Frost Advisory 23, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
855 AM PST Mon Nov 6 2017

.DISCUSSION...Other than a few leftover showers in portions of the
area, it will be dry with cloud cover gradually decreasing during
the day as shortwave ridging builds into the area. It will remain
dry tonight with clearing skies. The combination of clear skies,
a drier air mass and light winds will allow temperatures to drop
fairly quick after dark. It's possible portions of Douglas County
could drop to near or just below freezing. We'll look at this in
more detail.

Out next area of concern will be late Tuesday night through
Wednesday. The main impacts will be heavy precipitation and
strong winds. Right now, we think the focus for heavy
precipitation will be along the coast, coastal mountains and
around Mount Shasta. The strongest winds are expected in the
Shasta Valley, eastside and maybe portions of the Rogue Valley.
-Petrucelli

&&

.AVIATION...06/12Z TAF CYCLE...A few showers are still lingering
behind a cold front, but showers will diminish this morning, as will
mountain obscuration. Conditions are a mixed bag of VFR, MVFR and
IFR. Ceilings and visibilities will improve to VFR in most places by
this afternoon.

Tonight, stability increases, and with plenty of moisture from
recent rain and snow, LIFR conditions in fog and freezing fog are
likely in many valley locations to include KRBG, KMFR, and KLMT TAF
sites. SK

&&

.MARINE...Updated 620 AM PST Monday 06 November 2017...Steep seas
will continue to subside today. Conditions will further improve
early Tuesday. A strong front will move across the waters Tuesday
night and Wednesday and bring the potential for gales and very steep
seas. Confidence is now moderate for gales late Tuesday into
Wednesday (beyond 10 NM from shore), and there is low confidence on
another round of southerly gales Wednesday night into Thursday
morning. It's more likely that this additional front will result in
very steep seas but winds that are near but below gale force.

A period of relatively improved conditions is expected over the
weekend. SK

&&

.PREV DISCUSSION... /Issued 318 AM PST Mon Nov 6 2017/

Updated aviation and marine discussions.

DISCUSSION...Current observations are showing some light rain
and snow showers across the area. Snow levels are around 3000 to
3500 feet. These showers will continue to diminish throughout the
early morning leading to overall clearing skies by this evening.
The cold air will persist, and our trend of cooler than normal
temperatures will continue today. With the ridge of high pressure
building in today, the clear skies at night will allow
temperatures to plummet to some of the coldest of the fall.
Temperatures east of the Cascades will be in the teens to low
twenties. Meanwhile, temperatures will be in the mid to upper 20s
to low 30s west of the Cascades. Temperatures near the coast will
be slightly warmer with lows only dipping into the upper 30s to
low 40s. West of the Cascades, fog will set up along the coast and
many of the West Side valleys. This will help regulate
temperatures somewhat. If for some reason that the fog does not
form (especially for the coast), expect temperatures a few degrees
lower than forecast and the possibility for frost near the coast.
Despite this caveat, chances are good that fog will form for the
west side valleys, and that is reflected in the forecast.

The next system of note will arrive Tuesday night into Wednesday.
The models have come into excellent agreement regarding the
system, and are now bringing it in a smidge slower than previous
cycles. Although it is tempting to allow the current forecast to
ride to wait for more run-to-run consistency, the fact that all of
the models are in such good agreement takes precedence and have
pushed back the arrival a few hours. That being said, the general
consensus is that this system will be quite strong and bring a
good amount of rain, snow, and wind to southern Oregon and
northern California.

Regarding the wind, the trough is expected to negatively tilted.
This means that winds will be from the south to southeast across
much of southern Oregon and northern California. This will allow
for several of the north-south oriented valleys which also happen
to be our historically windy spots to pick up the breezy to strong
winds. Guidance is showing the possibility for advisory/high wind
warning winds across portions of the Shasta Valley with the Rogue
valley seeing breezy winds as well. The Cascades and some of the
higher terrain and north-south valleys east of the Cascades will
get quite breezy. The GFS is still showing a pressure Medford to
Redding gradient forecast of over 10 mb, but the ECMWF has
relaxed the gradient a bit. Winds aloft for the coast and the
coastal range are expected to be more of a due south, and thus
they may get some breezy winds, but they'll likely stay protected
from the high winds aloft that are forecast. Thus, will allow the
day shift with the next model runs to decide what to do regarding
advisory/watches.

Regarding the precipitation. Snow levels are expected to remain a
bit higher with this system as opposed to the system that went
through this past weekend. Snow levels will start around 6000 feet
and quickly decrease to around 5000 feet. Thus, the higher passes
and elevations are likely the ones to see any snow impacts. That
being said, with the southerly upslope flow at Mt. Shasta, chances
are that the snow level will be artificially lowered from the
heavier precipitation allowing for more snowfall in and around Mt.
Shasta City.

Meanwhile, moderate to heavy rain is going to be expected at the
coast and the Coastal Range on wednesday. This could create some
minor debris flows and flash flooding across the Chetco Bar
Wildfire Burn Scar, but confidence is not high enough to hoist a
flash flood watch quite yet. This will have to be evaluated by the
next shift. This system will be relatively long-lived as the
initial strong system will move through quickly on Wednesday but
allow for a few shortwaves to eject through the area on Friday
which will keep rain chances relatively high.

Then a quick break is expected Friday evening through Saturday
afternoon before the next system approaches the Pacific Northwest.
This system has the potential to be another relatively strong one,
with more winds and moderate rain possible. The models are still
carrying some differences, although both do suggest that it will
be wet Saturday night through at least Monday, if not longer. The
details still need to be worked out, and this system will need to
be watched for any potential impacts it will carry -Schaaf

&&

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

CA...None.

Pacific Coastal Waters...Gale Watch from Tuesday evening through Wednesday afternoon for
     PZZ370-376.