Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
436 am PDT Friday Oct 31 2014
Discussion...a surface low has moved into northeast Oregon with
its relatively slow moving associated cold front now bringing a steady rain
to most of our area. The front is now roughly along the Interstate
5 corridor and expected to exit across the east side this
afternoon. There will be scattered to numerous Post-frontal showers
that will be mainly on the west side this morning. Thus, rainfall
totals will be highest from the Cascades westward this morning
with afternoon and early evening precipitation amounts highest on
the east side. With additional lift from the heating of the day,
isolated thunderstorms may develop along the front across the east
side this afternoon.
The next feature of interest is a low centered offshore from
Washington with a surface trough along 130w that will bring
enhanced instability with an increase in showers and isolated
thunderstorms over the coastal waters into the coastal counties
In summary, the Halloween forecast has rain focused on the west
side through around 11 am, in Klamath and eastern Siskiyou
counties in the early afternoon then in lake and Modoc counties in
the late afternoon and evening. There will be some Post-frontal
showers/rain drops to Dodge on the west side in the afternoon and
early evening then getting toward 7 or 8 PM the frequency and
coverage of showers will increase with showery/wet weather and
dropping snow levels through Saturday morning. The snow level will
be near 7000 feet this morning then fall to 5500 feet this
evening and 5000 feet Saturday morning. Given that the lower snow
levels will occur with scattered to numerous showers...accumulations
are expected to be around an inch or two.
The weather pattern will remain active during the next week.
Lingering isolated showers on Saturday afternoon will be mainly
across lake and Modoc counties. The lower levels of the atmosphere
will remain moist Saturday afternoon through Sunday afternoon as a
ridge builds from the eastern Pacific into the Pacific northwest
with stubborn low level cloud cover and light overrunning/drizzly
showers possible in the coastal zones into Douglas County.
A warm front is expected to send moderate rain to Washington and
northern Oregon on Sunday night with the southern edge of the
front likely to also bring periods of light rain to areas west and
north of Jackson County through Monday.
For Monday afternoon through Tuesday evening, there is confidence that
the front will gradually weaken with the most substantial rain
remaining north of our area. But there is moderate to high
uncertainty on how far to the south the front will sag. The
probability of rain will be higher as one travels to the west and
north. But, southern Oregon rainfall may be very light per the
European model (ecmwf) model, or it may be more substantial per the GFS.
The GFS and European model (ecmwf) are still in agreement on the big picture at
middle-week with a chance of very light southwest Oregon showers due
to lingering low level moisture but stronger ridging that should
make Wednesday the warmest day of the week.
Thereafter, the next frontal system is expected. But, model
solutions quickly diverge with low confidence in the system's
characteristics, including its strength, timing, and snow levels.
Aviation...for the 31/06z taf cycle...a cold front will bring
widespread rain with MVFR ceilings and visible to areas west of the Cascades
through the night and it will gradually spread to the east side by
morning. While MVFR ceilings/visible will prevail, conditions will
occasionally drop into IFR during heavier bursts of rain. Mountains
will be obscured through Friday morning. Rain will taper to showers
on the west side as the front jumps the Cascades Friday morning with
improving conditions. Widespread rain with MVFR to IFR ceilings/visible are
expected east of the Cascades Friday morning through early afternoon
as the front moves through. -Wright
Marine...updated 320 am PDT Friday Oct 31 2014...
weak low pressure will remain over the waters through tonight. A
long period west swell will move into the coastal waters late this
morning. High pressure will then build southwest of the waters on
Saturday...moving over the waters Sunday. Models are fairly
consistent showing another long period northwest swell moving into
the waters Monday morning that peaks Monday night. -Sven
Pacific coastal waters...Small Craft Advisory for hazardous seas until
11 am PDT Saturday for pzz350-356-370-376.