Area Forecast Discussion
Issued by NWS Medford, OR

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133
FXUS66 KMFR 181105
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
305 AM PST Sat Nov 18 2017

.DISCUSSION...High pressure is building into the area, and showers
have ended. Cold temperatures and fog are expected tonight. Frost
advisories and freeze warnings remain in effect for much of the
Umpqua Basin and the coastal zones inland from the coast for
through mid-morning. It will be even colder elsewhere, but we are
beyond the growing season in other locations. Fog has developed in
many west side valleys and along the coast, and this is only
going to become thicker and more widespread as the night goes on.
Pretty much all our valley locations are expected to have fog by
sunrise, including the east side valleys. With warm air building
in aloft, there is also some question as to how soon (or if) fog
clears out. Guidance still shows fog decreasing by late morning,
and we`ll stick with that for now. However, there is a chance that
some valleys, the Umpqua, for example, clear very late or not at
all. This will make for a challenging temperature forecast... if
fog lingers all day, afternoon temperatures will be lower than
expected.

Otherwise, today should be a quiet weather day. Tonight into
Sunday morning, we`ll see another round of fog and cold
temperatures... though temperatures will be slightly warmer than
this morning. Frost will again be possible. Fog won`t stick around
as long Sunday, as the ridge axis will have shifted eastward...
allowing some mixing. An upper trough front will start
approaching, and on the front side of the trough, a stream of
moisture with tropical origins will bringing heavy precipitation
as early as Sunday evening. This system will be a wet one, but not
absurd for this time of year. From Sunday evening through Monday
evening, expect around 2 inches of rain near Brookings... 2 to 3
inches in the Coastal Range... 1 to 1.5 inches in the Illinois
Valley... up to an inch in Roseburg... and up to a half inch in
the Rogue Valley. Snow levels will start relatively low on the
east side... around 5000 feet due to cold air in place, but the
moist, warm airmass should bump them up to above 8000 Monday
morning.

For the 00z run, model agreement is surprisingly good... showing a
continued wet pattern at least through Thursday, with high snow
levels. Projections start to diverge Friday... but we`ll probably
a ridge build in by next weekend, bringing drier conditions.
-MSC/TRW

&&

.AVIATION...18/06Z TAF CYCLE...Expect MVFR/IFR ceilings/visibility
in stratus and fog in the valleys along the coast and north of the
Umpqua Divide through Saturday morning. These will expand over the
west side valleys and also in the valleys of western Siskiyou County
overnight into Saturday morning. VFR will prevail east of the
Cascades, but patchy fog may develop in some of the deeper valleys,
like the Klamath Basin, toward morning. VFR will return to most
areas Saturday afternoon, but low ceilings may last through mid-
afternoon in some of the deeper west side valleys. -Spilde

&&

.MARINE...Updated 200 AM PST Saturday 18 November 2017...High
pressure will remain over the coastal waters with mostly light winds
and low seas today. South winds will increase again ahead of the
next front Sunday with gales and very steep seas likely Sunday
afternoon. Confidence is high that seas will build to around 15 feet
Sunday night from Gold Beach north, with seas possibly building to
17 feet north of Coos Bay. Winds could decrease some Monday night
but are expected to increase to near gale again on Tuesday. As a
result we have extended the Gale Watch through Wednesday. Unsettled
weather will then continue through much of next week. /FB

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Frost Advisory until 8 AM PST this morning for ORZ021>023.
     Freeze Warning until 8 AM PST this morning for ORZ023.

CA...None.

Pacific Coastal Waters...Gale Watch from Sunday afternoon through Wednesday afternoon for
     PZZ350-356-370-376.

$$

MSC/FJB/TRW



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