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Area forecast discussion 
National Weather Service Medford or
910 PM PDT Friday Aug 26 2016

Discussion...other than areas of fog and low clouds along the
coast and a few high clouds passing through inland, our forecast
area will be quiet tonight. Expect highs this weekend to be a few
degrees cooler than today but will still be a few degrees above
seasonal norms. The new model runs continue to show a broad trough
settling in over the pac northwest from early next week. Aside from
breezy conditions Sunday and Monday that could present fire
weather concern, high temperatures in the Rogue Valley are
expected to fall into the 80s by Tuesday and staying in the lower
80s for the remainder of next week. /Fb

&&

Aviation...27/00z taf cycle...areas of IFR/LIFR conditions in low
clouds and fog are present along the coast and widespread over
the coastal waters. IFR/LIFR cigs and visibilities will will
become widespread along the coast this evening into tonight...and
continue through Saturday morning. There will be some partial
clearing along the coast Saturday afternoon...but the lower
conditions will persist offshore through Saturday. Inland areas
will remain clear through Saturday. /Cc

&&

Marine...updated 800 PM PDT Friday 26 August 2016...winds will
be light and variable through Monday. Seas are expected to remain
below Small Craft Advisory levels during this period. Seas of 6 to
7 feet at 9 seconds will gradually subside tonight to 5 to 6 feet
then down to 4 feet on Sunday. A couple weak fronts will move
onshore Tuesday and Thursday. Southerly winds will are expected
ahead of these fronts. However, current models show winds and seas
remaining below Small Craft Advisory criteria through late next
week. -Cc

&&

Previous discussion... /issued 325 PM PDT Friday Aug 26 2016/

Discussion...the 10-day forecast can be considered in 3 parts.
There is high confidence in continued hot and dry weather inland
with breezy afternoon and evening westerly winds...but cool with
stratus at the coast through this weekend. Then there is moderate
confidence in the details of a transition to a cooler, more active
pattern Monday through Wednesday. Thereafter, into the Holiday
weekend, there is very low confidence in the details but the upper
level pattern over the West Coast looks to remain trough-
dominated with a bias toward an active pattern that will bring at
least slightly cooler and most likely noticeably cooler than
normal temperatures with the potential for periods of showers.
The probability of rain from Wednesday Onward will be higher north
of our area.

Southerly flow at the coast will turn onshore tomorrow. This will
result in expanded stratus coverage tonight and only partial
breaks of sun at the coast during Saturday afternoon. Meantime,
the cooling inland compared to today will be difficult to
perceive, only a degree or two. There will be little change from
Saturday to Sunday while a trough swings across British Columbia
and flattens the West Coast ridge. The main change will be a trend
of slightly stronger afternoon and evening westerly winds, which
will continue into Monday. These winds will be strongest in lake
and Modoc counties.

Besides the stronger winds, there will be a few degrees of cooling
on Monday as the next large trough moves south out of the Gulf of
Alaska and a weak embedded shortwave trough swings northeast
across our region. This broad upper level trough will be the
dominant driver of our weather during mid-week. A slight chance of
showers and thunderstorms was introduced to the Cascades and
mainly the higher terrain of south central Oregon with decent
model agreement that a stronger shortwave will follow a similar
track to the northeast. The 12z GFS has its usual bias of being
fastest with this trough, so the forecast leans toward the European model (ecmwf)
idea of the shortwave moving through around peak heating of the
afternoon and evening. Any thunderstorms that develop on Tuesday
would likely produce little rainfall but coverage is not likely to
be more than isolated.

The upper level trough axis looks to remain offshore on Wednesday
but move closer to the coast. This would continue the cooling
trend and bring a surface trough with an increased probability of
at least coastal light rain or showers. The details of this system
are uncertain, but the probability is highest that it will be weak
and focused north of our area.

Thereafter, the evolution of features varies significantly from
model to model. The GFS is on the wetter and cooler side of the
range of solutions and suggests the possibility of west side
focused rainfall with a series of disturbances. The strongest/best
chance of rain being on day 7/Friday. The GFS MOS guidance
inherently trends toward climatology in its solution for day 7,
even with that bias it shows inland high temperatures around a
half dozen degrees below normal on Thursday then a dozen degrees
below normal on Friday. Meantime, the European model (ecmwf) solution is less
vigorous, keeps more of the energy north of our area and has MOS
guidance high temperature readings barely below normal.

Climatology favors the ECMWF, perhaps with a slant toward a
blended solution. What that would mean would be continued onshore
flow with persistent stratus and patchy mainly overnight fog at
the coast with a series of disturbances focused north of our
area...perhaps a few showers north of the Umpqua Divide.

Aviation...26/18z taf cycle...IFR/LIFR conditions in low clouds and
fog will continue to move north along the coast and over the coastal
waters...and all of the coast and coastal waters will be in these
conditions tonight through Saturday morning. There will be some
partial clearing along the coast Saturday afternoon...but the lower
conditions will persist offshore through Saturday. Inland areas
will remain clear through Saturday. -Jrs

Marine...updated 130 PM PDT Friday 26 August 2016...winds will
be light and variable through Monday. Seas are expected to remain
below Small Craft Advisory levels during this period. Seas of 6 to 7
feet at 9 seconds will gradually subside tonight to 5 to 6 feet then
down to 4 feet on Sunday. A couple weak fronts will move onshore
Tuesday and Thursday. Southerly winds will are expected ahead of
these fronts. However, current models show winds and seas remaining
below Small Craft Advisory criteria through late next week. -Cc

Fire weather...updated 200 PM PDT Friday 25 August 2016...hot and
dry weather will continue through the weekend...but not quite as hot
and dry as Friday. Winds will start to increase Sunday...but Monday
looks to be the big day in terms of wind. By that time it will be
significantly cooler and moister...and it looks like it will be a
borderline red flag warning scenario.

The models indicate the possibility of thunderstorms Tuesday...then
much cooler and wetter conditions from Wednesday into next
weekend. -Jrs

&&

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

California...none.

Pacific coastal waters...none.

$$

Fjb/dw/cc

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