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484
FXUS66 KMFR 241805
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1105 AM PDT Tue Sep 24 2024

Updated AVIATION Section

.DISCUSSION...
An extensive amplified ridge is seen in GOES-West water vapor
imagery covering most of the western third of the U.S. and
western Canada. The center of the ridge looks like a pinwheel
spinning right over western Oregon. The unusually strong high
pressure may allow some sites to break record highs today.
Medford`s record is 99 set in 1991 and it look like we might not
get quite that hot, but it should be close.

Looking offshore there`s a significant cold front seen crossing
140W as of 330am PDT. This front will continue toward Oregon,
reaching the Coos coast somewhere shortly after 11am Wednesday.
Through the afternoon, rainfall will remain limited the coast
and western Douglas county, with totals remaining mostly below a
tenth of an inch inland. Temperatures will cool 15-20 degrees for
Thursday, but another warming trend is expected with and a subtle
warmup with rebuilding high pressure thereafter through Saturday.

Another weak cold front is forecast to graze the northern part of
the CWA around Friday night with even lesser rainfall totals than
the system in the interim.

&&

.AVIATION...
-- Changed Discussion --
24/18Z TAFS...VFR prevails over the area late this
morning. This will continue through early this evening, then marine
stratus/fog offshore will move into North Bend around sunset with
conditions deteriorating to IFR/LIFR. Most immediate coastal areas
will have some form of restricted visibility or lower ceilings
overnight into Wednesday morning. Inland, VFR continues through most
of the overnight, but a deepening marine layer could bring MVFR
ceilings into Roseburg toward morning. A frontal system then could
bring some light rain to coastal areas and other areas north of the
Rogue-Umpqua Divide Wednesday afternoon. This front will cause gusty
W-SW winds (25-35kt) Wednesday afternoon and evening east of the
Cascades and in NE California. -Spilde
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&&

.MARINE...Updated 200 AM , September 23, 2024...Northerly winds
under a thermal trough are slowing as the trough weakens. A Small
Craft Advisory will remain in place through 11 AM today for steep
seas in waters south of Bandon.

Seas will calm through the middle of the week before west-
northwesterly swell arrives in area waters. Chaotic seas will start
to develop later Friday morning or early Friday afternoon. As the
swell continues to affect ares waters, a thermal trough will build
and bring gusty northerly winds on Friday as well. Chaotic seas are
expected in all waters, with a 20% chance of gale gusts over waters
south of Cape Blanco Friday evening into Saturday morning. Westerly
swell will ease going into next week, but northerly winds are
expected to sustain unsettled conditions. -TAD

&&

.FIRE WEATHER...Issued 200 PM Monday, September 23, 2024...
The thermal trough shifts northward and moves inland today with
much cooler temperatures along the Curry coast. Inland areas will
have the hottest day of the upcoming week with western valleys
rising well into the 90s and a few spots flirting with triple
digits.

The main fire weather risk comes Wednesday as an upper trough
swings through the PacNW. Gusty W-SW winds are expected in
advance of the trough from the Cascades eastward with at least a
few hours of windy conditions in portions of eastern Siskiyou,
Modoc and into Klamath/Lake counties. Expect most of those areas
to have 15-20 mph sustained winds during the afternoon with
frequent gusts of 35 mph. Local RAWS guidance for some of our most
exposed RAWS sites (Coffee Pot, Summit, Summer Lake, Timber Mtn)
is showing peak wind gusts in the 40-45 mph range. The limiting
factor though is that minRH values are shown to be in the 15-20%
range, slightly too high for a Fire Weather Watch. We`ll continue
to headline this risk though in the Fire Weather Planning Forecast.

Another weak trough/marine push is expected Friday afternoon/night.
This one doesn`t look as strong as the Wednesday trough. The next
stronger trough is shown to arrive over the weekend. This may
increase W-SW winds again over the East Side/Modoc County Saturday
afternoon/evening (winds may be similar to Wednesday) and RHs may
be down a bit as well. This could then induce another thermal
trough with a period of offshore NE winds Sunday into early next
week. Spilde/Stavish

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory until 11 AM PDT this
     morning for PZZ356-370-376.

&&

$$