Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Medford or
200 PM PST Mon Nov 11 2019
Discussion...11/12z NAM/GFS/ec in.
A long wave ridge off the coast will move onshore tonight. A
short wave moving up the back side of the ridge will push a
surface front onshore Tuesday.
Most, if not all, of the associated precipitation will remain
north of the area. The GFS ensemble is dry until Thursday night.
The ec ensemble does show some light precipitation for North Bend
but only 1 of the 50 members shows measurable precipitation. The
current forecast has a chance of rain across northern Coos and
northwest Douglas counties Tuesday afternoon. Had to tweak the
pops along the border with Portland for isc purposes. As for the
high temperatures, it will be a warm day on the South Coast with
weak offshore flow. Highs around Brookings will be 10-15 degrees
above normal while the rest of the coast will be less than 5
degrees above normal. The Umpqua basin will see highs 5-10 degrees
above normal. The rest of the area will see highs around 15
degrees above normal.
Once that system moves through the offshore ridge will return
along with dry weather everywhere. The Tuesday highs will be
similar to the Monday highs, except for the South Coast, which
will be cooler due to the return of marine air. Wednesday will
also be dry, with highs similar to the Tuesday highs.
The ridge will move onshore Wednesday, then an upper trough will
approach from the west. This will bring another front in Thursday
night, but Thursday will remain dry. Thursday highs will be
similar to the Wednesday highs, except a few degrees cooler on the
Given the continued stable conditions with light winds, and after
perusing the model soundings, the air stagnation advisory has been
extended until Wednesday afternoon.
Extended discussion (thursday night through monday)...overall the
pattern in this time period will be more active. At least in a
relative sense given it's been quiet over the past few weeks. The
operational models are in slightly better agreement with the
timing of the front (which is expected to be Thursday night). Both
models have trended higher with quantitative precipitation forecast amounts, but it still looks
like the front will lose it's punch as it moves inland Friday
Dry weather returns Friday afternoon as the front dissipates. Still
could not rule out a slight chance of showers along the Cascades.
Saturday through Sunday morning will be dry. Another front is
expected to approach the area Sunday afternoon. The models
vary on the timing and strength of sunday's front, but the general
consensus is this one will be a little stronger. The GFS is faster
to bring the front into the area Sunday afternoon, but suspect it's
too fast given the front is expected to be nearly parallel to the
upper flow. The European model (ecmwf) keeps the front further north.
Beyond Sunday, the operational models differ with the progression of
a stronger upper trough and thus progression of the front. The GFS
is quicker than the European model (ecmwf). With that said, several more of the
individual ensemble European model (ecmwf) members are showing measurable
precipitation Monday into Tuesday morning. Once the models
(both operational and ensembles) come into better agreement we'll
have higher confidence of measurable precipitation. Pops have been
increased during this time period. -Petrucelli
Aviation...for the 11/18z tafs...LIFR ceilings will persist near the
Umpqua valley for the early afternoon. There is a slight chance
that it Burns off before sunset, but we're not confident that will
happen at this moment. Outside the Umpqua valley look for VFR
conditions to persist for this evening. We should see fog develop
again tonight in the valleys west of the Cascades. LIFR ceilings are
expected in the Umpqua valley again with MVFR conditions possible in
the Rogue Valley.
Marine...updated 100 PM PST Monday 11 November 2019...seas remain
low for today, yet they will elevate slightly heading into Tuesday
into Wednesday. Eventually, a long period high swell will move into
the waters Thursday creating hazardous conditions to smaller crafts.
Increasing south winds will also arrive with this higher swell.
Sneaker waves will be a threat Thursday evening as this long period
swell moves into the waters and hits the beaches.
or...air stagnation advisory until 4 PM PST Wednesday for