Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 142237
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
237 PM PST Fri Dec 14 2018

.DISCUSSION...An unusually strong and sharply defined front is
making its way across the area, and as of this writing is just
beginning to pass over the Cascade crest. Strong winds will
continue to accompany this front as it passes through the East
Side this afternoon and evening, and High Wind Warnings and
Advisories remain in effect. Snow levels behind the front have
dropped considerably, down to just below 4000 feet, but
precipitation rates will also decrease. Therefore, snow is likely
to fall at many of the Cascade passes, as well as at Siskiyou
Summit, but we only expect to see a few inches to fall over the
next several hours, and no major impacts are expected.

Showers will continue this evening, then dissipate overnight as
high pressure briefly passes overhead. The exception will be the
south slopes of Mount Shasta, including Mount Shasta City and the
McCloud area, where upslope winds will continue to produce rain
and snow showers throughout the day.

The wet and windy pattern will continue, as we will begin to see
the effects of the next system by tomorrow evening. Gusty winds
return during the late afternoon, and precipitation should start
to make its way onshore in the evening and overnight.
Precipitation amounts should be higher than the previous, as this
front will be traveling slower and is expected to have much more
in the way of moisture. Snow levels will rise quickly to above
6000 feet by tomorrow evening, and will remain high until Sunday
evening, when the front passes and precipitation begins to taper
off. As a result, there is no threat expected from snow on any of
the area passes. Showers will continue into Monday as moist
onshore flow persists, and precipitation will never really leave
the area before the next front arrives Tuesday.

The Tuesday system is not expected to have the upper level support
of the previous events, but should still produce a fairly good
amount of precipitation, especially along the coast and the
Cascades, where the prevailing flow will be nearly perpendicular
to the terrain.

Models have trended a bit drier with the forecast from this point
on, with the preferred storm tack pushing north as upper level
ridging edges into California and builds north into southern
Oregon by midweek. There may be another front arriving late in the
week or early next weekend, but models are producing a wide array
of solutions, so confidence remains low. Have trended the
forecast towards a blend of the latest GFS and ECMWF, but expect
this will change as we head through the next several forecast
cycles. -BPN

&&

.AVIATION...For the 14/18Z TAFs...The main concern will be wind
speed shear for all the TAF sites, except for Klamath Falls. There
have been a few pireps reports indicating moderate turbulence around
1000 to 1500 feet above the ground. Strong winds have already
surfaced at North Bend, and should continue into early this
afternoon, before gradually decreasing. Low level wind shear is
expected to continue until the stronger winds surface and winds
aloft decrease after frontal passage, especially in the Shasta
Valley, the Rogue Valley and east of the Cascades.

VFR conditions prevail this morning. There are only a few patches of
LIFR fog in the Illinois Valley and north end of the Rogue Valley,
including Grants Pass with coverage limited due to strong winds
aloft and high level cloud cover. Ceilings will deteriorate to MVFR
at the coast first, then over much of the area with mountain
obscuration as the front pushes east. There`s a chance for brief
MVFR ceilings at the coast due to moderate to heavy precipitation as
the front move inland, but confidence is not high enough to put the
lower conditions in the North Bend TAF. -Petrucelli

&&

.MARINE...Updated 200 PM PST Friday 14 December 2018...The front has
moved onshore and winds have shifted southwest and are slowly
diminishing. Despite that, moderate to strong winds are still
expected through this evening. The most recent satellite hint a
surface low that developed along the front as it moved towards the
coast. This caused winds to ramp up fairly quickly earlier this
afternoon. Seas will remain hazardous through tonight. Seas will
improve for a brief time Saturday, but will come up again late
Saturday afternoon.

Improvement on Saturday morning will be slight and brief. Given the
brief break in the action, decided to keep the Hazardous Seas
Warning going through Saturday afternoon.

Another strong front will likely bring gales Saturday evening
through Sunday afternoon, and another swell train may bring the
highest seas of the season so far Sunday into Sunday night.
Confidence on gales is high, so went ahead and issued a gale warning
for all of the marine waters. Please see MWWMFR for more details.

After another brief break Sunday night into Monday morning, yet
another front will bring increasing south winds which could approach
gales late Monday afternoon and lasting through at least Tuesday
afternoon. Also high to very high seas are likely.

Multiple fronts are expected the rest of next week although there is
some consensus among the models that the storm track will shift
north of the waters. At the very least, we could still be dealing
with winds that will be at least small craft conditions. -Petrucelli


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 7 PM PST this evening for ORZ030-031.
     Wind Advisory until 7 PM PST this evening for ORZ029>031.
     High Surf Advisory until 4 AM PST Sunday for ORZ021-022.
     High Surf Warning from 4 AM Sunday to 4 PM PST Monday for
     ORZ021-022.
     Wind Advisory until 3 PM PST this afternoon for ORZ026.

CA...High Wind Warning until 7 PM PST this evening for CAZ085.
     Wind Advisory until 7 PM PST this evening for CAZ084-085.
     Winter Weather Advisory until 7 PM PST this evening for
     CAZ080-082.
     High Wind Warning until 3 PM PST this afternoon for CAZ081.

Pacific Coastal Waters...Gale Warning from 4 PM Saturday to 4 PM PST Sunday for
     PZZ350-356-370-376.
     Hazardous Seas Warning until 4 PM PST Saturday for
     PZZ350-356-370-376.

$$


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