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fxus66 kmfr 172231 

Area forecast discussion
National Weather Service Medford or
231 PM PST sun Nov 17 2019

Short through Wed. Evening...persistence is key to
tomorrow mornings forecast. Not expecting fog at any locations
that it was not at this morning. The main change to the fog
forecast is the addition of freezing fog for the Klamath Falls
basin. There is a chance that freezing fog will not be the
initial Mode, but as temperatures begin to fall it will be for
some places.

Monday afternoon through Tuesday morning a front will pass
through. The low pressure will pass to the north, somewhere just
north of the Oregon, Washington state border. This will be a
favorable position for most of southern Oregon to be impacted by a
modest front. Perhaps the best news from this, is that the
expiration of the air stagnation advisory should be lifted after
Monday morning for the valleys east of the Cascades and on Tuesday
for west side valleys in Jackson County. Both locations are
expected to have strong transport winds, in the lowest 2km, and
mixing well above 1000ft. The west side valleys also have the
added benefit for a chance of measurable rain, to create further

Not many changes were made to the rain forecast with models
largely being in agreement with each other and with the previous
runs. It even seems that the European model (ecmwf) ensemble members have gained
some agreement with the gefs. This means that the gefs on the low
end and the ewmffe on the high end have helped to balance the
blends that incorporate them, to look quite agreeable as compared
to higher resolution guidance that is becoming available for this
system. Currently expecting the coastal ranges to receive between
0.25 to 0.5 inches of rain and coastal valleys between 0.20 and
0.35 inches. In the Umpqua basin between 0.10 and 0.20 is
expected. In the Rogue Valley up to 0.05 inches is expected along
the Cascade foothills, while the valley floor, if it receives
rain, may only get up to 0.02 inches. From about Prospect south to
Howard Prairie, along the Cascades, between 0.10 and 0.25 inches
expected, with greater amounts to the north. From Prospect north
along the Cascades anywhere from 0.25 to 0.75 inches may fall. The
highest peaks, around Crater Lake, could also gain up to two
inches of snow. However, snow levels are not expected to fall to
pass height until after the precipitation has ended. None, or very
minimal, amounts of rain are expected for northern California and
places east of the Cascades.

Tuesday night to Wednesday there will be a modestly quick transition
back to a ridging pattern. A thermal trough will develop over the
marine waters and will be quite strong for this time of year.
While winds over the land will gain an east, offshore flow.

Long term...Wednesday evening through Sunday...deep northeast flow will be in
full swing by Wednesday evening. The strength of this wind event is
significant for this time of year. The National Weather Service ensemble table (using a
combination of Canadian and GFS ensemble data) suggests some of the
strongest northeast winds that this area can see in mid-late
November. We've increased winds in the forecast for the high
terrain, especially in northern California and from the Cascades

We'll be communicating with fire agencies about this wind event
because the air mass will be drying out quickly while the winds are
still very gusty. We are especially focused on the Cascades, western
Siskiyou County, and the Coast Range for the combination of gusty
winds and low humidity. These areas will likely see some rainfall
before the wind event, so vegetation won't be as dry as it is
currently. Still, this is the high-impact aspect of the extended
forecast, and we'll be focused on this during the next several days.

On Thursday the air mass will be very dry from the surface up to
500mb (about 20000ft). Winds will trend lower compared to late
Wednesday, and sunshine will be abundant. Afternoon temperatures
will be near normal east of the Cascades and above normal west of
the Cascades. Air quality should be good compared to recent days
because of the recent frontal passage and gusty winds. Morning fog
in the valleys on Thursday is less likely than recent days because
of the drying air mass. We'll remain dry through Saturday at least
with continued above normal afternoon temperatures.

Looking further out, the latest suite of model data suggests the
potential for a pattern change late next weekend or next week. We're
a bit skeptical of this based on the very dry air mass entering the
picture in the near-term and the recent tendency for models to
overdo precipitation in the extended. However, we do need
Rain/Mountain snow, and it's good to see some data suggesting


Aviation...for the 17/18z tafs...over the coastal waters
and at the coast...areas of IFR cig/vsbys in low clouds and fog are
lifting and clearing this morning but will return late this
afternoon and evening and persist into Monday morning. West of the
Cascades...areas of IFR cigs/vsbys in low clouds and fog in the
valleys will clear to VFR by late this morning. The lower conditions
will return to the same areas tonight, persisting into Monday
morning. From the Cascades east...IFR conditions in fog and low
clouds have recently cleared, but the lower conditions will return
to the same areas tonight, persisting into Monday morning. Keene


Marine...updated 200 PM PST Sunday 17 November 2019...light north
winds tonight will turn southerly Monday morning, then increase by
afternoon as a front approaches the coastal waters. The front will
pass Monday evening, then a thermal trough, supported by offshore
winds aloft, will produce gusty north winds and steep to very steep
seas Tuesday morning through Wednesday evening. During this time,
models suggest that areas of gale force winds are possible south of
Cape Blanco, but am not confident winds will get that strong. Given
the wind fetch and duration of the event, confidence is much higher
for very steep and hazardous seas, and as a result, a hazardous seas
watch has been issued.

Conditions should improve late in the week as the thermal trough
weakens and dissipates, but building westerly long-period swell may
continue to produce steep sea concerns into the weekend. -Bpn


Mfr watches/warnings/advisories...
or...air stagnation advisory until noon PST Monday for orz029>031.
Air stagnation advisory until noon PST Tuesday for orz026.


Pacific coastal waters...Small Craft Advisory from 1 PM Monday to 7 am PST Tuesday for
Hazardous seas watch from Tuesday morning through late Wednesday

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