Small Craft Advisory 40, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
1051 AM PDT Fri Apr 20 2018

.Updated Aviation Discussion Below.

.DISCUSSION...Only minor updates this morning...mostly to bring
sky grids in line with current observations and to bump
temperatures up a few degrees in the west side valleys for this
afternoon.

Today will be a quiet day weather wise. An upper level ridge will
bring warm temperatures and dry conditions for the forecast area
through this afternoon and evening. A weak front will move through
the area late tonight into Saturday morning bringing mid-level
clouds and light precipitation to the coast and areas north of the
Umpqua Divide. Zonal flow behind the front will keep temperatures
seasonable for Saturday and dry conditions will prevail again. For
more details on the weather to follow beyond Saturday, see the
previous discussion below. /BR-y

&&

.AVIATION...20/18Z TAF CYCLE...At the coast, VFR conditions will
continue this afternoon. Short range guidance has been consistent
the last few hours showing IFR CIGs developing around 2z as marine
stratus develops ahead of an approaching front. Have introduced the
lower conditions to develop at North Bend at 2z, but it could be
delayed by an hour or two. CIGS are expected to improve Saturday
morning, however confidence on the the timing indicated in the TAF
at North Bend is low, so watch for updates.

Inland Westside, VFR CIGS will continue into tonight. Cigs will
lower late tonight and could hover close to MVFR towards daybreak
Saturday with partial mountain obscuration mainly along and north of
the Umpqua Divide and west facing slopes of the Cascades. Elsewhere,
including Medford and Klamath Falls, VFR conditions will continue
through the TAF period. -Petrucelli

&&

.MARINE...Updated 845 AM PDT Thursday 19 April 2018...Light winds
and seas are expected today. A weak front will move through the
waters tonight, then dissipate as it moves inland early Saturday
morning. A west swell will build into the waters during the day
Saturday with seas expected to approach 10 feet by Saturday
afternoon.

A thermal trough will develop along the coast Saturday afternoon and
persist through at least Sunday. This will bring strong north winds
and steep to very steep seas Saturday afternoon through Sunday
evening. Gale force are possible for areas south of Gold Beach.
Steep to very steep are expected across the waters Saturday
afternoon through Sunday evening with very steep seas expected
mainly for areas south of Cape Arago. The most recent model runs
continue to show gales. So, confidence is moderate to high on gales
and very steep seas developing this weekend.

Winds and seas will gradually lower Sunday night and Monday.
However, continued areas of very steep seas are possible Sunday
night and areas of small craft advisory level winds and seas are
possible Monday into Monday night. -CC/Petrucelli

&&

.PREV DISCUSSION... /Issued 333 AM PDT Fri Apr 20 2018/

DISCUSSION...The upper level ridge that moved in behind the
exiting upper low is over the region this morning, with offshore
flow spreading east of the Cascades by sunrise. With the upper
ridge and the offshore flow with the thermal trough along the
coast clear skies are present this morning over almost all of the
forecast area. With temperatures around 10 degrees higher than
they were at this time yesterday, in spite of similar clear skies
as yesterday, the 4 to 7 degree warm up from yesterday continues
to look on track. The upper level ridge transitions to a zonal
flow pattern this evening with a weak front washing out over the
region Saturday morning. Light precip is possible at the coast,
but the main effect of this front will be a weak marine push with
higher humidities. An upper level trough moves through Sunday, and
models continue to show weak instability in extreme southeast
portions of the forecast area. However, the flow is northerly
through early Sunday afternoon, and no moist unstable air is
feeding into the region prior to the indicated instability. Some
towering cumulus will likely be the result in most of the area,
with maybe the Warners in Modoc county seeing anything grow
beyond that. An upper level ridge builds in again behind the
exiting trough with offshore flow returning and remaining through
mid week. This will bring increasing temperatures through mid week
with highs in the upper 70s and lower 80s in the west side valleys
by Tuesday. Sven

AVIATION...20/06Z TAF CYCLE...VFR will prevail overnight. Patchy
MVFR/IFR in low clouds and/or fog could develop in some west side
valleys and along the coast late tonight into Friday morning;
otherwise, VFR will predominate. -FB

&&

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

CA...None.

Pacific Coastal Waters...Gale Watch from Saturday afternoon through
Sunday evening for      PZZ356-376.      Hazardous Seas Watch from
Saturday afternoon through Sunday      evening for PZZ350-356-370-
376.

MNF/SBN/CC/MAP