Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 230431

Area Forecast Discussion
National Weather Service Medford OR
931 PM PDT Fri Sep 22 2017

Updates have been made and sent this evening to update the
overnight minimum temperature forecast, add frost and fog wording
to some valley areas, increase seas at and near buoy 27, and
to adjust the marine hazard area slightly. BTL


Confidence is high that tonight through Saturday morning will not
be as cold as it was last night into this morning. 24 hour change
forecasts from all of the models that did best with last night`s
lows indicate it will be warmer. Additionally, the sounding this
afternoon indicated the free air temperature at about 5,000 feet
MSL to be 4 degrees Celsius (7.2 degrees Fahrenheit) warmer than
it was 24 hours ago.

It should be noted that 2 calendar day record lows were broken at
our primary climate sites this morning, and 1 was tied. These were
a new record of 25F at Klamath Falls (previous 26F in 1968), a new
record of 29F at Montague (previous 32F set in 1968), and a tied
record of 31F at Mount Shasta City (last set in 1927).

High pressure will continue to build into the forecast area
tomorrow resulting in a stellar autumn day. It will be a few
degrees warmer, with mostly sunny to partly cloudy skies. BTL


.AVIATION...23/00Z TAF CYCLE...Areas of IFR cigs and IFR/MVFR
visibilities in patchy fog are expected to develop tonight and early
Saturday morning  west of the Coastal ranges. Also isolated patchy
fog with MVFR visibilities and MVFR/IFR cigs is expected in the
Umpqua valley late tonight and early Saturday morning. Brief patchy
fog and MVFR vis/cigs is possible in the lower Rogue and Illinois
valley but confidence is low on how much may develop. Fog is
expected to clear between 16-18z Saturday morning. Elsewhere,
generally VFR conditions are expected through the next 24 hours. -CC


.MARINE...Updated 245 PM PDT Friday, 22 September 2017...Short period
northwest swell will gradually diminish late tonight through
Saturday. However, a thermal trough will bring gusty north winds and
areas of steep seas south of Cape Blanco. Winds and seas south of
Cape Blanco will peak around 20 to 25 kt each afternoon and evening
through early next week. Through Saturday, steep seas will be a mix
of short period northwest swell and wind waves. Swell will diminish
Saturday night then north winds are expected to increase slightly
Sunday and Monday afternoon with small craft winds and seas south of
Cape Blanco. On Tuesday, winds may increase further with a mix of
small craft and gales possible by late Tuesday afternoon and Tuesday
evening. This may bring small craft conditions north of Cape Blanco
late Tuesday with a mix of gales and small craft conditions possible
south of Cape Blanco. North winds will lower Wednesday into
Wednesday night. -CC


.PREV DISCUSSION... /Issued 302 PM PDT Fri Sep 22 2017/

DISCUSSION...The sky is clearing in areas west of the Cascades
but cloudy sky remains to the east. Expect clearing on the east
side tonight and below freezing temperatures are still expected in
the Klamath and Tulelake basins. A freeze warning and frost
advisory continues for those two areas, but this will be the last
issuance for the year as areas east of the Cascades have gone
through a deep freeze. There are still pockets in the valleys west
of the Cascades where low temperatures tonight will be in the
frost range and patchy frost can be expected in rural valleys east
of Medford, as well as eastern Douglas County, and the
Scott/Shasta Valleys in Siskiyou County. Part of the Klamath River
Valley near Oak Knoll could also see overnight temperatures in the
middle 30s.

A warming and drying trend is on track starting Saturday that is
expected to continue at least through the middle of next week.
High temperatures in the western valleys will still be a few
degrees below normal Saturday, warming to around normal on Sunday
then warming to about 5 degrees above normal early next week. At
the coast the thermal trough is starting to form with offshore
northeast to east winds already starting to appear at the upper
slopes. This could present a fire weather concern with a warm and
dry offshore winds at night but condition is not expected to be
as strong as in recent offshore events. The GFS model show the
thermal trough area expanding north into the Coos Bay area around
Wednesday. If this scenario verifies, North Bend and Coos Bay
could be quite warm during the middle of next week.

A weak front could move through the area around Friday. With each
run the GFS is showing this system to be weaker with the ECMWF
barely indicating any changes. We are keeping the forecast dry
through the end of next week with some increase in clouds on
Friday. The next chance for rain may not be until the first or
second week of October. /FB


OR...Frost Advisory from 2 AM to 9 AM PDT Saturday for ORZ029.
     Freeze Warning from 2 AM to 9 AM PDT Saturday for ORZ029.

CA...Frost Advisory from 2 AM to 9 AM PDT Saturday for CAZ084.
     Freeze Warning from 2 AM to 9 AM PDT Saturday for CAZ084.

Pacific Coastal Waters...
- Small Craft Advisory until 5 PM PDT Tuesday for PZZ356-376.


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