Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 180521
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
920 PM PST Tue Jan 17 2017

.The first band of precipitation for this system is reaching the
Cascades at this time, bringing mostly light amounts. winds have
been high at the coast for a while now with gusts above 60mph at
Flynn Prairie. Current forecast looks on track and will not update
this evening. Sven

.SHORT TERM...(Tonight through Thursday)...Radar, satellite, and
ground observations indicate that the first storm of a very
active pattern has begun to move ashore. Winds are starting to
pick up at the coast with Port Orford already showing wind gusts
of 40 mph. The Medford to Redding gradient has increased to 11.5
mb continues so it continues to show warning level winds for the
Shasta Valley and the usual windier spots on the Eastside. The
flow still isn`t completely aligned properly for the Rogue Valley,
but have left the wind advisory in the Rogue Valley as well. In
addition, guidance still shows warning level winds at the Coast.

We have increased the amount of rainfall expected at the coast.
This has created the possibility for the Coquille River at
Coquille and the Rogue River at Agness to generate flooding
concerns. Have continued the areal flood watch due to this. There
is some potential for rainfall rates to be in excess of 0.50"/hour
at times late tonight through Wednesday --particularly near
Brookings.

As far as wintry precipitation is concerned, the forecast gets a
bit tricky. It should be noted that profiles along and south and
east of the Cascades show an elevated warm layer (>0 degrees C)
tonight into Wednesday morning. Temperatures may be below freezing
at the surface at the onset of precipitation, so there is a slight
chance of freezing rain. Road temperatures currently are above
freezing, so this could prevent most of the adverse travel impacts
to freezing rain. Confidence in freezing rain is not particularly
high, so have left it to a slight chance and have not issued any
advisories for freezing rain.

Snowfall amounts, on the other hand, have trended higher in many
places in Siskiyou County. The problem is that the details of the
models remain slightly skewed. We are expecting a rain-snow mix
for much of the area, but if the precipitation remains heavy for
a while snow levels could plummet and, much of that precipitation
could fall as heavy, wet snow and cause impacts from hazardous
travel to broken tree limbs or downed powerlines. Confidence in
the precip falling as mostly heavy, wet snow is moderate to
high--particularly near Mount Shasta, and we have expanded the
winter storm warnings in much of Siskiyou County, but also for
Mount Ashland as well. -Schaaf

.LONG TERM...Thursday night through Tuesday...A very active pattern
continues in the extended. Another strong frontal system will move
through our area Thursday night and Friday bringing heavy
precipitation and strong winds. Snow levels will be lower than
preceding systems (around 3500 feet), so heavy snow is much more
likely to produce impacts in the mountains this time around. While
wind, heavy rain, and snow headlines are almost a given with this
system, we will wait for the current system to run its course before
hoisting another large set of hazard products. The moisture plume
will be aimed at us through the day Friday and into Saturday, Thus
the coast will continue to see heavy rainfall, with snow over the
mountains.

There may be a brief break Saturday before the next system barrels
in Saturday night and Sunday. The models are in decent agreement
that this system could be a whopper in terms of wind with all
showing strong and deepening low pressure moving inside 130W. The
strongest by far is the Canadian, and it shows low pressure
exploding down to 965 millibars as it curves north just inside 130W
roughly off of Coos Bay. The other models have more of a double-
barreled low pressure system, which we`ve seen sap a lot of energy
out of our recurving systems before. This will bear watching as the
stronger solutions could produce a significant wind storm. We won`t
get too excited just yet, but I did ramp up winds and pops for
Sunday. Sunday`s system will probably be the last really strong one
for a while, but models do suggest cool, damp weather continuing
into next week. -Wright


&&

.AVIATION...18/00Z TAF CYCLE...Conditions are deteriorating at the
coast this evening as winds and rain increase, and MVFR/IFR ceilings
develop. These conditions will continue into tomorrow, and mountain
obscuration will gradually spread inland. Similar conditions will
develop over the rest of the west side this evening, but downsloping
winds will likely keep conditions VFR much of the night around KMFR.
Until the moderate to strong southerly winds begin to surface, low
level wind shear is a possible in West Side terminals. Strong
southeast winds are expected to surface at KMFR tomorrow morning as
pressure gradients tighten.

