Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 191125

Area Forecast Discussion
National Weather Service Medford OR
425 AM PDT Wed Sep 19 2018

.DISCUSSION...Models are increasingly showing rain-free conditions
for most of the forecast area over the next 7 days. A cold front
will bring a chance of rain to the coast and areas from the Umpqua
Divide northward late Friday into Saturday. Otherwise, no rainfall
is expected through the extended.

In the near-term, a moderate-strength thermal trough pattern is
developing at the coast, and this will bring breezy conditions and
low humidity to mainly areas west of Interstate 5 to include the
Coast Range and Illinois Valley. See more about this in the Fire
Weather Discussion below, but this pattern will continue through
Thursday. Temperatures across the forecast area will be below
normal through Thursday, except for areas near Brookings (moreso
in the higher terrain northeast of Brookings) which will see warm
conditions due to northeast winds and a Chetco Effect.

On Friday, the thermal trough pattern weakens as a cold front
approaches from the west. This will help create breezy northwest
to westerly winds across the forecast area Friday afternoon. Rain
chances begin near the coast Friday night and peak Saturday
morning. Amounts should be less than a tenth of an inch, and the
latest/00Z GFS suggests dry conditions while the 00Z EC features
the light rainfall.

Saturday`s temperatures will dip by several degrees behind the
cold front. Models are suggesting that a blocking pattern
sets up Sunday into the middle of next week, with the forecast
area sandwiched between a cutoff low well offshore and upper
trough well to the northeast. Details about how warm the air mass
gets next week are fuzzy, but conditions do look dry.
Additionally, models are suggesting another thermal trough pattern
Sunday through Tuesday. Though there is a large variance in how
warm next week becomes, there is potential for temperatures
reaching 10 degrees above normal by the middle of next week.


.AVIATION...For the 19/12Z TAFs...VFR will continue over most of the
forecast area, with the exception of the coast. IFR cigs have
developed along the coast north of Cape Blanco. Cigs could lift to
MVFR periodically, but generally don`t expect clearing until later
this morning. Otherwise, expect strong north winds over the marine
waters particularly south of Cape Blanco, and strong northwest winds
inland this afternoon.


.MARINE...Updated 200 AM PDT Wednesday 19 September 2018...Strong
winds and steep wind-driven seas will continue today as a thermal
trough remains oriented along the coast. Expect the thermal trough
to weaken Friday as an upper trough approaches. This system will
bring a front through the northern waters, which could bring
precipitation off the coast of Coos Bay to Reedsport, but more
likely will be farther north. High pressure aloft will build this
weekend, bringing a return of a strong surface thermal trough and
strong north winds with steep seas early next week.


.FIRE WEATHER...Updated 4 AM PDT Wednesday, 19 September 2018...
High pressure will build over the area through Thursday. This high,
the axis of which will be centered to our north, will result in
northeast winds each night and morning across the higher elevations
of Curry and Siskiyou counties. For tonight into Wednesday morning,
RH recoveries are expected to be moderate to good, and winds in the
sustained 10-15 mph range. This thermal trough pattern (moderate in
strength) will be most pronounced on Thursday, and winds will peak
in the sustained 15-25 mph range in the late morning to early
afternoon time period.

On Friday, an upper trough and associated dry cold front will move
in from the west and weaken the surface thermal trough pattern.
Westerly winds will increase and become gusty east of the Cascades
as a dry cold front moves through. RHs will be low enough that this
may warrant a headline, though there is some uncertainty regarding
the magnitude of the winds and whether or not these winds will be
coincident with critical RHs.

Rain showers will be possible late Friday into Saturday along and
near the coastal ranges, along the Umpqua Divide northward, and into
the Cascades north of Crater Lake National Park. Models are
increasingly suggesting dry conditions with breezy northeast winds
(another thermal trough pattern) Sunday into Tuesday.
Climatologically speaking, many of our most robust east winds have
occurred during the last week of September and the first week of
October, so this certainly bears some watching. BTL/Keene




Pacific Coastal Waters...Small Craft Advisory until 11 PM PDT Thursday for PZZ356-376.

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