Wildfire in California, July 22 to 31, 2020

Area Forecast Discussion
National Weather Service Medford OR
853 AM PDT Wed Jul 22 2020

.DISCUSSION...Forecast is in pretty good shape this morning with only
some minor adjustments to marine winds to account for lesser wind
around buoy 027. Main story today is the afternoon thunderstorm
event. We observed about 150 strikes in the county warning area
yesterday, and it looks likely we'll at least double that amount
today. Thunderstorms this afternoon will be limited to Siskiyou
county and the east side, and a few storms could contain
downdrafts with wind gusts of 40 to 60 mph. This should be of
heightened concern for anyone working in fire today. Stavish

&&

.AVIATION...For the 22/12Z TAF Cycle...IFR ceilings along the
coast, just offshore into the Coquille Basin will persist through
the morning. The exception could be from around Port Orford and
points south to southwest over the waters.

The marine stratus will erode towards the coast this afternoon, but
it may not be enough for ceilings to improve to VFR at North Bend
thus we'll keep the lower conditions in the TAF. The marine stratus
will push inland into the Coquille Basin.

Elsewhere, VFR conditions are expected through the TAF period. Gusty
winds are expected at the TAF sites for the late afternoon and early
evening. The other main concern will be thunderstorms east of the
Cascades and in portions of northern California during the afternoon
and evening. Some of these storms may be strong, and will be most
numerous over Modoc and Lake Counties. Could not rule out an
isolated thunderstorm at Klamath Falls, but the guidance is showing
a low probability of that happening. For now did not mention any
thunder at Klamath Falls, but later shifts will need to take another
look at this when new data comes in. So watch for updates on this.
-Petrucelli

&&

.MARINE...Updated 845 AM PDT Wednesday, 22 July 2020...Moderate
north winds will continue today south of Cape Blanco, though there
is currently an lighter wind eddy in the Buoy 27 to Brookings
area this morning. Winds will then diminish this evening with a
relative break in the weather tonight into early Thursday. North
winds will then increase again Thursday afternoon and evening with
Small Craft Advisory level conditions likely. Gales will be
possible across the coastal waters south of Cape Blanco both
Friday and Saturday afternoons and evenings. ~BTL

&&

.PREV DISCUSSION... /Issued 444 AM PDT Wed Jul 22 2020/
Updated Aviation Discussion. DISCUSSION...The Red Flag Warning
continues this afternoon and evening for much of northern
California and south central Oregon. The excluded portions are
northwest Siskiyou County, the vicinity of Mount Shasta, and far
western and northern portions of Klamath County. While, scattered
coverage of storms is expected to be greatest from Modoc County
into southern Lake County. Significant lightning is expected with
these thunderstorms which is likely to result in new fire starts.
Gusty outflow winds are also expected from some of the
thunderstorms. These storms will be faster moving than those of
Tuesday, with steering flow generally west at 10 mph.

Low pressure just offshore of the San Francisco Bay Area will
shift inland today while a dry cold front at the southern Oregon
coast moves to near the Cascades. This front is in advance of a
trough near the Alaskan coast. Instability will increase from
this afternoon into the early evening in the region of moist mid-
level air ahead of the front. On Thursday, the front and region of
greatest instability will be well east of our area, but the
trigger of a weak shortwave does warrant including a slight chance
of thunderstorms for the Warner Mountains of far eastern Lake
County during late Thursday.

This pattern will also continue thick low clouds at the coast
through Thursday morning, especially north of Cape Blanco, with a
few brief breaks in the stratus possible late this afternoon. The
stratus on Thursday night will follow more of the typical pattern
of late night and early morning coverage, mainly north of Cape
Blanco. This will also bring a brief cooling trend across our
area, just through Thursday, as the upper trough axis swings
across the Pacific Northwest. This will result in high
temperatures generally right around normal on Thursday.

Model agreement remains very good through Sunday. This leads to
high confidence in a new warming trend Friday into Sunday, with
a ridge building into our region and highs on Sunday quite
similar to those of yesterday. There should be a stable air mass
over the area on Friday and Saturday, then at least a modest
increase in available moisture on Sunday with cumulus cloud
development over Modoc County into southern Lake County. These
finer scale details are tough to discern this far in advance, but
a bump up to mentioning a risk of thunderstorms is possible as we
draw nearer to Sunday.

Model agreement quickly deteriorates beyond Sunday, especially
beyond Monday. But, the upper level pattern on Monday may bear a
slight similarity to that of today. As such, a slight chance of
thunderstorms was included for some of the higher terrain from the
Cascades eastward.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 11 PM PDT this evening for ORZ624-625.

CA...Red Flag Warning until 11 PM PDT this evening for
     CAZ280-281-284-285.

Pacific Coastal Waters...Small Craft Advisory until 5 AM PDT Thursday
     for PZZ356-376.