Small Craft Advisory 62, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
855 PM PDT SUN JUN 5 2016

.DISCUSSION...As expected, strong surface heating in combination
with increasing moisture helped to generate thunderstorms across
the forecast area today. Modoc County has received 336 lightning
strikes in the past 12 hours with Klamath County coming in second
with 310 lightning strikes. Even though the afternoon balloon
sounding showed 2000+ J/KG of CAPE, only a few lightning strikes
occurred in the area as thunderstorms couldn't really get going
there. Thunderstorms are diminishing in general with a few
stronger cells remaining in Siskiyou and Lake Counties.
Precipitation observations under these storms have been hard to
come by, but what has been observed indicates the potential for
heavy rain continues until a drier air mass moves in.

Tonight, high resolution models like the HRRR are suggesting the
potential for nighttime thunderstorms over the Cascades and even
portions of the West Side. Also, the GFS20 and NAM12 show
shortwave activity meandering around the area. Therefore, I have
added a thunderstorm chance for the Rogue Valley through just
after midnight.

Tomorrow, instability, hot temperatures, and plenty of moisture
continue to fuel the chance for thunderstorms. However, a lot of
the post-processed guidance show lower probabilities for
thunderstorms, likely due to less shortwave activity in the area.
Additionally, the GFS20 has generally lower instability across the
forecast area tomorrow.

The heat advisory continues for Western Siskiyou, Josephine, and
Jackson Counties tomorrow and can be found at NPWMFR. All guidance
points to about 100 degrees in Medford tomorrow afternoon.
Moderate to strong onshore flow will bring temperatures down
tonight into the 50s or low 60s in the Umpqua Basin, and that's
why the heat advisory will end there.

The flash flood watch for area wildfire burn scars will end
tonight too, basically because confidence in thunderstorm coverage
is less for tomorrow compared to today.

Please see the previous discussion below for more details on the
thunderstorm chances and a cool down in the extended.

&&

.AVIATION...For the 06/00Z TAF cycle...LIFR conditions along the
Coos coast will remain prevalent through Monday morning with a
fairly good onshore wind gradient. This should also allow MVFR
conditions to reach Ropseburg after midnight tonight and last for a
couple hours. Thunderstorms over the Cascades and in northern CA
will gradually weaken this evening however a slight chance for
storms will remain through the night. Local MVFR conditions could
occur with thunderstorms. -mts

&&

.MARINE...Updated 300 PM PDT Sun 5 June 2016...North winds will
increase tonight through Monday as a thermal trough develops along
the South Oregon coast. Little change was made overall to the
forecast. Good confidence in gale force winds and hazardous to
affect waters mainly south of Cape Blanco and beyond 5 to 10 nm
from shore. Models similar in showing decreasing winds and seas as
high pressure building in from the west over the waters Tuesday
through Wednesday. Weak low pressure and a cold front move in from
the northwest Friday.

&&

.PREV DISCUSSION... /Issued 241 PM PDT SUN JUN 5 2016/

SHORT TERM...

Latest radar imagery shows storms firing in northern California,
and looking outside our office window, we see some towering
cumulus clouds along the Cascade range. None the less, storms
should continue to fire this afternoon into the evening hours.

There is a decent amount of potential instability over our cwa to
give us some stronger storms this evening. Dew points are
currently sitting in the lower 60's on the westside in some
locations, so we believe 1500-2000 j/kg of CAPE is reasonable for
this afternoon. SPC has also put the Eastside in a marginal risk
for thunderstorms. Latest high res guidance suggests storms
concentrated more in Siskiyou and Modoc counties instead of along
the Cascade range. None the less, storms along the Cascades are
still possible. Furthermore, precipitable water was 1.3 inches for
the 12z sounding. We still believe flash flooding is possible on
larger burn scars, especially if we see training thunderstorms. In
addition, latest radar imagery from KMAX shows very slow moving
storms in northern California. None the less, we're still keeping
the flash flood watch for the large burn scars on the Cascade
range.

As for the heat concerns, above average temperatures aloft will
continue for Monday before a slight flow shift allows for
slightly cooler temperatures into Tuesday. Then we'll see north
west winds kick up and drop the highs into the 80's. With this
northwest flow shift, we'll see multiple cold fronts approach the
region.

As for the continued chance of thunderstorms, it's very hard to
see a solid forcing mechanism for thunderstorms after today, yet
models seem content to keep thunderstorms in the forecast through
Wednesday.Therefore, we have a very low confidence in convection
Monday through Tuesday.

-Smith

LONG TERM...Thursday (June 9th) through Sunday (June 12th)...Models
remain in good agreement in the extended period. It will be much
cooler than we've seen, especially late this week into the weekend
as a relatively strong upper trough moves through the Pacific
Northwest. A front will already be east of us on Thursday with some
showers and east side thunder possible. Highs on Thursday will be
around normal, which is a far cry from what we've been seeing. The
cooler air and better chance for precipitation comes Friday and
Saturday as the upper low moves through. Temperatures during that
stretch will be 5-10 degrees below normal, and snow levels may drop
below 5000 feet Friday night and Saturday. Precipitation will be
lessening by the time that happens, so we don't expect much impact
from snow, but it just shows how cool the airmass is expected to be.
Temperatures will probably rebound a little on Sunday and Monday
with diminishing precipitation chances. But both the GFS and ECMWF
are showing another chilly cold front moving through around the
middle of next week. -Wright

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Heat Advisory until 11 PM PDT this evening for ORZ023-025.
     Flash Flood Watch until 11 PM PDT this evening for ORZ027>029.
     Heat Advisory until 8 PM PDT Monday for ORZ024-026>028.

CA...Flash Flood Watch until 11 PM PDT this evening for CAZ083>085.
     Heat Advisory until 8 PM PDT Monday for CAZ080-081.

Pacific Coastal Waters...Small Craft Advisory until 11 AM PDT Tuesday for
     PZZ350-356-370-376.
     Gale Warning from 11 AM to 11 PM PDT Monday for PZZ356-376.
     Hazardous Seas Warning from 11 AM Monday to 5 AM PDT Tuesday for
     PZZ356-370-376.

NSK/TRW/MTS