East of the Cascades...conditions will likely remain VFR through the
night with spotty precipitation, but strong south winds will develop
tomorrow morning. The combination of low level shear and mountain
wave turbulence may create a bumpy ride into coastal terminals
through Wednesday, and then all inland terminals later tonight
through Wednesday.

Notably, some of the worst flying conditions over the next 24 hours
will be around Mount Shasta City where strong upslope flow and low
freezing levels will bring plenty of mountain obscuration,
visibility and ceiling concerns, as well as increased icing
potential. Lastly, freezing levels everywhere will drop
significantly late Wednesday as a cold front moves through.
-Wright/SK

&&

.MARINE...Updated 300 PM PST Tuesday 17 January 2017...Storm
force winds will develop late this afternoon into tonight with
these strong winds continuing into Wednesday. Peak winds are
expected tonight and Wednesday morning with peak seas late tonight
through Wednesday afternoon. Combined southerly wind waves and
west swell are likely to become very high and very steep tonight
then peak in the 18 to 27 foot range on Wednesday. Winds will
diminish by Wednesday evening. Very steep hazardous seas will
gradually decrease Wednesday evening but will remain steep
Wednesday night into Thursday. Another strong front is expected
Thursday night and may bring a period of gales. There is moderate
confidence that very long period west swell will build into the
waters behind this front Friday into Saturday, peaking in the 25
to 30 foot range at a period of 17 to 18 seconds. This will bring
extremely dangerous conditions to the waters, bars, and coastline
as these very high and very steep seas build into the waters.
-CC/SK

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning from 4 AM Wednesday to 4 AM PST Thursday for
     ORZ030-031.
     Wind Advisory from 4 AM Wednesday to 4 AM PST Thursday for
     ORZ029>031.
     Winter Weather Advisory from 10 AM Wednesday to 4 AM PST
     Thursday for ORZ027-028.
     High Wind Warning until 4 PM PST Wednesday for ORZ021-022.
     Flood Watch from 10 PM PST this evening through late Wednesday
     night for ORZ022-024.
     High Surf Advisory from 10 PM this evening to 7 PM PST Wednesday
     for ORZ021-022.
     Wind Advisory from 10 PM this evening to 10 PM PST Wednesday for
     ORZ026.
     Winter Storm Warning from 10 AM to 10 PM PST Wednesday for
     ORZ028.

CA...High Wind Warning from 4 AM Wednesday to 4 AM PST Thursday for
     CAZ085.
     Wind Advisory from 4 AM Wednesday to 4 AM PST Thursday for
     CAZ084-085.
     Flood Watch from 10 PM PST this evening through late Wednesday
     night for CAZ080.
     Winter Storm Warning from 4 AM Wednesday to 4 AM PST Thursday
     for CAZ081.
     Winter Storm Warning from 4 AM Wednesday to 4 AM PST Thursday
     for CAZ082-083.
     Winter Storm Warning from 4 AM Wednesday to 4 AM PST Thursday
     for CAZ080.
     High Wind Warning from 10 PM this evening to 10 PM PST Wednesday
     for CAZ081.
     Wind Advisory from 10 PM this evening to 10 PM PST Wednesday for
     CAZ081.

Pacific Coastal Waters...Small Craft Advisory for hazardous seas
from 10 PM Wednesday to      4 PM PST Thursday for PZZ350-356-370-
376.      Storm Warning from 10 PM this evening to 4 PM PST
Wednesday for      PZZ356-376.      Gale Warning until 4 PM PST
Wednesday for PZZ350-356-370-376.      Hazardous Seas Warning from 4
PM to 10 PM PST Wednesday for      PZZ350-356-370-376.      Storm
Warning until 4 PM PST Wednesday for PZZ350-370.

$$

BMS/TRW/NSK



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