Wildfire in Oregon, November 1 to 9, 2018

Area Forecast Discussion
National Weather Service Medford OR
840 PM PDT Wed Oct 31 2018

.DISCUSSION...Deep, moist onshore flow continues over our area
this evening, and as this deeply saturated airmass is forced over
the terrain, light rain and drizzle is squeezed out. Over the
last hour, numerous sites (primarily coast and mountains) have
received measurable rain, but just barely, with most locations
only registering a hundredth - the bare minimum amount of rain
that can be called "measurable." Guidance is unanimous in the
precipitation diminishing from south to north through the night as
a ridge begins amplifying over the area and heights rise. Even as
rain ends, it will remain damp and drippy over the west side as
all this residual moisture congeals into stratus and fog. Indeed,
this is already happening in the Rogue Valley around Medford, and
these clouds and fog will likely ebb and flow at most west side
locations throughout the night. A couple of changes were needed
this evening: to change the weather to rain and drizzle rather
than showers since none of this is convective in the least and to
insert some fog this evening. The new forecast will be sent
shortly. -Wright

&&

.AVIATION...For the 01/00Z TAFs...Areas of IFR/LIFR cigs/vsbys in
low clouds, fog, drizzle and showers will persist into Thursday
morning with the greatest coverage along the coast and in the west
side valleys. Higher terrain will be obscured. All areas will
clear to VFR by Thursday afternoon, but the lower conditions will
return to the coastal and west side valleys Thursday night into
Friday morning.

&&

.MARINE...Updated 800 PM PDT Wednesday 31 October 2018...High
pressure will build over the waters Thursday, then weaken Friday.
A weak front will move onshore Friday, then high pressure will
return Saturday. Another weak front will move onshore Saturday
night into Sunday. Yet another front may move in Monday night.
Moderate northwest swell trains will move through tonight, Friday
and again Sunday into early next week.

&&

.PREV DISCUSSION... /Issued 257 PM PDT Wed Oct 31 2018/

SHORT TERM...Halloween night through Saturday night...Light
showers have been occurring all day across southern Oregon and the
Siskiyous of northern California. Measurable precipitation has
made as far south as Slater Butte in northern California, and this
trend will continue through this evening since the system is
moving a bit more slowly than earlier anticipated. The heaviest
rain showers will be tied to the terrain, particularly in southern
Oregon. This means that halloween revelry in Ashland may be a bit
more sloppy than spooky, but other West Side Valleys will have
the potential to see the light rain (almost drizzle-like
consistency) this evening. The east side should be relatively
dry, as should most of northern California.

Tomorrow, the ridge builds back in, and warmer temperatures are
expected area wide. Areas near the coast will see the smallest
change in temperature with the West Side valleys seeing the
largest change. Then, another system appears to arrive Thursday
night into Friday morning. This system will work to flatten
(weaken) the ridge allowing for a bit more potent system to arrive
during the late weekend. Models are suggesting that the Thursday
night system could arrive as late as Friday morning which is a bit
later than previous forecasts, but have decided to only nudge the
timing backward for now. Conditions with this storm will be
similar to the one occurring now with only light precipitation
expected. Snow levels will begin to drop after the front passes
through, but still stay above the mountain passes.

Another quick break is expected on Saturday with the next system
arriving Saturday night. The model trend is also a little slower
than the previous forecast suggested, and only nudged accordingly.
More information on this beneficial atmospheric river will be
provided in the long term discussion since the bulk of the weather
concerns will be experienced then. -Schaaf

LONG TERM...Sunday, Nov 4th through Wednesday night, Nov 7th...
Deterministic and ensemble model guidance have continued with
their leanings of 24 hours ago with a frontal system moving in
from the northwest Sunday into Monday. Our official forecast
continues to lean more on the ECMWF and Weather Prediction Center
solutions, which is also supported by the output of the National
Blend of Models (NBM) output. The GFS operational model continues
to be the driest solution of the usual mix, and the GEFS continues
to be wetter than it, indicating that the operational run is
drier than the mean of the ensemble members. Therefore, the
overall forecast was only adjusted slightly, with precipitation
amounts lowered for the Saturday night through Monday morning time
frame by less than 20% for all areas, but by less than 10% for
most areas. All in all, the collective model guidance has trended
only slightly lower on QPF for most areas than it did 24 hours
ago. On the other hand, POPs have been trended upward where
confidence in measurable rainfall is growing, primarily centered
on Douglas County, and generally for our Oregon areas west of the
Cascades. Some light QPF amounts were added to southeastern
portions of the forecast area to be consistent with recent trends
in the ECMWF. Altogether, storm total amounts of a half inch to
1.1 inches are expected for Douglas and Coos counties.

Beyond Monday, temperatures have been lowered based on model
trends and expectations that the air mass will gradually dry out
and, therefore cool. -Lutz

&&

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

CA...None.

Pacific Coastal Waters...None.