Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 201552
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
852 AM PDT Wed Mar 20 2019

.DISCUSSION.., 8 AM observations were showing rain across
southern Siskiyou County, especially near Mt. Shasta City.
Otherwise, radar returns are largely focused in the Siskiyous
along the California and Oregon border. There are some light
returns spread out across southern Oregon as well. That being
said, most of the returns are actually not reaching the ground.
This is because the observed sounding at the Medford Office as
well as several forecast soundings around the area are showing
low to mid level dryness. As a result the virga (or precipitation
that falls, but evaporates before reaching the ground) will work
to moisten the atmosphere through the morning into the afternoon
across most of the area in order for showers to reach the ground.
That being said, showers are likely already reaching the ground in
the higher terrain of the Siskiyous and Cascades. Regardless, any
precipitation will be light today.

Some ensembles are showing the potential for thunder this afternoon,
mainly across the Cascades and areas to the east as others suggest
the Umpqua area to be the winners today; but am not enthusiastic
about the chances quite yet as it appears that we may not have all
of the ingredients necessary. But the fact that some of the clouds
appear to be dissipating (via satellite imagery) makes things
interesting. For now, am not making changes to the forecast; but
will reserve the right to change the forecast if cumulus buildups
(or pre- thunderstorm clouds) start developing. -Schaaf

&&

.MARINE...Updated 800 AM PDT Wednesday, 10 March 2019...
Low pressure currently moving in from the southwest will bring a
slight increase in south wind, as well as more showers today. These
showers are likely to taper off tonight, while light southerly wind
continues. Southerly winds will increase to advisory levels early
Friday and then may reach gale force beyond 10 nautical miles of the
coast during the day Friday. The latest models suggest winds
slightly stronger than our current forecast indicates, with
sustained south winds of 30 to as high as 40 kt possible during the
Gale Watch time period Friday. Building long period west swell
Friday and southerly wind waves are also expected to result in
hazardous seas, likely peaking in 12 to 17 foot range. While winds
will then diminish, elevated long period swell is expected to
continue to bring conditions hazardous to small craft through the
weekend.

It should be noted that a Beach Hazards Statement has been issued
for an increased threat of sneaker waves Thursday afternoon into
Thursday night, due to the expected long period swell. This swell,
when peaking through Saturday, is expected to produce hazardous bar
conditions and higher than normal surf. -BTL/BPN


&&

.PREV DISCUSSION... /Issued 611 AM PDT Wed Mar 20 2019/

SHORT TERM...Upper level troughing stretches from a low center
near the Aleutians into California this morning. One particularly
vigorous shortwave within the system is moving northward through
central California this morning. Locally, there are echoes on
radar that look like precipitation, but the majority of this is
probably still aloft as evidenced by the fact that virtually none
of our obs sites have shown any rain over the last few hours.
Nevertheless, there is band of significant rain south of Redding
and moving north at this hour. Guidance shows that band mostly
affecting Siskiyou and Modoc counties later this morning, but some
of it will certainly creep across the border into Oregon today.
The locations in Oregon that are most likely to see rain today are
those prone to southeast upslope flow like the Cascades/Siskiyous
and east side mountains as well as the Klamath Falls area. While
those are the favored areas today, I wouldn`t rule out rain
anywhere in our forecast area. That said, it`s not hard to imagine
the Rogue Valley being in a rain shadow today. As a result of all
this, today will be much cooler than yesterday in most areas.

As a portion of the trough closes off and moves through California
tonight and into the Great Basin tomorrow, precipitation becomes
more scattered over our area. However, with deep, moist southeast
flow continuing, rain chances continue almost everywhere through
tomorrow. Those areas prone to southeast upslope will still remain
favored, of course. The next significant wave in the pattern is
expected to bring widespread valley rain, high mountain snow, and
locally breezy winds Friday. The extended forecast remains largely
unchanged, and the discussion from yesterday follows. -Wright

LONG TERM...Saturday through Wednesday, March 23-27, 2019...
Following Friday night`s front, an upper trough axis will move
through the CWA Saturday. As the front pushes through the Great
Basin, steadier precipitation across far SE sections in the
morning will end, while most other areas have a brief break post-
front. Showers are expected to re-develop as instability increases
later Saturday morning and Saturday afternoon. There could be
some potent showers out there, especially along and west of the
Cascades, but model thunder parameters are not that impressive at
this time.

Showers should end with the loss of instability Saturday evening,
then short wave ridging builds in overnight Saturday into Sunday.
The air mass doesn`t look cold enough to have a large impact on
agriculture, with forecasted low temperatures in the low to mid 30s
for the west side valleys Sunday morning.

With the ridge in place Sunday, overall, dry, mild weather is
expected with highs in the low to mid 60s west of the Cascades and
in the low to mid 50s over the east side. Locally breezy conditions
may develop in the afternoon.

The next front offshore will approach the coast Sunday night, then
move onshore Monday. There should be a period of gusty south to
southeast winds in advance of the front, especially in the typical
locations like the Shasta Valley, southern end of the Rogue Valley
and over the east side. While a period of steadier precipitation
will likely accompany the front, especially along and west of the
Cascades, it doesn`t appear to be a big rain-maker at this time.

Broad SW flow aloft will set up Monday night with another
disturbance offshore expected to move into the area Tuesday.
There is a reasonable amount of spread in the guidance with respect
to this system, with some models taking it north into our area, but
others keeping it farther south with most of the heavier
precipitation directed into California. Have gone with a blend of
solutions here, but this still keeps the best precipitation across
our southern and western zones. Either way, we`ll maintain an
unsettled weather pattern into mid-next week with temperatures
fairly close to seasonal averages. -Spilde

AVIATION...For the 20/12Z TAFS...
Moderately strong winds above a surface inversion could lead to low
level turbulence in the Klamath Falls area this morning through 18Z.
Otherwise, a wave of low pressure will continue to move through the
area today bringing showers, most numerous in California and,
primarily focused in the Mount Shasta area. While partial mountain
obscurations will occur throughout the day, MVFR valley ceilings are
expected to be almost only for Siskiyou County, lowest in the Mount
Shasta area. This evening through tonight the showers will taper
off. Periodic/brief MVFR is possible for much of the forecast area,
especially for the coast and Umpqua Basin, this evening through
tonight. BTL

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Beach Hazards Statement from Thursday afternoon through late
     Thursday night for ORZ021-022.

CA...None.

Pacific Coastal Waters...Gale Watch from late Thursday night through Friday afternoon for
     PZZ370-376.

$$



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