Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 221622

Area Forecast Discussion
National Weather Service Medford OR
922 AM PDT Mon May 22 2017

.UPDATE...Satellite imagery shows that the marine layer along the
coast has mostly receeded. Expect clear skies over the entire CWA
and offshore to northerly winds over the coast this afternoon. Low
clouds and patchy fog will return to the coast late tonight. Highs
today will be warmer than yesterday...generally 10 to 20 degrees
above normal. Tuesday should be just as hot...but a low swinging
into the area Tuesday night should bring temperatures down to just
5 to 10 degrees above normal Wednesday afternoon. Thunderstorm
potential Tuesday and Wednesday looks low...but left it in the
forecast for now and will further assess that potential today and
update in the afternoon forecast package. Otherwise, current
forecast is on track...see previous discussion for more
information -MSC


.MARINE....Updated 830 AM PDT Monday, 22 May 2017...The thermal
trough pattern is weaker this morning than yesterday, but should
strengthen today with gales expected to begin south of Cape Blanco
Tuesday afternoon. Confidence in when gales start over the waters
within 10 NM from shore south of Cape Blanco is low to moderate
at this time, so will maintain at watch at this time. Gales are
expected to begin for portions of the area north of the cape
Tuesday night into Wednesday. Fog will continue to be an
intermittent concern...mainly beyond a few miles from shore. Gales
are currently expected to subside by Thursday morning as the
thermal trough pattern weakens. SK/SBN


.PREV DISCUSSION... /Issued 700 AM PDT Mon May 22 2017/

Updated aviation discussion.

SHORT TERM...A strong upper level ridge will continue over the
region today into Tuesday bringing hot temperatures to inland
areas. Temperatures are expected to soar into the mid 90s across
west side valleys today and into the mid 80s for valleys east of
the Cascades. These temperatures are around 15 to 20 degrees
above normal for this time of year. People who may be impacted by
this heat should take extra precautions, especially during the
hottest part of the day. Additionally, area rivers may have fast
moving and very cold water. People near rivers and streams should
be aware of the danger of very cold and swift moving water.

On Tuesday, an upper trough will begin move southeastward out of
the Gulf of Alaska. Expect continued hot temperatures across the
area though on Tuesday, expect for a decrease in temperatures
along the coast and a slight decrease of temperatures in the
Umpqua Valley.

As the upper low to the north moves inland over British Columbia
and then to eastward Tuesday night and Wednesday, models show a
broad trough moving over the Pacific Northwest. This will result
in cooler temperatures. As the trough moves inland, also expect a
marine push of low clouds from the coast into the Umpqua on
Tuesday night and Wednesday morning. A weak, but relatively dry,
front moving across the area on Wednesday may also result in a few
showers or thunderstorms in portions of Northern California.
Models have trended lower on the chance for showers and
thunderstorms Wednesday afternoon and evening and have limited
this risk mainly to areas in southern Siskiyou and Modoc counties.
The main impact from this weather system will be cooler
temperatures with high temperatures lowering into the 70s to 80s
across most inland areas.

Heading into Thursday and Friday, models continue to show some
variability on the exact position of the upper trough and a
shortwave disturbance moving down the trough and into the region.
The trough axis is forecast to remain east of the area. However,
depending on the track of the shortwave disturbance moving down
the back side of this trough on Thursday and into Friday, may see
a slight chance for showers of thunderstorms over eastern portions
of the CWA, mainly into Lake County. Also on Friday, the ECMWF
and GFS show some mid level moisture and daytime instability
bringing a slight chance for a few showers or thunderstorms to
western Siskiyou County.

Late Friday into Friday night, the upper ridge off the coast will
rebuild over the Pacific Northwest. The ridge will continue over
the region into the weekend with a gradual warming trend. Some
southerly moisture is expected to move up from the Sierras and
into the area on the weekend. This combined with daytime
instability, may bring a slight chance for thunderstorms, mainly
into Northern California. The lack of a significant trigger may
keep thunderstorm chances low. Of note, the GFS is indicating an
upper trough and low approaching the Pacific Northwest coast as
early as late Sunday while the ECMWF is much slower with the
movement and strength of this low. This upper low may bring
additional disturbances and moisture into the area as it
approaches late Sunday into early next week, resulting in a chance
to slight chance for showers and thunderstorms over inland areas.
Confidence is low in the details for Sunday into early next week
due to model variability though.


.AVIATION...22/12Z TAF CYCLE...LIFR conditions are being observed
from Reedsport to Cape Blanco this morning. Clearing should occur
along and near the coast by about 18Z this morning. A return of
IFR conditions is expected this evening at the coast from Cape
Blanco northward. Elsewhere, VFR is expected for the next 24
hours. SK




Pacific Coastal Waters...Gale Watch from Tuesday morning through Thursday morning for
     Small Craft Advisory until 11 AM PDT Thursday for
     Gale Watch from Tuesday evening through Thursday morning for
     Small Craft Advisory until 11 PM PDT Tuesday for PZZ376.


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