Wildfire in Oregon, July 21 to 31, 2020

Area Forecast Discussion
National Weather Service Medford OR
915 AM PDT Tue Jul 21 2020

.DISCUSSION...Current satellite imagery is showing the marine
layer push across Coos and coastal Douglas County with largely
clear skies elsewhere. In Medford at 8:15 AM, it was already 70
degrees, so our temperatures are going to be hot once again. Our
heat advisory continues through this evening. Please see the
NPWMFR for more details. We also may get a couple of thunderstorms
(isolated) south of the Siskiyou and east of the Cascades. This
is well-forecast, so no changes are needed in this update.

The main areas that we will be looking at will be the thunderstorm
potential for tomorrow, as well as taking a look at temperatures
as we look to rise again late this week. -Schaaf/Rogers

&&

.PREV DISCUSSION... /Issued 523 AM PDT Tue Jul 21 2020/

DISCUSSION...A weak but broad upper trough along the northern
California coast, and a dry cold front ahead of/associated with a
northern Pacific trough will be the main drivers of our short term
weather.

The forecast for the next week is largely consistent with the
previous issuance. Though, a focus was placed on increasing the
coverage and duration of coastal low clouds through Thursday
morning, and fine tuning the probability of both isolated late day
thunderstorms today and isolated to scattered coverage on
Wednesday. This includes a continued Fire Weather Watch
/PDXRFWMFR/ from late Wednesday morning through Wednesday evening
over eastern Siskiyou County, southeastern Klamath County, and
most of Modoc and Lake counties.

Some of the aforementioned consistent aspects include
temperatures, with another very hot day expected today for inland
locations. Highs will generally be 5 to 15 degrees above normal
with similar readings as occurred Monday afternoon. A dry cold
front will push into western Oregon on Wednesday, then east of our
area by Thursday morning. As a result, temperatures will be
closer to normal during the remainder of this week.

Breaks in the coastal stratus are expected this afternoon, then the
mid-level onshore flow with the front will bring a longer duration
of stratus/less clearing during Wednesday afternoon with farther
inland extent from late this evening through Wednesday into
Thursday morning.

Instability, available amounts of mid-level moisture, and the
strength of mid-level steering flow all still look to be greater
on Wednesday afternoon than this afternoon. But, thunderstorms in
our area on both days look to be largely restricted to northern
California and south central Oregon...Siskiyou, Modoc, Klamath,
and Lake Counties. The bulk of model solutions continue to show
the most favorable conditions for thunderstorm development on both
days over central and eastern Siskiyou County across southeastern
Klamath County, Modoc County, and Lake County. Isolated
thunderstorms this afternoon will be very slow moving (mainly
driven by a south wind at 5 mph becoming a west wind at 5 mph in
the evening) with many of the storms likely remaining anchored to
the higher terrain.

There is better model agreement on storm location this afternoon,
which largely supports the inherited forecast. Meanwhile, there
is higher uncertainty related to the inland extent reached by the
dry cold front by the time that peak heating approaches on
Wednesday. The 00Z and 06Z GFS data sets are among the slowest
solutions, which would suggests some possibility of a few storms
developing late Wednesday farther north and west in Siskiyou
County. Another aspect not supported by the other models, but
worth mentioning and monitoring is that the very recently arrived
06Z GFS nudges a pocket of that farther west and north instability
on Wednesday evening from north central Siskiyou County across
far southeast Jackson County, near Pilot Rock and Parker Mountain.
What is most likely on Wednesday is a focus for activity on Modoc
and Lake Counties with a west-southwest to west steering flow of 5
to 15 mph.

The dry front will push this region of instability east of our
area on Thursday afternoon, although the remnants of the front
itself could help isolated thunderstorms develop along it, over
far eastern Lake County. A much drier air mass at mid-levels will
be in place behind the front. The air mass is likely to remain
stable at least through the weekend with a persistent trough over
western Canada.

Another strong warming trend is possible early next week, and
along with it may come the next concern for thunderstorm
development.

AVIATION...For the 21/06Z TAF Cycle...The stratus is covering all
of the coastal waters and inland over the Coquille Basin. A repeat
of the burning off of the stratus to just offshore will return this
afternoon. Gusty winds are likely mainly from Cape Blanco north
along the coast and just offshore. Winds south of Cape Blanco at
the coast are not expected to be as strong, but it will still be
rather windy just offshore.

Elsewhere, VFR conditions are expected through the TAF period. Gusty
winds are possible late in the afternoon and evening at Roseburg and
Klamath Falls. Breezy winds are also possible in Medford in the same
e time period.

The main concern will be isolated thunderstorms in northern
California into southern Klamath and Lake counties Tuesday afternoon
into early Tuesday evening with gusty and erratic winds near any
storms. -Petrucelli

MARINE...Updated 200 AM PDT Tuesday, 21 July 2020...The thermal
trough will remain in place resulting in moderate north winds,
especially offshore and south of Cape Blanco to around Gold Beach
through tonight. The continued northerly fetch of winds will keep
seas elevated and hovering right around Small Craft Advisory
criteria through Wednesday evening with small craft conditions
likely to be mainly confined to south of Cape Blanco by this
evening. Winds will remain comparatively lower near the coast south
of Gold Beach.

Winds will diminish briefly as the thermal trough weakens Wednesday
night into Thursday morning, then is expected to strengthen again
Thursday afternoon with at least small craft conditions south of
Cape Blanco and possibly hazardous seas conditions from around Gold
Beach south and beyond 5 nm from shore. Winds are expected to
strengthen further with gales possible towards the end of the week
and possibly lasting into next weekend. North winds will remain
highest during the afternoons/evenings. -Petrucelli

FIRE WEATHER...Updated 800 PM PDT Monday 20 July 2020...Overnight
into early Tuesday morning humidity recoveries will be poor to
moderate again over the mountains over Siskiyou and Modoc counties
as well as far southwest Oregon.

Moisture and instability will increase Tuesday as an upper level
low moves onshore to our south. Isolated thunderstorms are
expected across the mountains of northern California with a few
developing farther north into fire zones 624/625. Scattered
coverage is not expected. By Wednesday, conditions will be
sufficient for scattered storms in roughly the same areas, and a
fire weather watch for abundant lightning on dry fuels is in
effect. See PDXRFWMFR for details. Temperatures will be
closer to normal during the latter portion of the week.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Fire Weather Watch from Wednesday morning through Wednesday
     evening for ORZ624-625.
     Heat Advisory until 8 PM PDT this evening for ORZ024-026.

CA...Fire Weather Watch from Wednesday morning through Wednesday
     evening for CAZ284-285.
     Heat Advisory until 8 PM PDT this evening for CAZ080-081.

Pacific Coastal Waters...Small Craft Advisory until 8 PM PDT this evening for
     PZZ350-356-370-376.
     Hazardous Seas Warning from noon today to 5 AM PDT Wednesday for
     PZZ356-376.