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Area forecast discussion 
National Weather Service Medford or
920 PM PST Wednesday Feb 10 2016

Discussion...the 00z GFS is in and the forecast still looks on
track with an active but not stormy pattern through the weekend. A
shortwave offshore from northern California will move northeast
across our area late tonight. It will produce mainly virga and
sprinkles late tonight through Thursday morning with cloud bases
at 8000 to 10000 feet. But there is a slight chance of measureable
rain...mainly west of Interstate 5 in southwest Oregon and
especially over the coastal range. There will not be any flurries
with the snow level around 9000 feet.

Breaks in the clouds will increase Thursday afternoon into
Thursday night. Another weak system...a cold front...has a higher
probability of producing light mainly west side precipitation
Friday before dissipating early Friday evening. The weakness of
the system is represented by both the expected quantitative precipitation forecast...generally less
than a quarter of an inch...and that snow levels are forecast to
drop to only around 5500 to 6000 feet.

A following system brushing past to the north will continue broken
but thin high cloud cover Saturday before another light
precipitation producer is expected to arrive Saturday night with
weak following disturbances continuing some light showers Sunday
into Sunday evening. As with the others...the probability will be
highest in southwest Oregon and northward.

High pressure will likely provide a break early next week. A
stronger/colder is possible at mid-week...reaching the coast as
early as Tuesday night.

&&

Aviation...for the 11/00z taf cycle...VFR conditions will prevail
into Thursday evening...except for local MVFR ceilings/visibilities in light
rain or drizzle with higher terrain obscured near the coast and in
the Coast Range...mainly late tonight through Thursday morning.
-Jrs

&&

Marine...updated 300 PM PST Wednesday Feb 10 2016...a weak cold
front will weaken near the coast this evening. A slightly stronger
cold front will move onshore Thursday night. Moderate west swell
will develop Thursday night and persist into Sunday. Another weak
front will move onshore Friday night. A stronger front will move
onshore Saturday night into Sunday. Offshore high pressure will
build early next week. -Jrs

&&

Previous discussion... /issued 214 PM PST Wednesday Feb 10 2016/

Discussion...the ridge axis is now to our east and a southwest flow
has set up bringing high and middle level clouds through the area. This
will continue into tonight. Tonight, a warm front will move towards
the area then lift north on Thursday. Some of the models continue to
show show precipitation breaking out inland tonight and during the
day Thursday. In particular the 12z GFS is the most bullish with the
coverage of the qpf, but suspect this may be a bit overdone. In
short the upper ridge is still rather strong and should be enough to
weaken any system that moves inland tonight into Thursday. Currently
we have mostly slight chance of precipitation for inland locations and
can't see any reason to increase them at this point.

Additional shortwave activity ahead of the approaching trough will
move through Thursday evening, then the main upper trough pushes east
into the area Friday morning. This will bring the best chance for
measurable rain. Snow levels will lower on Friday, but will remain
Above All the passes through Friday evening. A moist westerly flow
aloft will continue Friday night with most showers along and west of
the Cascades, but they are expected to be light with snow levels
between 4500 and 5000 feet. Therefore were not expecting much, if
any impact on any of the roads in the Cascades.

500 mb heights increase some as weak ridging builds into the area
Saturday. Conditions should be dry during the day, then a warm front
will arrive Saturday night bringing steady light to moderate
precipitation. The best chance for heavier precipitation will be in
the northern part of the area west of the Cascades Saturday
evening, then the focus will shift south Saturday night. Snow
levels Saturday night will increase and likely be Above All the
passes. -Petrucelli

Long term...Sunday through Wednesday...a warm front with good
isentropic ascent will ride over the top of a Flat Ridge on
Sunday. This combined with deep onshore west-northwest flow will
result in rain, focused on north and west facing terrain along
and west of the Cascades with lighter rain in the valleys. Rain
chances diminish south and east of the mountains. Snow levels will
be well above the major passes and likely above 8000 feet in most
areas. The warm front will shift northward in the afternoon and
isentropic lift will ease...effectively shutting off rainfall
from south to north across the County Warning Area late Sunday afternoon and
night.

Models indicate the ridge will strengthen a bit over the area Monday
with most, if not all precipitation remaining to the north of the
County Warning Area. Models differ a bit with respect to another shortwave riding
over the ridge Monday night into Tuesday. The GFS keeps it way to
the north where it would have no impact on our weather. The ecwmf
though has it farther south. Due to the uncertainty, we have
indicated slight chance to chance probability of precipitation from the coast to the Cascades
and north of the Umpqua Divide. It should stay dry in the Rogue
Valley.

Confidence is fairly high that the next significant upper trough to
impact the area will arrive Tuesday night into Wednesday. The surface
cold front will be just offshore late Tuesday night, then move across
the area Wednesday into Wednesday night. Rain is likely from the
coast to the Cascades with high chances even over the east side.
Snow levels start out high ahead of the front, but could drop down to
3000 feet behind the front by Thursday morning. -Spilde

&&

Mfr watches/warnings/advisories...
or...
California...none.

Pacific coastal waters...Small Craft Advisory for hazardous seas from
4 am Thursday to 10 PM PST Sunday for pzz350-356-370-376.
Small Craft Advisory from 10 am Thursday to 4 am PST Friday for
pzz370-376.

$$

Dw/map/jrs

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