355
FXUS66 KMFR 081703
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
903 AM PST Fri Nov 8 2024

.DISCUSSION...Satellite imagery is showing fog in the Umpqua Basin
and also portions of the Rogue Valley between Agness and Grants
Pass. We pushed the dense fog advisory out until 10 am this
morning since web cams are still showing some low visibility
conditions along I-5. Fog will dissipate late this morning and
probably completely clear by noon. High pressure will maintain dry
weather area wide the rest of today with some high clouds at
times, especially west of the Cascades. No further updates are
expected this morning. -Spilde


&&

.AVIATION...08/18Z TAFS...VFR conditions prevail across much of the
region and will do so through the TAF period. The exception being
areas of LIFR conditions in fog/low clouds in the Umpqua Basin and
the coastal river valleys. These lower conditions will clear to VFR
by late this morning with VFR prevailing thereafter. The pattern
will begin shifting late today into Saturday, and there will be an
increase in mid and high level cloud cover later today into
Saturday. The marine layer will return to the coast this evening,
likely bringing the return of MVFR ceilings tonight along the coast.
/BR-y


&&

.MARINE...Updated 830 AM PST Friday, November 8, 2024...

Sub-advisory conditions will continue though early Saturday, though
seas will gradually increase tonight into Saturday as the pattern
becomes more active. Two fronts will move through this weekend, one
Saturday afternoon/evening and another Sunday night into Monday. The
first front, the weaker of the two, will bring increasing south
winds tonight into Saturday with building westerly swell. This will
result in conditions hazardous to small craft for much of the outer
waters north of Cape Blanco, since combined wave heights will
approach 10 feet. A Small Craft Advisory has been issued for late
Saturday morning into the evening. Farther south, where winds will
be lighter, seas will be swell dominated and remain mostly below 10
feet. That front will stall and dissipate over the waters Saturday
night before the second front, the stronger one, moves through late
Sunday into Monday. This will likely bring a period of moderate to
heavy rain, gales and steep to very steep, chaotic seas. Models
continue to show this system being followed by another large, long
period swell, peaking around next Tuesday. Early indications are
showing peak swells 17-21 feet with a period of 15-16 seconds. This
would maintain very high and very steep seas through midweek. -
Spilde/Hermansen


&&

.PREV DISCUSSION... /Issued 332 AM PST Fri Nov 8 2024/

DISCUSSION (Today through Thursday)...

Overview:

A strong upper level system is still anticipated to start impacting
the area as early as Saturday/Saturday night with precipitation and
strong wind speeds over the Cascades/eastside. However, the wind
will be most impactful Sunday night through Monday night across the
eastside with a secondary system. This system will bring several
rounds of rainfall to the area, with heavy rainfall possible along
and near the coast where some areas could see several inches of
rainfall over ~48 hours (Sun-Tues). Higher elevations along the
Cascades will see snowfall during this timeframe, and upwards near
two feet of snowfall will be possible in and around Crater Lake
through a ~24-36hr window Monday morning through Tuesday afternoon.

Further Details:

Ridging aloft will slowly erode tonight as a cut-off low positioned
over the Four Corners region begins to eject over the Central Plains
tonight into Saturday. Once that cut-off low ejects over the Plains,
this will allow for a trough to form over the Pacific and transition
over the PacNW through the end of the weekend. Behind this initial
open wave trough is another shortwave. These two features will
essentially lead to several rounds of precipitation starting
Saturday afternoon/evening and going into middle of next week. This
doesn`t mean it will precipitate this entire period, but we are
looking at several opportunities across the region at varying times
and coverage. From Highway 140 north through the Cascades we are
looking at the potential for heavy snowfall, especially around
Crater Lake. Snow levels will start around 7K to 9K feet until
Saturday when they lower to about 6K to 7K feet, but Monday through
Tuesday these will lower to around 4K feet. That Monday through
Tuesday timeframe will be the most impactful for snowfall and we may
need to consider a winter weather hazard. Forecast soundings for
Crater Lake indicate very strong lapse rates within the dendritic
growth zone and ample lift. The wind speeds will also be
orthogonal to the Cascades which should allow for efficient
upslope flow in addition to dynamic lifting. All in all, we are
looking at the potential for impressive snowfall rates
(0.50"-1.00"/hr) and at least minor impacts over passes,
especially areas above 5000 feet Monday through Tuesday morning.

The rainfall along and near the coast could be impactful as well
given the heaviest rain could be falling during the Monday morning
commute. Precipitable water values will be around 1.00"-1.25"
along/near the coast with strong theta-e advection in the low/mid
levels. Areas in both Coos and Curry county could experience the
heaviest rain, but western parts of both Douglas (near the coast)
and Josephine counties could also see these higher amounts as well
albeit not quite as high as coastal areas. Overall, these areas
mentioned could experience localized flash flooding, so plan for
extra commute times during the rainfall.

-Guerrero

AVIATION...08/12Z TAFS...Signs of fog are starting to show up on
satellite imagery in the Umpqua Basin. Guidance does not have high
confidence in a solid marine layer developing over North Bend, so
right now periods of MVFR visibilities look possible. LIFR
conditions have returned to the Umpqua Basin, and the fog will
likely clear out by late morning.

Clouds are starting to move into the area this morning, but ceilings
should stay at VFR levels after the fog lifts. Precipitation is not
expected until Saturday.

-TAD/Hermansen

MARINE...Updated 200 AM PST Friday, November 8, 2024...

Light winds and seas are expected today, though we`ll likely see a
bit of a surge of cloud cover up the coast as surface winds shift to
southerly.

Two fronts will move through this weekend, one Saturday
afternoon/evening and another Sunday night into Monday. The first
front, the weaker of the two, will bring increasing south winds
Friday night into Saturday with building westerly swell. This will
result in conditions hazardous to small craft for much of the outer
waters north of Cape Blanco, since combined wave heights will
approach 10 feet. A Small Craft Advisory has been issued for late
Saturday morning into the evening. Farther south, where winds will
be lighter, seas will be swell dominated and remain mostly below 10
feet. That front will stall and dissipate over the waters Saturday
night before the second front, the stronger one, moves through late
Sunday into Monday. This will likely bring a period of moderate to
heavy rain, gales and steep to very steep, chaotic seas. Models
continue to show this system being followed by another large, long
period swell, peaking around next Tuesday. Early indications are
showing peak swells 17-21 feet with a period of 15-16 seconds. This
would maintain very high and very steep seas through midweek.

-Spilde/Hermansen

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Dense Fog Advisory until 10 AM PST this morning for ORZ023.

CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory from 10 AM to 10 PM PST
     Saturday for PZZ370.

&&

$$

MAS/MNF/JWG/ANH