065
FXUS66 KMFR 011315
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
615 AM PDT Tue Sep 1 2026

.KEY MESSAGES...

* An unusually strong system for early September will bring
  wetting rain to the region with gusty winds along the coast.

* Rock slides are possible along highways 42, 138 and 38.

* Pockets of frost are possible Tuesday night east of the
  Cascades.

* Temperatures will be 15 to 25 degrees cooler than normal
  Wednesday and Thursday.

&&

.DISCUSSION...

It was a breezy day Monday afternoon with a closed low spinning
off the Oregon coast. That closed low will approach the Oregon
coast this afternoon and bring a 20 to 50 percent chance of
showers to the region. The thunderstorm probabilities are <10%, so
pretty unlikely we`ll observe and lightning within our portion of
Oregon and California.

This closed low will become a short wave and pass through southern
Oregon Tuesday evening. Another wave and surface low will
strengthen off the coast Wednesday. The ECMWF ensembles have a
small spread of how strong the low gets, although they all stay
above 990mb. This low and cold front will bring wind and
precipitation to the region during Wednesday afternoon and
evening.

The one thing that did stand out was the extreme forecast
index(EFI) producing values of 1 over the marine waters with a
shift of tails(SOT) of 2. This would suggest this is a very strong
wind event for September and there is a smaller set of ensemble
members predicting significantly stronger wind gusts than what is
in the model climatology for this time of year. These wind EFI
and SOT values don`t push inland, so these really stronger winds
will be along the immediate coast with gusts to 45 mph. Also for
clarity, these winds are pretty typical for a winter storm in
December, although it is fairly unusually in early September.

Aside from the winds, this first front will bring wetting rain to
locations west of the Cascades. As the front moves eastwards, it
looks like areas east of the Cascades will likely see wetting
rain Wednesday night into Thursday. Again, the EFI and SOT
products are highlighting locations east of the Cascades from 0Z
Thursday to 0Z Friday. Some precipitation records will likely fall
on the 2nd and 3rd.

As for the impacts, rock slides along highways 38,42 and 138 are
possible with this first rain of the season. Also, roads could be
slick on Tuesday as a lighter rain brings up some oil to the
surface. Those slick roads could continue early into the front
passage Wednesday afternoon. It`s also not out of the question for
a few power outages along the coast as this wind hits some
stressed vegetation.

Eventually, temperatures will cool behind the front with lows
falling into the 40`s east of the Cascades and upper 40`s and
lower 50`s west of the Cascades. There is some concern for frost
according to the NBM as it`s forecasting lows in the mid 30`s in
Klamath Falls. However, most deterministic guidance has lows in
the lower 40`s with the scattered to widespread cloud cover.
However, frost could occur in some locations Tuesday night before
the big cold front. Temperatures will be 15 to 25 degrees cooler
than normal for early September. Mount Shasta City may only hit 57
degrees on Wednesday and 59 degrees on Thursday for highs, which
would be record minimum maximums for the respective days, cooler
than normal indeed.

Finally, ensembles keep this upper level low over us for a while.
It looks like it could just linger into Monday with spotty showers
persisting across Oregon. Kind of hard to believe we could see 5
to 6 days of rain around the region in early September. Ensemble
members vary greatly on location and intensity of the QPF from
Friday onward, although there should be something within southern
Oregon and northern California.

-Smith

&&

.AVIATION (12Z TAFs)... A mix of LIFR and IFR stratus at the coast
and into the coastal valleys will thicken into this morning and fill
into Roseburg(KRBG). After 18Z, ceilings away from the coast will
lift to VFR levels. Areas of MVFR will linger at the coast
through the day and into Tuesday evening.

Much farther inland, conditions will remain VFR with gusty
southerly winds around KLMT.

-Smith

&&

.MARINE...Updated 230 AM PDT Tuesday, September 1st... Winds will
begin to increase out of the south today with conditions becoming
hazardous to smaller crafts Tuesday night. A cold front will move
through the area Wednesday afternoon bringing gales and steep to
very steep seas. Winds ease Wednesday night and Thursday. Building
westerly swell Thursday night into Friday may bring steep seas to
the waters.

-Smith

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Frost Advisory from 4 AM to 8 AM PDT Wednesday for ORZ029>031.

CA...Frost Advisory from 4 AM to 8 AM PDT Wednesday for CAZ085.

PACIFIC COASTAL WATERS...Gale Warning from 5 AM to 7 PM PDT Wednesday
     for PZZ350-356-370-376.

&&

$$