Gale Warning 11, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
925 AM PDT Fri Apr 5 2019

.DISCUSSION...The next frontal system is moving onshore currently.
Expect periods of rain along and ahead of the front with some
gusty winds in the usual locations like the Shasta Valley and east
of the Cascades. The front is moving quickly so expect
precipitation to become showery behind the front from west to
east this afternoon. Even so, could still be enough instability
to produce a couple of isolated lightning strikes here or there.
Best chance for this to occur will be west of the Cascades. Aside
from some lingering showers, there should be a break tonight,
though rain will likely move back onto the coast late tonight as
the next disturbance moves in. Forecast is on track, so will not
update. -Marc

&&

.AVIATION...For the 05/12Z TAFS...
Low level wind shear is expected in some areas this morning,
primarily along and near the coast to areas inland to Roseburg and
Grants Pass. Rain will drop visibilities to MVFR, at times, mainly
along the coast and in the Umpqua Basin, and ceilings will fall to
MVFR with localized IFR with the front as it progresses inland.
Isolated thunderstorms are possible along and near the front, mostly
along and near the coast and into central Douglas County. It will
become breezy this afternoon and evening. Expect partial terrain
obscurations throughout the day. BTL

&&

.MARINE...Updated 800 AM PDT Friday, 5 April 2019...
A fairly strong cold front will continue to move through the coastal
waters this morning with gales and very steep seas mainly northwest
and west of Cape Blanco. Building west swell this afternoon and
evening will continue to keep seas at Small Craft Advisory levels.

Saturday through Sunday morning long period west swell will build
likely resulting in seas peaking in the 17 to 22 foot range. It
should be noted that the incoming swell is very long period and is
expected to peak around 21 feet at 19 seconds in the Cape Blanco
area northward to west of Florence. Since we'll be dealing with
chaotic seas Saturday afternoon due to a combination of the large
westerly swell and steep wind driven seas, the Hazardous Seas Watch
is valid over the entire area. This heavy long period swell,
especially combined with wind driven seas, will make bar crossings
hazardous and extremely difficult. This will also result in
dangerous surf conditions, so a High Surf Advisory has been issued
for Saturday afternoon and night due to breakers of 25 to 28 feet.
Also, expect periods of moderate to heavy rain Saturday through
Monday morning. Seas are expected to subside early next week. BTL

&&

.PREV DISCUSSION... /Issued 605 AM PDT Fri Apr 5 2019/

SHORT TERM...We've now entered a wet and unsettled pattern that
is going bring lots of rain, occasional wind, and high mountain
snow through at least early next week and possibly well into next
week. The first frontal system is now approaching our coast and
will move onshore late this morning and inland this afternoon and
evening. This will bring precipitation to all west side areas, and
pops have been raised in these locations. As the front crosses the
Cascades and downslope winds kick in, precipitation may break up a
bit on the east side. Nevertheless, high pops are warranted over
there as well. The heaviest rain will occur in the typical upslope
areas: coast, coastal mountains, and Mt. Shasta area. But the
front is moving right along, so we don't expect excessive amounts
even in these locations. Another aspect to this front is wind.
Wind advisories are already in place in the Shasta Valley and east
side, and these look reasonable. Finally, as the parent upper
trough axis arrives at the coast later this morning and then into
west side locations this afternoon, thunderstorms will be
possible.

There will be a break between systems tonight, but rain moves
right back in Saturday as the next wave of low pressure pushes
through to our north. This, too, will bring another round of wind
to the waters and some inland areas on Saturday.

On Sunday, a more substantial moisture plume (an atmospheric
river) moves into our area and will remain aimed at us through
Monday. This system is currently out past the dateline, and water
vapor shows that its moisture plume originates from the deep
tropics in the central Pacific. As this plume arrives at the coast
early Sunday morning, heavy rain develops over the coast and
coastal ranges. The plume gradually sags south along the coast
during the day Sunday and then lifts back north Monday in response
to another area of low pressure riding along the front. This has
a classic atmospheric river look to it, and thus is likely to
produce very heavy rain totals. Our forecast currently shows on
the order of 6-9 inches of rain Sunday through Monday for the
coastal mountains of Curry and western Josephine counties. While
we've been through a relatively dry period recently, this amount
of rain may cause problems, especially over burn scars from recent
fires. Flood watches remain in effect for these areas, and they
will be watched closely. Nothing was changed beyond Monday, and
the previous extended discussion follows for reference. -Wright

LONG TERM...Tuesday through Thursday Night...The kicker trough
that pushes the atmospheric river and very heavy rain out of the
forecast area will be overhead Tuesday. This means showers are
likely at least for the first part of the day. A brief break in
precipitation is expected late Tuesday before upper troughing
begins to push southward over the forecast area Wednesday into
Thursday. This pattern suggests unstable, cool, showery
conditions, and if the upper low does move overhead, thunderstorms
will be possible.

One concern surrounding this cold air mass expected next week is
cold temperatures for area growers. It's too early to tell what
nights may feature partly or mostly clear skies, but keep in mind
the potential for cold overnight temperatures by mid to late next
week.

AVIATION...For the 05/12Z TAFS...
Low level wind shear is expected in some areas this morning,
primarily along and near the coast to areas inland to Roseburg and
Grants Pass. Rain will drop visibilities to MVFR, at times, mainly
along the coast and in the Umpqua Basin, and ceilings will fall to
MVFR with localized IFR with the front as it progresses inland.
Isolated thunderstorms are possible along and near the front, mostly
along and near the coast and into central Douglas County. It will
become breezy this afternoon and evening. Expect partial terrain
obscurations throughout the day. BTL

MARINE...Updated 315 AM PDT Friday, 5 April 2019...
A fairly strong cold front will continue to move through this
morning with gales and very steep seas mainly northwest and west of
Cape Blanco. Building west swell this afternoon and evening will
continue to keep seas at Small Craft Advisory levels.

Saturday through Sunday morning long period west swell will build
likely resulting in seas peaking in the 17 to 22 foot range. It
should be noted that the incoming swell is very long period and is
expected to peak around 21 feet at 19 seconds in the Cape Blanco
area northward to west of Florence. Since we'll be dealing with
chaotic seas Saturday afternoon due to a combination of the large
westerly swell and steep wind driven seas, the Hazardous Seas Watch
is valid over the entire area. This heavy long period swell,
especially combined with wind driven seas, will make bar crossings
hazardous and extremely difficult. This will also result in
dangerous surf conditions, so a High Surf Advisory has been issued
for Saturday afternoon and night due to breakers of 25 to 28 feet.
Also, expect periods of moderate to heavy rain Saturday through
Monday morning. Seas are expected to subside early next week. BTL

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 8 PM PDT this evening for ORZ030-031.
     High Surf Advisory from 11 AM Saturday to 5 AM PDT Sunday for
     ORZ021-022.
     Flood Watch from Saturday evening through Monday morning for
     ORZ021>024.

CA...Flood Watch from Saturday evening through Monday morning for
     CAZ080.
     Wind Advisory until 5 PM PDT this afternoon for CAZ081.

Pacific Coastal Waters...Hazardous Seas Watch from Saturday morning through Sunday
     morning for PZZ350-356-370-376.
     Gale Warning until 5 PM PDT this afternoon for
     PZZ350-356-370-376.
     High Surf Advisory from 11 AM Saturday to 5 AM PDT Sunday for
     PZZ350-356.

MAS/MAS/MAS

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