Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
351 am PDT Thursday Sep 3 2015
Discussion...a cold front that moved through late Wednesday has
left most of the area 5 to 10 degrees cooler versus this time versus
yesterday. Evening shift put up a frost advisory for some of the
east side. The day shift today will need to consider the same for
tonight and Friday night as the center of an unusually cold upper
low dives in overhead. This low will bring the coolest air of the
season with a cold core of -25c at 500 millibars. As the trough
swings eastward and skies clear Saturday night into Sunday...
there will be a threat for freezing morning temperatures across
much of The Lowlands east of the Cascades. A Special Weather
Statement will cover this upcoming potential for frost and freeze
for agricultural interests.
Rain with this system today should remain fairly slim. The 88d is
currently showing some weak echoes streaming southwest to
northeast between Klamath Falls and Lakeview in region of colder
cloud tops between -10 to -15c in thicker cloud. Per the RUC and
hrrr forecasts, we did bump up probabilities a bit for a hundredth
or two our there around Southern Lake County with short wave
energy overriding the slowly progressing frontal zone. This should
taper off this evening with a fairly uneventful night in store.
Activity will increase Friday with the approach of the deep upper
low from the north. Fairly strong short wave energy is forecast to
dig through the base of the trough over southern Oregon and northern
California Friday afternoon and evening. With the cold air aloft,
numerous showers and a slight chance for thunderstorms with some
localized moderate rains are in store. The best shot at good rain
will be east of the Cascades. Due to building confidence based on
support from recent model runs, have also bumped up probability of precipitation a bit
more in this time frame.
Showers will be lingering into Saturday morning mainly from the
Cascades east. Snow levels early Saturday should bottom out between
6000 and 6500 feet over the Cascades, and more like 7kft in
northern California. So, a little dusting on the higher terrain
looks likely. Some uncertainty exists for areas in Lake County
where the more significant precipitation will fall. The Warners including
Hart Mountain area above 6500 feet should be aware of the potential for
a little more snow there.
As the system clears out Saturday afternoon and night, this will
leave Sunday morning with a fair potential to freeze in many areas
of what looks like mainly lake and Modoc counties. A warming trend
looks likely thereafter through late week. Stavish
Aviation...for the 03/06z taf cycle...along the coast expect
mainly VFR conditions with isolated MVFR/ ceilings through early this
morning...becoming VFR by 18z. Inland, for areas west of the
Cascades, conditions will be mainly VFR but onshore flow will
maintain some middle clouds along and just west of the Cascades late
tonight and early this morning. This will bring areas of mountain
obscuration near the Cascades. Also areas of MVFR ceilings are
expected to develop in the Umpqua basin late tonight into early
this morning...with clearing around 17z. East of the Cascades,
expect some light showers and areas of mountain obscurations
through the morning as a front shifts eastward over the
area...with VFR in the afternoon and evening. /Cc
Marine...updated 1030 PM PDT Wednesday 2 September 2015...a trough
of low pressure will move through the waters tonight through Friday
with periods of showers possible. In addition, this system will
bring a slight chance of thunderstorms over the waters Friday
morning. Winds will increase tonight through Thursday...with seas
becoming a mix of swell and short period wind wave by Thursday
evening. Some smaller longer period swells will be mixed in. The
coastal waters will be dominated by moderate to strong north winds
Thursday through the weekend...with Small Craft Advisory conditions
south of Cape Blanco. There is enough support from models to bring
Small Craft Advisory conditions into the inner waters south of Gold
Beach Thursday afternoon and evening. Moderate north winds continue
Friday into Saturday. Then winds are forecast to strengthen Sunday
into Monday with gales possible in the southern outer waters. Strong
northerly winds are likely to persist through early next week.
or...frost advisory until 8 am PDT this morning for orz029>031.
Pacific coastal waters...Small Craft Advisory from 11 am this morning
to 11 am PDT Friday for pzz376.
Small Craft Advisory for hazardous seas from 11 PM this evening
to 11 am PDT Friday for pzz376.
Small Craft Advisory from 11 am this morning to 11 PM PDT this
evening for pzz356.