Small Craft Advisory 66, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
826 PM PDT Mon Jul 23 2018

.DISCUSSION...Thunderstorms are ongoing across portions of
Siskiyou County as well as showers trying to develop into storms
in eastern Modoc County. These storms are dissipating as they
cross the California and Oregon border, but this could change over
the next few hours as previous storms prime the area with more
moisture.

Otherwise, smoke; heat; and poor air quality are the main stories
around most of southern Oregon and northern California. The
exceptions to this will be for most of the coast (north of Gold
Beach) and the Umpqua Basin. Portions further east (Lakeview and
Alturas) are seeing minimal smoke effects, and are not nearly as
bad as Jackson and Josephine Counties. This pattern is expected to
continue for the next several days, and will be the overall
status quo for the foreseeable future. Have decided to not make
any chances to the forecast for now. -Schaaf

&&

.AVIATION...For the 24/00Z TAFs...Wildfire smoke continues over
most of the inland areas west of the Southern Oregon Cascades as
well as some locations just east of the Cascades. MVFR
visibilities/cigs and local IFR conditions will prevail over these
areas, especially in Jackson and Josephine counties.

Along the coast and over the coastal waters, areas of IFR cigs/vsbys
will continue tonight and Tuesday morning with conditions becoming
VFR along the coast in the late morning and early afternoon.

Outside of the smoke and marine stratus, VFR conditions will
prevail. However, there will be isolated afternoon and evening
thunderstorms over northern California and from the Cascades east
this evening and on Tuesday. Gusty winds and hail are possible near
these thunderstorms. -CC

&&

.MARINE...Updated 800 PM PDT Monday 23 July 2018...Offshore high
pressure and a thermal trough inland will persist through this
week. Light to moderate north winds will persist with the
strongest winds south of Cape Blanco in the afternoons and
evenings. These winds are expected to briefly reach small craft
advisory criteria late Tuesday afternoon and early Tuesday evening
between Cape Blanco and Gold Beach, mainly beyond 5 nm from
shore. However, have kept with the small craft for hazardous seas
due to the small area and time frame affected.

Steep seas will linger north of Cape Blanco mainly beyond 15 nm from
shore. On Tuesday, expect the steep seas to occur from Cape Blanco
south. Small craft conditions are expected Wednesday through at
least Friday but may expand north of Cape Blanco. -CC

&&

.PREV DISCUSSION... /Issued 248 PM PDT Mon Jul 23 2018/

DISCUSSION...The latest visible image shows marine stratus along
the coast, north of Cape Blanco and high level cloud deck ahead of
a weak upper low near 135W and 35N. Also cumulus build ups are
taking shape over the Cascades, Siskiyous, higher terrain east of
the Cascades and northern California. So far one lightning strike
has been observed in Shasta County (which is south of our forecast
area). Meanwhile areas of smoke continue to plague the westside
valley locations.

There's good agreement most of the instability will be confined in
northern California from the Marble Mountains east-northeast into
Medicine Lake and Northwest Modoc County. The only difference from
yesterday is the upper flow (steering winds) is slightly more
southerly. Therefore there is concern for a few isolated
thunderstorms to pop up over the southern Cascades, Siskiyous and
east of the Cascades. The one limiting factor for isolated
thunderstorm development along the southern Cascades and Siskiyous
will be the extent of the smoke. If the smoke remains thick enough,
it will act to inhibit thunderstorm formation.

Also unlike yesterday, PWAT's are higher. The Medford sounding this
morning showed PWAT at 1.16 inches. So there's more moisture, but
the model soundings show a dry sub-layer and there's a chance any
little if any rain that comes from any storms will not reach the
ground. The exception will be from the Marble Mountains northeast to
Medicine Lake where moisture is more abundant. Also gusty winds are
possible near any storms. Therefore the concern is heightened for
new starts from lightning.

Isolated storms will fizzle out later this evening with dry
conditions overnight. The GFS hangs on to some QPF tonight in
Northern California while the NAM and short range high res models do
not. Note: Yesterday's GFS also shows QPF in the overnight period
and nothing materialized. Given the fact mid level moisture is
decreasing and losing daytime heating and little or no trigger,
suspect the GFS is overdone, so we'll go with dry conditions
tonight.

The threat of thunderstorms exist again Tuesday afternoon as some
monsoonal moisture from the Sierra Nevada moves north into our area.
It looks like the best chance for thunderstorms will be in the
Sierras, but still cannot not rule out something in northern
California and east of the Cascades late in the afternoon and
evening. The reason for this is mid level moisture and instability
will be increasing and the models hint at weak embedded shortwaves.

Thursday through next weekend will be dry with no threat of
thunderstorms.

Were looking at hot temperatures just about everywhere with near or
triple digit values for the Rogue, Illinois, Applegate, Shasta,
Scott and Klamath River valleys into next weekend. For now we'll
keep the forecast high temperatures slightly below guidance due to
the smoke, but if it clears out enough, then we could be looking at
higher max values. There will be some, but not a lot of relief in
the overnight period tonight and Tuesday night. Thus, a heat
advisory remains in effect. Please see NPWMFR for more details. The
coast will be the only place where temperatures will be near normal
with a persistent weak onshore flow. -Petrucelli

FIRE WEATHER...Updated 300 PM PDT Monday 23 July 2018...
Latest satellite imagery shows widespread smoke west of the Cascades
with some upper level clouds starting to move into the area. The
radar is also starting to show some convective activity in northern
California as we hit our convective temperature.  We feel that
thunderstorms will form in northern California this afternoon and
drift into the eastern parts of the Cascades outside of the smoked
over areas.  Given some model disagreement in convection, still feel
that the threat for storms will be isolated this afternoon and
evening.

Thunderstorms are still possible Tuesday afternoon and evening as an
upper level low over the Pacific and a ridge to the east continue to
bring in some moisture to southern Oregon.  Model soundings suggest
there is plenty of instability in northern California away from the
smoke, so we'll have a slight chance for thunderstorms yet again on
Tuesday.

The other topic will be temperatures warming up today and for the
next few days as highs push into the upper 90's in the smoke filled
valleys.  RH's shouldn't be that dry with this extra moisture moving
into the region from the south.  They will start to dry out on
Wednesday night with moderate recoveries on the mid elevation
ridges.

-Smith

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Heat Advisory until 11 PM PDT Wednesday for ORZ024-026.

CA...Heat Advisory until 11 PM PDT Wednesday for CAZ080>082.

Pacific Coastal Waters...Small Craft Advisory for hazardous seas until 5 AM PDT Wednesday
     for PZZ356-376.
     Small Craft Advisory for hazardous seas until 5 AM PDT Tuesday
     for PZZ350-370.

BMS/CC/MAP

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