches to
rain earliest if cold air is scoured out. As warm air aloft moves
in, a period of freezing rain is a possibility for most valleys
west and east of the Cascades. Ice accumulation, given freezing
rain rarely is observed in this area, has been difficult to pin
down, and we are suggesting about 0.05 inches of ice possible
Saturday morning in West Side valleys. This would be enough to
cause big problems and dangerous traveling/walking conditions. We
want to make clear that as the snow changes to rain/freezing rain,
road conditions could become very slippery with water over ice.
Road temperature models suggest that road temperatures should bump
above freezing by noon in most places west of the Cascades.
Snowfall rates will be highest Saturday morning in the Mount Shasta
area, with one inch per hour rates affecting areas of I-5 in
Northern California. Severe travel impacts are expected.
Snow and ice will change to rain Saturday afternoon west of the
Cascades, and it will take until Saturday night for areas east of
the Cascades to warm enough to change to rain.
Sunday morning through Wednesday morning...The next system in
line will move into the region by early Sunday morning. This
system will come in with higher snow levels and temperatures above
freezing in the west side valleys. With the decent snow pack over
all of the region, including the west side valley floors, the
addition of this melting snow will contribute to the amount of
rain, possibly causing localized flooding with the branches, ice
and other debris from the previous days clinging snow. This debris
with ice may plug drains and culverts with the heavier rain rates.
The Curry coast and Josephine county will see the greatest risk of
flooding, but western portions of Jackson and Siskiyou county mat
also see localized flooding with blocked drains and culverts as
well as small streams through early Monday morning. The next
system that moves in Tuesday continues to indicate a strong
atmospheric river event. With snow levels rising above 7000 feet
with this heavy rain event, snowfall will once again add
significantly to the run-off, and this is currently expected to
cause some main-stem flooding with the Coquille at Coquille
currently indicating flood next Wednesday. Sven
Wednesday through Friday...A flat westerly jetstream will
continue into northern California with another atmospheric river
event. While the heavier rain will be over northern California
south of Mount Shasta, snow melt will contribute to rises in
rivers across our forecast area. The Rogue River at Agness is
forecast to rise to near flood stage. The South Fork of the
Coquille River at Myrtle Point and the Coquille River at Coquille
are forecast to rise above flood stage, with the South Fork
almost reaching moderate flood. Moreover, the flow at the Chetco
River at Brookings is forecast to increase to just above 30,000
cfs. In northern California, the Pit River at Canby is forecast to
rise to near but not quite reaching Flood Stage.
In addition to flooding potential, we could also have issues with
winds as the GFS brings a low pressure into the coastal waters
around Wednesday. We may not see a decrease in precipitation until
Friday when a short wave ridge is forecast to move in. Snow levels
during this timeframe will be 4000-5000 feet lowering to 2000-3000
feet behind the cold front on Friday. /FB
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning from 1 AM Saturday to 4 AM PST Sunday for
ORZ030-031.
Winter Weather Advisory from 10 PM this evening to 4 PM PST
Saturday for ORZ025-027-028.
Flood Watch from Saturday evening through Sunday evening for
ORZ021-022-024-026-028.
Winter Storm Warning from 10 PM this evening to noon PST
Saturday for ORZ024-026.
Winter Storm Warning from 1 AM to 10 AM PST Saturday for ORZ023.
Winter Storm Warning from 10 PM this evening to 10 PM PST
Saturday for ORZ029.
CA...Flood Watch from Saturday evening through Sunday evening for
CAZ080-081.
Winter Storm Warning from 10 PM this evening to 10 PM PST
Saturday for CAZ084-085.
Winter Storm Warning from 10 PM this evening to 4 PM PST
Saturday for CAZ080.
Winter Storm Warning from 10 PM this evening to 10 PM PST
Saturday for CAZ082-083.
Winter Storm Warning from 10 PM this evening to 4 PM PST
Saturday for CAZ081.
Pacific Coastal Waters...Small Craft Advisory until 7 AM PST Sunday for
PZZ350-356-370-376.
Hazardous Seas Warning from 7 AM Sunday to 10 PM PST Monday for
PZZ350-356.
Hazardous Seas Warning from 4 AM Saturday to 10 PM PST Monday
for PZZ370-376.
15/15/15