Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 222201
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
301 PM PDT Thu Oct 22 2020

.DISCUSSION...A few forecast challenges over the next 7 days with
most of the attention through Monday on fire weather concerns (see
the lengthy fire weather discussion below).

Issued another freeze warning for the western valleys except for
a frost advisory again in the Umpqua Basin. Low temperatures
Friday should be a couple of degrees colder than Thursday morning
due to a colder daytime high today and drier air (lower
dewpoints). Higher clouds could move into the region early Friday
morning from the northwest but most areas will be clear or mostly
clear. This could be the last freeze warning of the season for
these areas depending on how cold it gets Friday morning. The
Umpqua Basin and coast will see frost/freeze products continue.

A cold front will move through our region Friday night and early
Saturday followed by progressively colder and drier air mass.
This front will bring light rain to mainly the coast, Umpqua, and
Cascades but there is a chance of measureable rain south of these
areas too. The most precipitation will occur in the Cascades from
about Crater Lake northward due to stronger upslope flow. There
should be a little snow early Saturday morning at Crater Lake.

Behind this front there will be modified arctic air blowing into
our region from the northeast as a 1040+ mb high pressure center
moves from Canada into the northern Rockies. These north to northeast
winds will likely become gusty late Saturday night and Sunday on
the mountain slopes and ridges but could also make it into the
valleys, especially east of the Cascades and across the Shasta
Valley in Siskiyou County. Low temperatures will be especially
tricky due to winds and the cold airmass. Single digits and teens
will occur Sunday and Monday mornings on the east side and some of
these areas could even see lower wind chills.

After the gusty winds on Sunday into early Monday a large area of
Pacific high pressure will build from the west and remain over the
area much of the week. This high will keep dry air around with
large swings in daytime and nightime temperatures.
Sandler

&&

.AVIATION...For the 22/18Z TAFS...VFR conditions are expected
through the TAF period. Gusty winds are expected again along the
coast and just offshore late this morning into this evening.
-Petrucelli

&&

.MARINE...Updated 200 PM PDT Thursday, 22 Oct 2020...A strong
thermal through will continue tonight, then weaken Friday. Moderate
to strong north winds will continue through tonight with gales
likely south of Cape Blanco and beyond 5 nm from shore south of
Gold Beach and beyond 8 nm from shore. Elsewhere, expect small
craft conditions.

The thermal trough will gradually weaken Friday morning as a front
approaches the northern waters. This will result in winds
diminishing for a brief time from late Friday morning into Friday
night. Saturday, winds and seas will increase and will remain
windy through the start of next week, with at least another round
of small craft conditions and the potential for very steep
hazardous seas conditions in the southern outer waters.
-Petrucelli

&&

.FIRE WEATHER...Updated 200 PM PDT Thursday Oct 22 2020...

The thermal trough has returned along the coast, and winds have
already shifted to the northeast and intensified over the ridgelines
of the Cascades, Siskiyous, and the southern Coastal Ranges, with
reports of gusts over 35 mph already being recorded at Red MOund and
Quail Prairie. Humidities have also started to lower, and conditions
will only get drier as the east winds continue today and tonight.
Humidities and winds are still expected to approach critical
thresholds, and a Red Flag Warning remains in effect for the upper
slopes and ridges for fire zones 280 and 621, including the Slater
and Red Salmon Fires, for today and tonight. In all, it looks like
the Slater Fire will suffer the stronger winds with somewhat higher
humidities, while the Red Salmon Complex in Siskiyou County will see
the lower humidities but also marginally weaker winds. Generally
speaking, this event will be similar to the one we saw last week.

A front arrives Friday into Saturday, and once again, breezy winds
are expected over the higher terrain and the East Side.
Precipitation chances will be a bit more robust and should spread
over most of the forecast area, with wetting rains possible (though
not likely) along the coast, the Umpqua Basin, and the western
slopes of the Cascades. Only light rainfall is expected elsewhere.

The coldest air mass of the season so far is expected to dig south
into the region behind the front. Combined with the rebounding
thermal trough along the coast, a sharp east/west gradient is
expected to develop, likely resulting in another east wind event for
the region, although it appears more and more likely that this will
be a strong, multi-day event. Breezy to gusty east winds, dry
conditions, and widespread moderate to poor recoveries are expected
Sunday through at least the middle of next week. That being said,
some of our guidance has continued to trend this event stronger, and
ensembles are showing this to be possibly one of our more extreme
events for this time of year, with some model guidance suggesting
gusts up to 50 mph over the ridges of Curry, eastern Josephine, and
western Siskiyou Counties Sunday evening. Meanwhile, the Cascades
could see wind gusts to 45 mph and some of our valleys (southern
Rogue, Shasta) could see wind gusts to 30 mph. Have issued a Fire
Weather Watch for this event with a little earlier timing than our
neighbors since our winds will begin to increase in the north a
little earlier and travel southward. The concerns with this event
will hinge on any rainfall amounts and coverage with the preceding
front, as well as if winds mix into the valleys versus being only
for the upper slopes and ridges. Areas not receptive to fire
spread (the coast) will continue to see a headline in the FWF in
addition to the Fire Weather Watch.

Although the winds will decrease Monday, they will remain from the
east, so relief will not come from a marine push. Thus, recoveries
will remain in the poor to moderate range. A weak disturbance could
pass overhead Tuesday, briefly disrupting the pattern.
-Schaaf/BPN

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Fire Weather Watch from late Saturday night through Monday
     morning for ORZ619>623.
     Frost Advisory from 2 AM to 9 AM PDT Friday for ORZ023.
     Freeze Warning from 2 AM to 9 AM PDT Friday for ORZ024-026.
     Red Flag Warning until 11 AM PDT Friday for ORZ621.

CA...Fire Weather Watch from late Saturday night through Monday
     morning for CAZ280>282.
     Red Flag Warning until 11 AM PDT Friday for CAZ280.
     Freeze Warning from 2 AM to 9 AM PDT Friday for CAZ080>082.

Pacific Coastal Waters...Small Craft Advisory until 5 PM PDT Friday for
     PZZ350-356-370-376.
     Gale Warning until 5 AM PDT Friday for PZZ356-376.
     Hazardous Seas Warning from 5 AM to 11 AM PDT Friday for PZZ376.

$$



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