Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 011659

Area Forecast Discussion
National Weather Service Medford OR
859 AM PST Wed Mar 1 2017

.UPDATE...Patchy fog will continue in west side valleys for a few
hours, but should clear off by late morning. With an upper ridge
positioned over the PacNW, expect generally quiet weather today
in our forecast area. A few short waves will pass over the north
side, bringing a few clouds to our area, so skies won`t be
perfectly clear, but today will likely be the sunniest day during
this forecast period. Tomorrow afternoon, we will begin
transitioning back into a wetter pattern. A weak shortwave will
bring increased cloud cover and the possibility of rain along the
coast late tomorrow. Heavier precipitation will approach the coast
Friday ahead of a stronger cold front...with snow levels dropping
over the weekend behind the front, and a showery pattern
continuing over the weekend.

No updates have been made this
morning, as current forecast appears on track. The main focus
today will be nailing down the details for this weekend,
particularly snow levels and precipitation amounts. For more
information, see previous discussion. -MSC


.AVIATION...01/12Z TAF CYCLE...Areas of IFR ceilings and visibility
due to low clouds and fog can be expected in the valleys west of the
Cascades this morning, including at KRBG. Patchy IFR may also sneak
into KMFR for a few hours this morning. Expect VFR to return by late
morning most areas, though lower conditions may last into early
afternoon in the deeper valleys. MVFR ceilings along the coast from
Port Orford northward should lift to VFR by mid-late morning. Expect
low clouds/fog to return overnight into Thursday morning for west
side valleys.

East of the Cascades and in northern California, VFR will prevail,
but patchy fog may reduce visibility briefly this morning and again
early Thursday morning. -Spilde


.MARINE...Updated 300 AM PST Wednesday 1 March 2017...Weak high
pressure today through Thursday with winds 15 kt or less and seas
generally 6 to 8 feet will be followed by the next series of
significant fronts Friday into the weekend. Steep to very
steep seas and the potential for gales, particularly on Friday, will
accompany this return to an active weather pattern. -Spilde


.PREV DISCUSSION... /Issued 344 AM PST Wed Mar 1 2017/

Short Term...A very weak ridge of high pressure aloft will
remain over our area through the next 24 hours. It will be strong
enough to deflect precipitation north of us, but clouds will
continue to stream through the ridge. There has been enough
clearing this morning to allow low clouds and fog to form in the
west side valleys. Currently, it is confined to the Umpqua basin
and down into western Siskiyou, but with temp/dewpoint spreads at
only 1 or 2C in the Illinois and Rogue valleys, it isn`t too far
off from forming here either. Once these lower clouds break up,
today should be a cool but quiet day weather-wise with some
sunshine. We expect a repeat of valley fog and low cloud tonight,
followed by some sun again tomorrow.

Precipitation chances increase at the north coast Thursday night
as the next frontal system approaches. We probably won`t see rain
advance much inland from the coast through the day Friday as the
main system digs off the B.C. coast and slows up the progression
of the front. However, as the closed low moves closer to us and
the front moves inland Friday night, we should see a good shot of
rain at the coast and into western Siskiyou County. Snow levels
will be low enough, around 4500 feet, that we will likely see
enough snow in the Cascades to cause some travel troubles. The
models have been slowing this system down in the past few runs, so
confidence on the timing of the front and the resultant
precipitation is moderate at best. -Wright

LONG TERM...Saturday through Tuesday.
Model agreement has increased regarding the weekend forecast with
the GFS trending toward the wetter and cooler ECMWF solution.

The next front is forecast to be reaching the coast at the start of
Saturday with the highest probability of Saturday precipitation from
the Cascades westward and highest amounts at the coast to the
coastal range. The southwest flow ahead of the upper low with the
low likely to be positioned offshore of Washington or Vancouver
Island will likely result in slightly higher than normal snow levels
around 4500 to 5000 feet.

The next wave, a surface trough associated with the axis of the
upper level low is forecast to swing inland Saturday night. It is
likely to be stronger than the preceding front and would result in
falling snow levels into Sunday. By the end of Saturday night, model
differences become larger and more important with the GFS indicating
a colder solution of a broader trough moving eastward with its base
farther to the south. For the sake of simplicity, the Sunday
weather grid was left in terms of rain/snow though at some point
relatively early in the day there is likely to be a transition to
a showery air mass with light to locally moderate precipitation
amounts. Sunday precipitation will be favored on west to northwest
facing slopes. Sunday snow levels are forecast to drop to around
1500 to 2500 feet with warm soil and road temperatures helping to
limit valley snow accumulations. Model differences regarding
Monday and Tuesday are significant, but there is general agreement
on a continued active pattern with a high probability of
precipitation and rising snow levels. -DW




Pacific Coastal Waters...None.


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