Wildfire in Oregon, November 1 to 7, 2023

Area Forecast Discussion
National Weather Service Medford OR
620 PM PDT Tue Oct 31 2023

.SYNOPSIS...The weather will become active late Wednesday night
through early next week. An atmospheric river will bring plenty of
rain to the region. There is a very low chance(5%) of the rain
being excessive along the coast this weekend. If the excessive
does occur, then the rain could produce rock slides and isolated
flooding.

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.DISCUSSION...

Another mild fall day across the forecast area with temperatures
pushing into the 60's. High pressure remains built in over the
forecast area, although it will break down as upper level heights
slowly decrease later tonight into Wednesday. South west flow
will increase ahead of the next low and temperatures will still
remain higher than normal. Some areas might even be slightly
warmer on Wednesday as the southwest flow enhances downsloping
over some areas. In addition, the moist southwest flow will
increase precipitation chances along the Oregon coast. The best
chances will be along the Central Oregon coast north of Coos Bay.
Precipitation will be light once the warm front pushes through mid
day Wednesday.

Weather impacts will be minimal Wednesday as there won't be a lot
of precipitation in our forecast area. We're forecast under 0.15
inches of rain for all locations and many areas will indeed stay
dry on Wednesday as the warm front loses some organization and
almost stalls out.

As an upper level low strengthens off the British Columbia
coastline, southwest flow will persist and a cold front will
begin to push into this warm moist flow around Thursday morning.
This is when our area will begin to see wetting rainfall(>0.25
inches). Most of the rain will fall within the Kalmiopsis
Wilderness and areas in Curry County. This is a pretty typical
storm system for fall and doesn't appear that hazardous. Only
minor impacts are anticipated at this time. Areas within Curry
County will see 2-3 inches of rain in 24 hours with most areas
west of the Cascades seeing 0.5 to 1.5 inches of rain. Areas east
of the Cascades will see less than 0.5 inches of rain.

By Friday morning, the dynamics of everything appear to diminish.
However, the probability of precipitation still remains around 70
percent Friday morning. It's entirely possible the rain keeps
falling at a lower rate over southern Oregon. The ensembles and
NBM seem to think so with the probability precipitation remaining
high.

The concern turns towards the weekend when we're on the receiving end
of another atmospheric river. The confidence is low in this case
as the full suite of ensembles show the atmospheric river being
fairly dry and fairly wet. The worst case scenario has prompted an
excessive rain risk issued by weather prediction center. The risk
is marginal(~5%), which is fairly accurate given the small sample
set of data showing excessive rain. If the excessive rain did
occur, then the Kalmiopsis Wilderness could see up to 12-16
inches of rain in 24 hours, which is a pretty healthy chunk. It's
also worth stating that 5% of the drier solutions show rain
accumulation under 1 inch. In any case, an atmospheric river will
likely impact some section of the west coast this weekend. Where
and how intense seems to still be up in the air. Lastly, this is a
warm airmass, so snow level swill be 9000 to 10000 feet, so no
snow except up on Mt. Shasta.

Even after the weekend, ensembles keep the wet trend of weather
continuing. The probability of precipitation remains high(>80%)
Monday into Tuesday as the atmosphere remains active.

-Smith

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.AVIATION...01/00Z TAFs...Widespread mid to high level clouds will
move across the region tonight ahead of a warm front that lifts
north of the area Wednesday. Mainly VFR conditions are expected
tonight. However, there is a chance that LIFR conditions will
develop at KRBG late tonight into Wednesday morning but it will
depend on the extent and thickness of the higher clouds above.

Lowering ceilings are expected during the day on Wednesday.
Precipitation may reach the coast by late in the day but much of it
could hold off until Wednesday evening. Freezing levels along the
coast and offshore will remain above 10,000 feet (MSL). Sandler

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.MARINE...Updated 100 PM Tuesday October 31, 2023...Relatively
light winds and seas will continue under high pressure today, with
areas of fog and low stratus. A warm front will move through
Wednesday with gradually increasing south winds and steadily
increasing wind seas.

Stronger south winds are expected to develop Wednesday night into
Thursday when a cold front arrives and pushes through the coastal
waters. Advisory strength south winds and steep to very steep seas
are expected, with brief periods of gale force gusts possible. Some
improvement is possible on Friday, but will be short lived as
another strong front is likely Friday night into Saturday. The
outlook is for gradual improvement early next week with swell
dominated seas.

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.MFR WATCHES/WARNINGS/ADVISORIES...
OR...CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory from 5 PM Wednesday to
     8 PM PDT Thursday for PZZ356-376.

Hazardous Seas Warning from 5 PM Wednesday to 8 PM PDT Thursday
     for PZZ350-356-370-376.

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