Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 250451

Area Forecast Discussion
National Weather Service Medford OR
951 PM PDT Fri May 24 2019

.DISCUSSION...The forecast has been updated to fine tune the
probability of precipitation and precipitation amounts expected
from Saturday afternoon through Monday night. Sunday and Monday
will be better days to be at the coast, while inland locations
will have their most pleasant weekend weather during the day on
Saturday. Confidence is high in the forecast through Sunday, while
there have been run-to-run model differences in the coverage and
typical intensity of afternoon and evening showers and
thunderstorms on Monday. The recently arrived 00Z model data has
trended back toward a wetter/more active solution. As such, there
is still uncertainty in whether convective showers will be more or
less numerous late in the day on Monday compared to late in the
day on Sunday.

Most notable will be widespread rain showers and high elevation
snow showers (snow levels around 5500 feet near Crater Lake and
6000 to 7000 feet elsewhere) during Saturday night into early
Sunday morning. There will be a bit of a lull during the remainder
of Sunday morning. But, additional showers with a slight chance
of thunderstorms will become more numerous during Sunday afternoon
and evening...especially from the southern Oregon Cascades
southward and eastward. Shower activity will diminish but not end
during Monday morning, then increase again Monday afternoon into
the evening.

First, the thunderstorms that formed over eastern Lake County this
afternoon into the early evening have dissipated, while a
training line of thunderstorms producing heavy rain will persist
over south central Modoc County in the vicinity of the city of
Likely through the remainder of this evening.

These lingering thunderstorms are along the axis of a closed upper
level low and are expected to weaken and shift south into Shasta
and Lassen Counties overnight. The low will weaken but linger near
the Warner Mountains through Saturday with showers likely and a
slight chance of thunderstorms. Meantime, a broad stronger/colder/faster
moving low will track southward to Vancouver Island overnight
then to offshore of northern Oregon by Saturday evening, and the
northern California coast by Sunday morning. This will produce
light showers along the southern Oregon coast and into Douglas
County during Saturday afternoon. A wet or very wet Saturday night
will follow with the heaviest precipitation along the Cascade
crest from Crater Lake to Mount Shasta and southward.


.AVIATION...For the 25/00Z TAFS...Scattered showers and isolated
thunderstorms are expected this evening from SE Siskiyou to Modoc
and SE Lake Counties. Some showers may linger there overnight. Most
of the rest of the area will be VFR through Saturday. However, MVFR
stratus will impact coastal areas of Coos and Curry Counties, mainly
north of Brookings tonight. MVFR will spread inland to the Umpqua
Valley, including Roseburg later this evening and last through
Saturday. Showers will become more numerous north and west of the
Umpqua Divide Saturday afternoon, then widespread showers, MVFR
ceilings and terrain obscurations will overspread much of the
area Saturday night into Sunday. -Spilde


.MARINE...Updated 200 PM PDT Friday 24 May 2019...High pressure
offshore and a thermal trough near the coast will produce gusty
north winds and steep to very steep seas through Sunday evening. The
strongest winds and heaviest seas will occur beyond roughly 3 nm
from shore, and should peak tonight through Saturday night. The
thermal trough will move inland Sunday night and wind and seas will
diminish at that time. Conditions will remain low through Wednesday,
but north winds could return by late in the week. -BPN


.PREV DISCUSSION... /Issued 509 PM PDT Fri May 24 2019/

SHORT TERM...Tonight through Memorial Day...2:00 PM Satellite
pictures are showing some clouds across portions of southern
Oregon and northern California. Mot of the clouds are of the
altocumulus variety which signals a change from high pressure to a
bit wetter weather. This is true even now as an upper level low
slides inland from the north into our area. This low will, and a
secondary low currently near Alaska will provide the majority of
our wet weather this weekend as they slowly slide south over the
coast. Expect areas north of the Umpqua Divide to see some showers
this afternoon and evening and then areas of Siskiyou, Modoc, and
southern Lake County will have the potential for an isolated
Thunderstorm or two this evening.

If you have outdoor plans for the holiday weekend, hopefully they
include plans or alternatives for wet weather. Saturday morning
will be dry for many places with the showers being most likely
north of the Umpqua Divide, the Coast, and far eastern Lake and
Modoc Counties. Some people may even wake up Saturday morning and
be fooled the dry weather with partly to mostly cloudy skies. But
showers will filter into the rest of southern Oregon and northern
California by Saturday evening as the low slides southward.
Rainfall amounts aren`t expected to be extremely heavy during the
day but could become heavier Saturday night. It is worth noting
that if this were occurring over the winter, we`d be worried about
Valley Snows. That being said, expect Saturday to be cooler than
today (except for the coast which will be similar). Snow levels
will be above Siskiyou Summit Pass around 4700 feet, but could
drop below Lake of the Woods pass. Snowfall, however, should not
be a huge issue for the pass with up to 2 inches being possible in
the Cascades above 5000 feet.

Saturday night will see some moderate to heavy rain for this time
of year, especially along the Cascades, the Siskiyous, and the
Shasta and Trinity Mountains. Additionally, the showers could be
locked to terrain overnight. The Weather Prediction Center has
placed us in a marginal risk for exceeding guidance for flash
floods in the Cascades south of the Oregon and California border.
With rain and snowmelt, this will need to be monitored in the
coming days as rises in small streams and creeks will be possible.
Main stem rivers are not expected to flood at this time.

Sunday will continue the overall rainy pattern, except for the
coast which my begin to dry out. The low pressure system will
continue to dig southward. Temperatures will rebound somewhat, but
it will still be cooler than normal. With any sun, there will be
some unstable air which could create thunderstorms, particularly
along and east of the Cascades. These thunderstorms may filter
into the Rogue Valley, including Medford and Ashland, but any
thunderstorms west of the Cascades will be isolated in nature.
Thunderstorms should not impact any festival proceedings in
Grants Pass.

For Memorial Day, the showers and thunderstorms will be possible for
one last day for most areas along and east of the Coastal Range.
Temperatures will recover to be near normal again. The showers and
thunderstorms will largely be decreasing by Monday evening and
night when things become a bit drier.

LONG TERM...Tue 28 May through Fri 31 May 2019.

The extended forecast period will begin with a long wave ridge
offshore and a trough over the intermountain states.  Short waves
diving down the back side of the downstream trough will support
showers over the area east of the Cascades Tuesday.  The west side
will remain dry during this interval. Inland high temperatures will
be around normal values.

A short wave will move over the ridge and onshore into southern
Oregon Tuesday night.  It will then dig into northern California
Wednesday into Wednesday night, carving a weak trough over the area
as it does so. The cooler air aloft will help destabilize the air
mass, and that combined with surface heating will support shower
activity, mainly in the afternoon and evening. The exception will be
the coast and the Umpqua Basin, where the marine layer will minimize
surface heating. Those areas will remain dry. Inland highs on the
west side will be 5-10 degrees above normal while the rest of the
area will see near normal temperatures.

The upper trough will drift very slowly east Thursday into Friday.
There won`t be much in the way of upstream ridging so the upper
level flow will back from northwest-north to zonal during this
interval. Shower activity will diminish and shift farther east with
time.  Inland highs will be 5-10 degrees above normal Thursday.
Friday highs will be similar to the Thursday highs on the west
side and while east side highs will be a few degrees warmer than
the Thursday highs.




Pacific Coastal Waters...Small Craft Advisory until 11 AM PDT Monday
     for PZZ350-356-370-376.
     Hazardous Seas Warning until 2 AM PDT Sunday for


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